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  • Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
  • American Meteorological Society
  • MDPI Publishing
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  • 1
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    European Summer Wet-Bulb Temperature: Spatiotemporal Variations and Potential Drivers (2024)
    American Meteorological Society
    In:  EPIC3Journal of Climate, American Meteorological Society, 37(6), pp. 2059-2080, ISSN: 0894-8755
    Details
    Publication Date: 2024-04-22
    Description: Heat stress is projected to intensify with global warming, causing significant socioeconomic impacts and threatening human health. Wet-bulb temperature (WBT), which combines temperature and humidity effects, is a useful indicator for assessing regional and global heat stress variability and trends. However, the variations of European WBT and their underlying mechanisms remain unclear. Using observations and reanalysis datasets, we demonstrate a remarkable warming of summer WBT during the period 1958–2021 over Europe. Specifically, the European summer WBT has increased by over 1.08C in the past 64 years. We find that the increase in European summer WBT is driven by both near-surface warming temperatures and increasing atmospheric moisture content. We identify four dominant modes of European summer WBT variability and investigate their linkage with the large-scale atmospheric circulation and sea surface temperature anomalies. The first two leading modes of the European WBT variability exhibit prominent interdecadal to long-term variations, mainly driven by a circumglobal wave train and concurrent sea surface temperature variations. The last two leading modes of European WBT variability mainly show interannual variations, indicating a direct and rapid response to large-scale atmospheric dynamics and nearby sea surface temperature variations. Further analysis shows the role of global warming and changes in midlatitude circulations in the variations of summer WBT. Our findings can enhance the understanding of plausible drivers of heat stress in Europe and provide valuable insights for regional decision-makers and climate adaptation planning.
    Repository Name: EPIC Alfred Wegener Institut
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  • 2
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    Hurricane Sally (2020) shifts the ocean thermal structure across the inner core during rapid intensification over the shelf (2023)
    American Meteorological Society
    Details
    Publication Date: 2023-02-25
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(11), (2022): 2841–2852, https://doi.org/10.1175/jpo-d-22-0025.1.
    Description: Prediction of rapid intensification in tropical cyclones prior to landfall is a major societal issue. While air–sea interactions are clearly linked to storm intensity, the connections between the underlying thermal conditions over continental shelves and rapid intensification are limited. Here, an exceptional set of in situ and satellite data are used to identify spatial heterogeneity in sea surface temperatures across the inner core of Hurricane Sally (2020), a storm that rapidly intensified over the shelf. A leftward shift in the region of maximum cooling was observed as the hurricane transited from the open gulf to the shelf. This shift was generated, in part, by the surface heat flux in conjunction with the along- and across-shelf transport of heat from storm-generated coastal circulation. The spatial differences in the sea surface temperatures were large enough to potentially influence rapid intensification processes suggesting that coastal thermal features need to be accounted for to improve storm forecasting as well as to better understand how climate change will modify interactions between tropical cyclones and the coastal ocean.
    Description: This research was made possible by the NOAA RESTORE Science Program (NA17NOS4510101 and NA19NOS4510194) and the NASA Physical Oceanography program (80NSSC21K0553 and WBS 281945.02.25.04.67) and NOAA IOOS program via GCOOS (NA16NOS0120018). The authors declare that they have no competing interests.
    Keywords: Seas/gulfs/bays ; Atmosphere–ocean interaction ; Currents ; Tropical cyclones ; Buoy observations ; In situ oceanic observations
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  • 3
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    Impact of Gulf Stream warm-core rings on slope water intrusion into the Gulf of Maine (2023)
    American Meteorological Society
    Details
    Publication Date: 2023-02-25
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(8), (2022): 1797–1815, https://doi.org/10.1175/JPO-D-21-0288.1.
    Description: Intruding slope water is a major source of nutrients to sustain the high biological productivity in the Gulf of Maine (GoM). Slope water intrusion into the GoM is affected by Gulf Stream warm-core rings (WCRs) impinging onto the nearby shelf edge. This study combines long-term mooring measurements, satellite remote sensing data, an idealized numerical ocean model, and a linear coastal-trapped wave (CTW) model to examine the impact of WCRs on slope water intrusion into the GoM through the Northeast Channel. Analysis of satellite sea surface height and temperature data shows that the slope sea region off the GoM is a hotspot of ring activities. A significant linear relationship is found between interannual variations of ring activities in the slope sea region off the GoM and bottom salinity at the Northeast Channel, suggesting the importance of WCRs in modulating variability of intruding slope water. Analysis of the mooring data reveals enhanced slope water intrusion through bottom-intensified along-channel flow following impingements of WCRs on the nearby shelf edge. Numerical simulations qualitatively reproduce the observed WCR impingement processes and associated episodic enhancement of slope water intrusion in the Northeast Channel. Diagnosis of the model result indicates that baroclinic CTWs excited by the ring–topography interaction are responsible for the episodically intensified subsurface along-channel inflow, which carries more slope water into the GoM. A WCR that impinges onto the shelf edge to the northeast of the Northeast Channel tends to generate stronger CTWs and cause stronger enhancement of the slope water intrusion into the GoM.
    Description: This study is supported by the National Science Foundation through Grant OCE-1634965.
    Keywords: Continental shelf/slope ; Channel flows ; Mesoscale processes ; In situ oceanic observations ; Satellite observations ; Numerical analysis/modeling
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  • 4
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    Lifelong, learning-augmented robot navigation (2023)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-02-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Aeronautics and Astronautics at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2023.
    Description: Simultaneous localization and mapping (SLAM) is the process by which a robot constructs a global model of an environment from local observations of it; this is a fundamental perceptual capability supporting planning, navigation, and control. We are interested in improving the expressiveness and operational longevity of SLAM systems. In particular, we are interested in leveraging state-of-the-art machine learning methods for object detection to augment the maps robots can build with object-level semantic information. To do so, a robot must combine continuous geometric information about its trajectory and object locations with discrete semantic information about object classes. This problem is complicated by the fact that object detection techniques are often unreliable in novel environments, introducing outliers and making it difficult to determine the correspondence between detected objects and mapped landmarks. For robust long-term navigation, a robot must contend with these discrete sources of ambiguity. Finally, even when measurements are not corrupted by outliers, long-term SLAM remains a challenging computational problem: typical solution methods rely on local optimization techniques that require a good “initial guess,” and whose computational expense grows as measurements accumulate. The first contribution of this thesis addresses the problem of inference for hybrid probabilistic models, i.e., models containing both discrete and continuous states we would like to estimate. These problems frequently arise when modeling e.g., outlier contamination (where binary variables indicate whether a measurement is corrupted), or when performing object-level mapping (where discrete variables may represent measurement-landmark correspondence or object categories). The former application is crucial for designing more robust perception systems. The latter application is especially important for enabling robots to construct semantic maps; that is, maps containing objects whose states are a mixture of continuous (geometric) information and (discrete) categorical information (such as class labels). The second contribution of this thesis is, a novel spectral initialization method which is efficient to compute, easy to implement, and admits the first formal performance guarantees for a SLAM initialization method. The final contribution of this thesis aims to curtail the growing computational expense of long-term SLAM. In particular, we propose an efficient algorithm for graph sparsification capable of reducing the computational burden of SLAM methods without significantly degrading SLAM solution quality. Taken together, these contributions improve the robustness and efficiency of robot perception approaches in the lifelong setting.
    Description: This work was generously supported by the NSF Graduate Research Fellowship Program (GRFP), ONR Neuro-Autonomy MURI grant N00014-19-1-2571, ONR grant N00014-18-1-2832, and the MIT-Portugal Program Flagship Project: Knowledge to Data.
    Keywords: Navigation ; Robotics ; Mapping
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 5
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    A regime shift on Weddell Sea continental shelves with local and remote physical-biogeochemical implications is avoidable in a 2°C scenario (2023)
    American Meteorological Society
    In:  EPIC3Journal of Climate, American Meteorological Society, pp. 1-40, ISSN: 0894-8755
    Details
    Publication Date: 2023-09-04
    Description: 〈jats:title〉Abstract〈/jats:title〉 〈jats:p〉Tipping points in the Earth system describe critical thresholds beyond which a single component, part of the system, or the system as a whole changes from one stable state to another. In the present-day Southern Ocean, the Weddell Sea constitutes an important dense-water formation site, associated with efficient deep-ocean carbon and oxygen transfer and low ice-shelf basal melt rates. Here, a regime shift will occur when continental shelves are continuously flushed with warm, oxygen-poor offshore waters from intermediate depth, leading to less efficient deep-ocean carbon and oxygen transfer and higher ice-shelf basal melt rates. We use a global ocean–biogeochemistry model including ice-shelf cavities and an eddy-permitting grid in the southern Weddell Sea to address the susceptibility of this region to such a system change for four 21〈jats:sup〉st〈/jats:sup〉-century emission scenarios. Assessing the projected changes in shelf–open ocean density gradients, bottom-water properties, and on-shelf heat transport, our results indicate that the Weddell Sea undergoes a regime shift by 2100 in the highest-emission scenario SSP5-8.5, but not yet in the lower-emission scenarios. The regime shift is imminent by 2100 in the scenarios SSP3-7.0 and SSP2-4.5, but avoidable under the lowest-emission scenario SSP1-2.6. While shelf-bottom waters freshen and acidify everywhere, bottom waters in the Filchner Trough undergo accelerated warming and deoxygenation following the system change, with implications for local ecosystems and ice-shelf basal melt. Additionally, deep-ocean carbon and oxygen transfer decline, implying that the local changes ultimately affect ocean circulation, climate, and ecosystems globally.〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
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  • 6
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    Atmospheric and Surface Processes, and Feedback Mechanisms Determining Arctic Amplification: A Review of First Results and Prospects of the (AC)3 Project (2023)
    American Meteorological Society
    In:  EPIC3Bulletin of the American Meteorological Society, American Meteorological Society, 104(1), pp. e208-e242, ISSN: 0003-0007
    Details
    Publication Date: 2023-04-26
    Description: Mechanisms behind the phenomenon of Arctic amplification are widely discussed. To contribute to this debate, the (AC)3 project was established in 2016 (www.ac3-tr.de/). It comprises modeling and data analysis efforts as well as observational elements. The project has assembled a wealth of ground-based, airborne, shipborne, and satellite data of physical, chemical, and meteorological properties of the Arctic atmosphere, cryosphere, and upper ocean that are available for the Arctic climate research community. Short-term changes and indications of long-term trends in Arctic climate parameters have been detected using existing and new data. For example, a distinct atmospheric moistening, an increase of regional storm activities, an amplified winter warming in the Svalbard and North Pole regions, and a decrease of sea ice thickness in the Fram Strait and of snow depth on sea ice have been identified. A positive trend of tropospheric bromine monoxide (BrO) column densities during polar spring was verified. Local marine/biogenic sources for cloud condensation nuclei and ice nucleating particles were found. Atmospheric–ocean and radiative transfer models were advanced by applying new parameterizations of surface albedo, cloud droplet activation, convective plumes and related processes over leads, and turbulent transfer coefficients for stable surface layers. Four modes of the surface radiative energy budget were explored and reproduced by simulations. To advance the future synthesis of the results, cross-cutting activities are being developed aiming to answer key questions in four focus areas: lapse rate feedback, surface processes, Arctic mixed-phase clouds, and airmass transport and transformation.
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Chemical controls on the cycling and reactivity of marine dissolved organic matter (2023)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-02-10
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Marine Chemistry at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2023.
    Description: Marine dissolved organic matter (DOM) is an actively cycling reservoir of carbon containing thousands of unique compounds. To describe the complex dynamics that govern the biological transformation and decomposition of compounds in this molecular black box, models of DOM reactivity use chemical characteristics, as well as environmental parameters, to describe trends in the turnover time of classes of DOM. In this thesis, I describe two projects that examine hypotheses regarding the turnover of two classes of DOM. In the 1st project, I test the assumption made by the size–reactivity continuum hypothesis that high molecular weight (〉 1 kDa) DOM (HMWDOM) represents a diagenetic intermediate between large labile material and small recalcitrant compounds. Size-fractions of HMWDOM were collected using size-exclusion chromatography, and the changes in MW and chemical composition of the fractions were studied using diffusion-ordered spectroscopy. The size fraction carbon isotopic values were correlated with the proportion of humic substances in the fractions. Through linear modeling, the apparent radiocarbon ages of the two major components of HMWDOM were determined to be 1-3 yrs and 2-4 kyrs, respectively. Combined with the measurements of MW distribution this work demonstrates that HMWDOM is composed of two components that have contrasting decomposition pathways in the ocean. HMWDOM cannot be treated as a single DOM pool when incorporated into models of DOM diagenesis. The 2nd project in this dissertation examines the remineralization of phosphonates, compounds with a direct C-P bond, in the lower euphotic zone using a newly developed fluorescent assay, which measures the activity of carbon-phosphorus lyase. C-P lyase activity (CLA) profiles from the North Pacific Subtropical Gyre (NPSG) showed a sharp activity maximum near the deep-chlorophyll maximum (DCM). High-resolution nutrient measurements suggest that this subsurface CLA maximum is the result of a high nitrate flux at the top of the nitracline. The composition of particulate-P through the euphotic zone was also examined. While phosphonates were not detected in suspended particles, a significant amount of aminoethylphosphonate was measured in sinking material, suggesting eukaryotic material may be an important source of phosphonates to the ocean.
    Description: The studies described in this dissertation were supported by the Simons Foundation (SCOPE award 329108 to D.M.K. and D.J.R.), the Gordon and Betty Moore Foundation (3794; D.M.K. and 6000; D.J.R.), and the National Science Foundation (NSF: OCE-1634080; D.J.R.) and I thank them for their support.
    Keywords: Dissolved organic matter ; Phosphonate ; Carbon cycle
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  • 8
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    Mass transfer and chemical interactions in subduction zones (2023)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-02-10
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2023.
    Description: Subduction zones are important sites of material recycling on Earth, with volatiles playing key roles in mass transfer processes and magma formation. This thesis investigates outstanding questions associated with a continuum of interrelated processes that occur as oceanic plates descend in subduction zones by integrating petrological and geochemical constraints from exhumed high-pressure rocks and erupted arc magmas, high pressure-temperature laboratory experiments, and thermodynamic calculations. Chapters 2 and 3 investigate the fluid-mediated reactions between mafic and ultramafic rocks at conditions relevant to the slab-mantle interface and show that Mg-metasomatism of mafic rocks to form chlorite-rich assemblages is favored and is likely more pervasive in subduction zones than in oceanic settings. Contrary to common belief, talc is unlikely to form in high abundance in ultramafic rocks metasomatized by Si-rich slabderived fluids. This means that talc-rich assemblages formed via Si-metasomatism along the slabmantle interface are less likely to be playing prominent roles in volatile transport, in facilitating slow-slip events, and in controlling the decoupling-coupling transition of the plate interface. Chapter 4 experimentally investigates the phase equilibria, melting, and density evolution of mélange rocks that formed by mixing and fluid-rock interactions. Results show that melting of mélanges is unlikely to occur along slab-tops at pressures ≤ 2.5 GPa. Accordingly, diapirism into the hotter mantle wedge would be required to initiate melting. The density contrast between mélanges and the overlying mantle would allow for buoyancy-driven diapirism at relatively low pressures and melting could subsequently occur in the hotter mantle wedge during ascent. However, diapir buoyancy may be limited at higher pressures due to the formation of abundant garnet especially in mélange rocks with peraluminous composition. Chapter 5 experimentally investigates the compositions of melts and mineral residues from melting of a mantle wedge hybridized with small amounts of mélange rocks to simulate an end-member scenario where solid mélange diapirs dynamically interact with the mantle wedge. Results from laboratory experiments show that melting of a mélange-hybridized mantle wedge can produce melts that display compositional characteristics similar to arc magmas. Finally, Chapter 6 presents new interpretations on the evolution of slab-to-mantle transfer mechanisms from subduction initiation to arc maturity. Analyses of published magma compositions from global arcs reveal that melting of mélange plays an increasingly important role in magma formation as slab-tops cool and arcs mature over time. This trend is attributed to the deepening of the decoupled plate interface during subduction where mélange zones can form more extensively and contribute to the melting process more significantly. Taken together, this thesis highlights (i) the dynamic connection between mechanical mixing of different lithologies and fluid-rock interactions along the slab-mantle interface, (ii) how these processes modify the petrophysical and geochemical properties of subducted materials, and (iii) how these processes collectively influence the mechanisms of slabto-mantle transfer, elemental cycles, and the formation of arc magmas worldwide.
    Description: This work has been supported financially by the National Science Foundation-Office of International Science & Engineering, Petrology & Geochemistry (NSF-OISE) PIRE, Award# 1545903 to F.K. and the Geoprisms program Collaborative Research Award# 1852610 to V.L.R. Research support through the WHOI Ocean Ventures Fund, US Science Support Program E-FIRE European Training Fund, WHOI Conference Fund are awarded to E.A.C.
    Keywords: Subduction zones ; Fluid-rock interactions ; Mass transfer
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  • 9
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    Marine parasites in island-like disturbed habitats (2023)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-02-10
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2023.
    Description: Parasites are taxonomically and functionally diverse members of biological communities, and can play key roles in species interactions, community structure, and ecosystem functioning. For their reliance on host species, parasites are theorized to be particularly sensitive to disturbances that alter host diversity and abundance, especially in isolated habitats, which present challenges to introduction and establishment. In this thesis, I investigate habitat isolation and disturbance as drivers of parasite diversity, with an emphasis on parasite life history strategies related to colonization and persistence. I focus on an island-like, frequently disturbed habitat, deep sea hydrothermal vents at 9°50’N on the East Pacific Rise, to explore the boundaries of parasite persistence in an extreme environment. First, I analyze recovery in the vent community for 11 years after a catastrophic eruption in 2006 to test successional hypotheses in a new setting with distinct fauna and a chemosynthesis-based food web. Second, I compare parasite diversity at isolated, disturbed vents to marine ecosystems that are similarly isolated but undisturbed (atoll sandflat) and both well connected and undisturbed (kelp forest). Overall, parasite diversity within host species was not significantly lower at vents, but the vent community had many fewer parasite species because there are fewvertebrate predator species (fish). Parasites with indirect (multi-host) life cycles were relatively diverse in the disturbed environment, which contradicts expectation based on theory. To explore this further, I investigate the three-host life cycles of trematodes at vents, whichwas the most diverse and abundant parasite taxon. All life stages of the trematode life cyclewere discovered in vent fauna and several taxawere traced across multiple life stages via morphology and genetics. Finally, I use a computational model to investigate how different parasite strategies (colonization capability and impact on hosts) contribute to parasite success under a range of disturbance conditions in island habitats. Parasites that reduce host reproduction reached higher densities than parasites that cause mortality across all disturbance frequencies explored, and disturbance facilitated the evolution of more virulent parasites. These studies demonstrate that life history traits and the ability to adapt allow diverse parasite taxa to persist in isolated, ephemeral environments.
    Description: I extend my thanks to the grantors and funding agencies who supported my research, including NSF grants OCE-1829773 and OCE-84773500, the Grassle Student Fellowship Fund, and the Ocean Ventures Fund.
    Keywords: Parasites ; Hydrothermal vents ; Disturbance
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  • 10
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    The biogeochemistry of methane isotopologues in marine and lacustrine sediments (2023)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-02-01
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geochemistry at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2023.
    Description: Methane is a globally significant greenhouse gas, energy resource, and it is a product and reactant of microbial metabolisms. Multiple sources and sinks of methane can be challenging to distinguish from each other, thus complicating the understanding of methane budgets and the effects of microbes on mediating Earth’s carbon cycle. The relative abundances of methane isotopologues (e.g., 12CH4, 13CH4, 12CH3D, and 13CH3D) record process-based information about the formation conditions, transport, and fate of methane, and in select environments can serve as a temperature proxy. This geochemical tool is herein applied to methane from marine and lacustrine sediments to test assumptions about prevailing mechanisms of its formation and consumption in these settings. This thesis describes 1) three studies about biogeochemical insights gained by quantifying the relative abundance of clumped methane isotopologue, 13CH3D, in samples from marine and lacustrine sediments, and 2) one foray into method development to improve the quantification of methane in these environments. Chapter 2 presents a global survey of marine gas hydrates where isotope-based temperatures are used to assess whether linkages between methane sources and seepage-associated seafloor features match putative geologic models. Chapter 3 describes two kilometer-scale profiles of methane isotopologues from marine sediments, where the relationship between expected sediment temperature and isotope-based temperature is used to evaluate the temperature limit of microbial processing and abiotic re-equilibration mechanisms. Chapter 4 reports the largest set of methane isotopologue data from ebullition in a single lake basin, which is used to gauge the relative importance of aerobic and anaerobic methane oxidation in the study site and recommend a general sampling strategy to constrain methane source signatures in similar lake settings. Chapter 5 explains the development of a method to quantify the in situ concentration of methane based on ratios of dissolved gases, and its comparison to four other methane quantification methods for surface sediments from marine cold seeps. The findings from this research contribute to ongoing efforts to understand the sedimentary carbon cycle and microbial activity in remote environments.
    Description: The works described in this thesis was made possible by grants to my advisor from sources including the National Science Foundation (EAR-1852946 to S.O.), U.S. Science Support Program Office associated with the International Ocean Discovery program (OCE-14-50528 to D.T.W and S.O.), the Deep Carbon Observatory Deep Life Community Grant (to S.O.), MISTI Japan, and the mTerra Catalyst Fund (to S.O. and E.L). From 2017-2018 I was funded by the MIT Presidential Fellowship, and from 2018-2020 I was funded as a fellow through the MIT Energy Initiative. The collection of samples from the Scotian Slope was funded by the WHOI Ocean Ventures Fund (to E.L.). The Montrym Fund for student climate research (to E.L) funded the sampling of Upper Mystic Lake. My participation in the 2018 ECORD Summer School was funded by the U.S. Science Support Program Office, and the MIT GSC Conference fund providing funding for my participation in the AGU 2021 Fall Meeting and Goldschmidt 2022.
    Keywords: Isotopologues ; Methane ; Sediment
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  • 11
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    Perceive, predict, and plan: robotic expeditionary science in oceanic spatiotemporal fields (2023)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-02-01
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Autonomous Systems at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2023.
    Description: An improved understanding of our ocean would allow us to characterize the largest habitable biosphere on planet Earth, quantify the geochemical processes that control Earth’s climate, and develop responsible regulations for controlling the natural resources stored in its depths. Expeditionary science is the art of collecting in situ observations of an environment to build approximate models of underlying properties that move us towards this understanding. Robotic platforms are a critical technology for collecting observations of the ocean. Depth-capable autonomous underwater vehicles (AUVs) are commonly used to build static maps of the seafloor by executing pre-programmedsurveys. However, there is growing urgency to generate rich data products of spatiotemporal distributions that characterize the physics and chemistry of the deep ocean biogeosphere. In this thesis, the problem of charting dynamic deep sea hydrothermal plumes with depth-capable AUVs is investigated. Effectively collecting samples of geochemical plumes using the operationally preferred strategy of pre-specifying surveys requires access to a dynamics model of the advective currents, bathymetric updrafts, and turbulent mixing at a hydrothermal site. In practice, however, access to this information is unavailable, imperfect, or only partially known, and so a model of plume dynamics must be inferred from observations and subsequently leveraged to improve future sampling performance. As most in situ scientific instruments yield point-measurements, considerable uncertainty is placed over the form of the dynamics in purely data-driven solutions. Challenges related to planning under uncertainty for geochemical surveys in the deep ocean are addressed in this thesis by embedding scientific knowledge as a strong inductive prior for tractable model learning and decision-making. Algorithmic contributions of this thesis show how plumes can be perceived from field data, their fate predicted far into the future (e.g., multiple days), and informative fixed trajectories planned which place an AUV in the right place at the right time. Scientific assessment of observational data collected with AUV Sentry during field trials in the Guaymas Basin, Gulf of California are interwoven with algorithmic analyses, demonstrating how intelligent perception, prediction, and planning enables novel insights about hydrothermal plumes.
    Description: Financial support for my research was provided by the National Defense Graduate Fellowship Program and the MIT Martin Family Society of Fellows for Sustainability. Research activities for the RR2107 cruise were funded by NSF OCE OTIC #1842053, a WHOI Innovation Technology Award, NOAA Ocean Exploration #NA18OAR0110354, and Schmidt Marine Technology Partners Award #G-21-62431.
    Keywords: Autonomy ; Hydrothermalism ; Adaptive sampling
    Repository Name: Woods Hole Open Access Server
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  • 12
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    Distributions and perturbations of the marine dissolved cobalt cycle in a changing ocean (2023)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-02-01
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Marine Biogeochemistry at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2023.
    Description: Cobalt is a necessary nutrient for many marine phytoplankton, but its hybrid-type nature results in small marine inventories that make it one of the scarcest bioactive trace metals in the oceans. This study examines the marine dissolved cobalt cycle in two regions: the Pacific Ocean and Antarctic coastal seas. In the North Pacific, elevated cobalt stoichiometries among phytoplankton were linked to nitrogen, iron and phosphate stress protein biomarkers at the boundaries of oceanographic provinces and upwelling zones, providing insight into the flexibility of cobalt stoichiometry. In both regions, perturbations to the marine cobalt cycle were either predicted or observed; in the equatorial Pacific, the dissolved cobalt inventory was predicted to increase by up to 28% due to the expansion of oxygen minimum zones in a warmer ocean, while in the Antarctic, melting ice shelves have the potential to shift the nutrient regime from iron limitation towards zinc and vitamin B12 limitation, resulting in higher cobalt demand and a lower dissolved cobalt inventory. When the global cobalt cycle was estimated throughout four of Earth’s systems (the lithosphere, biosphere, hydrosphere and the anthroposphere – the human environment), it was determined that the scale of the cobalt flux through the anthroposphere is only one order of magnitude lower than the inventory of the entire hydrosphere (10(9) mol Co yr-1 and 10(10) mol Co, respectively), revealing a vulnerability to anthropogenic perturbation of the marine cobalt inventory through human mining, use and disposal of cobalt if appropriate pollution abatement, disposal and recycling infrastructure is not established. In light of observed and predicted changes to cobalt biogeochemistry, this research suggests that the marine cobalt cycle is particularly vulnerable to anthropogenic perturbation from both global climate change and pollution due to its low ocean inventory and interconnection to other nutrient biogeochemical cycles.
    Description: My work in the Saito Lab was supported by several National Science Foundation grants, including awards for the GEOTRACES GP15 program (OCE-1736599, OCE-1756138, OCE-1657781 and OCE-1736601), the CICLOPS expedition via the Office of Polar Programs (OPP-1643684, OPP-1644073 and OPP-1643845), and the CLIO Biogeochemical AUV project (OCE-1924554 and OCE-1658067), as well as funding from the Watson Foundation.
    Keywords: GEOTRACES ; Ross Sea ; Anthropogenic cobalt
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  • 13
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    Quantifying pelagic primary production and respiration via an automated in-situ incubation system (2023)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-02-02
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2023.
    Description: Pelagic photosynthesis and respiration serve critical roles in controlling the dissolved oxygen concentration (DO) in seawater. The consumption and production via pelagic primary production are of particular importance in surface ocean and in shallow aquatic ecosystems where photosynthetically active radiation (PAR) is abundant. However, the dynamic nature and large degree of heterogeneity in these ecosystems pose substantial challenges for providing accurate estimates of marine primary production and metabolic state. The resulting lack of data in these systems hinders efforts in scaling and including primary production in predictive models. To bridge the gap, we developed and validated a novel automated water incubator that measures in-situ rates of photosynthesis and respiration. The automated water incubation system uses commercially available optodes and microcontrollers to record continuous measurements of DO within a closed chamber at desired intervals. With fast response optodes, the incubation system produced measurements of photosynthesis and respiration with hourly resolution, resolving diel signals in the water column. The high temporal resolution of the timeseries also enabled the development of Monte-Carlo simulation as a new data analysis technique to calculate DO fluxes, with improved performance in noisy timeseries. Deployment of the incubator was conducted near Ucantena Island, Massachusetts, USA. The data captured diel fluctuations in metabolic fluxes with hourly resolution, allowed for a more accurate correlation between oxygen cycling and environmental conditions, and provided improved characterization of the pelagic metabolic state.
    Description: This thesis work was supported by NSF OTIC grant 1841092 to PI Collin Ward and Matt Long and WHOI Academic Office. The early work was also supported by NSF-REU Summer Student Fellowship program at WHOI. The subsequent development portion of this project was supported by WHOI-ADI OCIA to PI Matt Long and Ben Van Mooy.
    Keywords: Metabolic fluxes ; Automated incubation ; Monte-Carlo simulation ; In-situ sensing ; UV biofouling control
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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    Physical and biological processes at the Middle Atlantic Bight shelf-break front (2023)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-02-02
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2023.
    Description: The Middle Atlantic Bight (MAB) is a highly productive ecosystem, supporting several economically important commercial fisheries. Chlorophyll enhancement at the MAB shelf-break front has been observed only intermittently, despite numerous studies that suggest persistent upwelling at the front. High resolution cross-frontal transect crossings were collected from three two-week cruises in April 2018, May 2019, and July 2019. Chapter 2 focused on applying a novel method of classifying planktonic images taken by a Video Plankton Recorder to enable processing of the large volumes of data collected with the instrument. Chapter 3 investigated cross-frontal trends by temporally averaging in both Eulerian and frontally-aligned coordinates. For April 2018, transient chlorophyll enhancement was seen at the front in individual transects and within the frontally-aligned mean transect, but not within the Eulerian mean transect. The Eulerian mean for May 2019 showed chlorophyll enhancement as a result of frontal eddies, which were further explored in chapter 4. No frontal enhancement was observed in July 2019. The frontal eddies observed in May 2019 were simulated using an idealized model, which showed that upwelling occurred within both of the frontal eddies, despite having opposite rotational directions. This result was consistent with nutrient enhancement observed within the centers of both eddies. Biological enhancement within each eddy was observed, which may have been a result of advection from source waters and/or a local response to upwelled nutrients. The influence of frontal variability and frontal eddies on nutrients and plankton at the front argues for the necessity for 3-D models to fully explain frontal behavior and its effects on biological responses.
    Description: The research in this thesis was supported by the National Science Foundation (OCE-1657803) and the Dalio Foundation. Support from the WHOI Academic Programs Office is gratefully acknowledged.
    Keywords: Plankton ; Fronts ; Eddies
    Repository Name: Woods Hole Open Access Server
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    Static and dynamic performance of the RBRargo3 CTD (2023)
    American Meteorological Society
    Details
    Publication Date: 2023-02-17
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(10), (2022): 1525–1539, https://doi.org/10.1175/jtech-d-21-0186.1.
    Description: The static and dynamic performances of the RBRargo3 are investigated using a combination of laboratory-based and in situ datasets from floats deployed as part of an Argo pilot program. Temperature and pressure measurements compare well to co-located reference data acquired from shipboard CTDs. Static accuracy of salinity measurements is significantly improved using 1) a time lag for temperature, 2) a quadratic pressure dependence, and 3) a unit-based calibration for each RBRargo3 over its full pressure range. Long-term deployments show no significant drift in the RBRargo3 accuracy. The dynamic response of the RBRargo3 demonstrates the presence of two different adjustment time scales: a long-term adjustment O(120) s, driven by the temperature difference between the interior of the conductivity cell and the water, and a short-term adjustment O(5–10) s, associated to the initial exchange of heat between the water and the inner ceramic. Corrections for these effects, including dependence on profiling speed, are developed.
    Keywords: Data processing/distribution ; In situ oceanic observations ; Profilers ; Oceanic
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    Dynamics of eddying abyssal mixing layers over sloping rough topography (2023)
    American Meteorological Society
    Details
    Publication Date: 2023-02-28
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(12),(2022): 3199-3219, https://doi.org/10.1175/jpo-d-22-0009.1.
    Description: The abyssal overturning circulation is thought to be primarily driven by small-scale turbulent mixing. Diagnosed water-mass transformations are dominated by rough topography “hotspots,” where the bottom enhancement of mixing causes the diffusive buoyancy flux to diverge, driving widespread downwelling in the interior—only to be overwhelmed by an even stronger upwelling in a thin bottom boundary layer (BBL). These water-mass transformations are significantly underestimated by one-dimensional (1D) sloping boundary layer solutions, suggesting the importance of three-dimensional physics. Here, we use a hierarchy of models to generalize this 1D boundary layer approach to three-dimensional eddying flows over realistically rough topography. When applied to the Mid-Atlantic Ridge in the Brazil Basin, the idealized simulation results are roughly consistent with available observations. Integral buoyancy budgets isolate the physical processes that contribute to realistically strong BBL upwelling. The downward diffusion of buoyancy is primarily balanced by upwelling along the sloping canyon sidewalls and the surrounding abyssal hills. These flows are strengthened by the restratifying effects of submesoscale baroclinic eddies and by the blocking of along-ridge thermal wind within the canyon. Major topographic sills block along-thalweg flows from restratifying the canyon trough, resulting in the continual erosion of the trough’s stratification. We propose simple modifications to the 1D boundary layer model that approximate each of these three-dimensional effects. These results provide local dynamical insights into mixing-driven abyssal overturning, but a complete theory will also require the nonlocal coupling to the basin-scale circulation.
    Description: We acknowledge funding support from National Science Foundation Awards 1536515, 1736109, and 2149080. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant 174530.
    Description: 2023-05-18
    Keywords: Abyssal circulation ; Diapycnal mixing ; Meridional overturning circulation ; Topographic effects ; Upwelling/downwelling ; Bottom currents/bottom water
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    Eddy vertical structure and variability: deepglider observations in the North Atlantic (2023)
    American Meteorological Society
    Details
    Publication Date: 2023-02-28
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(6), (2022): 1091–1110, https://doi.org/10.1175/JPO-D-21-0068.1.
    Description: Hundreds of full-depth temperature and salinity profiles collected by Deepglider autonomous underwater vehicles (AUVs) in the North Atlantic reveal robust signals in eddy isopycnal vertical displacement and horizontal current throughout the entire water column. In separate glider missions southeast of Bermuda, subsurface-intensified cold, fresh coherent vortices were observed with velocities exceeding 20 cm s−1 at depths greater than 1000 m. With vertical resolution on the order of 20 m or less, these full-depth glider slant profiles newly permit estimation of scaled vertical wavenumber spectra from the barotropic through the 40th baroclinic mode. Geostrophic turbulence theory predictions of spectral slopes associated with the forward enstrophy cascade and proportional to inverse wavenumber cubed generally agree with glider-derived quasi-universal spectra of potential and kinetic energy found at a variety of locations distinguished by a wide range of mean surface eddy kinetic energy. Water-column average spectral estimates merge at high vertical mode number to established descriptions of internal wave spectra. Among glider mission sites, geographic and seasonal variability implicate bottom drag as a mechanism for dissipation, but also the need for more persistent sampling of the deep ocean.
    Description: This work was funded by NSF Grant 1736217 and would not have been possible without the help of Kirk O’Donnell, James Bennett, Noel Pelland, and all contributors to Deepglider development. We additionally thank the captain crew of the R/V Atlantic Explorer and the BATS team at the Bermuda Institute of Ocean Sciences, particularly Rod Johnson, as well as Seakeepers International for their professionalism, capability, and generous assistance in deploying and recovering gliders.
    Keywords: North Atlantic Ocean ; Eddies ; Mesoscale processes ; Turbulence ; Energy transport ; In situ oceanic observations ; Oceanic variability
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    Diapycnal displacement, diffusion, and distortion of tracers in the ocean (2023)
    American Meteorological Society
    Details
    Publication Date: 2023-03-02
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(12), (2022): 3221–3240, https://doi.org/10.1175/jpo-d-22-0010.1.
    Description: Small-scale mixing drives the diabatic upwelling that closes the abyssal ocean overturning circulation. Indirect microstructure measurements of in situ turbulence suggest that mixing is bottom enhanced over rough topography, implying downwelling in the interior and stronger upwelling in a sloping bottom boundary layer. Tracer release experiments (TREs), in which inert tracers are purposefully released and their dispersion is surveyed over time, have been used to independently infer turbulent diffusivities—but typically provide estimates in excess of microstructure ones. In an attempt to reconcile these differences, Ruan and Ferrari derived exact tracer-weighted buoyancy moment diagnostics, which we here apply to quasi-realistic simulations. A tracer’s diapycnal displacement rate is exactly twice the tracer-averaged buoyancy velocity, itself a convolution of an asymmetric upwelling/downwelling dipole. The tracer’s diapycnal spreading rate, however, involves both the expected positive contribution from the tracer-averaged in situ diffusion as well as an additional nonlinear diapycnal distortion term, which is caused by correlations between buoyancy and the buoyancy velocity, and can be of either sign. Distortion is generally positive (stretching) due to bottom-enhanced mixing in the stratified interior but negative (contraction) near the bottom. Our simulations suggest that these two effects coincidentally cancel for the Brazil Basin Tracer Release Experiment, resulting in negligible net distortion. By contrast, near-bottom tracers experience leading-order distortion that varies in time. Errors in tracer moments due to realistically sparse sampling are generally small (〈20%), especially compared to the O(1) structural errors due to the omission of distortion effects in inverse models. These results suggest that TREs, although indispensable, should not be treated as “unambiguous” constraints on diapycnal mixing.
    Description: We acknowledge funding support from National Science Foundation Awards 1536515 and 1736109. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant 174530. This research is also supported by the NOAA Climate and Global Change Postdoctoral Fellowship Program, administered by UCAR’s Cooperative Programs for the Advancement of Earth System Science (CPAESS) under Award NA18NWS4620043B.
    Description: 2023-05-18
    Keywords: Diapycnal mixing ; Diffusion ; Upwelling/downwelling ; Bottom currents/bottom water ; Tracers
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    Impacts of Arctic Sea Ice on Cold Season Atmospheric Variability and Trends Estimated from Observations and a Multi-model Large Ensemble (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-03-01
    Description: To examine the atmospheric responses to Arctic sea ice variability in the Northern Hemisphere cold season (from October to the following March), this study uses a coordinated set of large-ensemble experiments of nine atmospheric general circulation models (AGCMs) forced with observed daily varying sea ice, sea surface temperature, and radiative forcings prescribed during the 1979–2014 period, together with a parallel set of experiments where Arctic sea ice is substituted by its climatology. The simulations of the former set reproduce the near-surface temperature trends in reanalysis data, with similar amplitude, and their multimodel ensemble mean (MMEM) shows decreasing sea level pressure over much of the polar cap and Eurasia in boreal autumn. The MMEM difference between the two experiments allows isolating the effects of Arctic sea ice loss, which explain a large portion of the Arctic warming trends in the lower troposphere and drive a small but statistically significant weakening of the wintertime Arctic Oscillation. The observed interannual covariability between sea ice extent in the Barents–Kara Seas and lagged atmospheric circulation is distinguished from the effects of confounding factors based on multiple regression, and quantitatively compared to the covariability in MMEMs. The interannual sea ice decline followed by a negative North Atlantic Oscillation–like anomaly found in observations is also seen in the MMEM differences, with consistent spatial structure but much smaller amplitude. This result suggests that the sea ice impacts on trends and interannual atmospheric variability simulated by AGCMs could be underestimated, but caution is needed because internal atmospheric variability may have affected the observed relationship.
    Description: Published
    Description: 8419–8443
    Description: 2A. Fisica dell'alta atmosfera
    Description: JCR Journal
    Keywords: Arctic ; Sea ice ; Atmospheric circulation ; Climate models ; 01.01. Atmosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Atlantic Multidecadal Variability and North Atlantic Jet: A Multimodel View from the Decadal Climate Prediction Project (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-02-14
    Description: The influence of the Atlantic multidecadal variability (AMV) on the North Atlantic storm track and eddy-driven jet in the winter season is assessed via a coordinated analysis of idealized simulations with state-of-the-art coupled models. Data used are obtained from a multimodel ensemble of AMV± experiments conducted in the framework of the Decadal Climate Prediction Project component C. These experiments are performed by nudging the surface of the Atlantic Ocean to states defined by the superimposition of observed AMV± anomalies onto the model climatology. A robust extratropical response is found in the form of a wave train extending from the Pacific to the Nordic seas. In the warm phase of the AMV compared to the cold phase, the Atlantic storm track is typically contracted and less extended poleward and the low-level jet is shifted toward the equator in the eastern Atlantic. Despite some robust features, the picture of an uncertain and model-dependent response of the Atlantic jet emerges and we demonstrate a link between model bias and the character of the jet response.
    Description: Published
    Description: 347-360
    Description: 4A. Oceanografia e clima
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 21
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    Temporal evolution of a geostrophic current under sea ice: analytical and numerical solutions (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-21
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(6),(2022): 1191-1204, https://doi.org/10.1175/jpo-d-21-0242.1.
    Description: A simplified quasigeostrophic (QG) analytical model together with an idealized numerical model are used to study the effect of uneven ice–ocean stress on the temporal evolution of the geostrophic current under sea ice. The tendency of the geostrophic velocity in the QG model is given as a function of the lateral gradient of vertical velocity and is further related to the ice–ocean stress with consideration of a surface boundary layer. Combining the analytical and numerical solutions, we demonstrate that the uneven stress between the ice and an initially surface-intensified, laterally sheared geostrophic current can drive an overturning circulation to trigger the displacement of isopycnals and modify the vertical structure of the geostrophic velocity. When the near-surface isopycnals become tilted in the opposite direction to the deeper ones, a subsurface velocity core is generated (via geostrophic setup). This mechanism should help understand the formation of subsurface currents in the edge of Chukchi and Beaufort Seas seen in observations. Furthermore, our solutions reveal a reversed flow extending from the bottom to the middepth, suggesting that the ice-induced overturning circulation potentially influences the currents in the deep layers of the Arctic Ocean, such as the Atlantic Water boundary current.
    Description: This work was funded by the National Key Research and Development Program of China (Grant 2017YFA0604600), the National Natural Science Foundation of China (Grant 41676019), the Fundamental Research Funds for the Central Universities (Grant 2019B81214), the Postgraduate Research and Practice Innovation Program of Jiangsu Province (Grant KYCX19_0384), and the National Science Foundation (MAS, Grants OPP-1822334, OCE-2122633).
    Keywords: Arctic ; Sea ice ; Channel flows ; Vertical motion ; Ekman pumping ; Idealized models ; Quasigeostrophic models
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  • 22
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    Anthropogenic and natural radioisotopes as tracers for contaminant sources and particulate fluxes (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2022.
    Description: Radioactive isotopes act as nuclear clocks that are utilized to trace and measure rates of chemical, biological, physical, and geological oceanographic processes. This thesis seeks to utilize both artificial (e.g., released from anthropogenic sources) and natural radioisotopes as tracers within the Pacific Ocean basin. Artificial radioisotopes released as a result of the 2011 Fukushima Daiichi nuclear power plants accident have the potential to negatively impact human and environmental health. This study evaluates 137Cs, 90Sr, and 129I concentrations in seawater off the coast of Japan, reconciles the sources of contaminated waters, and assesses the application of 137Cs/90Sr, 129I/137Cs, and 129I/90Sr as oceanic tracers. The analysis of activity ratios suggests a variety of sources, including ongoing sporadic and independent releases of radiocontaminants. Though decreasing, concentrations remain elevated compared to preaccident levels. Future planned releases of stored water from the reactor site may affect the surrounding environment; and thus, continued efforts to understand the distribution and fate of these radionuclides are warranted. Naturally-occurring radioisotopes (e.g., the 238U-234Th series used in this thesis) can give insight into surface export and remineralization of particulate organic carbon (POC) and trace metals (TMs). POC and TMs play a vital role in regulating the biological carbon pump (BCP), which in turn helps to moderate atmospheric CO2 levels by transporting carbon to the deep ocean, where it can be sequestered on timescales of centuries to millennia. Through this thesis we utilize the 238U:234Th disequilibrium method throughout the GEOTRACES GP15 Pacific Meridional Transect in order o provide basin-scale estimates of POC export and remineralization. There is only limited, recent use of this method to constrain TM fluxes, and as such this study also seeks to further develop this method for use in understanding TM cycling through comparative flux studies in the North Pacific.
    Description: Funding sources for this thesis include the Gordon and Betty Moore Foundation, the Deerbrook Charitable Trust, NSF OCE award no. 1356630 and no. 1735445, and the NSF GRFP.
    Keywords: Radioactive tracers ; Carbon cycling ; Trace metal cycling
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  • 23
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    Assessing the potential for Zn limitation of marine primary production: proteomic characterization of the low Zn stress response in marine diatoms (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 2022.
    Description: Marine diatoms are abundant photoautotrophic algae that contribute significantly to photosynthetic carbon fixation and export throughout the oceans. Zinc is an important micronutrient in algal metabolism, with scarce dissolved concentrations in the upper euphotic zone reflecting high biological demand. In this thesis, I investigated the response of marine diatoms to Zn scarcity to characterize metabolic mechanisms used to combat Zn stress. I began by assaying the ability to metabolically substitute cobalt (Co) in place of Zn in four diatom species and found that enhanced abilities to use Co are likely an adaptation to high surface dCo:dZn ratios in the native environment. I next demonstrated that Zn/Co metabolic substitution in diatoms is not universal using culture studies of Chaetoceros neogracile RS19, which has an absolute Zn requirement. Using global proteomic analysis, I then identified and characterized diatom ZCRP-A and ZCRP-B, a putative Zn-chaperone and membrane-tethered Zn acquisition protein, respectively, as two proteins involved in the low-Zn response. I demonstrated that these proteins are widespread in marine phytoplankton and can be deployed as protein biomarkers of Zn stress in the field. I furthermore documented both the detection of ZCRPs in the Southern Ocean and the existence of Zn/Fe co-limitation within the natural phytoplankton population in Terra Nova Bay, demonstrating that Zn co-limitation can indeed occur in the field, even in high macronutrient waters. Lastly, I explored the relative demand of Zn and cadmium (Cd) within the Southern Ocean community using stable 67Zn and 110Cd tracers, documenting a high demand for both metals during the austral 2017-2018 summer season and investigating the cycling of these elements within this important region. Overall, this dissertation provides new information regarding Zn acquisition and homeostasis mechanisms within marine algae and demonstrates that Zn co-limitation in the field is not only possible, but detectable via protein biomarkers.
    Description: I am very fortunate to have been financially supported over the course of my PhD by awards granted to the Saito Lab, specifically by National Institutes of Health (NIH) grant R01GM135709, Gordon and Betty Moore Foundation grant 3782, and National Science Foundation (NSF) grants OCE-1657766, OCE-1658030, OCE-1736599, OCE-1850719, and OCE-1924554.
    Keywords: Zinc ; Diatoms ; Proteomic
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    A three-dimensional inertial model for coastal upwelling along western boundaries (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-10-12
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(10), (2022): 2431-2444, https://doi.org/10.1175/jpo-d-22-0024.1.
    Description: A three-dimensional inertial model that conserves quasigeostrophic potential vorticity is proposed for wind-driven coastal upwelling along western boundaries. The dominant response to upwelling favorable winds is a surface-intensified baroclinic meridional boundary current with a subsurface countercurrent. The width of the current is not the baroclinic deformation radius but instead scales with the inertial boundary layer thickness while the depth scales as the ratio of the inertial boundary layer thickness to the baroclinic deformation radius. Thus, the boundary current scales depend on the stratification, wind stress, Coriolis parameter, and its meridional variation. In contrast to two-dimensional wind-driven coastal upwelling, the source waters that feed the Ekman upwelling are provided over the depth scale of this baroclinic current through a combination of onshore barotropic flow and from alongshore in the narrow boundary current. Topography forces an additional current whose characteristics depend on the topographic slope and width. For topography wider than the inertial boundary layer thickness the current is bottom intensified, while for narrow topography the current is wave-like in the vertical and trapped over the topography within the inertial boundary layer. An idealized primitive equation numerical model produces a similar baroclinic boundary current whose vertical length scale agrees with the theoretical scaling for both upwelling and downwelling favorable winds.
    Description: This research is supported in part by the China Scholarship Council (201906330102). H. G. is financially supported by the China Scholarship Council to study at WHOI for 2 years as a guest student. M.S. is supported by the National Science Foundation Grant OCE-1922538. Z. C. is supported by the ‘Taishan/Aoshan’ Talents program (2017ASTCPES05) the Fundamental Research Funds for the Central Universities (202072001).
    Description: 2023-03-30
    Keywords: Ekman pumping/transport ; Upwelling/downwelling ; Coastal flows
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    Shear turbulence in the high-wind Southern Ocean using direct measurements (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-10-12
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(10), (2022): 2325–2341, https://doi.org/10.1175/jpo-d-21-0015.1.
    Description: The ocean surface boundary layer is a gateway of energy transfer into the ocean. Wind-driven shear and meteorologically forced convection inject turbulent kinetic energy into the surface boundary layer, mixing the upper ocean and transforming its density structure. In the absence of direct observations or the capability to resolve subgrid-scale 3D turbulence in operational ocean models, the oceanography community relies on surface boundary layer similarity scalings (BLS) of shear and convective turbulence to represent this mixing. Despite their importance, near-surface mixing processes (and ubiquitous BLS representations of these processes) have been undersampled in high-energy forcing regimes such as the Southern Ocean. With the maturing of autonomous sampling platforms, there is now an opportunity to collect high-resolution spatial and temporal measurements in the full range of forcing conditions. Here, we characterize near-surface turbulence under strong wind forcing using the first long-duration glider microstructure survey of the Southern Ocean. We leverage these data to show that the measured turbulence is significantly higher than standard shear-convective BLS in the shallower parts of the surface boundary layer and lower than standard shear-convective BLS in the deeper parts of the surface boundary layer; the latter of which is not easily explained by present wave-effect literature. Consistent with the CBLAST (Coupled Boundary Layers and Air Sea Transfer) low winds experiment, this bias has the largest magnitude and spread in the shallowest 10% of the actively mixing layer under low-wind and breaking wave conditions, when relatively low levels of turbulent kinetic energy (TKE) in surface regime are easily biased by wave events.
    Description: This paper is VIMS Contribution 4103. Computational resources were provided by the VIMS Ocean-Atmosphere and Climate Change Research Fund. AUSSOM was supported by the OCE Division of the National Science Foundation (1558639).
    Keywords: Turbulence ; Wind shear ; Boundary layer ; Parameterization
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  • 26
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    Human-autonomy teaming for improved diver navigation (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2022.
    Description: Diving operations are inherently complex due to navigation and communication limitations. Until recently, fixed-beacon acoustic localization techniques have served as the primary means of improving diver navigation. However, modern artificial intelligence and acoustic modem technologies have enabled accurate relative navigation methods between a diver and an autonomous vehicle. Human-robot collaboration takes advantage of each member’s strengths to create the most effective team. This concept proves especially advantageous within the ocean domain, where humans are naturally deficient navigators. Yet humans serve as the team’s creative spirit, offering the critical thinking and flexibility needed to succeed in an unpredictable and dynamic environment. Recent underwater human-robot cooperative navigation systems typically rely on autonomous surface vehicles (ASVs), specially designed underwater vehicles, or stereo cameras. This thesis proposes a diver navigation method exhibiting significantly improved accuracy over dead reckoning without relying on a surface presence, cameras, or fixed acoustic beacons. Specifically, we develop and evaluate the communication architecture and autonomous behaviors required to guide a diver to a target location using subsurface humanautonomous underwater vehicle (AUV) teaming with no requirement for ocean current data or exact diver speeds. By depending on acoustic communication and commercial AUV navigation capabilities, our method has increased accessibility, applicability, and robustness over former techniques. We utilize the Woods Hole Oceanographic Institution (WHOI) Micromodem 2’s twoway-travel-time (TWTT) capability to enable range-only single-beacon navigation between two kayaks serving as proxies for the diver and Remote Environmental Monitoring Units (REMUS) 100 AUV. During processing, a nonlinear least-squares (NLS) method, called incremental smoothing and mapping 2 (iSAM2), utilizes odometry and range measurements to provide real-time diver position estimates given unknown ocean currents. Field experiments demonstrate an average online endpoint error of 4.53 meters after transits four hundred meters long. Additionally, simulations test our method’s performance in more challenging situations than those experienced in the field. Overall, this research progresses the interoperability of divers and AUVs.
    Description: The United States Navy funded my graduate education. The Office of Naval Research also partially supported this work under grant N00014-18-1-2832.
    Keywords: Human-autonomy teaming ; Autonomous underwater vehicle ; Diver navigation
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    Molecular characterization of organically bound copper in the marine environment (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 2022.
    Description: Marine microbes require copper (Cu) for a variety of key enzymes and can therefore experience limitation when concentrations are low. However, when Cu concentrations are too high, it becomes toxic causing decreased cell growth and even cell death. Laboratory culture experiments have shown that a diverse array of microbes produce organic ligands that complex Cu (CuL) and buffer the free ion concentration, which is the most bioavailable fraction. In this way, the microbes impose a control on the speciation of Cu, decreasing the toxic effects of Cu and making seawater conditions favorable for growth. Studies have shown that CuL complexes produced in laboratory cultures have similar complexation strengths to those found in seawater samples, which suggests a biological source of CuLs in seawater where dissolved Cu is almost entirely bound by organic ligands. However, information about individual CuL complexes is lacking which limits our understanding of the sources, sinks, and cycling of dissolved Cu. In order to fill this gap in knowledge, molecular level information about CuL complexes produced in culture and found in seawater must be obtained. To investigate this, liquid chromatography (LC) was coupled to two mass spectrometers (MS), an inductively coupled plasma (ICP) MS and an electrospray ionization (ESI) MS. By using data supplied by both techniques, the molecular charateristics of CuLs were determined laboratory cultures of the marine diatom Phaeodactylum tricornutum and the cyanobacterium Synechococcus, as well as investigating the distribution of CuLs in natural seawater samples along a line from 56°N to 20°S, along 152°W through the north and central Pacific Ocean. The CuLs identified in laboratory cultures had molecular formulae and fragmentation patterns characteristic of linear tetrapyrroles, a group of organic compounds commonly found in biological systems. This identification was further supported by absorbance and nuclear magnetic resonance spectroscopy. The distribution of CuLs in the Pacific Ocean showed a highly dynamic and complex mixture of ligands, closely tied to biological cycles.
    Description: Funding for this work was provided by the National Science Foundation Graduate Research Fellowship Program (NSF award 1122374) for providing three years of funding. Thank you to the National Science Foundation Chemical Oceanography Program (NSF award OCE-1736280 and OCE-2045223) and the Simons Collaboration on Ocean Processes and Ecology (award P49476). A portion of this work was performed at the National High Magnetic Field Laboratory in Tallahassee, Florida, which is supported through NSF DMR 11-57490, and the State of Florida.
    Keywords: Organic ligands ; Copper ; LC-MS
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    Barium isotope cycling in the marine environment: pathways of fractionation and implications for paleoceanographic applications (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 2022.
    Description: Removal of particulate organic carbon (POC) from sunlit surface waters into the deep ocean represents a climatically important sink of atmospheric carbon dioxide (CO2), linking the biogeochemical cycling of POC to CO2-driven climate change. As POC is not well preserved in the sediment record, other proxies, including the chemistry of barium (Ba) in the ocean and through the sedimentary record, offer an avenue to investigate oceanic carbon export through Earth’s history. This thesis seeks to constrain the controls on the formation, cycling, and isotopic signature of the main particulate phase of marine barium, the mineral barite (BaSO4) through its inception in the water column, during deposition, and ultimately into the rock record. To that end, I characterize the depth, spatial region, and general controls on particulate Ba formation in the South Pacific Ocean through shipboard experimentation and find that particulate Ba forms mainly in the surface of the Polar Frontal Zone in the presence of large particles and microbial activity. Next, I characterize the effect of ion exchange on BaSO4, a process previously unstudied under marine conditions, in a laboratory setting. Ion exchange occurs rapidly between dissolved Ba and BaSO4 and imparts a characteristic net offset between the Ba isotope composition of the dissolved and solid phase, which arises through a combination of Ba isotope fractionation during both precipitation and dissolution. Finally, I investigate the role of ion exchange in marine settings using co-located pore fluids and sedimented BaSO4. Modeling constrained by data from natural samples produce results that are consistent with the laboratory study, suggesting that this mode of isotopic fractionation impacts Ba isotopes in the environment and must be accounted for when applying Ba based climate proxies.
    Description: Funding for this work was provided by the National Science Foundation (OCE-2023456 & OCE-1827401), the Woods Hole Oceanographic Institution Ocean Ventures Fund, a National Science Foundation Graduate Research Fellowship (2017250048), and Woods Hole Oceanographic Institution.
    Keywords: Barium isotopes ; Geochemistry ; Paleoceanography
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    The Gulf Stream: along-stream evolution of volume transport and water properties observed by underwater gliders (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2021.
    Description: The Gulf Stream, the western boundary current of the subtropical North Atlantic, plays a key role in the Earth’s climate system with its poleward volume and heat transports being major components of the upper limb of the Atlantic Meridional Overturning Circulation. Extensive observations collected using Spray autonomous underwater gliders from 2004 through 2020 fill a 1500-km-long gap in longer-term sustained subsurface measurements of the Gulf Stream. The gliders provide concurrent, high-resolution measurements of Gulf Stream hydrography and velocity over more than 15 degrees of latitude between Florida and New England. These observations are used to characterize the along-stream evolution of Gulf Stream volume transport; its long-known poleward increase is shown to result primarily from entrainment of subthermocline waters. Antarctic Intermediate Water, which makes up the deepest waters within the Gulf Stream in the Florida Strait, is eroded through both vertical mixing and lateral stirring as it flows downstream. Satellite-based observations of sea surface height coincident with the glider observations are used to evaluate the efficacy of inferring Gulf Stream transport from remotely sensed measurements. The detailed analyses of Gulf Stream transport and water property evolution herein provide targets for regional and global circulation models to replicate.
    Description: We gratefully acknowledge funding from the National Science Foundation (OCE-0220769, OCE-1633911, OCE-1923362, OCE-1558521), NOAA’s Global Ocean Monitoring and Observing Program (NA14OAR4320158, NA19OAR4320074), the Office of Naval Research (N000141713040), WHOI’s Oceans and Climate Change Institute, Eastman Chemical Company, and the W. Van Alan Clark, Jr. Chair for Excellence in Oceanography at WHOI (awarded to Breck Owens).
    Keywords: Gulf Stream ; Autonomous underwater gliders ; Volume transport
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    Constraining natural and anthropogenic disturbances in the delivery of coastal ecosystem services (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2022.
    Description: Coastal ecosystems provide key services that benefit human wellbeing yet are undergoing rapid degradation due to natural and anthropogenic pressures. This thesis seeks to understand how disturbances impact salt marsh and estuarine ecosystem functioning in order to refine their role in coastal ecosystem service delivery and predict future resilience. Salt marsh survival relative to sealevel rise increasingly relies on the accumulation and preservation of soil organic carbon (SOC). Firstly, I characterized SOC development and turnover in a New England salt marsh and found that salt marsh soils typically store marsh grass-derived compounds that are reworked over centuries-to-millennia. Next, I assessed how two common marsh disturbances – natural ponding and anthropogenic mosquito ditching – affect salt marsh carbon cycling and storage. Salt marsh ponds deepen through soil erosion and decomposition of long-buried marsh peat. Further, the SOC lost during pond development is not fully recouped once drained ponds are revegetated and virtually indistinguishable from the surrounding marsh. Mosquito ditches, which were installed in ~ 90% of New England salt marshes during the Great Depression, did not significantly alter marsh carbon storage. In Buzzards Bay, Massachusetts, a US National Estuary, we tested relationships among measures of estuarine water quality, recreational activity, and local socioeconomic conditions to understand how the benefits of cultural ecosystem services are affected by shifts in water quality associated with global change and anthropogenic activity. Over a 24-year period, water quality degradation coinciding with increases in Chlorophyll a is associated with declines in fishery abundance and cultural ecosystem service values ($0.08 – 0.67 million USD). In combination, incorporation of both anthropogenic and natural disturbances to coastal ecosystem functioning and service delivery can produce improved estimates of ecosystem service valuation for effective resource decision-making under future climate scenarios.
    Description: Funding for this work was provided by John D. and Catherine T. MacArthur Foundation (Grant no. 14-106159-000-CFP), National Science Foundation (OCE1233678), National Oceanic and Atmospheric Administration, National Oceanic and Atmospheric Administration – National Estuaries Research Reserve Collaborative (NA14OAR4170104 and NA- 14NOS4190145), Woods Hole Sea Grant (NA14OAR4170104), MIT Sea Grant (subaward number 5710004045), Ocean Ventures Fund, the Marine Policy Center Johnson Endowment, and Woods Hole Oceanographic Institution.
    Keywords: Salt marsh ; Geochemistry ; Carbon storage
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    Questions and clarity: insights from applying computational methods to paleoclimate archives (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Marine Geology & Geophysics at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 2022.
    Description: It is a scientifically accepted fact that the Earth’s climate is presently undergoing significant changes with the potential for immense negative impacts on human society. As evidence of these impacts become clear and common, it becomes ever more important to constrain the nature, magnitude, and speed of changes to Earth systems. A fundamentally important tool to this understanding is the Earth’s past, recorded in the geologic record. There, lie examples of climate change under various forcings: important data for understanding the fundamental dynamics of climate change on our planet. However, when a climate signal is written in the geologic record, it is coded into the language of proxies and distorted by time. This thesis endeavors to decode that record using a variety of computational methods on a number of challenging proxies, to draw more information from the climate past than has previously been possible. First, machine learning and computer vision are used to decipher the primary, centimeter-scale textures of carbonate deposits in Searles Valley and Mono Lake, California. This work is able to connect facies in the tufa at Searles, grown during the Last Glacial Period, and those forming presently at Mono Lake. Next, the tracks of icebergs purged during Heinrich Events are simulated using the MIT General Circulation Model. This work, running multiple experiments exploring different aspects internal and external to the icebergs, reveals wind and sediment partitioning as centrally important to the spatial extent of Heinrich Layers. Each of these works considers a traditional geologic archive – a carbonate facies, a marine sediment layer – and uses computational methods to approach that archive from a different perspective. By applying these new methods, more information can be gleaned from the geologic record, building a richer narrative of the Earth’s climate history. The final chapter of this thesis discusses effective teaching and strategies for building communities to support teaching practice in Earth Science departments.
    Description: This thesis work was funded by the MIT EAPS Rasmussen and Whiteman Fellowships, NSF Project Number NSF-EAR-1903544, and the WHOI Academic Programs Office.
    Keywords: Paleoclimate ; Iceberg ; Modeling
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    Closing the water cycle from observations across scales: where do we stand? (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-05-27
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 102(10), (2021): E1897–E1935, https://doi.org/10.1175/BAMS-D-19-0316.1.
    Description: Life on Earth vitally depends on the availability of water. Human pressure on freshwater resources is increasing, as is human exposure to weather-related extremes (droughts, storms, floods) caused by climate change. Understanding these changes is pivotal for developing mitigation and adaptation strategies. The Global Climate Observing System (GCOS) defines a suite of essential climate variables (ECVs), many related to the water cycle, required to systematically monitor Earth’s climate system. Since long-term observations of these ECVs are derived from different observation techniques, platforms, instruments, and retrieval algorithms, they often lack the accuracy, completeness, and resolution, to consistently characterize water cycle variability at multiple spatial and temporal scales. Here, we review the capability of ground-based and remotely sensed observations of water cycle ECVs to consistently observe the hydrological cycle. We evaluate the relevant land, atmosphere, and ocean water storages and the fluxes between them, including anthropogenic water use. Particularly, we assess how well they close on multiple temporal and spatial scales. On this basis, we discuss gaps in observation systems and formulate guidelines for future water cycle observation strategies. We conclude that, while long-term water cycle monitoring has greatly advanced in the past, many observational gaps still need to be overcome to close the water budget and enable a comprehensive and consistent assessment across scales. Trends in water cycle components can only be observed with great uncertainty, mainly due to insufficient length and homogeneity. An advanced closure of the water cycle requires improved model–data synthesis capabilities, particularly at regional to local scales.
    Description: WD acknowledges ESA’s QA4EO (ISMN) and CCI Soil Moisture projects. WD, CRV, AG, and KL acknowledge the G3P project, which has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement 870353. MIH and MS acknowledge ESA’s CCI Water Vapour project. MS and RH acknowledges the support by the EUMETSAT member states through CM SAF. DGM acknowledges support from the European Research Council (ERC) under Grant Agreement 715254 (DRY–2–DRY). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).
    Description: 2022-04-01
    Keywords: Hydrologic cycle ; Satellite observations ; Surface fluxes ; Surface observations ; Water masses/storage ; Water budget/balance
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    Bay of Bengal intraseasonal oscillations and the 2018 monsoon onset (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-05-27
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 102(10), (2021): E1936–E1951, https://doi.org/10.1175/BAMS-D-20-0113.1.
    Description: In the Bay of Bengal, the warm, dry boreal spring concludes with the onset of the summer monsoon and accompanying southwesterly winds, heavy rains, and variable air–sea fluxes. Here, we summarize the 2018 monsoon onset using observations collected through the multinational Monsoon Intraseasonal Oscillations in the Bay of Bengal (MISO-BoB) program between the United States, India, and Sri Lanka. MISO-BoB aims to improve understanding of monsoon intraseasonal variability, and the 2018 field effort captured the coupled air–sea response during a transition from active-to-break conditions in the central BoB. The active phase of the ∼20-day research cruise was characterized by warm sea surface temperature (SST 〉 30°C), cold atmospheric outflows with intermittent heavy rainfall, and increasing winds (from 2 to 15 m s−1). Accumulated rainfall exceeded 200 mm with 90% of precipitation occurring during the first week. The following break period was both dry and clear, with persistent 10–12 m s−1 wind and evaporation of 0.2 mm h−1. The evolving environmental state included a deepening ocean mixed layer (from ∼20 to 50 m), cooling SST (by ∼1°C), and warming/drying of the lower to midtroposphere. Local atmospheric development was consistent with phasing of the large-scale intraseasonal oscillation. The upper ocean stores significant heat in the BoB, enough to maintain SST above 29°C despite cooling by surface fluxes and ocean mixing. Comparison with reanalysis indicates biases in air–sea fluxes, which may be related to overly cool prescribed SST. Resolution of such biases offers a path toward improved forecasting of transition periods in the monsoon.
    Description: This work was supported through the U.S. Office of Naval Research’s Departmental Research Initiative: Monsoon Intraseasonal Oscillations in the Bay of Bengal, the Indian Ministry of Earth Science’s Ocean Mixing and Monsoons Program, and the Sri Lankan National Aquatic Resources Research and Development Agency. We thank the Captain and crew of the R/V Thompson for their help in data collection. Surface atmospheric fields included fluxes were quality controlled and processed by the Boundary Layer Observations and Processes Team within the NOAA Physical Sciences Laboratory. Forecast analysis was completed by India Meteorological Department. Drone image was taken by Shreyas Kamat with annotations by Gualtiero Spiro Jaeger. We also recognize the numerous researchers who supported cruise- and land-based measurements. This work represents Lamont-Doherty Earth Observatory contribution number 8503, and PMEL contribution number 5193.
    Description: 2022-04-01
    Keywords: Atmosphere-ocean interaction ; Monsoons ; In situ atmospheric observations ; In situ oceanic observations
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    On the origins of the oceanic ultraviolet catastrophe (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-09-25
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(4), (2022): 597–616, https://doi.org/10.1175/jpo-d-21-0121.1.
    Description: We provide a first-principles analysis of the energy fluxes in the oceanic internal wave field. The resulting formula is remarkably similar to the renowned phenomenological formula for the turbulent dissipation rate in the ocean, which is known as the finescale parameterization. The prediction is based on the wave turbulence theory of internal gravity waves and on a new methodology devised for the computation of the associated energy fluxes. In the standard spectral representation of the wave energy density, in the two-dimensional vertical wavenumber–frequency (m–ω) domain, the energy fluxes associated with the steady state are found to be directed downscale in both coordinates, closely matching the finescale parameterization formula in functional form and in magnitude. These energy transfers are composed of a “local” and a “scale-separated” contributions; while the former is quantified numerically, the latter is dominated by the induced diffusion process and is amenable to analytical treatment. Contrary to previous results indicating an inverse energy cascade from high frequency to low, at odds with observations, our analysis of all nonzero coefficients of the diffusion tensor predicts a direct energy cascade. Moreover, by the same analysis fundamental spectra that had been deemed “no-flux” solutions are reinstated to the status of “constant-downscale-flux” solutions. This is consequential for an understanding of energy fluxes, sources, and sinks that fits in the observational paradigm of the finescale parameterization, solving at once two long-standing paradoxes that had earned the name of “oceanic ultraviolet catastrophe.”
    Description: The authors gratefully acknowledge support from the ONR Grant N00014-17-1-2852. YL gratefully acknowledges support from NSF DMS Award 2009418.
    Description: 2022-09-25
    Keywords: Ocean ; Gravity waves ; Nonlinear dynamics ; Ocean dynamics ; Mixing ; Fluxes ; Isopycnal coordinates ; Nonlinear models
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    The effects of uncorrelated measurement noise on SWOT estimates of sea-surface height, velocity and vorticity (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-08-12
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(7), (2022): 1053–1083, https://doi.org/10.1175/jtech-d-21-0167.1.
    Description: The Ka-band Radar Interferometer (KaRIn) on the Surface Water and Ocean Topography (SWOT) satellite will revolutionize satellite altimetry by measuring sea surface height (SSH) with unprecedented accuracy and resolution across two 50-km swaths separated by a 20-km gap. The original plan to provide an SSH product with a footprint diameter of 1 km has changed to providing two SSH data products with footprint diameters of 0.5 and 2 km. The swath-averaged standard deviations and wavenumber spectra of the uncorrelated measurement errors for these footprints are derived from the SWOT science requirements that are expressed in terms of the wavenumber spectrum of SSH after smoothing with a filter cutoff wavelength of 15 km. The availability of two-dimensional fields of SSH within the measurement swaths will provide the first spaceborne estimates of instantaneous surface velocity and vorticity through the geostrophic equations. The swath-averaged standard deviations of the noise in estimates of velocity and vorticity derived by propagation of the uncorrelated SSH measurement noise through the finite difference approximations of the derivatives are shown to be too large for the SWOT data products to be used directly in most applications, even for the coarsest footprint diameter of 2 km. It is shown from wavenumber spectra and maps constructed from simulated SWOT data that additional smoothing will be required for most applications of SWOT estimates of velocity and vorticity. Equations are presented for the swath-averaged standard deviations and wavenumber spectra of residual noise in SSH and geostrophically computed velocity and vorticity after isotropic two-dimensional smoothing for any user-defined smoother and filter cutoff wavelength of the smoothing.
    Description: This research was supported by NASA Grant NNX16AH76G.
    Keywords: Sea level ; Altimetry ; Remote sensing ; Satellite observations ; Error analysis
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    Turbulent mixing variability in an energetic standing meander of the Southern Ocean (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-08-29
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(8), (2022): 1593-1611, https://doi.org/10.1175/jpo-d-21-0180.1.
    Description: This study presents novel observational estimates of turbulent dissipation and mixing in a standing meander between the Southeast Indian Ridge and the Macquarie Ridge in the Southern Ocean. By applying a finescale parameterization on the temperature, salinity, and velocity profiles collected from Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats in the upper 1600 m, we estimated the intensity and spatial distribution of dissipation rate and diapycnal mixing along the float tracks and investigated the sources. The indirect estimates indicate strong spatial and temporal variability of turbulent mixing varying from O(10−6) to O(10−3) m2 s−1 in the upper 1600 m. Elevated turbulent mixing is mostly associated with the Subantarctic Front (SAF) and mesoscale eddies. In the upper 500 m, enhanced mixing is associated with downward-propagating wind-generated near-inertial waves as well as the interaction between cyclonic eddies and upward-propagating internal waves. In the study region, the local topography does not play a role in turbulent mixing in the upper part of the water column, which has similar values in profiles over rough and smooth topography. However, both remotely generated internal tides and lee waves could contribute to the upward-propagating energy. Our results point strongly to the generation of turbulent mixing through the interaction of internal waves and the intense mesoscale eddy field.
    Description: The observations were funded through grants from the Australian Research Council Discovery Project (DP170102162) and Australia’s Marine National Facility. Surface drifters were provided by Dr. Shaun Dolk of the Global Drifter Program. AC was supported by an Australian Research Council Postdoctoral Fellowship. AC, HEP, and NLB acknowledge support from the Australian Government Department of the Environment and Energy National Environmental Science Program and the ARC Centre of Excellence in Climate Extremes. KP acknowledges the support from the National Science Foundation.
    Keywords: Diapycnal mixing ; Eddies ; Fronts ; Inertia-gravity waves ; Ocean dynamics
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    A shelf water cascading event near Cape Hatteras (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-08-25
    Description: Author Posting. © American Meteorological Society , 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Han, L., Seim, H., Bane, J., Todd, R. E., & Muglia, M. A shelf water cascading event near Cape Hatteras. Journal of Physical Oceanography, 51(6), (2021): 2021–2033, https://doi.org/10.1175/JPO-D-20-0156.1.
    Description: Carbon-rich Middle Atlantic Bight (MAB) and South Atlantic Bight (SAB) shelf waters typically converge on the continental shelf near Cape Hatteras. Both are often exported to the adjacent open ocean in this region. During a survey of the region in mid-January 2018, there was no sign of shelf water export at the surface. Instead, a subsurface layer of shelf water with high chlorophyll and dissolved oxygen was observed at the edge of the Gulf Stream east of Cape Hatteras. Strong cooling over the MAB and SAB shelves in early January led to shelf waters being denser than offshore surface waters. Driven by the density gradient, the denser shelf waters cascaded beneath the Gulf Stream and were subsequently entrained into the Gulf Stream, as they were advected northeastward. Underwater glider observations 80 km downstream of the export location captured 0.44 Sv (1 Sv ≡ 106 m3 s−1) of shelf waters transported along the edge of the Gulf Stream in January 2018. In total, as much as 7 × 106 kg of carbon was exported from the continental shelf to a greater depth in the open ocean during this 5-day-long cascading event. Earlier observations of near-bottom temperature and salinity at a depth of 230 m captured several multiday episodes of shelf water at a location that was otherwise dominated by Gulf Stream water, indicating that the January 2018 cascading event was not unique. Cascading is an important, yet little-studied pathway of carbon export and sequestration at Cape Hatteras.
    Description: This research was funded by the National Science Foundation (Grants OCE-1558920 to University of North Carolina at Chapel Hill and OCE-1558521 to Woods Hole Oceanographic Institution) as part of PEACH. We acknowledge and thank Sara Haines for the processing and QC of the mooring data, and we thank the PEACH group for helpful discussions and for their support. Additional thanks are given to the crew of R/V Armstrong (AR-26).
    Keywords: Continental shelf/slope ; Fronts ; In situ oceanic observations
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    Longwave radiation corrections for the OMNI Buoy Network (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-07-13
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(2), (2022): 271–282. https://doi.org/10.1175/jtech-d-21-0069.1.
    Description: The inception of a moored buoy network in the northern Indian Ocean in 1997 paved the way for systematic collection of long-term time series observations of meteorological and oceanographic parameters. This buoy network was revamped in 2011 with Ocean Moored buoy Network for north Indian Ocean (OMNI) buoys fitted with additional sensors to better quantify the air–sea fluxes. An intercomparison of OMNI buoy measurements with the nearby Woods Hole Oceanographic Institution (WHOI) mooring during the year 2015 revealed an overestimation of downwelling longwave radiation (LWR↓). Analysis of the OMNI and WHOI radiation sensors at a test station at National Institute of Ocean Technology (NIOT) during 2019 revealed that the accurate and stable amplification of the thermopile voltage records along with the customized datalogger in the WHOI system results in better estimations of LWR↓. The offset in NIOT measured LWR↓ is estimated first by segregating the LWR↓ during clear-sky conditions identified using the downwelling shortwave radiation measurements from the same test station, and second, finding the offset by taking the difference with expected theoretical clear-sky LWR↓. The corrected LWR↓ exhibited good agreement with that of collocated WHOI measurements, with a correlation of 0.93. This method is applied to the OMNI field measurements and again compared with the nearby WHOI mooring measurements, exhibiting a better correlation of 0.95. This work has led to the revamping of radiation measurements in OMNI buoys and provides a reliable method to correct past measurements and improve estimation of air–sea fluxes in the Indian Ocean.
    Description: KJJ and RV thank Ministry of Earth Sciences (MoES), Government of India, Secretary, MoES, and Director, NIOT, for the support and encouragement in carrying out the work under the National Monsoon Mission, Ocean Mixing and Monsoon (OMM) program. AT, JTF, and RAW thank Office of Naval Research Grants N00014-19-12410 and N00014-17-12880, United States, for funding and support. The OOS team at NIOT is acknowledged for their efforts in maintaining the OMNI buoy network in North Indian Ocean. We acknowledge Dr. B.W. Blomquist, University of Colorado, for his support in computing clear-sky radiation and Iury T. Simoes-Sousa, University of Massachusetts, Dartmouth, for the graphics. NCMRWF, MoES, Government of India, is acknowledged for NGFS reanalysis dataset, which is produced under the collaboration between NCMRWF, IITM, and IMD.
    Keywords: Algorithms ; Buoy observations ; In situ oceanic observations ; Instrumentation/sensors ; Quality assurance/control
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    Quantifying spread in spatiotemporal changes of upper-ocean heat content estimates: an internationally coordinated comparison (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-09-14
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 35(2), (2022): 851–875, https://doi.org/10.1175/JCLI-D-20-0603.1.
    Description: The Earth system is accumulating energy due to human-induced activities. More than 90% of this energy has been stored in the ocean as heat since 1970, with ∼60% of that in the upper 700 m. Differences in upper-ocean heat content anomaly (OHCA) estimates, however, exist. Here, we use a dataset protocol for 1970–2008—with six instrumental bias adjustments applied to expendable bathythermograph (XBT) data, and mapped by six research groups—to evaluate the spatiotemporal spread in upper OHCA estimates arising from two choices: 1) those arising from instrumental bias adjustments and 2) those arising from mathematical (i.e., mapping) techniques to interpolate and extrapolate data in space and time. We also examined the effect of a common ocean mask, which reveals that exclusion of shallow seas can reduce global OHCA estimates up to 13%. Spread due to mapping method is largest in the Indian Ocean and in the eddy-rich and frontal regions of all basins. Spread due to XBT bias adjustment is largest in the Pacific Ocean within 30°N–30°S. In both mapping and XBT cases, spread is higher for 1990–2004. Statistically different trends among mapping methods are found not only in the poorly observed Southern Ocean but also in the well-observed northwest Atlantic. Our results cannot determine the best mapping or bias adjustment schemes, but they identify where important sensitivities exist, and thus where further understanding will help to refine OHCA estimates. These results highlight the need for further coordinated OHCA studies to evaluate the performance of existing mapping methods along with comprehensive assessment of uncertainty estimates.
    Description: AS is supported by a Tasmanian Graduate Research Scholarship, a CSIRO-UTAS Quantitative Marine Science top-up, and by the Australian Research Council (ARC) (CE170100023; DP160103130). CMD was partially supported by ARC (FT130101532) and the Natural Environmental Research Council (NE/P019293/1). RC was supported through funding from the Earth Systems and Climate Change Hub of the Australian Government’s National Environmental Science Program. TB is supported by the Climate Observation and Monitoring Program, National Oceanic and Atmosphere Administration, U.S. Department of commerce. GCJ and JML are supported by NOAA Research and the NOAA Ocean Climate Observation Program. This is PMEL contribution number 5065. JAC is supported by the Centre for Southern Hemisphere Oceans Research (CSHOR), jointly funded by the Qingdao National Laboratory for Marine Science and Technology (QNLM, China) and the Commonwealth Scientific and Industrial Research Organization (CSIRO, Australia) and Australian Research Council’s Discovery Project funding scheme (project DP190101173). The research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). Data used in this study are available on request.
    Keywords: Bias ; Interpolation schemes ; In situ oceanic observations ; Uncertainty ; Oceanic variability ; Trends
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    Direction finding and likelihood ratio detection for oceanographic HF radars (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-09-15
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(2), (2022): 223–235, https://doi.org/10.1175/JTECH-D-21-0110.1.
    Description: Previous work with simulations of oceanographic high-frequency (HF) radars has identified possible improvements when using maximum likelihood estimation (MLE) for direction of arrival; however, methods for determining the number of emitters (here defined as spatially distinct patches of the ocean surface) have not realized these improvements. Here we describe and evaluate the use of the likelihood ratio (LR) for emitter detection, demonstrating its application to oceanographic HF radar data. The combined detection–estimation methods MLE-LR are compared with multiple signal classification method (MUSIC) and MUSIC parameters for SeaSonde HF radars, along with a method developed for 8-channel systems known as MUSIC-Highest. Results show that the use of MLE-LR produces similar accuracy, in terms of the RMS difference and correlation coefficients squared, as previous methods. We demonstrate that improved accuracy can be obtained for both methods, at the cost of fewer velocity observations and decreased spatial coverage. For SeaSondes, accuracy improvements are obtained with less commonly used parameter sets. The MLE-LR is shown to be able to resolve simultaneous closely spaced emitters, which has the potential to improve observations obtained by HF radars operating in complex current environments.
    Description: This work was supported by the National Science Foundation (NSF) under Grant OCE-1658475. Computing resources were provided by the UCSB Center for Scientific Computing through an NSF MRSEC (DMR-1720256) and NSF CNS-1725797.
    Keywords: Ocean ; Algorithms ; Data quality control ; Radars/radar observations ; Remote sensing ; Surface observations ; Quality assurance/control
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    Kinetic energy transfers between mesoscale and submesoscale motions in the open ocean’s upper layers (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-09-15
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(1),(2022): 75–97, https://doi.org/10.1175/JPO-D-21-0099.1.
    Description: Mesoscale eddies contain the bulk of the ocean’s kinetic energy (KE), but fundamental questions remain on the cross-scale KE transfers linking eddy generation and dissipation. The role of submesoscale flows represents the key point of discussion, with contrasting views of submesoscales as either a source or a sink of mesoscale KE. Here, the first observational assessment of the annual cycle of the KE transfer between mesoscale and submesoscale motions is performed in the upper layers of a typical open-ocean region. Although these diagnostics have marginal statistical significance and should be regarded cautiously, they are physically plausible and can provide a valuable benchmark for model evaluation. The cross-scale KE transfer exhibits two distinct stages, whereby submesoscales energize mesoscales in winter and drain mesoscales in spring. Despite this seasonal reversal, an inverse KE cascade operates throughout the year across much of the mesoscale range. Our results are not incompatible with recent modeling investigations that place the headwaters of the inverse KE cascade at the submesoscale, and that rationalize the seasonality of mesoscale KE as an inverse cascade-mediated response to the generation of submesoscales in winter. However, our findings may challenge those investigations by suggesting that, in spring, a downscale KE transfer could dampen the inverse KE cascade. An exploratory appraisal of the dynamics governing mesoscale–submesoscale KE exchanges suggests that the upscale KE transfer in winter is underpinned by mixed layer baroclinic instabilities, and that the downscale KE transfer in spring is associated with frontogenesis. Current submesoscale-permitting ocean models may substantially understate this downscale KE transfer, due to the models’ muted representation of frontogenesis.
    Description: The OSMOSIS experiment was funded by the U.K. Natural Environment Research Council (NERC) through Grants NE/1019999/1 and NE/101993X/1. ACNG acknowledges the support of the Royal Society and the Wolfson Foundation, and XY that of a China Scholarship Council PhD studentship.
    Keywords: Ageostrophic circulations ; Dynamics ; Eddies ; Energy transport ; Frontogenesis/frontolysis ; Instability ; Mesoscale processes ; Nonlinear dynamics ; Ocean circulation ; Ocean dynamics ; Small scale processes ; Turbulence
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    Seasonality of the mesoscale inverse cascade as inferred from global scale-dependent eddy energy observations (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-09-01
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(8), (2022): 1677-1691, https://doi.org/10.1175/jpo-d-21-0269.1.
    Description: Oceanic mesoscale motions including eddies, meanders, fronts, and filaments comprise a dominant fraction of oceanic kinetic energy and contribute to the redistribution of tracers in the ocean such as heat, salt, and nutrients. This reservoir of mesoscale energy is regulated by the conversion of potential energy and transfers of kinetic energy across spatial scales. Whether and under what circumstances mesoscale turbulence precipitates forward or inverse cascades, and the rates of these cascades, remain difficult to directly observe and quantify despite their impacts on physical and biological processes. Here we use global observations to investigate the seasonality of surface kinetic energy and upper-ocean potential energy. We apply spatial filters to along-track satellite measurements of sea surface height to diagnose surface eddy kinetic energy across 60–300-km scales. A geographic and scale-dependent seasonal cycle appears throughout much of the midlatitudes, with eddy kinetic energy at scales less than 60 km peaking 1–4 months before that at 60–300-km scales. Spatial patterns in this lag align with geographic regions where an Argo-derived estimate of the conversion of potential to kinetic energy is seasonally varying. In midlatitudes, the conversion rate peaks 0–2 months prior to kinetic energy at scales less than 60 km. The consistent geographic patterns between the seasonality of potential energy conversion and kinetic energy across spatial scale provide observational evidence for the inverse cascade and demonstrate that some component of it is seasonally modulated. Implications for mesoscale parameterizations and numerical modeling are discussed.
    Description: This work was generously funded by NSF Grants OCE-1912302, OCE-1912125 (Drushka), and OCE-1912325 (Abernathey) as part of the Ocean Energy and Eddy Transport Climate Process Team.
    Keywords: Eddies ; Energy transport ; Mesoscale processes ; Turbulence ; Oceanic mixed layer ; Altimetry ; Seasonal cycle
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    A note on the depth of sidelobe contamination in acoustic doppler current profiles (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-09-23
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(1), (2022): 31–35, https://doi.org/10.1175/JTECH-D-21-0075.1.
    Description: Acoustic Doppler current profilers (ADCP) do not provide reliable water velocity measurements near the sea surface or bottom because acoustic sidelobe reflections from the boundary contaminate the Doppler velocity measurements. The apparent depth of the center of the sidelobe reflection is zsl = ha[1 − cos(θ)], where ha is the distance from the ADCP acoustic head to the sea surface and θ is the ADCP beam angle. However, sidelobe contamination extends one and a half ADCP bins below zsl as the range gating of the acoustic return causes overlap between adjacent ADCP bins. Consequently, the contaminated region z 〈 zsl + 3Δz/2 is deeper than traditionally suggested, with a dependence on bin size Δz. Direct observations confirming both the center depth of the sidelobe reflection and the depth of contamination are presented for six bottom-mounted, upward-looking ADCPs. The sidelobe reflection is isolated by considering periods of weak wind stresses when the sea surface is smooth and there is nearly perfect reflection of the main beams away from the ADCP and hence little acoustic return from the main beams to the ADCP.
    Description: This analysis was supported by NSF OCE 1558874 for Kirincich and Lentz. Plueddemann was supported by the Global Ocean Monitoring and Observing Program of the National Oceanic and Atmospheric Administration (CPO Fund Reference Number 100007298), through the Cooperative Institute for the North Atlantic Region (CINAR) under Cooperative Agreement NA14OAR4320158.
    Keywords: Acoustic measurements/effects ; Data processing/distribution ; Profilers ; oceanic
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    Observed deep cyclonic eddies around Southern Greenland (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-06
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 51(10), (2021): 3235–3252, https://doi.org/10.1175/JPO-D-20-0288.1.
    Description: Recent mooring measurements from the Overturning in the Subpolar North Atlantic Program have revealed abundant cyclonic eddies at both sides of Cape Farewell, the southern tip of Greenland. In this study, we present further observational evidence, from both Eulerian and Lagrangian perspectives, of deep cyclonic eddies with intense rotation (ζ/f 〉 1) around southern Greenland and into the Labrador Sea. Most of the observed cyclones exhibit strongest rotation below the surface at 700–1000 dbar, where maximum azimuthal velocities are ~30 cm s−1 at radii of ~10 km, with rotational periods of 2–3 days. The cyclonic rotation can extend to the deep overflow water layer (below 1800 dbar), albeit with weaker azimuthal velocities (~10 cm s−1) and longer rotational periods of about one week. Within the middepth rotation cores, the cyclones are in near solid-body rotation and have the potential to trap and transport water. The first high-resolution hydrographic transect across such a cyclone indicates that it is characterized by a local (both vertically and horizontally) potential vorticity maximum in its middepth core and cold, fresh anomalies in the deep overflow water layer, suggesting its source as the Denmark Strait outflow. Additionally, the propagation and evolution of the cyclonic eddies are illustrated with deep Lagrangian floats, including their detachments from the boundary currents to the basin interior. Taken together, the combined Eulerian and Lagrangian observations have provided new insights on the boundary current variability and boundary–interior exchange over a geographically large scale near southern Greenland, calling for further investigations on the (sub)mesoscale dynamics in the region.
    Description: OOI mooring data are based upon work supported by the National Science Foundation under Cooperative Agreement 1743430. S. Zou, A. Bower, and H. Furey gratefully acknowledge the support from the Physical Oceanography Program of the U.S. National Science Foundation Grant OCE-1756361. R.S. Pickart acknowledges support from National Science Foundation Grants OCE-1259618 and OCE-1756361. N. P. Holliday and L. Houpert were supported by NERC programs U.K. OSNAP (NE/K010875) and U.K. OSNAP-Decade (NE/T00858X/1).
    Keywords: North Atlantic Ocean ; Cyclogenesis/cyclolysis ; Lagrangian circulation/transport ; Mesoscale processes ; Ocean circulation
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    The climatological rise in winter temperature- and dewpoint-based thaw events and their impact on snow depth on Mount Washington, New Hampshire (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-06
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Applied Meteorology and Climatology 60(9), (2021): 1361–1370, https://doi.org/10.1175/JAMC-D-20-0254.1.
    Description: We analyze how winter thaw events (TE; T 〉 0°C) are changing on the summit of Mount Washington, New Hampshire, using three metrics: the number of TE, number of thaw hours, and number of thaw degree-hours for temperature and dewpoint for winters from 1935/36 to 2019/20. The impact of temperature-only TE and dewpoint TE on snow depth are compared to quantify the different impacts of sensible-only heating and sensible-and-latent heating, respectively. Results reveal that temperature and dewpoint TE for all metrics increased at a statistically significant rate (p 〈 0.05) over the full time periods studied for temperature (1935/36–2019/20) and dewpoint (1939/40–2019/20). Notably, around 2000/01, the positive trends increased for most variables, including dewpoint-thaw degree-hours that increased by 82.11 degree-hours decade−1 during 2000–20, which is approximately 5 times as faster as the 1939–2020 rate of 17.70 degree-hours decade−1. Furthermore, a clear upward shift occurred around 1990 in the lowest winter values of thaw hours and thaw degree-hours—winters now have a higher baseline amount of thaw than before 1990. Snow-depth loss during dewpoint TE (0.36 cm h−1) occurred more than 2 times as fast as temperature-only TE (0.14 cm h−1). With winters projected to warm throughout the twenty-first century in the northeastern United States, it is expected that the trends in winter thaw events, and the sensible and latent energy that they bring, will continue to rise and lead to more frequent winter flooding, fewer days of good quality snow for winter recreation, and changes in ecosystem function.
    Keywords: Atmosphere ; Snowmelt/icemelt ; Snowpack ; Winter/cool season ; Climate change ; Humidity ; Latent heating/cooling ; Snow cover ; Temperature
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    3D structure of striations in the North Pacific (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-06
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 51(12),(2021): 3651–3662, https://doi.org/10.1175/JPO-D-21-0076.1.
    Description: Ocean striations are composed of alternating quasi-zonal band-like flows; this kind of organized structure of currents can be found in all the world’s oceans and seas. Previous studies have mainly been focused on the mechanisms of their generation and propagation. This study uses the spatial high-pass filtering to obtain the three-dimensional structure of ocean striations in the North Pacific in both the z coordinate and σ coordinate based on 10-yr averaged Simple Ocean Data Assimilation version 3 (SODA3) data. First, we identify an ideal-fluid potential density domain where the striations are undisturbed by the surface forcing and boundary effects. Second, using the isopycnal layer analysis, we show that on isopycnal surfaces the orientations of striations nearly follow the potential vorticity (PV) contours, while in the meridional–vertical plane the central positions of striations are generally aligned with the latitude of zero gradient of the relative PV. Our analysis provides a simple dynamical interpretation and better understanding for the role of ocean striations.
    Description: This work is supported by the National Natural Science Foundation of China (42076025, 41676021), the Key Special Project for introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0306), the National Basic Research Program (973 Program) of China (2013CB956201). The numerical simulation is supported by the High Performance Computing Division in the South China Sea Institute of Oceanography. The authors thank Tingjin Guan for the help in enhancing drawing quality.
    Keywords: Currents ; Jets ; Mesoscale processes ; Potential vorticity ; Isopycnal coordinates
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    Impacts of Arctic sea ice on cold season atmospheric variability and trends estimated from observations and a multimodel large ensemble (2022)
    American Meteorological Society
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    Publication Date: 2022-06-06
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Liang, Y.-C., Frankignoul, C., Kwon, Y.-O., Gastineau, G., Manzini, E., Danabasoglu, G., Suo, L., Yeager, S., Gao, Y., Attema, J. J., Cherchi, A., Ghosh, R., Matei, D., Mecking, J., Tian, T., & Zhang, Y. Impacts of Arctic sea ice on cold season atmospheric variability and trends estimated from observations and a multimodel large ensemble. Journal of Climate, 34(20), (2021): 8419–8443, https://doi.org/10.1175/JCLI-D-20-0578.s1.
    Description: To examine the atmospheric responses to Arctic sea ice variability in the Northern Hemisphere cold season (from October to the following March), this study uses a coordinated set of large-ensemble experiments of nine atmospheric general circulation models (AGCMs) forced with observed daily varying sea ice, sea surface temperature, and radiative forcings prescribed during the 1979–2014 period, together with a parallel set of experiments where Arctic sea ice is substituted by its climatology. The simulations of the former set reproduce the near-surface temperature trends in reanalysis data, with similar amplitude, and their multimodel ensemble mean (MMEM) shows decreasing sea level pressure over much of the polar cap and Eurasia in boreal autumn. The MMEM difference between the two experiments allows isolating the effects of Arctic sea ice loss, which explain a large portion of the Arctic warming trends in the lower troposphere and drive a small but statistically significant weakening of the wintertime Arctic Oscillation. The observed interannual covariability between sea ice extent in the Barents–Kara Seas and lagged atmospheric circulation is distinguished from the effects of confounding factors based on multiple regression, and quantitatively compared to the covariability in MMEMs. The interannual sea ice decline followed by a negative North Atlantic Oscillation–like anomaly found in observations is also seen in the MMEM differences, with consistent spatial structure but much smaller amplitude. This result suggests that the sea ice impacts on trends and interannual atmospheric variability simulated by AGCMs could be underestimated, but caution is needed because internal atmospheric variability may have affected the observed relationship.
    Description: We acknowledge support by the Blue-Action Project (the European Union’s Horizon 2020 research and innovation programme, #727852, http://www.blue-action.eu/index.php?id=3498). The WHOI–NCAR group was supported by the U.S. National Science Foundation (NSF) Office of Polar Programs Grants 1736738 and 1737377. Their computing and data storage resources, including the Cheyenne supercomputer (doi:10.5065/D6RX99HX), were provided by the Computational and Information Systems Laboratory at NCAR. NCAR is a major facility sponsored by the U.S. NSF under Cooperative Agreement No. 1852977. Guillaume Gastineau was granted access to the HPC resources of TGCC under the allocations A5-017403 and A7-017403 made by GENCI. The SST and SIC data were downloaded from the U.K. Met Office Hadley Centre Observations Datasets (http://www.metoffice.gov.uk/hadobs/hadisst). The work by NLeSC was carried out on the Dutch national e-infrastructure with the support of SURF Cooperative. The simulations of IAP AGCM were supported by the National Key R&D Program of China 2017YFE0111800. The NorESM2-CAM6 simulations were performed on resources provided by UNINETT Sigma2–the National Infrastructure for High Performance Computing and Data Storage in Norway (nn2343k, NS9015K).
    Keywords: Arctic ; Sea ice ; Atmospheric circulation ; Climate models
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    Impact of SST and surface waves on Hurricane Florence (2018): a coupled modeling investigation (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-10
    Description: Author Posting. © American Meteorological Society , 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Zambon, J. B., He, R., Warner, J. C., & Hegermiller, C. A. Impact of SST and surface waves on Hurricane Florence (2018): a coupled modeling investigation. Weather and Forecasting, 36(5), (2021): 1713–1734, https://doi.org/10.1175/WAF-D-20-0171.1.
    Description: Hurricane Florence (2018) devastated the coastal communities of the Carolinas through heavy rainfall that resulted in massive flooding. Florence was characterized by an abrupt reduction in intensity (Saffir–Simpson category 4 to category 1) just prior to landfall and synoptic-scale interactions that stalled the storm over the Carolinas for several days. We conducted a series of numerical modeling experiments in coupled and uncoupled configurations to examine the impact of sea surface temperature (SST) and ocean waves on storm characteristics. In addition to experiments using a fully coupled atmosphere–ocean–wave model, we introduced the capability of the atmospheric model to modulate wind stress and surface fluxes by ocean waves through data from an uncoupled wave model. We examined these experiments by comparing track, intensity, strength, SST, storm structure, wave height, surface roughness, heat fluxes, and precipitation in order to determine the impacts of resolving ocean conditions with varying degrees of coupling. We found differences in the storm’s intensity and strength, with the best correlation coefficient of intensity (r = 0.89) and strength (r = 0.95) coming from the fully coupled simulations. Further analysis into surface roughness parameterizations added to the atmospheric model revealed differences in the spatial distribution and magnitude of the largest roughness lengths. Adding ocean and wave features to the model further modified the fluxes due to more realistic cooling beneath the storm, which in turn modified the precipitation field. Our experiments highlight significant differences in how air–sea processes impact hurricane modeling. The storm characteristics of track, intensity, strength, and precipitation at landfall are crucial to predictability and forecasting of future landfalling hurricanes.
    Description: This work has been supported by the U.S. Geological Survey Coastal/Marine Hazards and Resources Program, and by Congressional appropriations through the Additional Supplemental Appropriations for Disaster Relief Act of 2019 (H.R. 2157). The authors also wish to acknowledge research support through NSF Grant OCE-1559178 and NOAA Grant NA16NOS0120028. We also wish to thank Chris Sherwood from the U.S. Geological Survey for his help in deriving wave length from WAVEWATCH III data.
    Keywords: Hurricanes/typhoons ; Hindcasts ; Numerical weather prediction/forecasting ; Coupled models ; Ocean models
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    Using acoustic travel time to monitor the heat variability of glacial Fjords (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-10
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 38(9), (2021): 1535–1550, https://doi.org/10.1175/JTECH-D-20-0176.s1.
    Description: Monitoring the heat content variability of glacial fjords is crucial to understanding the effects of oceanic forcing on marine-terminating glaciers. A pressure-sensor-equipped inverted echo sounder (PIES) was deployed midfjord in Sermilik Fjord in southeast Greenland from August 2011 to September 2012 alongside a moored array of instruments recording temperature, conductivity, and velocity. Historical hydrography is used to quantify the relationship between acoustic travel time and the vertically averaged heat content, and a new method is developed for filtering acoustic return echoes in an ice-influenced environment. We show that PIES measurements, combined with a knowledge of the fjord’s two-layer density structure, can be used to reconstruct the thickness and temperature of the inflowing water. Additionally, we find that fjord–shelf exchange events are identifiable in the travel time record implying the PIES can be used to monitor fjord circulation. Finally, we show that PIES data can be combined with moored temperature records to derive the heat content of the upper layer of the fjord where moored instruments are at great risk of being damaged by transiting icebergs.
    Description: FS and MA acknowledge funding from the Kerr Family Foundation and the Grossman Family Foundation through the Woods Hole Oceanographic Institution. MA is supported by a grant from the National Science Foundation Office of Polar Programs (1332911). FS and RS acknowledge support from NSF OCE-1657601 and from the Heising-Simons Foundation.
    Keywords: Glaciers ; Ice sheets ; Acoustic measurements/effects ; In situ oceanic observations
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    Moored turbulence measurements using pulse-coherent doppler sonar (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-10
    Description: Author Posting. © American Meteorological Society , 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Zippel, S. F., Farrar, J. T., Zappa, C. J., Miller, U., St Laurent, L., Ijichi, T., Weller, R. A., McRaven, L., Nylund, S., & Le Bel, D. Moored turbulence measurements using pulse-coherent doppler sonar. Journal of Atmospheric and Oceanic Technology, 38(9), (2021): 1621–1639, https://doi.org/10.1175/JTECH-D-21-0005.1.
    Description: Upper-ocean turbulence is central to the exchanges of heat, momentum, and gases across the air–sea interface and therefore plays a large role in weather and climate. Current understanding of upper-ocean mixing is lacking, often leading models to misrepresent mixed layer depths and sea surface temperature. In part, progress has been limited by the difficulty of measuring turbulence from fixed moorings that can simultaneously measure surface fluxes and upper-ocean stratification over long time periods. Here we introduce a direct wavenumber method for measuring turbulent kinetic energy (TKE) dissipation rates ϵ from long-enduring moorings using pulse-coherent ADCPs. We discuss optimal programming of the ADCPs, a robust mechanical design for use on a mooring to maximize data return, and data processing techniques including phase-ambiguity unwrapping, spectral analysis, and a correction for instrument response. The method was used in the Salinity Processes Upper-Ocean Regional Study (SPURS) to collect two year-long datasets. We find that the mooring-derived TKE dissipation rates compare favorably to estimates made nearby from a microstructure shear probe mounted to a glider during its two separate 2-week missions for O(10−8) ≤ ϵ ≤ O(10−5) m2 s−3. Periods of disagreement between turbulence estimates from the two platforms coincide with differences in vertical temperature profiles, which may indicate that barrier layers can substantially modulate upper-ocean turbulence over horizontal scales of 1–10 km. We also find that dissipation estimates from two different moorings at 12.5 and at 7 m are in agreement with the surface buoyancy flux during periods of strong nighttime convection, consistent with classic boundary layer theory.
    Description: This work was funded by NASA as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS), supporting field work for SPURS-1 (NASA Grant NNX11AE84G), for SPURS-2 (NASA Grant NNX15AG20G), and for analysis (NASA Grant 80NSSC18K1494). Funding for early iterations of this project associated with the VOCALS project and Stratus 9 mooring was provided by NSF (Awards 0745508 and 0745442). Additional funding was provided by ONR Grant N000141812431 and NSF Award 1756839. The Stratus Ocean Reference Station is funded by the Global Ocean Monitoring and Observing Program of the National Oceanic and Atmospheric Administration (CPO FundRef Number 100007298), through the Cooperative Institute for the North Atlantic Region (CINAR) under Cooperative Agreement NA14OAR4320158. Microstructure measurements made from the glider were supported by NSF (Award 1129646).
    Keywords: Ocean ; Turbulence ; Atmosphere-ocean interaction ; Boundary layer ; Oceanic mixed layer ; In situ oceanic observations
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    Impacts of ocean currents on the South Indian Ocean extratropical storm track through the relative wind effect (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-17
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 34(22), (2021): 9093–9113, https://doi.org/10.1175/JCLI-D-21-0142.1.
    Description: This study examines the role of the relative wind (RW) effect (wind relative to ocean current) in the regional ocean circulation and extratropical storm track in the south Indian Ocean. Comparison of two high-resolution regional coupled model simulations with and without the RW effect reveals that the most conspicuous ocean circulation response is the significant weakening of the overly energetic anticyclonic standing eddy off Port Elizabeth, South Africa, a biased feature ascribed to upstream retroflection of the Agulhas Current (AC). This opens a pathway through which the AC transports the warm and salty water mass from the subtropics, yielding marked increases in sea surface temperature (SST), upward turbulent heat flux (THF), and meridional SST gradient in the Agulhas retroflection region. These thermodynamic and dynamic changes are accompanied by the robust strengthening of the local low-tropospheric baroclinicity and the baroclinic wave activity in the atmosphere. Examination of the composite life cycle of synoptic-scale storms subjected to the high-THF events indicates a robust strengthening of the extratropical storms far downstream. Energetics calculations for the atmosphere suggest that the baroclinic energy conversion from the basic flow is the chief source of increased eddy available potential energy, which is subsequently converted to eddy kinetic energy, providing for the growth of transient baroclinic waves. Overall, the results suggest that the mechanical and thermal air–sea interactions are inherently and inextricably linked together to substantially influence the extratropical storm tracks in the south Indian Ocean.
    Description: Seo acknowledges the support from the NSF (OCE-2022846), NOAA (NA19OAR4310376), ONR (N00014-17-12398), and the Andrew W. Mellon Foundation Endowed Fund for Innovative Research at Woods Hole Oceanographic Institution (WHOI). Song is supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2019R1C1C1003663). O’Neill was supported by the NASA Grants 80NSSC19K1117 and 80NSSC19K1011.
    Keywords: Atmosphere-ocean interaction ; Extratropical cyclones ; Wind stress ; Boundary currents ; Storm tracks
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    Export of ice sheet meltwater from Upernavik Fjord, West Greenland (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-17
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(3), (2022): 363–382, https://doi.org/10.1175/jpo-d-21-0084.1.
    Description: Meltwater from Greenland is an important freshwater source for the North Atlantic Ocean, released into the ocean at the head of fjords in the form of runoff, submarine melt, and icebergs. The meltwater release gives rise to complex in-fjord transformations that result in its dilution through mixing with other water masses. The transformed waters, which contain the meltwater, are exported from the fjords as a new water mass Glacially Modified Water (GMW). Here we use summer hydrographic data collected from 2013 to 2019 in Upernavik, a major glacial fjord in northwest Greenland, to describe the water masses that flow into the fjord from the shelf and the exported GMWs. Using an optimum multi-parameter technique across multiple years we then show that GMW is composed of 57.8% ± 8.1% Atlantic Water (AW), 41.0% ± 8.3% Polar Water (PW), 1.0% ± 0.1% subglacial discharge, and 0.2% ± 0.2% submarine meltwater. We show that the GMW fractional composition cannot be described by buoyant plume theory alone since it includes lateral mixing within the upper layers of the fjord not accounted for by buoyant plume dynamics. Consistent with its composition, we find that changes in GMW properties reflect changes in the AW and PW source waters. Using the obtained dilution ratios, this study suggests that the exchange across the fjord mouth during summer is on the order of 50 mSv (1 Sv ≡ 106 m3 s−1) (compared to a freshwater input of 0.5 mSv). This study provides a first-order parameterization for the exchange at the mouth of glacial fjords for large-scale ocean models.
    Description: This work was partially supported by the Centre for Climate Dynamics (SKD) at the Bjerknes Centre for Climate Research. The authors thank NASA and the OMG consortium for making observational data freely available, and acknowledge M. Morlighem for good support in the early stages of this project. MM and LHS and would also like to thank Ø. Paasche, the ACER project, and the U.S. Norway Fulbright Foundation for the Norwegian Arctic Chair Grant 2019–20 that made the visit to Scripps Institution of Oceanography possible. FS acknowledges support from the DOE Office of Science Grant DE-SC0020073, Heising-Simons Foundation and from NSF and OCE-1756272. DAS acknowledges support from U.K. NERC Grants NE/P011365/1, NE/T011920/1, and NERC Independent Research Fellowship NE/T011920/1. MW was supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, California Institute of Technology, administered by the Universities Space Research Association under contract with NASA. CSA would like to acknowledge Geocenter Denmark for support to the project “Upernavik Glacier.”
    Keywords: Ocean ; Arctic ; Atlantic Ocean ; Glaciers ; Ice sheets ; Buoyancy ; Entrainment ; In situ oceanic observations ; Annual variations
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    Near-resonances of superinertial and tidal fluctuations at islands (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-03
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 51(9), (2021): 2721–2733, https://doi.org/10.1175/JPO-D-20-0298.1.
    Description: A linear numerical model of an island or a tall seamount is used to explore superinertial leaky resonances forced by ambient vertically and horizontally uniform current fluctuations. The model assumes a circularly symmetric topography (including a shallow reef) and allows realistic stratification and bottom friction. As long as there is substantial stratification, a number of leaky resonances are found, and when the island’s flanks are narrow relative to the internal Rossby radius, some of the near-resonant modes resemble leaky internal Kelvin waves. Other “resonances” resemble higher radial mode long gravity waves as explored by Chambers. The near-resonances amplify the cross-reef velocities that help fuel biological activity. Results for cases with the central island replaced by a lagoon do not differ greatly from the island case which has land at the center. As an aside, insight is provided on the question of offshore boundary conditions for superinertial nearly trapped waves along a straight coast.
    Keywords: Baroclinic flows ; Internal waves ; Kelvin waves
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    Time scales of the Greenland freshwater anomaly in the subpolar North Atlantic (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-03
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 34(22), (2021): 8971–8987, https://doi.org/10.1175/JCLI-D-20-0610.1.
    Description: The impact of increasing Greenland freshwater discharge on the subpolar North Atlantic (SPNA) remains unknown as there are uncertainties associated with the time scales of the Greenland freshwater anomaly (GFWA) in the SPNA. Results from numerical simulations tracking GFWA and an analytical approach are employed to estimate the response time, suggesting that a decadal time scale (13 years) is required for the SPNA to adjust for increasing GFWA. Analytical solutions obtained for a long-lasting increase of freshwater discharge show a non-steady-state response of the SPNA with increasing content of the GFWA. In contrast, solutions for a short-lived pulse of freshwater demonstrate different responses of the SPNA with a rapid increase of freshwater in the domain followed by an exponential decay after the pulse has passed. The derived theoretical relation between time scales shows that residence time scales are time dependent for a non-steady-state case and asymptote the response time scale with time. The residence time of the GFWA deduced from Lagrangian experiments is close to and smaller than the response time, in agreement with the theory. The Lagrangian analysis shows dependence of the residence time on the entrance route of the GFWA and on the depth. The fraction of the GFWA exported through Davis Strait has limited impact on the interior basins, whereas the fraction entering the SPNA from the southwest Greenland shelf spreads into the interior regions. In both cases, the residence time of the GFWA increases with depth demonstrating long persistence of the freshwater anomaly in the subsurface layers.
    Description: D. S. Dukhovskoy and E. P. Chassignet were funded by the DOE (Award DE-SC0014378) and HYCOM NOPP (Award N00014-19-1-2674). The HYCOM-CICE simulations were supported by a grant of computer time from the DoD High-Performance Computing Modernization Program at NRL SSC. G. Platov was funded by the RSF N19-17-00154. P. G. Myers was funded by an NSERC Discovery Grant (Grant RGPIN 04357). A. Proshutinsky was funded by FAMOS project (NSF Grant NSF 14-584).
    Keywords: North Atlantic Ocean ; Lagrangian circulation/transport ; Ocean circulation ; Differential equations ; Ocean models
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    Topographic influences on the wind-driven exchange between marginal seas and the open ocean (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-03
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 51(12),(2021): 3663–3678, https://doi.org/10.1175/JPO-D-21-0058.1.
    Description: The wind-driven exchange through complex ridges and islands between marginal seas and the open ocean is studied using both numerical and analytical models. The models are forced by a steady, spatially uniform northward wind stress intended to represent the large-scale, low-frequency wind patterns typical of the seasonal monsoons in the western Pacific Ocean. There is an eastward surface Ekman transport out of the marginal sea and westward geostrophic inflows into the marginal sea. The interaction between the Ekman transport and an island chain produces strong baroclinic flows along the island boundaries with a vertical depth that scales with the ratio of the inertial boundary layer thickness to the baroclinic deformation radius. The throughflows in the gaps are characterized by maximum transport in the center gap and decreasing transports toward the southern and northern tips of the island chain. An extended island rule theory demonstrates that throughflows are determined by the collective balance between viscosity on the meridional boundaries and the eastern side boundary of the islands. The outflowing transport is balanced primarily by a shallow current that enters the marginal sea along its equatorward boundary. The islands can block some direct exchange and result in a wind-driven overturning cell within the marginal sea, but this is compensated for by eastward zonal jets around the southern and northern tips of the island chain. Topography in the form of a deep slope, a ridge, or shallow shelves around the islands alters the current pathways but ultimately is unable to limit the total wind-driven exchange between the marginal sea and the open ocean.
    Description: This research is supported in part by the China Scholarship Council (201906330102). H. G. is financially supported by the China Scholarship Council to study at WHOI for 2 years as a guest student. M. A. S. is supported by the National Science Foundation Grant OCE-1922538.
    Keywords: Ekman pumping/transport ; Ocean circulation ; Topographic effects
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    Two distinct modes of climate responses to the anthropogenic aerosol forcing changes (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-16
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 35(11), (2022): 3445-3457, https://doi.org/10.1175/jcli-d-21-0656.1.
    Description: Unlike greenhouse gases (GHGs), anthropogenic aerosol (AA) concentrations have increased and then decreased over the past century or so, with the timing of the peak concentration varying in different regions. To date, it has been challenging to separate the climate impact of AAs from that due to GHGs and background internal variability. We use a pattern recognition method, taking advantage of spatiotemporal covariance information, to isolate the forced patterns for the surface ocean and associated atmospheric variables from the all-but-one forcing Community Earth System Model ensembles. We find that the aerosol-forced responses are dominated by two leading modes, with one associated with the historical increase and future decrease of global mean aerosol concentrations (dominated by the Northern Hemisphere sources) and the other due to the transition of the primary sources of AA from the west to the east and also from Northern Hemisphere extratropical regions to tropical regions. In particular, the aerosol transition effect, to some extent compensating the global mean effect, exhibits a zonal asymmetry in the surface temperature and salinity responses. We also show that this transition effect dominates the total AA effect during recent decades, e.g., 1967–2007.
    Description: All three authors are supported by U.S. National Science Foundation (OCE-2048336). The Community Earth System Model project is supported primarily by the National Science Foundation (https://www.cesm.ucar.edu/projects/community-projects/LENS/data-sets.html and https://www.cesm.ucar.edu/working_groups/CVC/simulations/cesm1-single_forcing_le.html).
    Keywords: Aerosol radiative effect ; Climate Change ; Climate variability ; Sea surface temperature ; Salinity
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    Global Oceans [in “State of the Climate in 2020”] (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-09
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 102(8), (2021): S143–S198, https://doi.org/10.1175/BAMS-D-21-0083.1.
    Description: This chapter details 2020 global patterns in select observed oceanic physical, chemical, and biological variables relative to long-term climatologies, their differences between 2020 and 2019, and puts 2020 observations in the context of the historical record. In this overview we address a few of the highlights, first in haiku, then paragraph form: La Niña arrives, shifts winds, rain, heat, salt, carbon: Pacific—beyond. Global ocean conditions in 2020 reflected a transition from an El Niño in 2018–19 to a La Niña in late 2020. Pacific trade winds strengthened in 2020 relative to 2019, driving anomalously westward Pacific equatorial surface currents. Sea surface temperatures (SSTs), upper ocean heat content, and sea surface height all fell in the eastern tropical Pacific and rose in the western tropical Pacific. Efflux of carbon dioxide from ocean to atmosphere was larger than average across much of the equatorial Pacific, and both chlorophyll-a and phytoplankton carbon concentrations were elevated across the tropical Pacific. Less rain fell and more water evaporated in the western equatorial Pacific, consonant with increased sea surface salinity (SSS) there. SSS may also have increased as a result of anomalously westward surface currents advecting salty water from the east. El Niño–Southern Oscillation conditions have global ramifications that reverberate throughout the report.
    Description: Argo data used in the chapter were collected and made freely available by the International Argo Program and the national programs that contribute to it. (https://argo.ucsd.edu, https://www.ocean-ops. org). The Argo Program is part of the Global Ocean Observing System. Many authors of the chapter are supported by NOAA Research, the NOAA Global Ocean Monitoring and Observing Program, or the NOAA Ocean Acidification Program. • L. Cheng is supported by National Natural Science Foundation of China (42076202) and Strategic Priority Research Program of the Chinese Academy of Sciences (XDB42040402. • R. E. Killick is supported by the Met Office Hadley Centre Climate Programme funded by BEIS and Defra. PMEL contribution numbers 5214, 5215, 5216, 5217, and 5247.
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    Double diffusion, shear instabilities, and heat impacts of a pacific summer water intrusion in the Beaufort Sea (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-06-13
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Fine, E., MacKinnon, J., Alford, M., Middleton, L., Taylor, J., Mickett, J., Cole, S., Couto, N., Boyer, A., & Peacock, T. Double diffusion, shear instabilities, and heat impacts of a pacific summer water intrusion in the Beaufort Sea. Journal of Physical Oceanography, 52(2), (2022): 189–203, https://doi.org/10.1175/jpo-d-21-0074.1.
    Description: Pacific Summer Water eddies and intrusions transport heat and salt from boundary regions into the western Arctic basin. Here we examine concurrent effects of lateral stirring and vertical mixing using microstructure data collected within a Pacific Summer Water intrusion with a length scale of ∼20 km. This intrusion was characterized by complex thermohaline structure in which warm Pacific Summer Water interleaved in alternating layers of O(1) m thickness with cooler water, due to lateral stirring and intrusive processes. Along interfaces between warm/salty and cold/freshwater masses, the density ratio was favorable to double-diffusive processes. The rate of dissipation of turbulent kinetic energy (ε) was elevated along the interleaving surfaces, with values up to 3 × 10−8 W kg−1 compared to background ε of less than 10−9 W kg−1. Based on the distribution of ε as a function of density ratio Rρ, we conclude that double-diffusive convection is largely responsible for the elevated ε observed over the survey. The lateral processes that created the layered thermohaline structure resulted in vertical thermohaline gradients susceptible to double-diffusive convection, resulting in upward vertical heat fluxes. Bulk vertical heat fluxes above the intrusion are estimated in the range of 0.2–1 W m−2, with the localized flux above the uppermost warm layer elevated to 2–10 W m−2. Lateral fluxes are much larger, estimated between 1000 and 5000 W m−2, and set an overall decay rate for the intrusion of 1–5 years.
    Description: This work was supported by ONR Grant N00014-16-1-2378 and NSF Grants PLR 14-56705 and PLR-1303791, NSF Graduate Research Fellowship Grant DGE-1650112, as well as by the Postdoctoral Scholar Program at Woods Hole Oceanographic Institution, with funding provided by the Weston Howland Jr. Postdoctoral Scholarship.
    Keywords: Arctic ; Diapycnal mixing ; Diffusion ; Fluxes ; Instability ; Mixing ; Turbulence
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    The air-launched autonomous micro observer (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-08-05
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(4), (2022): 491–502, https://doi.org/10.1175/jtech-d-21-0046.1.
    Description: The Air-Launched Autonomous Micro Observer (ALAMO) is a versatile profiling float that can be launched from an aircraft to make temperature and salinity observations of the upper ocean for over a year with high temporal sampling. Similar in dimensions and weight to an airborne expendable bathythermograph (AXBT), but with the same capability as Argo profiling floats, ALAMOs can be deployed from an A-sized (sonobuoy) launch tube, the stern ramp of a cargo plane, or the door of a small aircraft. Unlike an AXBT, however, the ALAMO float directly measures pressure, can incorporate additional sensors, and is capable of performing hundreds of ocean profiles compared to the single temperature profile provided by an AXBT. Upon deployment, the float parachutes to the ocean, releases the air-deployment package, and immediately begins profiling. Ocean profile data along with position and engineering information are transmitted via the Iridium satellite network, automatically processed, and then distributed by the Global Telecommunications System for use by the operational forecasting community. The ALAMO profiling mission can be modified using the two-way Iridium communications to change the profiling frequency and depth. Example observations are included to demonstrate the ALAMO’s utility.
    Description: This work was supported by the National Oceanographic and Atmospheric Administration under Grants NA13OAR4830233 (as part of CINAR Sandy Supplemental funding from the Disaster Relief Appropriations Act of 2013) and NA14OAR4320158 and by Office of Naval Research under Grants N0001416WX01384, N0001416WX01262, and N000141512293. ALAMO floats are commercially available from MRV Systems, LLC (https://www.mrvsys.com).
    Keywords: Ocean ; Hurricanes ; Ocean dynamics ; Mixed layer ; Aircraft observations ; Instrumentation/sensors
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    Frontogenesis, mixing, and stratification in estuarine channels with curvature (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-12-09
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(7), (2022): 1333-1350, https://doi.org/10.1175/jpo-d-21-0298.1.
    Description: Idealized numerical simulations were conducted to investigate the influence of channel curvature on estuarine stratification and mixing. Stratification is decreased and tidal energy dissipation is increased in sinuous estuaries compared to straight channel estuaries. We applied a vertical salinity variance budget to quantify the influence of straining and mixing on stratification. Secondary circulation due to the channel curvature is found to affect stratification in sinuous channels through both lateral straining and enhanced vertical mixing. Alternating negative and positive lateral straining occur in meanders upstream and downstream of the bend apex, respectively, corresponding to the normal and reversed secondary circulation with curvature. The vertical mixing is locally enhanced in curved channels with the maximum mixing located upstream of the bend apex. Bend-scale bottom salinity fronts are generated near the inner bank upstream of the bend apex as a result of interaction between the secondary flow and stratification. Shear mixing at bottom fronts, instead of overturning mixing by the secondary circulation, provides the dominant mechanism for destruction of stratification. Channel curvature can also lead to increased drag, and using a Simpson number with this increased drag coefficient can relate the decrease in stratification with curvature to the broader estuarine parameter space.
    Description: The research leading to these results was funded by NSF Awards OCE-1634481 and OCE-2123002.
    Description: 2022-12-09
    Keywords: Estuaries ; Mixing ; Secondary circulation ; Fronts ; Tides ; Numerical analysis/modeling
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    Wind-forced variability of the zonal overturning circulation (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-11-01
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(5),(2022): 65-979, https://doi.org/10.1175/jpo-d-21-0174.1.
    Description: The mechanisms of wind-forced variability of the zonal overturning circulation (ZOC) are explored using an idealized shallow water numerical model, quasigeostrophic theory, and simple analytic conceptual models. Two wind-forcing scenarios are considered: midlatitude variability in the subtropical/subpolar gyres and large-scale variability spanning the equator. It is shown that the midlatitude ZOC exchanges water with the western boundary current and attains maximum amplitude on the same order of magnitude as the Ekman transport at a forcing period close to the basin-crossing time scale for baroclinic Rossby waves. Near the equator, large-scale wind variations force a ZOC that increases in amplitude with decreasing forcing period such that wind stress variability on annual time scales forces a ZOC of O(50) Sv (1 Sv ≡ 106 m3 s−1). For both midlatitude and low-latitude variability the ZOC and its related heat transport are comparable to those of the meridional overturning circulation. The underlying physics of the ZOC relies on the influences of the variation of the Coriolis parameter with latitude on both the geostrophic flow and the baroclinic Rossby wave phase speed as the fluid adjusts to time-varying winds.
    Description: This study was supported by National Science Foundation Grants OCE-1947290 and OCE-2122633.
    Description: 2022-11-01
    Keywords: Ekman pumping/transport ; Mass fluxes/transport ; Planetary waves ; Rossby waves
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    On the development of SWOT in situ calibration/validation for short-wavelength ocean topography (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-11-01
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(5), (2022): 595–617, https://doi.org/10.1175/jtech-d-21-0039.1.
    Description: The future Surface Water and Ocean Topography (SWOT) mission aims to map sea surface height (SSH) in wide swaths with an unprecedented spatial resolution and subcentimeter accuracy. The instrument performance needs to be verified using independent measurements in a process known as calibration and validation (Cal/Val). The SWOT Cal/Val needs in situ measurements that can make synoptic observations of SSH field over an O(100) km distance with an accuracy matching the SWOT requirements specified in terms of the along-track wavenumber spectrum of SSH error. No existing in situ observing system has been demonstrated to meet this challenge. A field campaign was conducted during September 2019–January 2020 to assess the potential of various instruments and platforms to meet the SWOT Cal/Val requirement. These instruments include two GPS buoys, two bottom pressure recorders (BPR), three moorings with fixed conductivity–temperature–depth (CTD) and CTD profilers, and a glider. The observations demonstrated that 1) the SSH (hydrostatic) equation can be closed with 1–3 cm RMS residual using BPR, CTD mooring and GPS SSH, and 2) using the upper-ocean steric height derived from CTD moorings enable subcentimeter accuracy in the California Current region during the 2019/20 winter. Given that the three moorings are separated at 10–20–30 km distance, the observations provide valuable information about the small-scale SSH variability associated with the ocean circulation at frequencies ranging from hourly to monthly in the region. The combined analysis sheds light on the design of the SWOT mission postlaunch Cal/Val field campaign.
    Description: The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). All authors are supported by the SWOT project. J. T. Farrar was partially supported by NASA NNX16AH76G.
    Description: 2022-11-01
    Keywords: Internal waves ; Ocean dynamics ; Small scale processes ; Altimetry ; Global positioning systems (GPS) ; In situ oceanic observations ; Ship observations
    Repository Name: Woods Hole Open Access Server
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    Low-frequency dynamic ocean response to barometric-pressure loading (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-11-04
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(11), (2022): 2627-2641, https://doi.org/10.1175/jpo-d-22-0090.1.
    Description: Changes in dynamic manometric sea level ζm represent mass-related sea level changes associated with ocean circulation and climate. We use twin model experiments to quantify magnitudes and spatiotemporal scales of ζm variability caused by barometric pressure pa loading at long periods (≳1 month) and large scales (≳300km) relevant to Gravity Recovery and Climate Experiment (GRACE) ocean data. Loading by pa drives basin-scale monthly ζm variability with magnitudes as large as a few centimeters. Largest ζm signals occur over abyssal plains, on the shelf, and in marginal seas. Correlation patterns of modeled ζm are determined by continental coasts and H/f contours (H is ocean depth and f is Coriolis parameter). On average, ζm signals forced by pa represent departures of ≲10% and ≲1% from the inverted-barometer effect ζib on monthly and annual periods, respectively. Basic magnitudes, spatial patterns, and spectral behaviors of ζm from the model are consistent with scaling arguments from barotropic potential vorticity conservation. We also compare ζm from the model driven by pa to ζm from GRACE observations. Modeled and observed ζm are significantly correlated across parts of the tropical and extratropical oceans, on shelf and slope regions, and in marginal seas. Ratios of modeled to observed ζm magnitudes are as large as ∼0.2 (largest in the Arctic Ocean) and qualitatively agree with analytical theory for the gain of the transfer function between ζm forced by pa and wind stress. Results demonstrate that pa loading is a secondary but nevertheless important contributor to monthly mass variability from GRACE over the ocean.
    Description: The authors acknowledge support from the National Aeronautics and Space Administration through the GRACE Follow-On Science Team (Grant 80NSSC20K0728) and the Sea Level Change Team (Grant 80NSSC20K1241). The contribution from I. F. and O. W. represents research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (Grant 80NM0018D0004).
    Keywords: Barotropic flows ; Large-scale motions ; Ocean circulation ; Planetary waves ; Potential vorticity ; Sea level
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  • 64
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    High resolution, in-situ studies of seawater carbonate chemistry and carbon cycling in coastal systems using CHANnelized Optical System II (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 2022.
    Description: Study of the marine CO2 system is critical for understanding global carbon cycling and the impacts of changing ocean chemistry on marine ecosystems. This thesis describes the development of a near-continuous, in-situ dissolved inorganic carbon (DIC) sensor, CHANnelized Optical System (CHANOS) II, suitable for deployment from both mobile and stationary platforms. The system delivers DIC measurements with an accuracy of 2.9 (laboratory) or 9.0 (field) μmol kg-1, at a precision of ~4.9-5.5 μmol kg-1. Time-series field deployments in the Pocasset River, MA, revealed seasonal and episodic biogeochemical shifts in DIC, including two different responses to tropical storm and nor’easter systems. Towed surface mapping deployments across Waquoit Bay, MA, highlighted the export of DIC from salt marshes through tidal water. High resolution (〈100 m) data collected during ROV deployments over deep coral mounds on the West Florida Slope revealed a much wider DIC range (~1900 – 2900 μmol kg-1) across seafloor and coral habitats than was observed through the few bottle samples collected during the dives (n = 5, 2190.9 ± 1.0 μmol kg-1). These deployments highlight the need to investigate deep sea biogeochemistry at high spatial scales in order to understand the range of environmental variation encountered by benthic communities.
    Description: Funding for this work was provided by the National Science Foundation (OCE Award No. 1233654, OCE 1635388, OCE 1841092), National Oceanic and Atmospheric Administration Office of Ocean Exploration and Research (NA18OAR0110352), MIT Seagrant (2017-R/RCM-51), and Woods Hole Oceanographic Institution (Ocean Ventures Fund, Grassle Fellowship).
    Keywords: DIC ; sensor ; ROV
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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    Long-distance radiation of Rossby Waves from the equatorial current system (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of [publisher] for personal use, not for redistribution. The definitive version was published in Farrar, J. T., Durland, T., Jayne, S. R., & Price, J. F. Long-distance radiation of Rossby Waves from the equatorial current system. Journal of Physical Oceanography, 51(6), (2021): 1947–1966, https://doi.org/10.1175/JPO-D-20-0048.1.
    Description: Measurements from satellite altimetry are used to show that sea surface height (SSH) variability throughout much of the North Pacific Ocean is coherent with the SSH signal of the tropical instability waves (TIWs) that result from instabilities of the equatorial currents. This variability has regular phase patterns consistent with freely propagating barotropic Rossby waves radiating energy away from the unstable equatorial currents, and the waves clearly propagate from the equatorial region to at least 30°N. The pattern of SSH variance at TIW frequencies exhibits remarkable patchiness on scales of hundreds of kilometers, which we interpret as being due to the combined effects of wave reflection, refraction, and interference. North of 40°N, more than 6000 km from the unstable equatorial currents, the SSH field remains coherent with the near-equatorial SSH variability, but it is not as clear whether the variability at the higher latitudes is a simple result of barotropic wave radiation from the tropical instability waves. Even more distant regions, as far north as the Aleutian Islands off of Alaska and the Kamchatka Peninsula of eastern Russia, have SSH variability that is significantly coherent with the near-equatorial instabilities. The variability is not well represented in the widely used gridded SSH data product commonly referred to as the AVISO or DUACS product, and this appears to be a result of spatial variations in the filtering properties of the objective mapping scheme.
    Description: This work was supported by NASA Grants NNX13AE46G, NNX14AM71G, and NNX17AH54G.
    Keywords: Pacific Ocean ; Barotropic flows ; Instability ; Planetary waves ; Rossby waves ; Topographic effects
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    On the estimation of deep Atlantic ventilation from fossil radiocarbon records. part I: modern reference estimates (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 51(6),(2021): 1842–1872, https://doi.org/10.1175/JPO-D-20-0153.1.
    Description: Radiocarbon dates of fossil carbonates sampled from sediment cores and the seafloor have been used to infer that deep ocean ventilation during the last ice age was different from today. In this first of two companion papers, the time-averaged abyssal circulation in the modern Atlantic is estimated by combining a hydrographic climatology, observational estimates of volume transports, Argo float velocities at 1000 m, radiocarbon data, and geostrophic dynamics. Different estimates of modern circulation, obtained from different prior assumptions about the abyssal flow and different errors in the geostrophic balance, are produced for use in a robust interpretation of fossil records in terms of deviations from the present-day flow, which is undertaken in Part II. We find that, for all estimates, the meridional transport integrated zonally and averaged over a hemisphere, ⟨Vk⟩, is southward between 1000 and 4000 m in both hemispheres, northward between 4000 and 5000 m in the South Atlantic, and insignificant between 4000 and 5000 m in the North Atlantic. Estimates of ⟨Vk⟩ obtained from two distinct prior circulations—one based on a level of no motion at 4000 m and one based on Argo float velocities at 1000 m—become statistically indistinguishable when Δ14C data are considered. The transport time scale, defined as τk=Vk/⟨Vk⟩, where Vk is the volume of the kth layer, is estimated to about a century between 1000 and 3000 m in both the South and North Atlantic, 124 ± 9 yr (203 ± 23 yr) between 3000 and 4000 m in the South (North) Atlantic, and 269 ± 115 yr between 4000 and 5000 m in the South Atlantic.
    Description: This work has been supported by Grant OCE-1702417 from the U.S. National Science Foundation.
    Keywords: Atlantic Ocean ; Abyssal circulation ; Tracers ; Inverse methods
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    Simulated Mid-Holocene and Last Interglacial Climate Using Two Generations of AWI-ESM (2022)
    American Meteorological Society
    In:  EPIC3Journal of Climate, American Meteorological Society, 35(23), pp. 7811-7831, ISSN: 0894-8755
    Details
    Publication Date: 2023-06-23
    Description: Numerical simulations allow us to gain a comprehensive understanding of the underlying mechanisms of past, present, and future climate changes. The mid-Holocene (MH) and the last interglacial (LIG) were the two most recent warm episodes of Earth’s climate history and are the focus of paleoclimate research. Here, we present results of MH and LIG simulations with two versions of the state-of-the-art Earth system model AWI-ESM. Most of the climate changes in MH and LIG compared to the preindustrial era are agreed upon by the two model versions, including 1) enhanced seasonality in surface temperature that is driven by the redistribution of seasonal insolation; 2) a northward shift of the intertropical convergence zone (ITCZ) and tropical rain belt; 3) a reduction in annual mean Arctic sea ice concentration; 4) weakening and northward displacement of the Northern Hemisphere Hadley circulation, which is related to the decrease and poleward shift of the temperature gradient from the subtropical to the equator in the Northern Hemisphere; 5) a westward shift of the Indo-Pacific Walker circulation due to anomalous warming over the Eurasia and North Africa during boreal summer; and 6) an expansion and intensification of Northern Hemisphere summer monsoon rainfall, with the latter being dominated by the dynamic component of moisture budget (i.e., the strengthening of wind circulation). However, the simulated responses of the Atlantic meridional overturning circulation (AMOC) in the two models yield different results for both the LIG and the MH. AMOC anomalies between the warm interglacial and preindustrial periods are associated with changes in North Atlantic westerly winds and stratification of the water column at the North Atlantic due to changes in ocean temperature, salinity, and density.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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    A new structure for the Sea Ice Essential Climate variables of the Global Climate Observing System (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-12-01
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 103(6), (2022): E1502-E1521, https://doi.org/10.1175/bams-d-21-0227.1.
    Description: Climate observations inform about the past and present state of the climate system. They underpin climate science, feed into policies for adaptation and mitigation, and increase awareness of the impacts of climate change. The Global Climate Observing System (GCOS), a body of the World Meteorological Organization (WMO), assesses the maturity of the required observing system and gives guidance for its development. The Essential Climate Variables (ECVs) are central to GCOS, and the global community must monitor them with the highest standards in the form of Climate Data Records (CDR). Today, a single ECV—the sea ice ECV—encapsulates all aspects of the sea ice environment. In the early 1990s it was a single variable (sea ice concentration) but is today an umbrella for four variables (adding thickness, edge/extent, and drift). In this contribution, we argue that GCOS should from now on consider a set of seven ECVs (sea ice concentration, thickness, snow depth, surface temperature, surface albedo, age, and drift). These seven ECVs are critical and cost effective to monitor with existing satellite Earth observation capability. We advise against placing these new variables under the umbrella of the single sea ice ECV. To start a set of distinct ECVs is indeed critical to avoid adding to the suboptimal situation we experience today and to reconcile the sea ice variables with the practice in other ECV domains.
    Description: PH’s contribution was funded under the Australian Government’s Antarctic Science Collaboration Initiative program, and contributes to Project 6 of the Australian Antarctic Program Partnership (ASCI000002). PH acknowledges support through the Australian Antarctic Science Projects 4496 and 4506, and the International Space Science Institute (Bern, Switzerland) project #405.
    Description: 2022-12-01
    Keywords: Sea ice ; Climate change ; Climatology ; Climate records
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    A time-dependent Sverdrup relation and its application to the Indian Ocean (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-11-27
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(6), (2022): 1233-1244, https://doi.org/10.1175/jpo-d-21-0223.1.
    Description: The Sverdrup relation is the backbone of wind-driven circulation theory; it is a simple relation between the meridional transport of the wind-driven circulation in the upper ocean and the wind stress curl. However, the relation is valid for steady circulation only. In this study, a time-dependent Sverdrup relation is postulated, in which the meridional transport in a time-dependent circulation is the sum of the local wind stress curl term and a time-delayed term representing the effect of the eastern boundary condition. As an example, this time-dependent Sverdrup relation is evaluated through its application to the equatorial circulation in the Indian Ocean, using reanalysis data and a reduced gravity model. Close examination reveals that the southward Somali Current occurring during boreal winter is due to the combination of the local wind stress curl in the Arabian Sea and delayed signals representing the time change of layer thickness at the eastern boundary.
    Description: This work is supported by NSFC (41822602, 41976016, 42005035, 42076021), the Strategic Priority Research Program of Chinese Academy of Sciences (XDB42000000, XDA 20060502), Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0306), Guangdong Basic and Applied Basic Research Foundation (2021A1515011534), Youth Innovation Promotion Association CAS, ISEE2021ZD01, and LTOZZ2002. The numerical simulation is supported by the High-Performance Computing Division in the South China Sea Institute of Oceanology.
    Description: 2022-11-27
    Keywords: Ocean circulation ; Ocean dynamics ; Rossby waves ; Wind stress curl
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    Interannual and seasonal along-shelf current variability and dynamics: seventeen years of observations from the southern New England inner shelf (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-12-21
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(12), (2022): 2923–2933, https://doi.org/10.1175/jpo-d-22-0064.1.
    Description: The characteristics and dynamics of depth-average along-shelf currents at monthly and longer time scales are examined using 17 years of observations from the Martha’s Vineyard Coastal Observatory on the southern New England inner shelf. Monthly averages of the depth-averaged along-shelf current are almost always westward, with the largest interannual variability in winter. There is a consistent annual cycle with westward currents of 5 cm s−1 in summer decreasing to 1–2 cm s−1 in winter. Both the annual cycle and interannual variability in the depth-average along-shelf current are predominantly driven by the along-shelf wind stress. In the absence of wind forcing, there is a westward flow of ∼5 cm s−1 throughout the year. At monthly time scales, the depth-average along-shelf momentum balance is primarily between the wind stress, surface gravity wave–enhanced bottom stress, and an opposing pressure gradient that sets up along the southern New England shelf in response to the wind. Surface gravity wave enhancement of bottom stress is substantial over the inner shelf and is essential to accurately estimating the bottom stress variation across the inner shelf.
    Description: The National Science Foundation, Woods Hole Oceanographic Institution, the Massachusetts Technology Collaborative, and the Office of Naval Research have supported the construction and maintenance of MVCO. The analysis presented here was partially funded by the National Science Foundation under Grants OCE 1558874 and OCE 1655686.
    Keywords: Continental shelf/slope ; Coastal flows ; Momentum ; Ocean dynamics ; Wind stress
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    Turbulent thermal-wind driven coastal upwelling: current observations and dynamics (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-12-21
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(12), (2022): 2909-2921, https://doi.org/10.1175/jpo-d-22-0063.1.
    Description: A remarkably consistent Lagrangian upwelling circulation at monthly and longer time scales is observed in a 17-yr time series of current profiles in 12 m of water on the southern New England inner shelf. The upwelling circulation is strongest in summer, with a current magnitude of ∼1 cm s−1, which flushes the inner shelf in ∼2.5 days. The average winter upwelling circulation is about one-half of the average summer upwelling circulation, but with larger month-to-month variations driven, in part, by cross-shelf wind stresses. The persistent upwelling circulation is not wind-driven; it is driven by a cross-shelf buoyancy force associated with less-dense water near the coast. The cross-shelf density gradient is primarily due to temperature in summer, when strong surface heating warms shallower nearshore water more than deeper offshore water, and to salinity in winter, caused by fresher water near the coast. In the absence of turbulent stresses, the cross-shelf density gradient would be in a geostrophic, thermal-wind balance with the vertical shear in the along-shelf current. However, turbulent stresses over the inner shelf attributable to strong tidal currents and wind stress cause a partial breakdown of the thermal-wind balance that releases the buoyancy force, which drives the observed upwelling circulation. The presence of a cross-shelf density gradient has a profound impact on exchange across this inner shelf. Many inner shelves are characterized by turbulent stresses and cross-shelf density gradients with lighter water near the coast, suggesting turbulent thermal-wind-driven coastal upwelling may be a broadly important cross-shelf exchange mechanism.
    Description: The National Science Foundation, Woods Hole Oceanographic Institution, the Massachusetts Technology Collaborative, and the Office of Naval Research have supported the construction and maintenance of MVCO. The analysis presented here was partially funded by the National Science Foundation under Grants OCE 1558874 and OCE 1655686.
    Keywords: Buoyancy ; Coastal flows ; Currents ; Dynamics ; Lagrangian circulation/transport ; Upwelling/downwelling
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  • 72
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    Deep-current intraseasonal variability interpreted as topographic Rossby waves and deep eddies in the Xisha Islands of the South China Sea (2022)
    American Meteorological Society
    Details
    Publication Date: 2022-12-16
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(7), (2022): 1415–1430. https://doi.org/10.1175/JPO-D-21-0147.1.
    Description: Strong subinertial variability near a seamount at the Xisha Islands in the South China Sea was revealed by mooring observations from January 2017 to January 2018. The intraseasonal deep flows presented two significant frequency bands, with periods of 9–20 and 30–120 days, corresponding to topographic Rossby waves (TRWs) and deep eddies, respectively. The TRW and deep eddy signals explained approximately 60% of the kinetic energy of the deep subinertial currents. The TRWs at the Ma, Mb, and Mc moorings had 297, 262, and 274 m vertical trapping lengths, and ∼43, 38, and 55 km wavelengths, respectively. Deep eddies were independent from the upper layer, with the largest temperature anomaly being 〉0.4°C. The generation of the TRWs was induced by mesoscale perturbations in the upper layer. The interaction between the cyclonic–anticyclonic eddy pair and the seamount topography contributed to the generation of deep eddies. Owing to the potential vorticity conservation, the westward-propagating tilted interface across the eddy pair squeezed the deep-water column, thereby giving rise to negative vorticity west of the seamount. The strong front between the eddy pair induced a northward deep flow, thereby generating a strong horizontal velocity shear because of lateral friction and enhanced negative vorticity. Approximately 4 years of observations further confirmed the high occurrence of TRWs and deep eddies. TRWs and deep eddies might be crucial for deep mixing near rough topographies by transferring mesoscale energy to small scales.
    Description: This work was supported by the National Natural Science Foundation of China (92158204, 91958202, 42076019, 41776036, 91858203), the Open Project Program of State Key Laboratory of Tropical Oceanography (project LTOZZ2001), and Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0304).
    Description: 2022-12-16
    Keywords: Abyssal circulation ; Ocean circulation ; Ocean dynamics ; Intraseasonal variability
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    The barrier layer effect on the heat and freshwater balance from moored observations in the eastern Pacific fresh pool (2022)
    American Meteorological Society
    Details
    Publication Date: 2023-01-27
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(8), (2022): 1705-1730, https://doi.org/10.1175/jpo-d-21-0243.1.
    Description: Formation and evolution of barrier layers (BLs) and associated temperature inversions (TIs) were investigated using a 1-yr time series of oceanic and air–sea surface observations from three moorings deployed in the eastern Pacific fresh pool. BL thickness and TI amplitude showed a seasonality with maxima in boreal summer and autumn when BLs were persistently present. Mixed layer salinity (MLS) and mixed layer temperature (MLT) budgets were constructed to investigate the formation mechanism of BLs and TIs. The MLS budget showed that BLs were initially formed in response to horizontal advection of freshwater in boreal summer and then primarily maintained by precipitation. The MLT budget revealed that penetration of shortwave radiation through the mixed layer base is the dominant contributor to TI formation through subsurface warming. Geostrophic advection is a secondary contributor to TI formation through surface cooling. When the BL exists, the cooling effect from entrainment and the warming effect from detrainment are both significantly reduced. In addition, when the BL is associated with the presence of a TI, entrainment works to warm the mixed layer. The presence of BLs makes the shallower mixed layer more sensitive to surface heat and freshwater fluxes, acting to enhance the formation of TIs that increase the subsurface warming via shortwave penetration.
    Description: SK is supported by JSPS Overseas Research Fellowships. JS and SK are supported by NASA Grant 80NSSC18K1500. JTF and the mooring deployment were funded by NASA Grants NNX15AG20G and 80NSSC18K1494. DZ is supported by NASA Grant 80NSSC18K1499. This publication is partially funded by the Cooperative Institute for Climate, Ocean, and Ecosystem Studies (CICOES) under NOAA Cooperative Agreement NA20OAR4320271, Contribution 2021-1152. This is PMEL Contribution 5268.
    Description: 2023-01-27
    Keywords: Ocean ; North Pacific Ocean ; Tropics ; Entrainment ; Oceanic mixed layer ; Salinity
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    Potential Vorticity and Instability in the Pacific Equatorial Undercurrent West of the Galápagos Archipelago (2022)
    American Meteorological Society
    Details
    Publication Date: 2023-02-01
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(8), (2022): 1927-1943, https://doi.org/10.1175/jpo-d-21-0124.1.
    Description: The Galápagos Archipelago lies on the equator in the path of the eastward flowing Pacific Equatorial Undercurrent (EUC). When the EUC reaches the archipelago, it upwells and bifurcates into a north and south branch around the archipelago at a latitude determined by topography. Since the Coriolis parameter (f) equals zero at the equator, strong velocity gradients associated with the EUC can result in Ertel potential vorticity (Q) having sign opposite that of planetary vorticity near the equator. Observations collected by underwater gliders deployed just west of the Galápagos Archipelago during 2013–16 are used to estimate Q and to diagnose associated instabilities that may impact the Galápagos Cold Pool. Estimates of Q are qualitatively conserved along streamlines, consistent with the 2.5-layer, inertial model of the EUC by Pedlosky. The Q with sign opposite of f is advected south of the Galápagos Archipelago when the EUC core is located south of the bifurcation latitude. The horizontal gradient of Q suggests that the region between 2°S and 2°N above 100 m is barotropically unstable, while limited regions are baroclinically unstable. Conditions conducive to symmetric instability are observed between the EUC core and the equator and within the southern branch of the undercurrent. Using 2-month and 3-yr averages, e-folding time scales are 2–11 days, suggesting that symmetric instability can persist on those time scales.
    Description: This work was supported by the National Science Foundation (Grants OCE-1232971 and OCE-1233282), the NASA Earth and Space Science Fellowship Program (Grant 80NSSC17K0443), and the Global Ocean Monitoring and Observing Program of the National Oceanographic and Atmospheric Administration (NA13OAR4830216). Color maps are from Thyng et al. (2016).
    Description: 2023-02-01
    Keywords: Currents ; In situ oceanic observations ; Instability ; Mixing ; Ocean dynamics ; Pacific Ocean ; Potential vorticity ; Tropics
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    On characterizing ocean kinematics from surface drifters (2022)
    American Meteorological Society
    Details
    Publication Date: 2023-02-01
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(8), (2022): 1183-1198, https://doi.org/10.1175/jtech-d-21-0068.1.
    Description: Horizontal kinematic properties, such as vorticity, divergence, and lateral strain rate, are estimated from drifter clusters using three approaches. At submesoscale horizontal length scales O(1–10)km, kinematic properties become as large as planetary vorticity f, but challenging to observe because they evolve on short time scales O(hourstodays). By simulating surface drifters in a model flow field, we quantify the sources of uncertainty in the kinematic property calculations due to the deformation of cluster shape. Uncertainties arise primarily due to (i) violation of the linear estimation methods and (ii) aliasing of unresolved scales. Systematic uncertainties (iii) due to GPS errors, are secondary but can become as large as (i) and (ii) when aspect ratios are small. Ideal cluster parameters (number of drifters, length scale, and aspect ratio) are determined and error functions estimated empirically and theoretically. The most robust method—a two-dimensional, linear least squares fit—is applied to the first few days of a drifter dataset from the Bay of Bengal. Application of the length scale and aspect-ratio criteria minimizes errors (i) and (ii), and reduces the total number of clusters and so computational cost. The drifter-estimated kinematic properties map out a cyclonic mesoscale eddy with a surface, submesoscale fronts at its perimeter. Our analyses suggest methodological guidance for computing the two-dimensional kinematic properties in submesoscale flows, given the recently increasing quantity and quality of drifter observations, while also highlighting challenges and limitations.
    Description: This research was supported by the Office of Naval Research (ONR) Departmental Research Initiative ASIRI under Grant N00014-13-1-0451 (SE and AM) and Grant N00014-13-1-0477 (VH and LC). The authors thank the captain and crew of the R/V Roger Revelle, and Andrew Lucas with the Multiscale Ocean Dynamics group at the Scripps Institution for Oceanography for providing the FastCTD data collected in 2015, which was supported by ONR Grant N00014-13-1-0489, as well as Eric D’Asaro for helpful discussions and Lance Braasch for assistance with the drifter dataset. AM and SE further thank NSF (Grant OCE-I434788) and ONR (Grant N00014-16-1-2470) for support. VH and LC were additionally supported by ONR Grants N00014-15-1-2286, N00014-14-1-0183, N00014-19-1-26-91 and NOAA Global Drifter Program (GDP) Grant NA15OAR4320071.
    Description: 2023-02-01
    Keywords: Indian Ocean ; Eddies ; Frontogenesis/frontolysis ; Fronts ; Lagrangian circulation/transport ; Ocean circulation ; Ocean dynamics
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    Geometry of the meridional overturning circulation at the Last Glacial Maximum (2022)
    American Meteorological Society
    Details
    Publication Date: 2023-02-01
    Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 35(17), (2022): 5465-5482, https://doi.org/10.1175/jcli-d-21-0671.1.
    Description: Understanding the contribution of ocean circulation to glacial–interglacial climate change is a major focus of paleoceanography. Specifically, many have tried to determine whether the volumes and depths of Antarctic- and North Atlantic–sourced waters in the deep ocean changed at the Last Glacial Maximum (LGM; ∼22–18 kyr BP) when atmospheric pCO2 concentrations were 100 ppm lower than the preindustrial. Measurements of sedimentary geochemical proxies are the primary way that these deep ocean structural changes have been reconstructed. However, the main proxies used to reconstruct LGM Atlantic water mass geometry provide conflicting results as to whether North Atlantic–sourced waters shoaled during the LGM. Despite this, a number of idealized modeling studies have been advanced to describe the physical processes resulting in shoaled North Atlantic waters. This paper aims to critically assess the approaches used to determine LGM Atlantic circulation geometry and lay out best practices for future work. We first compile existing proxy data and paleoclimate model output to deduce the processes responsible for setting the ocean distributions of geochemical proxies in the LGM Atlantic Ocean. We highlight how small-scale mixing processes in the ocean interior can decouple tracer distributions from the large-scale circulation, complicating the straightforward interpretation of geochemical tracers as proxies for water mass structure. Finally, we outline promising paths toward ascertaining the LGM circulation structure more clearly and deeply.
    Description: S.K.H. was supported by the Investment in Science Fund at WHOI and the John E. and Anne W. Sawyer Endowed Fund in Support of Scientific Staff. F.J.P. was supported by a Stanback Postdoctoral Fellowship at Caltech.
    Description: 2023-02-01
    Keywords: Diapycnal mixing ; Meridional overturning circulation ; Ocean circulation
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    Coastal evolution on Earth and Titan (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: The morphology of a shoreline can provide insight into the processes that have modified the coast. This thesis investigates how coastal processes can leave fingerprints on the morphology of a coast in sandy environments (barrier islands) and detachment-limited environments (rocky coasts of Earth and possibly Titan). Barrier islands are dynamic and ephemeral, facing an uncertain future from climate change and anthropogenic redistribution of sediment. To evaluate barrier resilience to sea-level rise, I propose a novel dimensionless metric called the Washover Ratio which compares cross-shore (overwash) and alongshore transport. Using this ratio, I find that decreases in overwash flux within the narrow middle section—possibly representing the effects of development—lead to a diminished response to sea-level rise across the entire barrier, and therefore a more vulnerable barrier overall. Further investigation of the balance between overwash and alongshore sediment transport allows for an evaluation of barrier island stability to overwash-induced breaching, which is applied to barriers in the Gulf of Mexico. Beyond Earth, Titan, Saturn’s largest moon, is home to the only other active coastlines in our solar system. However, data is sparse for this icy moon. I investigate the signatures of coastal processes found in the planform shape of its coasts using a combination of landscape evolution models and measurements of shoreline shape. Results show that the coastlines of Titan’s seas are consistent with those of both modelled and Earth lakes with flooded river valleys that have been subsequently eroded by waves, particularly when waves saturate (no longer grow in height) at scales up to 10s of km.
    Description: Work toward this thesis was funded by the National Science Foundation (NSF) and National Aeronautics and Space Administration (NASA). NSF funding was awarded through the Graduate Research Fellowship Program (#1745302) and the Coupled Natural Hazards program (#CNH-1518503). NASA funding was awarded through the Cassini Data Analysis Program (#80NSSC18K1057) and (#80NSSC20K0484).
    Keywords: Barrier Island ; Geomorphology ; Titan
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    A practical search with Voronoi distributed autonomous marine swarms (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: The search for underwater threats in littoral regions is a problem that has been researched for nearly a century. However, recent developments in autonomy and robotics have made this issue more complex. The advent of capable autonomous underwater vehicles presents a 21st century flare to this traditional problem. These vehicles can be smaller, quieter, and expendable. Therefore, new methods and tactics used to detect and track these vehicles are needed. The use of a swarm of marine robots can increase the likelihood of uncovering these threats. This thesis provides various Voronoi partition-based methods to autonomously control a swarm of identically capable autonomous surface vessels in a limited coverage and tracking problem. These methods increase the probability of interdiction of an adversary vehicle crossing a defined region. The results achieved from Monte Carlo simulations demonstrate how different protocols of swarm movement can improve detection probability as compared to a stationary swarm provided the detection capability does not change. The swarm control algorithms are employed on Clearpath Heron USVs to validate the autonomy algorithms.
    Keywords: Swarm Autonomy Search
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    High frequency acoustic propagation and modeling in stratified estuaries (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: Acoustic propagation measurements are made in a highly variable and stratified estuary using high frequency transducers (120kHz) on tripods placed across the main channel of the river flow. The measurements are taken in the Connecticut River across several tidal cycles, when the flood tide causes a wedge of seawater to press up the river bed, beneath the fresh water, and then be eroded and pushed back out during the ebb. BELLHOP, implemented via Matlab, is a beam/ray tracing method and is used to model the acoustic propagation in this environment using collected temperature, salinity, and depth data. Multiple modeling comparisons are done over the period of three full tidal cycles, totaling a thousand separate modeling runs and compiled into a time series. Arrival times measurements from the transducer system were able to be accurately modeled, validating BELLHOP as a useful tool in modeling this very dynamic and challenging acoustic environment.
    Description: This thesis would not have been possible with the data collected by Dr. Andone Lavery, Jonathan Fincke and others, originally funded by the Office of Naval Research (through ONR Grant #N00014-11-10058).
    Keywords: Acoustic Propagation ; Acoustic Modeling ; BELLHOP
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    The fate of anthropogenic nitrogen in a redox stratified pond: an isotopic approach (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science in Chemical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: The environmental effects of both increased urbanization and eutrophication are of growing global concern. Coastal areas, like those found on Cape Cod, Massachusetts, often experience severe impacts associated with the biogeochemical effects accompanying increased nitrogen pollution. Cape Cod is home to roughly 1,000 ponds and lakes which play an important role in local ecosystems, but the cycling of nitrogen in these waters is not well understood. The goal of this research is to identify the major biogeochemical cycling processes responsible for the fate of nitrogen in a nitrogen-rich, coastal, stratified pond. The investigation was carried out through regular high-resolution measurement and monitoring of environmental conditions, nitrogen speciation, and isotopic composition over the course of a summer. Elevated nitrogen concentrations coupled with strong redox gradients make Siders Pond an ideal place for studying dynamics of nitrogen transformations, giving insight into nitrogen retention or removal, which influence water quality. These data demonstrate significant dissolved nitrogen loss from the pond over the course of the summer as well as internal nitrogen cycling that promotes dissolved nitrogen accumulation to extreme levels in the deepest depths. The physical dynamics of mixing promote a coupling of nitrification and denitrification across this redox gradient, driving N loss while also supplying the sunlit waters with nutrient-rich deep water. A simple time-resolved box model suggests that approximately 50% of the upwardly delivered N is removed, while the other portion supports recycling through photosynthetic uptake. While dissolved organic nitrogen (DON) is widely considered refractory material and is rarely measured or reported in environmental studies, here there is evidence for a large and dynamic pool of DON within Siders Pond suggesting important dynamics between organic and inorganic pools in regulating N loss. While nitrate is a commonly used measurement for assessing N contamination, this work highlights the parallel importance of monitoring additional species (including ammonium and DON) for determining eutrophication/contamination. A deeper understanding of Siders Pond can be used to elucidate nitrogen cycling dynamics in analogous redox-stratified systems, including other lakes and ponds, or modern ocean regions such as the Santa Barbara and Cariaco Basins and the Baltic and Black Seas.
    Description: National Science Foundation (project number NSF-1924236)
    Keywords: Nitrogen ; Stable isotopes ; Lakes and ponds
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    Exploring the role of reactive oxygen species (ROS) in marine ecosystem health and function (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: With the rapid decline of coastal ecosystems such as coral reefs and seagrasses, it is crucial to better understand the health of these ecosystem to prevent future loss. Reactive oxygen speices (ROS), such as superoxide and hydrogen peroxide, play an underappreciated role in both organism health and ecosystem biogeochemical cycles. This thesis lays the foundation to measure and identify ROS production by coral in situ and through genomic analysis while also highlighting the important role that ROS can play within biogeochemical cycling within seagrass ecosystems. To measure in situ extracellular superoxide, we develop the first DIver-operated Submersible Chemiluminescent sensOr (DISCO), enabling high resolution, non-invasive measurements in real time. We further refine DISCO by making it more compact, user-friendly, adaptable, and robust, enabling measurements of superoxide across a diversity of environments. Using DISCO, I observe species-specific variation in extracellular superoxide concentrations associated with healthy coral. Despite these variations across species, bioinformatic analysis of coral proteins reveal that nearly all coral species have the extracellular superoxide-producing enzyme NADPH oxidase (NOX), and thus the genetic potential to produce extracellular superoxide. This suggests that coral species likely exhibit differential NOX regulation and expression as a function of physiological responses to external stressors, which may play a role in coral immunity. I then turn to seagrass ecosystems, where I observe rapid hydrogen peroxide production and decay through predominantly reductive pathways. This has implications on the environmental redox state and biogeochemical cycling, impacting the ecosystem services that seagrasses provide to marine environments and coastal communities. Overall, this thesis highlights the potential role that ROS may be playing in organism and ecosystem health and lays the groundwork to further develop ROS as a tool to protect these coastal ecosystems against further degradation.
    Description: Funding for this work was provided by the following grants: NSF GRFP (2016230168), Schmidt Marine Technology Partners (G-1801-57385 andG-2010-59878), WHOI Ocean Ventures Fund (2020 and 2021), and the MIT Wellington and Irene Loh Fund Fellowship (4000111995).
    Keywords: Reactive oxygen species ; Coral ; Seagrass
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    In-situ characterization of sea state with improved navigation on an Autonomous Underwater Glider (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: This thesis presents an Autonomous Underwater Glider (AUG) architecture with improved onboard navigation and acoustics-based sensing intended to enable basin-scale unattended surveys of our Earth’s most remote oceans. Traditional AUGs have long-been an important platform for oceanographic surveys due to their high endurance and autonomy, yet lack the operational flexibility to operate in many regions of scientific interest and the sensing capability to capture scientific data at the air-sea interface. Particularly of interest is the marginal ice zone (MIZ) in the Arctic and the Southern Ocean, as both are vitally important to understanding global climate trends, yet prohibitively expensive to persistently monitor with support vessels. To fill this observational gap, the sensing, navigation, and adaptability of AUGs must be improved. This is possible by employing onboard acoustic sensing for sea state observation and navigation, as well as incorporating vehicle improvements targeting maneuverability and intelligent adaptability to evolving environmental states. To enable persistent monitoring of both the water-column and air-sea interface, this thesis proposes an improved vehicle architecture for a more capable AUG, a real-time DVLaided navigation process that leverages ocean current sensing to limit localization error, and a subsea acoustics-based sea state characterization method capable of analyzing wave spectra under-ice and with zero surface expression. These methods are evaluated with respect to extensive laboratory experiments and field data collected during in-situ implementation.
    Description: Support for this research was provided through grants from the National Science Foundation (NSF) Navigating the New Arctic Grant (NNA #1839063) and the National Ocean Partnership Program (NOPP) Enhanced Propulsion Integrated Capability - Deep Autonomous Underwater Glider (EPIC-DAUG) grant (NA19OAR0110408).
    Keywords: Autonomous Underwater Glider ; Underwater Navigation ; Acoustic Sensing
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    An inverse modeling approach to investigate deep ocean ventilation from radiocarbon records (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: The goal of this project is to investigate the relationship between paleoceanographic radiocarbon records and the ventilation history of deep oceanic basins during the last 40 kyrs. Deep ocean ventilation changes, especially changes in Atlantic meridional overturning circulation (AMOC), are often invoked to explain the deglacial rise in atmospheric carbon dioxide (CO2) concentration as inferred from ice core records. Much of our current understanding regarding ventilation of the deep ocean during the deglaciation comes from records of the radiocarbon concentration of benthic foraminifera and deep-sea corals (paleo-Δ14C data). Here, we combine a global compilation of paleo-Δ14C data for the past 40 kyrs with a 16-box model of the world ocean (except the Arctic Ocean) to address two key questions: (1) To what extent can the paleo-Δ14C data be explained by atmospheric Δ14C variations when deep ventilation rates are fixed to modern ocean estimates? and (2) To what extent can the paleo- Δ 14C data be explained by atmospheric Δ 14C variations when the ventilation rates are allowed to vary? To address these questions, the box model is fitted to the paleo-Δ14C data using the following sequential methods of optimal estimation theory: the linear Kalman filter, the Extended Kalman Filter, the Rauch-Tung-Striebel (RTS) smoother, and a linearized RTS smoother. We find that 62–76% (depending on the assumptions made about air-sea 14CO2 exchange) of the paleo-Δ 14C data for the past 40 kyrs can be explained by the modern flow rates as represented in the box model, if the model is forced with the IntCal20 reconstruction of atmospheric Δ14C. When the flow rates in the model are allowed to vary with time, 74-89% of the data can be explained by the model. Here, the range in data that can be explained reflects the different assumptions about the errors in the air-sea 14CO2 exchange and in the random walk used to model the temporal evolution of flow rates. It is concluded that changes in deep ocean ventilation may have occurred from 20 and 10 ka, thereby contributing to the deglacial CO2 rise, but that the spatial pattern of ventilation changes may have been complex, with a strengthening of the downwelling branch of the AMOC and a weakening of its deep southward branch during this time.
    Description: This project was supported by the United States National Science Foundation, grant number 1903427, which made this work possible.
    Keywords: Paleoceanography ; Modeling ; Ventilation
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    Query-driven adaptive sampling (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: Automated information gathering allows exploration of environments where data is limited and gathering observations introduces risk, such as underwater and planetary exploration. Typically, exploration has been performed in service of a query, with a unique algorithm developed for each mission. Yet this approach does not allow scientists to respond to novel questions as they are raised. In this thesis, we develop a single approach for a broad range of adaptive sampling missions with risk and limited prior knowledge. To achieve this, we present contributions in planning adaptive missions in service of queries, and modeling multi-attribute environments. First, we define a query language suitable for specifying diverse goals in adaptive sampling. The language fully encompasses objectives from previous adaptive sampling approaches, and significantly extends the possible range of objectives. We prove that queries expressible in this language are not biased in a way that avoids information. We then describe a Monte Carlo tree search approach to plan for all queries in our language, using sample based objective estimators embedded within tree search. This approach outperforms methods that maximize information about all variables in hydrocarbon seep search and fire escape scenarios. Next, we show how to plan when the policy must bound risk as a function of reward. By solving approximating problems, we guarantee risk bounds on policies with large numbers of actions and continuous observations, ensuring that risks are only taken when justified by reward. Exploration is limited by the quality of the environment model, so we introduce Gaussian process models with directed acyclic structure to improve model accuracy under limited data. The addition of interpretable structure allows qualitative expert knowledge of the environment to be encoded through structure and parameter constraints. Since expert knowledge may be incomplete, we introduce efficient structure learning over structural models using A* search with bounding conflicts. By placing bounds on likelihood of substructures, we limit the number of structures that are trained, significantly accelerating search. Experiments modeling geographic data show that our model produces more accurate predictions than existing Gaussian process methods, and using bounds allows structure to be learned in 50% of the time.
    Description: The work in this thesis was supported by the Exxon Mobil Corporation as part of the MIT Energy Initiative under the project ‘Autonomous System for Deep Sea Hydrocarbon Detection and Monitoring’, NASA’s PSTAR program under the project ‘Cooperative Exploration with Under-actuated Autonomous Vehicles in Hazardous Environments’, and the Vulcan Machine Learning Center for Impact under the project ‘Machine Learning Based Persistent Autonomous Underwater Scientific Studies’.
    Keywords: Adaptive sampling ; Chance constrained planning ; Guassian process regression
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    Variations in marine microbiomes: from habitat to host (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: Microorganisms are the dominant life form on Earth and inextricably tied to the ecology and evolution of all multicellular life, including marine animals. As the importance of microorganisms to our conception of life gains prominence, animals (and other macroorganisms) are increasingly viewed as “holobionts”, an assemblage of the host plus all its symbiotic microbes. This dissertation examines holobiont biology from the perspective of the microbial communities that live in and around marine hosts. Using both amplicon and metagenomic sequencing, I study the microbiomes of reef-associated seawater and Atlantic killifish to better understand habitat and host effects on microbiome structure. In two Caribbean reef systems, I used examined the biogeography of reef water microbes. I found that the microbiome of reef seawater varies with reef system and individual reefs but that microbiomes within individual reefs were similar to each other and did not vary with benthic composition. The regionalism of reef seawater microbiomes was further assessed upon incorporation of global scale data from five additional studies, which revealed that microbial communities were more distinct with increasing geographic distance. These results contribute to our understanding of the coral holobiont’s microbial environment and can inform monitoring efforts for reef health. Atlantic killifish populations can be categorized as sensitive or tolerant to industrial pollutants based on history of pollutant exposure. Thus, they are an excellent “natural laboratory” for understanding the combined effect of environment and host on microbiome composition. I examined the gut microbiomes of two populations of wild fish as well as captive fish originating from each of these wild populations. I found that living in and adapting to polluted waters can impact microbiome composition and structure, resulting in a microbiome that appears more disordered. Additionally, captivity resulted in a complete turnover of dominant microbial taxa, indicating the environment plays a large role in shaping killifish gut microbiomes. This dissertation demonstrates that diverse systems, from coral reefs to killifish, can benefit from a better understanding of its associated microorganisms. For holobiont studies, these results highlight the importance of considering the context of microbial communities, from environment to host population.
    Description: My time in the MIT-WHOI Joint Program was supported by the Civil and Environmental Engineering department at MIT, the Schoettler scholarship fund, the National Science Foundation, and the Academic Programs Office at WHOI. The research presented here was supported by Rockefeller Philanthropy Advisors, the Dalio Foundation, and NSF awards OCE-1938147 and NSF OCE-1928761 to Amy Apprill; Joint Initiative Funds from the W. Andrew Mellon Foundation to Amy Apprill and Mark Hahn; and Ocean Venture Fund to Lei Ma.
    Keywords: Microbiome ; Killifish ; Coral
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    Oceanic ambient noise in the Arctic on the Chukchi Shelf: broadband characteristics and environmental drivers (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: This thesis encompasses an analysis of underwater ambient noise collected by the yearlong Canada Basin Acoustic Propagation Experiment (CANAPE) on the Chukchi Shelf of the Arctic. This location contained the Beaufort Duct, a significant effect of climate change on the Arctic’s underwater soundscape. A study of the statistical and probability metrics was conducted on a frequency band of 50-1900 Hz to examine the relation between environmental drivers and noise patterns. The presence of ice typically decreases broadband ambient noise, when compared to ice-free seas. However, the Beaufort Duct under ice increases the ambient noise levels below 1 kHz. The relationship between ambient noise and the environment is further explored by studying the link between distant ice movements and ambient levels Correlation between the two is found to exist from 300-1500 Hz, as distant ( 500 km) ice drift motion appears to drive noise levels at the receiver.
    Description: Funding sources include the US Navy and Office of Naval Research.
    Keywords: Arctic ; Ambient ; Noise
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    Insights from geodynamic models into ice flow, mantle magmatism, and their interactions (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2023.
    Description: In this thesis, I use geodynamic models to study processes within the Earth’s mantle and cryosphere. I begin by quantifying previously unconsidered sources of magmatic CO2. In Chapter 2, I predict how small concentrations of CO2 found in passively upwelling mantle throughout ocean basins may generate low-degree carbonate melting. I find the flux of CO2 segregated by these melts rivals the flux from mid-ocean ridges. In Chapter 3, I model how the deglaciation of the Yellowstone ice cap caused a reduction in mantle pressures and enhanced melting 19-fold. I predict the additional melting segregates a globally-significant mass of CO2, potentially playing a role in positive feedbacks between deglaciation and climate. I suggest enhanced melting may be important in other magmatically-active, continental settings undergoing rapid deglaciation — for instance, under the collapse of the West Antarctic Ice Sheet (WAIS). This thesis next explores glaciological factors controlling WAIS stability, associated with the fracturing of ice sheet margins supported by floating ice shelves. The Marine Ice Cliff Instability posits ice cliffs above a critical height collapse under their own weight, initiating runaway ice sheet retreat. In Chapter 4, I model the formation of marine ice cliffs, as an Antarctic ice shelf is removed. I show that over ice-shelf collapse timescales longer than a few days (consistent with observations), ice cliffs comprised of intact ice are more stable, undergoing viscous flow rather than brittle fracture. I next investigate interactions between viscous and brittle processes, guided by observations on a modern Antarctic ice shelf. In Chapter 5, I model deformation at the McDonald Ice Rumples (MIR), formed as the Brunt Ice Shelf is grounded into a bathymetric high. The MIR are characterized by concentric folds intersected by radial fractures, implying viscous and brittle behavior, respectively. I interpret these features to constrain ice rheology and strength. More broadly, this final chapter highlights how leveraging glaciological observations as natural experiments places constraints on the phenomenological laws which govern ice and (analogously) mantle flow. In summary, jointly developing models of both ice and mantle flow better constrains the dynamics of each system (solid Earth and cryosphere) and their interactions.
    Description: I was funded by an NSF Graduate Research Fellowship, WHOI’s Karen L. Von Damm Fellowship, and NSFGEO-NERC grant 1853918.
    Keywords: Solid Earth ; Cryosphere
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    Developing in situ instrumentation to monitor anthropogenic change (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mechanical and Oceanographic Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2023.
    Description: To predict and mitigate anthropogenic impacts on the ocean, we must understand the underlying systems that govern the ocean’s response to inputs (e.g. carbon dioxide, pollutants). Analytical models can be used to generate predictions and simulate intervention strategies, but they must be grounded with empirical observations. Unfortunately, there exists a technological gap: in situ instrumentation is often lacking or nonexistent for key parameters influenced by anthropogenic inputs. While discrete bottle samples can be collected and analyzed for these parameters, their limited spatiotemporal resolution constrains scientific inquiry. To help fill the technological gap, this dissertation presents the development of instrumentation for the ocean inorganic carbon system and microplastics. The first few chapters present the development process of CSPEC, a deep-sea laser spectrometer designed to measure the ocean carbon system through alternating measurements of the partial pressure of carbon dioxide (pCO2) and dissolved inorganic carbon (DIC). CSPEC uses tunable diode laser absorption spectroscopy (TDLAS) to measure the CO2 content of dissolved gas extracted via a membrane inlet. Chapter 2 derives membrane equilibration dynamics from first principles, thus enabling informed design decisions. The analytical results showed that cross-sensitivity to other dissolved gases can be introduced by the equilibration method, regardless of the specificity of the gas-side instrumentation. A new method, hybrid equilibration, leverages the membrane equilibration dynamics to improve time response without incurring cross-sensitivity. Chapter 3 presents POCO, a surface pCO2 instrument that employs TDLAS and a depth-compatible membrane inlet. Through laboratory and field-testing, POCO demonstrated that hybrid equilibration overcame the gas flux limitation of deep-sea membrane inlets. Chapter 4 presents CSPEC, which successfully mapped the carbon system near different hydrothermal features at 2000 m in Guaymas Basin, becoming one of the first DIC instruments field-tested at depth. Chapter 5 introduces impedance spectroscopy for quantifying microplastics directly in water. Microplastics were successfully counted, sized, and differentiated from biology in the laboratory: a step toward in situ quantification. The analytical tools and measurement systems presented in this dissertation represent a significant step towards increasing the spatiotemporal resolution of carbon system and microplastic measurements, thus enabling broader scientific inquiry in the future.
    Description: This research was supported by the following funding sources: NSF Grant # OCE-1454067 NSF Grant # OCE-184-2053 Link Foundation Ocean Engineering and Instrumentation Ph.D. Fellowship MITMartin Family Society of Fellows for Sustainability Richard Saltonstall Charitable Foundation National Academies Keck Future Initiative (NAFKI DBS13)
    Keywords: In situ ; Disssolved inorganic carbon ; Microplastics
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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    Balancing exploration and exploitation: task-targeted exploration for scientific decision-making (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: How do we collect observational data that reveal fundamental properties of scientific phenomena? This is a key challenge in modern scientific discovery. Scientific phenomena are complex—they have high-dimensional and continuous state, exhibit chaotic dynamics, and generate noisy sensor observations. Additionally, scientific experimentation often requires significant time, money, and human effort. In the face of these challenges, we propose to leverage autonomous decision-making to augment and accelerate human scientific discovery. Autonomous decision-making in scientific domains faces an important and classical challenge: balancing exploration and exploitation when making decisions under uncertainty. This thesis argues that efficient decision-making in real-world, scientific domains requires task-targeted exploration—exploration strategies that are tuned to a specific task. By quantifying the change in task performance due to exploratory actions, we enable decision-makers that can contend with highly uncertain real-world environments, performing exploration parsimoniously to improve task performance. The thesis presents three novel paradigms for task-targeted exploration that are motivated by and applied to real-world scientific problems. We first consider exploration in partially observable Markov decision processes (POMDPs) and present two novel planners that leverage task-driven information measures to balance exploration and exploitation. These planners drive robots in simulation and oceanographic field trials to robustly identify plume sources and track targets with stochastic dynamics. We next consider the exploration- exploitation trade-off in online learning paradigms, a robust alternative to POMDPs when the environment is adversarial or difficult to model. We present novel online learning algorithms that balance exploitative and exploratory plays optimally under real-world constraints, including delayed feedback, partial predictability, and short regret horizons. We use these algorithms to perform model selection for subseasonal temperature and precipitation forecasting, achieving state-of-the-art forecasting accuracy. The human scientific endeavor is poised to benefit from our emerging capacity to integrate observational data into the process of model development and validation. Realizing the full potential of these data requires autonomous decision-makers that can contend with the inherent uncertainty of real-world scientific domains. This thesis highlights the critical role that task-targeted exploration plays in efficient scientific decision-making and proposes three novel methods to achieve task-targeted exploration in real-world oceanographic and climate science applications.
    Description: This material is based upon work supported by the NSF Graduate Research Fellowship Program and a Microsoft Research PhD Fellowship, as well as the Department of Energy / National Nuclear Security Administration under Award Number DE-NA0003921, the Office of Naval Research under Award Number N00014-17-1-2072, and DARPA under Award Number HR001120C0033.
    Keywords: Decision-making ; Robotics ; Exploration
    Repository Name: Woods Hole Open Access Server
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    Mechanisms of tidal dispersion in a salt marsh estuary (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: Dispersion in estuaries sets the length of salinity intrusion and the horizontal mixing rate of waterborne constituents, including larvae, nutrients, sediments, and contaminants. While bulk calculations of dispersion are readily estimated using traditional field measurements, the mechanisms contributing to the total dispersion are difficult to identify because they require high temporal and spatial resolution to measure. Recent advances in field techniques and numerical modeling have enabled the isolated study of various mechanisms contributing to dispersion, many of which vary on tidal time-scales and over small spatial scales. The objective of this thesis is to use a combination of high-resolution field measurements and numerical modeling to determine the mechanisms of dispersion that maintain the salt balance in the North River (Marshfield, MA), a tidally-dominated salt marsh estuary with complex topography. First, a field campaign was conducted to determine the dispersion associated with the out-of-phase exchange between tributary creeks and the main channel. Then, numerical simulations of an idealized estuary were conducted and a novel quasi-Lagrangian approach was applied to analyze the sources of dispersive salt fluxes throughout the estuary. A second field campaign was conducted to evaluate the spatial variability of shear dispersion, particularly near regions of abrupt topographic variations. The key result from this thesis is obtained through the first application of the theoretical moving plane framework of Dronkers & van de Kreeke (1986), which confirms quantitatively that all landward salt flux at a fixed location must result from spatial correlations in velocity and salinity within a tidal excursion of the fixed location. Based on this result, the sources of the landward salt flux can be directly identified based on the spatial and tidal variations of shear dispersion, which can vary strongly due to its dependence on the local tidal currents, along-channel salinity gradient, and bathymetry. This thesis identifies and quantifies various mechanisms of topographically-induced tidal dispersion and thus highlights the dominant role of topography in controlling the processes that contribute to mixing and transport in short, tidally-energetic estuaries.
    Description: The work presented in this thesis was funded largely by the National Science Foundation through a Graduate Student Research Fellowship (No. 1122374) in addition to NSF Grants OCE-1634490 and OCE-2123002. Additional funding was also provided from WHOI through the Michael J. Kowalski Fellowship for Ocean Science & Engineering and from MIT through an OGE Diversity Fellowship.
    Keywords: Estuary ; Salinity ; Dispersion
    Repository Name: Woods Hole Open Access Server
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    Developing the next generation of Autonomous Underwater Gliders (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: This thesis presents a novel, hybrid Autonomous Underwater Glider (AUG) architecture developed for improved performance in shallow, high-current environments while maintaining all capabilities inherent to a deep, 1000m-rated AUG. Numerous regions of scientific interest, such as the marginal ice zone (MIZ) and continental shelf breaks present significant challenges to conventional AUG operations due to a combination of changing ocean currents and depths. AUGs are traditionally optimized for performance in shallow (less than 200m) or deep water (200m to 1000m) environments. The design of a buoyancy drive on a deep-rated AUG does not support the pump rate required for fast inflections in narrow depth bands. Contained within this thesis is the framework to expand the operational envelope of a Teledyne Webb Research (TWR) G3 Slocum glider through substantial modification of the glider’s hardware components backed by rigorous hydrodynamic analysis and computational fluid dynamics (CFD) modelling. Since AUGs are limited in both speed and maneuverability, the goal of this thesis is to improve and modify the glider’s flight characteristics, specifically the glider’s speed through water, its inflection rate, and its efficiency. These performance improvements are accomplished through the introduction of a high-power thruster, modified wings, and aft fin surfaces. The modified glider’s efficacy is evaluated through various laboratory experiments and field data obtained in Buzzards Bay and the Caribbean Sea. Design concepts for a future, more advanced glider are also discussed.
    Description: Support for this research was provided through grants from the National Science Foundation (NSF) Navigating the New Arctic Grant (NNA #1839063) and the National Ocean Partnership Program (NOPP) Enhanced Propulsion Integrated Capability - Deep Autonomous Underwater Glider (EPIC-DAUG) grant (NA19OAR0110408).
    Keywords: AUG ; Glider ; Slocum
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    Multimodel Subseasonal Forecasts of Spring Cold Spells: Potential Value for the Hazelnut Agribusiness (2021)
    American Meteorological Society
    Details
    Publication Date: 2021-05-12
    Description: Producing probabilistic subseasonal forecasts of extreme events up to six weeks in advance is crucial for many economic sectors. In agribusiness, this time scale is particularly critical because it allows for mitigation strategies to be adopted for counteracting weather hazards and taking advantage of opportunities. For example, spring frosts are detrimental for many nut trees, resulting in dramatic losses at harvest time. To explore subseasonal forecast quality in boreal spring, identified as one of the most sensitive times of the year by agribusiness end users, we build a multisystem ensemble using four models involved in the Subseasonal to Seasonal Prediction project (S2S). Two-meter temperature forecasts are used to analyze cold spell predictions in the coastal Black Sea region, an area that is a global leader in the production of hazelnuts. When analyzed at the global scale, the multisystem ensemble probabilistic forecasts for near-surface temperature are better than climatological values for several regions, especially the tropics, even many weeks in advance; however, in the coastal Black Sea, skill is low after the second forecast week. When cold spells are predicted instead of near-surface temperatures, skill improves for the region, and the forecasts prove to contain potentially useful information to stakeholders willing to put mitigation plans into effect. Using a cost–loss model approach for the first time in this context, we show that there is added value of having such a forecast system instead of a business-as-usual strategy, not only for predictions released 1–2 weeks ahead of the extreme event, but also at longer lead times.
    Description: Published
    Description: 237–254
    Description: 4A. Oceanografia e clima
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Potential vorticity dynamics of the arctic halocline (2021)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 50(9), (2020): 2491-2506, doi:10.1175/JPO-D-20-0056.1.
    Description: An idealized two-layer shallow water model is applied to the study of the dynamics of the Arctic Ocean halocline. The model is forced by a surface stress distribution reflective of the observed wind stress pattern and ice motion and by an inflow representing the flow of Pacific Water through Bering Strait. The model reproduces the main elements of the halocline circulation: an anticyclonic Beaufort Gyre in the western basin (representing the Canada Basin), a cyclonic circulation in the eastern basin (representing the Eurasian Basin), and a Transpolar Drift between the two gyres directed from the upwind side of the basin to the downwind side of the basin. Analysis of the potential vorticity budget shows a basin-averaged balance primarily between potential vorticity input at the surface and dissipation at the lateral boundaries. However, advection is a leading-order term not only within the anticyclonic and cyclonic gyres but also between the gyres. This means that the eastern and western basins are dynamically connected through the advection of potential vorticity. Both eddy and mean fluxes play a role in connecting the regions of potential vorticity input at the surface with the opposite gyre and with the viscous boundary layers. These conclusions are based on a series of model runs in which forcing, topography, straits, and the Coriolis parameter were varied.
    Description: This study was supported by National Science Foundation Grant OPP-1822334. Comments and suggestions from two anonymous referees greatly helped to improve the paper.
    Description: 2021-02-17
    Keywords: Eddies ; Ekman pumping/transport ; Ocean circulation ; Ocean dynamics ; Potential vorticity ; Shallow-water equations
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    Tropical widening from global variations to regional impacts (2021)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 101(6), (2020): E897-E904, doi:10.1175/BAMS-D-19-0047.1.
    Description: Over the past 15 years, numerous studies have suggested that the sinking branches of Earth’s Hadley circulation and the associated subtropical dry zones have shifted poleward over the late twentieth century and early twenty-first century. Early estimates of this tropical widening from satellite observations and reanalyses varied from 0.25° to 3° latitude per decade, while estimates from global climate models show widening at the lower end of the observed range. In 2016, two working groups, the U.S. Climate Variability and Predictability (CLIVAR) working group on the Changing Width of the Tropical Belt and the International Space Science Institute (ISSI) Tropical Width Diagnostics Intercomparison Project, were formed to synthesize current understanding of the magnitude, causes, and impacts of the recent tropical widening evident in observations. These working groups concluded that the large rates of observed tropical widening noted by earlier studies resulted from their use of metrics that poorly capture changes in the Hadley circulation, or from the use of reanalyses that contained spurious trends. Accounting for these issues reduces the range of observed expansion rates to 0.25°–0.5° latitude decade‒1—within the range from model simulations. Models indicate that most of the recent Northern Hemisphere tropical widening is consistent with natural variability, whereas increasing greenhouse gases and decreasing stratospheric ozone likely played an important role in Southern Hemisphere widening. Whatever the cause or rate of expansion, understanding the regional impacts of tropical widening requires additional work, as different forcings can produce different regional patterns of widening.
    Description: We thank U.S. CLIVAR and ISSI for funding the two working groups. We thank all members of the working groups for helpful discussions, and the U.S. CLIVAR and ISSI offices and their sponsoring agencies (NASA, NOAA, NSF, DOE, ESA, Swiss Confederation, Swiss Academy of Sciences, and University of Bern) for supporting these groups and activities.
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    Mean conditions and seasonality of the West Greenland boundary current system near Cape Farewell (2021)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 50(10), (2020): 2849-2871, https://doi.org/10.1175/JPO-D-20-0086.1.
    Description: The structure, transport, and seasonal variability of the West Greenland boundary current system near Cape Farewell are investigated using a high-resolution mooring array deployed from 2014 to 2018. The boundary current system is comprised of three components: the West Greenland Coastal Current, which advects cold and fresh Upper Polar Water (UPW); the West Greenland Current, which transports warm and salty Irminger Water (IW) along the upper slope and UPW at the surface; and the Deep Western Boundary Current, which advects dense overflow waters. Labrador Sea Water (LSW) is prevalent at the seaward side of the array within an offshore recirculation gyre and at the base of the West Greenland Current. The 4-yr mean transport of the full boundary current system is 31.1 ± 7.4 Sv (1 Sv ≡ 106 m3 s−1), with no clear seasonal signal. However, the individual water mass components exhibit seasonal cycles in hydrographic properties and transport. LSW penetrates the boundary current locally, through entrainment/mixing from the adjacent recirculation gyre, and also enters the current upstream in the Irminger Sea. IW is modified through air–sea interaction during winter along the length of its trajectory around the Irminger Sea, which converts some of the water to LSW. This, together with the seasonal increase in LSW entering the current, results in an anticorrelation in transport between these two water masses. The seasonality in UPW transport can be explained by remote wind forcing and subsequent adjustment via coastal trapped waves. Our results provide the first quantitatively robust observational description of the boundary current in the eastern Labrador Sea.
    Description: A.P., R.S.P., F.B., D.J.T., and A.L.R. were funded by Grants OCE-1259618 and OCE-1756361 from the National Science Foundation. I.L.B, F.S., and J.H. were supported by U.S. National Science Foundation Grants OCE-1258823 and OCE-1756272. Mooring data from MA2 was funded by the European Union 7th Framework Programme (FP7 2007-2013) under Grant 308299 (NACLIM) and the Horizon 2020 research and innovation program under Grant 727852 (Blue-Action). J.K. and M.O. acknowledge EU Horizon 2020 funding Grants 727852 (Blue-action) and 862626 (EuroSea) and from the German Ministry of Research and Education (RACE Program). G.W.K.M. acknowledges funding from the Natural Sciences and Engineering Research Council.
    Keywords: Boundary currents ; Convection ; Deep convection ; Transport ; In situ oceanic observations ; Seasonal cycle
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    Coherent pathways for vertical transport from the Surface Ocean to Interior (2021)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 101(11), (2020): E1996-E2004, https://doi.org/10.1175/BAMS-D-19-0305.1.
    Description: A long-standing challenge in oceanography is the observing, modeling, and prediction of vertical transport, which links the sunlit and atmospherically mediated surface boundary layer with the deeper ocean. Vertical motions play a critical role in the exchange of heat, freshwater, and biogeochemical tracers between the surface and the ocean interior. The most intense vertical velocities occur at horizontal scales less than 10 km, making them difficult to observe in the ocean and to resolve in models. Understanding how finescale turbulent motions and 0.1–10 km submesoscale processes contribute to the large-scale budgets of nutrients, oxygen, carbon, and heat and affect sea surface temperature, the air–sea exchange of gases, and the carbon cycle is one of the key challenges in oceanography.
    Description: CALYPSO is a Departmental Research Initiative (DRI) funded by the U.S. Office of Naval Research (ONR). It is a collaborative program involving more than 30 scientists and students and multiple institutions in the United States, Spain, and Italy. Measurements were conducted from the NRV Alliance, Pourquoi Pas?, and SOCIB. We are grateful to the captains and crews of these research vessels and the technical and scientific staff involved in making measurements, running models, analyzing data, and providing support.
    Description: 2021-05-01
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    The heterogeneity and volatile content of Earth’s mantle, magmas and crust (2021)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2021.
    Description: This thesis explores the volatile content of the mantle, subducted oceanic crust, and arc magmas as well as the structure of slow spreading ocean crust and the heterogeneity of Earth’s upper mantle. In Chapter 2, I directly explore the halogen (F and Cl) content of mantle minerals in situ, then use these measurements to assess the halogen content of the upper mantle. In Chapter 3, I investigate the volatile content of Raspas eclogites (SW Ecuador), a proxy for deeply subducted oceanic crust, to evaluate volatile transfer from crustal generation at divergent plate boundaries (e.g., mid-ocean ridges) to recycling of ocean crust at subduction zones. In Chapter 4, I use the H2O content of nominally anhydrous minerals in plutonic arc cumulates to elucidate the H2O content of the melts from which the rocks crystallized. In this way, I assert that primitive arc magmas may contain 4–10 wt.% H2O and through fractional crystallization up to ~20 wt.% H2O, making them far more hydrous than traditional methods (i.e., olivine-hosted melt inclusions) surmise. In Chapter 5, I show that mantle peridotite exposed along the 16ºN region of the Mid-Atlantic Ridge originated in an arc setting and has been remixed into subridge mantle, indicating that the sub-ridge mantle is more heterogeneous and depleted than inferences made from mid-ocean ridge basalts suggest. Chapter 6 surveys the life cycle of oceanic core complexes through zircon geochronology and posits an updated framework for understanding the termination of oceanic core complexes, and more broadly oceanic detachment faults. Together, this contribution highlights the chemical heterogeneity of the mantle, and quantifies the full extent of volatiles hosted by mantle and crustal reservoirs.
    Description: The Stanley Watson Fellowship (WHOI) provided financial support during my first year of graduate school. The Academic Programs Office Ocean Venture Fund (WHOI) provided seed funding which initiated Chapters 3 and 4, and ultimately led to two funded NSF proposals. These resources are vital to JP students, and I am incredibly grateful for them. Primary support was provided by the National Science Foundation grants to Veronique Le Roux (EAR P&G #1524311, #1839128, #1855302) and Henry Dick (MG&G #1637130, #1657983).
    Keywords: Geochemistry of the crust and mantle ; Volatile elements ; Tectonics
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    Vertical fluxes in the upper ocean (2021)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2021.
    Description: Oceanic fronts at the mesoscale and submesoscale are associated with enhanced vertical motion, which strengthens their role in global biogeochemical cycling as hotspots of primary production and subduction of carbon from the surface to the interior. Using process study models, theory, and field observations of biogeochemical tracers, this thesis improves understanding of submesoscale vertical tracer fluxes and their influence on carbon cycling. Unlike buoyancy, vertical transport of biogeochemical tracers can occur both due to the movement of isopycnals and due to motion along sloping isopycnals. We decompose the vertical velocity below the mixed layer into two components in a Lagrangian frame: vertical velocity along sloping isopycnal surfaces and the adiabatic vertical velocity of isopycnal surfaces and demonstrate that vertical motion along isopycnal surfaces is particularly important at submesoscales (1-10 km). The vertical flux of nutrient, and consequently the new production of phytoplankton depends not just on the vertical velocity but on the relative time scales of vertical transport and nutrient uptake. Vertical nutrient flux is maximum when the biological timescale of phytoplankton growth matches the vertical velocity frequency. Export of organic matter from the surface and the interior requires water parcels to cross the mixed layer base. Using Lagrangian analysis, we study the dynamics of this process and demonstrate that geostrophic and ageostrophic frontogenesis drive subduction along density surfaces across the mixed layer base. Along-front variability is an important factor in subduction. Both the physical and biological modeling studies described above are used to interpret observations from three research cruises in the Western Mediterranean. We sample intrusions of high chlorophyll and particulate organic carbon below the euphotic zone that are advected downward by 100 meters on timescales of days to weeks. We characterize the community composition in these subsurface intrusions at a lateral resolution of 1–10 km. We observe systematic changes in community composition due to the changing light environment and differential decay of the phytoplankton communities in low-light environments, along with mixing. We conclude that advective fluxes could make a contribution to carbon export in subtropical gyres that is equal to the sinking flux.
    Description: The work in this dissertation was funded by a NDSEG fellowship, Martin Fellowship, Grassle fellowship, Montrym grant, WHOI Academic Programs Office, and Office of Naval Research CALYPSO DRI grant N00014-16-1-3130.
    Keywords: Vertical velocity ; Submesoscale dynamics ; Biophysical interactions
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    Environmental effects of the Beaufort Lens on underwater acoustic communications during Arctic operations (2021)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2021.
    Description: Operations in the Arctic Ocean are increasingly important due to the changing environment and the resulting global implications. These changes range from the availability of new global trade routes, accessibility of newly available resources in the area, and national security interests of the United States in the region. It’s necessary to build a greater understanding of the undersea environment and how it’s changing since these environmental changes have a direct impact on adjusting future operations in the region and looming global changes as less Arctic ice is present. The recent presence of the Beaufort Lens is changing the acoustic propagation paths throughout the Arctic region. Here a network of buoys were employed to communicate with an Autonomous Undersea Vehicle (AUV) while it operated under the ice throughout the Beaufort Lens with the goal of achieving near GPS quality navigation. The acoustic communications paths were compared using a vertical array throughout the Beaufort Lens. This beam forming was compared to the prediction from BELLHOP. As well, since acoustic communications are affected by multi-path, attenuation and interference from other sources it was interesting to note that bottom bounce was sometimes a reliable acoustic path.
    Keywords: Arctic ; Beaufort Lens ; Acoustic communications
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    Investigating chromium cycling in global oxygen deficient zones with chromium isotopes (2021)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2021.
    Description: Chromium (Cr) isotopes have shown great potential as a paleo-redox proxy to trace the redox conditions of ancient oceans and atmosphere. However, its cycling in modern environments is poorly constrained. In my thesis, I attempt to fill in the gap of our understanding of chromium cycling in the modern ocean, with a focus on the redox processes in global oxygen deficient zones (ODZs). Firstly, we developed a method to analyze Cr isotopes of different Cr redox species. Tests on processing conditions demonstrated its robustness in obtaining accurate Cr isotope data. It is applicable to both frozen and fresh samples. This method allows us to investigate the redox cycling of Cr that is hard to unravel by existing total Cr methods. Secondly, in the Eastern Tropical North Pacific (ETNP), Eastern Tropical South Pacific (ETSP) and Arabian Sea ODZs, their total dissolved Cr profiles show preferential reduction of isotopically light Cr(VI) to Cr(III), which is scavenged and exported to deeper oceans. Applying our new method to ETNP and ETSP ODZ seawater samples, we observed Cr(VI) reduction in both ODZs with a similar fractionation factor. This indicates similar mechanisms may be controlling Cr(VI) reduction in the two ODZs. Cr(III) maximum coincides with Fe(II) and secondary nitrite maximums in the upper core of both ODZs. Shipboard incubations with spiked Fe(II) showed fast Cr(VI) reduction occurring in the ETNP ODZ. But neither Fe(II) nor microbes were reducing Cr(VI) directly. Thirdly, we calculated the isotope effects of Cr scavenging in the ETNP and ETSP ODZs. Thetwo ODZs show a similar isotope partitioning during Cr scavenging. And spatial variability is observed in the ETNP ODZ. Our calculated scavenged Cr isotope ratio is lighter than that of the total dissolved Cr from the same depth. It is also comparable to that of reducing or anoxic sediments, which implies that Cr isotopes can be used as an archive for local redox conditions.
    Description: This research was supported by an anonymous MIT Fellowship, Praceis Presidential Fellowship, Frederick A. Middleton Fellowship, the US National Science Foundation (NSF Award No. OCE-1459287, OCE-1736996, OCE-1924050 and DEB-1542240) and the Center for Microbial Oceanography: Research and Education (C-MORE, NSF-OIA Award No. EF-0424599).
    Keywords: Chromium isotopes ; Oxygen deficient zones ; Redox cycling
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