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Aim: Patterns of benthic biodiversity at the macroecological scale remain poorly characterised throughout the Chilean latitudinal gradient, in part due to the lack of integrated databases, uneven sampling effort, and the use of species richness alone to quantify biodiversity. Different diversity measures, encompassing taxonomic and functional components, may give us extra information on biodiversity relevant to conservation planning and management. Thus, evaluating the spatial complementarity of these measures is essential. Location: Coast and continental shelf of Chile. Methods: The latitudinal gradient of Chile was divided into five ecoregions according to the Marine Ecosystems of the World classification. Using a 55 × 55 km equal area grid, we estimated the incidence coverage‐based estimator (ICE), taxonomic distinctness (Δ+) and three measures of functional diversity: functional richness (FRic), functional evenness (FEve) and functional divergence (FDiv). For each measure, we described spatial patterns, identified hotspots, evaluated hotspot congruence and evaluated complementarity between measures. Results: Diversity patterns varied between ecoregions and over the latitudinal gradient. ICE and Δ+ peaked in the Chiloense and Channels and Fjords ecoregions. Δ+ and FRic present a similar pattern at mid‐latitudes. FEve showed a contrary pattern, principally with FRic. Areas with high numbers of hotspots differed spatially according to each metric, and three latitudinal bands were observed. ICE, Δ+ and FRic were positively correlated, but the hotspot overlap at the grid cell level was more limited. Main Conclusions: The complementarity between taxonomic and functional diversity measures is limited when we observe the overlap between grid cells representing hotspots. However, some regions are consistently identified as highly diverse, with the Magellanic Province (Chiloense and Channels and Fjords ecoregions) being the most important for the richness, taxonomic and functional diversity of benthos. Confirmation of the importance of this region can help prioritise conservation efforts. [ABSTRACT FROM AUTHOR]

Hourly, year‐round flow cytometry has made it possible to relate seasonal environmental variability to the population dynamics of the smallest, most abundant phytoplankton on the Northeast US Shelf. To evaluate whether the insights from these data extend to Synechococcus farther from shore, we analyze flow cytometry measurements made continuously from the underway systems on 21 cruises traveling between the Martha's Vineyard Coastal Observatory (MVCO) and the continental shelf break. We describe how seasonal patterns in Synechococcus, which have been documented in detail at MVCO, occur across the region with subtle variation. We find that the underlying relationship between temperature and division rate is consistent across the shelf and can explain much of the observed spatial variability in concentration. Connecting individual cell properties to annual and regional patterns in environmental conditions, these results demonstrate the value of autonomous monitoring and create an improved picture of picophytoplankton dynamics within an economically important ecosystem. [ABSTRACT FROM AUTHOR]

Picophytoplankton are a ubiquitous component of marine plankton communities and are expected to be favored by global increases in seawater temperature and stratification associated with climate change. Eukaryotic and prokaryotic picophytoplankton have distinct ecology, and global models predict that the two groups will respond differently to future climate scenarios. At a nearshore observatory on the Northeast US Shelf, however, decades of year‐round monitoring have shown these two groups to be highly synchronized in their responses to environmental variability. To reconcile the differences between regional and global predictions for picophytoplankton dynamics, we here investigate the picophytoplankton community across the continental shelf gradient from the nearshore observatory to the continental slope. We analyze flow cytometry data from 22 research cruises, comparing the response of picoeukaryote and Synechococcus communities to environmental variability across time and space. We find that the mechanisms controlling picophytoplankton abundance differ across taxa, season, and distance from shore. Like the prokaryote, Synechococcus, picoeukaryote division rates are limited nearshore by low temperatures in winter and spring, and higher temperatures offshore lead to an earlier spring bloom. Unlike Synechococcus, picoeukaryote concentration in summer decreases dramatically in offshore surface waters and exhibits deeper subsurface maxima. The offshore picoeukaryote community appears to be nutrient limited in the summer and subject to much greater loss rates than Synechococcus. This work both produces and demonstrates the necessity of taxon‐ and site‐specific knowledge for accurately predicting the responses of picophytoplankton to ongoing environmental change. [ABSTRACT FROM AUTHOR]

Recent observations suggest that El Niño–Southern Oscillation (ENSO) impacts basal melting of West Antarctic ice shelves, yet sparse ocean observations limit our understanding of the associated processes. Here we investigate how ENSO events modulate subsurface West Antarctic shelf temperatures using high‐resolution global ocean‐sea ice model simulations. During El Niño, the subsurface shelf warming between 150 m and the shelf bottom can be up to 0.5°C in front of ice shelves. This warming arises from a weaker Amundsen Sea Low (ASL) and weaker coastal easterlies that reduce on‐shelf Ekman transport of cold surface waters, enabling enhanced transport of warm Circumpolar Deep Water (CDW) onto the shelf. A largely opposite response occurs during La Niña, with a stronger ASL and stronger Ekman transport that results in less cross‐shelf CDW transport and cooling in the subsurface. These findings have implications for interpreting basal melting on interannual to decadal time‐scales in West Antarctica. Plain Language Summary: El Niño‐Southern Oscillation (ENSO) is the Earth's dominant year‐to‐year climate variation. The impacts of its two phases, El Niño and La Niña, extend from the tropics to Antarctica through atmospheric waves. Past studies have suggested that West Antarctic ice shelves melt more during El Niño because of warmer ocean waters at the ice shelf bases. However, oceanic changes during El Niño lead to warming on the shelf near the ice which is difficult to isolate. That is because ENSO is only one of many drivers that impact shelf water temperatures. In this work, we simulate isolated ENSO events using an ocean circulation model. We show that during El Niño, the on‐shelf flow of cold surface waters in West Antarctica, driven by coastal easterly winds, is reduced because the winds weaken. To balance out this mass deficit at the surface, more warm CDW flows onto the continental shelf below. During La Niña, we see a largely opposite response. Stronger coastal easterlies increase the on‐shelf flow of cold surface waters and less CDW is flowing onto the shelf. Our results show the link between ENSO and mass loss of the West Antarctic ice shelves and ice sheet. Key Points: Ocean‐sea ice model simulations of El Niño and La Niña events illustrate how they modulate West Antarctic shelf temperaturesEl Niño weakens coastal easterlies, reduces on‐shelf Ekman flow of cold waters, increasing cross‐shelf flow of warm Circumpolar Deep Water (CDW)The La Niña shelf circulation response is largely opposite and reduces cross‐shelf transport of warm CDW [ABSTRACT FROM AUTHOR]

The Ross Sea is a highly productive system characterized by a seasonal succession of phytoplankton groups. However, most of the current understanding is based on observations on the continental shelf in spring and summer at relatively coarse taxonomic resolution. Here, we characterize community composition (class to species) using V4‐18S rRNA gene metabarcoding on transects to and across the Ross Sea (shelf‐slope and oceanic subregions) during two voyages covering the Austral summer–autumn progression in successive years. Phytoplankton composition shifted from low‐diversity diatom‐dominated (50%) communities during the summer to more diverse dinoflagellate‐dominated (48%) systems during the lower‐productivity autumn season. Prymnesiophyceae abundance was low on both voyages (10%), except on the southeast shelf‐slope, where Phaeocystis antarctica dominated a shallow mixed layer, contrary to its reported preference for deep‐mixing conditions. Amplicon sequence variant analysis identified distinct spatial patterns for two P. antarctica genotypes yet clustered certain species of Bacillariophyta and Prymnesiophyceae, indicating similar environmental preference for genotypes in these groups. Multivariate analysis of environmental drivers found a higher correlation of community composition variation with salinity and macronutrients, but less so with mixed layer depth, considered a primary determinant of taxonomic composition in the Ross Sea. Comparison between years established that community composition was temporally more stable in oceanic relative to shelf‐slope waters. This study of seasonal variation of phytoplankton community composition at finer taxonomic resolution provided insights into species‐ and strain‐specific distribution, ecological preferences, and relationships to environmental conditions in the wider Ross Sea to inform modeling and projection of future regional changes. [ABSTRACT FROM AUTHOR]

Widespread hypoxia occurs seasonally across the Oregon continental shelf, and the duration, intensity, and frequency of hypoxic events have increased in recent years. In hypoxic regions, iron reduction can liberate dissolved Fe(II) from continental shelf sediments. Fe(II) was measured in the water column across the continental shelf and slope on the Oregon coast during summer 2022 using both a trace metal clean rosette and a high‐resolution benthic gradient sampler. In the summer, Fe(II) concentrations were exceptionally high (40–60 nM) within bottom waters and ubiquitous across the Oregon shelf, reflecting the low oxygen condition (40–70 μM) at that time. The observed inverse correlation between Fe(II) and bottom water oxygen concentrations is in agreement with expectations based on previous work that demonstrates oxygen is a major determinant of benthic Fe fluxes. Rapid attenuation of Fe(II) from the benthic boundary layer (within 1 m of the seafloor) probably reflects efficient cross‐shelf advection. One region, centered around Heceta Bank (~ 44°N) acts a hotspot for Fe release on the Oregon continental shelf, likely due to its semi‐retentive nature and high percent mud content in sediment. The results suggest that hypoxia is an important determinant of the inventory of iron is Oregon shelf waters and thus ultimately controls the importance of continental margin‐derived iron to the interior of the North Pacific Basin. [ABSTRACT FROM AUTHOR]

Oilfield production is controlled by a wide range of geological and engineering parameters, many of which are at least partially interrelated. This paper uses multivariate statistical methods (principal component analysis, regression analysis and analysis of variance) to determine how these parameters are related, and which of them are most significant in controlling and predicting oilfield performance. The analysis is based on a database of publicly available oilfield data from the United Kingdom Continental Shelf (UKCS), from which a series of geological, engineering and fluid‐related control variables from 136 fields were pre‐processed and analyzed. This dataset is a subset of a much wider project database for UKCS oil, gas and condensate fields. For this study, the project database was divided into two datasets: a first dataset with 10 parameters from 136 fields, and a second, more detailed dataset with 27 parameters from 38 fields. Both datasets were analysed using principal component analysis in order to investigate possible correlations between numerically/statistically interrogable predictor variables such as porosity, permeability, number of production wells, gas‐oil ratio and reservoir temperature. A regression analysis was then carried out on the predictor variables in order to obtain a ranking of predictability (i.e. how indicative a predictor is of a particular outcome) and sensitivity (how sensitive an outcome is to slight changes in a predictor) in relation to recovery factor based on R‐squared and regression coefficient values. The results showed that key variables from the principal component analysis included field size, number of production wells, PVT, gross depositional environment and reservoir quality. High‐ranking parameters of predictability and sensitivity from the regression analysis were found to include API, net‐to‐gross, porosity and reservoir depth. These results are consistent with previous studies and suggest that it should be possible to forecast oilfield recovery based on only a few selected input variables. As a preliminary test of forecasting ability of the variable permutations put forward, a best‐subsets multiple regression was carried out using a statistical software package and yielded results which corroborated the main findings. [ABSTRACT FROM AUTHOR]

The northeastern part of the North Atlantic subpolar gyre is a key passage for the Atlantic Meridional Overturning Circulation upper cell. To this day, the precise pathway and intensity of bottom currents in this area is not clear. In this study, we make use of regional high resolution numerical modeling to suggest that the main bottom current flowing south of Iceland originates from both the Faroe‐Banks Channel and the Iceland‐Faroe Ridge and then flows along the topographic slope. When flowing over the rough topography, this bottom current generates a 200 m large bottom mixed layer. We further demonstrate that many submesoscale structures are generated at the southernmost tip of the Icelandic shelf, which subsequently spread water masses in the Iceland Basin. These findings have major implication for the understanding of the water masses transport in the North Atlantic, and also for the distribution of benthic species along the Icelandic shelf. Plain Language Summary: Water masses formed in the Arctic Ocean overflow into the North Atlantic at the bottom of the ocean, forming the so‐called upper cell of the Atlantic Meridional Overturning Circulation (AMOC). The pathway of the currents carrying these water masses is still under debate due to a lack of observations. In this study, we discuss in details the pathway of these bottom currents in the specific area south of Iceland. We show that a steady current flows along the Icelandic continental shelf, and then divide in smaller structures when reaching the southernmost tip of Iceland. We also show that on its way, the current mixes the bottom layer of the ocean. These findings have major implication in the understanding of heat and carbon transport at depth in this area, which constitute an important response of the climate to anthropogenic forcing. Key Points: An intense bottom boundary current originating from the Iceland‐Faroe Ridge and the Faroe Bank Channel flows along the Icelandic ShelfThe rough topography and the intensity of the current lead to bottom mixing and sustain a large bottom mixed layerSubsmesoscale structures generated locally participate in the spreading of deep water masses in the Iceland Basin [ABSTRACT FROM AUTHOR]

The Outer Continental Shelf of the Gulf of Mexico (GOM) is populated with numerous oil and natural gas (ONG) platforms which produce NOx (NOx = NO + NO2), a major component of air pollution. The Bureau of Ocean Energy Management (BOEM) is mandated to ensure that the air quality of coastal states is not degraded by these emissions. As part of a NASA‐BOEM collaboration, we conducted a satellite data‐based analysis of nitrogen dioxide (NO2) patterns and trends in the GOM. Data from the OMI and TROPOMI sensors were used to obtain 18+ year records of tropospheric column (TrC) NO2 in three GOM regions: (a) Houston urban area, (b) near shore area off the Louisiana coast, and a (c) deepwater area off the Louisiana coast. The 2004–2022 time series show a decreasing trend for the urban (−0.027 DU/decade) and near shore (−0.0022 DU/decade) areas, and an increasing trend (0.0019 DU/decade) for the deepwater area. MERRA‐2 wind and TROPOMI NO2 data were used to reveal several NO2 hotspots (up to 25% above background values) under calm wind conditions near individual platforms. The NO2 signals from these deepwater platforms and the high density of shallow water platforms closer to shore were confirmed by TrC NO2 anomalies of up to 10%, taking into account the monthly TrC NO2 climatology over the GOM. The results presented in this study establish a baseline for future estimates of emissions from the ONG hotspots and provide a methodology for analyzing NO2 measurements from the new geostationary TEMPO instrument. Plain Language Summary: Oil and natural gas operations emit nitrogen oxides (NOx), which are major air pollutants and precursors to ground‐level ozone. The Bureau of Ocean Energy Management (BOEM) agency is responsible for managing planned oil and natural gas (ONG) activity on the outer continental shelf, and is mandated to ensure related emissions do not degrade air quality of coastal states. In collaboration with BOEM, we used satellite data from the OMI and TROPOMI sensors to construct an 18+ year record of tropospheric nitrogen dioxide (NO2), a proxy for NOx, in the Gulf Coast region. These time series focused on three areas: (a) Houston urban, (b) off the Louisiana coast, and (c) deepwater Gulf off Louisiana. These regions experienced changes in tropospheric column NO2 of −13.7%, −5.8%, and +5.4% per decade, respectively. We also identified NO2 hotspots from ONG platforms using TROPOMI NO2 averages under calm wind conditions. The ONG deepwater platforms enhance NO2 background amounts by 7%–13% on average, and up to 25% for the Mars and Olympus platforms combined. The results presented here will facilitate our work on emissions estimates from these sources and on applications to the recently launched TEMPO instrument. Key Points: Satellite NO2 records and trends of urban, coastal and deep water areas from 2005 to 2022, are presentedClassifying NO2 over the Gulf of Mexico (GOM) under various wind conditions highlights typical patterns in average NO2 valuesGOM NO2 hotspots from deepwater platforms were identified by TROPOMI under calm wind conditions, the largest of which is over Mars/Olympus [ABSTRACT FROM AUTHOR]

Simplifying complex species interactions can facilitate tracking and predicting functional responses to ecological stressors. This is important for highly migratory pelagic predators, exploiting diverse prey fields as they respond to dynamic environments. We reconstructed the historical resource use of albacore tuna (Thunnus alalunga) globally from the 1900s to 2015 and confirmed highly biodiverse diets with 308 prey species, and an additional 238 taxa at coarser taxonomic resolution. We synthesised prey diversity into seven functional trait guilds using hierarchical divisive clustering algorithms as a function of four traits that describe habitat use and influence predator–prey encounter rates – prey habitat association vertically in the water column, horizontally along the coastal to pelagic gradient, seasonal and diel vertical migratory behaviour. We explored variability in historical composition of albacore diets across geographies based on species identity, individual trait information and functional trait guilds using a multi‐matrix modelling framework. Taxonomic information remains important for trophic ecology, however, species‐based diet composition in albacore tuna was highly variable across geographies and years sampled, making interpretation of these patterns difficult. By simplifying species identity into habitat‐based traits, we highlight changes in prey resources consumed, such as the historical importance of near‐surface epipelagic prey resources from coastal to oceanic habitats, and seasonally migrating continental shelf prey, with less frequent pulses of deeper water and demersal taxa. Trait information and trait guilds serve as useful classification frameworks for identifying functionally redundant food web linkages across biodiverse prey, and will prove useful in tracking predators' foraging responses to changing resource availability. [ABSTRACT FROM AUTHOR]

The aim of this study was to analyze the effects of climate and marine variability on the catches of Lutjanus purpureus in three sectors of the Amazon Continental Shelf. Remote sensing data were compared with landings (CPUE) between 1997 and 2007 and analyzed for partial influence obtained through the Generalized Additive Model. Additionally, significant variables were analyzed through Wavelet Cross‐Spectrum, and periods of high correlation between variables in space and time were identified. The results indicated a high coherence between catch per unit effort (CPUE) and environmental variables on an interannual scale, suggesting that Red Snapper fishing is mainly influenced by the seasonal effects of oceanographic variables. These results suggest that fluctuations in Red Snapper catches between 1997 and 2007 may be the result of natural processes that occur in the Amazon Continental Shelf every year in synergy with environmental variables, which are also indirectly affected by the El Niño–Southern Oscillation (ENSO) pattern. [ABSTRACT FROM AUTHOR]

To gain a better understanding of the mechanisms underlying spatial heterogeneity in ichthyoplankton communities in the SW Atlantic, we examined for the first time the latitudinal and continental shelf–slope gradients in ichthyoplankton structure and oceanographic features in the Campos Basin during the relaxation phase of coastal upwellings (late autumn to early winter). This region, located on SE Brazil's continental margin, is the most productive offshore oil basin in the country and has ecological relevance owing to the existence of areas that experiences mesoscale (tens to hundreds of kilometers) processes (eddies, filaments, and upwelling) caused by the interaction of continental shelf and slope circulation with deep water masses. The present study collected a total of 3892 fish eggs and 10,030 larvae from 36 sampling stations, averaging 22 eggs per 100 m3 and 56 larvae per 100 m3. A total of 250 taxa (5 for fish eggs and 248 for larvae) were identified, encompassing 80 families and 145 genera. Species distribution exhibited a considerable degree of spatial variability, which was related mostly to hydrological characteristics. In general, greater densities were associated with higher nutrient concentrations areas. Through distance‐based Redundancy Analysis, some discriminating species were found to associate with certain areas of the continental shelf characterized by colder temperatures. The ichthyoplankton distribution patterns suggested a potential influence from mesoscale oceanographic fronts, specifically those that induce upwelling of the cold and nutrient‐rich South Atlantic Central Water. Nonetheless, the methodologies used in this study faced challenges in distinctly identifying these processes. [ABSTRACT FROM AUTHOR]

Continental margins develop long submarine slopes, linking the shallow shelves along the continental landmasses to the deep abyssal plain. They are the results of a complex interaction between destructive and constructive processes, although by and large they are sites of deposition. There is a great amount of variation between the length, height, smoothness, gradient and variation thereof between the slope profiles; however, there is also recurring similarity in their shape. The similitude has suggested systematic relationships between the shape and the processes forming them, and led to studies on geomorphological categorisation based on curvatures. The potential for prediction of along-strike variations and connection between morphology and sedimentary process is herein approached through broadening the mathematical functions used, detailed measurement, observation and curve-fitting of over 150 passive continental margins. Previously, three functions have been used to categorise submarine slopes. The present study finds that four mathematical functions closely match the slopes: Linear, Gaussian, exponential and quadratic (positive and negative/inverse), and reveals that the fourth slope, the quadratic, is by far the most common. While exponential and quadratic slopes are similar there is a crucial difference in the way in which the angle of the slope changes. This study suggests that quadratic slopes represent systematically decreasing sediment deposition with distance, previously attributed to exponential slopes. Exponential slopes meanwhile, represent slope readjustment profiles with upper sediment bypass and lower slope aggradation. Linear slopes, which form the longest low-angle slopes, form in response to high sediment input. Abrupt shelf-edges form in shallower water and develop longer slope aprons, suggesting formation from erosional processes. This implies that the quintessential sigmoidal (s-shaped, Gaussian function) slope, with a smooth rollover, represents the fundamental depositional slope profile. [ABSTRACT FROM AUTHOR]

We used local P and S waves, and regional Lg waves to investigate the Mw 4.9 Offshore Jeju Island earthquake, whose records show evidence of a complex rupture. This earthquake provides a rare window to understand the seismogenesis of moderate‐sized earthquakes on the southern Korea–East China Sea continental shelf. We computed the relative source time functions (RSTFs) by aligning the signals on the origin time of the main and its empirical Green's function (EGF) events, allowing us to use them as differential times of the EGF pair. We determined subevent locations using direct‐wave RSTFs, and captured the rupture variability of the two large subevents using waveform inversion of stacked Lg‐wave RSTFs. The first subevent rupture started by two weak nucleation phases and propagated slowly and bilaterally. Then the second subevent ruptured westward. Our analysis demonstrates that the Lg‐wave train observed at regional distances is useful in investigating detailed slip history. Plain Language Summary: In‐depth studies of small‐to‐moderate‐sized earthquakes in offshore regions are often limited by sparse seismographic station coverage and a lack of close observations. Here, we demonstrate the effective use of local P and S waves and regional Lg waves to investigate the detailed rupture process of the 2021 Mw 4.9 Offshore Jeju Island, Korea earthquake. Lg wave is a guided S wave composed of a superposition of post‐critical reflections in the crust. Detailed seismological analyses using Lg waves revealed that earthquake rupture processes can be spatially complex even in areas with low seismic activity. Our analysis demonstrates that the Lg wave observed at distances greater than 150 km from the epicenter alleviates the limited local station coverage and can be a very useful signal to image the detailed slip history of the earthquake. Our analysis revealed the rupture complexity of the earthquake, expressed as a cascade of four sequential ruptures consisting of two small nucleation phases and two large subevents. Such detailed knowledge of earthquake rupture evolution is critical for understanding seismogenesis in this stable continental region setting. Key Points: We demonstrate an approach to capture the complex rupture process of an offshore moderate‐sized earthquake using limited observationsDirect P and S waves and Lg waves are used to image a spatiotemporal slip history of the Mw 4.9 Offshore Jeju Island, Korea earthquakeResults show a cascading rupture of four subevents on a fault, offering a deeper understanding of event mechanism in low‐seismicity regions [ABSTRACT FROM AUTHOR]

Research on intertidal mussel assemblages and associated communities has revealed that complexity and structure are influenced by environmental heterogeneity and local‐scale factors affecting recruitment. Research in situ in eastern and western Pacific intertidal ecosystems has suggested drivers of species diversity and community structure encompassing large geographic scales, however, there are major gaps in geographic coverage. Our aim is to fill some of these gaps by analyzing macrofaunal functional group diversity and effects of environmental factors on intertidal mussel communities from three distinct marine ecoregions in the southern and northern hemispheres. We identified the effects of algal cover and environmental heterogeneity on species richness and evenness, and we modeled factors effecting mussel layer complexity from assemblages in three marine ecoregions. We analyzed macrofaunal species diversity within one of the austral ecoregions based on the width of the coastal shelf. Species richness was highest in samples from the northern hemisphere while evenness was highest in samples from the southern hemisphere. Similarity in functional group structure for all communities sampled was ≤55% (Bray–Curtis dissimilarity) and ≤35% (Chao–Jaccard dissimilarity). Wave exposure had a significant effect on shell length and complexity of mussel matrices on rocky bench platforms. The presence of algal cover had a strong effect on species richness in mussel matrices regardless of complexity, while algal canopies had no effect on species evenness. Overall, this study provides significant new insight on the community complexity of mussel beds in parts of the world which have been poorly studied in this regard. [ABSTRACT FROM AUTHOR]

Actinium‐227 (227Ac) has been used as a powerful tracer of diapycnal mixing in the ocean, assuming that it is conservative and originates mainly from deep‐sea sediments. However, here we show an unexpectedly large source (continental margin) and sink (scavenging) of 227Ac in the ocean, based on high‐resolution 227Ac distributions obtained for the first time by mooring Mn‐fibers in the East Sea (Japan Sea). Although we expected a decrease in radium‐228 (228Ra) to 227Ac ratios with depth owing to their different half‐lives, the ratios increased with depth in the upper layer, indicating efficient removal of 227Ac by particle scavenging. In addition, unusually high 227Ac activities (∼15 dpm m−3) were observed in the surface layer, likely due to the horizontal transport of 227Ac‐enriched shelf water. Thus, our results suggest refining our understanding of the geochemical cycle and application of 227Ac in the ocean. Plain Language Summary: Distributions of 227Ac provide crucial information for the vertical mixing of the deep ocean on timescales of up to 100 years. However, behaviors of 227Ac in the ocean have not been well understood to date because of its extremely low concentration. In this study, we for the first time determined high‐resolution 227Ac profiles by mooring Mn‐fibers in a marginal sea of the northwestern Pacific Ocean. Our results display that the shelf source inputs as well as efficient removal by particle scavenging have been overlooked so far. In particular, we emphasize that the removal of 227Ac by particle scavenging revealed in this study should be considered when using 227Ac as a tracer of mixing rates in the ocean. Key Points: The high‐resolution measurement of 227Ac with our Mn‐fiber mooring method agrees very well with the onboard Mn‐fiber filtration methodSignificantly high 227Ac activities, which might originate from the 227Ac‐enriched shelf water, are observed in the surface layer (0–100 m)High 227Ac scavenging rates are calculated based on the increasing trend of 228Ra to 227Ac ratio with depth in the upper layer (0–1,000 m) [ABSTRACT FROM AUTHOR]

The presence of a late Quaternary ice sheet/ice shelf over the East Siberian Sea has been proposed in several papers. Here, we further document its duration/resilience based on the sedimentary, bulk mineralogical, and geochemical (organic matter content and its stable isotopic composition, U‐Th series) properties of a core raised from the southernmost Mendeleev Ridge. The chronostratigraphy of the studied core was mainly built from the 230Th excess (230Thxs) distribution and decay downcore. At the core‐top, peaking 230Thxs values during the early MIS 3 and mid‐MIS 1 encompassing an MIS 2 hiatus were observed. As documented in several papers, these peaks suggest seasonally open ice conditions over proximal continental shelves. Below, the interval spanning MIS 4 and possibly MIS 5d records major ice‐rafting events illustrated by overall high coarse‐fraction contents. Underlying MIS 5e, down to MIS 11, the sediment depicts relatively low sand (1.7±2.5 dw%), high clay (33.5±4.7 dw%), and very low organic carbon (0.10±0.06 dw%) contents, and low δ13Corg values (−24.3±0.9‰). This section is interpreted as recording fine sediment transport by deep currents and/or meltwater plumes below a resilient ice cover, only interrupted by a few short‐duration events. These events include (i) detrital carbonate pulses assigned to deglacial events along the NW Laurentide Ice Sheet margin (Termination (T) III), and (ii) intervals with some planktonic foraminifer occurrences, likely relating to their advection from open areas of the Arctic Ocean (MIS 5e, 9 and 11). All Terminations, but TII and the early MIS 3, show peaking Mn/Al values linked to the submergence of Arctic shelves under a rising sea level. We conclude that the resilient ice cover, likely an ice shelf, has been present over the southern Mendeleev Ridge during most of the interval after the Mid‐Pleistocene Transition and was favoured by the low summer insolation of the MIS 14 to 10 interval. [ABSTRACT FROM AUTHOR]

The development of low‐oxygen zones threatening marine life (hypoxia) occurs annually in multiple coastal regions of the world. The largest estuary of the continental United States, the Chesapeake Bay, typically has ≈10 km3 of water with dioxygen concentrations <3 mg L−1 in July. As numerical methods for refining model resolutions in targeted areas are becoming common, there is interest in assessing the feasibility of simulating coastal hazards such as hypoxia in Earth System Models (ESMs). These coupled models are typically not constrained by observations and thus likely to feature systematic biases in their land, atmosphere, or ocean components. This study relies on four numerical experiments to evaluate the sensitivity of Chesapeake Bay hypoxia to changes or biases in its external physical forcings. Hypoxia exhibits only a minor decrease (−1.6%) after reducing the Bay's terrestrial freshwater discharge by 9.5% (but keeping terrestrial nutrient loadings the same). Changes in freshwater discharges have their largest impact on hypoxia during one extreme event (−37% during 2011 tropical storm Lee). Similarly, changing oceanic conditions on the shelf or their temporal frequency impact hypoxia by only 5%–6%, indicating that the latter is predominantly dictated by local conditions. Although these results are promising from the perspective of ESMs, additional components of ESMs will need to be evaluated before general conclusions can be reached. We notably speculate that the Bay's hypoxia would exhibit higher sensitivity to other forcings not examined here, notably air temperatures and nutrient loadings. Plain Language Summary: Many coastal embayments of the world experience the development of "dead zones" during the summer, defined by very low concentrations of oxygen in water. The dead zones negatively affect the ecosystem including commercially‐important fisheries. Such a dead zone can be found every summer in the Chesapeake Bay, the largest and most productive estuary in the continental United States. Although these phenomena are typically the focus of local or regional managers, recent improvements in computer capabilities raise the possibility that dead zones could be successfully represented in the same type of computer simulators used for century‐long projections of the Earth's climate. Such simulators would provide a long term projection for the severity of dead zones throughout the world. The present study examines whether a realistic representation of the Chesapeake Bay dead zone can be obtained using information from these global computer simulations. The results show that the representation of the dead zone is not substantially different when using the global data sets selected for this study. This positive outcome opens the door for additional tests that should focus on other components of the global simulators, notably air temperatures and nutrients inputs from the land to the coastal embayments. Key Points: Chesapeake Bay hypoxia shows only a weak sensitivity to continental shelf conditions and variabilityChanges in shelf hydrography propagate throughout the Bay but surface temperatures are set by the meteorological forcingShort term hydrological events are not always captured well by global land models which can impact hypoxia substantially [ABSTRACT FROM AUTHOR]

Stratigraphy along the Brazilian Equatorial Margin is a crucial guide to the geodynamic history of rifting of Pangea and formation of the South Atlantic Ocean. Understanding the evolution of the Brazilian Equatorial Margin, which intersects the Saint Paul and Romanche Fracture Zones on the western margin of South Atlantic Ocean, is also key for reconstructing eustatic histories and natural resource exploration. In this study, we quantify the stratigraphic and subsidence histories of three sedimentary basins--Barreirinhas, Ceará, Potiguar--that sit within the margin. Stratigraphy was mapped using ca. 900-line-km of two-dimensional seismic data. Biostratigraphic and check-shot data from 23 wells drilled on the continental shelf, slope and in the distal parts of these basins were used to date and depth-convert stratigraphy. Check-shot data were also used to parameterise compaction. The mapped stratigraphy was backstripped to calculate subsidence histories for the basins. Subsidence curves were decompacted, water-loaded and corrected for palaeo-water depths using biostratigraphic data from well reports. The mapped stratigraphy of the Barreirinhas and Ceará Basins and theoretical subsidence curves indicate that stretching factors did not exceed 1.6. These values suggest that these basins can be regarded as failed rifts. In contrast, more distal stratigraphy mapped in the Potiguar Basin to the south indicates that it stretched by a factor of 5-6. Calculated subsidence histories indicate that this basin formed primarily because of Cretaceous rifting and Cretaceous to Recent post-rift thermal sag, with amplitudes governed by the amount of initial stretching. [ABSTRACT FROM AUTHOR]

Observed Antarctic sea ice trends up to 2015 have a distinct regional and seasonal pattern, with a loss during austral summer and autumn in the Bellingshausen and Amundsen Seas, and a year‐round increase in the Ross Sea. Global climate models generally failed to reproduce the magnitude of sea ice trends implying that the models miss relevant mechanisms. One possible mechanism is basal meltwater, which is generally not included in the current generation of climate models. Previous work on the effects of meltwater on sea ice has focused on thermodynamic processes. However, local freshening also leads to dynamic changes, affecting ocean currents through geostrophic balance. Using a coupled ocean/sea‐ice/ice‐shelf model, we demonstrate that basal melting can intensify coastal currents in West Antarctica and the westward transport of sea ice. This change in transport results in sea ice anomalies consistent with observations, and may explain the disparity between climate models and observations. Plain Language Summary: Observed sea ice trends around Antarctica vary throughout the year and from region to region. In particular, there was a sea ice loss in summer in West Antarctica and year‐round increase in the Ross Sea up to 2015. Global climate models are not able to reproduce these sea ice trends which is a hint that climate models are missing some important mechanisms in the region. One mechanism that is not included in most climate models is meltwater from the base of floating ice shelves and which spreads into the ocean. Basal meltwater can create a situation where there is less dense water near the ice shelves next to denser waters offshore. Such a lateral density gradient will result in faster ocean flows that redistribute existing sea ice. In this study, we use an ocean model that includes ice shelves as well as sea ice and show that this mechanism can create sea ice anomalies that match the observed trends in West Antarctica and the Ross Sea. Our results suggest that including basal meltwater and its effect on the ocean flow in global climate models is important to reproduce observed sea ice trends. Key Points: An ocean/sea‐ice/ice‐shelf model reveals intensified basal meltwater provokes dynamic changes in ocean currents and sea ice distributionThe change in transport results in sea ice anomalies consistent with observations near the West Antarctic and Ross Sea coast before 2016Basal meltwater is generally not included in climate models which might explain why the models fail to reproduce the observed sea ice trend [ABSTRACT FROM AUTHOR]

This study investigates long‐term sea level changes in the South China Sea (SCS) using a validated high‐resolution regional ocean model simulation for the Maritime Continent. The contributions of ocean mass redistribution and steric sea level are examined to understand the sea level variations. The ocean bottom pressure (OBP) serves as an indicator of sea level variations linked to alterations in ocean mass flux. The OBP accounts for over 80% of the total sea level change over the shelves, while the steric sea level emerges as the dominant factor, contributing over 50% to the sea level change in the deep SCS. Luzon Strait transport shows a weakening trend in the last six decades, resulting in higher heat accumulation and larger steric expansion in the deep SCS. The ocean mass redistribution acts as a mechanism to balance the contrasting steric induced sea level changes over the deep SCS and shallow continental shelves. Plain Language Summary: The South China Sea (SCS) has vast continental shelves covering more than half of its surface area. The study investigates long‐term sea level changes in the SCS using an ocean general circulation model simulation, considering steric sea level (water expansion due to temperature and salinity changes) and ocean mass redistribution. The analysis showed a significant increase in steric sea level in the deep SCS, while the contribution of ocean mass redistribution decreased. The mass redistribution was responsible for over 80% of the total sea level change, except in the deep SCS, where steric sea level dominated. Weakened flow from the Pacific Ocean to the SCS led to more heat accumulation and higher steric expansion in the deep SCS, causing water to redistribute toward the shelves. Key Points: About 80% of the sea level changes over the South China Sea (SCS) shelves are attributed to the redistribution of ocean mass from deeper regionsThe SCS throughflow has exhibited a weakening trend over the past six decadesSteric sea level changes, driven by fluctuations in Luzon Strait transport, dominate long‐term sea level variations in the SCS [ABSTRACT FROM AUTHOR]

Zooplankton plays an essential role in marine ecosystems as the link between primary producers (phytoplankton) and higher trophic levels in food webs, and as a dynamic pool of recruits for invertebrates and fish. Zooplankton communities are diverse with a patchy distribution at different spatial scales, influenced by oceanographic processes. The continental shelf of eastern South Africa is narrow and exposed to the western‐boundary Agulhas Current, with some shelter against strong directional flow provided by the broader KwaZulu‐Natal Bight, a coastal offset adjacent to an estuary. We compared zooplankton species richness, diversity and relative abundance of key taxa among sheltered and exposed shelf areas using metabarcoding and community analysis, to explore the ecological role of the bight in a highly dynamic ocean region. Metabarcoding recovered higher richness and diversity at a finer resolution than could previously be achieved with traditional microscopy. Of 271 operational taxonomic units (OTUs) recovered through metabarcoding, 63% could be matched with >95% sequence similarity to reference barcodes. OTUs were dominated by malacostracan crustaceans (161 spp.), ray‐finned fishes (45 spp.) and copepods (28 spp.). Species richness, diversity and the relative abundance of key taxa differed between sheltered and exposed shelf areas. Lower species richness in the bight was partly attributed to structurally homogeneous benthic habitats, and an associated reduction of meroplanktonic species originating from local benthic–pelagic exchange. High relative abundance of a ray‐finned fish in the bight, as observed based on fish eggs and read counts, confirmed that the bight is an important fish spawning area. Overall, zooplankton metabarcoding outputs were congruent with findings of previous ecological research using more traditional methods of observation. [ABSTRACT FROM AUTHOR]

In recent years, significant efforts have been directed towards extracting deep shale gas (SG) in Luzhou. Understanding the factors influencing the accumulation and preservation of SG in the section extending from the Upper Ordovician Wufeng (WF) Formation (Fm) through the Lower Silurian Longmaxi (LMX) Fm is crucial for its large‐scale, profitable development. The shale layers in the LMX Fm located in the Luzhou‐Zigong area in the southern part of the Sichuan Basin have undergone unique geological processes, including deep deposition, intensive uplift, erosion and deformation. The Luzhou block, situated in the low‐fold zone in southern Sichuan between the southern slope of the paleo‐uplift in central Sichuan and the down‐warping fold zone in south‐eastern Sichuan, was studied using seismic, well‐log, drilling and core analysis and test data to understand its tectonic, sedimentary, reservoir and fracture characteristics and identify the principal factors controlling gas accumulation in this area. The study found that SG in the Luzhou block is primarily distributed in the WF Fm through the Longyi1 sub‐member. Class I continuous reservoirs, 2.6–20.3 m in thickness, are mainly found in the Longyi11–13 sublayers and those with large continuous thickness produced high yields during tests. Gentle anticlinal zones and wide, gentle tectonic structures with relatively high‐pressure coefficients have formed in this area. High‐angle fractures (HACs) in this area tend to accumulate free gas and, therefore, facilitate the accumulation and production of SG. The study concludes that the continuous thickness of Class I reservoirs and natural HACs controlled by the centre of the deep‐water continental shelf are the primary factors controlling SG accumulation in the Luzhou block. [ABSTRACT FROM AUTHOR]

Holohalaelurus regani and Scyliorhinus capensis are relatively small catsharks, which both occur off the continental shelf around South Africa and are often caught together as by‐catch in demersal trawls. The present study used data collected during annual demersal research surveys conducted between 2009 and 2015 and is a first attempt at modeling the potential intra‐ and interspecific associations, by maturity stage and depth, of H. regani and S. capensis to elucidate species‐specific patterns in their distributions in South African waters. Intraspecifically, both species displayed a wide overlap in distribution between maturity stages, but only H. regani displayed marked changes in distribution with maturity stage, with mature individuals found further eastwards and occupying deeper waters than immature individuals. Interspecifically, the two catsharks displayed an inverse relationship in their distribution, with an increase in the abundance of H. regani and a decrease in the abundance of S. capensis when moving from the south coast to the west coast. Some localized patches of co‐occurrence were, however, evident between species and maturity stages, especially in offshore areas. Overall, our results indicated a stronger co‐occurrence of mature and immature stages within each species and a rather weak co‐occurrence of maturity stages between the two species. The spatial information provided in the present study provides useful information on how sharks with similar morphologies and lifestyles may partition their habitat as a mechanism for potentially reducing competition between them. [ABSTRACT FROM AUTHOR]

Climate change is influencing polar bear (Ursus maritimus) habitat, diet, and behavior but the effects of these changes on their physiology is not well understood. Blood‐based biomarkers are used to assess the physiologic health of individuals but their usefulness for evaluating population health, especially as it relates to changing environmental conditions, has rarely been explored. We describe links between environmental conditions and physiologic functions of southern Beaufort Sea polar bears using data from blood samples collected from 1984 to 2018, a period marked by extensive environmental change. We evaluated associations between 13 physiologic biomarkers and circumpolar (Arctic oscillation index) and regional (wind patterns and ice‐free days) environmental metrics and seasonal and demographic co‐variates (age, sex, season, and year) known to affect polar bear ecology. We observed signs of dysregulation of water balance in polar bears following years with a lower annual Arctic oscillation index. In addition, liver enzyme values increased over time, which is suggestive of potential hepatocyte damage as the Arctic has warmed. Biomarkers of immune function increased with regional‐scale wind patterns and the number of ice‐free days over the Beaufort Sea continental shelf and were lower in years with a lower winter Arctic oscillation index, suggesting an increased allocation of energetic resources for immune processes under these conditions. We propose that the variation in polar bear immune and metabolic function is likely indicative of physiologic plasticity, a response that allows polar bears to remain in homeostasis even as they experience changes in nutrition and habitat in response to changing environments. [ABSTRACT FROM AUTHOR]

Aim: Theory predicts fish community biomass to decline with increasing temperature due to higher metabolic losses resulting in less efficient energy transfer in warm‐water food webs. However, whether these metabolic predictions explain observed macroecological patterns in fish community biomass is virtually unknown. Here, we test these predictions by examining the variation in demersal fish biomass across productive shelf regions. Location: Twenty one continental shelf regions in the North Atlantic and Northeast Pacific. Time Period: 1980–2015. Major Taxa Studied: Marine teleost fish and elasmobranchs. Methods: We compiled high‐resolution bottom trawl survey data of fish biomass containing 166,000 unique tows and corrected biomass for differences in sampling area and trawl gear catchability. We examined whether relationships between net primary production and demersal fish community biomass are mediated by temperature, food‐web structure and the level of fishing exploitation, as well as the choice of spatial scale of the analysis. Subsequently, we examined if temperature explains regional changes in fish biomass over time under recent warming. Results: We find that biomass per km2 varies 40‐fold across regions and is highest in cold waters and areas with low fishing exploitation. We find no evidence that temperature change has impacted biomass within marine regions over the time period considered. The biomass variation is best explained by an elementary trophodynamic model that accounts for temperature‐dependent trophic efficiency. Main Conclusions: Our study supports the hypothesis that temperature is a main driver of large‐scale cross‐regional variation in fish community biomass. The cross‐regional pattern suggests that long‐term impacts of warming will be negative on biomass. These results provide an empirical basis for predicting future changes in fish community biomass and its associated services for human wellbeing that is food provisioning, under global climate change. [ABSTRACT FROM AUTHOR]

Aim: The criteria used to define the International Union for Conservation of Nature (IUCN) Red List categories are essentially based on demographic parameters at the species level, but they do not integrate species' traits or their roles in ecosystems. Consequently, current IUCN‐based protection measures may not be sufficient to conserve ecosystem functioning and services. Some species may have a singular combination of traits associated with unique functions. Such functionally distinct species are increasingly recognized as a key facet of biodiversity since they are, by definition, functionally irreplaceable. The aim of this study is to investigate whether threatened species are also functionally rare and to identify which traits determine extinction risk. Location: European continental shelf seas. Time period: 1984–2020. Major taxa studied: Marine fish. Methods: Using newly compiled trait information of 425 marine fish species in European waters, and more than 30 years of scientific bottom trawl surveys, we estimated the functional distinctiveness, restrictedness and scarcity of each species and cross‐referenced it with their IUCN conservation status. Results: In European continental shelf seas, 38% of the species threatened with extinction (9 out of 24 species) were identified as the most functionally distinct. By mapping extinction risk in the multidimensional species trait space, we showed that species with the greatest risk of extinction are long‐lived and of high trophic level. We also identified that the most functionally distinct species are sparsely distributed (4% of the total area on average) and have scarce abundances (<1% of the relative mean abundance of common species). Main Conclusions: Because a substantial proportion of threatened species are functionally distinct and thus may play unique roles in ecosystem functioning, we stress that species traits—especially functional rarity—should become an indispensable step in the development of conservation management plans. [ABSTRACT FROM AUTHOR]

The Acoupa weakfish, Cynoscion acoupa, is an important fishery resource of the Brazilian North coast that is commercially valuable, particularly for its gas bladder (fish maw), which is exported to Asian markets. However, because of intensive fishing and lack of reliable data, the Acoupa weakfish is classified as Vulnerable by the IUCN. We used Fisheries Performance Indicators (FPIs) to evaluate C. acoupa fisheries on the Amazon continental shelf, to inform management actions. The ecological indicator had the lowest score due to increased fishing effort associated with high demand for the fish maw, and the co‐management indicator was also unsatisfactory due to the predominance of fishing entrepreneurs and a lack of sustainable management practices. Our findings showed that the C. acoupa fishery is precarious in its sustainability, mainly because of harvest and co‐management which were the least satisfactory metrics. [ABSTRACT FROM AUTHOR]

The Froan Basin and Frøya High are two major structural elements located on the Mid‐Norwegian Continental Shelf and are separated from the Halten Terrace by major west‐dipping normal fault zones. Compared to the Halten Terrace, the Froan Basin and Frøya High are relatively under‐explored and remain poorly understood in terms of their Late Jurassic tectono‐stratigraphic evolution. Upper Jurassic, shallow marine, syn‐rift deposits (i.e. Rogn Formation) are present locally, but their source, delivery system and depositional environment are not yet well understood. Improving our understanding of how fault activity and rift‐shoulder uplift influenced rift physiography and paleowater depths is crucial when developing depositional models in this region. In this study, we present a model of the Late Jurassic rift physiography of the Froan Basin and Frøya High based on seismic reflection and well data and reverse subsidence modelling. We show that during the Late Jurassic to Early Cretaceous, major footwall uplift caused the Frøya High and the western margin of the central Froan Basin to be subaerially exposed, forming an intra‐rift footwall island. Shallow marine areas to the east, immediately adjacent to the footwall island, accumulated sediment supplied from the uplifted and partially eroded footwall. In contrast, the Trøndelag Platform, north of the Froan Basin and Frøya High, remained submerged throughout the rift episode. We therefore suggest that the extent of the shallow marine system was controlled by the magnitude of footwall uplift along the western margin of the basin and that sediment dispersal was influenced by the coastal paleogeomorphology of the back‐tilted footwall. [ABSTRACT FROM AUTHOR]

The internal structure and architecture of evaporite sequences is often overlooked, with attention frequently concentrating on the external geometries that salt bodies form. The availability of extensive 3D seismic data affords the opportunity to interpret the internal structures within these evaporite sequences and comprehensively characterise the different structural facies over large areas. This paper concentrates on the Zechstein Supergroup evaporite deposits within the Southern North Sea of the United Kingdom's Continental Shelf. This analysis of the internal structural complexity and stratigraphic heterogeneity utilises 26,000 km2 of 3D seismic data together with over 96 wells from the Southern North Sea. Characterisation of the different structural facies present was undertaken alongside mapping their spatial distribution to understand the relationship they have with one another and the structural evolution that may have been taken. This work has (1) characterised and mapped six different internal structural facies present within the Zechstein with increasing levels of deformation; (2) shown the internal lithological heterogeneity is indicative of variations in the vertical strength profile of layered evaporite sequences; (3) discontinuous high‐amplitude reflections within the Zechstein are as a result of the geometries being too steeply dipping for the seismic data to image; and (4) the ability to possibly predict the internal heterogeneity of areas of poorly imaged salt, such as within large diapiric salt structures, from surrounding structural facies. These findings suggest that there is significant internal complexity even within areas of the basin with minor mobilisation to the external salt geometry. [ABSTRACT FROM AUTHOR]

We investigate feedbacks between subsurface continental shelf ocean temperatures and Antarctic glacial melt using a coupled climate model. The model was forced with SSP5‐8.5 and an uncoupled projection of basal melt and calving fluxes. SSP5‐8.5 forcing with fixed pre‐industrial glacial melt warms all continental shelves, such that historically "cool" and "fresh" shelves transition to "warm." Additional glacial melt, added at depth, cools the Eastern Ross, Amundsen, and Bellingshausen seas, suggesting a negative feedback on basal melt—a novel result for a coarse resolution coupled model. From the Weddell Sea, along East Antarctica, and into the western Ross Sea—where continental shelves transition to a "warm" state—additional glacial melt increases temperatures at the continental shelf sea floor, suggesting a positive feedback. The sign of the glacial melt–subsurface temperature feedback is critically dependent on continental shelf properties, climate state, and the vertical distribution of glacial melt inputs. Plain Language Summary: Antarctic ice shelves lose mass as freshwater—primarily from melting at their base and when icebergs break off. We know that the rate at which Antarctic ice shelves are losing mass is increasing and we expect this freshwater input into the ocean to increase further in a warmer world. Most climate models do not include a representation of this changing freshwater input, and its climatic impacts are uncertain. One particularly important climate impact is how the additional freshwater changes the subsurface ocean temperature. If freshwater warms/cools the coastal ocean it could increase/decrease melt in a positive/negative feedback loop. But existing studies disagree about this effect and even about the sign of the feedback. We added a timeseries of freshwater input to a climate model and ran experiments with strong climate warming to investigate this feedback. The sign of the feedback varies by region. Where climate change drives a cold coastal ocean to transition to a new warmer state, we find that freshwater causes a strong additional warming (a positive feedback). Where the coastal ocean is already warm in the present day and warms in future, freshwater reduces this warming (a negative feedback). To achieve the negative feedback freshwater must be added at depth. Key Points: A glacial melt projection is added to a 1° coupled climate model under SSP5‐8.5 to investigate ocean temperature feedbacksAdditional glacial melt cools the Eastern Ross, Amundsen, and Bellingshausen seas at depth, but warms elsewhereThe addition of glacial melt at depth is necessary to generate the cooling response [ABSTRACT FROM AUTHOR]

The recent discovery of warm ocean water near the Totten Ice Shelf (TIS) has increased attention to the Sabrina Coast in East Antarctica. We report the result of 6‐day helicopter‐based observations conducted during the 61st Japanese Antarctic Research Expedition (JARE61), revealing warm ocean water (0.5–1°C) occupying a large previously unsampled area of the Sabrina Coast (116.5°E−120°E) below 550–600 m. Along the TIS front, we observe modified Circumpolar Deep Water (mCDW) well above freezing (∼−0.7°C), consistent with previous work. We identify glacial meltwater outflow from the TIS cavity west of 116°E. No signs of mCDW intrusions toward the Moscow University Ice Shelf cavity are observed; however, those observations were limited to only two shallow (∼330 m) profiles. We also highlight the advantages of helicopter‐based observations for accessibility, speed, maneuverability, and cost‐efficiency. The combination of ship‐ and helicopter‐based observations using the JARE61 approach will increase the potential of future polar oceanographic observations. Plain Language Summary: Totten Glacier hosts the most rapidly thinning ice in East Antarctica. This record of thinning is due to rapid melt along the grounding line of the Totten Ice Shelf (TIS), where warm ocean water from the open ocean flows into ice shelf cavities. To understand the pathways and mechanisms of warm water inflow, ocean observations for entire continental shelf regions are necessary. This has historically not been possible due to intense sea ice and icebergs in the region. To overcome this problem, we conducted a 6‐day helicopter‐based oceanographic campaign during the 61st Japanese Antarctic Research Expedition. Our measurements show that warm ocean water occupies a large area of the continental shelf off the TIS. We identify glacial meltwater outflow from the TIS cavity west of 116°E, which provides direct evidence of TIS melting. We also show that helicopter‐based measurements are better for the following aspects; (a) helicopter operations are insensitive to sea ice conditions, (b) helicopter travels faster than a ship, (c) helicopter can conduct measurement in a small ice crack, and (d) helicopter is cheaper to operate than an ice breaker. By combining ship‐based and helicopter‐based approaches, we may be able to enhance the efficiency of future polar oceanographic observations. Key Points: Six‐day helicopter‐based observations retrieved 67 temperature profiles covering the entire continental shelf region off the Totten Ice Shelf (TIS)Between 116.5°E and 120°E, modified Circumpolar Deep Water can be found uniformly over the continental shelf region below 550–600 mGlacial meltwater outflow from the TIS cavity is identified west of 116°E [ABSTRACT FROM AUTHOR]

Obtaining high spatiotemporal resolution surface currents with wide coverage is of great importance for understanding marine physical and biogeochemical processes, as well as practical applications. This study utilizes the sequential hourly images from the Himawari‐8 geostationary satellite to map the semidiurnal M2 surface tidal current pattern over the shallow shelf (<100 m) of the northern South China Sea. The comparison between the satellite‐derived tidal currents and the High‐Frequency Radar observations shows good agreement. The satellite‐derived tidal currents are also fairly comparable to the prediction of the regional tidal model from Oregon State University. The detided daily mean surface flows provide an apparent representation of the spatial pattern of the Guangdong Coastal Current (GCC) and its synoptic variability, well consistent with the simultaneous sea surface temperature and salinity satellite observations. The observed surface flows are compared to the Copernicus Marine Environment Monitoring Service daily model currents, and the model findings are in good agreement with the observations, indicating the sensitivity of the GCC to rapid changes of northeasterly winds. This study highlights the potential of the Himawari‐8 geostationary satellite in measuring sea surface currents over a broad, shallow continental shelf. Plain Language Summary: This study used hourly images from the Himawari‐8 geostationary satellite to map the semidiurnal M2 surface tidal current pattern in the shallow shelf (<100 m) of the Northern South China Sea. The satellite‐derived results are compared to high‐frequency radar observations and a regional tidal model from Oregon State University and are found to be in good agreement. The satellite observations also provide a representation of the spatial pattern of the Guangdong Coastal Current (GCC) and its synoptic variability, which are well consistent with sea surface temperature and salinity observations. The observed surface flows are also in good agreement with the Copernicus Marine Environment Monitoring Service daily model currents, showing the sensitivity of the GCC to rapid changes of northeasterly winds. This study demonstrates the usefulness of the Himawari‐8 geostationary satellite in measuring surface currents over a broad, shallow continental shelf. Key Points: Semidiurnal M2 tidal currents are derived from the Himawari‐8 geostationary imageryThe satellite‐derived mean flows reveal the spatial pattern of a strong, broad Guangdong Coastal Current and its synoptic scale variabilitySatellite‐derived tidal and mean currents are used for evaluating the model outputs [ABSTRACT FROM AUTHOR]

Different timescale contributions to the sea‐level variation in the South China Sea (SCS) are evaluated in this paper. On seasonal timescale, the large variance of the sea‐level anomaly (SLA) could account for more than 70% of the monthly sea‐level variation in the western shallow continental shelf and the area of Luzon cold eddy. Besides, the seasonal explained variance percentage (skill) has 2 weak centres (50%–70%) off eastern Vietnam, which is related to the summertime eddy pair in the SCS. On interannual‐to‐decadal (low‐frequency) timescale, the skill has two large‐value regions (Zone A and Zone B). Zone A is characterized by double centres off eastern Vietnam, but the meridional position of the double centres is farther north than that of the eddy pair. The skill in Zone A is in the range of 35%–55%, and about 50%–70% of the low‐frequency variation comes from the steric effect. Zone B is off the west coast of the Philippines. The skill in Zone B increases southward, and it is dominated by the wind‐induced dynamic process which is attributed to the remote Rossby wave from the tropical Pacific. Based on the S‐EOF analysis, the SEOF‐1 mode mainly portrays the decadal variation of the SLA, while the SEOF‐2 mode reflects the interannual variation of the SLA. In Zone B, almost all of the low‐frequency variation could be attributed to ENSO and PDO, especially to PDO which has a larger contribution. However, the double centres in Zone A are governed by the SCS summer monsoon, instead of ENSO and PDO. [ABSTRACT FROM AUTHOR]

The temporal variation of heat budget in the lower layer of the eastern Ross Sea shelf (ERSS) is crucial for understanding the stability of ice shelves in the Ross Sea. In this study, a 6‐year (2005–2010) simulation from the Southern Ocean State Estimate (SOSE) is employed to analyse the interannual variations of heat budget in the lower layer of the ERSS and the controlling mechanisms. The results reveal that the annual change in the heat content of the study region is dominated by the horizontal heat advection term, and only in 2015 the vertical advection and diffusion terms also play an important role. The horizontal advection term is affected by the intrusion of warm circumpolar deep water (CDW) onto the shelf across the northern boundary of the ERSS, the transport of cold dense shelf water (DSW) from the western Ross Sea shelf, and the transport of CDW across the western boundary of the ERSS. The contributions of these physical processes to the change in annual heat content vary between years. The interannual variation of the CDW intrusion is associated with the strength of eddy activity over the slope, and the interannual variation of heat transports associated with DSW is affected by both the extent of DSW on the western shelf and the coastal circulations that affect the eastward spread of DSW. [ABSTRACT FROM AUTHOR]

The Antarctic Slope Current is guided by the topographic gradient of the Antarctic continental slope and creates a dynamical barrier between the continental shelf and the open ocean. The current's vertical structure varies around the continent affecting cross‐slope water mass exchange with consequences for Antarctic mass loss, ventilation of the deep ocean, and carbon uptake. The Antarctic Slope Current is surface‐intensified in many regions but bottom‐intensified in regions of dense overflows. This study investigates the role of dense overflows in modifying the dynamics of the bottom‐intensified flow using a 0.1° global ocean‐sea ice model. The occurrence of bottom‐intensification is tightly linked with dense overflows and bottom speeds correlate with dense overflows on interannual time scales. A lack of vertical connectivity between the bottom and surface flow, however, suggests that the along‐slope bottom water flows are coincidentally co‐located with the Antarctic Slope Current, rather than dynamically a part of the current. Plain Language Summary: The Antarctic Slope Current is a narrow ocean current that travels around Antarctica following the continental slope. It separates the shallow and cold continental shelf from much warmer waters in the open ocean. Intrusions of the relatively warm water across the continental slope impacts melting of Antarctic ice shelves and global sea level rise. Understanding what controls the strength and variability of the Antarctic Slope Current is therefore important. The Antarctic Slope Current usually has the largest velocities near the surface, but there are regions where there is also a strong bottom flow. We use a coupled ocean‐sea ice model and show that the bottom flow is controlled by the export of very dense shelf water that flows down the continental slope in a few locations around the continent. However, the bottom and surface flow does not vary together on interannual time scales which tells us that the two components of the Antarctic Slope Current are largely independent. The result is important as the formation of dense shelf water is expected to reduce in the future which will impact the deep flow, but not the surface component. Key Points: Simulations reveal a close spatial relationship between the bottom‐intensified Antarctic Slope Current and Dense Shelf Water exportInterannual variability of Dense Shelf Water is reflected in the bottom speed of the bottom‐intensified Antarctic Slope CurrentThe surface component varies independently from the bottom‐intensified flow implying two distinct, co‐located currents [ABSTRACT FROM AUTHOR]

The Southern Ocean, a globally important CO2 sink, is one of the most susceptible regions in the world to climate change. Phytoplankton of the coastal shelf waters around the Western Antarctic Peninsula have been experiencing rapid warming over the past decades and current ongoing climatic changes will expose them to ocean acidification and high light intensities due to increasing stratification. We conducted a multiple‐stressor experiment to evaluate the response of the still poorly studied key Antarctic cryptophyte species Geminigera cryophila to warming in combination with ocean acidification and high irradiance. Based on the thermal growth response of G. cryophila, we grew the cryptophyte at suboptimal (2°C) and optimal (4°C) temperatures in combination with two light intensities (medium light: 100 μmol photons m−2 s−1 and high light [HL]: 500 μmol photons m−2 s−1) under ambient (400 μatm pCO2) and high pCO2 (1000 μatm pCO2) conditions. Our results reveal that G. cryophila was not susceptible to high pCO2, but was strongly affected by HL at 2°C, as both growth and carbon fixation were significantly reduced. In comparison, warming up to 4°C stimulated the growth of the cryptophyte and even alleviated the previously observed negative effects of HL at 2°C. When grown, however, at temperatures above 4°C, the cryptophyte already reached its maximal thermal limit at 8°C, pointing out its vulnerability toward even higher temperatures. Hence, our results clearly indicate that warming and high light and not pCO2 control the growth of G. cryophila. [ABSTRACT FROM AUTHOR]

Productivity in the Arctic is expected to increase as temperatures and the number of open water days rise. With this increased productivity, the coastal shelves of the Arctic Ocean may act as a sink for atmospheric carbon. However, this storage is dependent on a sufficient nitrogen (N) supply and current literature on biogeochemical rates of N uptake in this region is severely limited. Here, we report the spatial extent and rate at which the aquatic microbial community utilizes inorganic and organic N substrates in the Alaskan Arctic during late summer. Uptake rates (> 0.3 μm) were measured in 2016 and 2017 using isotopically labeled ammonium (NH4+), nitrate (NO3−), urea, and mixed algal amino acids. Rates of NH4+ regeneration were also measured to investigate the contribution of remineralized N to primary production. Primary production was estimated using isotopically labeled bicarbonate. We found that N species uptake varied by location. Although NH4+ was the form of N taken up at the greatest rate at most sites, we also found that uptake rates of urea could be greater than NO3− and that amino acid uptake was widespread. Supporting previous studies, NO3− uptake rates were correlated with primary production rates. Variability in nutrient reservoirs and sampling conditions in the Chukchi Sea between the 2 yr were responsible for some of the variances observed in estimated NH4+ recycling rates and primary production. Understanding which N sources support this late‐season primary production requires obtaining uptake rates for a diverse range of inorganic and organic N substrates. [ABSTRACT FROM AUTHOR]

Basement highs form one of many potential sediment source areas during the evolution of continental rifts and rifted margins and add to the topographic complexity typical of active rifts. Footwall basement highs acting as a source area to sedimentary systems in the hangingwall of major faults have been documented in many systems worldwide. However, the back‐tilted footwall dip slopes of such highs have received comparatively little attention. Here, we investigate a subsurface case study from the Norwegian continental shelf, where catchments and shallow marine syn‐rift sedimentary systems on a dip slope are preserved due to early transgression of an intra‐rift high. At the onset of Late Jurassic rifting, the Frøya High emerged as a prominent, N‐S trending, 25 km‐wide basement high tilted towards the east in response to several kilometres of displacement along the Klakk Fault Complex, a major normal fault zone at the Frøya High's western edge. Using well‐calibrated 3D seismic reflection data, we observe a series of conspicuous Upper Jurassic wedges along the eastern edge of the Frøya High along the margin of the Froan Basin. Internally, these wedges show sigmoidal geometries marking top and foresets of clinoform packages with a maximum thickness of ca. 200 m with foresets between 30 and 200 m high, dipping ca. 10° towards the east, southeast and northeast. We interpret these wedges to represent a series of eastward prograding deltas positioned along a constructional shoreline, connected to E‐W trending valleys and river catchments up‐dip. The deltas show strong progradation, interpreted to reflect the impact of the continued uplift of their catchments prior to the abrupt termination of sediment supply from drainage capture by footwall scarp drainages. The presence of a connected, largely constructional shoreline has implications for Late Jurassic sediment distribution around the Frøya High, providing primary sedimentary input for longshore‐driven sedimentary systems in the Draugen Ridge to the north. Comparisons with other syn‐rift dip slope systems highlight a broadly similar evolution but shows a distinct lack of the protracted backstepping observed in other dip slope systems. We postulate that different structural configurations of dip slope systems, being footwall uplift or hangingwall subsidence driven, may drive the strongly progradational character of the deltaic systems on the Frøya High. The Frøya High example highlights the need to constrain primary sediment input points to aid the interpretation of volumetrically significant, but short‐lived and subtle depositional systems, especially within complex, tectonically active settings. [ABSTRACT FROM AUTHOR]

In this study, the assimilation of tide gauge and altimetry data into a two‐dimensional barotropic numerical model for the southwestern Atlantic continental shelf (SWACS) was developed. To do this, the preoperative 4‐day storm surges ensemble prediction system developed by Dinápoli et al. (2021, Journal of the Royal Meteorological Society147: 557–572) was implemented for the SWACS. This new configuration, called "Model for Storm Surge Simulations" (M3S), considers a curvilinear grid that covers the SWACS with higher resolution along the shoreline (from 2 to 10 km). M3S was forced with an ensemble of 60 members conformed by the combination of perturbations of the eight principal tidal constituents and of the atmospheric products derived from the Global Ensemble Forecast System. Tidal gauge and altimetry data were assimilated in an asynchronous mode using the four‐dimensional‐ensemble square‐root filter (4DEnSRF). The system was developed and validated forecasting two strong positive storm surges. Results show that 4DEnSRF's innovations produce a positive impact upon the forecast skill up to 2 days. Hence, the 4‐day forecast can be divided into two parts: the first 2 days with a stronger dependence on the initial conditions and the other 2 days purely driven by external forcing. It was found that a symmetric assimilation window of 12 hr length produces the best initial condition. Under this configuration, 4DEnSRF removes biases and improves the timing of the M3S forecasted solutions. The largest improvements were observed at the northern SWACS, where more chaotic processes, such as the atmospheric circulation, explain a large part of the sea‐surface height variability. No significant improvements were found at the southern SWACS, which can be attributed to the strong tidal dynamics that characterise the zone. Our results show that the incorporation of 4DEnSRF into M3S can significantly improve the forecast in the SWACS and also the accuracy of the short‐range detection of storm surges. [ABSTRACT FROM AUTHOR]

The biogeochemical cycling of nitrogen (N) plays a critical role in supporting marine ecosystems and controlling primary production. Nitrification, the oxidation of ammonia (NH3) by microorganisms, is an important process in the marine N cycle, supplying nitrate (NO3−), the primary source of N that fuels new phytoplankton growth, and the primary substrate for the microbial process of denitrification. Understanding nitrification in the Chukchi Sea, the shallow sea overlying the continental shelf north of Alaska and the Bering Strait, is particularly important as phytoplankton growth there has been shown to be limited by N. However, the controls on nitrification in the water column and potential effects of climate change remain unknown. This study seeks to characterize the controls on nitrification in the Chukchi Sea. We found light to be a strong control on nitrification rates. Nitrification was undetectable at light levels above 23 μmol photons m−2 s−1. Subsequently, sea ice concentration was related to nitrification, with rates being higher at stations with high ice cover where light transmission to the water column was reduced. High ammonium (NH4+) concentrations also enhanced nitrification, suggesting that nitrifying organisms were substrate‐limited, likely due to competition for NH4+ from phytoplankton. Unlike previous experimental studies, we found that nitrification rates were higher under low pH conditions. As the effects of ocean acidification and warming disproportionately impact the Arctic, nitrification rates will undoubtedly be affected. Our results will help guide future studies on potential implications of climate change on the biogeochemistry of N in the Chukchi Sea. [ABSTRACT FROM AUTHOR]

Broadly similar Early to Middle Jurassic stratigraphic sequences including bimodal igneous rocks of the Sanandaj–Sirjan Zone of Iran and the Sakarya Zone of Turkey suggest that these formed in a common tectonic setting in an extensional basin that evolved from a terrestrial magmatic rift to a marine shelf and passive continental margin. Whole‐rock chemistry and Sr–Nd isotope signatures indicate derivation of mafic melts from partial melting of the subcontinental lithosphere. Decompression associated with extension led to 5%–30% partial melting of spinel–garnet lherzolite with minor involvement of continental crust, producing tholeiitic to transitional basaltic magma. Extensional basins inverted during the Mid‐Late Jurassic. These relationships suggest the Early to Middle Jurassic formation of a volcanic rifted margin on the SW Eurasian margin, similar to that of offshore Norway. [ABSTRACT FROM AUTHOR]

We investigate the amplitude and frequency of directional geomagnetic change since 15 ka in the Northern North Atlantic (∼67°N) using five "ultra‐high" resolution continental shelf sediment cores deposited at rates greater than 1 m/kyr. The ages of these cores are constrained by 103 radiocarbon dates with reservoir ages assessed through tephra correlation to terrestrial archives. Our study aims to address many of the uncertainties that are common in sedimentary paleomagnetic studies, including signal attenuation in low to moderate resolution archives and difficulty to demonstrate reproducibility in higher resolution archives. The "ultra‐high" accumulation rates of our cores reduce "lock‐in" and smoothing uncertainties associated with magnetic acquisition processes. Abundant radiocarbon dates along with an objective alignment algorithm provide a test of signal reproducibility at sub‐millennial timescales. The paleomagnetic secular variation (PSV) signal, evaluated as individual records and as a new stack (GREENICE15k), validates prior results, but provides stronger geochronological constraints, demonstrates a reproducible PSV signal and amplitude, and extends through the abrupt Bølling–Allerød and Younger Dryas climate transitions of the latest Pleistocene. While broadly consistent with time‐varying spherical harmonic models and varve dated records from Northern Europe, we demonstrate greater variance and higher amplitudes—particularly at sub‐millennial timescales. This robust variability on centennial timescales is rarely observed or discussed, but is likely important to our understanding of some of the most intriguing aspects of the geodynamo. Plain Language Summary: Our study used mud from the seafloor to investigate changes in Earth's magnetic field in the Northern North Atlantic region over the past 15 thousand years. Magnetic minerals eroded from rocks and deposited on the seafloor can preserve a record of the geomagnetic field, like little compass needles suspended in mud. We obtained sediment cores from areas near land with very high accumulation rates, which are rare in the modern ocean, that can record short magnetic field variations that occur on the timescale of centuries. We used radiocarbon dating to determine the ages of the sediment samples and a new alignment algorithm to verify the accuracy and consistency of the magnetic signal we observed. Understanding these short geomagnetic field variations is challenging, but it is key to unlocking many mysteries about the past and future of Earth's magnetic field. Key Points: Sediment cores with ultra‐high accumulation rates are used to study directional changes in the Northern North Atlantic's geomagnetic fieldStudy addresses uncertainties in sedimentary paleomagnetic research, such as signal attenuation, chronology, and reproducibilityStudy reveals robust variability on centennial timescales with greater variance than generally observed over the last 15,000 years [ABSTRACT FROM AUTHOR]

Functional morphology investigates the relationships between morphological characters and external factors, such as environmental, physical and ecological features. Here, we evaluate the functional relationships between body shape and trophic ecology of a tropical demersal marine fish community using geometric morphometrics techniques and modelling, hypothesizing that shape variables could partially explain fish trophic level. Fish were collected over the continental shelf of northeast Brazil (4–9°S). Analysed fish were distributed into 14 orders, 34 families and 72 species. Each individual was photographed in lateral view, and 18 landmarks were distributed along the body. A principal component analysis (PCA) applied on morphometric indices revealed that fish body elongation and fin base shape were the main axes of variation explaining the morphology. Low trophic levels (herbivore and omnivore) are characterized by deep bodies and longer dorsal and anal fin bases, while predators present elongated bodies and narrow fin bases. Fin position (dorsal and anal fins) on the fish body is another important factor contributing to (i) body stability at high velocity (top predators) or (ii) manoeuvrability (low trophic levels). Using multiple linear regression, we verified that 46% of trophic level variability could be explained by morphometric variables, with trophic level increasing with body elongation and size. Interestingly, intermediate trophic categories (e.g., low predators) presented morphological divergence for a given trophic level. Our results, which can likely be expanded to other tropical and nontropical systems, show that morphometric approaches can provide important insights into fish functional characteristics, especially in trophic ecology. [ABSTRACT FROM AUTHOR]

Understanding the influence of ocean conditions on predator–prey relationships can provide insight for ecosystem‐based fisheries management. Pacific hake (Merluccius productus) are abundant and commercially important groundfish in the California Current Ecosystem (CCE) that consume euphausiids (krill) as a major prey item. We used data from the biennial joint U.S.‐Canada Integrated Ecosystem & Acoustic Trawl Survey for Pacific hake (2007–2019, n = 8 surveys) to quantify co‐occurrence of age 2+ hake with krill in relation to bottom depth, continental shelf break location, surface chlorophyll‐a, and 100‐m temperature. Vertical distributions of hake varied among years and were not correlated to krill depth. Hake hotspots occurred primarily off the Oregon coast and near Cape Mendocino, while most krill hotspots occurred in the northern CCE. The probability of co‐occurrence was greatest during cool ocean conditions (100‐m temperature 1°C below average), averaging 41.0% and extending throughout most of the CCE. During warm ocean conditions (100‐m temperature 1°C above average), predicted co‐occurrence averaged 17.0% and was concentrated near Cape Mendocino. These results indicate that hake‐krill co‐occurrence is a function of predator and prey spatial distributions and overall krill abundance. Furthermore, temperature influences hake‐krill co‐occurrence and may explain some of the variation in hake growth and recruitment to the fishery. [ABSTRACT FROM AUTHOR]

Numerical mixing, the spurious mixing primarily generated by the discretization of advection, is often significant in estuarine and coastal models due to sharp, energetic fronts. We compare on‐ and offline estimates of numerical mixing in a submesoscale‐resolving realistic simulation of the ocean state over the Texas‐Louisiana continental shelf. While offline estimates of numerical mixing differ from online estimates, offline methods may be the only analysis available. We use two methods to estimate numerical mixing offline based on the residuals of the salinity squared s2 and volume‐mean salinity variance s′2 ${s}^{{\prime }^{2}}$ budgets. The s′2 ${s}^{{\prime }^{2}}$ budget overestimates the time‐averaged online numerical mixing by 60% at hourly output. The s2 budget compares poorly due to large truncation errors associated with the tendency and advection terms. The residual of the s2 budget starts to converge to the s′2 ${s}^{{\prime }^{2}}$ budget as output frequency increases to 10 min—an unrealistic frequency for long‐term coastal ocean simulations—but neither method unconditionally converges to the online method and therefore cannot be recommended for generic analysis of numerical mixing. We also investigate the effects of horizontal resolution on numerical mixing using a two‐way nested grid with the online method. The volume‐integrated numerical mixing constitutes 57% of the bulk physical mixing—the mixing prescribed by the turbulence closure scheme—in the coarse model and may exceed the physical mixing by half an order of magnitude. We find numerical mixing is reduced by 35% on average in the nested model, likely due to new dynamical processes that emerge in the nested simulation. Plain Language Summary: Numerical models are powerful tools for studying the general circulation of the ocean, allowing us to examine the ocean's complex relationship with Earth's weather and climate in greater detail than observations allow. However, numerical ocean models are prone to several types of numerical errors because they represent physical processes with discrete approximations. One of these errors is numerical mixing, a process by which the discretized transport of tracers by currents generates spurious mixing. Recent studies suggest numerical mixing can be as large as the physical mixing prescribed by a parameterization, especially in regions with strong tracer gradients, such as in estuaries or the coastal ocean. In this study, we examine numerical salinity mixing using a combination of on‐ and offline methods in a model of the ocean state over the Texas‐Louisiana continental shelf in the Gulf of Mexico. Offline methods rely on existing model output and are often easier to implement than online methods. However, offline methods trade numerical accuracy for convenience because online methods require modifying a model's source code and re‐running it. We find offline estimates of numerical mixing should not be used because they may be inaccurate even at impractically high resolution. Key Points: We use offline salinity variance budgets to quantify numerical mixing due to the discretization of advection in a coastal ocean modelNumerical mixing estimated from s2 and s′2 ${s}^{{\prime }^{2}}$ budgets does not converge to the online method at high model output frequenciesOnline analysis indicates the volume‐integrated numerical mixing exceeds the physical mixing for a significant portion of the simulation [ABSTRACT FROM AUTHOR]

Bottom waters of the northeast Pacific continental shelf naturally experience localized hypoxic conditions, with significant influences on food webs and biogeochemical cycling. In August 2021, extreme hypoxia was detected from several measurement platforms along the southern British Columbia continental shelf, with oxygen concentration <60 μmol kg−1, and a difference from the seasonal climatology of more than 2 standard deviations. Early and intense remote upwelling and local density shifts were associated with an anomalously strong spring phytoplankton bloom, which likely stimulated localized respiration of subsurface organic matter. This event was concurrent with unsuitable habitat for Pacific halibut and calcite and aragonite undersaturation throughout most of the water column. The drivers of this extreme low oxygen event could be enhanced under future climate change, with potentially significant impacts on marine ecology and biogeochemistry. Plain Language Summary: Most marine organisms consume oxygen, and are therefore impacted when seawater oxygen concentrations reach low values. Extreme low oxygen concentrations are rare in the coastal waters of British Columbia, Canada. However, unusually strong oxygen depletion was observed off the coast of Vancouver Island during summer 2021. Unusually strong, early season upwelling winds along the California coast impacted Vancouver Island by causing nutrient‐rich water to be mixed into the surface, stimulating a large and earlier than usual spring phytoplankton bloom. Decomposition of the bloom‐derived organic carbon consumed local subsurface oxygen throughout the spring and summer. These subtle changes in timing and intensity of seasonal processes likely caused this low oxygen event, which was also associated with high concentrations of inorganic carbon, leading to ocean acidification. Such extreme low oxygen events, even if short‐lived, can have a significant impact on marine ecosystems, restricting the habitat available for groundfish species, such as Pacific halibut, and impacting the formation of carbonate shells by various organisms. The drivers of extreme low oxygen events are projected to intensify as climate change progresses. Key Points: Widespread extreme hypoxia was observed throughout the water column along the southern British Columbia continental shelf in summer 2021Early and intense upwelling followed by a strong biological response contributed to oxygen depletion in subsurface watersMultiple indices suggest that this extreme event was concurrent with unsuitable habitat conditions for groundfish and calcifying organisms [ABSTRACT FROM AUTHOR]

Historical and contemporary processes drive spatial patterns of genetic diversity. These include climate‐driven range shifts and gene flow mediated by biogeographical influences on dispersal. Assessments that integrate these drivers are uncommon, but critical for testing biogeographic hypotheses. Here, we characterize intraspecific genetic diversity and spatial structure across the entire distribution of a temperate seagrass to test marine biogeographic concepts for southern Australia. Predictive modeling was used to contrast the current Posidonia australis distribution to its historical distribution during the Last Glacial Maximum (LGM). Spatial genetic structure was estimated for 44 sampled meadows from across the geographical range of the species using nine microsatellite loci. Historical and contemporary distributions were similar, with the exception of the Bass Strait. Genetic clustering was consistent with the three currently recognized biogeographic provinces and largely consistent with the finer‐scale IMCRA bioregions. Discrepancies were found within the Flindersian province and southwest IMCRA bioregion, while two regions of admixture coincided with transitional IMCRA bioregions. Clonal diversity was highly variable but positively associated with latitude. Genetic differentiation among meadows was significantly associated with oceanographic distance. Our approach suggests how shared seascape drivers have influenced the capacity of P. australis to effectively track sea level changes associated with natural climate cycles over millennia, and in particular, the recolonization of meadows across the Continental Shelf following the LGM. Genetic structure associated with IMCRA bioregions reflects the presence of stable biogeographic barriers, such as oceanic upwellings. This study highlights the importance of biogeography to infer the role of historical drivers in shaping extant diversity and structure. [ABSTRACT FROM AUTHOR]

There are distinct bodies of cultural knowledge attached to the sea. In this paper we orient the focus towards the nature and extent of cultural framings of sea territories, as inclusive of submerged landscapes, for Indigenous maritime peoples in northern Australia. This approach is distinguished by a pluralist methodology and reorients the primal focus of a human geography and broader geographical scholarship concerning submerged landscapes to begin with an Indigenous perspective. Engaging ethnographic accounts of Indigenous Australian knowledges of Sea Country, as inclusive of ancient pre‐inundation landscapes that lie out‐of‐sight on Australia's continental shelves, highlights the potential for a more expansive vision of human connections to the past and present continental landmass of Australia. Indigenous oral traditions, Dreaming Ancestor narratives and songlines provide extensive detail to assist in understanding these parts of the greater Australian landmass and in this paper are brought into relation with recent sea floor mapping efforts which operate to draw back the water and reveal commensurable geographies upon which to envision possibilities for socialised realms of human emplacement. Both bodies of knowledge generate information of submerged landscapes that call for an expansion of thinking on where the land ends and the sea begins and how submerged terrestrial landscapes are understood across cultures as part of human geography. The approach outlined here calls for a habit of bringing principled systems of understanding to stand together as part of an explanatory schema for a world populated by and yet differentially known by people. [ABSTRACT FROM AUTHOR]

In the last 20 years, the southeastern Bering Sea has shifted its thermal variability to longer‐term (4–6 years) ocean–ecosystem temperature stanzas. Age‐0 walleye pollock (Gadus chalcogrammus) populations respond to thermal changes with horizontal (east–west) shifts in spatial distribution over the continental shelf, though there are limited data on whether thermally mediated vertical shifts in distribution also occur. Vertical shifts may impact predator–prey overlap between age‐0 pollock and their lipid‐rich prey, calanoid copepods and euphausiids, resulting in different feeding conditions that ultimately affect fish body condition prior to winter onset. For this study, we analyzed acoustic backscatter measured during acoustic trawl surveys over the southeastern Bering Sea shelf in cold years (2011, 2012) and warm years (2014 and 2016) to determine the vertical distribution of age‐0 pollock. This study presents evidence that age‐0 pollock changes in vertical distribution were related to changes in ocean annual temperature. Age‐0 pollock went from occurring deeper in the water column during cold periods to being surface‐oriented during warm periods, potentially exacerbating spatial mismatches between pollock and prey. We relate patterns in a vertical position to physical water column properties, feeding, and bioenergetic condition of collected pollock and discuss implications for recruitment success during different thermal oceanographic stanzas. [ABSTRACT FROM AUTHOR]