ALBERT

Description: We compare differences and similarities in the annual stratospheric HNO3 cycle derived from ground‐based measurements at the South Pole during 1993 and 1995, after correcting an error in earlier published profile retrievals for 1993 which led to under estimation of mixing ratios. The data series presented here provide profiling over the range ∼16–48 km, and cover the fall‐winter‐spring cycle in the behavior of HNO3 in the extreme Antarctic with a large degree of temporal overlap. With the exception of one gap of 20 days, the combined data sets cover a full annual cycle. The record shows an increase in HNO3 above 30 km occurring about 20 days before sunset, which appears to be the result of higher altitude heterogeneous conversion of NOx as photolysis diminishes. Both years show a strong increase in HNO3 beginning about polar sunset, in a layer peaking at about 25 km, as additional NOx is heterogeneously converted to nitric acid. When temperatures drop to the polar stratospheric cloud (PSC) formation range near the end of May, gas phase HNO3 is rapidly reduced in the lower stratosphere, although at least 2–3 weeks of temperatures ≤192 K appear to be required to complete most of the gas‐phase removal at the upper end of the depletion range (22–25 km). Despite a significant difference in residual sulfate loading from the explosion of Mount Pinatubo, there appears to be little gross difference in the timing and effects of PSC formation in removing gas phase HNO3 in these 2 years, though removal may be more rapid in 1995. Incorporation of gas phase HNO3 into PSCs appears to be nearly complete up to ∼25 km by midwinter. We also see a repeat of the formation of gas phase HNO3 in the middle stratosphere in early midwinter of 1995 with about the same timing as in 1993, suggesting that this phenomenon is driven by a repetition of dynamical transport and appropriate temperatures and pressures in the polar night, and not (as has been suggested) by ion‐based heterogeneous chemistry that requires triggering by large relativistic electron fluxes. High‐altitude HNO3 production peaks during a period of ∼20 days, but appears to persist for up to ∼40 days in the 40–45 km range, ceasing well before sunrise. This HNO3 descends rapidly throughout the production period, at a rate in good agreement with theoretically determined midwinter subsidence rates. As noted in earlier studies, later warming of this region above PSC evaporation temperatures does not cause reappearance of large amounts of HNO3, indicating that most PSCs gravitationally sink out of the stratosphere before early spring. We present evidence that smaller PSCs do evaporate to ∼1 to 3.5 ppbv of HNO3 in the lower stratosphere, however, working downward from ∼25 km as temperatures rise during the late winter. There is a delay of ∼15 days after sunrise before photolysis causes significant depletion in the altitude range below ∼30 km, where subsidence has carried virtually all higher‐altitude HNO3 by polar sunrise. Some continued subsidence and photolysis combine to keep mixing ratios less than ∼5 ppbv below 30 km until the final breakdown of the vortex in November brings larger amounts of HNO3 with air from lower latitudes.

Description: Published

Description: 17739-17750

Description: 5A. Ricerche polari e paleoclima

Description: JCR Journal

Description: Seismic hazard modeling is a multidisciplinary science that aims to forecast earthquake occurrence and its resultant ground shaking. Such models consist of a probabilistic framework that quantifies uncertainty across a complex system; typically, this includes at least two model components developed from Earth science: seismic source and ground motion models. Although there is no scientific prescription for the forecast length, the most common probabilistic seismic hazard analyses consider forecasting windows of 30 to 50 years, which are typically an engineering demand for building code purposes. These types of analyses are the topic of this review paper. Although the core methods and assumptions of seismic hazard modeling have largely remained unchanged for more than 50 years, we review the most recent initiatives, which face the difficult task of meeting both the increasingly sophisticated demands of society and keeping pace with advances in scientific understanding. A need for more accurate and spatially precise hazard forecasting must be balanced with increased quantification of uncertainty and new challenges such as moving from time‐independent hazard to forecasts that are time dependent and specific to the time period of interest. Meeting these challenges requires the development of science‐driven models, which integrate all information available, the adoption of proper mathematical frameworks to quantify the different types of uncertainties in the hazard model, and the development of a proper testing phase of the model to quantify its consistency and skill. We review the state of the art of the National Seismic Hazard Modeling and how the most innovative approaches try to address future challenges.

Description: Published

Description: e2019RG000653

Description: 6T. Studi di pericolosità sismica e da maremoto

Description: JCR Journal

Description: An edited version of this paper was published by AGU. Copyright (2016) American Geophysical Union.

Description: The accuracy of earthquake locations and their correspondence with subsurface geology depends strongly on the accuracy of the available seismic velocity model. Most modern methods to construct a velocity model for earthquake location are based on the inversion of passive source seismological data. Another approach is the integration of high-resolution geological and geophysical data to construct deterministic velocity models in which earthquake locations can be directly correlated to the geological structures. Such models have to be kinematically consistent with independent seismological data in order to provide precise hypocenter solutions. We present the Altotiberina (AT) seismic model, a three-dimensional velocity model for the Upper Tiber Valley region (Northern Apennines, Italy), constructed by combining 300 km of seismic reflection profiles, 6 deep boreholes (down to 5 km depth), detailed data from geological surveys and direct measurements of P- and S-wave velocities performed in situ and in laboratory. We assess the robustness of the AT seismic model by locating 11,713 earthquakes with a non-linear, global-search inversion method and comparing the probabilistic hypocenter solutions to those calculated in three previously published velocity models, constructed by inverting passive seismological data only. Our results demonstrate that the AT seismic model is able to provide higher-quality hypocenter locations than the previous velocity models. Earthquake locations are consistent with the subsurface geological structures and show a high degree of spatial correlation with specific lithostratigraphic units, suggesting a lithological control on the seismic activity evolution.

Description: Published

Description: 8113-8135

Description: 4T. Sismicità dell'Italia

Description: JCR Journal

Description: [1] We present the first intercomparison between the two most comprehensive records of gas‐phase HNO3 profiles in the Antarctic stratosphere, covering the greater part of 1993 and 1995. We compare measurements by the Stony Brook Ground‐Based Millimeter‐wave Spectrometer (GBMS) at the South Pole with Version 5 HNO3 data from the Microwave Limb Sounder (MLS) aboard the Upper Atmospheric Research Satellite. Trajectory tracing was used to select MLS measurements in the 70°–80°S latitude band that sampled air observed by the GBMS during passage over the Pole. When temperatures were near the HNO3 condensation range, additional screening was performed to select MLS measurements that sampled air parcels within 1.5 K of the temperature they experienced over the Pole. Quantitative comparisons are given at 7 different potential temperature levels spanning the range ∼19–30 km. Agreement between the data sets is quite good between 465 and 655 K (∼20–25 km) during a large fraction of the year. Agreement is best during winter and spring, when seasonally averaged differences are generally within 1 ppbv below ∼25 km. At higher altitudes, and during summer and fall, the agreement becomes worse, and GBMS measurements can exceed MLS values by more than 3 ppbv. We provide evidence that differences occurring in the lower stratosphere during fall are due to lack of colocation between the two data sets during a period of strong poleward gradients in HNO3. Remaining discrepancies between GBMS and MLS V5 HNO3 measurements are thought to be due to instrumental or retrieval biases.

Description: Published

Description: id 4809

Description: 5A. Ricerche polari e paleoclima

Description: JCR Journal

Description: Producing probabilistic subseasonal forecasts of extreme events up to six weeks in advance is crucial for many economic sectors. In agribusiness, this time scale is particularly critical because it allows for mitigation strategies to be adopted for counteracting weather hazards and taking advantage of opportunities. For example, spring frosts are detrimental for many nut trees, resulting in dramatic losses at harvest time. To explore subseasonal forecast quality in boreal spring, identified as one of the most sensitive times of the year by agribusiness end users, we build a multisystem ensemble using four models involved in the Subseasonal to Seasonal Prediction project (S2S). Two-meter temperature forecasts are used to analyze cold spell predictions in the coastal Black Sea region, an area that is a global leader in the production of hazelnuts. When analyzed at the global scale, the multisystem ensemble probabilistic forecasts for near-surface temperature are better than climatological values for several regions, especially the tropics, even many weeks in advance; however, in the coastal Black Sea, skill is low after the second forecast week. When cold spells are predicted instead of near-surface temperatures, skill improves for the region, and the forecasts prove to contain potentially useful information to stakeholders willing to put mitigation plans into effect. Using a cost–loss model approach for the first time in this context, we show that there is added value of having such a forecast system instead of a business-as-usual strategy, not only for predictions released 1–2 weeks ahead of the extreme event, but also at longer lead times.

Description: Published

Description: 237–254

Description: 4A. Oceanografia e clima

Description: JCR Journal

Description: Mineral dust plays an important role in the atmospheric radiation budget as well as in the ocean carbon cycle through fertilization and by ballasting of settling organic matter. However, observational records of open‐ocean dust deposition are sparse. Here, we present the spatial and temporal evolution of Saharan dust deposition over 2 years from marine sediment traps across the North Atlantic, directly below the core of the Saharan dust plume, with highest dust fluxes observed in summer. We combined the observed deposition fluxes with model simulations and satellite observations and argue that dust deposition in the Atlantic is predominantly controlled by summer rains. The dominant depositional pathway changes from wet deposition in summer to dry deposition in winter. Wet deposition has previously been suggested to increase the release of dust‐derived nutrients and their bioavailability, which may be a key contributor to surface‐ocean productivity in remote and oligotrophic parts of the oceans.

Description: The Northeast Greenland Ice Stream (NEGIS) is an important dynamic component contributing to the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The ice stream geometry and surface velocities in the onset region of the NEGIS are not yet sufficiently well reproduced by ice sheet models. We present an assessment of the basal conditions of the onset region in a systematic analysis of airborne ultra-wideband radar data. Our data yield a new detailed model of ice-thickness distribution and basal topography in the upstream part of the ice stream. We observe a change from a smooth to a rougher bed where the ice stream widens from 10 to 60 km, and a distinct roughness anisotropy, indicating a preferred orientation of subglacial structures. The observation of off-nadir reflections that are symmetrical to the bed reflection in the radargrams suggests that these structures are elongated subglacial landforms, which in turn indicate potential streamlining of the bed. Together with basal water routing pathways, our observations hint to two different zones in this part of the NEGIS: an accelerating and smooth upstream region, which is collecting water, with reduced basal traction, and in the further downstream part, where the ice stream is slowing down and is widening, with a distribution of basal water towards the shear margins. Our findings support the hypothesis that the NEGIS is strongly interconnected to the subglacial water system in its onset region, but also to the subglacial substrate and morphology.

Description: Changes in ocean gateway configuration can induce basin‐scale rearrangements in ocean current characteristics. However, there is large uncertainty in the relative timing of the Oligocene/Miocene subsidence histories of the Greenland‐Scotland Ridge (GSR) and the Fram Strait (FS). By using a climate model, we investigate the temperature and salinity changes in response to the subsidence of these two key ocean gateways during early to middle Miocene. For a singular subsidence of the GSR, we detect warming and a salinity increase in the Nordic Seas and the Arctic Ocean. As convection sites shift to the north of Iceland, North Atlantic Deep Water (NADW) is formed at cooler temperatures. The associated deep ocean cooling and upwelling of deep waters to the Southern Ocean surface can cause a cooling in the southern high latitudes. These characteristic responses to the GSR deepening are independent of the FS being shallow or deep. An isolated subsidence of the FS gateway for a deep GSR shows less pronounced warming and salinity increase in the Nordic Seas. Arctic temperatures remain unaltered, but a stronger salinity increase is detected, which further increases the density of NADW. The increase in salinity enhances the contribution of NADW to the abyssal ocean at the expense of the colder southern source water component. These relative changes largely counteract each other and cause a negligible warming in the upwelling regions of the Southern Ocean.

Description: The Antarctic Circumpolar Current (ACC) is the world's largest current system connecting all three major basins of the global ocean. Our knowledge of glacial‐interglacial changes in ACC dynamics in the southeast Pacific is not well constrained and presently only based on reconstructions covering the last glacial cycle. Here we use a combination of mean sortable silt grain size of the terrigenous sediment fraction (10–63 μm, "Sortable Silt") and X‐ray fluorescence scanner‐derived Zr/Rb ratios as flow strength proxies to examine ACC variations at the Pacific entrance to the Drake Passage (DP) in the vicinity of the Subantarctic Front. Our results indicate that at the DP entrance, ACC strength varied by ~6–16% on glacial‐interglacial time scales, yielding higher current speeds during interglacial times and reduced current speeds during glacials. We provide evidence that previous observations of a reduction in DP throughflow during the last glacial period are part of a consistent pattern extending for at least the last 1.3 Ma. The orbital‐scale cyclicity follows well‐known global climate changes from prevailing ca. 41‐kyr cycles in the early part of the record (1.3 Ma to 850 ka; marine isotope stage 21) across the mid‐Pleistocene transition into the middle and late Pleistocene 100‐kyr world. A comparison to a bottom water flow record from the deep western boundary current off New Zealand (Ocean Drilling Program Site 1123) reveals anti‐phased changes between the two sites. The enhanced supply of deep water along the DP and into the Atlantic Ocean during interglacials corresponds to a weakened flow of the SW Pacific deep western boundary current.

Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 33(4), (2020): 1535-1545, doi:10.1175/JCLI-D-19-0547.1.

Description: In a transient warming scenario, the North Atlantic is influenced by a complex pattern of surface buoyancy flux changes that ultimately weaken the Atlantic meridional overturning circulation (AMOC). Here we study the AMOC response in the CMIP5 experiment, using the near-geostrophic balance of the AMOC on interannual time scales to identify the role of temperature and salinity changes in altering the circulation. The thermal wind relationship is used to quantify changes in the zonal density gradients that control the strength of the flow. At 40°N, where the overturning cell is at its strongest, weakening of the AMOC is largely driven by warming between 1000- and 2000-m depth along the western margin. Despite significant subpolar surface freshening, salinity changes are small in the deep branch of the circulation. This is likely due to the influence of anomalously salty water in the subpolar intermediate layers, which is carried northward from the subtropics in the upper limb of the AMOC. In the upper 1000 m at 40°N, salty anomalies due to increased evaporation largely cancel the buoyancy increase due to warming. Therefore, in CMIP5, temperature dynamics are responsible for AMOC weakening, while freshwater forcing instead acts to strengthen the circulation in the net. These results indicate that past modeling studies of AMOC weakening, which rely on freshwater hosing in the subpolar gyre, may not be directly applicable to a more complex warming scenario.

Description: We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups (listed in Table 1 of this paper) for producing and making available their model output. We also thank John Marshall for helpful discussions on the driving mechanisms of the AMOC, and three anonymous reviewers whose comments greatly improved the manuscript. This work was supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program Award 80NSSC17K0372, and by National Science Foundation Award OCE-1433132.

Description: 2020-07-20

Description: Methane emissions from northern high latitude wetlands constitute a major uncertainty in the atmospheric methane (CH4) budget during the Holocene. To reconstruct northern wetland methane emissions, we used an empirical model based on syntheses of observations of peat initiation from more than 3600 radiocarbon-dated basal peat ages, plant-macrofossil-derived peatland type from more than 250 peat cores from sites across the northern high latitudes, and observed CH4 emissions averaged from modern-day wetland types in order to explore the effects of wetland expansion and changes in wetland type. Peatland basal ages and plant macrofossil records showed the widespread formation of fens in major northern wetland complexes before 8000 BP. After 8000 BP, new fen formation continued, but widespread peatland succession (to bogs) and permafrost aggradation also occurred. Reconstructed CH4 emissions from peatlands increased rapidly between 10,600 BP and 6900 BP due to fen formation and expansion, then stabilized after 5000 BP at 42 ± 25 Tg CH4 y-1, as high methane-emitting fens transitioned to lower methane-emitting bogs and permafrost peatlands. Permafrost formation in northern peatlands after 1000 BP decreased CH4 emissions by 20% to 34 ± 21 Tg y-1 by the present day. Warming temperatures, changes in peatland hydrology, and permafrost thaw will likely change the magnitude of northern peatland emissions in the future.

Description: Infrastructure and anthropogenic impacts are expanding across the Arctic. A consistent record of human impact is required in order to quantify the changes and to assess climate change impacts on the communities. We derived a first panarctic satellite-based record of expanding infrastructure and anthropogenic impacts along all permafrost affected coasts (100 km buffer) within the H2020 project Nunataryuk based on Sentinel-1/2 satellite imagery. C-band synthetic aperture radar and multi-spectral information is combined through a machine learning framework. Depending on region, we identified up to 50% more information (human presence) than in OpenStreetMap. The combination with satellite records on vegetation change (specifically NDVI from Landsat since 2000) allowed quantification of recent expansion of infrastructure. Most of the expanded human presence occurred in Russia related predominantly to oil/gas industry. The majority of areas with human presence will be subject to thaw by mid-21st century based on ground temperature trends derived from the ESA CCI+ Permafrost time series (1997-2019). Of specific concern in this context are also settlements located directly at permafrost affected coasts. An efficient erosion rate monitoring scheme needs to be developed and combined with settlement records in order to assess the risk for local communities and infrastructure. Relevant progress in the framework of the ESA EO4PAC project will be discussed.

Description: Retrogressive thaw slumps (RTS) are typical landforms indicating processes of rapid thawing and degrading permafrost. Their abundance is increasing in many regions and quantifying their dynamics is of high importance for assessing geomorphic, hydrologic, and biogeochemical impacts of climate change in the Arctic. Here we present a deep-learning (DL) based semantic segmentation framework to detect RTS, using high-resolution multi-spectral PlanetScope, topographic (ArcticDEM elevation and slope), and medium-resolution multi-temporal Landsat Trend data. We created a highly automated processing pipeline, which is designed to allow reproducible results and to be flexible for multiple input data types. The processing workflow is based on the pytorch deep-learning framework and includes a variety of different segmentation architectures (UNet, UNet++, DeepLabV3), backbones and includes common data transformation techniques such as augmentation or normalization. We tested (training, validation) our DL based model in six different regions of 100 to 300 km² size across Canada, and Siberia. We performed a regional cross-validation (5 regions training, 1 region validation) to test the spatial robustness and transferability of the algorithm. Furthermore, we tested different architectures, backbones and loss-functions to identify the best performing and most robust parameter sets. For training the models we created a database of manually digitized and validated RTS polygons. The resulting model performance varied strongly between different regions with maximum Intersection over Union (IoU) scores between 0.15 and 0.58. The strong regional variation emphasizes the need for sufficiently large training data, which is representative of the diversity of RTS types. However, the creation of good training data proved to be challenging due to the fuzzy definition and delineation of RTS. We are further continuing to improve the usability and the functionality to add further datasets and classes. We will show first results from the upscaling beyond small test areas towards large spatial clusters of extensive RTS presence e.g. Peel Plateau in NW Canada.

Description: With the Earth’s climate rapidly warming, the Arctic represents one of the most vulnerable regions to environmental change. These northern high latitude regions experience intensified fire seasons and especially tundra fires are projected to become more frequent and severe. Fires in permafrost regions have extensive impacts, including the initiation of thermokarst (rapid thaw of ice-rich ground), as they combust the upper organic soil layers which provide insulation to the permafrost below. Rapid permafrost thaw is, thus, often observable in fire scars in the first years post-disturbance. In polygonal ice-wedge landscapes, this becomes most prevalent through melting ice wedges and degrading troughs. The further these ice wedges degrade, the more troughs will likely connect and build an extensive hydrological network with changing patterns and degrees of connectivity that influences hydrology and runoff. While subsiding troughs over melting ice wedges may host new ponds, an increasing connectivity may also subsequently lead to more drainage of ponds, which in turn can limit further thaw and help stabilize the landscape. To quantify the changes in such dynamic landscapes over large regions, highly automated methods are needed that allow extracting information on the geomorphic state and changes over time of ice-wedge trough networks from remote sensing data. We developed a computer vision algorithm to automatically derive ice-wedge polygonal networks and the current microtopography of the degrading troughs from very high resolution, airborne laserscanning-based digital terrain models. We represent the networks as graphs (a concept from the computer sciences to describe complex networks) and apply methods from graph theory to describe and quantify hydrological network characteristics of the changing landscape. In fire scars, we especially observe rapidly growing networks and fast micromorphological change in those degrading troughs. In our study, we provide a space-for-time substitution comparing fire scars throughout the Alaskan tundra of up to 70 years since the fire disturbance, to show how this type of disturbed landscape evolves over time.

Description: Using our custom visualization tool for multitemporal Landsat satellite imagery we discovered, to our knowledge, an undocumented mega-landslide in far-east Siberia, which occurred in summer 2017 (https://bit.ly/2WYRLM1; 61.55°N; 170.01°E). To create and visualize this unique dataset, we processed temporal trends of multispectral indices of 〉100,000 Landsat images for a period from 2000-2019 using the freely available Google Earth Engine cloud processing platform (https://ingmarnitze.users.earthengine.app/view/hotspottcvisapp). The megaslide has a size of 3.66 km² and using the ArcticDEM data we estimate a volume movement of ~20 Mm³. With this size and volume, the landslide is among the largest globally known in recent decades. The landslide is accompanied by a smaller one (0.31 km², 1 Mm³) about 600 m further east, which already occurred in summer 2015. The large landslide caused the formation of several small lakes by blocking two valleys with debris and within newly formed crevasses near the hilltop, which are still persisting as of August 2021. As this event occurred in a remote valley far from any settlement, no visible damage to infrastructure or human livelihoods was detected. The remoteness has likely led to being not detected, like many similar, albeit a lot smaller, erosion features in the Arctic permafrost region. In this presentation we will show the main properties of the landslide, potential trigger mechanisms in the traditional sense. As this region is located along the fringes of permafrost presence we will discuss its potential connection to the rapidly warming climate in the high latitudes. Further, we will discuss how such a large event remained undetected for several years. We discuss and highlight the value of our landscape change visualization tool based on Landsat trend analysis (see Nitze et al., AGU 2020), which helped us to identify this extreme event. With more and more available data sources, this tool in addition to automated image analysis (e.g. deep-learning) or seismic analysis will help to uncover the hidden processes and dynamics of the Earth’s surface.

Description: Several decades of research have provided insight into patterns of and controls on thermokarst initiation and expansion, yet studies tend to focus on individual types of thermokarst (i.e., thaw lake formation and subsequent drainage) in particular regions. Today, we are left with uneven knowledge about abrupt permafrost thaw both conceptually and regionally. The goal of this presentation is to summarize recent advancements in monitoring thermokarst and its impact on soil, vegetation, and water while also framing a call to action for the next decade of research. Over the next decade, permafrost researchers must align their efforts on several fronts to not only increase our knowledge about changing permafrost but to align this knowledge with key community and policy needs. To support climate change planning and adaptation, northern communities need future thaw vulnerability mapped at scales relevant to their needs, which will require a suite of downscaled and new mapping and remote sensing products. Thermokarst predisposition maps based on circumpolar datasets greatly overestimate the area vulnerable to thermokarst, which can lead to poor planning and climate anxiety. In some situations, existing mapping products may be useful for downscaling with more detailed input data. In other situations, entirely new approaches may be required to support local action. A second key need for community relevant research is the ability to detect and monitor early warning indicators of thermokarst. Such information is needed to support scenario planning and to help mitigate the risks to social, cultural, and physical infrastructure created by permafrost change. We are evaluating the potential for using changes in vegetation, wetting/drying and topography as early warning indicators of thermokarst, all of which can be remotely sensed. Finally, integrating fine-scale disturbances such as thermokarst into large scale models remains a key challenge but critical for supporting sound climate policy. While a diversity of permafrost modeling approaches is necessary, we outline guiding principles that will help enhance model comparisons, assimilation of simulated data across spatiotemporal scales, and the ability for policy decisions to be rapidly informed by emerging science on permafrost change.

Description: 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(13), (2022): e2022GL098554, https://doi.org/10.1029/2022GL098554.

Description: Summertime heavy rainfall and its resultant floods are among the most harmful natural hazards in the US Midwest, one of the world's primary crop production areas. However, seasonal forecasts of heavy rain, currently based on preseason sea surface temperature anomalies (SSTAs), remain unsatisfactory. Here, we present evidence that sea surface salinity anomalies (SSSAs) over the tropical western Pacific and subtropical North Atlantic are skillful predictors of summer time heavy rainfall one season ahead. A one standard deviation change in tropical western Pacific SSSA is associated with a 1.8 mm day−1 increase in local precipitation, which excites a teleconnection pattern to extratropical North Pacific. Via extratropical air-sea interaction and long memory of midlatitude SSTA, a wave train favorable for US Midwest heavy rain is induced. Combined with soil moisture feedbacks bridging the springtime North Atlantic salinity, the SSSA-based statistical prediction model improves Midwest heavy rainfall forecasts by 92%, complementing existing SSTA-based frameworks.

Description: This study is supported by the NSF PREEVENTS program under ICER-1663138 (LL) and ICER-1663704 (RWS and CCU).

Description: 2023-01-07

Description: 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): e2021JC018276, https://doi.org/10.1029/2021JC018276.

Description: Coastal communities across the United States (U.S.) are experiencing an increase in the frequency of high-tide flooding (HTF). This increase is mainly due to sea-level rise (SLR), but other factors such as intra- to inter-annual mean sea level variability, tidal anomalies, and non-tidal residuals also contribute to HTF events. Here we introduce a novel decomposition approach to develop and then analyze a new database of different sea-level components. Those components represent processes that act on various timescales to contribute to HTF along the U.S. coastline. We find that the relative importance of components to HTF events strongly varies in space and time. Tidal anomalies contribute the most along the west and northeast coasts, where HTF events mostly occur in winter. Non-tidal residuals are most important along the Gulf of Mexico and mid-Atlantic coasts, where HTF events mostly occur in fall. We also quantify the minimum number of components that were required to cause HTF events in the past and how this number changed over time. The results highlight that at present, due to SLR, fewer components are needed to combine to push water levels above HTF thresholds, but tidal anomalies alone are still not sufficient to reach HTF thresholds in most locations. Finally, we explore how co-variability between different components leads to compounding effects. In some places, positive correlation between sea-level components leads to significantly more HTF events than would be expected if sea-level components were uncorrelated, whereas in other places negative correlation leads to fewer HTF events.

Description: his work was supported by NASA's Sea Level Change Team award number 80NSSC20K1241. S.L. also acknowledges support by the China Scholarship Council (no. 201904910413) and the Ministry of Science and Technology of the People's Republic of China (grant no. 2011YQ120045).

Description: 2023-01-14

Description: Numerical simulations allow us to gain a comprehensive understanding of the underlying mechanisms of past, present, and future climate changes. The mid-Holocene (MH) and the last interglacial (LIG) were the two most recent warm episodes of Earth’s climate history and are the focus of paleoclimate research. Here, we present results of MH and LIG simulations with two versions of the state-of-the-art Earth system model AWI-ESM. Most of the climate changes in MH and LIG compared to the preindustrial era are agreed upon by the two model versions, including 1) enhanced seasonality in surface temperature that is driven by the redistribution of seasonal insolation; 2) a northward shift of the intertropical convergence zone (ITCZ) and tropical rain belt; 3) a reduction in annual mean Arctic sea ice concentration; 4) weakening and northward displacement of the Northern Hemisphere Hadley circulation, which is related to the decrease and poleward shift of the temperature gradient from the subtropical to the equator in the Northern Hemisphere; 5) a westward shift of the Indo-Pacific Walker circulation due to anomalous warming over the Eurasia and North Africa during boreal summer; and 6) an expansion and intensification of Northern Hemisphere summer monsoon rainfall, with the latter being dominated by the dynamic component of moisture budget (i.e., the strengthening of wind circulation). However, the simulated responses of the Atlantic meridional overturning circulation (AMOC) in the two models yield different results for both the LIG and the MH. AMOC anomalies between the warm interglacial and preindustrial periods are associated with changes in North Atlantic westerly winds and stratification of the water column at the North Atlantic due to changes in ocean temperature, salinity, and density.

Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(11), (2022): 2841–2852, https://doi.org/10.1175/jpo-d-22-0025.1.

Description: Prediction of rapid intensification in tropical cyclones prior to landfall is a major societal issue. While air–sea interactions are clearly linked to storm intensity, the connections between the underlying thermal conditions over continental shelves and rapid intensification are limited. Here, an exceptional set of in situ and satellite data are used to identify spatial heterogeneity in sea surface temperatures across the inner core of Hurricane Sally (2020), a storm that rapidly intensified over the shelf. A leftward shift in the region of maximum cooling was observed as the hurricane transited from the open gulf to the shelf. This shift was generated, in part, by the surface heat flux in conjunction with the along- and across-shelf transport of heat from storm-generated coastal circulation. The spatial differences in the sea surface temperatures were large enough to potentially influence rapid intensification processes suggesting that coastal thermal features need to be accounted for to improve storm forecasting as well as to better understand how climate change will modify interactions between tropical cyclones and the coastal ocean.

Description: This research was made possible by the NOAA RESTORE Science Program (NA17NOS4510101 and NA19NOS4510194) and the NASA Physical Oceanography program (80NSSC21K0553 and WBS 281945.02.25.04.67) and NOAA IOOS program via GCOOS (NA16NOS0120018). The authors declare that they have no competing interests.

Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(8), (2022): 1797–1815, https://doi.org/10.1175/JPO-D-21-0288.1.

Description: Intruding slope water is a major source of nutrients to sustain the high biological productivity in the Gulf of Maine (GoM). Slope water intrusion into the GoM is affected by Gulf Stream warm-core rings (WCRs) impinging onto the nearby shelf edge. This study combines long-term mooring measurements, satellite remote sensing data, an idealized numerical ocean model, and a linear coastal-trapped wave (CTW) model to examine the impact of WCRs on slope water intrusion into the GoM through the Northeast Channel. Analysis of satellite sea surface height and temperature data shows that the slope sea region off the GoM is a hotspot of ring activities. A significant linear relationship is found between interannual variations of ring activities in the slope sea region off the GoM and bottom salinity at the Northeast Channel, suggesting the importance of WCRs in modulating variability of intruding slope water. Analysis of the mooring data reveals enhanced slope water intrusion through bottom-intensified along-channel flow following impingements of WCRs on the nearby shelf edge. Numerical simulations qualitatively reproduce the observed WCR impingement processes and associated episodic enhancement of slope water intrusion in the Northeast Channel. Diagnosis of the model result indicates that baroclinic CTWs excited by the ring–topography interaction are responsible for the episodically intensified subsurface along-channel inflow, which carries more slope water into the GoM. A WCR that impinges onto the shelf edge to the northeast of the Northeast Channel tends to generate stronger CTWs and cause stronger enhancement of the slope water intrusion into the GoM.

Description: This study is supported by the National Science Foundation through Grant OCE-1634965.

Description: 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: Solid Earth 127(8), (2022): e2021JB023814, https://doi.org/10.1029/2021jb023814.

Description: Early arrival traveltime tomography and full waveform inversion were conducted on downward continued streamer seismic data at Dante's Domes oceanic core complex (OCC), providing unprecedented details of shallow P wave velocity structure. Together with reverse time migration images, seafloor morphology, in situ geological samples, magnetic and gravity data, the seismic constraints are used to infer the lithological distribution along the seismic profiles. Based on the striking similarity in velocity structure beneath the corrugated domes with other OCCs and drilling results from Atlantis Massif, we confidently reconfirmed the Southern Dome as dominantly gabbroic rocks, and the Northern Dome as serpentinized peridotites. A series of isolated gabbroic bodies embedded in the diabase and basaltic layers is observed in the breakaway zone, suggesting that the initiation of Dante's Domes OCC occurred over a long period during which there were several failed attempts to form a long-lived detachment fault. This early development of the OCC probably occurred under a regime of alternating magma starvation and magma replenishment. The predominantly gabbroic section, beneath the Southern Dome and extending to termination, indicates the OCC has been created with relatively high magma flux. We also imaged distinct shallow subseafloor reflections which are also termed as D reflectors underneath the corrugated domes. The location of the D reflectors is similar to those in the Atlantis Massif, with depths well correlated with the top of exhumed gabbroic bodies and the discontinuities in the D reflectors between gabbroic bodies. Our findings contribute to the understanding of processes controlling the OCCs initiation and evolution at slow spreading ridges.

Description: This research was supported by the National Natural Science Foundation of China (91858207), Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (GML2019ZD0205), and Guangdong Basic and Applied Basic Research Foundation (2021B1515020023). M. X. acknowledges support from Special Foundation for National Science and Technology Basic Research Program of China (2018FY100505), Guangdong NSF research team project (2017A030312002), K. C. Wong Education Foundation (GJTD-2018-13), and the Chinese Academy of Sciences (Y4SL021001, QYZDY-SSWDQC005, 133244KYSB20180029, 131551KYSB20200021, and ISEE2021PY03). J. P. C. acknowledges support from the Independent Research and Development Program at WHOI.

Description: 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(8),(2022): e2022JC018737, https://doi.org/10.1029/2022jc018737.

Description: Gulf Stream Warm Core Rings (WCRs) have important influences on the New England Shelf and marine ecosystems. A 10-year (2011–2020) WCR dataset that tracks weekly WCR locations and surface areas is used here to identify the rings' path and characterize their movement between 55 and 75°W. The WCR dataset reveals a very narrow band between 66 and 71°W along which rings travel almost due west along ∼39°N across isobaths – the “Ring Corridor.” Then, west of the corridor, the mean path turns southwestward, paralleling the shelfbreak. The average ring translation speed along the mean path is 5.9 cm s−1. Long-lived rings (lifespan 〉150 days) tend to occupy the region west of the New England Seamount Chain (NESC) whereas short-lived rings (lifespan 〈150 days) tend to be more broadly distributed. WCR vertical structures, analyzed using available Argo float profiles indicate that rings that are formed to the west of the NESC have shallower thermoclines than those formed to the east. This tendency may be due to different WCR formation processes that are observed to occur along different sections of the Gulf Stream. WCRs formed to the east of the NESC tend to form from a pinch-off mechanism incorporating cores of Sargasso Sea water and a perimeter of Gulf Stream water. WCRs that form to the west of the NESC, form from a process called an aneurysm. WCRs formed through aneurysms comprise water mostly from the northern half of the Gulf Stream and are smaller than the classic pinch-off rings.

Description: AS and AG are grateful for financial support from NOAA (NA11NOS0120038), NSF (OCE-1851242 and OCE-2123283), SMAST, and UMass Dartmouth. GG was supported by NSF under grant OCE-1657853. MA was supported by NSF under grant OCE-2122726 and by ONR under grant N00014-22-1-2112.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biasi, J., Asimow, P., Horton, F., & Boyes, X. Eruption rates, tempo, and stratigraphy of Paleocene flood basalts on Baffin Island, Canada. Geochemistry, Geophysics, Geosystems, 23(9), (2022): e2021GC010172, https://doi.org/10.1029/2021gc010172.

Description: High-temperature melting in mantle plumes produces voluminous eruptions that are often temporally coincident with mass extinctions. Paleocene Baffin Island lavas—products of early Iceland mantle plume activity—are exceptionally well characterized geochemically but have poorly constrained stratigraphy, geochronology, and eruptive tempos. To provide better geologic context, we measured seven stratigraphic sections of the volcanic deposits and collected paleomagnetic data from 38 sites in the lavas and underlying Cretaceous sediments (Quqaluit Fm.). The average paleomagnetic pole from this study does not overlap with the expected pole for a stable North American locality at 60 Ma, yet the data have sufficient dispersion to average out secular variation. After ruling out other possibilities, we find that the picrites were probably erupted during a polarity transition, over less than 5 kyr. If so, the average eruption interval was ∼67 years per flow for the thickest sequence of exposed lavas. We also calculate that the flood basalts had a minimum total volume of ∼176 km3 (excluding submerged lavas in Baffin Bay). This implies a minimum eruption rate of ∼0.035 km3 yr−1, which is similar to rates found in West Greenland lavas but less than rates found in larger flood basalts. Despite this, the Baffin and West Greenland lavas temporally correlate with the “End C27n event” (a period of ∼2°C global warming) and may be its underlying cause.

Description: his work was supported by the National Science Foundation (award #1911699 to F. Horton and award #2052963 to J. Biasi), Woods Hole Oceanographic Institution (WHOI) Andrew W. Mellon Foundation Endowed Fund for Innovative Research, a National Geographic Society grant (#CP4-144R-18), and internal funding from the Caltech Geological and Planetary Sciences Division.

Description: 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(15), (2022): e2022GL099185, https://doi.org/10.1029/2022gl099185.

Description: Several large strike slip faults in central and northern California accommodate plate motions through aseismic creep. Although there is no consensus regarding the underlying cause of aseismic creep, aqueous fluids and mechanically weak, velocity-strengthening minerals appear to play a central role. This study integrates field observations and thermodynamic modeling to examine possible relationships between the occurrence of serpentinite, silica-carbonate rock, and CO2-rich aqueous fluids in creeping faults of California. Our models predict that carbonation of serpentinite leads to the formation of talc and magnesite, followed by silica-carbonate rock. While abundant exposures of silica-carbonate rock indicate complete carbonation, serpentinite-hosted CO2-rich spring fluids are strongly supersaturated with talc at elevated temperatures. Hence, carbonation of serpentinite is likely ongoing in parts of the San Andres Fault system and operates in conjunction with other modes of talc formation that may further enhance the potential for aseismic creep, thereby limiting the potential for large earthquakes.

Description: This work was supported by National Science Foundation (NSF) grants NSF-EAR-1220280 to F. K. and J. L., NSF-EAR-1219908 to D. G., and NSF-OCE-2001728 to J. L.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marsay, C. M., Landing, W. M., Umstead, D., Till, C. P., Freiberger, R., Fitzsimmons, J. N., Lanning, N. T., Shiller, A. M., Hatta, M., Chmiel, R., Saito, M., & Buck, C. S. Does sea spray aerosol contribute significantly to aerosol trace element loading? a case study from the US GEOTRACES Pacific Meridional Transect (GP15). Global Biogeochemical Cycles, 36(8), (2022): e2022GB007416. https://doi.org/10.1029/2022GB007416.

Description: Atmospheric deposition represents a major input for micronutrient trace elements (TEs) to the surface ocean and is often quantified indirectly through measurements of aerosol TE concentrations. Sea spray aerosol (SSA) dominates aerosol mass concentration over much of the global ocean, but few studies have assessed its contribution to aerosol TE loading, which could result in overestimates of “new” TE inputs. Low-mineral aerosol concentrations measured during the U.S. GEOTRACES Pacific Meridional Transect (GP15; 152°W, 56°N to 20°S), along with concurrent towfish sampling of surface seawater, provided an opportunity to investigate this aspect of TE biogeochemical cycling. Central Pacific Ocean surface seawater Al, V, Mn, Fe, Co, Ni, Cu, Zn, and Pb concentrations were combined with aerosol Na data to calculate a “recycled” SSA contribution to aerosol TE loading. Only vanadium was calculated to have a SSA contribution averaging 〉1% along the transect (mean of 1.5%). We derive scaling factors from previous studies on TE enrichments in the sea surface microlayer and in freshly produced SSA to assess the broader potential for SSA contributions to aerosol TE loading. Maximum applied scaling factors suggest that SSA could contribute significantly to the aerosol loading of some elements (notably V, Cu, and Pb), while for others (e.g., Fe and Al), SSA contributions largely remained 〈1%. Our study highlights that a lack of focused measurements of TEs in SSA limits our ability to quantify this component of marine aerosol loading and the associated potential for overestimating new TE inputs from atmospheric deposition.

Description: This research was supported by the National Science Foundation (NSF) grants OCE-1756103 to C. S. Buck, OCE-1756104 to W. M. Landing, OCE-1737024 to A.M. Shiller, OCE-1736906 to M. Hatta, OCE-1736875 to C. P. Till, OCE-1737167 to J. N. Fitzsimmons, and OCE-1736599 to M. Saito. In addition, N. T. Lanning was supported by the NSF Graduate Research Fellowship Program award 1746932.

Description: 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: Solid Earth 127(8), (2022): e2022JB024497, https://doi.org/10.1029/2022JB024497.

Description: During plastic deformation, strain weakening can be achieved, in part, via strain energy reduction associated with intragranular boundary development and grain boundary formation. Grain boundaries (in 2D) are segments between triple junctions, that connect to encircle grains; every boundary segment in the encircling loop has a high (〉10°) misorientation angle. Intragranular boundaries terminate within grains or dissect grains, usually containing boundary segments with a low (〈10°) misorientation angle. We analyze electron backscatter diffraction (EBSD) data from ice deformed at −30°C (Th≈ 0.9). Misorientation and weighted Burgers vector (WBV) statistics are calculated along planar intragranular boundaries. Misorientation angles change markedly along each intragranular boundary, linking low- (〈10°) and high-angle (10–38°) segments that exhibit distinct misorientation axes and WBV directions. We suggest that these boundaries might be produced by the growth and intersection of individual intragranular boundary segments comprising dislocations with distinct slip systems. There is a fundamental difference between misorientation axis distributions of intragranular boundaries (misorientation axes mostly confined to ice basal plane) and grain boundaries (no preferred misorientation axis). These observations suggest during progressive subgrain rotation, intragranular boundaries remain crystallographically controlled up to large misorientation angles (〉〉10°). In contrast, the apparent lack of crystallographic control for grain boundaries suggests misorientation axes become randomized, likely due to the activation of additional mechanisms (such as grain boundary sliding) after grain boundary formation, linking boundary segments to encircle a grain. Our findings on ice intragranular boundary development and grain boundary formation may apply more broadly to other rock-forming minerals (e.g., olivine, quartz).

Description: 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). Open access publishing facilitated by University of Otago, as part of the Wiley – University of Otago agreement via the Council of Australian University Librarians.

Description: 〈jats:title〉Abstract〈/jats:title〉 〈jats:p〉Tipping points in the Earth system describe critical thresholds beyond which a single component, part of the system, or the system as a whole changes from one stable state to another. In the present-day Southern Ocean, the Weddell Sea constitutes an important dense-water formation site, associated with efficient deep-ocean carbon and oxygen transfer and low ice-shelf basal melt rates. Here, a regime shift will occur when continental shelves are continuously flushed with warm, oxygen-poor offshore waters from intermediate depth, leading to less efficient deep-ocean carbon and oxygen transfer and higher ice-shelf basal melt rates. We use a global ocean–biogeochemistry model including ice-shelf cavities and an eddy-permitting grid in the southern Weddell Sea to address the susceptibility of this region to such a system change for four 21〈jats:sup〉st〈/jats:sup〉-century emission scenarios. Assessing the projected changes in shelf–open ocean density gradients, bottom-water properties, and on-shelf heat transport, our results indicate that the Weddell Sea undergoes a regime shift by 2100 in the highest-emission scenario SSP5-8.5, but not yet in the lower-emission scenarios. The regime shift is imminent by 2100 in the scenarios SSP3-7.0 and SSP2-4.5, but avoidable under the lowest-emission scenario SSP1-2.6. While shelf-bottom waters freshen and acidify everywhere, bottom waters in the Filchner Trough undergo accelerated warming and deoxygenation following the system change, with implications for local ecosystems and ice-shelf basal melt. Additionally, deep-ocean carbon and oxygen transfer decline, implying that the local changes ultimately affect ocean circulation, climate, and ecosystems globally.〈/jats:p〉

Description: Mechanisms behind the phenomenon of Arctic amplification are widely discussed. To contribute to this debate, the (AC)3 project was established in 2016 (www.ac3-tr.de/). It comprises modeling and data analysis efforts as well as observational elements. The project has assembled a wealth of ground-based, airborne, shipborne, and satellite data of physical, chemical, and meteorological properties of the Arctic atmosphere, cryosphere, and upper ocean that are available for the Arctic climate research community. Short-term changes and indications of long-term trends in Arctic climate parameters have been detected using existing and new data. For example, a distinct atmospheric moistening, an increase of regional storm activities, an amplified winter warming in the Svalbard and North Pole regions, and a decrease of sea ice thickness in the Fram Strait and of snow depth on sea ice have been identified. A positive trend of tropospheric bromine monoxide (BrO) column densities during polar spring was verified. Local marine/biogenic sources for cloud condensation nuclei and ice nucleating particles were found. Atmospheric–ocean and radiative transfer models were advanced by applying new parameterizations of surface albedo, cloud droplet activation, convective plumes and related processes over leads, and turbulent transfer coefficients for stable surface layers. Four modes of the surface radiative energy budget were explored and reproduced by simulations. To advance the future synthesis of the results, cross-cutting activities are being developed aiming to answer key questions in four focus areas: lapse rate feedback, surface processes, Arctic mixed-phase clouds, and airmass transport and transformation.

Description: We present measurements of soil CO2 effluxes combined with soil (222Rn) and (220Rn) from two high-degassing areas on the lower flanks of Mt. Etna volcano (ZE-SV on the E flank and PAT on the SW flank). Measurements were conducted periodically from June 2006 to January 2009 in the ZE-SV area and January 2007 to January 2009 in the PAT area. The results showed significant variations in discharge activity and style. Log values of (220Rn)/(222Rn) and CO2 efflux generally follow a negative correlation, herein parameterized as the Soil Gas Disequilibrium Index (SGDI). Deviations of the SGDI from this negative correlation provide insight into variance of localized and shallow system conditions, namely rock fracturing, residual magma degassing, and near surface interactions between magmatic gases and groundwater. Statistical analysis highlighted signal anomalies, both negative and positive, that were modeled according to the physical properties and the modes of transport for each of the SGDI gas components. The revealed anomalies show correspondence with episodes of magma ascent and eruption, thereby demonstrating the potential of using the SGDI as another instrument for forecasting volcanic activity. An important strength of the SGDI, compared to other magma gas proxies like CO2 or SO2, is that the very short and very different half-lives of 222Rn (t1/2 = 3.85 days) and 220Rn (t1/2 = 55 seconds) provide unique information on the timescales of soil gas transport. Coupling the SGDI with other pre-eruptive proxies enhances the volcanological community’s response capabilities, which is critical for effective hazard mitigation.

Description: Published

Description: 167-202

Description: 4V. Processi pre-eruttivi

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Fabbrizzi, A., Parnell‐Turner, R., Gregg, P., Fornari, D., Perfit, M., Wanless, V., & Anderson, M. Relative timing of off‐axis volcanism from sediment thickness estimates on the 8°20’N seamount chain, East Pacific Rise. Geochemistry, Geophysics, Geosystems, 23(9), (2022): e2022GC010335, https://doi.org/10.1029/2022gc010335.

Description: Volcanic seamount chains on the flanks of mid-ocean ridges record variability in magmatic processes associated with mantle melting over several millions of years. However, the relative timing of magmatism on individual seamounts along a chain can be difficult to estimate without in situ sampling and is further hampered by Ar40/Ar39 dating limitations. The 8°20’N seamount chain extends ∼170 km west from the fast-spreading East Pacific Rise (EPR), north of and parallel to the western Siqueiros fracture zone. Here, we use multibeam bathymetric data to investigate relationships between abyssal hill formation and seamount volcanism, transform fault slip, and tectonic rotation. Near-bottom compressed high-intensity radiated pulse, bathymetric, and sidescan sonar data collected with the autonomous underwater vehicle Sentry are used to test the hypothesis that seamount volcanism is age-progressive along the seamount chain. Although sediment on seamount flanks is likely to be reworked by gravitational mass-wasting and current activity, bathymetric relief and Sentry vehicle heading analysis suggest that sedimentary accumulations on seamount summits are likely to be relatively pristine. Sediment thickness on the seamounts' summits does not increase linearly with nominal crustal age, as would be predicted if seamounts were constructed proximal to the EPR axis and then aged as the lithosphere cooled and subsided away from the ridge. The thickest sediments are found at the center of the chain, implying the most ancient volcanism there, rather than on seamounts furthest from the EPR. The nonlinear sediment thickness along the 8°20’N seamounts suggests that volcanism can persist off-axis for several million years.

Description: This work was supported by National Science Foundation awards OCE-1356610, OCE-1356822, OCE-1357150, OCE-1754419, OCE-1834797, OCE-2001314, and OCE-2001331.

Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(8), (2022): 1705-1730, https://doi.org/10.1175/jpo-d-21-0243.1.

Description: Formation and evolution of barrier layers (BLs) and associated temperature inversions (TIs) were investigated using a 1-yr time series of oceanic and air–sea surface observations from three moorings deployed in the eastern Pacific fresh pool. BL thickness and TI amplitude showed a seasonality with maxima in boreal summer and autumn when BLs were persistently present. Mixed layer salinity (MLS) and mixed layer temperature (MLT) budgets were constructed to investigate the formation mechanism of BLs and TIs. The MLS budget showed that BLs were initially formed in response to horizontal advection of freshwater in boreal summer and then primarily maintained by precipitation. The MLT budget revealed that penetration of shortwave radiation through the mixed layer base is the dominant contributor to TI formation through subsurface warming. Geostrophic advection is a secondary contributor to TI formation through surface cooling. When the BL exists, the cooling effect from entrainment and the warming effect from detrainment are both significantly reduced. In addition, when the BL is associated with the presence of a TI, entrainment works to warm the mixed layer. The presence of BLs makes the shallower mixed layer more sensitive to surface heat and freshwater fluxes, acting to enhance the formation of TIs that increase the subsurface warming via shortwave penetration.

Description: SK is supported by JSPS Overseas Research Fellowships. JS and SK are supported by NASA Grant 80NSSC18K1500. JTF and the mooring deployment were funded by NASA Grants NNX15AG20G and 80NSSC18K1494. DZ is supported by NASA Grant 80NSSC18K1499. This publication is partially funded by the Cooperative Institute for Climate, Ocean, and Ecosystem Studies (CICOES) under NOAA Cooperative Agreement NA20OAR4320271, Contribution 2021-1152. This is PMEL Contribution 5268.

Description: 2023-01-27

Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(8), (2022): 1927-1943, https://doi.org/10.1175/jpo-d-21-0124.1.

Description: The Galápagos Archipelago lies on the equator in the path of the eastward flowing Pacific Equatorial Undercurrent (EUC). When the EUC reaches the archipelago, it upwells and bifurcates into a north and south branch around the archipelago at a latitude determined by topography. Since the Coriolis parameter (f) equals zero at the equator, strong velocity gradients associated with the EUC can result in Ertel potential vorticity (Q) having sign opposite that of planetary vorticity near the equator. Observations collected by underwater gliders deployed just west of the Galápagos Archipelago during 2013–16 are used to estimate Q and to diagnose associated instabilities that may impact the Galápagos Cold Pool. Estimates of Q are qualitatively conserved along streamlines, consistent with the 2.5-layer, inertial model of the EUC by Pedlosky. The Q with sign opposite of f is advected south of the Galápagos Archipelago when the EUC core is located south of the bifurcation latitude. The horizontal gradient of Q suggests that the region between 2°S and 2°N above 100 m is barotropically unstable, while limited regions are baroclinically unstable. Conditions conducive to symmetric instability are observed between the EUC core and the equator and within the southern branch of the undercurrent. Using 2-month and 3-yr averages, e-folding time scales are 2–11 days, suggesting that symmetric instability can persist on those time scales.

Description: This work was supported by the National Science Foundation (Grants OCE-1232971 and OCE-1233282), the NASA Earth and Space Science Fellowship Program (Grant 80NSSC17K0443), and the Global Ocean Monitoring and Observing Program of the National Oceanographic and Atmospheric Administration (NA13OAR4830216). Color maps are from Thyng et al. (2016).

Description: 2023-02-01

Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(8), (2022): 1183-1198, https://doi.org/10.1175/jtech-d-21-0068.1.

Description: Horizontal kinematic properties, such as vorticity, divergence, and lateral strain rate, are estimated from drifter clusters using three approaches. At submesoscale horizontal length scales O(1–10)km, kinematic properties become as large as planetary vorticity f, but challenging to observe because they evolve on short time scales O(hourstodays). By simulating surface drifters in a model flow field, we quantify the sources of uncertainty in the kinematic property calculations due to the deformation of cluster shape. Uncertainties arise primarily due to (i) violation of the linear estimation methods and (ii) aliasing of unresolved scales. Systematic uncertainties (iii) due to GPS errors, are secondary but can become as large as (i) and (ii) when aspect ratios are small. Ideal cluster parameters (number of drifters, length scale, and aspect ratio) are determined and error functions estimated empirically and theoretically. The most robust method—a two-dimensional, linear least squares fit—is applied to the first few days of a drifter dataset from the Bay of Bengal. Application of the length scale and aspect-ratio criteria minimizes errors (i) and (ii), and reduces the total number of clusters and so computational cost. The drifter-estimated kinematic properties map out a cyclonic mesoscale eddy with a surface, submesoscale fronts at its perimeter. Our analyses suggest methodological guidance for computing the two-dimensional kinematic properties in submesoscale flows, given the recently increasing quantity and quality of drifter observations, while also highlighting challenges and limitations.

Description: This research was supported by the Office of Naval Research (ONR) Departmental Research Initiative ASIRI under Grant N00014-13-1-0451 (SE and AM) and Grant N00014-13-1-0477 (VH and LC). The authors thank the captain and crew of the R/V Roger Revelle, and Andrew Lucas with the Multiscale Ocean Dynamics group at the Scripps Institution for Oceanography for providing the FastCTD data collected in 2015, which was supported by ONR Grant N00014-13-1-0489, as well as Eric D’Asaro for helpful discussions and Lance Braasch for assistance with the drifter dataset. AM and SE further thank NSF (Grant OCE-I434788) and ONR (Grant N00014-16-1-2470) for support. VH and LC were additionally supported by ONR Grants N00014-15-1-2286, N00014-14-1-0183, N00014-19-1-26-91 and NOAA Global Drifter Program (GDP) Grant NA15OAR4320071.

Description: 2023-02-01

Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 35(17), (2022): 5465-5482, https://doi.org/10.1175/jcli-d-21-0671.1.

Description: Understanding the contribution of ocean circulation to glacial–interglacial climate change is a major focus of paleoceanography. Specifically, many have tried to determine whether the volumes and depths of Antarctic- and North Atlantic–sourced waters in the deep ocean changed at the Last Glacial Maximum (LGM; ∼22–18 kyr BP) when atmospheric pCO2 concentrations were 100 ppm lower than the preindustrial. Measurements of sedimentary geochemical proxies are the primary way that these deep ocean structural changes have been reconstructed. However, the main proxies used to reconstruct LGM Atlantic water mass geometry provide conflicting results as to whether North Atlantic–sourced waters shoaled during the LGM. Despite this, a number of idealized modeling studies have been advanced to describe the physical processes resulting in shoaled North Atlantic waters. This paper aims to critically assess the approaches used to determine LGM Atlantic circulation geometry and lay out best practices for future work. We first compile existing proxy data and paleoclimate model output to deduce the processes responsible for setting the ocean distributions of geochemical proxies in the LGM Atlantic Ocean. We highlight how small-scale mixing processes in the ocean interior can decouple tracer distributions from the large-scale circulation, complicating the straightforward interpretation of geochemical tracers as proxies for water mass structure. Finally, we outline promising paths toward ascertaining the LGM circulation structure more clearly and deeply.

Description: S.K.H. was supported by the Investment in Science Fund at WHOI and the John E. and Anne W. Sawyer Endowed Fund in Support of Scientific Staff. F.J.P. was supported by a Stanback Postdoctoral Fellowship at Caltech.

Description: 2023-02-01

Description: 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(3), (2021): e2020GB006764, https://doi.org/10.1029/2020GB006764

Description: Export of Particulate Organic Carbon (POC) is mainly driven by gravitational sinking. Thus, traditionally, it is thought that larger, faster-sinking particles make up most of the POC export flux. However, this need not be the case for particles whose sinking speeds are comparable to the vertical velocities of a dynamic flow field that can influence the descent rate of particles. Particles with different settling speeds are released in two process-oriented model simulations of an upper ocean eddying flow in the Northeast Pacific to evaluate the impact of (1) ocean dynamics on the respective contribution of the different sinking-velocity classes to POC export, and (2) the particle number size-spectrum slope. The analysis reveals that the leading export mechanism changes from gravitationally driven to advectively driven as submesoscale dynamics become more active in the region. The vertical velocity associated with submesoscale dynamics enhances the contribution of slower-sinking particles to POC export flux by a factor ranging from 3 to 10, especially where the relative abundance of small particles is large (i.e., steep particle size-spectrum slope). Remineralization generally decreases the total amount of biomass exported, but its impact is weaker in dynamical regimes where submesoscale dynamics are present and export is advectively driven. In an advectively driven export regime, remineralization processes counter-intuitively enhance the role of slower-sinking particles to the point where these slower-sinking velocity classes dominate the export, therefore challenging the traditional paradigm for POC export. This study demonstrates that slow-sinking particles can be a significant contribution, and at times, even dominate the export flux.

Description: The work was funded by NASA grant NNX16AR48 G, to complement the EXport Processes in the global Ocean from RemoTe Sensing (EXPORTS) program.

Description: 2021-08-17

Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(10), (2022): 1525–1539, https://doi.org/10.1175/jtech-d-21-0186.1.

Description: The static and dynamic performances of the RBRargo3 are investigated using a combination of laboratory-based and in situ datasets from floats deployed as part of an Argo pilot program. Temperature and pressure measurements compare well to co-located reference data acquired from shipboard CTDs. Static accuracy of salinity measurements is significantly improved using 1) a time lag for temperature, 2) a quadratic pressure dependence, and 3) a unit-based calibration for each RBRargo3 over its full pressure range. Long-term deployments show no significant drift in the RBRargo3 accuracy. The dynamic response of the RBRargo3 demonstrates the presence of two different adjustment time scales: a long-term adjustment O(120) s, driven by the temperature difference between the interior of the conductivity cell and the water, and a short-term adjustment O(5–10) s, associated to the initial exchange of heat between the water and the inner ceramic. Corrections for these effects, including dependence on profiling speed, are developed.

Description: 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(19), (2021): e2021GL095088, https://doi.org/10.1029/2021GL095088.

Description: The physical circulation of the Southern Ocean sets the surface concentration and thus air-sea exchange of CO2. However, we have a limited understanding of the three-dimensional circulation that brings deep carbon-rich waters to the surface. Here, we introduce and analyze a novel high-resolution ocean model simulation with active biogeochemistry and online Lagrangian particle tracking. We focus our attention on a subset of particles with high dissolved inorganic carbon (DIC) that originate below 1,000 m and eventually upwell into the near-surface layer (upper 200 m). We find that 71% of the DIC-enriched water upwelling across 1,000 m is concentrated near topographic features, which occupy just 33% of the Antarctic Circumpolar Current. Once particles upwell to the near-surface layer, they exhibit relatively uniform pCO2 levels and DIC decorrelation timescales, regardless of their origin. Our results show that Southern Ocean bathymetry plays a key role in delivering carbon-rich waters to the surface.

Description: Riley X. Brady was supported by the Department of Energy's Computational Science Graduate Fellowship (DE-FG02-97ER25308), and particularly benefited from the fellowship's summer practicum at Los Alamos National Lab. Nicole S. Lovenduski and Riley X. Brady were further supported by the U.S. Department of Energy Biological and Environmental Research program (DE-SC0022243) and by the National Science Foundation (NSF-PLR 1543457; NSF-OCE 1924636; NSF-OCE 1752724; NSF-OCE 1558225). Mathew E. Maltrud and Phillip J. Wolfram were supported as part of the Energy Exascale Earth System Model (E3SM) project, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. This research used resources provided by the Los Alamos National Laboratory Institutional Computing Program, which is supported by the U.S. Department of Energy National Nuclear Security Administration under Contract No. 89233218CNA000001.

Description: 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: Biogeosciences 127(8), (2022): e2022JG006810, https://doi.org/10.1029/2022jg006810.

Description: Submarine groundwater discharge (SGD) has been widely recognized as an important source of dissolved nutrients in coastal waters and affects nutrient biogeochemistry. In contrast, little information is available on SGD impacts on coastal carbon budgets. Here, we assessed the SGD and associated carbon (dissolved inorganic carbon [DIC] and total alkalinity [TA]) fluxes in Liaodong Bay (the largest bay of the Bohai Sea, China) and discussed their border implications for coastal DIC budget and buffering capacity. Based on 223Ra and 228Ra mass balance models, the SGD flux was estimated to be (0.92–1.43) × 109 m3 d−1. SGD was the largest contributor of DIC, accounting for 55%–77% of the total DIC sources. The low ratio (〈1) of SGD-derived TA to DIC fluxes and negative correlation between radium isotopes and pH in seawater implied that SGD would potentially reduce seawater pH in Liaodong Bay. Combining the groundwater carbon data in Liaodong Bay with literature data, we found that the SGD-derived DIC flux off China was 4–9 times greater than those from rivers. By analyzing the TA/DIC ratios in groundwater along the Chinese coast and related carbon fluxes, SGD was thought to partially reduce the CO2 buffer capacity in receiving seawater. These results obtained at the bay scale and national scale suggest that SGD is a significant component of carbon budget and may play a critical role in modulating coastal buffering capacity and atmospheric CO2 sequestration.

Description: his research was supported by National Natural Science Foundation of China (Grant Nos. 42130703, 42007170) and the Science, Technology and Innovation Commission of Shenzhen (Grant No. 20200925174525002.

Description: 2023-01-20

Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(12),(2022): 3199-3219, https://doi.org/10.1175/jpo-d-22-0009.1.

Description: The abyssal overturning circulation is thought to be primarily driven by small-scale turbulent mixing. Diagnosed water-mass transformations are dominated by rough topography “hotspots,” where the bottom enhancement of mixing causes the diffusive buoyancy flux to diverge, driving widespread downwelling in the interior—only to be overwhelmed by an even stronger upwelling in a thin bottom boundary layer (BBL). These water-mass transformations are significantly underestimated by one-dimensional (1D) sloping boundary layer solutions, suggesting the importance of three-dimensional physics. Here, we use a hierarchy of models to generalize this 1D boundary layer approach to three-dimensional eddying flows over realistically rough topography. When applied to the Mid-Atlantic Ridge in the Brazil Basin, the idealized simulation results are roughly consistent with available observations. Integral buoyancy budgets isolate the physical processes that contribute to realistically strong BBL upwelling. The downward diffusion of buoyancy is primarily balanced by upwelling along the sloping canyon sidewalls and the surrounding abyssal hills. These flows are strengthened by the restratifying effects of submesoscale baroclinic eddies and by the blocking of along-ridge thermal wind within the canyon. Major topographic sills block along-thalweg flows from restratifying the canyon trough, resulting in the continual erosion of the trough’s stratification. We propose simple modifications to the 1D boundary layer model that approximate each of these three-dimensional effects. These results provide local dynamical insights into mixing-driven abyssal overturning, but a complete theory will also require the nonlocal coupling to the basin-scale circulation.

Description: We acknowledge funding support from National Science Foundation Awards 1536515, 1736109, and 2149080. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant 174530.

Description: 2023-05-18

Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(6), (2022): 1091–1110, https://doi.org/10.1175/JPO-D-21-0068.1.

Description: Hundreds of full-depth temperature and salinity profiles collected by Deepglider autonomous underwater vehicles (AUVs) in the North Atlantic reveal robust signals in eddy isopycnal vertical displacement and horizontal current throughout the entire water column. In separate glider missions southeast of Bermuda, subsurface-intensified cold, fresh coherent vortices were observed with velocities exceeding 20 cm s−1 at depths greater than 1000 m. With vertical resolution on the order of 20 m or less, these full-depth glider slant profiles newly permit estimation of scaled vertical wavenumber spectra from the barotropic through the 40th baroclinic mode. Geostrophic turbulence theory predictions of spectral slopes associated with the forward enstrophy cascade and proportional to inverse wavenumber cubed generally agree with glider-derived quasi-universal spectra of potential and kinetic energy found at a variety of locations distinguished by a wide range of mean surface eddy kinetic energy. Water-column average spectral estimates merge at high vertical mode number to established descriptions of internal wave spectra. Among glider mission sites, geographic and seasonal variability implicate bottom drag as a mechanism for dissipation, but also the need for more persistent sampling of the deep ocean.

Description: This work was funded by NSF Grant 1736217 and would not have been possible without the help of Kirk O’Donnell, James Bennett, Noel Pelland, and all contributors to Deepglider development. We additionally thank the captain crew of the R/V Atlantic Explorer and the BATS team at the Bermuda Institute of Ocean Sciences, particularly Rod Johnson, as well as Seakeepers International for their professionalism, capability, and generous assistance in deploying and recovering gliders.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Seltzer, A. M., & Tyne, R. L. Retrieving a “Weather Balloon” from the last Ice Age. AGU Advances, 3(4), (2022): e2022AV000747, https://doi.org/10.1029/2022AV000747.

Description: “How cold was the last ice age?” is a question that paleoclimate scientists have been trying to answer for decades. Constraining the magnitude of climate change since the Last Glacial Maximum (∼20,000 years ago) can help improve our understanding of Earth's climate sensitivity and, therefore enhance our ability to predict future change (Tierney et al., 2020). Of course, there is no single answer to this question: there is spatial structure to LGM temperature change that is linked to fundamental climate system properties and processes. Consequently, paleoclimate scientists have focused on variations of this question, like “What was the latitudinal gradient of LGM temperature change?” (Chiang et al., 2003), “What was the land-sea contrast?” (Rind & Peteet, 1985) or “What was the change in ocean heat content?” (Bereiter et al., 2018). These questions inform large-scale atmospheric and oceanic circulation, the intensity of the water cycle, and planetary energy balance; the answers to these questions come from proxies like planktic and benthic foraminifera, speleothems, ice cores, pollen records, ancient groundwater, lake sediments, and glacial moraines, to name a few. In short, the paleoclimate community has developed a proxy “tool kit” equipped to map changes across the Earth's surface and into the ocean interior; but, until now, no “tool” existed for the upper atmosphere.

Description: © The Author(s), 2023. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Timmermans, M.-L., & Toole, J. The Arctic Ocean’s Beaufort Gyre. Annual Review of Marine Science, 15(1), (2023): 223-248, https://doi.org/10.1146/annurev-marine-032122-012034.

Description: The Arctic Ocean's Beaufort Gyre is a dominant feature of the Arctic system, a prominent indicator of climate change, and possibly a control factor for high-latitude climate. The state of knowledge of the wind-driven Beaufort Gyre is reviewed here, including its forcing, relationship to sea-ice cover, source waters, circulation, and energetics. Recent decades have seen pronounced change in all elements of the Beaufort Gyre system. Sea-ice losses have accompanied an intensification of the gyre circulation and increasing heat and freshwater content. Present understanding of these changes is evaluated, and time series of heat and freshwater content are updated to include the most recent observations.

Description: Support was provided by the National Science Foundation Office of Polar Programs and the Office of Naval Research.

Description: 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(8), (2022): e2022GB007320, https://doi.org/10.1029/2022GB007320.

Description: Biogeochemical cycles in the Arctic Ocean are sensitive to the transport of materials from continental shelves into central basins by sea ice. However, it is difficult to assess the net effect of this supply mechanism due to the spatial heterogeneity of sea ice content. Manganese (Mn) is a micronutrient and tracer which integrates source fluctuations in space and time while retaining seasonal variability. The Arctic Ocean surface Mn maximum is attributed to freshwater, but studies struggle to distinguish sea ice and river contributions. Informed by observations from 2009 IPY and 2015 Canadian GEOTRACES cruises, we developed a three-dimensional dissolved Mn model within a 1/12° coupled ocean-ice model centered on the Canada Basin and the Canadian Arctic Archipelago (CAA). Simulations from 2002 to 2019 indicate that annually, 87%–93% of Mn contributed to the Canada Basin upper ocean is released by sea ice, while rivers, although locally significant, contribute only 2.2%–8.5%. Downstream, sea ice provides 34% of Mn transported from Parry Channel into Baffin Bay. While rivers are often considered the main source of Mn, our findings suggest that in the Canada Basin they are less important than sea ice. However, within the shelf-dominated CAA, both rivers and sediment resuspension are important. Climate-induced disruption of the transpolar drift may reduce the Canada Basin Mn maximum and supply downstream. Other micronutrients found in sediments, such as Fe, may be similarly affected. These results highlight the vulnerability of the biogeochemical supply mechanisms in the Arctic Ocean and the subpolar seas to climatic changes.

Description: This work was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) Climate Change and Atmospheric Research Grant: GEOTRACES (RGPCC 433848-12) and VITALS (RGPCC 433898), an NSERC Discovery Grant (RGPIN-2016-03865) to SEA, and by the University of British Columbia through a four year fellowship to BR. Computing resources were provided by Compute Canada (RRG 2648 RAC 2019, RRG 2969 RAC 2020, and RRG 1541 RAC 2021).

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Shinevar, W., Jagoutz, O., & Behn, M. WISTFUL: whole‐rock interpretative seismic toolbox for ultramafic lithologies. Geochemistry, Geophysics, Geosystems, 23(8), (2022): e2022GC010329, https://doi.org/10.1029/2022gc010329.

Description: To quantitatively convert upper mantle seismic wave speeds measured into temperature, density, composition, and corresponding and uncertainty, we introduce the Whole-rock Interpretative Seismic Toolbox For Ultramafic Lithologies (WISTFUL). WISTFUL is underpinned by a database of 4,485 ultramafic whole-rock compositions, their calculated mineral modes, elastic moduli, and seismic wave speeds over a range of pressure (P) and temperature (T) (P = 0.5–6 GPa, T = 200–1,600°C) using the Gibbs free energy minimization routine Perple_X. These data are interpreted with a toolbox of MATLAB® functions, scripts, and three general user interfaces: WISTFUL_relations, which plots relationships between calculated parameters and/or composition; WISTFUL_geotherms, which calculates seismic wave speeds along geotherms; and WISTFUL_inversion, which inverts seismic wave speeds for best-fit temperature, composition, and density. To evaluate our methodology and quantify the forward calculation error, we estimate two dominant sources of uncertainty: (a) the predicted mineral modes and compositions, and (b) the elastic properties and mixing equations. To constrain the first source of uncertainty, we compiled 122 well-studied ultramafic xenoliths with known whole-rock compositions, mineral modes, and estimated P-T conditions. We compared the observed mineral modes with modes predicted using five different thermodynamic solid solution models. The Holland et al. (2018, https://doi.org/10.1093/petrology/egy048) solution models best reproduce phase assemblages (∼12 vol. % phase root-mean-square error [RMSE]) and estimated wave speeds. To assess the second source of uncertainty, we compared wave speed measurements of 40 ultramafic rocks with calculated wave speeds, finding excellent agreement (Vp RMSE = 0.11 km/s). WISTFUL easily analyzes seismic datasets, integrates into modeling, and acts as an educational tool.

Description: Funding for this study was provided by NSF Grants EAR-17-22935 (OJ) and EAR-18-44340 (MB).

Description: Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(12), (2022): 3221–3240, https://doi.org/10.1175/jpo-d-22-0010.1.

Description: Small-scale mixing drives the diabatic upwelling that closes the abyssal ocean overturning circulation. Indirect microstructure measurements of in situ turbulence suggest that mixing is bottom enhanced over rough topography, implying downwelling in the interior and stronger upwelling in a sloping bottom boundary layer. Tracer release experiments (TREs), in which inert tracers are purposefully released and their dispersion is surveyed over time, have been used to independently infer turbulent diffusivities—but typically provide estimates in excess of microstructure ones. In an attempt to reconcile these differences, Ruan and Ferrari derived exact tracer-weighted buoyancy moment diagnostics, which we here apply to quasi-realistic simulations. A tracer’s diapycnal displacement rate is exactly twice the tracer-averaged buoyancy velocity, itself a convolution of an asymmetric upwelling/downwelling dipole. The tracer’s diapycnal spreading rate, however, involves both the expected positive contribution from the tracer-averaged in situ diffusion as well as an additional nonlinear diapycnal distortion term, which is caused by correlations between buoyancy and the buoyancy velocity, and can be of either sign. Distortion is generally positive (stretching) due to bottom-enhanced mixing in the stratified interior but negative (contraction) near the bottom. Our simulations suggest that these two effects coincidentally cancel for the Brazil Basin Tracer Release Experiment, resulting in negligible net distortion. By contrast, near-bottom tracers experience leading-order distortion that varies in time. Errors in tracer moments due to realistically sparse sampling are generally small (〈20%), especially compared to the O(1) structural errors due to the omission of distortion effects in inverse models. These results suggest that TREs, although indispensable, should not be treated as “unambiguous” constraints on diapycnal mixing.

Description: We acknowledge funding support from National Science Foundation Awards 1536515 and 1736109. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant 174530. This research is also supported by the NOAA Climate and Global Change Postdoctoral Fellowship Program, administered by UCAR’s Cooperative Programs for the Advancement of Earth System Science (CPAESS) under Award NA18NWS4620043B.

Description: 2023-05-18

Description: 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(9), (2022): e2021GB007145, https://doi.org/10.1029/2021gb007145.

Description: In this study, we compare mechanistic and empirical approaches to reconstruct the air-sea flux of biological oxygen (F[O2]bio-as) by parameterizing the physical oxygen saturation anomaly (ΔO2[phy]) in order to separate the biological contribution from total oxygen. The first approach matches ΔO2[phy] to the monthly climatology of the argon saturation anomaly from a global ocean circulation model's output. The second approach derives ΔO2[phy] from an iterative mass balance model forced by satellite-based physical drivers of ΔO2[phy] prior to the sampling day by assuming that air-sea interactions are the dominant factors driving the surface ΔO2[phy]. The final approach leverages the machine-learning technique of Genetic Programming (GP) to search for the functional relationship between ΔO2[phy] and biophysicochemical parameters. We compile simultaneous measurements of O2/Ar and O2 concentration from 14 cruises to train the GP algorithm and test the validity and applicability of our modeled ΔO2[phy] and F[O2]bio-as. Among the approaches, the GP approach, which incorporates ship-based measurements and historical records of physical parameters from the reanalysis products, provides the most robust predictions (R2 = 0.74 for ΔO2[phy] and 0.72 for F[O2]bio-as; RMSE = 1.4% for ΔO2[phy] and 7.1 mmol O2 m−2 d−1 for F[O2]bio-as). We use the empirical formulation derived from GP approach to reconstruct regional, inter-annual, and decadal variability of F[O2]bio-as based on historical oxygen records. Overall, our study represents a first attempt at deriving F[O2]bio-as from snapshot measurements of oxygen, thereby paving the way toward using historical O2 data and a rapidly growing number of O2 measurements on autonomous platforms for independent insight into the biological pump.

Description: N. Cassar was supported by the “Laboratoire d'Excellence” LabexMER (ANR-10-LABX-19) and co-funded by a grant from the French government under the program “Investissements d'Avenir.” Y. Huang was supported by grants from the China NSF (Nos. 42130401 and 42141002). Y. Huang was also partly supported by Chinese State Scholarship Fund to study at Duke University as a joint PhD student (No. 201806310052). R. Eveleth was supported by the NSF GRFP under grant (No. 1106401). D. Nicholson was supported by the NSF OCE-1129973 and OCE-1923915.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sayani, H., Cobb, K., Monteleone, B., & Bridges, H. Accuracy and reproducibility of coral Sr/Ca SIMS timeseries in modern and fossil corals. Geochemistry, Geophysics, Geosystems, 23(9), (2022): e2021GC010068, https://doi.org/10.1029/2021gc010068.

Description: Coral strontium-to-calcium ratios (Sr/Ca) provide quantitative estimates of past sea surface temperatures (SST) that allow for the reconstruction of changes in the mean state and climate variations, such as the El Nino-Southern Oscillation, through time. However, coral Sr/Ca ratios are highly susceptible to diagenesis, which can impart artifacts of 1–2°C that are typically on par with the tropical climate signals of interest. Microscale sampling via Secondary Ion Mass Spectrometry (SIMS) for the sampling of primary skeletal material in altered fossil corals, providing much-needed checks on fossil coral Sr/Ca-based paleotemperature estimates. In this study, we employ a set modern and fossil corals from Palmyra Atoll, in the central tropical Pacific, to quantify the accuracy and reproducibility of SIMS Sr/Ca analyses relative to bulk Sr/Ca analyses. In three overlapping modern coral samples, we reproduce bulk Sr/Ca estimates within ±0.3% (1σ). We demonstrate high fidelity between 3-month smoothed SIMS coral Sr/Ca timeseries and SST (R = −0.5 to −0.8; p 〈 0.5). For lightly-altered sections of a young fossil coral from the early-20th century, SIMS Sr/Ca timeseries reproduce bulk Sr/Ca timeseries, in line with our results from modern corals. Across a moderately-altered section of the same fossil coral, where diagenesis yields bulk Sr/Ca estimates that are 0.6 mmol too high (roughly equivalent to −6°C artifacts in SST), SIMS Sr/Ca timeseries track instrumental SST timeseries. We conclude that 3–4 SIMS analyses per month of coral growth can provide a much-needed quantitative check on the accuracy of fossil coral Sr/Ca-derived estimates of paleotemperature, even in moderately altered samples.

Description: We'd also like to thank Yolande Berta and Georgia Tech's Center for Nanostructure Characterization for providing access to their SEM facilities, and the Khaled bin Sultan Living Ocean Foundation and The Nature Conservancy for financial and logistical support for field excursions to Palmyra. Funding for this work was provided by the National Science Foundation (Award Numbers 1502832 and 2002458 to K.M.C) and the National Oceanic and Atmospheric Administration (Award Number: NA11OAR4310165 to K.M.C).

Description: 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): e2019JC016007, doi:10.1029/2019JC016007.

Description: Benthic inputs of nutrients help support primary production in the Chukchi Sea and produce nutrient‐rich water masses that ventilate the halocline of the western Arctic Ocean. However, the complex biological and redox cycling of nutrients and trace metals make it difficult to directly monitor their benthic fluxes. In this study, we use radium‐228, which is a soluble radionuclide produced in sediments, and a numerical model of an inert, generic sediment‐derived tracer to study variability in sediment inputs to the Chukchi Sea. The 228Ra observations and modeling results are in general agreement and provide evidence of strong benthic inputs to the southern Chukchi Sea during the winter, while the northern shelf receives higher concentrations of sediment‐sourced materials in the spring and summer due to continued sediment‐water exchange as the water mass traverses the shelf. The highest tracer concentrations are observed near the shelfbreak and southeast of Hanna Shoal, a region known for high biological productivity and enhanced benthic biomass.

Description: This study presents data from multiple Arctic expeditions over the past two decades, and we are indebted to the captains, crews, and scientific parties that made this data collection possible. This work was funded by NSF awards OCE‐1458305 to M. Charette, OCE‐1458424 to W. Moore, OCE‐1434085 to D. Kadko, PLR‐1504333 to R. Pickart, and OPP‐1822334 to M. Spall. Funding was also provided by National Oceanic and Atmospheric Administration Grant NA14‐OAR4320158 to R. Pickart. L. Kipp was supported by an Ocean Frontier Institute Postdoctoral Fellowship. Radium data used in this manuscript are available in Table S1.

Description: 2020-10-27

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Tarry, D., Ruiz, S., Johnston, T., Poulain, P., Özgökmen, T., Centurioni, L., Berta, M., Esposito, G., Farrar, J., Mahadevan, A., & Pascual, A. Drifter observations reveal intense vertical velocity in a surface ocean front. Geophysical Research Letters, 49(18), (2022): e2022GL098969, https://doi.org/10.1029/2022gl098969.

Description: Measuring vertical motions represent a challenge as they are typically 3–4 orders of magnitude smaller than the horizontal velocities. Here, we show that surface vertical velocities are intensified at submesoscales and are dominated by high frequency variability. We use drifter observations to calculate divergence and vertical velocities in the upper 15 m of the water column at two different horizontal scales. The drifters, deployed at the edge of a mesoscale eddy in the Alboran Sea, show an area of strong convergence (urn:x-wiley:00948276:media:grl64766:grl64766-math-0001(f)) associated with vertical velocities of −100 m day−1. This study shows that a multilayered-drifter array can be an effective tool for estimating vertical velocity near the ocean surface.

Description: This research was supported by the Office of Naval Research (ONR) Departmental Research Initiative CALYPSO under program officers Terri Paluszkiewicz and Scott Harper. The authors' ONR Grant No. are as follows: DT, SR, AM, and AP N000141613130, TMSJ N000146101612470, PP N000141812418, TO N000141812138, LRC N000141712517, and N00014191269, MB and GE N000141812782 and N000141812039, and JTF N000141812431.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biasi, J., Tivey, M., & Fluegel, B. Volcano monitoring with magnetic measurements: a simulation of eruptions at axial seamount, Kilauea, Baroarbunga, and Mount Saint Helens. Geophysical Research Letters, 49(17), (2022): e2022GL100006, https://doi.org/10.1029/2022GL100006.

Description: Monitoring of active volcanic systems is a challenging task due in part to the trade-offs between collection of high-quality data from multiple techniques and the high costs of acquiring such data. Here we show that magnetic data can be used to monitor volcanoes by producing similar data to gravimetric techniques at significantly lower cost. The premise of this technique is that magma and wall rock above the Curie temperature are magnetically “transparent,” but not stationary within the crust. Subsurface movements of magma can affect the crustal magnetic field measured at the surface. We construct highly simplified magnetic models of four volcanic systems: Mount Saint Helens (1980), Axial Seamount (2015–2020), Kīlauea (2018), and Bárðarbunga (2014). In all cases, observed or inferred changes to the magmatic system would have been detectable by modern magnetometers. Magnetic monitoring could become common practice at many volcanoes, particularly in developing nations with high volcanic risk.

Description: This work was supported by the NSF Grant No 2052963 to J. Biasi and an internal Woods Hole Oceanographic Institution grant to M. Tivey.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bullock, E., Kipp, L., Moore, W., Brown, K., Mann, P., Vonk, J., Zimov, N., & Charette, M. Radium inputs into the Arctic Ocean from rivers a basin‐wide estimate. Journal of Geophysical Research: Oceans, 127(9), (2022): e2022JC018964, https://doi.org/10.1029/2022jc018964.

Description: Radium isotopes have been used to trace nutrient, carbon, and trace metal fluxes inputs from ocean margins. However, these approaches require a full accounting of radium sources to the coastal ocean including rivers. Here, we aim to quantify river radium inputs into the Arctic Ocean for the first time for 226Ra and to refine the estimates for 228Ra. Using new and existing data, we find that the estimated combined (dissolved plus desorbed) annual 226Ra and 228Ra fluxes to the Arctic Ocean are [7.0–9.4] × 1014 dpm y−1 and [15–18] × 1014 dpm y−1, respectively. Of these totals, 44% and 60% of the river 226Ra and 228Ra, respectively are from suspended sediment desorption, which were estimated from laboratory incubation experiments. Using Ra isotope data from 20 major rivers around the world, we derived global annual 226Ra and 228Ra fluxes of [7.4–17] × 1015 and [15–27] × 1015 dpm y−1, respectively. As climate change spurs rapid Arctic warming, hydrological cycles are intensifying and coastal ice cover and permafrost are diminishing. These river radium inputs to the Arctic Ocean will serve as a valuable baseline as we attempt to understand the changes that warming temperatures are having on fluxes of biogeochemically important elements to the Arctic coastal zone.

Description: This study was a broad, collaborative effort that would not have been possible without contributions from numerous funding sources, including the National Science Foundation (NSF-0751525, NSF-1736277, NSF-1458305, NSF-1938873, NSF-2048067, NSF-2134865), the NERC-BMBF project CACOON [NE/R012806/1] (UKRI NERC) and BMBF-03F0806A, and an EU Starting Grant (THAWSOME-676982).

Description: The genus Phaeocystis is globally distributed, with blooms commonly occurring on continental shelves. This unusual phytoplankter has two major morphologies: solitary cells and cells embedded in a gelatinous matrix. Only colonies form blooms. Their large size (commonly 2 mm but up to 3 cm) and mucilaginous envelope allow the colonies to escape predation, but data are inconsistent as to whether colonies are grazed. Cultured Phaeocystis can also inhibit the growth of co-occurring phytoplankton or the feeding of potential grazers. Colonies and solitary cells use nitrate as a nitrogen source, although solitary cells can also grow on ammonium. Phaeocystis colonies might be a major contributor to carbon flux to depth, but in most cases, colonies are rapidly remineralized in the upper 300 m. The occurrence of large Phaeocystis blooms is often associated with environments with low and highly variable light and high nitrate levels, with Phaeocystis antarctica blooms being linked additionally to high iron availability. Emerging results indicate that different clones of Phaeocystis have substantial genetic plasticity, which may explain its appearance in a variety of environments. Given the evidence of Phaeocystis appearing in new systems, this trend will likely continue in the near future.

Description: Coastal upwelling, driven by alongshore winds and characterized by cold sea surface temperatures and high upper-ocean nutrient content, is an important physical process sustaining some of the oceans’ most productive ecosystems. To fully understand the ocean properties in eastern boundary upwelling systems, it is important to consider the depth of the source waters being upwelled, as it affects both the SST and the transport of nutrients toward the surface. Here, we construct an upwelling source depth distribution for parcels at the surface in the upwelling zone. We do so using passive tracers forced at the domain boundary for every model depth level to quantify their contributions to the upwelled waters. We test the dependence of this distribution on the strength of the wind stress and stratification using high-resolution regional ocean simulations of an idealized coastal upwelling system. We also present an efficient method for estimating the mean upwelling source depth. Furthermore, we show that the standard deviation of the upwelling source depth distribution increases with increasing wind stress and decreases with increasing stratification. These results can be applied to better understand and predict how coastal upwelling sites and their surface properties have and will change in past and future climates.

Description: Heat stress is projected to intensify with global warming, causing significant socioeconomic impacts and threatening human health. Wet-bulb temperature (WBT), which combines temperature and humidity effects, is a useful indicator for assessing regional and global heat stress variability and trends. However, the variations of European WBT and their underlying mechanisms remain unclear. Using observations and reanalysis datasets, we demonstrate a remarkable warming of summer WBT during the period 1958–2021 over Europe. Specifically, the European summer WBT has increased by over 1.08C in the past 64 years. We find that the increase in European summer WBT is driven by both near-surface warming temperatures and increasing atmospheric moisture content. We identify four dominant modes of European summer WBT variability and investigate their linkage with the large-scale atmospheric circulation and sea surface temperature anomalies. The first two leading modes of the European WBT variability exhibit prominent interdecadal to long-term variations, mainly driven by a circumglobal wave train and concurrent sea surface temperature variations. The last two leading modes of European WBT variability mainly show interannual variations, indicating a direct and rapid response to large-scale atmospheric dynamics and nearby sea surface temperature variations. Further analysis shows the role of global warming and changes in midlatitude circulations in the variations of summer WBT. Our findings can enhance the understanding of plausible drivers of heat stress in Europe and provide valuable insights for regional decision-makers and climate adaptation planning.

Description: 〈jats:p〉 For decades, multiple-driver/stressor research has examined interactions among drivers that will undergo large changes in the future: temperature, pH, nutrients, oxygen, pathogens, and more. However, the most commonly used experimental designs—present-versus-future and ANOVA—fail to contribute to general understanding or predictive power. Linking experimental design to process-based mathematical models would help us predict how ecosystems will behave in novel environmental conditions. We review a range of experimental designs and assess the best experimental path toward a predictive ecology. Full factorial response surface, fractional factorial, quadratic response surface, custom, space-filling, and especially optimal and sequential/adaptive designs can help us achieve more valuable scientific goals. Experiments using these designs are challenging to perform with long-lived organisms or at the community and ecosystem levels. But they remain our most promising path toward linking experiments and theory in multiple-driver research and making accurate, useful predictions. 〈/jats:p〉

Description: Rayleigh wave ellipticity measurements from seismic ambient noise recorded on the Greenland Ice Sheet (GrIS) show complex and anomalous behavior at wave periods sensitive to ice (T 〈 3–4 s). To understand these complex observations, we compare them with synthetic ellipticity measurements obtained from synthetic ambient noise computed for various seismic velocity and attenuation models, including surface wave overtone effects. We find that in dry snow conditions within the interior of the GrIS, to first order the anomalous ellipticity observations can be explained by ice models associated with the accumulation and densification of snow into firn. We also show that the distribution of ellipticity measurements is strongly sensitive to seismic attenuation and the thermal structure of the ice. Our results suggest that Rayleigh wave ellipticity is well suited for monitoring changes in firn properties and thermal composition of the Greenland and Antarctic ice sheets in a changing climate.

Description: Published

Description: e2023GL103673

Description: OST1 Alla ricerca dei Motori Geodinamici

Description: JCR Journal

Description: Arctic warming increases the degradation of permafrost soils but little is known about floodplain soils in the permafrost region. This study quantifies soil organic carbon (SOC) and soil nitrogen stocks, and the potential CH4 and CO2 production from seven cores in the active floodplains in the Lena River Delta, Russia. The soils were sandy but highly heterogeneous, containing deep, organic rich deposits with 〉60% SOC stored below 30 cm. The mean SOC stocks in the top 1 m were 12.9 ± 6.0 kg C m−2. Grain size analysis and radiocarbon ages indicated highly dynamic environments with sediment re-working. Potential CH4 and CO2 production from active floodplains was assessed using a 1-year incubation at 20°C under aerobic and anaerobic conditions. Cumulative aerobic CO2 production mineralized a mean 4.6 ± 2.8% of initial SOC. The mean cumulative aerobic:anaerobic C production ratio was 2.3 ± 0.9. Anaerobic CH4 production comprised 50 ± 9% of anaerobic C mineralization; rates were comparable or exceeded those for permafrost region organic soils. Potential C production from the incubations was correlated with total organic carbon and varied strongly over space (among cores) and depth (active layer vs. permafrost). This study provides valuable information on the carbon cycle dynamics from active floodplains in the Lena River Delta and highlights the key spatial variability, both among sites and with depth, and the need to include these dynamic permafrost environments in future estimates of the permafrost carbon-climate feedback.

Description: The regular movements of waves and tides are obvious representations of the oceans’ rhythmicity. But the rhythms of marine life span across ecological niches and timescales, including short (in the range of hours) and long (in the range of days and months) periods. These rhythms regulate the physiology and behavior of individuals, as well as their interactions with each other and with the environment. This review highlights examples of rhythmicity in marine animals and algae that represent important groups of marine life across different habitats. The examples cover ecologically highly relevant species and a growing number of laboratory model systems that are used to disentangle key mechanistic principles. The review introduces fundamental concepts of chronobiology, such as the distinction between rhythmic and endogenous oscillator–driven processes. It also addresses the relevance of studying diverse rhythms and oscillators, as well as their interconnection, for making better predictions of how species will respond to environmental perturbations, including climate change. As the review aims to address scientists from the diverse fields of marine biology, ecology, and molecular chronobiology, all of which have their own scientific terms, we provide definitions of key terms throughout the article.

Description: A fundamental statistic of climate variability is its spatiotemporal correlation function. Its complex structure can be concisely summarized by a frequency-dependent measure of the effective spatial degrees of freedom (ESDOF). Here we present, for the first time, frequency-dependent ESDOF estimates of global natural surface temperature variability from purely instrumental measurements, using the HadCRUT4 dataset (1850-2014). The approach is based on a newly developed method for estimating the frequency-dependent spatial correlation function from gappy data fields. Results reveal a multicomponent structure of the spatial correlation function, including a large-amplitude short-distance component (with weak time scale dependence) and a small-amplitude long-distance component (with increasing relative amplitude toward the longer time scales). Two frequency-dependent ESDOF measures are applied, each responding mainly to either of the two components. Both measures exhibit a significant ESDOF reduction from monthly to multidecadal time scales, implying an increase of the effective spatial scale of natural surface temperature fluctuations. Moreover, it is found that a good approximation to the global number of equally spaced samples needed to estimate the variance of global mean temperature is given, at any frequency, by the greater one of the two ESDOF measures, decreasing from ;130 at monthly to ;30 at multidecadal time scales. Finally, the multicomponent structure of the correlation function together with the detected ESDOF scaling properties indicate that the ESDOF reduction toward the longer time scales cannot be explained simply by diffusion acting on stochastically driven anomalies, as it might be suggested f rom simple stochastic-diffusive energy balance models.

Description: Climate variability occurs over wide ranges of spatial and temporal scales. It exhibits a complex spatial covariance structure, which depends on geographic location (e.g., tropics vs extratropics) and also consists of a superposition of (i) components with gradually decaying positive correlation functions and (ii) teleconnections that often involve anticorrelations. In addition, there are indications that the spatial covariance structure depends on frequency. Thus, a comprehensive assessment of the spatiotemporal covariance structure of climate variability would require an extensive set of statistical diagnostics. Therefore, it is often desirable to characterize the covariance structure by a simple summarizing metric that is easy to compute from datasets. Such summarizing metrics are useful, for example, in the context of comparisons between climate models or between models and observations. Here we introduce a frequency-dependent version of a simple measure of the effective spatial degrees of freedom. The measure is based on the temporal variance of the global average of some climate variable, and its novel aspect consists in its frequency dependence. We also provide a clear geometric interpretation of the measure. Its easy applicability is demonstrated using near-surface temperature and precipitation fields obtained from a paleoclimate model simulation. This application reveals a distinct scaling behavior of the spatial degrees of freedom as a function of frequency, ranging from monthly to millennial scales.

Description: Marine sedimentary records are a key archive when reconstructing past climate; however, mixing at the seabed (bioturbation) can strongly influence climate records, especially when sedimentation rates are low. By commingling the climate signal from different time periods, bioturbation both smooths climate records, by damping fast climate variations, and creates noise when measurements are made on samples containing small numbers of individual proxy carriers, such as foraminifera. Bioturbation also influences radiocarbon-based age-depth models, as sample ages may not represent the true ages of the sediment layers from which they were picked. While these effects were first described several decades ago, the advent of ultra-small-sample $^{14}$C dating now allows samples containing very small numbers of foraminifera to be measured, thus enabling us to directly measure the age-heterogeneity of sediment for the first time. Here, we use radiocarbon dates measured on replicated samples of 3-30 foraminifera to estimate age-heterogeneity for five marine sediment cores with sedimentation rates ranging from 2-30 cm kyr$^{-1}$. From their age-heterogeneities and sedimentation rates we infer mixing depths of 10-20 cm for our core sites. Our results show that when accounting for age-heterogeneity, the true error of radiocarbon dating can be several times larger than the reported measurement. We present estimates of this uncertainty as a function of sedimentation rate and the number of individuals per radiocarbon date. A better understanding of this uncertainty will help us to optimise radiocarbon measurements, construct age models with appropriate uncertainties and better interpret marine paleo records.

Description: NORP-SORP Workshop on Polar Fresh Water: Sources, Pathways and Impacts of Freshwater in Northern and Southern Polar Oceans and Seas (SPICE-UP) What: Up to 60 participants at a time and more than twice as many registrants in total from 20 nations and across experience levels met to discuss the current status of research on freshwater in both polar regions, future directions, and synergies between the Arctic and Southern Ocean research communities When: 19–21 September 2022 Where: Online

Description: 〈jats:title〉Abstract〈/jats:title〉 〈jats:p〉—J. BLUNDEN, T. BOYER, AND E. BARTOW-GILLIES〈/jats:p〉 〈jats:p〉Earth’s global climate system is vast, complex, and intricately interrelated. Many areas are influenced by global-scale phenomena, including the “triple dip” La Niña conditions that prevailed in the eastern Pacific Ocean nearly continuously from mid-2020 through all of 2022; by regional phenomena such as the positive winter and summer North Atlantic Oscillation that impacted weather in parts the Northern Hemisphere and the negative Indian Ocean dipole that impacted weather in parts of the Southern Hemisphere; and by more localized systems such as high-pressure heat domes that caused extreme heat in different areas of the world. Underlying all these natural short-term variabilities are long-term climate trends due to continuous increases since the beginning of the Industrial Revolution in the atmospheric concentrations of Earth’s major greenhouse gases.〈/jats:p〉 〈jats:p〉In 2022, the annual global average carbon dioxide concentration in the atmosphere rose to 417.1±0.1 ppm, which is 50% greater than the pre-industrial level. Global mean tropospheric methane abundance was 165% higher than its pre-industrial level, and nitrous oxide was 24% higher. All three gases set new record-high atmospheric concentration levels in 2022.〈/jats:p〉 〈jats:p〉Sea-surface temperature patterns in the tropical Pacific characteristic of La Niña and attendant atmospheric patterns tend to mitigate atmospheric heat gain at the global scale, but the annual global surface temperature across land and oceans was still among the six highest in records dating as far back as the mid-1800s. It was the warmest La Niña year on record. Many areas observed record or near-record heat. Europe as a whole observed its second-warmest year on record, with sixteen individual countries observing record warmth at the national scale. Records were shattered across the continent during the summer months as heatwaves plagued the region. On 18 July, 104 stations in France broke their all-time records. One day later, England recorded a temperature of 40°C for the first time ever. China experienced its second-warmest year and warmest summer on record. In the Southern Hemisphere, the average temperature across New Zealand reached a record high for the second year in a row. While Australia’s annual temperature was slightly below the 1991–2020 average, Onslow Airport in Western Australia reached 50.7°C on 13 January, equaling Australia's highest temperature on record.〈/jats:p〉 〈jats:p〉While fewer in number and locations than record-high temperatures, record cold was also observed during the year. Southern Africa had its coldest August on record, with minimum temperatures as much as 5°C below normal over Angola, western Zambia, and northern Namibia. Cold outbreaks in the first half of December led to many record-low daily minimum temperature records in eastern Australia.〈/jats:p〉 〈jats:p〉The effects of rising temperatures and extreme heat were apparent across the Northern Hemisphere, where snow-cover extent by June 2022 was the third smallest in the 56-year record, and the seasonal duration of lake ice cover was the fourth shortest since 1980. More frequent and intense heatwaves contributed to the second-greatest average mass balance loss for Alpine glaciers around the world since the start of the record in 1970. Glaciers in the Swiss Alps lost a record 6% of their volume. In South America, the combination of drought and heat left many central Andean glaciers snow free by mid-summer in early 2022; glacial ice has a much lower albedo than snow, leading to accelerated heating of the glacier. Across the global cryosphere, permafrost temperatures continued to reach record highs at many high-latitude and mountain locations.〈/jats:p〉 〈jats:p〉In the high northern latitudes, the annual surface-air temperature across the Arctic was the fifth highest in the 123-year record. The seasonal Arctic minimum sea-ice extent, typically reached in September, was the 11th-smallest in the 43-year record; however, the amount of multiyear ice—ice that survives at least one summer melt season—remaining in the Arctic continued to decline. Since 2012, the Arctic has been nearly devoid of ice more than four years old.〈/jats:p〉 〈jats:p〉In Antarctica, an unusually large amount of snow and ice fell over the continent in 2022 due to several landfalling atmospheric rivers, which contributed to the highest annual surface mass balance, 15% to 16% above the 1991–2020 normal, since the start of two reanalyses records dating to 1980. It was the second-warmest year on record for all five of the long-term staffed weather stations on the Antarctic Peninsula. In East Antarctica, a heatwave event led to a new all-time record-high temperature of −9.4°C—44°C above the March average—on 18 March at Dome C. This was followed by the collapse of the critically unstable Conger Ice Shelf. More than 100 daily low sea-ice extent and sea-ice area records were set in 2022, including two new all-time annual record lows in net sea-ice extent and area in February.〈/jats:p〉 〈jats:p〉Across the world’s oceans, global mean sea level was record high for the 11th consecutive year, reaching 101.2 mm above the 1993 average when satellite altimetry measurements began, an increase of 3.3±0.7 over 2021. Globally-averaged ocean heat content was also record high in 2022, while the global sea-surface temperature was the sixth highest on record, equal with 2018. Approximately 58% of the ocean surface experienced at least one marine heatwave in 2022. In the Bay of Plenty, New Zealand’s longest continuous marine heatwave was recorded.〈/jats:p〉 〈jats:p〉A total of 85 named tropical storms were observed during the Northern and Southern Hemisphere storm seasons, close to the 1991–2020 average of 87. There were three Category 5 tropical cyclones across the globe—two in the western North Pacific and one in the North Atlantic. This was the fewest Category 5 storms globally since 2017. Globally, the accumulated cyclone energy was the lowest since reliable records began in 1981. Regardless, some storms caused massive damage. In the North Atlantic, Hurricane Fiona became the most intense and most destructive tropical or post-tropical cyclone in Atlantic Canada’s history, while major Hurricane Ian killed more than 100 people and became the third costliest disaster in the United States, causing damage estimated at $113 billion U.S. dollars. In the South Indian Ocean, Tropical Cyclone Batsirai dropped 2044 mm of rain at Commerson Crater in Réunion. The storm also impacted Madagascar, where 121 fatalities were reported.〈/jats:p〉 〈jats:p〉As is typical, some areas around the world were notably dry in 2022 and some were notably wet. In August, record high areas of land across the globe (6.2%) were experiencing extreme drought. Overall, 29% of land experienced moderate or worse categories of drought during the year. The largest drought footprint in the contiguous United States since 2012 (63%) was observed in late October. The record-breaking megadrought of central Chile continued in its 13th consecutive year, and 80-year record-low river levels in northern Argentina and Paraguay disrupted fluvial transport. In China, the Yangtze River reached record-low values. Much of equatorial eastern Africa had five consecutive below-normal rainy seasons by the end of 2022, with some areas receiving record-low precipitation totals for the year. This ongoing 2.5-year drought is the most extensive and persistent drought event in decades, and led to crop failure, millions of livestock deaths, water scarcity, and inflated prices for staple food items.〈/jats:p〉 〈jats:p〉In South Asia, Pakistan received around three times its normal volume of monsoon precipitation in August, with some regions receiving up to eight times their expected monthly totals. Resulting floods affected over 30 million people, caused over 1700 fatalities, led to major crop and property losses, and was recorded as one of the world’s costliest natural disasters of all time. Near Rio de Janeiro, Brazil, Petrópolis received 530 mm in 24 hours on 15 February, about 2.5 times the monthly February average, leading to the worst disaster in the city since 1931 with over 230 fatalities.〈/jats:p〉 〈jats:p〉On 14–15 January, the Hunga Tonga-Hunga Ha'apai submarine volcano in the South Pacific erupted multiple times. The injection of water into the atmosphere was unprecedented in both magnitude—far exceeding any previous values in the 17-year satellite record—and altitude as it penetrated into the mesosphere. The amount of water injected into the stratosphere is estimated to be 146±5 Terragrams, or ∼10% of the total amount in the stratosphere. It may take several years for the water plume to dissipate, and it is currently unknown whether this eruption will have any long-term climate effect.〈/jats:p〉

Description: Forest degradation may be as widespread as deforestation in the Amazon, but its impact on energy, carbon, and water fluxes is less well understood.

Description: This month’s issue of Eos shows how scientists can sometimes get a better look at something by stepping far—much, much farther—away.

Description: The Fujiwhara effect—complex interactions between large storms nearby each other—can steer hurricanes and tropical storms but doesn’t typically create colossal tempests.

Description: Air temperatures in coastal ecosystems of Australia routinely exceed the optimum range for photosynthesis, hindering plants’ ability to take up atmospheric carbon.

Description: A tool from dynamic systems theory is helping atmospheric scientists identify how dust and moisture mix over West Africa.

Description: A unique automated planetary boundary layer (PBL) retrieval algorithm is proposed as a common cross-platform method for use with commercially available ceilometers for implementation under the redesigned U.S. Environmental Protection Agency Photochemical Assessment Monitoring Stations program. This algorithm addresses instrument signal quality and screens for precipitation and cloud layers before the implementation of the retrieval methodology using the Haar wavelet covariance transform method. Layer attribution for the PBL height is supported with the use of continuation and time-tracking parameters, and uncertainties are calculated for individual PBL height retrievals. Commercial ceilometer retrievals are tested against radiosonde PBL height and cloud-base height during morning and late afternoon transition times, critical to air quality model prediction and when retrieval algorithms struggle to identify PBL heights. A total of 58 radiosonde profiles were used and retrievals for nocturnal stable layers, residual layers and mixing layers were assessed. Overall good agreement was found for all comparisons with one system showing limitations for the cases of nighttime surface stable layers and daytime mixing layer. It is recommended that nighttime shallow stable layer retrievals be performed with a recommended minimum height or with additional verification. Retrievals of residual layer heights and mixing layer comparisons revealed overall good correlations to radiosonde heights (correlation coefficients, r2, ranging from 0.89 – 0.96 and bias ranging from ~ -131 to +63 m, and r2 from 0.88 – 0.97 and bias from -119 to +101 m, respectively).

Description: No Abstract available.