ALBERT

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125(6), (2020): e2019JB019239, doi:10.1029/2019JB019239.

Beschreibung: P‐to‐S‐converted waves observed in controlled‐source multicomponent ocean bottom seismometer (OBS) records were used to derive the Vp/Vs structure of Cascadia Basin sediments. We used P‐to‐S waves converted at the basement to derive an empirical function describing the average Vp/Vs of Cascadia sediments as a function of sediment thickness. We derived one‐dimensional interval Vp/Vs functions from semblance velocity analysis of S‐converted intrasediment and basement reflections, which we used to define an empirical Vp/Vs versus burial depth compaction trend. We find that seaward from the Cascadia deformation front, Vp/Vs structure offshore northern Oregon and Washington shows little variability along strike, while the structure of incoming sediments offshore central Oregon is more heterogeneous and includes intermediate‐to‐deep sediment layers of anomalously elevated Vp/Vs. These zones with elevated Vp/Vs are likely due to elevated pore fluid pressures, although layers of high sand content intercalated within a more clayey sedimentary sequence, and/or a higher content of coarser‐grained clay minerals relative to finer‐grained smectite could be contributing factors. We find that the proto‐décollement offshore central Oregon develops within the incoming sediments at a low‐permeability boundary that traps fluids in a stratigraphic level where fluid overpressure exceeds 50% of the differential pressure between the hydrostatic pressure and the lithostatic pressure. Incoming sediments with the highest estimated fluid overpressures occur offshore central Oregon where deformation of the accretionary prism is seaward vergent. Conversely, landward vergence offshore northern Oregon and Washington correlates with more moderate pore pressures and laterally homogeneous Vp/Vs functions of Cascadia Basin sediments.

Beschreibung: This research was funded by National Science Foundation (NSF) Grant OCE‐1657237 to J. P. C, OCE‐1657839 to A. F. A. and S. H., and OCE‐1657737 to S. M. C. Data used in this study were acquired with funding from NSF Grants OCE‐1029305 and OCE‐1249353. Data used in this research were provided by instruments from the Ocean Bottom Seismic Instrument Center (http://obsic.whoi.edu, formerly OBSIP), which is funded by the NSF. OBSIC/OBSIP data are archived at the IRIS Data Management Center (http://www.iris.edu) under network code X6 (https://doi.org/10.7914/SN/X6_2012). Data processing was conducted with Emerson‐Paradigm Software package Echos licensed to Woods Hole Oceanographic Institution under Paradigm Academic Software Program and MATLAB package SeismicLab of the University of Alberta, Canada (http://seismic-lab.physics.ualberta.ca), under GNU General Public License (MATLAB® is a registered trademark of MathWorks).

Beschreibung: 2020-11-28

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(8), (2020): e2020JC016068, doi:10.1029/2020JC016068.

Beschreibung: Labrador Sea Water (LSW) is a major component of the deep limb of the Atlantic Meridional Overturning Circulation, yet LSW transport pathways and their variability lack a complete description. A portion of the LSW exported from the subpolar gyre is advected eastward along the North Atlantic Current and must contend with the Mid‐Atlantic Ridge before reaching the eastern basins of the North Atlantic. Here, we analyze observations from a mooring array and satellite altimetry, together with outputs from a hindcast ocean model simulation, to estimate the mean transport of LSW across the Charlie‐Gibbs Fracture Zone (CGFZ), a primary gateway for the eastward transport of the water mass. The LSW transport estimated from the 25‐year altimetry record is 5.3 ± 2.9 Sv, where the error represents the combination of observational variability and the uncertainty in the projection of the surface velocities to the LSW layer. Current velocities modulate the interannual to higher‐frequency variability of the LSW transport at the CGFZ, while the LSW thickness becomes important on longer time scales. The modeled mean LSW transport for 1993–2012 is higher than the estimate from altimetry, at 8.2 ± 4.1 Sv. The modeled LSW thickness decreases substantially at the CGFZ between 1996 and 2009, consistent with an observed decline in LSW volume in the Labrador Sea after 1994. We suggest that satellite altimetry and continuous hydrographic measurements in the central Labrador Sea, supplemented by profiles from Argo floats, could be sufficient to quantify the LSW transport at the CGFZ.

Beschreibung: A. G. N. appreciates conversations with Kathy Donohue, Tom Rossby and Lisa Beal, which helped to interpret the results. J. B. P. acknowledges support from NSF through Grant OCE‐1947829. The authors thank all colleagues and ship crew involved in the R/V Meteor cruise M‐82/2 and Maria S. Merian cruise MSM‐21/2. The mooring data presented in this paper were funded by NSF through Grant OCE‐0926656.

Beschreibung: 2021-01-03

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 47(3), (2020): e2019GL086703, doi:10.1029/2019GL086703.

Beschreibung: Salt marsh assessments focus on vertical metrics such as accretion or lateral metrics such as open‐water conversion, without exploration of how the dimensions are related. We exploited a novel geospatial data set to explore how elevation is related to the unvegetated‐vegetated marsh ratio (UVVR), a lateral metric, across individual marsh “units” within four estuarine‐marsh systems. We find that elevation scales consistently with the UVVR across systems, with lower elevation units demonstrating more open‐water conversion and higher UVVRs. A normalized elevation‐UVVR relationship converges across systems near the system‐mean elevation and a UVVR of 0.1, a critical threshold identified by prior studies. This indicates that open‐water conversion becomes a dominant lateral instability process at a relatively conservative elevation threshold. We then integrate the UVVR and elevation to yield lifespan estimates, which demonstrate that higher elevation marshes are more resilient to internal deterioration, with an order‐of‐magnitude longer lifespan than predicted for lower elevation marshes.

Beschreibung: This study was supported by the USGS through the Coastal Marine Hazards/Resources Program, the National Park Service through the Natural Resource Preservation Program, and the U.S. Fish and Wildlife Service through the Science Support Partnership. Erika Lentz, Elizabeth Pendleton, Meagan Gonneea, Joel Carr, and two anonymous reviewers provided constructive advice on the study. S.F. was partly supported by US National Science Foundation award 1637630 (PIE LTER), 1832221 (VCR LTER). The geospatial data used in this study are published in the Coastal Wetlands Synthesis Products catalog on ScienceBase (https://www.sciencebase.gov/catalog/item/5b73325ee4b0f5d5787c5ff3).

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research- Biogeosciences 125(4), (2020): e2019JG005158, doi:10.1029/2019JG005158.

Beschreibung: Long‐term soil warming can decrease soil organic matter (SOM), resulting in self‐reinforcing feedback to the global climate system. We investigated additional consequences of SOM reduction for soil water holding capacity (WHC) and soil thermal and hydrological buffering. At a long‐term soil warming experiment in a temperate forest in the northeastern United States, we suspended the warming treatment for 104 days during the summer of 2017. The formerly heated plot remained warmer (+0.39 °C) and drier (−0.024 cm3 H2O cm−3 soil) than the control plot throughout the suspension. We measured decreased SOM content (−0.184 g SOM g−1 for O horizon soil, −0.010 g SOM g−1 for A horizon soil) and WHC (−0.82 g H2O g−1 for O horizon soil, −0.18 g H2O g−1 for A horizon soil) in the formerly heated plot relative to the control plot. Reduced SOM content accounted for 62% of the WHC reduction in the O horizon and 22% in the A horizon. We investigated differences in SOM composition as a possible explanation for the remaining reductions with Fourier transform infrared (FTIR) spectra. We found FTIR spectra that correlated more strongly with WHC than SOM, but those particular spectra did not differ between the heated and control plots, suggesting that SOM composition affects WHC but does not explain treatment differences in this study. We conclude that SOM reductions due to soil warming can reduce WHC and hydrological and thermal buffering, further warming soil and decreasing SOM. This feedback may operate in parallel, and perhaps synergistically, with carbon cycle feedbacks to climate change.

Beschreibung: We would like to acknowledge Jeffery Blanchard, Priya Chowdhury, Kristen DeAngelis, Luiz Dominguez‐Horta, Kevin Geyer, Rachelle Lacroix, Xaiojun Liu, William Rodriguez, and Alexander Truchonand and for assistance with field sampling. We would like to acknowledge Michael Bernard for assistance with field sampling and lab work. We would like to acknowledge Aaron Ellison for statistical consultation. This research was financially supported by the U.S. National Science Foundation's Long Term Ecological Research Program (NSF‐DEB‐0620443 and NSF‐DEB‐1237491), the Long Term Research in Environmental Biology Program (NSF DEB‐1456528) , and the U.S. Department of Energy (DOE‐DE‐SC0005421 and DOE‐DE‐SC0010740). Data used in this study are available from the Harvard Forest Data Archive (Datasets HF018‐03, HF018‐04, and HF018‐13), accessible at https://harvardforest.fas.harvard.edu/harvard‐forest‐data‐archive.

Beschreibung: 2020-10-04

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(8), (2020): e2020JC016445, doi:10.1029/2020JC016445.

Beschreibung: The Mid‐Atlantic Bight (MAB) Cold Pool is a bottom‐trapped, cold (temperature below 10°C) and fresh (practical salinity below 34) water mass that is isolated from the surface by the seasonal thermocline and is located over the midshelf and outer shelf of the MAB. The interannual variability of the Cold Pool with regard to its persistence time, volume, temperature, and seasonal along‐shelf propagation is investigated based on a long‐term (1958–2007) high‐resolution regional model of the northwest Atlantic Ocean. A Cold Pool Index is defined and computed in order to quantify the strength of the Cold Pool on the interannual timescale. Anomalous strong, weak, and normal years are categorized and compared based on the Cold Pool Index. A detailed quantitative study of the volume‐averaged heat budget of the Cold Pool region (CPR) has been examined on the interannual timescale. Results suggest that the initial temperature and abnormal warming/cooling due to advection are the primary drivers in the interannual variability of the near‐bottom CPR temperature anomaly during stratified seasons. The long persistence of temperature anomalies from winter to summer in the CPR also suggests a potential for seasonal predictability.

Beschreibung: This work was funded by the National Oceanic and Atmospheric Administration through Awards NOAA‐NA‐15OAR4310133 and NOAA‐NA‐13OAR4830233 and the National Science Foundation Awards OCE‐1049088, OCE‐1419584, and OCE‐0961545.

Beschreibung: 2021-02-03

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(8), (2020): e2020JC016197, doi:10.1029/2020JC016197.

Beschreibung: Synoptic shipboard measurements, together with historical hydrographic data and satellite data, are used to elucidate the detailed structure of the Atlantic Water (AW) boundary current system in the southern Canada Basin and its connection to the upstream source of AW in the Chukchi Borderland. Nine high‐resolution occupations of a transect extending from the Beaufort shelf to the deep basin near 152°W, taken between 2003 and 2018, reveal that there are two branches of the AW boundary current that flow beneath and counter to the Beaufort Gyre. Each branch corresponds to a warm temperature core and transports comparable amounts of Fram Strait Branch Water between roughly 200–700 m depth, although they are characterized by a different temperature/salinity (T/S) structure. The mean volume flux of the combined branches is 0.87 ± 0.13 Sv. Using the historical hydrographic data, the two branches are tracked upstream by their temperature cores and T/S signatures. This sheds new light on how the AW negotiates the Chukchi Borderland and why two branches emerge from this region. Lastly, the propagation of warm temperature anomalies through the region is quantified and shown to be consistent with the deduced circulation scheme.

Beschreibung: This work was funded by the following sources: National Science Foundation Grants PLR‐1504333, OPP‐1733564, and OPP‐1504394; National Oceanic and Atmospheric Administration Grant NA14OAR4320158; and National Aeronautics and Space Administration Grant NNX10AF42G.

Beschreibung: 2021-01-27

Beschreibung: Vegetation biomass is a globally important climate-relevant terrestrial carbon pool. Landsat, Sentinel-2 and Sentinel-1 satellite missions provide a landscape-level opportunity to upscale tundra vegetation communities and biomass in high latitude terrestrial environments. We assessed the applicability of landscape-level remote sensing for the low Arctic Lena Delta region in Northern Yakutia, Siberia, Russia. The Lena Delta is the largest delta in the Arctic and is located North of the treeline and the 10 °C July isotherm at 72° Northern Latitude in the Laptev Sea region. During the LENA2018 expedition, we set up plots for plant projective cover and Above Ground Biomass (AGB) and sampled shrubs for shrub-ring analyses. AGB is providing the magnitude of the carbon flux, whereas stand age is irreplaceable to provide the cycle rate. AGB data and shrub age data clearly show a separation between i) low disturbance landscape types with dominant AGB moss contribution, but always low vascular plant AGB (〈0.5 kg m-2) characterised by old shrubs of several decades of stand age versus ii) a much higher vascular plant AGB contribution (〉 0.5 kg m-2) with only young shrubs in high disturbance regimes. The low disturbance regimes are represented on the Holocene and Pleistocene delta terraces in form of azonal polygonal tundra complexes and softly dissected valleys with zonal tussock tundra. In contrast, the high disturbance regimes are sites of thermo-erosion such as along thermo-erosional valleys and on floodplains. We upscaled AGB and above ground carbon pool ages using a Sentinel-2 satellite acquisition from early August 2018. We classified via classification training using Elementary Sampling Units that are the 30 m x 30 m vegetation field plots. We then used the land cover classes and grouped them according to their settings either in high disturbance or low disturbance regimes with each associated AGB value ranges and shrub age regimes. We also evaluated circum-Arctic harmonized ESA GlobPermafrost land cover and vegetation height remote sensing products covering subarctic to Arctic land cover types for the central Lena Delta. The products are freely available and published in the PANGAEA data repository under https://doi.org/10.1594/PANGAEA.897916 and https://doi.org/10.1594/PANGAEA.897045. ESA GlobPermafrost land cover and vegetation height remote sensing products and our Sentinel-2 derived AGB product for the central Lena Delta shows realistic spatial patterns of landcover classes and biomass distribution at landscape level. However, in all products, the high biomass patches of high shrubs in the tundra landscape could not spatially be resolved as they are confined to patchy and linear distribution, not representing large enough areas suitable for upscaling. We found that high disturbance regimes with linked high and rapid AGB fluxes are distributed mainly on the floodplains and as patches along thermoerosioal features, e.g. valleys. Whereas the low disturbance landscapes on Yedoma upland tundra and Holocene terraces occur with larger area coverage representing decades slower and in magnitude smaller AGB fluxes.

Beschreibung: Muography represents a recent and innovative tool for investigating the interior of active volcanoes. However, when dealing with frequently erupting open-vent volcanoes such as Stromboli, any result should take into con- sideration the structural and morphology changes caused by the eruptive activity. This may cause either summit collapses by magma withdrawal, or morphology growth by the accumulations of a fallout from the explosive activity, or more often a combination of both. In this chapter, we present an integration of various techniques, comprising muography and digital elevation model reconstruction, together with GBInSAR ground deformation and volcano seismicity, to reconstruct the geometry of the shallow magma supply system of the volcano and its changes in time. We show how muography can display the interior of the volcano as well as its outer growth, being sensitive to all volume changes that occurred between the framed surface and the detector. This was discovered in Stromboli by comparing digital topography in the interval between 2010 and 2012, when the rapid growth of the volcano summit by the accumulation of ballistic products in the area between the crater zone and the muon detec- tor occurred. This deposit, together with the filling in of the graben-like depression, formed during the 2007 eruption, by fallout during the persistent explosive activity, contributed to generating a remarkable anomaly in the summit area of the volcano visualized by muography. In addition, the shallow feeding system of the volcano was surveyed by GBInSAR and seismicity, which allowed us to reconstruct its path up to a depth of a few hundred meters.

Beschreibung: Published

Beschreibung: 75-91

Beschreibung: 2V. Struttura e sistema di alimentazione dei vulcani

Beschreibung: Cenozoic climate changes have been linked to tectonic activity and variations in atmospheric CO2 concentrations. Here we present Miocene and Pliocene sensitivity experiments performed with the climate model COSMOS. The experiments contain changes with respect to paleogeography, ocean gateway configuration, and atmospheric CO2 concentrations, as well as a range of vertical mixing coefficients in the ocean. For the Mid-Miocene, we show that the impact of ocean mixing on surface temperature is comparable to the effect of the possible range in reconstructed CO2 concentrations. In combination with stronger vertical mixing, relatively moderate CO2-concentrations of 450 ppmv enable global mean surface, deep-water and meridional temperature characteristics representative of Mid-Miocene Climatic Optimum (MMCO) reconstructions. The Miocene climate shows a reduced meridional temperature gradient and reduced seasonality. In the case of enhanced mixing, surface and deep ocean temperatures show significant warming of up to 5-10°C and an Arctic temperature anomaly of more than 12°C. In the Pliocene simulations, the impact of vertical mixing and CO2 is less important for the deep ocean, which we interpret as a different sensitivity dependence on the background state and mixed layer dynamics. We find a significant reduction in surface albedo and effective emissivity for either a high level of atmospheric CO2 or increased vertical mixing. Our mixing sensitivity experiments provide a warm deep ocean via ocean heat uptake. We propose that the mixing hypothesis can be tested by reconstructions of the thermocline and seasonal paleoclimate data indicating a lower seasonality relative to today.

Beschreibung: As air temperatures rise and sea ice cover declines in the Arctic, permafrost coastal cliffs thaw more rapidly and wave energy rises. Thus, as the open water season continues to lengthen, climate change triggers a large part of the Arctic shoreline to become increasingly vulnerable to erosion. Arctic erosion supplies nutrient-laden and carbon-rich sediment into nearshore ecosystems. A retreating coastline also has consequences for residential, cultural, and industrial infrastructure. Despite its importance, erosion is currently neglected in global climate models, and existing physics-based numerical models of Arctic shoreline erosion are too complex and regionally-focused to be applied on a pan-Arctic scale. Here, we apply our simplified numerical erosion model, ArcticBeach v1.0, to the entire Arctic coastline. ArcticBeach v1.0 has previously been shown to simulate retreat rates at two sites that differ substantially in their main mechanisms of retreat (sub-aerial erosion/thaw slumping versus notch/block erosion). The model uses heat and sediment volume balances in order to predict horizontal cliff retreat and vertical erosion of a fronting beach. It contains an erosion module that uses empirical equations to estimate cross-shore sediment transport, coupled to a storm surge module forced by wind. We present Arctic maps of regional variation in trends in 2-meter air temperature, sea ice concentration, and wind speed.

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 125(2), (2020): e2019JC015400, doi:10.1029/2019JC015400.

Beschreibung: One of the foci of the Forum for Artic Modeling and Observational Synthesis (FAMOS) project is improving Arctic regional ice‐ocean models and understanding of physical processes regulating variability of Arctic environmental conditions based on synthesis of observations and model results. The Beaufort Gyre, centered in the Canada Basin of the Arctic Ocean, is an ideal phenomenon and natural laboratory for application of FAMOS modeling capabilities to resolve numerous scientific questions related to the origin and variability of this climatologic freshwater reservoir and flywheel of the Arctic Ocean. The unprecedented volume of data collected in this region is nearly optimal to describe the state and changes in the Beaufort Gyre environmental system at synoptic, seasonal, and interannual time scales. The in situ and remote sensing data characterizing ocean hydrography, sea surface heights, ice drift, concentration and thickness, ocean circulation, and biogeochemistry have been used for model calibration and validation or assimilated for historic reconstructions and establishing initial conditions for numerical predictions. This special collection of studies contributes time series of the Beaufort Gyre data; new methodologies in observing, modeling, and analysis; interpretation of measurements and model output; and discussions and findings that shed light on the mechanisms regulating Beaufort Gyre dynamics as it transitions to a new state under different climate forcing.

Beschreibung: We would like to thank all FAMOS participants (https://web.whoi.edu/famos/ and https://famosarctic.com/) and collaborators of the Beaufort Gyre Exploration project (https://www.whoi.edu/beaufortgyre) for their continued enthusiasm, creativity, and support during all stages of both projects. This research is supported by the National Science Foundation Office of Polar Programs (projects 1845877, 1719280, and 1604085). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. Arctic dynamic topography/geostrophic currents data were provided by the Centre for Polar Observation and Modelling, University College London (www.cpom.ucl.ac.uk/dynamic_topography; Armitage et al. (2016, 2017). The other data used in this paper are available at the NCAR/NCEP (https://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html), NSIDC (https://nsidc.org/), NSF's Arctic data center (https://arcticdata.io/; Keywords for data search are “Beaufort Gyre”, “Krishfield” or “Proshutinsky”), and WHOI Beaufort Gyre exploration website (www.whoi.edu/beaufortgyre).

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 125(4), (2020): e2019JC016006, doi:10.1029/2019JC016006.

Beschreibung: Equatorward flow of Middle Atlantic Bight (MAB) shelf waters meets poleward flowing South Atlantic Bight shelf waters over the continental shelf near Cape Hatteras, NC, leading to net export of shelf waters into the deep ocean. This export occurs in close proximity to the Gulf Stream, which separates from the continental margin near Cape Hatteras. Observations from sustained underwater glider surveys of the outer continental shelf and slope north of Cape Hatteras from spring 2017 to spring 2019 are used to examine the mean and variability of MAB shelf water export in the region. The 0.3 Sv (1 Sv = 106 m3 s−1) time‐mean export of MAB shelf water south of 37°N was dominated by discrete export events; 50% of export occurred during the 17% of the time during which transport was more than 1 standard deviation above the mean. These events typically occurred in late spring and summer of both years when equatorward flow into the region peaked. Export of MAB shelf water was correlated with equatorward flow into the region, which was itself correlated with the density gradient across the continental shelf break. Observations during specific time periods that capture extrema in MAB shelf water export are examined to highlight the variability in shelf‐deep ocean exchange scenarios in the Hatteras region. These include near‐surface export driven by hurricanes, subsurface export below the northern edge of the Gulf Stream, and a multi‐month near‐cessation of export.

Beschreibung: Patrick Deane at WHOI and the Instrument Development Group at the Scripps Institution of Oceanography were key to the success of the Spray glider operations. Mike Muglia, Trip Taylor, and Nick DeSimone at the East Carolina University Coastal Studies Institute (CSI) provided support for glider deployments and recoveries. WHOI Summer Student Fellow Devon Gaynes assisted with analysis related to 2017 hurricanes. Spray glider observations used here are available from http://spraydata.ucsd.edu and should be cited using the following DOIs: 10.21238/S8SPRAY2675 (Todd & Owens, 2016) and 10.21238/S8SPRAY0880 (Todd, 2020). Buoy winds are available from the National Data Buoy Center (https://www.ndbc.noaa.gov). SST imagery was obtained from the Mid‐Atlantic Regional Association Coastal Ocean Observing System (MARACOOS) THREDDS server (http://tds.maracoos.org/thredds/ARCHIVE-SST.html). Automated Tropical Cyclone Forecast System data are available online (https://ftp.nhc.noaa.gov/atcf/). PEACH was funded by the National Science Foundation (OCE‐1558521). Colormaps are from Thyng et al. (2016).

Beschreibung: 2020-09-17

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(5), (2020): e2020JC016123, doi:10.1029/2020JC016123.

Beschreibung: The processes underlying the strong Kuroshio encountering a cape at the southernmost tip of Taiwan are examined with satellite‐derived chlorophyll and temperature maps, a drifter trajectory, and realistic model simulations. The interaction spurs the formation of submesoscale cyclonic eddies that trap cold and high‐chlorophyll water and the formation of frontal waves between the free stream and the wake flow. An observed train of eddies, which have relative vorticity about one to four times the planetary vorticity (f), is shed from the recirculation that occurs in the immediate lee of the cape as a result of flow separation. These propagate downstream at a speed of 0.5–0.6 m s−1. Farther downstream, the corotation and merging of two or three adjacent eddies are common owing to the topography‐induced slowdown of eddy propagation farther downstream. It is found that the relative vorticity of a corotating system (1.2f) is 70% weaker than that of a single eddy due to the increase of eddy diameter from ~16 to ~33 km, in agreement with Kelvin's circulation theorem. The shedding period of the submesoscale eddies is strongly modulated by either diurnal or semidiurnal tidal flows, which typically reach 0.2–0.5 m s−1, whereas its intrinsic shedding period is insignificant. The frontal waves predominate in the horizontal free shear layer emitted from the cape, as well as a density front. Energetics analysis suggests that the wavy features result primarily from the growth of barotropic instability in the free shear layer, which may play a secondary process in the headland wake.

Beschreibung: Yu‐Hsin Cheng was supported by the CWB of Taiwan through Grant 1062076C. Ming‐Huei Chang was supported by the Ministry of Science and Technology of Taiwan (MOST) under Grants 103‐2611‐M‐002‐018, 105‐2611‐M‐002‐012, and 107‐2611‐M‐002‐015. Sen Jan was supported with MOST Grants 101‐2611‐M‐002‐018‐MY3, 103‐2611‐M‐002‐011, and 105‐2119‐M‐002‐042. Magdalena Andres was supported by the U.S. Office of Naval Research Grant N000141613069.

Beschreibung: 2020-10-23

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 21(6), (2020): e2020GC008957, doi:10.1029/2020GC008957.

Beschreibung: At the Galapagos triple junction in the equatorial Pacific Ocean, the Cocos‐Nazca spreading center does not meet the East Pacific Rise (EPR) but, instead, rifts into 0.4 Myr‐old lithosphere on the EPR flank. Westward propagation of Cocos‐Nazca spreading forms the V‐shaped Galapagos gore. Since ~1.4 Ma, opening at the active gore tip has been within the Cocos‐Galapagos microplate spreading regime. In this paper, bathymetry, magnetic, and gravity data collected over the first 400 km east of the gore tip are used to examine rifting of young lithosphere and transition to magmatic spreading segments. From inception, the axis shows structural segmentation consisting of rifted basins whose bounding faults eventually mark the gore edges. Rifting progresses to magmatic spreading over the first three segments (s1–s3), which open between Cocos‐Galapagos microplate at the presently slow rates of ~19–29 mm/year. Segments s4–s9 originated in the faster‐spreading (~48 mm/year) Cocos‐Nazca regime, and well‐defined magnetic anomalies and abyssal hill fabric close to the gore edges show the transition to full magmatic spreading was more rapid than at present time. Magnetic lineations show a 20% increase in the Cocos‐Nazca spreading rate after 1.1 Ma. The near‐axis Mantle Bouguer gravity anomaly decreases eastward and becomes more circular, suggesting mantle upwelling, increasing temperatures, and perhaps progression to a developed melt supply beneath segments. Westward propagation of individual Cocos‐Nazca segments is common with rates ranging between 12 and 54 mm/year. Segment lengths and lateral offsets between segments increase, in general, with distance from the tip of the gore.

Beschreibung: E. M. and H. S. are grateful to the National Science Foundation for funding this work and to InterRidge and the University of Leeds for providing support for a number of the international students and scholars who were able to participate on the cruise. We are also grateful for the extraordinary work of the Captain and crew of R/V Sally Ride , whose efficiency and good cheer made the cruise such a success. We thank M. Ligi and two anonymous reviewers for their comments which greatly improved the manuscript. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

Beschreibung: 2020-11-11

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 22(3), (2021): e2020GC009472, https://doi.org/10.1029/2020GC009472.

Beschreibung: Carbonatite volcanism remains poorly understood compared to silicic volcanism due to the scarcity of carbonatite volcanoes worldwide and because volcanic H2O and CO2—major components in carbonatite volcanic systems—are not well preserved in the rock record. To further our understanding of carbonatite genesis, we utilize the non-traditional thallium (Tl) isotope system in Khanneshin carbonatites in Afghanistan. These carbonatites contain 250–30,000 ng/g Tl and have ε205Tl values (−4.6 to +4.6) that span much of the terrestrial igneous range. We observe that δ18OVSMOW (+8.6‰ to +23.5‰) correlates positively with δ13CVPDB (−4.6‰ to +3.5‰) and ε205Tl up to δ18O = 15‰. Rayleigh fractionation of calcite from an immiscible CO2-H2O fluid with a mantle-like starting composition can explain the δ18O and δ13C—but not ε205Tl—trends. Biotite fractionates Tl isotopes in other magmatic settings, so we hypothesize that a Tl-rich hydrous brine caused potassic metasomatism (i.e., biotite fenitization) of wall rock that increased the ε205Tl of the residual magma-fluid reservoir. Our results imply that, in carbonatitic volcanic systems, simultaneous igneous differentiation and potassic metasomatism increase ε205Tl, δ18O, δ13C, and light rare earth element concentrations in residual fluids. Our fractionation models suggest that the Tl isotopic compositions of the primary magmas were among the isotopically lightest (less than or equal to ε205Tl = −4.6) material derived from the mantle for which Tl isotopic constraints exist. If so, the ultimate source of Tl in Khanneshin lavas—and perhaps carbonatites elsewhere—may be recycled ocean crust.

Beschreibung: This project was supported by funding from Woods Hole Oceanographic Institution Independent Research & Development funds and the National Science Foundation (Award #1911699).

Beschreibung: 2021-07-27

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Lattaud, J., Broder, L., Haghipour, N., Rickli, J., Giosan, L., & Eglinton, T., I. Influence of hydraulic connectivity on carbon burial efficiency in Mackenzie Delta lake sediments. Journal of Geophysical Research: Biogeosciences, 126(3), (2021): e2020JG006054, https://doi.org/10.1029/2020JG006054.

Beschreibung: The Arctic is undergoing accelerated changes in response to ongoing modifications to the climate system, and there is a need for local to regional scale records of past climate variability in order to put these changes into context. The Mackenzie Delta region in northern Canada is populated by numerous small shallow lakes. They are classified as no-, low-, and high-closure (NC, LC, and HC, respectively) lakes, reflecting varying degrees of connection to the river main stem, and have different sedimentation characteristics. This study examines sedimentological (mineral surface area, grain size), carbon isotopic (bulk and molecular-level) and inorganic isotopic (neodymium) characteristics of sediment cores from three lakes representing each class. We find that HC lake sediments exhibit strikingly different properties from the other lake sediments. Specifically, they are characterized by higher organic carbon loadings per unit mineral surface area and with relatively minor influence from allochthonous, petrogenic (rock-derived) organic carbon. In contrast, LC and NC lakes have the potential to record basin-scale climatic changes at a high resolution by virtue of enhanced detrital sedimentation. Overall the delta lakes have the capacity to bury about 2 MtC year−1, with little changes in the last 200 years. However, in the (near) future, an increased number of high closure lakes might change the carbon burial efficiency of the Mackenzie Delta as they seem to retain less carbon than NC and LC lakes.

Beschreibung: J. Lattaud was funded by a Rubicon grant (019.183EN.002) from NWO, Netherlands Organization for scientific research.

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Jackson, R. L., Gabric, A. J., Matrai, P. A., Woodhouse, M. T., Cropp, R., Jones, G. B., Deschaseaux, E. S. M., Omori, Y., McParland, E. L., Swan, H. B., & Tanimoto, H. Parameterizing the impact of seawater temperature and irradiance on dimethylsulfide (DMS) in the Great Barrier Reef and the contribution of coral reefs to the global sulfur cycle. Journal of Geophysical Research:Oceans, 126(3), (2021): e2020JC016783, https://doi.org/10.1029/2020JC016783.

Beschreibung: Biogenic emissions of dimethylsulfide (DMS) are an important source of sulfur to the atmosphere, with implications for aerosol formation and cloud albedo over the ocean. Natural aerosol sources constitute the largest uncertainty in estimates of aerosol radiative forcing and climate and thus, an improved understanding of DMS sources is needed. Coral reefs are strong point sources of DMS; however, this coral source of biogenic sulfur is not explicitly included in climatologies or in model simulations. Consequently, the role of coral reefs in local and regional climate remains uncertain. We aim to improve the representation of tropical coral reefs in DMS databases by calculating a climatology of seawater DMS concentration (DMSw) and sea-air flux in the Great Barrier Reef (GBR), Australia. DMSw is calculated from remotely sensed observations of sea surface temperature and photosynthetically active radiation using a multiple linear regression model derived from field observations of DMSw in the GBR. We estimate that coral reefs and lagoon waters in the GBR (∼347,000 km2) release 0.03–0.05 Tg yr−1 of DMS (0.02 Tg yr−1 of sulfur). Based on this estimate, global tropical coral reefs (∼600,000 km2) could emit 0.08 Tg yr−1 of DMS (0.04 Tg yr−1 of sulfur), with the potential to influence the local radiative balance.

Beschreibung: Australian Research Council. Grant Number: DP150101649 National Science Foundation (NSF). Grant Number: 1543450 Ministry of Education, Culture, Sports, Science and Technology Grants-in-Aid for Scientific Research. Grant Number: 23310016,16H02967,24241010,15H01732 Ministry of Education, Culture, Sports, Science and Technology Grant-in-Aid for Young Scientists. Grant Number: 17K12812

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 126(3), (2021): e2020JB021136, https://doi.org/10.1029/2020JB021136.

Beschreibung: The Geomagnetic Polarity Time Scale (GPTS) provides a basis for the geological timescale, quantifies geomagnetic field behavior, and gives a time framework for geologic studies. We build a revised Middle to Late Jurassic GPTS by using a new multiscale magnetic profile, combining sea surface, midwater, and autonomous underwater vehicle near-bottom magnetic anomaly data from the Hawaiian lineation set in the Pacific Jurassic Quiet Zone (JQZ). We correlate the new profile with a previously published contemporaneous magnetic sequence from the Japanese lineation set. We then establish geomagnetic polarity block models as a basis for our interpretation of the origin and nature of JQZ magnetic anomalies and a GPTS. A significant level of coherency between short-wavelength anomalies for both the Japanese and Hawaiian lineation magnetic anomaly sequences suggests the existence of a regionally coherent field during this period of rapid geomagnetic reversals. Our study implies the rapid onset of the Mesozoic Dipole Low from M42 through M39 and then a subsequent gradual recovery in field strength into the Cenozoic. The new GPTS, together with the Japanese sequence, extends the magnetic reversal history from M29 back in time to M44. We identify a zone of varying, difficult-to-correlate anomalies termed the Hawaiian Disturbed Zone, which is similar to the zone of low amplitude, difficult-to-correlate anomalies in the Japanese sequence termed the Low Amplitude Zone (LAZ). We suggest that the LAZ, bounded by M39–M41 isochrons, may in fact represent the core of what is more commonly known as the JQZ crust.

Beschreibung: This study is funded by National Science Foundation grants OCE-1029965 (Tominaga, Tivey, and Lizarralde) and OCE-1233000 (Tominaga and Tivey) and OCE-1029573 (Sager).

Beschreibung: 2021-07-21

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 47(1), (2020): e2019GL085455, doi:10.1029/2019GL085455.

Beschreibung: The meridional coherence, connectivity, and regional inhomogeneity in long‐term sea surface temperature (SST) variability over the Northwest Atlantic continental shelf and slope from 1982–2018 are investigated using observational data sets. A meridionally concurrent large SST warming trend is identified as the dominant signal over the length of the continental shelf and slope between Cape Hatteras in North Carolina and Cape Chidley, Newfoundland and Labrador, Canada. The linear trends are 0.37 ± 0.06 and 0.39 ± 0.06 °C/decade for the shelf and slope regions, respectively. These meridionally averaged SST time series over the shelf and slope are consistent with each other and across multiple longer observational data sets with records dating back to 1900. The coherence between the long‐term meridionally averaged time series over the shelf and slope and basin‐wide averaged SST in the North Atlantic implies approximately two thirds of the warming trend during 1982–2018 may be attributed to natural climate variability and the rest to externally forced change including anthropogenic warming.

Beschreibung: We are grateful to the Editor Dr. Kathleen Donohue and two anonymous reviewers. This work was supported by NOAA's Climate Program Office's Modeling, Analysis, Predictions, and Projections (MAPP) program (NA19OAR4320074). We acknowledge our participation in MAPP's Marine Prediction Task Force. The data of NOAA OISST used in this study are available at NOAA Earth System Research Laboratory (https://www.esrl.noaa.gov/psd/data/gridded/data.noaa.oisst.v2.highres.html). The HadISST data set is available at Met Office, Hadley Centre (https://www.metoffice.gov.uk/hadobs/hadisst/). The COBE SST and NOAA ERSST data sets are available at NOAA Earth System Research Laboratory's Physical Sciences Division (https://www.esrl.noaa.gov/psd/data/gridded/data.cobe.html; https://www.esrl.noaa.gov/psd/data/gridded/data.noaa.ersst.v5.html). The near‐surface air temperature is available at Global Historical Climatology Network‐Monthly Database (https://www.ncdc.noaa.gov/data‐access/land‐based‐station‐data/land‐based‐datasets/global‐historical‐climatology‐network‐monthly‐version‐4). The data of SSH are available at Copernicus Marine Environment Monitoring Service (http://marine.copernicus.eu/services‐portfolio/access‐to‐products/?option=com_csw&view=details&product_id=SEALEVEL_GLO_PHY_ L4_REP_OBSERVATIONS_008_047).

Beschreibung: 2020-07-06

Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Proshutinsky, A., Krishfield, R., Toole, J. M., Timmermans, M-L., Williams, W. J., Zimmermann, S., Yamamoto-Kawai, M., Armitage, T. W. K., Dukhovskoy, D., Golubeva, E., Manucharyan, G. E., Platov, G., Watanabe, E., Kikuchi, T., Nishino, S., Itoh, M., Kang, S-H., Cho, K-H., Tateyama, K., & Zhao, J. Analysis of the Beaufort Gyre freshwater content in 2003-2018. Journal of Geophysical Research-Oceans, 124(12), (2019): 9658-9689, doi:10.1029/2019JC015281.

Beschreibung: Hydrographic data collected from research cruises, bottom‐anchored moorings, drifting Ice‐Tethered Profilers, and satellite altimetry in the Beaufort Gyre region of the Arctic Ocean document an increase of more than 6,400 km3 of liquid freshwater content from 2003 to 2018: a 40% growth relative to the climatology of the 1970s. This fresh water accumulation is shown to result from persistent anticyclonic atmospheric wind forcing (1997–2018) accompanied by sea ice melt, a wind‐forced redirection of Mackenzie River discharge from predominantly eastward to westward flow, and a contribution of low salinity waters of Pacific Ocean origin via Bering Strait. Despite significant uncertainties in the different observations, this study has demonstrated the synergistic value of having multiple diverse datasets to obtain a more comprehensive understanding of Beaufort Gyre freshwater content variability. For example, Beaufort Gyre Observational System (BGOS) surveys clearly show the interannual increase in freshwater content, but without satellite or Ice‐Tethered Profiler measurements, it is not possible to resolve the seasonal cycle of freshwater content, which in fact is larger than the year‐to‐year variability, or the more subtle interannual variations.

Beschreibung: National Science Foundation. Grant Numbers: PLR‐1302884,OPP‐1719280, and OPP‐1845877, PLR‐1303644 and OPP‐1756100, OPP‐1756100, PLR‐1303644, OPP‐1845877, OPP‐1719280, PLR‐1302884 Key Program of National Natural Science Foundation of China. Grant Number: 41330960 Global Change Research Program of China. Grant Number: 2015CB953900 Ministry of Education, Korea Japan Aerospace Exploration Agency (JAXA) /Earth Observation Research Center (EORC) Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT) Stanback Postdoctoral Fellowship Russian Foundation for Basic Research. Grant Number: 17‐05‐00382 Presidium of Russian Academy of Sciences HYCOM NOPP. Grant Number: N00014‐15‐1‐2594 DOE. Grant Number: DE‐SC0014378 National Aeronautics and Space Administration Tokyo University of Marine Science and Technology Department of Fisheries and Oceans Canada Woods Hole Oceanographic Institution

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Catunda, M. C. A., Bahr, A., Kaboth-Bahr, S., Zhang, X., Foukal, N. P., & Friedrich, O. Subsurface heat channel drove sea surface warming in the high-latitude North Atlantic during the Mid-Pleistocene Transition. Geophysical Research Letters, 48(11), (2021): e2020GL091899, https://doi.org/10.1029/2020GL091899.

Beschreibung: The Mid-Pleistocene Transition (MPT, 1,200–600 ka) marks the rapid expansion of Northern Hemisphere (NH) continental ice sheets and stronger precession pacing of glacial/interglacial cyclicity. Here, we investigate the relationship between thermocline depth in the central North Atlantic, subsurface northward heat transport and the initiation of the 100-kyr cyclicity during the MPT. To reconstruct deep-thermocline temperatures, we generated a Mg/Ca-based temperature record of deep-dwelling (∼800 m) planktonic foraminifera from mid-latitude North Atlantic at Site U1313. This record shows phases of pronounced heat accumulation at subsurface levels during the mid-MPT glacial driven by increased outflow of the Mediterranean Sea. Concurrent warming of the subtropical thermocline and subpolar surface waters indicates enhanced (subsurface) inter-gyre transport of warm water to the subpolar North Atlantic, which provided moisture for ice-sheet growth. Precession-modulated variability in the northward transport of subtropical waters imprinted this orbital cyclicity into NH ice-sheets after Marine Isotope Stage 24.

Beschreibung: Catunda and A. Bahr were funded by DFG project BA 3809/8, O.F. by DFG project FR 2544/11. S. Kaboth-Bahr acknowledges an Open-Topic Post-Doc Grant from the University of Potsdam. X.Z. was funded via the Lanzhou University (project 225000–830006) and National Science Foundation of China (Grant 42075047). N.F. was funded by the NSF Grant 1756361. Open access funding enabled and organized by Projekt DEAL.

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(5), (2021): e2020GL091461, https://doi.org/10.1029/2020GL091461.

Beschreibung: We investigate how the near-surface chlorophyll (CHL)-a evolves in Gulf Stream (GS) warm-core rings (WCRs) and cold-core rings (CCRs) using multi-platform satellite observations. Averaged CHL anomaly (CHLA) within the rings exhibits both positive and negative linear trends during the evolution of the WCRs while negative trends dominate in CCRs. This difference is associated with a variety of physical processes occurring during the evolution process. Meanwhile, eddy-centric analysis reveals four spatial patterns of CHLA long-term trends, some of which highlights the importance of rings in shaping surface CHL. Short-term fluctuations of CHLA in WCRs and CCRs are closely correlated with mixed layer depth and sea surface temperature anomaly and highlight the complex interplay between multiple mechanisms. In addition, we find higher concentration CHL in some WCRs than that in CCRs during the same season, providing an alternative view of the characteristics of the surface ecosystem in Gulf Stream rings.

Beschreibung: This work was supported by the National Science Foundation Ocean Science Division under grant OCE-1558960. JN was supported by the Fundamental Research Funds for the Central Universities (Hohai University) under grant B200203005 and the China Scholarship Council.

Beschreibung: 2021-08-16

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(4), (2021): e2020JC016789, https://doi.org/10.1029/2020JC016789.

Beschreibung: Argo profiling floats and L-band passive microwave remote sensing have significantly improved the global sampling of sea surface salinity (SSS) in the past 15 years, allowing the study of the range of SSS seasonal variability using concurrent satellite and in situ platforms. Here, harmonic analysis was applied to four 0.25° satellite products and two 1° in situ products between 2016 and 2018 to determine seasonal harmonic patterns. The 0.25° World Ocean Atlas (WOA) version 2018 was referenced to help assess the harmonic patterns from a long-term perspective based on the 3-year period. The results show that annual harmonic is the most characteristic signal of the seasonal cycle, and semiannual harmonic is important in regions influenced by monsoon and major rivers. The percentage of the observed variance that can be explained by harmonic modes varies with products, with values ranging between 50% and 72% for annual harmonic and between 15% and 19% for semiannual harmonic. The large spread in the explained variance by the annual harmonic reflects the large disparity in nonseasonal variance (or noise) in the different products. Satellite products are capable of capturing sharp SSS features on meso- and frontal scales and the patterns agree well with the WOA 2018. These products are, however, subject to the impacts of radiometric noises and are algorithm dependent. The coarser-resolution in situ products may underrepresent the full range of high-frequency small scale SSS variability when data record is short, which may have enlarged the explained SSS variance by the annual harmonic.

Beschreibung: L. Yu was funded by NASA Ocean Salinity Science Team (OSST) activities through Grant 80NSSC18K1335. FMB was funded by the NASA OSST through Grant 80NSSC18K1322. E. P. Dinnat was funded by NASA through Grant 80NSSC18K1443. This research is carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.

Beschreibung: 2021-09-17

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Schultz, C., Doney, S. C., Hauck, J., Kavanaugh, M. T., & Schofield, O. Modeling phytoplankton blooms and inorganic carbon responses to sea-ice variability in the West Antarctic Peninsula. Journal of Geophysical Research: Biogeosciences, 126(4), (2021): e2020JG006227, https://doi.org/10.1029/2020JG006227.

Beschreibung: The ocean coastal-shelf-slope ecosystem west of the Antarctic Peninsula (WAP) is a biologically productive region that could potentially act as a large sink of atmospheric carbon dioxide. The duration of the sea-ice season in the WAP shows large interannual variability. However, quantifying the mechanisms by which sea ice impacts biological productivity and surface dissolved inorganic carbon (DIC) remains a challenge due to the lack of data early in the phytoplankton growth season. In this study, we implemented a circulation, sea-ice, and biogeochemistry model (MITgcm-REcoM2) to study the effect of sea ice on phytoplankton blooms and surface DIC. Results were compared with satellite sea-ice and ocean color, and research ship surveys from the Palmer Long-Term Ecological Research (LTER) program. The simulations suggest that the annual sea-ice cycle has an important role in the seasonal DIC drawdown. In years of early sea-ice retreat, there is a longer growth season leading to larger seasonally integrated net primary production (NPP). Part of the biological uptake of DIC by phytoplankton, however, is counteracted by increased oceanic uptake of atmospheric CO2. Despite lower seasonal NPP, years of late sea-ice retreat show larger DIC drawdown, attributed to lower air-sea CO2 fluxes and increased dilution by sea-ice melt. The role of dissolved iron and iron limitation on WAP phytoplankton also remains a challenge due to the lack of data. The model results suggest sediments and glacial meltwater are the main sources in the coastal and shelf regions, with sediments being more influential in the northern coast.

Beschreibung: C. Schultz, S. C. Doney, M. T. Kavanaugh, and O. Schofield acknowledge support by the US National Science Foundation (Grant no. PLR-1440435), and C. Schultz and S. C. Doney acknowledge support from the University of Virginia. This research has also received funding from the Helmholtz Young Investigator Group Marine Carbon and Ecosystem Feedbacks in the Earth System (MarESys), Grant number VH-NG-1301.

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dzwonkowski, B., Fournier, S., Lockridge, G., Coogan, J., Liu, Z., & Park, K. Cascading weather events amplify the coastal thermal conditions prior to the shelf transit of Hurricane Sally (2020). Journal of Geophysical Research: Oceans, 126(12), (2021): e2021JC017957, https://doi.org/10.1029/2021JC017957.

Beschreibung: Changes in tropical cyclone intensity prior to landfall represent a significant risk to human life and coastal infrastructure. Such changes can be influenced by shelf water temperatures through their role in mediating heat exchange between the ocean and atmosphere. However, the evolution of shelf sea surface temperature during a storm is dependent on the initial thermal conditions of the water column, information that is often unavailable. Here, observational data from multiple monitoring stations and satellite sensors were used to identify the sequence of events that led to the development of storm-favorable thermal conditions in the Mississippi Bight prior to the transit of Hurricane Sally (2020), a storm that rapidly intensified over the shelf. The annual peak in depth-average temperature of 〉29°C that occurred prior to the arrival of Hurricane Sally was the result of two distinct warming periods caused by a cascade of weather events. The event sequence transitioned the system from below average to above average thermal conditions over a 25-day period. The transition was initiated with the passage of Hurricane Marco (2020), which mixed the upper water column, transferring heat downward and minimizing the cold bottom water reserved over the shelf. The subsequent reheating of the upper ocean by surface heat flux from the atmosphere, followed by downwelling winds, effectively elevated shelf-wide thermal conditions for the subsequent storm, Hurricane Sally. The coupling of climatological downwelling winds and warm sea surface temperature suggest regions with such characteristics are at an elevated risk for storm intensification over the shelf.

Beschreibung: his paper is a result of research funded by the National Oceanic and Atmospheric Administration's RESTORE Science Program under awards NA17NOS4510101 and NA19NOS4510194 to the University of South Alabama and Dauphin Island Sea Lab and by the NASA Physical Oceanography program under award 80NSSC21K0553 and WBS 281945.02.25.04.67 to the University of South Alabama and the Jet Propulsion Laboratory. A portion of this work was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. We thank the NASA Goddard Space Flight Center, Ocean Ecology Laboratory, Ocean Biology Processing Group for the Moderate-resolution Imaging Spectroradiometer (MODIS) Terra ocean color data; 2014 Reprocessing. NASA OB.DAAC, Greenbelt, MD, USA. 10.5067/AQUA/MODIS/MODIS_OC.2014.0.

Beschreibung: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49, (2022): e2021GL096180, https://doi.org/10.1029/2021gl096180.

Beschreibung: In the subtropical gyres, phytoplankton rely on eddies for transporting nutrients from depth to the euphotic zone. But, what controls the rate of nutrient supply for new production? We show that vertical nutrient flux both depends on the vertical motion within the eddying flow and varies nonlinearly with the phytoplankton growth rate. Flux is maximized when the growth rate matches the inverse of the decorrelation timescale for vertical motion. Using a three-dimensional ocean model and a linear nutrient uptake model, we find that phytoplankton productivity is maximized for a growth rate of 1/3 day−1, which corresponds to the timescale of submesoscale dynamics. Variability in the frequency of vertical motion across different physical features of the flow favors phytoplankton production with different growth rates. Such a growth-transport feedback can generate diversity in the phytoplankton community structure at submesoscales and higher net productivity in the presence of community diversity.

Beschreibung: MAF and AM were funded by N00014-16-1-3130 (ONR) and MAF was also supported by the Martin Fellowship, MIT.

Beschreibung: 2022-07-20

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Grooms, I., Loose, N., Abernathey, R., Steinberg, J. M., Bachman, S. D., Marques, G., Guillaumin, A. P., & Yankovsky, E. Diffusion-Based smoothers for spatial filtering of gridded geophysical data. Journal of Advances in Modeling Earth Systems, 13(9), (2021): e2021MS002552, https://doi.org/10.1029/2021MS002552.

Beschreibung: We describe a new way to apply a spatial filter to gridded data from models or observations, focusing on low-pass filters. The new method is analogous to smoothing via diffusion, and its implementation requires only a discrete Laplacian operator appropriate to the data. The new method can approximate arbitrary filter shapes, including Gaussian filters, and can be extended to spatially varying and anisotropic filters. The new diffusion-based smoother's properties are illustrated with examples from ocean model data and ocean observational products. An open-source Python package implementing this algorithm, called gcm-filters, is currently under development.

Beschreibung: I.G. and N.L. are supported by NSF OCE 1912332. R.A. is supported by NSF OCE 1912325. J.S. is supported by NSF OCE 1912302. S.B. and G.M. are supported by NSF OCE 1912420. A.G. and E.Y. are supported by NSF GEO 1912357 and NOAA CVP NA19OAR4310364.

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 126(10),(2021): e2021JB022228, https://doi.org/10.1029/2021JB022228.

Beschreibung: Seafloor massive sulfide deposits form in remote environments, and the assessment of deposit size and composition through drilling is technically challenging and expensive. To aid the evaluation of the resource potential of seafloor massive sulfide deposits, three-dimensional inverse modeling of geophysical potential field data (magnetic and gravity) collected near the seafloor can be carried out to further enhance geologic models interpolated from sparse drilling. Here, we present inverse modeling results of magnetic and gravity data collected from the active mound at the Trans-Atlantic Geotraverse hydrothermal vent field, located at 26°08′N on the Mid-Atlantic Ridge, using autonomous underwater vehicle and submersible surveying. Both minimum-structure and surface geometry inverse modeling methods were utilized. Through deposit-scale magnetic modeling, the outer extent of a chloritized alteration zone within the basalt host rock below the mound was resolved, providing an indication of the angle of the rising hydrothermal fluid and the depth and volume of seawater/hydrothermal mixing zone. The thickness of the massive sulfide mound was determined by modeling the gravity data, enabling the tonnage of the mound to be estimated at 2.17 ± 0.44 Mt through this geophysics-based, noninvasive approach.

Beschreibung: The authors would like to thank the captain, crew, and scientific team from the 2016 R/V Meteor M127 and 1994 R/V Yokosuka MODE'94 cruises for all their work collecting the data modeled in this study. C. Galley is funded through an NSERC Discovery Grant and Memorial University's School of Graduate Studies Grant.

Beschreibung: 2022-03-29

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Beasley, C., Kender, S., Giosan, L., Bolton, C. T., Anand, P., Leng, M. J., Nilsson-Kerr, K., Ullmann, C. V., Hesselbo, S. P., & Littler, K. Evidence of a South Asian proto-monsoon during the Oligocene-Miocene transition. Paleoceanography and Paleoclimatology, 36(9), (2021): e2021PA004278, https://doi.org/10.1029/2021PA004278.

Beschreibung: The geological history of the South Asian monsoon (SAM) before the Pleistocene is not well-constrained, primarily due to a lack of available continuous sediment archives. Previous studies have noted an intensification of SAM precipitation and atmospheric circulation during the middle Miocene (∼14 Ma), but no records are available to test how the monsoon changed prior to this. In order to improve our understanding of monsoonal evolution, geochemical and sedimentological data were generated for the Oligocene-early Miocene (30–20 Ma) from Indian National Gas Hydrate Expedition 01 Site NGHP-01-01A in the eastern Arabian Sea, at 2,674 m water depth. We find the initial glaciation phase (23.7–23.0 Ma) of the Oligocene-Miocene transition (OMT) to be associated with an increase in water column ventilation and water mass mixing, suggesting an increase in winter monsoon type atmospheric circulation, possibly driven by a relative southward shift of the intertropical convergence zone. During the latter part of the OMT, or “deglaciation” phase (23.0–22.7 Ma), a long-term decrease in Mn (suggestive of deoxygenation), increase in Ti/Ca and dissolution of the biogenic carbonate fraction suggest an intensification of a proto-summer SAM system, characterized by the formation of an oxygen minimum zone in the eastern Arabian Sea and a relative increase of terrigenous material delivered by runoff to the site. With no evidence at this site for an active SAM prior to the OMT we suggest that changes in orbital parameters, as well as possibly changing Tethyan/Himalayan tectonics, caused this step change in the proto-monsoon system at this intermediate-depth site.

Beschreibung: This research forms part of a PhD study funded by the Natural Environment Research Council (NERC) Centre for Doctoral Training in Oil & Gas (grant number NE/M00578X/1) awarded to C. Beasley, and was also supported by a NERC National Environmental Isotope Facility Steering Committee grant (IP-1865-1118) awarded to S. Kender. L. Giosan acknowledges funding from USSP and WHOI and thanks colleagues from the NGHP-01 expedition. C. Ullmann acknowledges funding via NERC grant NE/N018508/1.

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Goodkin, N. F., Samanta, D., Bolton, A., Ong, M. R., Hoang, P. K., Vo, S. T., Karnauskas, K. B., & Hughen, K. A. Natural and anthropogenic forcing of multi-decadal to centennial scale variability of sea surface temperature in the South China Sea. Paleoceanography and Paleoclimatology, 36(10), (2021): e2021PA004233, https://doi.org/10.1029/2021PA004233.

Beschreibung: Four hundred years of reconstructed sea surface temperatures (SSTs) from a coral located off the coast of Vietnam show significant multi-decadal to centennial-scale variability in wet and dry seasons. Wet and dry season SST co-vary significantly at multi-decadal timescales, and the Interdecadal Pacific Oscillation (IPO) explains the majority of variability in both seasons. A newly reconstructed wet season IPO index was compared to other IPO reconstructions, showing significant long-term agreement with varying amplitude of negative IPO signals based on geographic location. Dry season SST also correlates to sea level pressure anomalies and the East Asian Winter Monsoon, although with an inverse relationship from established interannual behavior, as previously seen with an ocean circulation proxy from the same coral. Centennial-scale variability in wet and dry season SST shows 300 years of near simultaneous changes, with an abrupt decoupling of the records around 1900, after which the dry season continues a long-term cooling trend while the wet season remains almost constant. Climate model simulations indicate greenhouse gases as the largest contributor to the decoupling of the wet and dry season SSTs and demonstrate increased heat advection to the western South China Sea in the wet season, potentially disrupting the covariance in seasonal SST.

Beschreibung: This research was supported by a Singapore National Research Fellowship to N.F. Goodkin (NRFF-2012-03) as administered by the Earth Observatory of Singapore and by a Singapore Ministry of Education Academic Research Fund Tier 2 award to N.F. Goodkin, K.A. Hughen, and K.B. Karnauskas (MOE-2016-T2-1-016). D. Samanta was partially supported by a Singapore Ministry of Education Tier 3 award (MOE2019-T3-1-004).

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 22(5), (2021): e2020GC009608, https://doi.org/10.1029/2020GC009608.

Beschreibung: Thallium (Tl) isotope ratios are an emerging tool that can be used to trace crustal recycling processes in arc lavas and ocean island basalts (OIBs). Thallium is a highly volatile metal that is enriched in volcanic fumaroles, but it is unknown whether degassing of Tl from subaerial lavas has a significant effect on their residual Tl isotope compositions. Here, we present Tl isotope and concentration data from degassing experiments that are best explained by Rayleigh kinetic isotope fractionation during Tl loss. Our data closely follow predicted isotope fractionation models in which TlCl is the primary degassed species and where Tl loss is controlled by diffusion and natural convection, consistent with the slow gas advection velocity utilized during our experiments. We calculate that degassing into air should be associated with a net Tl isotope fractionation factor of αnet = 0.99969 for diffusion and natural gas convection (low gas velocities) and αnet = 0.99955 for diffusion and forced gas convection (high gas velocities). We also show that lavas from three volcanoes in the Kamchatka arc exhibit Tl isotope and concentration patterns that plot in between the two different gas convection regimes, implying that degassing played an important role in controlling the observed Tl isotope compositions in these three volcanoes. Literature inspection of Tl isotope data for subaerial lavas reveals that the majority of these appear only minorly affected by degassing, although a few samples from both OIBs and arc volcanoes can be identified that likely experienced some Tl degassing.

Beschreibung: National Science Foundation (NSF). Grant Numbers: EAR 1829546

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(15), (2021): e2021GL092779, https://doi.org/10.1029/2021GL092779.

Beschreibung: Double diffusion refers to a variety of turbulent processes in which potential energy is released into kinetic energy, made possible in the ocean by the difference in molecular diffusivities between salinity and temperature. Here, we present a new method for estimating the kinetic energy dissipation rates forced by double-diffusive convection using temperature and salinity data alone. The method estimates the up-gradient diapycnal buoyancy flux associated with double diffusion, which is hypothesized to balance the dissipation rate. To calculate the temperature and salinity gradients on small scales we apply a canonical scaling for compensated thermohaline variance (or ‘spice’) on sub-measurement scales with a fixed buoyancy gradient. Our predicted dissipation rates compare favorably with microstructure measurements collected in the Chukchi Sea. Fine et al. (2018), https://doi.org/10.1175/jpo-d-18-0028.1, showed that dissipation rates provide good estimates for heat fluxes in this region. Finally, we show the method maintains predictive skill when applied to a sub-sampling of the Conductivity, Temperature, Depth (CTD) data.

Beschreibung: This work was supported by the Natural Environment Research Council (grant number NE/L002507/1).

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(5), (2021): e2020JC017042, https://doi.org/10.1029/2020JC017042.

Beschreibung: In frontal zones, water masses that are tens of kilometers in extent with origins in the mixed layer can be identified in the pycnocline for days to months. Here, we explore the pathways and mechanisms of subduction, the process by which water from the surface mixed layer makes its way into the pycnocline, using a submesoscale-resolving numerical model of a mesoscale front. By identifying Lagrangian trajectories of water parcels that exit the mixed layer, we study the evolution of dynamical properties from a statistical standpoint. Velocity- and buoyancy-gradients increase as water parcels experience both mesoscale (geostrophic) and submesoscale (ageostrophic) frontogenesis and subduct beneath the mixed layer into the stratified pycnocline along isopycnals that outcrop in the mixed layer. Subduction is transient and occurs in coherent regions along the front, the spatial and temporal scales of which influence the scales of the subducted water masses in the pycnocline. An examination of specific subduction events reveals a range of submesoscale features that support subduction. Contrary to the forced submesoscale processes that sequester low potential vorticity (PV) anomalies in the interior, we find that PV can be elevated in subducting water masses. The rate of subduction is of similar magnitude to previous studies (∼100 m/year), but the Lagrangian evolution of properties on water parcels and pathways that are unraveled in this study emphasize the role of submesoscale dynamics coupled with mesoscale frontogenesis.

Beschreibung: This research was funded by the ONR CALYPSO DRI grant N00014-16-1-3130. MAF was partially funded by a Martin Fellowship from MIT.

Beschreibung: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gawarkiewicz, G., Fratantoni, P., Bahr, F., & Ellertson, A. Increasing frequency of mid‐depth salinity maximum intrusions in the Middle Atlantic Bight. Journal of Geophysical Research: Oceans, 127(7), (2022): e2021JC018233, https://doi.org/10.1029./2021jc018233.

Beschreibung: Shelfbreak exchange processes have been studied extensively in the Middle Atlantic Bight. An important process occurring during stratified conditions is the Salinity Maximum Intrusion. These features are commonly observed at the depth of the seasonal pycnocline, and less frequently at the surface and bottom. Data collected from NOAA's National Marine Fisheries Service Ecosystem Monitoring program as well as data collected from the fishing industry in Rhode Island show that the middepth intrusions are now occurring much more frequently than was reported in a previous climatology of the intrusions (Lentz, 2003, https://doi.org/10.1029/2003JC001859). The intrusions have a greater salinity difference from ambient water and penetrate large distances shoreward of the shelf break relative to the earlier climatology. The longer term data from the Ecosystem Monitoring program indicates that the increase in frequency occurred in 2000, and thus may be linked to a recent regime shift in the annual formation rate of Warm Core Rings by the Gulf Stream. Given the increased frequency of these salty intrusions, it will be necessary to properly resolve this process in numerical simulations in order to account for salt budgets for the continental shelf and slope.

Beschreibung: Data collection for the Shelf Research Fleet and salary for G. Gawarkiewicz, F. Bahr, and A. Ellertson were provided by the van Beuren Charitable Foundation of Newport, RI. G. Gawarkiewicz, F. Bahr, and A. Ellertson were also supported in analysis of this data by NSF grant OCE-1851261.

Beschreibung: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wang, O., Lee, T., Piecuch, C., Fukumori, I., Fenty, I., Frederikse, T., Menemenlis, D., Ponte, R., & Zhang, H. Local and remote forcing of interannual sea‐level variability at Nantucket Island. Journal of Geophysical Research: Oceans, 127(6), (2022): e2021JC018275, https://doi.org/10.1029/2021jc018275.

Beschreibung: The relative contributions of local and remote wind stress and air-sea buoyancy forcing to sea-level variations along the East Coast of the United States are not well quantified, hindering the understanding of sea-level predictability there. Here, we use an adjoint sensitivity analysis together with an Estimating the Circulation and Climate of the Ocean (ECCO) ocean state estimate to establish the causality of interannual variations in Nantucket dynamic sea level. Wind forcing explains 67% of the Nantucket interannual sea-level variance, while wind and buoyancy forcing together explain 97% of the variance. Wind stress contribution is near-local, primarily from the New England shelf northeast of Nantucket. We disprove a previous hypothesis about Labrador Sea wind stress being an important driver of Nantucket sea-level variations. Buoyancy forcing, as important as wind stress in some years, includes local contributions as well as remote contributions from the subpolar North Atlantic that influence Nantucket sea level a few years later. Our rigorous adjoint-based analysis corroborates previous correlation-based studies indicating that sea-level variations in the subpolar gyre and along the United States northeast coast can both be influenced by subpolar buoyancy forcing. Forward perturbation experiments further indicate remote buoyancy forcing affects Nantucket sea level mostly through slow advective processes, although coastally trapped waves can cause rapid Nantucket sea level response within a few weeks.

Beschreibung: This 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). CGP was supported by NASA Sea Level Change Team awards 80NSSC20K1241 and 80NM0018D0004.

Beschreibung: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46(16), (2019): 9851-9860, doi:10.1029/2019GL083726.

Beschreibung: Coral reef calcification is expected to decline due to climate change stressors such as ocean acidification and warming. Projections of future coral reef health are based on our understanding of the environmental drivers that affect calcification and dissolution. One such driver that may impact coral reef health is heterotrophy of oceanic‐sourced particulate organic matter, but its link to calcification has not been directly investigated in the field. In this study, we estimated net ecosystem calcification and oceanic particulate organic carbon (POCoc) uptake across the Kāne'ohe Bay barrier reef in Hawai'i. We show that higher rates of POCoc uptake correspond to greater net ecosystem calcification rates, even under low aragonite saturation states (Ωar). Hence, reductions in offshore productivity may negatively impact coral reefs by decreasing the food supply required to sustain calcification. Alternatively, coral reefs that receive ample inputs of POCoc may maintain higher calcification rates, despite a global decline in Ωar.

Beschreibung: Data needed for calculations are available in the supporting information. Additional data can be provided upon request directly from the corresponding author or accessed by links provided in the supporting information. The authors declare no competing financial interests. We thank Texas Sea Grant for providing partial funding for this project to A. Kealoha through the Grants‐In‐Aid of Graduate Research Program. We also thank the NOAA Nancy Foster Scholarship for PhD program funding to A. Kealoha and Texas A&M University for funds awarded to Shamberger that supported this work. This research was also supported by funding from National Science Foundation Grant OCE‐1538628 to Rappé. The Hawaii Institute of Marine Biology (particularly the Rappé Lab and Jason Jones), NOAA's Coral Reef Ecosystem Program, Connie Previti, Serena Smith, and Chris Maupin were instrumental in sample collection and data analysis.

Beschreibung: 2020-02-22

Beschreibung: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Atmospheres 124 (17-18), (2019): 9773-9795, doi: 10.1029/2018JD029933.

Beschreibung: National Aeronautics and Space Administration's Orbiting Carbon Observatory‐2 (OCO‐2) satellite provides observations of total column‐averaged CO2 mole fractions (XCO2 ) at high spatial resolution that may enable novel constraints on surface‐atmosphere carbon fluxes. Atmospheric inverse modeling provides an approach to optimize surface fluxes at regional scales, but the accuracy of the fluxes from inversion frameworks depends on key inputs, including spatially and temporally dense CO2 observations and reliable representations of atmospheric transport. Since XCO2 observations are sensitive to both synoptic and mesoscale variations within the free troposphere, horizontal atmospheric transport imparts substantial variations in these data and must be either resolved explicitly by the atmospheric transport model or accounted for within the error covariance budget provided to inverse frameworks. Here, we used geostatistical techniques to quantify the imprint of atmospheric transport in along‐track OCO‐2 soundings. We compare high‐pass‐filtered (〈250 km, spatial scales that primarily isolate mesoscale or finer‐scale variations) along‐track spatial variability in XCO2 and XH2O from OCO‐2 tracks to temporal synoptic and mesoscale variability from ground‐based XCO2 and XH2O observed by nearby Total Carbon Column Observing Network sites. Mesoscale atmospheric transport is found to be the primary driver of along‐track, high‐frequency variability for OCO‐2 XH2O. For XCO2 , both mesoscale transport variability and spatially coherent bias associated with other elements of the OCO‐2 retrieval state vector are important drivers of the along‐track variance budget.

Beschreibung: The authors thank the leadership and participants of the NASA OCO‐2 mission and acknowledge financial support from NASA Award NNX15AH13G. A.D. Torres also acknowledges support from the NASA Earth and Space Science Fellowship Award 80NSSC17K0382. We thank TCCON for providing observations. We thank A. Jacobson and the National Oceanographic and Atmospheric Administration Earth System Research Laboratory in Boulder, CO, for providing CarbonTracker CT2017 data, available online (http://carbontracker.noaa.gov). We thank S. Wofsy for providing HIPPO data, funded by the National Science Foundation and NOAA and available online (https://www.eol.ucar.edu/field_projects/hippo). The TCCON Principal Investigators acknowledge funding from their national funding organizations. TCCON data were obtained from the archive at the https://tccondata.org Web site. NARR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site (https://www.esrl.noaa.gov/psd/).

Beschreibung: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Planets 124, (2019): 3095-3118, doi: 10.1029/2019JE005937.

Beschreibung: We applied localized gravity/topography admittance and correlation analysis, as well as the Markov chain Monte Carlo method, to invert for loading and flexural parameters of 21 subregions on Mars with five distinct tectonic types. The loading styles of the five tectonic types are distinct: The surface and subsurface loading in the polar and plain regions can be assumed to be largely uncorrelated, in contrast to the correlated loading associated with the volcanic montes and Valles Marineris. For the impact basins, we consider the initial topographic depression and mantle plug before postimpact surface loading. Our analyses yield four main results: (1) The inverted effective lithospheric thickness (Te) is highly dependent on assumptions of loading type. (2) There is a trend of increasing Te from the Noachian southern highlands (20–60 km) to the Hesperian northern lowlands (〉90 km) and from the Hesperian Elysium Mons (〈55 km) to the Hesperian/Amazonian Olympus Mons (〉105 km). These Te estimates are consistent with the thermal states at the time of loading, corresponding to a global secular cooling history with decreasing heat flux. (3) Our analyses suggest high‐density basaltic surface loading at the volcanic montes and Isidis basin, in contrast to the low‐density sedimentary surface loading at the Utopia and Argyre basins. (4) We find some degree of correlation between the surface and subsurface loading for the northern polar cap and the northern plains, likely due to earlier, larger polar deposits and ancient buried features, respectively.

Beschreibung: The gravity model JGMRO120d and topography model MarsTopo719 used in this paper were retrieved from the Geosciences Node of NASA's Planetary Data System (http://pds‐geosciences.wustl.edu/mro/mro‐m‐rss‐5‐sdp‐v1/mrors_1xxx/data/shadr/) and from the SHTOOLS package (http://sourceforge.net/projects/shtools/), respectively. The MATLAB codes to reproduce the data analysis, parameter estimation, and key figures are available in a github repository (https://github.com/MinaDing/marslithosphere/tree/v1.0.0, DOI: 10.5281/zenodo.3530057). We are grateful to Mark Wieczorek and Frederik Simons for sharing relevant software online. We thank Ken Tanaka for providing a digital map of Mars chronographic ages. We thank Brandon Johnson for consultation on the loading processes of impact basins. We also thank Editor Laurent Montesi and Steven A. Hauck, as well as Patrick McGovern and anonymous reviewers for their invaluable feedbacks. This work was supported by National Natural Science Foundation of China (41806067, 41890813, 91628301 and U1606401), Key Laboratory of Ocean and Marginal Sea Geology, Chinese Academy of Sciences (OMG18‐02), Chinese Academy of Sciences (Y4SL021001, QYZDY‐SSW‐DQC005 and 133244KYSB20180029), Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0205), Radio Science Gravity investigation of the NASA Mars Reconnaissance Orbiter mission (M.T.Z.), and National Science Foundation (EAR 1220280) and Henry Bigelow Chair for Excellence in Oceanography (J.L.).

Beschreibung: 2020-05-20

Beschreibung: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Spain, E. A., Johnson, S. C., Hutton, B., Whittaker, J. M., Lucieer, V., Watson, S. J., Fox, J. M., Lupton, J., Arculus, R., Bradney, A., & Coffin, M. F. Shallow seafloor gas emissions near Heard and McDonald Islands on the Kerguelen Plateau, Southern Indian Ocean. Earth and Space Science, 7(3), (2020): e2019EA000695, doi:10.1029/2019EA000695.

Beschreibung: Bubble emission mechanisms from submerged large igneous provinces remains enigmatic. The Kerguelen Plateau, a large igneous province in the southern Indian Ocean, has a long sustained history of active volcanism and glacial/interglacial cycles of sedimentation, both of which may cause seafloor bubble production. We present the results of hydroacoustic flare observations around the underexplored volcanically active Heard Island and McDonald Islands on the Central Kerguelen Plateau. Flares were observed with a split‐beam echosounder and characterized using multifrequency decibel differencing. Deep‐tow camera footage, water properties, water column δ3He, subbottom profile, and sediment δ13C and δ34S data were analyzed to consider flare mechanisms. Excess δ3He near McDonald Islands seeps, indicating mantle‐derived input, suggests proximal hydrothermal activity; McDonald Islands flares may thus indicate CO2, methane, and other minor gas bubbles associated with shallow diffuse hydrothermal venting. The Heard Island seep environment, with subbottom acoustic blanking in thick sediment, muted 3He signal, and δ13C and δ34S fractionation factors, suggest that Heard Island seeps may either be methane gas (possibly both shallow biogenic methane and deeper‐sourced thermogenic methane related to geothermal heat from onshore volcanism) or a combination of methane and CO2, such as seen in sediment‐hosted geothermal systems. These data provide the first evidence of submarine gas escape on the Central Kerguelen Plateau and expand our understanding of seafloor processes and carbon cycling in the data‐poor southern Indian Ocean. Extensive sedimentation of the Kerguelen Plateau and additional zones of submarine volcanic activity mean additional seeps or vents may lie outside the small survey area proximal to the islands.

Beschreibung: We thank the Australian Marine National Facility (MNF) for its support in the form of sea time on RV Investigator , support personnel, scientific equipment, and data management. We also thank the captain, crew, and fellow scientists of RV Investigator voyage IN2016_V01. We also thank specifically the following: T. Martin, F. Cooke, S. L. Sow, N. Bax, J. Ford, and F. Althaus, CSIRO (Commonwealth Scientific and Industrial Research Organisation); Echoview Software Pty. Ltd. (Hobart, Australia); C. Dietz and C. Cook, Central Science Laboratory, University of Tasmania; C. Wilkinson and T. Baumberger, National Oceanic and Atmospheric Administration; R. Carey, University of Tasmania; T. Holmes, Institute for Marine and Antarctic Studies, University of Tasmania; N. Polmear; and A. Post, Geoscience Australia. The overall science of the project is supported by Australian Antarctic Science Program (AASP) grant 4338. E.S.' PhD research is supported by the Australian Research Council's Special Research Initiative Antarctic Gateway Partnership (Project ID SR140300001) and by an Australian Government Research Training Program Scholarship. S.C.J. is supported by iCRAG under SFI, European Regional Development Fund, and industry partners, as well as ANZIC‐IODP. J.M.W. is supported by ARC grant DE140100376 and DP180102280. This is PMEL publication number 4910. All IN2016_V01 data and samples acquired on IN2016_V01 are made publicly available in accordance with MNF policy.

Beschreibung: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wang, J., Ma, Q., Wang, F., Lu, Y., & Pratt, L. J. Seasonal variation of the deep limb of the Pacific Meridional Overturning circulation at Yap-Mariana junction. Journal of Geophysical Research: Oceans, 125(7), (2020): e2019JC016017, doi:10.1029/2019JC016017.

Beschreibung: This study reveals the seasonal variability of the lower and upper deep branches of the Pacific Meridional Overturning Circulation (L‐PMOC and U‐PMOC) in the Yap‐Mariana Junction (YMJ) channel, a major gateway for deep flow into the western Pacific. On the western side of the YMJ channel, mooring observations in 2017 and in 1997 show the seasonal phase of the L‐PMOC at depths of 3,800–4,400 m: strong northward flow with speed exceeding 20 cm s−1 and lasting from December to next May and weak flow during the following 6 months. On the eastern side of the channel, mooring observations during 2014–2017 show two southward deep flows with broadly seasonal phases, one being the return flow of L‐PMOC below ~4,000 m and with the same phase of L‐PMOC but reduced magnitude. The second, shallower, southward deep flow corresponds to the U‐PMOC observed within 3,000–3,800 m and with opposite phase of L‐PMOC, that is, strong (weak) southward flow appearing during June–November (December–May). Seasonal variations of the L‐PMOC and U‐PMOC are accompanied by the seasonal intrusions of the Lower and Upper Circumpolar Waters (LCPW and UCPW) in lower and upper deep layers, which change the isopycnal structure and the deep currents in a way consistent with geostrophic balance.

Beschreibung: This study is supported by the National Natural Science Foundation of China (grants 91958204 and 41776022), the Strategic Priority Research Program of the Chinese Academy of Sciences (grant XDA22000000), the Key Research Program of Frontier Sciences, CAS (grant QYZDB‐SSW‐SYS034). F. Wang thanks the support from the Scientific and Technological Innovation Project by Qingdao National Laboratory for Marine Science and Technology (grant 2016ASKJ12), the National Program on Global Change and Air‐Sea Interaction (grant GASI‐IPOVAI‐01‐01), and the National Natural Science Foundation of China (grants 41730534 and 41421005). L. Pratt gratefully acknowledges the support by NSF (grant OCE‐1657870). Jianing Wang and Qiang Ma contributed equally to this work.

Beschreibung: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Black, E. E., Kienast, S. S., Lemaitre, N., Lam, P. J., Anderson, R. F., Planquette, H., Planchon, F., & Buesseler, K. O. Ironing out Fe residence time in the dynamic upper ocean. Global Biogeochemical Cycles, 34(9), (2020): e2020GB006592, doi:10.1029/2020GB006592.

Beschreibung: Although iron availability has been shown to limit ocean productivity and influence marine carbon cycling, the rates of processes driving iron's removal and retention in the upper ocean are poorly constrained. Using 234Th‐ and sediment‐trap data, most of which were collected through international GEOTRACES efforts, we perform an unprecedented observation‐based assessment of iron export from and residence time in the upper ocean. The majority of these new residence time estimates for total iron in the surface ocean (0–250 m) fall between 10 and 100 days. The upper ocean residence time of dissolved iron, on the other hand, varies and cycles on sub‐annual to annual timescales. Collectively, these residence times are shorter than previously thought, and the rates and timescales presented here will contribute to ongoing efforts to integrate iron into global biogeochemical models predicting climate and carbon dioxide sequestration in the ocean in the 21st century and beyond.

Beschreibung: We would like to thank S. Albani for providing the dust model results (Community Atmosphere Model, C4fn) and the three anonymous reviewers for their constructive comments. The U.S. GEOTRACES work was supported by the National Science Foundation (OCE‐1232669 and OCE‐1518110) and E. Black was also funded by a NASA Earth and Space Science Graduate Fellowship (NNX13AP31H) and the Ocean Frontier Institute. The GEOVIDE work was funded by the Flanders Research Foundation (G071512N), the Vrije Universiteit Brussel (SRP‐2), the French ANR Blanc GEOVIDE (ANR‐13‐BS06‐0014), ANR RPDOC BITMAP (ANR‐12‐PDOC‐0025‐01), IFREMER, CNRS‐INSU (programme LEFE), INSU OPTIMISP, and Labex‐Mer (ANR‐10‐LABX‐19).

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Planets 125(9), (2020): e2019JE006209, doi:10.1029/2019JE006209

Beschreibung: Saturn's moon Enceladus has a global subsurface ocean and a porous rocky core in which water‐rock reactions likely occur; it is thus regarded as a potentially habitable environment. For icy moons like Enceladus, tidal heating is considered to be the main heating mechanism, which has generally been modeled using viscoelastic solid rheologies in existing studies. Here we provide a new framework for calculating tidal heating based on a poroviscoelastic model in which the porous solid and interstitial fluid deformation are coupled. We show that the total heating rate predicted for a poroviscoelastic core is significantly larger than that predicted using a classical viscoelastic model for intermediate to large (〉1014 Pa·s) rock viscosities. The periodic deformation of the porous rock matrix is accompanied by interstitial pore fluid flow, and the combined effects through viscous dissipation result in high heat fluxes particularly at the poles. The heat generated in the rock matrix is also enhanced due to the high compressibility of the porous matrix structure. For a sufficiently compressible core and high permeability, the total heat production can exceed 10 GW—a large fraction of the moon's total heat budget—without requiring unrealistically low solid viscosities. The partitioning of heating between rock and fluid constituents depends most sensitively on the viscosity of the rock matrix. As the core of Enceladus warms and weakens over time, pore fluid motion likely shifts from pressure‐driven local oscillations to buoyancy‐driven global hydrothermal convection, and the core transitions from fluid‐dominated to rock‐dominated heating.

Beschreibung: 2021-01-28

Beschreibung: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Forsyth, J., Andres, M., & Gawarkiewicz, G. . Shelfreak jet structure and variability off New Jersey using ship of opportunity data from the CMV Oleander. Journal of Geophysical Research: Oceans, 125(9), (2020): e2020JC016455. doi:10.1029/2020JC016455.

Beschreibung: Repeat measurements of velocity and temperature profiles from the Container Motor Vessel (CMV) Oleander provide an unprecedented look into the variability on the New Jersey Shelf and upper continental slope. Here 1362 acoustic Doppler current profiler (ADCP) velocity sections collected between 1994 and 2018 are analyzed in both Eulerian and stream coordinate reference frames to characterize the mean structure of the Shelfbreak Jet, as well as its seasonal to decadal variability. The Eulerian mean Shelfbreak Jet has a maximum jet velocity of 0.12 m s−1. The maximum jet velocity peaks in April and May and reaches its minimum in July and August. In a stream coordinate framework, the jet is only identified in 61% of transects, and the mean stream coordinate Shelfbreak Jet has a maximum jet velocity of 0.32 m s−1. Evidence is found that Warm Core Rings, originating from the Gulf Stream arriving in the Slope Sea adjacent to the New Jersey Shelf, shift the Shelfbreak Jet onshore of its mean position or entirely shutdown the Shelfbreak Jet's flow. At interannual timescales, variability in the Shelfbreak Jet velocity is correlated with the temperature on the New Jersey Shelf 2 months later. When considered in a stream coordinate framework, Shelfbreak Jet have decreased over the time period considered in the study.

Beschreibung: J. F. and M. A. were supported by NSF OCE‐1634094 and OCE‐1924041. G. G was supported by NSF OCE‐1851261.

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 47(7), (2020): e2020GL087405, doi:10.1029/2020GL087405.

Beschreibung: The origin and distribution of the gabbroic bodies provide crucial information to understand the formation and evolution processes of the oceanic core complexes (OCCs). Nevertheless, images of the shape of the gabbroic bodies across the domes and gabbroic intrusion into the mantle have remained elusive. High‐resolution acoustic early‐arrival full waveform inversion tomography models obtained along and across the Kane OCC characterize the detailed lateral variability in structure and composition of the upper ~2 km of this well‐developed OCC. Reverse time migration images show the gabbroic plutons embedded in mantle rocks are seismically transparent, while more reflective sections correspond to the layered magmatic crust. Lithological interpretation shows heterogeneous distribution of gabbroic bodies within the Kane OCC, indicating strong spatial and temporal variability in magmatism during fault exhumation. Our results will also be of high value for future scientific ocean drilling efforts in the area.

Beschreibung: Seismic data acquisition was funded by NSF Grant OCE99‐87004. Data files can be obtained from Interdisciplinary Earth Data Alliance (IEDA) (https://doi.org/10.1594/IEDA/314508) (Tucholke & Collins, 2014). The velocity models and migrated seismic sections shown in the paper are freely available for download from 4TU. Centre for Research Data (doi:10.4121/uuid:3ef55160-4a5a-4d1a-b734-fe2b8d2871ae). Full waveform inversion was performed with the software TomoPlus (GeoTomo LLC) licensed to SCSIO. This research was supported by the National Natural Science Foundation of China (41676044 and 91858207) and Special Foundation for National Science and Technology Basic Research Program of China (2018FY100505). M. X. acknowledges supports from Guangdong NSF research team project (2017A030312002), K. C. Wong Education Foundation (GJTD‐2018‐13), Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (GML2019ZD0205), and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA13010105). J. P. C. acknowledges support from the Independent Research and Development Program at WHOI. J. P. Wang and X. R. Mu from China University of Petroleum are thanked for helping with the RTM setup.

Beschreibung: 2020-09-28

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125(9), (2020): e2020JB019743, doi:10.1029/2020JB019743.

Beschreibung: A multiscale magnetic survey of the northern basin of Yellowstone Lake was undertaken in 2016 as part of the Hydrothermal Dynamics of Yellowstone Lake Project (HD‐YLAKE)—a broad research effort to characterize the cause‐and‐effect relationships between geologic and environmental processes and hydrothermal activity on the lake floor. The magnetic survey includes lake surface, regional aeromagnetic, and near‐bottom autonomous underwater vehicle (AUV) data. The study reveals a strong contrast between the northeastern lake basin, characterized by a regional magnetic low punctuated by stronger local magnetic lows, many of which host hydrothermal vent activity, and the northwestern lake basin with higher‐amplitude magnetic anomalies and no obvious hydrothermal activity or punctuated magnetic lows. The boundary between these two regions is marked by a steep gradient in heat flow and magnetic values, likely reflecting a significant structure within the currently active ~20‐km‐long Eagle Bay‐Lake Hotel fault zone that may be related to the ~2.08‐Ma Huckleberry Ridge caldera rim. Modeling suggests that the broad northeastern magnetic low reflects both a shallower Curie isotherm and widespread hydrothermal activity that has demagnetized the rock. Along the western lake shoreline are sinuous‐shaped, high‐amplitude magnetic anomaly highs, interpreted as lava flow fronts of upper units of the West Thumb rhyolite. The AUV magnetic survey shows decreased magnetization at the periphery of the active Deep Hole hydrothermal vent. We postulate that lower magnetization in the outer zone results from enhanced hydrothermal alteration of rhyolite by hydrothermal condensates while the vapor‐dominated center of the vent is less altered.

Beschreibung: The lake surface and AUV magnetic data were acquired under National Park Service research permit YELL‐2016‐SCI‐7018 and the 2016 aeromagnetic data under research permit YELL‐2016‐SCI‐7056. We thank Sarah Haas, Stacey Gunther, Erik Oberg, Annie Carlson, and Patricia Bigelow at the Yellowstone Center for Resources for assistance with permitting and logistics, Ranger Jackie Sene for assistance with logistics and safety at Bridge Bay, Bob Gresswell for providing us with the U.S. Geological Survey (USGS) boat Alamar, the boat pilot Nick Heredia, and Robert Harris and Shaul Hurwitz for fruitful discussions. We are very thankful to Ocean Floor Geophysics (Brian Claus and Steve Bloomer) who provided the magnetometer for the AUV survey and preprocessed the data, and to the REMUS 600 team (Greg Packard and Greg Kurras) for operating and optimizing the AUV during lake operations. Data from the Newport and Boulder observatories were used to process the survey data. We thank the USGS Geomagnetism Program for supporting their operation and INTERMAGNET for promoting high standards of magnetic observatory practice (www.intermagnet.org). This research was funded by the National Science Foundation's Integrated Earth Systems program EAR‐1516361 (HD‐YLAKE project), USGS Mineral Resource and Volcano Hazard Programs, and benefited from major in‐kind support from the USGS Yellowstone Volcano Observatory. Maurice Tivey was supported under National Science Foundation Grant OCE‐1557455. During the course of this study, Claire Bouligand was a visiting scientist at the USGS in Menlo Park, California, USA, benefited from a delegation to Centre National de la Recherche Scientifique (CNRS), and received funding from CNRS‐INSU program SYSTER. ISTerre is part of Labex OSUG@2020 (ANR10 LABX56). Any use of trade, firm, or product names is for descriptive purposes and does not imply endorsement by the U.S. Government.

Beschreibung: 2021-01-27

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 125(10), (2020): e2020JG005664, doi:10.1029/2020JG005664.

Beschreibung: Shallow ponds are expanding in many salt marshes with potential impacts on ecosystem functioning. Determining how pond characteristics change over time and scale with physical dimensions and other spatial predictors could facilitate incorporation of ponds into projections of ecosystem change. We evaluated scaling relationships across six differently sized ponds in three regions of the high marshes within the Plum Island Ecosystems‐Long Term Ecological Research site (MA, USA). We further characterized diel fluctuations in surface water chemistry in two ponds to understand short‐term processes that affect emergent properties (e.g., habitat suitability). Primary producers drove oxygen levels to supersaturation during the day, while nighttime respiration resulted in hypoxic to anoxic conditions. Diel swings in oxygen were mirrored by pH and resulted in successive shifts in redox‐sensitive metabolisms, as indicated by nitrate consumption at dusk followed by peaks in ammonium and then sulfide overnight. Abundances of macroalgae and Ruppia maritima correlated with whole‐pond oxygen metabolism rates, but not with surface area (SA), volume (V), or SA:V. Moreover, there were no clear patterns in primary producer abundances, surface water chemistry, or pond metabolism rates across marsh regions supplied by different tidal creeks or that differed in distance to upland borders or creekbanks. Comparisons with data from 2 years prior demonstrate that plant communities and biogeochemical processes are not in steady state. Factors contributing to variability between ponds and years are unclear but likely include infrequent tidal exchange. Temporal and spatial variability and the absence of scaling relationships complicate the integration of high marsh ponds into ecosystem biogeochemical models.

Beschreibung: Thanks to S. McNichol, S. Jayne, E. Neel, and PIE‐LTER (NSF‐OCE1238212) for field assistance; I. Forbrich for meteorological data (Giblin & Forbrich, 2018); J. Jennings for dissolved nutrient analyses; J. Seewald for ion chromatograph access; and G. Mariotti for elevation data. C. Wilson and an anonymous reviewer provided comments that greatly improved our manuscript. A. C. S. was supported by NSF (OCE1233678), NOAA (NA14NOS4190145), and Sea Grant (NA14OAR4170104) awards, and A. D. by the MIT Undergraduate Research Opportunities Program.

Beschreibung: 2021-03-15

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Solid Earth 125(2), (2020): e2019JB018203, doi:10.1029/2019JB018203.

Beschreibung: Cold, low‐density diapirs arising from hydrated mantle and/or subducted sediments on the top of subducting slabs have been invoked to transport key chemical signatures to the source region of arc magmas. However, to date there have been few quantitative models to constrain melting in such diapirs. Here we use a two‐phase Darcy‐Stokes‐energy model to investigate thermal evolution, melting, and depletion in a buoyant sediment diapir ascending through the mantle wedge. Using a simplified 2‐D circular geometry, we investigate diapir evolution in three scenarios with increasing complexity. In the first two scenarios we consider instantaneous heating of a diapir by thermal diffusion with and without the effect of the latent heat of melting. Then, these simplified calculations are compared to numerical simulations that include melting, melt segregation, and the influence of depletion on the sediment solidus along pressure‐temperature‐time (P ‐T ‐t ) paths appropriate for ascent through the mantle wedge. The high boundary temperature induces a rim of high porosity, into which new melts are focused and then migrate upward. The rim thus acts like an annulus melt channel, while the effect of depletion buffers additional melt production. Solid matrix flow combined with recrystallization of melt pooled near the top of the diapir can result in large gradients in depletion across the diapir. These large depletion gradients can either be preserved if the diapir leaks melt during ascent, or rehomogenized in a sealed diapir. Overall our numerical simulations predict less melt production than the simplified thermal diffusion calculations. Specifically, we show that diapirs whose ascent paths favor melting beneath the volcanic arc will undergo no more than ~40–50% total melting.

Beschreibung: We thank careful reviews by Juliane Dannberg, Harro Schmeling, and Bernhard steinberger. This work is supported by NSF‐1316333 (MB & NZ), NSF‐1551023 (MB), NSF‐1316310 (CK), and by China's Thousand Talents Plan (2015) and NSFC‐41674098 funding to NZ. The public data repository of Deal.ii (www.dealii.org) is thanked for distributing the software and examples that are used in this study. Computational work was conducted in High‐performance Computing Platform of Peking University, Kenny cluster of WHOI, and Pawsey Supercomputing Centre of Western Australia. We thank Timo Heister and Juliane Dannberg for deal.II technical assistance. The data of mantle wedge thermal structure and diapir trajectories, and the source code to compute the model results are available in the Mendeley data (http://dx.doi.org/10.17632/73n8zkc68s.1).

Beschreibung: 2020-07-31

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Long, M. H. Aquatic biogeochemical eddy covariance fluxes in the presence of waves. Journal of Geophysical Research: Oceans, 126(2), (2021): e2020JC016637, https://doi.org/10.1029/2020JC016637.

Beschreibung: The eddy covariance (EC) technique is a powerful tool for measuring atmospheric exchange rates that was recently adapted by biogeochemists to measure aquatic oxygen fluxes. A review of aquatic biogeochemical EC literature revealed that the majority of studies were conducted in shallow waters where waves were likely present, and that waves biased sensor and turbulence measurements. This review identified that larger measurement heights shifted turbulence to lower frequencies, producing a spectral gap between turbulence and wave frequencies. However, some studies sampled too close to the boundary to allow for a spectral turbulence‐wave gap, and a change in how EC measurements are conducted and analyzed is needed to remove wave‐bias. EC fluxes have only been derived from the time‐averaged product of vertical velocity and oxygen, often resulting in wave‐bias. Presented is a new analysis framework for removing wave‐bias by accumulation of cross‐power spectral densities below wave frequencies. This analysis framework also includes new measurement guidelines based on wave period, currents, and measurement heights. This framework is applied to sand, seagrass, and reef environments where traditional EC analysis resulted in wave‐bias of 7.0% ± 9.2% error in biogeochemical (oxygen and H+) fluxes, while more variable and higher error was evident in momentum fluxes (10.5% ± 21.0% error). It is anticipated that this framework will lead to significant changes in how EC measurements are conducted and evaluated, and help overcome the major limitations caused by wave‐sensitive and slow‐response sensors, potentially expanding new chemical tracer applications and more widespread use of the EC technique.

Beschreibung: This work was supported by the Independent Research & Development Program at WHOI grant 25307and NSF OCE grants 1657727 and 1633951.

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 126(2), (2021): e2020JB019962, https://doi.org/10.1029/2020JB019962.

Beschreibung: The largest slip in great megathrust earthquakes often occurs in the 10–30 km depth range, yet seismic imaging of the material properties in this region has proven difficult. We utilize a dense onshore‐offshore passive seismic dataset from the southernmost Cascadia subduction zone where seismicity in the mantle of the subducted Gorda Plate produces S‐to‐P and P‐to‐S conversions generated within a few km of the plate interface. These conversions typically occur in the 10–20 km depth range at either the top or bottom of a ∼5 km thick layer with a high Vp/Vs that we infer to be primarily the subducted crust. We use their arrival times and amplitudes to infer the location of the top and bottom of the subducted crust as well as the velocity contrasts across these discontinuities. Comparing with both the Slab1.0 and the updated Slab2 interface models, the Slab2 model is generally consistent with the converted phases, while the Slab1.0 model is 1–2 km deeper in the 2–20 km depth range and ∼6–8 km too deep in the 10–20 km depth range between 40.25°N and 40.4°N. Comparing the amplitudes of the converted phases to synthetics for simplified velocity structures, the amplitude of the converted phases requires models containing a ∼5 km thick zone with at least a ∼10%–20% reduction in S wave velocity. Thus, the plate boundary is likely contained within or at the top of this low velocity zone, which potentially indicates a significant porosity and fluid content within the seismogenic zone.

Beschreibung: This work is funded by National Science Foundation Award Numbers EAR‐1520690.

Beschreibung: 2021-07-25

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 125(1), (2020): e2019JG005414, doi:10.1029/2019JG005414.

Beschreibung: A survey of 25 coastal‐draining rivers across the Canadian Arctic Archipelago (CAA) shows that these systems are distinct from the largest Arctic rivers that drain watersheds extending far south of the Arctic circle. Observations collected from 2014 to 2016 illustrate the influences of seasonal hydrology, bedrock geology, and landscape physiography on each river's inorganic geochemical characteristics. Summertime data show the impact of coincident gradients in lake cover and surficial geology on river geochemical signatures. In the north and central CAA, drainage basins are generally smaller, underlain by sedimentary bedrock, and their hydrology is driven by seasonal precipitation pulses that undergo little modification before they enter the coastal ocean. In the southern CAA, a high density of lakes stores water longer within the terrestrial system, permitting more modification of water isotope and geochemical characteristics. Annual time‐series observations from two CAA rivers reveal that their concentration‐discharge relationships differ compared with those of the largest Arctic rivers, suggesting that future projections of dissolved ion fluxes from CAA rivers to the Arctic Ocean may not be reliably made based on compositions of the largest Arctic rivers alone, and that rivers draining the CAA region will likely follow different trajectories of change under a warming climate. Understanding how these small, coastal‐draining river systems will respond to climate change is essential to fully evaluate the impact of changing freshwater inputs to the Arctic marine system.

Beschreibung: This work was only possible through a network of enthusiastic and devoted collaborators. Partners included Polar Knowledge Canada and the Canadian High Arctic Research Station, the Arctic Research Foundation, the Kugluktuk Angoniatit Association, and the Canadian Arctic GEOTRACES Program. We acknowledge support from the Department of Fisheries and Oceans Canada, the Woods Hole Oceanographic Institution Coastal Ocean Institute, The G. Unger Vetlesen Foundation, Jane and James Orr, and the Woods Hole Research Center. Many thanks go to Austin Maniyogena, Angulalik Pedersen, Adrian Schimnowski, JS Moore, Les Harris, Oksana Schimnowski, as well as Barbara Adjun, Amanda Dumond, and Johnny Nivingalok, and the captains and crew of the research vessels CCGS Amundsen and R/V Martin Bergmann, all of whom supported our research and helped with sample collection. Special thanks also go to Valier Galy, Zhaohui “Aleck” Wang, Marty Davelaar, Michiyo Yamamoto‐Kawai, Hugh McLean, Mike Dempsey, Baba Pedersen, Maureen Soon, Katherine Hoering, Sean Sylva, Ekaterina Bulygina, and Anya Suslova for their invaluable contributions during field program planning, preparations, and laboratory analyses. Robert Max Holmes is thanked for many fruitful discussions. We also thank several anonymous reviewers for their helpful comments on the paper's content and structure. All of the data presented in this paper can be found at https://doi.org/10.1594/PANGAEA.908497.

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(11), (2020): e2019JC015851, doi:10.1029/2019JC015851.

Beschreibung: Influences of the ocean mixed layer (OML) dynamics on intensity, pathway, and landfall of October 2012 Hurricane Sandy were examined through an experiment using the Weather Research and Forecasting (WRF) model. The WRF model was run for two cases with or without coupling to the OML. The OML in the WRF was calculated by an oceanic mixed layer submodel. The initial conditions of the depth and mean water temperature of the OML were specified using Global‐FVCOM and Global‐HYCOM fields. The comparison results between these two cases clearly show that including the OML dynamics enhanced the contribution of vertical mixing to the air‐sea heat flux. When the hurricane moved toward the coast, the local OML rapidly deepened with an increase of storm wind. Intense vertical mixing brought cold water in the deep ocean toward the surface to produce a cold wake underneath the storm, with the lowest sea temperature at the maximum wind zone. This process led to a significant latent heat loss from the ocean within the storm and hence rapid drops of the air temperature and vapor mixing ratio above the sea surface. As a result, the storm was intensified as the central sea level pressure dropped. Improving air pressure simulation with OML tended to reduce the storm size and strengthened the storm intensity and hence provided a better simulation of hurricane pathway and landfall.

Beschreibung: This work was supported by the MIT Sea Grant College Program through grant 2017‐R/RCM‐49C and 2012‐R/RC‐127, the NSF grants OCE1459096, OCE1332207, and OCE1332666, the NOAA‐funded IOOS NERACOOS program for NECOFS with subcontract numbers NA16NOS0120023 and NERACOOS A002 and A007, and the NOAA‐CINAR Hurricane Sandy fund. The development of the Global‐FVCOM system has been supported by NSF grants OCE1603000. S. Li was supported partially by the oversea Ph.D. fellowship from the China Scholarship Council (No. 1409010025).

Beschreibung: 2021-04-07

Beschreibung: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Evans, D. G., Frajka-Williams, E., Garabato, A. C. N., Polzin, K. L., & Forryan, A. Mesoscale eddy dissipation by a "zoo" of submesoscale processes at a western boundary. Journal of Geophysical Research: Oceans, 125(11), (2020): e2020JC016246, doi:10.1029/2020JC016246.

Beschreibung: Mesoscale eddies are ubiquitous dynamical features that tend to propagate westward and disappear along ocean western boundaries. Using a multiscale observational study, we assess the extent to which eddies dissipate via a direct cascade of energy at a western boundary. We analyze data from a ship‐based microstructure and velocity survey, and an 18‐month mooring deployment, to document the dissipation of energy in anticyclonic and cyclonic eddies impinging on the topographic slope east of the Bahamas, in the North Atlantic Ocean. These observations reveal high levels of turbulence where the steep and rough topographic slope modified the intensified northward flow associated with, in particular, anticyclonic eddies. Elevated dissipation was observed both near‐bottom and at mid depths (200–800 m). Near‐bottom turbulence occurred in the lee of a protruding escarpment, where elevated Froude numbers suggest hydraulic control. Energy was also radiated in the form of upward‐propagating internal waves. Elevated dissipation at mid depths occurred in regions of strong vertical shear, where the topographic slope modified the vertical structure of the northward eddy flow. Here, low Richardson numbers and a local change in the isopycnal gradient of potential vorticity (PV) suggest that the elevated dissipation was associated with horizontal shear instability. Elevated mid‐depth dissipation was also induced by topographic steering of the flow. This led to large anticyclonic vorticity and negative PV adjacent to the topographic slope, suggesting that centrifugal instability underpinned the local enhancement in dissipation. Our results provide a mechanistic benchmark for the realistic representation of eddy dissipation in ocean models.

Beschreibung: The MeRMEED project, DGE, EFW, ACNG and AF were funded under Natural Environment Research Council standard grant NE/N001745/2. ACNG further acknowledges the support of the Royal Society and the Wolfson Foundation.

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 21(11), (2020): e2020GC009074, doi:10.1029/2020GC009074.

Beschreibung: Marine ferromanganese deposits, often called the scavengers of the sea, adsorb and coprecipitate with a wide range of metals of great interest for paleo‐environmental reconstructions and economic geology. The long (up to ∼75 Ma), near‐continuous record of seawater chemistry afforded by ferromanganese deposits offers much historical information about the global ocean and surface earth including crustal processes, mantle processes, ocean circulation, and biogeochemical cycles. The extent to which the ferromanganese deposits hosting these geochemical proxies undergo diagenesis on the seafloor, however, remains an important and challenging factor in assessing the fidelity of such records. In this study, we employ multiple X‐ray techniques including micro–X‐ray fluorescence, bulk and micro–X‐ray absorption spectroscopy, and X‐ray powder diffraction to probe the structural, compositional, redox, and mineral changes within a single ferromanganese crust. These techniques illuminate a complex two‐dimensional structure characterized by crust growth controlled by the availability of manganese (Mn), a dynamic range in Mn oxidation state from +3.4 to +4.0, changes in Mn mineralogy over time, and recrystallization in the lower phosphatized portions of the crust. Iron (Fe) similarly demonstrates spatial complexity with respect to concentration and mineralogy, but lacks the dynamic range of oxidation state seen for Mn. Micrometer‐scale measurements of metal abundances reveal complex element associations between trace elements and the two major oxide phases, which are not typically resolvable via bulk analytical methods. These findings provide evidence of post‐depositional processes altering chemistry and mineralogy, and provide important geochemical context for the interpretation of element and isotopic records in ferromanganese crusts.

Beschreibung: This research is supported by NASA Exobiology NNX15AM046 to Scott D. Wankel and Colleen M. Hansel, NASA NESSF NNX15AR62H to Kevin M. Sutherland, and WHOI Ocean Exploration Institute to Colleen M. Hansel. The Stanford Synchrotron Radiation Lightsource was utilized in this study. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE‐AC02‐76SF00515.

Beschreibung: 2021-04-26

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wallace, E. J., Donnelly, J. P., van Hengstum, P. J., Winkler, T. S., McKeon, K., MacDonald, D., d'Entremont, N. E., Sullivan, R. M., Woodruff, J. D., Hawkes, A. D., & Maio, C. 1,050 years of hurricane strikes on long island in the Bahamas. Paleoceanography and Paleoclimatology, 36(3), (2021): e2020PA004156, https://doi.org/10.1029/2020PA004156.

Beschreibung: Sedimentary records of past hurricane activity indicate centennial-scale periods over the past millennium with elevated hurricane activity. The search for the underlying mechanism behind these active hurricane periods is confounded by regional variations in their timing. Here, we present a new high resolution paleohurricane record from The Bahamas with a synthesis of published North Atlantic records over the past millennium. We reconstruct hurricane strikes over the past 1,050 years in sediment cores from a blue hole on Long Island in The Bahamas. Coarse-grained deposits in these cores date to the close passage of seven hurricanes over the historical interval. We find that the intensity and angle of approach of these historical storms plays an important role in inducing storm surge near the site. Our new record indicates four active hurricane periods on Long Island that conflict with published records on neighboring islands (Andros and Abaco Island). We demonstrate these three islands do not sample the same storms despite their proximity, and we compile these reconstructions together to create the first regional compilation of annually resolved paleohurricane records in The Bahamas. Integrating our Bahamian compilation with compiled records from the U.S. coastline indicates basin-wide increased storminess during the Medieval Warm Period. Afterward, the hurricane patterns in our Bahamian compilation match those reconstructed along the U.S. East Coast but not in the northeastern Gulf of Mexico. This disconnect may result from shifts in local environmental conditions in the North Atlantic or shifts in hurricane populations from straight-moving to recurving storms over the past millennium.

Beschreibung: This work was funded by the National Science Foundation Graduate Research Fellowship (to E. J. W.), the Dalio Explore Foundation, and National Science Foundation grant OCE-1356708 (to J. P. D. and P. J. vH.).

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 126(3), (2021): e2021JB021709, https://doi.org/10.1029/2021JB021709.

Beschreibung: Serpentinites are increasingly recognized as playing an important role in the global geochemical cycle. However, discriminating the contributions of serpentinites to arc magmas from those of other subduction components is challenging. The Okinawa Trough is a back-arc basin developed behind the Ryukyu subduction zone, where magmas are extensively affected by sediment subduction. In this study, we reported the F-Cl concentrations and Sr-Nd-Pb-B isotopes of basaltic andesites from the Yaeyama Graben, Yonaguni Graben, and Irabu Knoll in the southern Okinawa Trough. The Irabu Knoll lavas show the most enrichment of fluid-mobile elements and F ± Cl, and have the heaviest B isotopes (δ11B: +6.6 ± 1.5‰). They also have decoupled Sr-Nd isotopes: higher 87Sr/86Sr (∼0.7049) but have no obvious decrease of 143Nd/144Nd (∼0.5128). Results from slab dehydration modeling and mixing calculations suggest that the heavy δ11B in the Irabu Knoll lavas is not consistent with fluids derived from altered oceanic crust (AOC), sediments, or wedge serpentinites (formed in the mantle wedge), but rather from slab serpentinites (formed within the subducting plate); sediments control the subduction input of Nd, whereas the decoupled Sr-Nd isotopes are most likely due to the excess radiogenic Sr carried by AOC fluids. Our results imply that recycling of serpentinite fluids and AOC fluids are usually coupled in subduction zones, as the arc lavas influenced by subducted serpentinite generally show Sr-Nd isotopes decoupling. The large variation of Sr-Nd-B isotopes observed in a relatively localized area is consistent with a focused migration through the mantle wedge of components from multiple sources.

Beschreibung: This study was funded by the National Natural Science Foundation of China (91958213), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB42020402), the China Postdoctoral Science Foundation (2019M662454), the Shandong Provincial Natural Science Foundation, China (ZR2020QD068 and ZR2020MD068), the International Partnership Program of the Chinese Academy of Sciences (133137KYSB20170003), the Special Fund for the Taishan Scholar Program of Shandong Province (ts201511061), and the China Scholarship Council (201709410550).

Beschreibung: 2021-09-12

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(15), (2021): e2021GL094469, https://doi.org/10.1029/2021GL094469.

Beschreibung: The magnitude of natural oceanic dissolved oxygen (DO) variability remains poorly understood due to the short duration of the observational record. Here we present a high-resolution (4–9 years) reconstruction of the Southern California oxygen minimum zone (OMZ) through the Common Era using redox-sensitive metals. Rapid OMZ intensification on multidecadal timescales reveals greater DO variability than observed in instrumental records. An anomalous interval of intensified OMZ between 1600–1750 CE contradicts the expectation of better-ventilated mid-depth North Pacific during cool climates. Although the influence of low-DO Equatorial Pacific Intermediate Water on the Southern California Margin was likely weaker during this interval, we attribute the observed rapid deoxygenation to reduced North Pacific Intermediate Water (NPIW) ventilation. NPIW ventilation thus appears very sensitive to atmospheric circulation reorganization (e.g., a weakened Siberian High and Aleutian Low). In addition to temperature-induced gas solubility, atmospheric forcing under future anthropogenic influences could amplify OMZ variability.

Beschreibung: The authors are grateful for financial supports from NSF (OCE-1851242), SMAST, and UMass Dartmouth. GG was supported by NSF under grants OCE-1657853 and OCE-1558521.

Beschreibung: 2022-01-16

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 47(22), (2020): e2020GL088692, doi:10.1029/2020GL088692.

Beschreibung: Rapid increases in upper 700‐m Indian Ocean heat content (IOHC) since the 2000s have focused attention on its role during the recent global surface warming hiatus. Here, we use ocean model simulations to assess distinct multidecadal IOHC variations since the 1960s and explore the relative contributions from wind stress and buoyancy forcing regionally and with depth. Multidecadal wind forcing counteracted IOHC increases due to buoyancy forcing from the 1960s to the 1990s. Wind and buoyancy forcing contribute positively since the mid‐2000s, accounting for the drastic IOHC change. Distinct timing and structure of upper ocean temperature changes in the eastern and western Indian Ocean are linked to the pathway how multidecadal wind forcing associated with the Interdecadal Pacific Oscillation is transmitted and affects IOHC through local and remote winds. Progressive shoaling of the equatorial thermocline—of importance for low‐frequency variations in Indian Ocean Dipole occurrence—appears to be dominated by multidecadal variations in wind forcing.

Beschreibung: This work was supported by the Alexander von Humboldt Foundation (CCU and SR), The Investment in Science Fund given primarily by WHOI Trustee and Corporation Members (CCU), James E. and Barbara V. Moltz Fellowship for climate‐related research (CCU), the ARC Centre of Excellence for Climate Extremes (CE170100023; CCU and MHE), ARC DP150101331 (CCU and MHE), and PW was supported through grant IndoArchipel from the Deutsche Forschungsgemeinschaft (DFG) as part of the Special Priority Program (SPP)‐1889”Regional Sea Level Change and Society” (SeaLevel).

Beschreibung: 2021-04-26

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 126(6), (2021): e2020JB021341, https://doi.org/10.1029/2020JB021341.

Beschreibung: Constraining how the physical properties and seismic responses of recently deposited sands change with time is important for understanding earthquake site response, subsurface fluid flow, and early stages of lithification. Currently, however, there is no detailed (cm-scale) assessment of how sand's physical properties and associated seismic velocities evolve over the first two centuries after deposition. Here, we integrate sedimentation rates with seismic velocity and sediment physical properties data to assess how the vadose zone sands at Port Royal Beach, Jamaica, change within 180 years after deposition. We show that compressional and shear wave velocities increase with sediment age, whereas porosity, grain size, sorting, mineralogy, and cementation fraction remain relatively unchanged during the same period. Rock physics models (constrained by the measured physical properties) predict constant seismic velocities at all sites regardless of sediment age, though misfits between modeled and observed velocities increase with sediment age. We explain these misfits by proposing that shallow sands undergo microstructural grain reorganization that leads to a more uniform distribution of grain contact forces with time. Our results imply that beach sands undergo a previously undocumented lithification process that occurs before compaction.

Beschreibung: The Society of Exploration Geophysicists Geoscientists without Borders Grant and the Institute for Earth, Science, and Man at Southern Methodist University partially supported this work.

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Johnson, J. E., Phillips, S. C., Clyde, W. C., Giosan, L., & Torres, M. E. Isolating detrital and diagenetic signals in magnetic susceptibility records from methane-bearing marine sediments. Geochemistry Geophysics Geosystems, 22(9), (2021): e2021GC009867, https://doi.org/10.1029/2021GC009867.

Beschreibung: Volume-dependent magnetic susceptibility (κ) is commonly used for paleoenvironmental reconstructions in both terrestrial and marine sedimentary environments where it reflects a mixed signal between primary deposition and secondary diagenesis. In the marine environment, κ is strongly influenced by the abundance of ferrimagnetic minerals regulated by sediment transport processes. Post-depositional alteration by H2S, however, can dissolve titanomagnetite, releasing reactive Fe that promotes pyritization and subsequently decreases κ. Here, we provide a new approach for isolating the detrital signal in κ and identifying intervals of diagenetic alteration of κ driven by organoclastic sulfate reduction (OSR) and the anaerobic oxidation of methane (AOM) in methane-bearing marine sediments offshore India. Using the correlation of a heavy mineral proxy from X-ray fluorescence data (Zr/Rb) and κ in unaltered sediments, we predict the primary detrital κ signal and identify intervals of decreased κ, which correspond to increased total sulfur content. Our approach is a rapid, high-resolution method that can identify overprinted κ resulting from pyritization of titanomagnetite due to H2S production in marine sediments. In addition, total organic carbon, total sulfur, and authigenic carbonate δ13C measurements indicate that both OSR and AOM can drive the observed κ loss, but AOM drives the greatest decreases in κ. Overall, our approach can enhance paleoenvironmental reconstructions and provide insight into paleo-positions of the sulfate-methane transition zone, past enhancements of OSR or paleo-methane seepage, and the role of detrital iron oxide minerals on the marine sediment sulfur sink, with consequences influencing the development of chemosynthetic biological communities at methane seeps.

Beschreibung: This research was supported by the American Chemical Society-Petroleum Research Fund Award #53006-ND8 and U.S. Department of Energy Grant #DE-FE0010120.

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Goldstein, E. B., Buscombe, D., Lazarus, E. D., Mohanty, S. D., Rafique, S. N., Anarde, K. A., Ashton, A. D., Beuzen, T., Castagno, K. A., Cohn, N., Conlin, M. P., Ellenson, A., Gillen, M., Hovenga, P. A., Over, J.-S. R., Palermo, R., Ratliff, K. M., Reeves, I. R. B., Sanborn, L. H., Straub, J. A., Taylor, L. A., Wallace E. J., Warrick, J., Wernette, P., Williams, H. E. Labeling poststorm coastal imagery for machine learning: measurement of interrater agreement. Earth and Space Science, 8(9), (2021): e2021EA001896, https://doi.org/10.1029/2021EA001896.

Beschreibung: Classifying images using supervised machine learning (ML) relies on labeled training data—classes or text descriptions, for example, associated with each image. Data-driven models are only as good as the data used for training, and this points to the importance of high-quality labeled data for developing a ML model that has predictive skill. Labeling data is typically a time-consuming, manual process. Here, we investigate the process of labeling data, with a specific focus on coastal aerial imagery captured in the wake of hurricanes that affected the Atlantic and Gulf Coasts of the United States. The imagery data set is a rich observational record of storm impacts and coastal change, but the imagery requires labeling to render that information accessible. We created an online interface that served labelers a stream of images and a fixed set of questions. A total of 1,600 images were labeled by at least two or as many as seven coastal scientists. We used the resulting data set to investigate interrater agreement: the extent to which labelers labeled each image similarly. Interrater agreement scores, assessed with percent agreement and Krippendorff's alpha, are higher when the questions posed to labelers are relatively simple, when the labelers are provided with a user manual, and when images are smaller. Experiments in interrater agreement point toward the benefit of multiple labelers for understanding the uncertainty in labeling data for machine learning research.

Beschreibung: The authors gratefully acknowledge support from the U.S. Geological Survey (G20AC00403 to EBG and SDM), NSF (1953412 to EBG and SDM; 1939954 to EBG), Microsoft AI for Earth (to EBG and SDM), The Leverhulme Trust (RPG-2018-282 to EDL and EBG), and an Early Career Research Fellowship from the Gulf Research Program of the National Academies of Sciences, Engineering, and Medicine (to EBG). U.S. Geological Survey researchers (DB, J-SRO, JW, and PW) were supported by the U.S. Geological Survey Coastal and Marine Hazards and Resources Program as part of the response and recovery efforts under congressional appropriations through the Additional Supplemental Appropriations for Disaster Relief Act, 2019 (Public Law 116-20; 133 Stat. 871).

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(8), (2021): e2021GL093127, https://doi.org/10.1029/2021GL093127.

Beschreibung: The seismometer deployed by the InSight lander measured the seismic velocity of the Martian crust. We use a rock physics model to interpret those velocities and constrain hydrogeological properties. The seismic velocity of the upper ∼10 km is too low to be ice-saturated. Hence there is no cryosphere that confines deeper aquifers and possibly no aquifers locally. An increase in seismic velocity at depths of ∼10 km could be explained by a few volume percent of mineral cement (1%–5%) in pore space and may document the past depth of aquifers.

Beschreibung: M. Manga was supported by NASA grant 80NSSC19K0545.

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(18), (2021): e2021GL092621, https://doi.org/10.1029/2021GL092621.

Beschreibung: In the subsurface ocean, O2 depleted because of organic matter remineralization is generally estimated based on apparent oxygen utilization (AOU). However, AOU is an imperfect measure of oxygen utilization because of O2 air-sea disequilibrium at the site of deepwater formation. Recent methodological and instrumental advances have paved the way to further deconvolve the processes driving the O2 signature. Using numerical model simulations of the global ocean, we show that the measurements of the dissolved O2/Ar ratio, which so far have been confined to the ocean surface, can provide improved estimates of oxygen utilization, especially in regions where the disequilibrium at the site of deepwater formation is associated with physical processes. We discuss applications of this new approach and implications for the current tracers relying on O2 such as remineralization ratios, respiratory quotients, and preformed nutrients. Finally, we propose a new composite geochemical tracer, [O2]bio combining dissolved O2/Ar and phosphate concentration. Being insensitive to photosynthesis and respiration, the change in this new tracer reflects gas exchange at the air-sea interface at the sites of deepwater formation.

Beschreibung: Nicolas Cassar was supported by the “Laboratoire d'Excellence” LabexMER (ANR-10-LABX-19) and cofunded by a grant from the French government under the program “Investissements d'Avenir.” Samar Khatiwala was supported by UK NERC grant NE/T009357/1. Ellen Cliff acknowledges support from the Rhodes Trust.

Beschreibung: 2022-03-13

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bretschneider, L., Hathorne, E. C., Bolton, C. T., Gebregiorgis, D., Giosan, L., Gray, E., Huang, H., Holbourn, A., Kuhnt, W., & Frank, M. Enhanced late miocene chemical weathering and altered precipitation patterns in the watersheds of the Bay of Bengal recorded by detrital clay radiogenic isotopes. Paleoceanography and Paleoclimatology, 36(9), (2021): e2021PA004252, https://doi.org/10.1029/2021PA004252.

Beschreibung: The late Miocene was a period of declining CO2 levels and extensive environmental changes, which likely had a large impact on monsoon strength as well as on the weathering and erosion intensity in the South Asian Monsoon domain. To improve our understanding of these feedback systems, detrital clays from the southern Bay of Bengal (International Ocean Discovery Program Site U1443) were analyzed for the radiogenic isotope compositions of Sr, Nd, and Pb to reconstruct changes in sediment provenance and weathering regime related to South Asian Monsoon rainfall from 9 to 5 Ma. The 100 kyr resolution late Miocene to earliest Pliocene record suggests overall low variability in the provenance of clays deposited on the Ninetyeast Ridge. However, at 7.3 Ma, Nd and Pb isotope compositions indicate a switch to an increased relative contribution from the Irrawaddy River (by ∼10%). This shift occurred during the global benthic δ13C decline, and we suggest that global cooling and increasing aridity resulted in an eastward shift of precipitation patterns leading to a more focused erosion of the Indo-Burman Ranges. Sr isotope compositions were decoupled from Nd and Pb isotope signatures and became more radiogenic between 6 and 5 Ma. Grassland expansion generating thick, easily weatherable soils may have led to an environment supporting intense chemical weathering, which is likely responsible for the elevated detrital clay 87Sr/86Sr ratios during this time. This change in Sr isotope signatures may also have contributed to the late Miocene increase of the global seawater Sr isotope composition.

Beschreibung: This research used samples and data provided by the International Ocean Discovery Program and was funded by the German Research Foundation (DFG) (grants HA 5751/6-1 & -2). C. T. Bolton acknowledges funding from the French ANR project iMonsoon (ANR-16-CE01-0004-01) and IODP France. W. Kuhnt acknowledges funding from the DFG (grant Ku649/36-1).

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 35(10), (2021): e2021GB007058, https://doi.org/10.1029/2021GB007058.

Beschreibung: Continental shelves are important sources of iron (Fe) in the land-dominated Arctic Ocean. To understand the export of Fe from the Arctic to Baffin Bay (BB) and the North Atlantic, we studied the alteration of the Fe signature in waters transiting the Canadian Arctic Archipelago (CAA). During its transit through the CAA, inflowing Arctic Waters from the Canada Basin become enriched in Fe as result of strong sediment resuspension and enhanced sediment-water interactions (non-reductive dissolution). These high Fe waters are exported to BB, where approximately 10.7 kt of Fe are delivered yearly from Lancaster Sound. Furthermore, if the two remaining main CAA pathways (Jones Sound and Nares Strait) are included, this shelf environment would be a dominant source term of Fe (dFe + pFe: 26–90 kt y−1) to Baffin Bay. The conservative Fe flux estimate (26 kt y−1) is 1.7–38 times greater than atmospheric inputs, and may be crucial in supporting primary production and nitrogen fixation in BB and beyond.

Beschreibung: This work was supported by the Natural Sciences and Engineering Research Council of Canada (Grant NSERC-CCAR), the Northern Scientific Training Program, and by the University of British Columbia through a Four Year Fellowship to B. Rogalla.

Beschreibung: 2022-03-20

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Durkin, C. A., Buesseler, K. O., Cetinic, I., Estapa, M. L., Kelly, R. P., & Omand, M. A visual tour of carbon export by sinking particles. Global Biogeochemical Cycles, 35(10), (2021): e2021GB006985, https://doi.org/10.1029/2021GB006985.

Beschreibung: To better quantify the ocean's biological carbon pump, we resolved the diversity of sinking particles that transport carbon into the ocean's interior, their contribution to carbon export, and their attenuation with depth. Sinking particles collected in sediment trap gel layers from four distinct ocean ecosystems were imaged, measured, and classified. The size and identity of particles was used to model their contribution to particulate organic carbon (POC) flux. Measured POC fluxes were reasonably predicted by particle images. Nine particle types were identified, and most of the compositional variability was driven by the relative contribution of aggregates, long cylindrical fecal pellets, and salp fecal pellets. While particle composition varied across locations and seasons, the entire range of compositions was measured at a single well-observed location in the subarctic North Pacific over one month, across 500 m of depth. The magnitude of POC flux was not consistently associated with a dominant particle class, but particle classes did influence flux attenuation. Long fecal pellets attenuated most rapidly with depth whereas certain other classes attenuated little or not at all with depth. Small particles (〈100 μm) consistently contributed ∼5% to total POC flux in samples with higher magnitude fluxes. The relative importance of these small particle classes (spherical mini pellets, short oval fecal pellets, and dense detritus) increased in low flux environments (up to 46% of total POC flux). Imaging approaches that resolve large variations in particle composition across ocean basins, depth, and time will help to better parameterize biological carbon pump models.

Beschreibung: This work was supported by an NSF EAGER award to C. A. Durkin (OCE-1703664), M. L. Estapa (OCE-1703422), and M. Omand (OCE-1703336), and also by the NASA EXPORTS program (80NSSC17K0662), a NASA New Investigator award to M. L. Estapa (NNX14AM01G), the Rhode Island Endeavor Program (RIEP), NASA's PACE mission, and the Schmidt Ocean Institute.

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(11), (2021): e2021JC017526, https://doi.org/10.1029/2021JC017526.

Beschreibung: The traditional understanding of the regional circulation in the Northwest Pacific marginal seas is that the Korean Coastal Current flows southward, following the isobaths of 20–50 m. However, an unusual tongue-shaped structure of cold water is observed in satellite SST data in January 2017, indicating a possible offshore spread of cold coastal water into the middle Southern Yellow Sea (SYS). Additional observations, including in situ hydrographic data as well as direct current measurement, also suggest this cross-shelf transport of the Korean Coastal Water in January 2017. Our analysis shows that this flow breaks through the isobaths at ∼37°N, moves southward between 50–75 m, and eventually veers anti-cyclonically at ∼35°N to join the western slope of the SYS. This circulation pattern is further supported by heat budget analysis. Diagnosis of potential vorticity (PV) reveals that the elevated negative PV anomaly imposed by surface wind stress favors this unusual cross-shelf transport. The change of wind pattern, although under a deceasing wind speed condition, plays an important role. This work provides an alternative view of the wintertime circulation pattern and motivates future studies of the variability of the coastal currents over interannual and longer time scales in the SYS.

Beschreibung: his study was supported by the Shandong Provincial Key Research and Development Program (2019JZZY020713, 2019GHY112057), the National Key Research and Development Program (2016YFC1401406, 2016YFA0600900), the National Natural Science Foundation of China (42076010, 42130403), National Fund Committee-Shandong joint fund (U1706215), the Fundamental Research Funds for the Central Universities (2020042010), and Ocean University of China-Woods Hole Oceanographic Institution Cooperative Research Initiative (24887).

Beschreibung: 2022-05-01

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Horner, T. J., Little, S. H., Conway, T. M., Farmer, J. R., Hertzberg, J. E., Janssen, D. J., Lough, A. J. M., McKay, J. L., Tessin, A., Galer, S. J. G., Jaccard, S. L., Lacan, F., Paytan, A., Wuttig, K., & GEOTRACES–PAGES Biological Productivity Working Group Members (2021). Bioactive trace metals and their isotopes as paleoproductivity proxies: an assessment using GEOTRACES-era data. Global Biogeochemical Cycles, 35(11), e2020GB006814. https://doi.org/10.1029/2020GB006814.

Beschreibung: Phytoplankton productivity and export sequester climatically significant quantities of atmospheric carbon dioxide as particulate organic carbon through a suite of processes termed the biological pump. Constraining how the biological pump operated in the past is important for understanding past atmospheric carbon dioxide concentrations and Earth's climate history. However, reconstructing the history of the biological pump requires proxies. Due to their intimate association with biological processes, several bioactive trace metals and their isotopes are potential proxies for past phytoplankton productivity, including iron, zinc, copper, cadmium, molybdenum, barium, nickel, chromium, and silver. Here, we review the oceanic distributions, driving processes, and depositional archives for these nine metals and their isotopes based on GEOTRACES-era datasets. We offer an assessment of the overall maturity of each isotope system to serve as a proxy for diagnosing aspects of past ocean productivity and identify priorities for future research. This assessment reveals that cadmium, barium, nickel, and chromium isotopes offer the most promise as tracers of paleoproductivity, whereas iron, zinc, copper, and molybdenum do not. Too little is known about silver to make a confident determination. Intriguingly, the trace metals that are least sensitive to productivity may be used to track other aspects of ocean chemistry, such as nutrient sources, particle scavenging, organic complexation, and ocean redox state. These complementary sensitivities suggest new opportunities for combining perspectives from multiple proxies that will ultimately enable painting a more complete picture of marine paleoproductivity, biogeochemical cycles, and Earth's climate history.

Beschreibung: T. J. Horner acknowledges support from NSF; S. H. Little from the UK Natural Environment Research Council (NE/P018181/1); T. M. Conway from the University of South Florida; and, J. R. Farmer from the Max Planck Society, the Tuttle Fund of the Department of Geosciences of Princeton University, the Grand Challenges Program of the Princeton Environmental Institute, and the Andlinger Center for Energy and the Environment of Princeton University.

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Brinkmann, I., Ni, S., Schweizer, M., Oldham, V. E., Quintana Krupinski, N. B., Medjoubi, K., Somogyi, A., Whitehouse, M. J., Hansel, C. M., Barras, C., Bernhard, J. M., & Filipsson, H. L. Foraminiferal Mn/Ca as bottom-water hypoxia proxy: an assessment of Nonionella stella in the Santa Barbara Basin, USA. Paleoceanography and Paleoclimatology, 36(11), (2021): e2020PA004167, https://doi.org/10.1029/2020PA004167.

Beschreibung: Hypoxia is of increasing concern in marine areas, calling for a better understanding of mechanisms leading to decreasing dissolved oxygen concentrations ([O2]). Much can be learned about the processes and implications of deoxygenation for marine ecosystems using proxy records from low-oxygen sites, provided proxies, such as the manganese (Mn) to calcium (Ca) ratio in benthic foraminiferal calcite, are available and well calibrated. Here we report a modern geochemical data set from three hypoxic sites within the Santa Barbara Basin (SBB), USA, where we study the response of Mn/Caforam in the benthic foraminifer Nonionella stella to variations in sedimentary redox conditions (Mn, Fe) and bottom-water dissolved [O2]. We combine molecular species identification by small subunit rDNA sequencing with morphological characterization and assign the SBB N. stella used here to a new phylotype (T6). Synchrotron-based scanning X-ray fluorescence (XRF) imaging and Secondary Ion Mass Spectrometry (SIMS) show low Mn incorporation (partition coefficient DMn 〈 0.05) and limited proxy sensitivity of N. stella, at least within the range of dissolved [O2] (2.7–9.6 μmol/l) and Mnpore-water gradients (2.12–21.59 μmol/l). Notably, even though intra- and interspecimen Mn/Ca variability (33% and 58%, respectively) was only partially controlled by the environment, Mn/Caforam significantly correlated with both pore-water Mn and bottom-water [O2]. However, the prevalent suboxic bottom-water conditions and limited dissolved [O2] range complicate the interpretation of trace-elemental trends. Additional work involving other oxygenation proxies and samples from a wider oxygen gradient should be pursued to further develop foraminiferal Mn/Ca as an indicator for hypoxic conditions.

Beschreibung: We acknowledge funding from the Swedish Research Council VR (grant numbers 2017-04190 and 2017-00671), the Crafoord Foundation, and the Royal Physiographic Society in Lund, Sweden. Shiptime provided by US NSF IOS 1557430. We acknowledge SOLEIL for provision of synchrotron radiation facilities and the beamline NANOSCOPIUM (proposal number 20181115). The synchrotron-based experiments were supported by CALIPSOplus under the EU Framework Programme for Research and Innovation HORIZON 2020 (grant agreement 730872). The SIMS analyses were jointly supported by the Swedish Museum of Natural History and Swedish Research Council. This is NordSIMS contribution No. 694. J. M. Bernhard and C. M. Hansel also acknowledge funding from the US National Science Foundation (IOS 1557430).

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hawco, N. J., Barone, B., Church, M. J., Babcock-Adams, L., Repeta, D. J., Wear, E. K., Foreman, R. K., Bjorkman, K. M., Bent, S., Van Mooy, B. A. S., Sheyn, U., DeLong, E. F., Acker, M., Kelly, R. L., Nelson, A., Ranieri, J., Clemente, T. M., Karl, D. M., & John, S. G. Iron depletion in the deep chlorophyll maximum: mesoscale eddies as natural iron fertilization experiments. Global Biogeochemical Cycles, 35(12), (2021): e2021GB007112, https://doi.org/10.1029/2021GB007112.

Beschreibung: In stratified oligotrophic waters, phytoplankton communities forming the deep chlorophyll maximum (DCM) are isolated from atmospheric iron sources above and remineralized iron sources below. Reduced supply leads to a minimum in dissolved iron (dFe) near 100 m, but it is unclear if iron limits growth at the DCM. Here, we propose that natural iron addition events occur regularly with the passage of mesoscale eddies, which alter the supply of dFe and other nutrients relative to the availability of light, and can be used to test for iron limitation at the DCM. This framework is applied to two eddies sampled in the North Pacific Subtropical Gyre. Observations in an anticyclonic eddy center indicated downwelling of iron-rich surface waters, leading to increased dFe at the DCM but no increase in productivity. In contrast, uplift of isopycnals within a cyclonic eddy center increased supply of both nitrate and dFe to the DCM, and led to dominance of picoeukaryotic phytoplankton. Iron addition experiments did not increase productivity in either eddy, but significant enhancement of leucine incorporation in the light was observed in the cyclonic eddy, a potential indicator of iron stress among Prochlorococcus. Rapid cycling of siderophores and low dFe:nitrate uptake ratios also indicate that a portion of the microbial community was stressed by low iron. However, near-complete nitrate drawdown in this eddy, which represents an extreme case in nutrient supply compared to nearby Hawaii Ocean Time-series observations, suggests that recycling of dFe in oligotrophic ecosystems is sufficient to avoid iron limitation in the DCM under typical conditions.

Beschreibung: The expedition and analyses were supported by the Simons Foundation SCOPE Grant 329108 to S. G. John, M. J. Church, D. J. Repeta, B. Van Mooy, E. F. DeLong, and D. M. Karl. N. J. Hawco was supported by a Simons Foundation Marine Microbial Ecology and Evolution postdoctoral fellowship (602538) and Simons Foundation grant 823167.

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 126(7), (2021): e2020JG005977, https://doi.org/10.1029/2020JG005977.

Beschreibung: Increasing Arctic temperatures are thawing permafrost soils and liberating ancient organic matter, but the fate of this material remains unclear. Thawing of permafrost releases dissolved organic matter (DOM) into fluvial networks. Unfortunately, tracking this material in Arctic rivers such as the Kolyma River in Siberia has proven challenging due to its high biodegradability. Here, we evaluate late summer abruptly thawed yedoma permafrost dissolved organic carbon (DOC) inputs from Duvannyi Yar. We implemented ultrahigh-resolution mass spectrometry alongside ramped pyrolysis oxidation (RPO) and isotopic analyses. These approaches offer insight into DOM chemical composition and DOC radiocarbon values of thermochemical components for a permafrost thaw stream, the Kolyma River, and their biodegraded counterparts (n = 4). The highly aliphatic molecular formula found in undegraded permafrost DOM contrasted with the comparatively aliphatic-poor formula of Kolyma River DOM, represented by an 8.9% and 2.6% relative abundance, respectively, suggesting minimal inputs of undegraded permafrost DOM in the river. RPO radiocarbon fractions of Kolyma River DOC exhibited no “hidden” aged component indicative of permafrost influence. Thermostability analyses suggested that there was limited biodegraded permafrost DOC in the Kolyma River, in part determined by the formation of high-activation energy (thermally stable) biodegradation components in permafrost DOM that were lacking in the Kolyma River. A mixing model based on thermostability and radiocarbon allowed us to estimate a maximum input of between 0.8% and 7.7% of this Pleistocene-aged permafrost to the Kolyma River DOC. Ultimately, our findings highlight that export of modern terrestrial DOC currently overwhelms any permafrost DOC inputs in the Kolyma River.

Beschreibung: This work was funded by NSF grants ANT-1203885 and PLR-1500169 to R.G.M.S. The work was also supported by the National Science Foundation Division of Chemistry through DMR-1644779 and the State of Florida.

Beschreibung: 2022-01-09

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 22(4), (2021): e2020GC009481, https://doi.org/10.1029/2020GC009481.

Beschreibung: The impact of submarine hydrothermal systems on organic carbon in the ocean—one of the largest fixed carbon reservoirs on Earth—could be profound. Yet, different vent sites show diverse fluid chemical compositions and the subsequent biological responses. Observations from various vent sites are to evaluate hydrothermal systems' impact on the ocean carbon cycle. A response cruise in May 2009 to an on-going submarine eruption at West Mata Volcano, northeast Lau Basin, provided an opportunity to quantify the organic matter production in a back-arc spreading hydrothermal system. Hydrothermal vent fluids contained elevated dissolved organic carbon, particulate organic carbon (POC), and particulate nitrogen (PN) relative to background seawater. The δ13C-POC values for suspended particles in the diffuse vent fluids (−15.5‰ and −12.3‰) are distinct from those in background seawater (−23 ± 1‰), indicative of unique carbon synthesis pathways of the vent microbes from the seawater counterparts. The first dissolved organic nitrogen concentrations reported for diffuse vents were similar to or higher than those for background seawater. Enhanced nitrogen fixation and denitrification removed 37%–89% of the total dissolved nitrogen in the recharging background seawater in the hydrothermal vent flow paths. The hydrothermal plume samples were enriched in POC and PN, indicating enhanced biological production. The total “dark” organic carbon production within the plume matches the thermodynamic prediction based on available reducing chemical substances supplied to the plume. This research combines the measured organic carbon contents with thermodynamic modeled results and demonstrates the importance of hydrothermal activities on the water column carbon production in the deep ocean.

Beschreibung: This project was supported by N.S.F. (OCE0929881, J. P. Cowen and K. H. Rubin), the NOAA PMEL VENTS (now Earth-Ocean Interactions) Program and the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement No. NA10OAR4320148, and the UH NASA Astrobiology Institute. The Ministry of Science and Technology of Taiwan award (MOST 107-2611-M-002-002, and MOST 108-2611-M-002-006 to H.-T. Lin). Ministry of Education (M.O.E.) Republic of China (Taiwan) 109L892601 to H.-T. Lin. SOEST contributions no. 11285, C-DEBI contribution no. 563. PMEL contribution no. 3996, JISAO contribution 2183.

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Water Resources Research 57(4), (2021): e2020WR028430, https://doi.org/10.1029/2020WR028430.

Beschreibung: We use yearlong vertical temperature profile time-series (seven thermistors at evenly spaced depth intervals from 10 to 70 cm) from five sites in and around the Deep Hole thermal area, southeast of Stevenson Island, Yellowstone Lake, to investigate heat and mass fluxes across the lake floor. The records demonstrate that thermal gradients in surficial sediments are modulated by a rich spectrum of bottom water temperature variations generated by hydrodynamic processes, and that sites inside the thermal area also respond to hydrothermal variations. We develop and implement a new method for estimating the sediment effective thermal diffusivity and pore fluid vertical flow rate that exploits the full spectrum of observed temperature variations to generate the parameter estimates, uncertainties, and metrics to assess statistical significance. Sediments at sites outside thermal areas have gradients of ∼7.5°C/m, in situ thermal diffusivities of ∼1.6 × 10−7 m2/s consistent with highly porous (80–90%) siliceous sediments, and experience hypolentic flow in the upper ∼20 cm. Sites inside the Deep Hole thermal area exhibit considerable spatial and temporal variability, with gradients of 1–32°C/m, and higher thermal diffusivities of ∼2–12 × 10−7 m2/s, consistent with hydrothermal alteration of biogenic silica to clays, quartz, and pyrite. Upward pore fluid flow at these sites is observed across multiple depth intervals, with maximum values of ∼3 cm/day. The observed spatial and temporal variability within the thermal area is consistent with upward finger flow combined with short wavelength convection within the porous sediments above a steam reservoir.

Beschreibung: This research was supported by the National Science Foundation Grants EAR-1516361 to Robert A. Sohn and EAR-1515283 to Robert N. Harris, and by the Independent Research and Development Program at the Woods Hole Oceanographic Institution (Robert A. Sohn). All work in Yellowstone National Park was completed under an authorized Yellowstone research permit (YELL-2018-SCI-7018).

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(5), (2021): e2020JC017091, https://doi.org/10.1029/2020JC017091.

Beschreibung: A region of exceptionally high macrofaunal benthic biomass exists in Barrow Canyon, implying a carbon export process that is locally concentrated. Here we offer an explanation for this benthic “hotspot” using shipboard data together with a set of dynamical equations. Repeat occupations of the Distributed Biological Observatory transect in Barrow Canyon reveal that when the northward flow is strong and the density front in the canyon is sharp, plumes of fluorescence and oxygen extend from the pycnocline to the seafloor in the vicinity of the hotspot. By solving the quasi-geostrophic omega equation with an analytical flow field fashioned after the observations, we diagnose the vertical velocity in the canyon. This reveals that, as the along stream flow converges into the canyon, it drives a secondary circulation cell with strong downwelling on the cyclonic side of the northward flow. The downwelling quickly advects material from the pycnocline to the seafloor in a vertical plume analogous to those seen in the observations. The plume occurs only when the phytoplankton reside in the pycnocline, since the near-surface vertical velocity is weak, also consistent with the observations. Using a wind-based proxy to represent the strength of the northward flow and hence the pumping, in conjunction with a satellite-derived phytoplankton source function, we construct a time series of carbon supply to the bottom of Barrow Canyon.

Beschreibung: This work was funded by National Science Foundation grants PLR-1504333 and OPP-1733564 (Robert S. Pickart, Frank Bahr), OPP-1822334 (Michael A. Spall), PLR-1304563 (Kevin R. Arrigo), OPP-1204082 and OPP-1702456 (Jacqueline M. Grebmeier); National Oceanic and Atmospheric Administration grants NA14OAR4320158 and NA19OAR4320074 (Robert S. Pickart, Peigen Lin, Leah T. McRaven), CINAR-22309.02 (Jacqueline M. Grebmeier).

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(5), (2021): e2020JC016922, https://doi.org/10.1029/2020JC016922.

Beschreibung: Mesoscale eddies redistribute heat, salt, and nutrients in oceans. The South Atlantic Ocean (SA) is a basin that has active mesoscale eddies for which characteristics of the three-dimensional structure and its leading mechanism are complex but have yet been studied sufficiently. Here based on ocean reanalysis datasets we use a composite analysis approach to analyze the mixed layer anomalous heat budget and find distinct two types of spatial patterns: dipole and monopole – mainly present in the northern and southern regions of the SA, respectively. The dipole can be attributed to ocean horizontal advection, especially to the combined effect of eddy anomalous meridional current and meridional gradient of mean temperature. The monopole, on the other hand, is associated with complex contributions, for which zonal and meridional advections play opposite roles as cooling or heating around the eddies. At the eddy center, the vertical advection is non-negligible, especially the mean upwelling and vertical temperature gradient playing a vital role in the formation of a monopole. The analysis of eddy meridional heat transport shows that the stirring component is dominant, and poleward in most areas, especially at high latitudes. Such analysis on the leading mechanism of eddy-induced temperature anomaly could help improve our understanding on meso- and small-scale air-sea interactions and eddy-induced heat transport in the SA.

Beschreibung: This work is supported by the National Key R&D Program of China (2017YFC1404100 and 2017YFC1404104) and the National Natural Science Foundation of China (Grant No. 41775100, 41830964) as well as Shandong Province’s “Taishan” Scientist Program and Qingdao “Creative and Initiative” frontier Scientist Program. This research is also supported by the Center for High Performance Computing and System Simulation, Pilot National Laboratory for Marine Science and Technology (Qingdao).

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(15), (2021): e2021GL093675, https://doi.org/10.1029/2021GL093675.

Beschreibung: Tide gauges provide a rich, long-term, record of the amplitude and spatiotemporal structure of interannual to multidecadal coastal sea-level variability, including that related to North American east coast sea level “hotspots.” Here, using wavelet analyses, we find evidence for multidecadal epochs of enhanced decadal (10–15 year period) sea-level variability at almost all long ( 70 years) east coast tide gauge records. Within this frequency band, large-scale spatial covariance is time-dependent; notably, coastal sectors north and south of Cape Hatteras exhibit multidecadal epochs of coherence ( 1960–1990) and incoherence ( 1990-present). Results suggest that previous interpretations of along coast covariance, and its underlying physical drivers, are clouded by time-dependence and frequency-dependence. Although further work is required to clarify the mechanisms driving sea-level variability in this frequency band, we highlight potential associations with the North Atlantic sea surface temperature tripole and Atlantic Multidecadal Variability.

Beschreibung: Christopher M. Little acknowledges funding support from NSF Grant OCE-1805029. CGP and RMP were funded through NASA Sea Level Change Team (CGP: Grant 80NSSC20K1241).

Beschreibung: 2022-01-15

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 126(4), (2021): e2020JB019395, https://doi.org/10.1029/2020JB019395.

Beschreibung: Improved understanding of the impact of crystal mush rheology on the response of magma chambers to magmatic events is critical for better understanding crustal igneous systems with abundant crystals. In this study, we extend an earlier model by Liao et al. (2018); https://doi.org/10.1029/2018jb015985 which considers the mechanical response of a magma chamber with poroelastic crystal mush, by including poroviscoelastic rheology of crystal mush. We find that the coexistence of the two mechanisms of poroelastic diffusion and viscoelastic relaxation causes the magma chamber to react to a magma injection event with more complex time-dependent behaviors. Specifically, we find that the system’s short-term evolution is dominated by the poroelastic diffusion process, while its long-term evolution is dominated by the viscoelastic relaxation process. We identify two post-injection timescales that represent these two stages and examine their relation to the material properties of the system. We find that better constraints on the poroelastic diffusion time are more important for the potential interpretation of surface deformation using the model.

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hudak, M. R., Bindeman, I. N., Loewen, M. W., & Giachetti, T. Syn-eruptive hydration of volcanic ash records pyroclast-water interaction in explosive eruptions. Geophysical Research Letters, 48(23), (2021): e2021GL094141, https://doi.org/10.1029/2021GL094141.

Beschreibung: Magma-water interaction can dramatically influence the explosivity of volcanic eruptions. However, syn- and post-eruptive diffusion of external (non-magmatic) water into volcanic glass remains poorly constrained and may bias interpretation of water in juvenile products. Hydrogen isotopes in ash from the 2009 eruption of Redoubt Volcano, Alaska, record syn-eruptive hydration by vaporized glacial meltwater. Both ash aggregation and hydration occurred in the wettest regions of the plume, which resulted in the removal and deposition of the most hydrated ash in proximal areas 〈50 km from the vent. Diffusion models show that the high temperatures of pyroclast-water interactions (〉400°C) are more important than the cooling rate in facilitating hydration. These observations suggest that syn-eruptive glass hydration occurred where meltwater was entrained at high temperature, in the plume margins near the vent. Ash in the drier plume interior remained insulated from entrained meltwater until it cooled sufficiently to avoid significant hydration.

Beschreibung: This work was supported by a Geological Society of America Bruce L. "Biff" Reed Scholarship Award and NSF Grant EAR 1822977.

Beschreibung: 2022-05-15

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(12), (2021): e2021JC017860, https://doi.org/10.1029/2021JC017860.

Beschreibung: An appropriate proxy could help to better understand dissolved oxygen variations in the past, helping to predict potential outcomes of future environmental changes. In the Changjiang Estuary (China), the foraminifer Cribrononion subincertum (C. subincertum) shows a distinct population maximum in the topmost sediment, an indication of an epifaunal species. Therefore, the geochemical composition of C. subincertum tests could record changes in the region’s bottom water chemistry. Our results showed that Mn/Ca ratios in tests of living (Rose-Bengal stained) C. subincertum analyzed by LA-ICP-MS were responsive to variations of bottom water dissolved oxygen concentrations, with average foraminiferal Mn/Ca ratios three times higher during low-oxygen period than in winter. In the uppermost centimeters of sediment, wider ranges of foraminiferal Mn/Ca occurred in summer compared to winter ranges. Our results imply that this epifaunal benthic foraminiferal species could serve as a useful benthic monitor with the Mn/Ca ratios representing a reliable proxy of hypoxia in the past.

Beschreibung: This study was financially supported by the Natural Science Foundation of China (NSFC Grants 41876075, 42130410, and 41620104001), and Fundamental Research Funds for the Central Universities (201841007, 201962003, and 201961012). JMB acknowledges the Investment in Science Fund at WHOI, which supported her participation in this project.

Beschreibung: 2022-06-17

Beschreibung: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 36(1), (2022): e2021GB007113, https://doi.org/10.1029/2021GB007113.

Beschreibung: Stordalen Mire is a peatland in the discontinuous permafrost zone in arctic Sweden that exhibits a habitat gradient from permafrost palsa, to Sphagnum bog underlain by permafrost, to Eriophorum-dominated fully thawed fen. We used three independent approaches to evaluate the annual, multi-decadal, and millennial apparent carbon accumulation rates (aCAR) across this gradient: seven years of direct semi-continuous measurement of CO2 and CH4 exchange, and 21 core profiles for 210Pb and 14C peat dating. Year-round chamber measurements indicated net carbon balance of −13 ± 8, −49 ± 15, and −91 ± 43 g C m−2 y−1 for the years 2012–2018 in palsa, bog, and fen, respectively. Methane emission offset 2%, 7%, and 17% of the CO2 uptake rate across this gradient. Recent aCAR indicates higher C accumulation rates in surface peats in the palsa and bog compared to current CO2 fluxes, but these assessments are more similar in the fen. aCAR increased from low millennial-scale levels (17–29 g C m−2 y−1) to moderate aCAR of the past century (72–81 g C m−2 y−1) to higher recent aCAR of 90–147 g C m−2 y−1. Recent permafrost collapse, greater inundation and vegetation response has made the landscape a stronger CO2 sink, but this CO2 sink is increasingly offset by rising CH4 emissions, dominated by modern carbon as determined by 14C. The higher CH4 emissions result in higher net CO2-equivalent emissions, indicating that radiative forcing of this mire and similar permafrost ecosystems will exert a warming influence on future climate.

Beschreibung: We would like to acknowledge the following funding in support of this project: Swedish Research Council (Vetenskapsrådet, VR) grants (NT 2007-4547 and NT 2013-5562 to P. Crill), U.S. Department of Energy grants (DE-SC0004632 and DE-SC0010580 to V. Rich and S. Saleska), and U.S. National Science Foundation MacroSystems Biology grant (NSF EF #1241037, PI Varner). This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under the Genomic Science program. We also acknowledge funding from the National Science Foundation for the EMERGE Biology Integration Institute, NSF Award #2022070.

Beschreibung: 2022-07-03

Beschreibung: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(1), (2022): e2021JC017424, https://doi.org/10.1029/2021JC017424.

Beschreibung: By compiling boreal summer (June to October) CO2 measurements from 1989 to 2019 on the Bering and eastern Chukchi Sea shelves, we find that the study areas act as a CO2 sink except when impacted by river runoff and wind-driven upwelling. The CO2 system in this area is seasonally dominated by the biological pump especially in the northern Bering Sea and near Hanna Shoal, while wind-driven upwelling of CO2-rich bottom water can cause episodic outgassing. Seasonal surface ΔfCO2 (oceanic fCO2 – air fCO2) is dominantly driven by temperature only during periods of weak CO2 outgassing in shallow nearshore areas. However, after comparing the mean summer ΔfCO2 during the periods of 1989–2013 and 2014–2019, we suggest that temperature does drive long-term, multi-decadal patterns in ΔfCO2. In the northern Chukchi Sea, rapid warming concurrent with reduced seasonal sea-ice persistence caused the regional summer CO2 sink to decrease. By contrast, increasing primary productivity caused the regional summer CO2 sink on the Bering Sea shelf to increase over time. While additional time series are needed to confirm the seasonal and annual trajectory of CO2 changes and ocean acidification in these dynamic and spatially complex ecosystems, this study provides a meaningful mechanistic analysis of recent changes in inorganic carbonate chemistry. As high-resolution time series of inorganic carbonate parameters lengthen and short-term variations are better constrained in the coming decades, we will have stronger confidence in assessing the mechanisms contributing to long-term changes in the source/sink status of regional sub-Arctic seas.

Beschreibung: We gratefully acknowledge the support of the funding agencies that supported this analysis, including the New Sustained Observations for Arctic Research project and the DBO-NCIS project (NA14OAR4320158, NA19OAR4320074) from the NOAA Arctic Research Program.

Beschreibung: 2022-06-17

Beschreibung: © The Author(s), [year]. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Barreyre, T., Parnell‐Turner, R., Wu, J., & Fornari, D. Tracking crustal permeability and hydrothermal response during seafloor eruptions at the East Pacific Rise, 9°50’N. Geophysical Research Letters, 49(3), (2022): e2021GL095459, https://doi.org/10.1029/2021gl095459.

Beschreibung: Permeability controls energy and matter fluxes in deep-sea hydrothermal systems fueling a 'deep biosphere' of microorganisms. Here, we indirectly measure changes in sub-seafloor crustal permeability, based on the tidal response of high-temperature hydrothermal vents at the East Pacific Rise 9°50’N preceding the last phase of volcanic eruptions during 2005–2006. Ten months before the last phase of the eruptions, permeability decreased, first rapidly, and then steadily as the stress built up, until hydrothermal flow stopped altogether ∼2 weeks prior to the January 2006 eruption phase. This trend was interrupted by abrupt permeability increases, attributable to dike injection during last phase of the eruptions, which released crustal stress, allowing hydrothermal flow to resume. These observations and models suggest that abrupt changes in crustal permeability caused by magmatic intrusion and volcanic eruption can control first-order hydrothermal circulation processes. This methodology has the potential to aid eruption forecasting along the global mid-ocean ridge network.

Beschreibung: This research is funded by National Science Foundation (NSF) grants to D. J. Fornari and T. Barreyre (OCE-1949485), and to R. Parnell-Turner (OCE-1948936). T. Barreyre was supported by the University of Bergen, Norway.

Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Fan, S., Cross, A. J., Prior, D. J., Goldsby, D. L., Hager, T. F., Negrini, M., & Qi, C. Crystallographic preferred orientation (CPO) development governs strain weakening in ice: insights from high-temperature deformation experiments. Journal of Geophysical Research: Solid Earth, 126(12), (2021): e2021JB023173, https://doi.org/10.1029/2021JB023173.

Beschreibung: Strain weakening leads to the formation of high-strain shear zones and strongly influences terrestrial ice discharge. In glacial flow models, strain weakening is assumed to arise from the alignment of weak basal planes—the development of a crystallographic preferred orientation, CPO—during flow. However, in experiments, ice strain weakening also coincides with grain size reduction, which has been invoked as a weakening mechanism in other minerals. To interrogate the relative contributions of CPO development and grain size reduction toward ice strain weakening, we deformed initially isotropic polycrystalline ice samples to progressively higher strains between −4 and −30°C. Microstructural measurements were subsequently combined with flow laws to separately model the mechanical response expected to arise from CPO development and grain size reduction. Magnitudes of strain weakening predicted by the constitutive flow laws were then compared with the experimental measurements. Flow laws that only consider grain size do not predict weakening with strain despite grain size reduction. In contrast, flow laws solely considering CPO effects can reproduce the measured strain weakening. Thus, it is reasonable to assume that strain weakening in ice is dominated by CPO development, at least under high temperature (Th ≥ 0.9) and high stress (〉1 MPa), like those in our experiments. We speculate that at high homologous temperatures (Th ≥ 0.9), CPO development will also govern the strain weakening behavior of other viscously anisotropic minerals, like olivine and quartz. Overall, we emphasize that geodynamic and glaciological models should incorporate CPOs to account for strain weakening, especially at high homologous temperatures.

Beschreibung: This work was supported by a NASA fund (grant no. NNX15AM69G) to David L. Goldsby and two Marsden Funds of the Royal Society of New Zealand (grant nos. UOO1116, UOO052) to David J. Prior. Sheng Fan was supported by the University of Otago doctoral scholarship, the Antarctica New Zealand doctoral scholarship, a research grant from New Zealand Ministry of Business, Innovation and Employment through the Antarctic Science Platform (ANTA1801) (grant no. ASP-023-03), and a New Zealand Antarctic Research Institute (NZARI) Early Career Researcher Seed Grant (grant no. NZARI 2020-1-5).

Beschreibung: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Slater, D., Carroll, D., Oliver, H., Hopwood, M., Straneo, F., Wood, M., Willis, J., & Morlighem, M. Characteristic depths, fluxes and timescales for Greenland’s tidewater glacier fjords from subglacial discharge‐driven upwelling during summer. Geophysical Research Letters, 49(10),(2022): e2021GL097081, https://doi.org/10.1029/2021gl097081.

Beschreibung: Greenland's glacial fjords are a key bottleneck in the earth system, regulating exchange of heat, freshwater and nutrients between the ice sheet and ocean and hosting societally important fisheries. We combine recent bathymetric, atmospheric, and oceanographic data with a buoyant plume model to show that summer subglacial discharge from 136 tidewater glaciers, amounting to 0.02 Sv of freshwater, drives 0.6–1.6 Sv of upwelling. Bathymetric analysis suggests that this is sufficient to renew most major fjords within a single summer, and that these fjords provide a path to the continental shelf that is deeper than 200 m for two-thirds of the glaciers. Our study provides a first pan-Greenland inventory of tidewater glacier fjords and quantifies regional and ice sheet-wide upwelling fluxes. This analysis provides important context for site-specific studies and is a step toward implementing fjord-scale heat, freshwater and nutrient fluxes in large-scale ice sheet and climate models.

Beschreibung: DAS acknowledges support from NERC Independent Research Fellowship NE/T011920/1. DAS and FS acknowledge support from NSF award 2020547. HO acknowledges support from a WHOI Postdoctoral Scholar award. MW and JKW performed this work at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Beschreibung: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Planets 125(10),(2020): e2020JE006394, doi:10.1029/2020JE006394.

Beschreibung: Compositional heterogeneities within Europa's ice shell likely impact the dynamics and habitability of the ice and subsurface ocean, but the total inventory and distribution of impurities within the shell are unknown. In sea ice on Earth, the thermochemical environment at the ice‐ocean interface governs impurity entrainment into the ice. Here, we simulate Europa's ice‐ocean interface and bound the impurity load (1.053–14.72 g/kg [parts per thousand weight percent, or ppt] bulk ice shell salinity) and bulk salinity profile of the ice shell. We derive constitutive equations that predict ice composition as a function of the ice shell thermal gradient and ocean composition. We show that evolving solidification rates of the ocean and hydrologic features within the shell produce compositional variations (ice bulk salinities of 5–50% of the ocean salinity) that can affect the material properties of the ice. As the shell thickens, less salt is entrained at the ice‐ocean interface, which implies Europa's ice shell is compositionally homogeneous below ~1 km. Conversely, the solidification of water filled fractures or lenses introduces substantial compositional variations within the ice shell, creating gradients in mechanical and thermal properties within the ice shell that could help initiate and sustain geological activity. Our results suggest that ocean materials entrained within Europa's ice shell affect the formation of geologic terrain and that these structures could be confirmed by planned spacecraft observations.

Beschreibung: This study was supported by the NASA Earth and Space Science Fellowship, grants NNX16AP43H S01 and NNX16AP43H S002. Britney Schmidt was additionally supported by the Europa Clipper Mission. Resources supporting this work were provided by the NASA High‐End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center.

Beschreibung: 2021-03-20

Beschreibung: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Warner, J. C., Geyer, W. R., Ralston, D. K., & Kalra, T. Using tracer variance decay to quantify variability of salinity mixing in the Hudson River Estuary. Journal of Geophysical Research: Oceans, 125(12), (2020): e2020JC016096, https://doi.org/10.1029/2020JC016096.

Beschreibung: The salinity structure in an estuary is controlled by time‐dependent mixing processes. However, the locations and temporal variability of where significant mixing occurs is not well‐understood. Here we utilize a tracer variance approach to demonstrate the spatial and temporal structure of salinity mixing in the Hudson River Estuary. We run a 4‐month hydrodynamic simulation of the tides, currents, and salinity that captures the spring‐neap tidal variability as well as wind‐driven and freshwater flow events. On a spring‐neap time scale, salinity variance dissipation (mixing) occurs predominantly during the transition from neap to spring tides. On a tidal time scale, 60% of the salinity variance dissipation occurs during ebb tides and 40% during flood tides. Spatially, mixing during ebbs occurs primarily where lateral bottom salinity fronts intersect the bed at the transition from the main channel to adjacent shoals. During ebbs, these lateral fronts form seaward of constrictions located at multiple locations along the estuary. During floods, mixing is generated by a shear layer elevated in the water column at the top of the mixed bottom boundary layer, where variations in the along channel density gradients locally enhance the baroclinic pressure gradient leading to stronger vertical shear and more mixing. For both ebb and flood, the mixing occurs at the location of overlap of strong vertical stratification and eddy diffusivity, not at the maximum of either of those quantities. This understanding lends a new insight to the spatial and time dependence of the estuarine salinity structure.

Beschreibung: This study was funded through the Coastal Model Applications and Field Measurements Project and the Cross‐shore and Inlets Project, US Geological Survey Coastal Marine Hazards and Resources Program. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government.

Beschreibung: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Haumann, F. A., Moorman, R., Riser, S. C., Smedsrud, L. H., Maksym, T., Wong, A. P. S., Wilson, E. A., Drucker, R., Talley, L. D., Johnson, K. S., Key, R. M., & Sarmiento, J. L. Supercooled Southern Ocean waters. Geophysical Research Letters, 47(20), (2020): e2020GL090242, doi:10.1029/2020GL090242.

Beschreibung: In cold polar waters, temperatures sometimes drop below the freezing point, a process referred to as supercooling. However, observational challenges in polar regions limit our understanding of the spatial and temporal extent of this phenomenon. We here provide observational evidence that supercooled waters are much more widespread in the seasonally ice‐covered Southern Ocean than previously reported. In 5.8% of all analyzed hydrographic profiles south of 55°S, we find temperatures below the surface freezing point (“potential” supercooling), and half of these have temperatures below the local freezing point (“in situ” supercooling). Their occurrence doubles when neglecting measurement uncertainties. We attribute deep coastal‐ocean supercooling to melting of Antarctic ice shelves and surface‐induced supercooling in the seasonal sea‐ice region to wintertime sea‐ice formation. The latter supercooling type can extend down to the permanent pycnocline due to convective sinking plumes—an important mechanism for vertical tracer transport and water‐mass structure in the polar ocean.

Beschreibung: F. A. H. was supported by the Swiss National Science Foundation (SNSF; Schweizerischer Nationalfonds zur Förderung der wissenschaftlichen Forschung) grant numbers P2EZP2_175162 and P400P2_186681. This work was supported by the National Science Foundation (NSF) Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) Project under the NSF Award PLR‐1425989. R. M. would like to thank the National Oceanic and Atmospheric Administration (NOAA) GFDL for mentorship and computational support. S. R. was also supported by the U.S. Argo grant and NOAA grant NA15OAR4320063 to the University of Washington. L. H. S. thanks the Fulbright Foundation for the U.S.‐Norway Arctic Chair grant. We are deeply thankful to the large number of scientists, technicians, and funding agencies contributing to these databases, being responsible for the collection and quality control of the high‐quality data that form the basis of this work. We thank Josh Plant for his initial notification on very low temperatures observed in some of the float profiles. We would also like to thank the students, teachers, and schools who are participating in the SOCCOM Adopt‐a‐Float program. Four of the floats used in this study were adopted and have a clear signal of supercooling. These participants are listed in Table S1.

Beschreibung: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49(12), (2022): e2022GL097779, https://doi.org/10.1029/2022GL097779.

Beschreibung: Outer-rise faults are predominantly concentrated near ocean trenches due to subducted plate bending. These faults play crucial roles in the hydration of subducted plates and the consequent subducting processes. However, it has not yet been possible to develop high-resolution structures of outer-rise faults due to the lack of near-field observations. In this study we deployed an ocean bottom seismometer (OBS) network near the Challenger Deep in the Southernmost Mariana Trench, between December 2016 and June 2017, covering both the overriding and subducting plates. We applied a machine-learning phase detector (EQTransformer) to the OBS data and found more than 1,975 earthquakes. An identified outer-rise event cluster revealed an outer-rise fault penetrating to depths of 50 km, which was inferred as a normal fault based on the extensional depth from tomographic images in the region, shedding new lights on water input at the southmost Mariana subduction zone.

Beschreibung: This study is supported by National Natural Science Foundation of China (Nos. 91858207, 92158205, 41890813), Hong Kong Research Grant Council Grants (No. 14304820), Award from CORE (a joint research center for ocean research between QNLM and HKUST), Chinese Academy of Sciences (Nos. Y4SL021001, QYZDY-SSW-DQC005), and Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (No. GML2019ZD0205), Faculty of Science at CUHK.

Beschreibung: 2022-12-06

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(17), (2021): e2021GL094128, https://doi.org/10.1029/2021GL094128.

Beschreibung: Ocean warming is causing declines of coral reefs globally, raising critical questions about the potential for corals to adapt. In the central equatorial Pacific, reefs persisting through recurrent El Niño heatwaves hold important clues. Using an 18-year record of coral cover spanning three major bleaching events, we show that the impact of thermal stress on coral mortality within the Phoenix Islands Protected Area (PIPA) has lessened over time. Disproportionate survival of extreme thermal stress during the 2009–2010 and 2015–2016 heatwaves, relative to that in 2002–2003, suggests that selective mortality through successive heatwaves may help shape coral community responses to future warming. Identifying and facilitating the conditions under which coral survival and recovery can keep pace with rates of warming are essential first steps toward successful stewardship of coral reefs under 21st century climate change.

Beschreibung: Support was provided by the US National Science Foundation (NSF) 1737311 to A. L. Cohen; The Atlantic Donor Advised Fund to A. L. Cohen; a Woods Hole Oceanographic Institution post-doctoral scholarship to M. D. Fox; the Robertson Foundation, The Prince Albert Foundation, the New England Aquarium, and the Akiko Shiraki Dynner Fund.

Beschreibung: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49(11), (2022): e2021GL097618, https://doi.org/10.1029/2021GL097618.

Beschreibung: Krypton-81 dating provides new insights into the timing, mechanisms, and extent of meteoric flushing versus retention of saline fluids in the subsurface in response to changes in geologic and/or climatic forcings over 50 ka to 1.2 Ma year timescales. Remnant Paleozoic seawater-derived brines associated with evaporites in the Paradox Basin, Colorado Plateau, are beyond the 81Kr dating range (〉1.2 Ma) and have likely been preserved due to negative fluid buoyancy and low permeability. 81Kr dating of formation waters above the evaporites indicates topographically-driven meteoric recharge and salt dissolution since the Late Pleistocene (0.03–0.8 Ma). Formation waters below the evaporites (up to 3 km depth), in basal aquifers, contain relatively young meteoric water components (0.4–1.1 Ma based on 81Kr) that partially flushed remnant brines and dissolved evaporites. We demonstrate that recent, rapid denudation of the Colorado Plateau (〈4–10 Ma) activated deep, basinal-scale flow systems as recorded in 81Kr groundwater age distributions.

Beschreibung: Funding for this research was provided by the W.M. Keck Foundation, CIFAR Earth 4D Subsurface Science and Exploration program, NSF EAR (#2120733), National Key Research and Development Program of China (Grant No. 2016YFA0302200), and National Natural Science Foundation of China (Grants No. 41727901). McIntosh and Ballentine are fellows of the CIFAR Earth4D Subsurface Science and Exploration program.

Beschreibung: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(4), (2021): e2020JC016757, https://doi.org/10.1029/2020JC016757.

Beschreibung: The along-shelf circulation in the Northwest Atlantic (NWA) Ocean is characterized by an equatorward flow from Greenland's south coast to Cape Hatters. The mean flow is considered to be primarily forced by freshwater discharges from rivers and glaciers while its variability is driven by both freshwater fluxes and wind stress. In this study, we hypothesize and test that the wind stress is important for the mean along-shelf flow. A two-layer model with realistic topography when forced by wind stress alone simulates a circulation system on the NWA shelves that is broadly consistent with that derived from observations, including an equatorward flow from Greenland coast to the Mid-Atlantic Bight (MAB). The along-shelf sea-level gradient is close to a previous estimate based on observations. The along-shelf flows exhibit strong seasonal variations with along-shelf transports being strong in fall/winter and weak in spring/summer, consistent with available observations. It is found that the NWA shelf circulation is affected by both wind-driven gyres through their western boundary currents and wind-stress forcing on the shelf especially along the coasts of Newfoundland and Labrador. The local wind stress forcing has more direct impacts on flows in shallower waters along the coast while the open-ocean gyres tend to affect the circulations along the outer shelf. Our conclusion is that wind stress is an important forcing of the main along-shelf flows in the NWA. One objective of this study is to motivate further examination of whether wind stress is as important as freshwater forcing for the mean flow.

Beschreibung: Both Yang and Chen are also supported by NOAA Climate Program Office's Climate Variability and Prediction Program under grant NA20OAR4310398. JY is supported by Woods Hole Oceanographic Institution (WHOI) W. V. A. Clark Chair for Excellence in Oceanography and NSF Ocean Science Division under grant OCE1634886. Chen is supported by WHOI Independent Research and Development award.

Beschreibung: 2021-09-30

Beschreibung: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(7), (2022): e2021JC018333, https://doi.org/10.1029/2021JC018333.

Beschreibung: As part of a project focused on the coastal fisheries of Isla Natividad, an island on the Pacific coast of Baja California, Mexico, we conducted a 2-1/2 year study of flows at two sites within the island's kelp forests. At one site (Punta Prieta), currents are tidal, whereas at the other site (Morro Prieto), currents are weaker and may be more strongly influenced by wind forcing. Satellite estimates of the biomass of the giant kelp (Macrocystis pyrifera) for this period varied between 0 (no kelp) and 3 kg/m2 (dense kelp forest), including a period in which kelp entirely was absent as a result of the 2014–2015 “Warm Blob” in the Eastern Pacific. During this natural “deforestation experiment”, alongshore velocities at both sites when kelp was present were substantially weaker than when kelp was absent, with low-frequency alongshore currents attenuated more than higher frequency ones, behavior that was the same at both sites despite differences in forcing. The attenuation of cross-shore flows by kelp was less than alongshore flows; thus, residence times for water inside the kelp forest, which are primarily determined by cross-shore velocities, were only weakly affected by the presence or absence of kelp. The flow changes we observed in response to changes in kelp density are important to the biogeochemical functioning of the kelp forest in that slower flows imply longer residence times, and, are also ecologically relevant in that reduced tidal excursions may lead to more localized recruitment of planktonic larvae.

Beschreibung: The work we describe here was supported by NSF grants DEB 1212124, OCE 1416934, OCE 1736830, and OCE 2022927, by an equipment grant from the Kuwait Foundation for the Advancement of Sciences, and through grants from the Marisla Foundation, Packard Foundation, and Walton Family Foundation.

Beschreibung: 2022-12-24

Beschreibung: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49(12), (2022): e2021GL097598, https://doi.org/10.1029/2021GL097598.

Beschreibung: The ocean is inhomogeneous in hydrographic properties with diverse water masses. Yet, how this inhomogeneity has evolved in a rapidly changing climate has not been investigated. Using multiple observational and reanalysis datasets, we show that the spatial standard deviation (SSD) of the global ocean has increased by 1.4 ± 0.1% in temperature and 1.5 ± 0.1% in salinity since 1960. A newly defined thermohaline inhomogeneity index, a holistic measure of both temperature and salinity changes, has increased by 2.4 ± 0.1%. Climate model simulations suggest that the observed ocean inhomogeneity increase is dominated by anthropogenic forcing and projected to accelerate by 200%–300% during 2015–2100. Geographically, the rapid upper-ocean warming at mid-to-low latitudes dominates the temperature inhomogeneity increase, while the increasing salinity inhomogeneity is mainly due to the amplified salinity contrast between the subtropical and subpolar latitudes.

Beschreibung: This work is supported by the Strategic Priority Research Program of Chinese Academy of Sciences (grant XDB42000000 and XDB40000000), the National Key R&D Program of China (2017YFA0603200), and the Shandong Provincial Natural Science Foundation (ZR2020JQ17), and the U.S. National Science Foundation Physical Oceanography Program (OCE- 2048336).

Beschreibung: 2022-12-23

Beschreibung: This paper is not subject to U.S. copyright. The definitive version was published in ten Brink, U. S., Vanacore, E. A., Fielding, E. J., Chaytor, J. D., Lopez-Venegas, A. M., Baldwin, W. E., Foster, D. S., & Andrews, B. D. Mature diffuse tectonic block boundary revealed by the 2020 southwestern Puerto Rico seismic sequence. Tectonics, 41(3), (2022): e2021TC006896, https://doi.org/10.1029/2021TC006896.

Beschreibung: Distributed faulting typically tends to coalesce into one or a few faults with repeated deformation. The progression of clustered medium-sized (≥Mw4.5) earthquakes during the 2020 seismic sequence in southwestern Puerto Rico (SWPR), modeling shoreline subsidence from InSAR, and sub-seafloor mapping by high-resolution seismic reflection profiles, suggest that the 2020 SWPR seismic sequence was distributed across several short intersecting strike-slip and normal faults beneath the insular shelf and upper slope of Guayanilla submarine canyon. Multibeam bathymetry map of the seafloor shows significant erosion and retreat of the shelf edge in the area of seismic activity as well as slope-parallel lineaments and submarine canyon meanders that typically develop over geological time. The T-axis of the moderate earthquakes further matches the extension direction previously measured on post early Pliocene (∼〉3 Ma) faults. We conclude that although similar deformation has likely taken place in this area during recent geologic time, it does not appear to have coalesced during this time. The deformation may represent the southernmost part of a diffuse boundary, the Western Puerto Rico Deformation Boundary, which accommodates differential movement between the Puerto Rico and Hispaniola arc blocks. This differential movement is possibly driven by the differential seismic coupling along the Puerto Rico—Hispaniola subduction zone. We propose that the compositional heterogeneity across the island arc retards the process of focusing the deformation into a single fault. Given the evidence presented here, we should not expect a single large event in this area but similar diffuse sequences in the future.

Beschreibung: 2022-08-08