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Floating ice shelves fringing Antarctica are susceptible to melting from above, because the atmosphere is getting warmer, and from below, because the ocean is warm. Much of the evidence collected [...]

State‐of‐the‐art climate models simulate a large spread in the mean‐state Atlantic meridional overturning circulation (AMOC), with strengths varying between 12 and 25 Sv. Here, we introduce a framework for understanding this spread by assessing the balance between the thermal‐wind expression and surface water mass transformation in the North Atlantic. The intermodel spread in the mean‐state AMOC strength is shown to be related to the overturning scale depth: climate models with a larger scale depth tend to have a stronger AMOC. We present a physically motivated scaling relationship that links intermodel variations in the scale depth to surface buoyancy fluxes and stratification in the North Atlantic, and thus connects North Atlantic surface processes to the interior overturning circulation. Climate models with a larger scale depth tend to have stronger surface buoyancy loss and weaker stratification in the North Atlantic. These results offer a framework for reducing mean‐state AMOC biases in climate models. The Atlantic meridional overturning circulation—a branch of ocean currents confined to the Atlantic basin—strongly influences regional climate by redistributing heat, freshwater and carbon throughout the ocean. Understanding the processes that control the strength of this circulation feature, particularly in state‐of‐the‐art climate models, remains an active area of research. In this study, we introduce a conceptual framework to understand the processes that contribute to a large spread in the strength of the Atlantic meridional overturning circulation across climate models. We find climate models that exhibit a stronger circulation also have a deeper circulation. We introduce another expression to show that climate models with a deeper circulation also have stronger surface buoyancy loss and weaker stratification in the North Atlantic, which allows for more formation of dense waters that supply the southward flowing component of the Atlantic meridional overturning circulation. These results provide a framework for reducing biases in simulating the present‐day Atlantic meridional overturning circulation in climate models. The thermal‐wind expression captures the intermodel spread in mean‐state AMOC strength across climate modelsIntermodel variations in the AMOC strength are related to intermodel variations in the overturning scale depthModels with a stronger AMOC have a larger scale depth, and stronger surface buoyancy loss and weaker stratification in the North Atlantic The thermal‐wind expression captures the intermodel spread in mean‐state AMOC strength across climate models Intermodel variations in the AMOC strength are related to intermodel variations in the overturning scale depth Models with a stronger AMOC have a larger scale depth, and stronger surface buoyancy loss and weaker stratification in the North Atlantic

The West Antarctic Ice Sheet is experiencing rapid thinning of its floating ice shelves, largely attributed to oceanic basal melt. Numerical models suggest that the Bellingshausen Sea has a key role in setting water properties in the Amundsen Sea and further downstream. Yet, observations confirming these pathways of volume and tracer exchange between coast and shelf break and their impact on inter‐sea exchange remain sparse. Here we analyze the circulation and distribution of glacial meltwater at the boundary between the Bellingshausen Sea and the Amundsen Sea using a combination of glider observations from January 2020 and hydrographic data from instrumented seals. Meltwater distributions over previously unmapped western regions of the continental shelf and slope reveal two distinct meltwater cores with different optical backscatter properties. At Belgica Trough, a subsurface meltwater peak is linked with hydrographic properties from Venable Ice Shelf. West of Belgica Trough, the vertical structure of meltwater concentration changes, with peak values occurring at greater depths and denser isopycnals. Hydrographic analysis suggests that the western (deep) meltwater core is supplied from the eastern part of Abbot Ice Shelf, and is exported to the shelf break via a previously‐overlooked bathymetric trough (here named Seal Trough). Hydrographic sections constructed from seal data reveal that the Antarctic Coastal Current extends west past Belgica Trough, delivering meltwater to the Amundsen Sea. Each of these circulation elements has distinct dynamical implications for the evolution of ice shelves and water masses both locally and downstream, in the Amundsen Sea and beyond. Floating ice shelves in West Antarctica are thinning, which is largely due to melting of the ice shelf base by the ocean. Here, measurements of ocean temperature, salinity, and dissolved oxygen, collected by a remotely‐controlled underwater vehicle (a glider), are used to estimate the amount of ice shelf meltwater released in the Bellingshausen Sea. Distinct cores of meltwater can be distinguished by the amount of suspended material that is present in the water, which we attribute to meltwater following different circulation pathways after entering the ocean. Historical data from seals equipped with temperature and salinity sensors provide additional information about how the meltwater circulates in the region. The seal data show the presence of a narrow coastal current that brings meltwater from the Bellingshausen Sea into the Amundsen Sea. The pathways of meltwater revealed in this study suggest an important influence of the Bellingshausen Sea on ice shelves throughout West Antarctica. Hydrographic observations identify both shelf‐break and coastal meltwater pathways from the western Bellingshausen Sea into the Amundsen SeaDifferences in optical backscatter properties associated with meltwater are related to distinct coast‐to‐shelf break pathwaysThe main pathway to the shelf break is via Seal Trough, identified as the de factowestern boundary of the Bellingshausen Sea Hydrographic observations identify both shelf‐break and coastal meltwater pathways from the western Bellingshausen Sea into the Amundsen Sea Differences in optical backscatter properties associated with meltwater are related to distinct coast‐to‐shelf break pathways The main pathway to the shelf break is via Seal Trough, identified as the de factowestern boundary of the Bellingshausen Sea

Enceladus is believed to have a saltwater global ocean, heated at the ocean–core interface and losing heat to the floating ice shell above. This configuration suggests an important role for vertical convection. The ice shell has dramatic meridional thickness variations that, in steady state, must be sustained by the ocean circulation against processes acting to remove these anomalies. This could be achieved through spatially separated regions of freezing and melting at the ocean–ice interface. Here, we use an idealized, dynamical ocean model forced by an observationally guided density flux at the ocean–ice interface to argue that Enceladus’s interior ocean should support a meridional overturning circulation. This circulation establishes an interior density structure that is more complex than in studies that have focused only on vertical convection, including a shallow freshwater lens in the polar regions. Spatially separated sites of ice formation and melt enable Enceladus to sustain significant vertical and horizontal stratification, which influences interior heat transport and is critical for understanding the relationship between a global ocean and the planetary energy budget. On the basis of our model, the presence of low salinity layers near the polar ocean–ice interface implies the ocean’s bulk salinity could substantially exceed values inferred from Cassini plume samples.

Ocean heat exchanges at the marginal ice zone (MIZ) play an important role in melting sea ice. Mixed‐layer eddies transport heat and ice floes across the MIZ, facilitating the pack's access to warm waters. This study explores these frontal dynamics using disk‐shaped floes coupled to an upper‐ocean model simulating the sea ice edge. Numerical experiments reveal that small floes respond more strongly to fine‐scale ocean currents, which favors higher dispersion rates and weakens sea ice drag onto the underlying ocean. Floes with radii smaller than resolved turbulent filaments (∼2–4 km) result in a wider and more energetic MIZ, by a factor of 70% each, compared to larger floes. We hypothesize that this floe size dependency may affect sea ice break‐up by controlling oceanic energy propagation into the MIZ and modulate the sea ice pack's melt rate by regulating lateral heat transport toward the sea ice cover. Sea ice forms as a thin layer of frozen ocean waters, which breaks into individual floes due to the action of waves, ocean currents, and atmospheric winds. At the edge of the pack, these floes are vulnerable to warm waters in the open ocean, which can favor the melt of sea ice. The transport of heat from the open ocean into ice‐covered regions is not well represented in existing climate models, notably due to their poor spatial resolution and their inability to represent the dynamics of individual floes. In this study, we use a regional numerical model to investigate how fine‐scale ocean currents (2–30 km) can help transport heat toward a sea ice pack composed of broken‐up floes. We find that this heat transport is most efficient when floes are small, because they cannot efficiently damp the mechanical energy from the surface currents and they are easily transported into the open ocean by these currents. These two processes combined may lead to sea ice melt feedbacks that are currently not captured by coarser climate models. The sensitivity of sea ice dispersion and upper‐ocean energetics to floe size is considered at a mesoscale frontFloes smaller than turbulent filaments disperse more strongly and lead to a wider marginal ice zoneThese small floes allow for stronger eddy kinetic energy propagation and heat transport into the pack The sensitivity of sea ice dispersion and upper‐ocean energetics to floe size is considered at a mesoscale front Floes smaller than turbulent filaments disperse more strongly and lead to a wider marginal ice zone These small floes allow for stronger eddy kinetic energy propagation and heat transport into the pack

Oceanic macroturbulence is efficient at stirring and transporting tracers. The dynamical properties of this stirring can be characterized by statistically quantifying tracer structures. Here, we characterize the macroscale (1–100 km) tracer structures observed by two Seagliders downstream of the Southwest Indian Ridge in the Antarctic Circumpolar Current (ACC). These are some of the first glider observations in an energetic standing meander of the ACC, a region associated with enhanced ventilation. The small‐scale density variance in the mixed layer (ML) was relatively enhanced near the surface and base of the ML, while being muted at mid‐depth in the ML, suggesting the formation mechanism to be associated with ML instabilities and eddies. In addition, ML density fronts were formed by comparable contributions from temperature and salinity gradients. In the interior, along‐isopycnal spectra and structure functions of spice indicated that there is relatively lower variance at smaller scales than would be expected based on non‐local stirring, suggesting that flows smaller than the deformation radius play a role in the cascade of tracers to small scales. These interior spice anomalies spanned across isopycnals, and were found to be about 3–5 times flatter than the aspect ratio that would be expected for O(1) Burger number flows like interior QG dynamics, suggesting the ratio of vertical shear to horizontal strain is greater than N/f. This further supports that small‐scale flows, with high‐mode vertical structures, impact tracer distributions. Ocean eddies and fronts are efficient at stirring and generating tracer structures spanning a wide range of scales. This stirring is important for uptake of tracers, particularly in the Southern Ocean where sloping density surfaces provide a direct pathway from the surface into the interior. While the qualitative nature of stirring seems clear, quantitatively characterizing properties of this stirring is necessary to build accurate parameterizations and understand how the ocean is ventilated. One way to characterize this is by quantifying the distribution of the tracer concentration as a function of scale. Here, we do this characterization by analyzing data collected by two gliders in a region where the mean current of the Southern Ocean meanders as it flows over topography, and is likely to be a hot spot for ventilation. This analysis reveals that relatively small eddies generated by a process known as mixed layer instability are active in the mixed layer and play an important role in setting the near‐surface stratification. Surprisingly, tracer structure below the mixed layer also indicates that flows with small horizontal and vertical scales play a role in stirring. This challenges conventional wisdom, which assumes that only the largest eddies are important for stirring. Glider observations were used to analyze tracer structure at scales ≤100 km in the Antarctic Circumpolar CurrentThe vertical structure of density variance in the mixed layer (ML) is suggestive of ML instabilities and eddiesSmall‐scale flows contribute to stirring in the interior, as indicated by passive tracer structure Glider observations were used to analyze tracer structure at scales ≤100 km in the Antarctic Circumpolar Current The vertical structure of density variance in the mixed layer (ML) is suggestive of ML instabilities and eddies Small‐scale flows contribute to stirring in the interior, as indicated by passive tracer structure

The ocean is the largest solar energy collector on Earth. The amount of heat it can store is modulated by its complex circulation, which spans a broad range of spatial scales, from metres to thousands of kilometres. In the classical paradigm, fine oceanic scales, less than 20 km in size, are thought to drive a significant downward heat transport from the surface to the ocean interior, which increases oceanic heat uptake. Here we use a combination of satellite and in situ observations in the Antarctic Circumpolar Current to diagnose oceanic vertical heat transport. The results explicitly demonstrate how deep-reaching submesoscale fronts, with a size smaller than 20 km, are generated by mesoscale eddies of size 50–300 km. In contrast to the classical paradigm, these submesoscale fronts are shown to drive an anomalous upward heat transport from the ocean interior back to the surface that is larger than other contributions to vertical heat transport and of comparable magnitude to air–sea fluxes. This effect can remarkably alter the oceanic heat uptake and will be strongest in eddy-rich regions, such as the Antarctic Circumpolar Current, the Kuroshio Extension and the Gulf Stream, all of which are key players in the climate system.

The ocean transports vast amounts of heat around the planet, helping to regulate regional climate. One important component of this heat transport is the movement of warm water from equatorial regions toward the poles, with colder water flowing in return. Here, we introduce a framework relating meridional heat transport to the diabatic processes of surface forcing and turbulent mixing that move heat across temperature classes. Applied to a (1/4)° global ocean model the framework highlights the role of the tropical Indo‐Pacific in the global ocean heat transport. A large fraction of the northward heat transport in the Atlantic is ultimately sourced from heat uptake in the eastern tropical Pacific. Turbulent mixing moves heat from the warm, shallow Indo‐Pacific circulation to the cold deeper‐reaching Atlantic circulation. Our results underscore a renewed focus on the tropical oceans and their role in global circulation pathways. Heat budget analysis reveals links between meridional and diathermal ocean heat transportsLarge fraction of Atlantic northward heat transport is sourced from eastern tropical Pacific heat uptakeTurbulent mixing transfers heat from warm shallow Indo‐Pacific circulation to cold deep‐reaching Atlantic circulation

Estimates of the kinetic energy transfer from the wind to the ocean are often limited by the spatial and temporal resolution of surface currents and surface winds. Here we examine the wind work in a pair of global, very high‐resolution (1/48° and 1/24°) MIT general circulation model simulations in Latitude‐Longitude‐polar Cap (LLC) configuration that provide hourly output at spatial resolutions of a few kilometers and include tidal forcing. A cospectrum analysis of wind stress and ocean surface currents shows positive contribution at large scales (>300 km) and near‐inertial frequency and negative contribution from mesoscales, tidal frequencies, and internal gravity waves. Larger surface kinetic energy fluxes are in the Kuroshio in winter at large scales (40 mW/m2) and mesoscales (−30 mW/m2). The Kerguelen region is dominated by large scale (∼20 mW/m2), followed by inertial oscillations in summer (13 mW/m2) and mesoscale in winter (−12 mW/m2). Kinetic energy fluxes from internal gravity waves (−0.1 to −9.9 mW/m2) are generally stronger in summer. Surface kinetic energy fluxes in the LLC simulations are 4.71 TW, which is 25–85% higher than previous global estimates from coarser (1/6–1/10°) general ocean circulation models; this is likely due to improved representation of wind variability (6‐hourly, 0.14°, operational European Center for Medium‐Range Weather Forecasts). However, the low wind power input to the near‐inertial frequency band obtained with LLC (0.16 TW) compared to global slab models suggests that wind variability on time scales less than 6 hr and spatial scales less than 15 km are critical to better representing the wind power input in ocean circulation models. Surface kinetic energy fluxes from LLC simulations lead to 4.71 TW, this is 25–85% higher than previous global estimatesThere is positive contribution to wind power input (WPI) at large scale and near‐inertial (NI) band, and negative WPI at mesoscale, tidal frequencies and IGWsLow WPI at NI band (0.16 TW) suggests that wind variability on scales <6 hr and <15 km are critical to better representing WPI in GCMs

High‐latitude Northern Hemisphere climate during the last glacial period was characterized by a series of abrupt climate changes, known as Dansgaard‐Oeschger events, which were recorded in Greenland ice cores as shifts in the oxygen isotopic composition of the ice. These shifts in inferred Northern Hemisphere high‐latitude temperature have been linked to changes in Atlantic meridional overturning strength. The response of ocean overturning circulation to forcing is nonlinear and a hierarchy of models have suggested that it may exist in multiple steady state configurations. Here, we use a time‐dependent coarse‐resolution isopycnal model with four density classes and two basins, linked by a Southern Ocean to explore overturning states and their stability to changes in external parameters. The model exhibits hysteresis in both the steady state stratification and overturning strength as a function of the magnitude of North Atlantic Deep Water formation. Hysteresis occurs as a result of two nonlinearities in the model—the surface buoyancy distribution in the Southern Ocean and the vertical diffusivity profile in the Atlantic and Indo‐Pacific basins. We construct a metric to assess circulation configuration in the model, motivated by observations from the Last Glacial Maximum, which show a different circulation structure from the modern. We find that circulation configuration is primarily determined by North Atlantic Deep Water density. The model results are used to suggest how ocean conditions may have influenced the pattern of Dansgaard‐Oeschger events across the last glacial cycle. Southern Ocean buoyancy forcing and vertical diffusivity distribution may give rise to hysteresis in the overturning circulationHysteresis curves are sensitive to NADW density and Southern Ocean sea ice extentCirculation configuration (“figure‐eight” versus “two‐cell”) is primarily sensitive to NADW density

The Antarctic Slope Current (ASC) is a coherent circulation feature that rings the Antarctic continental shelf and regulates the flow of water toward the Antarctic coastline. The structure and variability of the ASC influences key processes near the Antarctic coastline that have global implications, such as the melting of Antarctic ice shelves and water mass formation that determines the strength of the global overturning circulation. Recent theoretical, modeling, and observational advances have revealed new dynamical properties of the ASC, making it timely to review. Earlier reviews of the ASC focused largely on local classifications of water properties of the ASC's primary front. Here we instead provide a classification of the current's frontal structure based on the dynamical mechanisms that govern both the along‐slope and cross‐slope circulation; these two modes of circulation are strongly coupled, similar to the Antarctic Circumpolar Current. Highly variable motions, such as dense overflows, tides, and eddies are shown to be critical components of cross‐slope and cross‐shelf exchange, but understanding of how the distribution and intensity of these processes will evolve in a changing climate remains poor due to observational and modeling limitations. Results linking the ASC to larger modes of climate variability, such as El Niño, show that the ASC is an integral part of global climate. An improved dynamical understanding of the ASC is still needed to accurately model and predict future Antarctic sea ice extent, the stability of the Antarctic ice sheets, and the Southern Ocean's contribution to the global carbon cycle. The continent of Antarctica is surrounded by the Southern Ocean, which transports heat poleward toward the Antarctic margins while also influencing atmospheric wind and sea ice patterns. At the very southern boundary of the Southern Ocean, a narrow westward flowing circulation feature, known as the Antarctic Slope Current (ASC), forms where the Antarctic continental slope meets the continental shelf. Here relatively warm waters—a few degrees above the freezing temperature— rise up toward the continental shelf. Despite this circumpolar delivery of heat toward Antarctica, the ability of this warm water to cross the ASC and to access the continental shelf varies greatly due to this current's dynamical properties. In some regions, the ASC forms a strong barrier to heat transport, and shelf waters remain cold and fresh. Elsewhere, the ASC provides a much weaker barrier, and warm water floods the shelf including under floating ice shelves, which can lead to enhanced ice shelf melt rates and ultimately to the destabilization of Antarctica's ice sheets. This review provides a summary of recent observational, modeling, and theoretical efforts to describe the structure and variability of the ASC, and offers insight into how future changes in the ASC may impact global climate. Dynamical properties of the Antarctic Slope Current (ASC) that impact heat transport are reviewedA geographical classification of the ASC's frontal structure is presentedThe potential for feedbacks between the ASC circulation and larger‐scale climate is summarized

Surface ocean temperature and velocity anomalies at meso‐ and sub‐meso‐scales induce wind stress anomalies. These wind‐front interactions, referred to as thermal (TFB) and current (CFB) feedbacks, respectively, have been studied in isolation at mesoscale, yet they have rarely been considered in tandem. Here, we assess the combined influence of TFB and CFB and their relative impact on surface wind stress derivatives. Analyses are based on output from two regions of the Southern Ocean in a coupled simulation with local ocean resolution of 2 km. Considering both TFB and CFB shows regimes of interference, which remain mostly linear down to the simulation resolution. The jointly‐generated wind stress curl anomalies approach 10−5N m−3, ∼20 times stronger than at mesoscale. The synergy of both feedbacks improves the ability to reconstruct wind stress curl magnitude and structure from both surface vorticity and SST gradients by 12%–37% on average, compared with using either feedback alone. Surface ocean temperature and velocity anomalies at 0.1–100 km scales imprint their signatures on the surface wind stress, which in turn supplies the ocean with momentum. This process is called wind‐front interaction and typically referred to as thermal and current feedbacks when generated by temperature gradients and velocity gradients, respectively. Previously, studies using satellite observations and regional numerical models have studied either feedback in isolation; consideration of both feedbacks in tandem remains immature. Here, we present an approach that assesses both feedbacks' combined and relative impact on the surface wind stress, using output from an air‐sea coupled simulation. This approach allows us to identify constructive and destructive patterns of how the two feedbacks interact, which remain mostly linear down to the simulation resolution. The jointly‐generated wind stress derivative anomalies are 20 times stronger than observed previously at larger scales. Considering both feedbacks, reconstructions of wind stress derivatives are viable and have 10%–40% less error on average compared with using either feedback by itself. Contributions from either feedback in modifying wind stress fields vary temporally and can be related to physical properties such as surface wind speed and air‐sea temperature difference across the studied area. Surface temperature gradients and vorticity anomalies at scales down to O(10) km impact wind stress curl and divergence jointlyWind‐front interactions at sub‐mesoscales are at least an order of magnitude stronger than at mesoscalesReconstruction of the wind stress curl using both thermal and current feedback is 10%–40% more accurate than relying on a single feedback Surface temperature gradients and vorticity anomalies at scales down to O(10) km impact wind stress curl and divergence jointly Wind‐front interactions at sub‐mesoscales are at least an order of magnitude stronger than at mesoscales Reconstruction of the wind stress curl using both thermal and current feedback is 10%–40% more accurate than relying on a single feedback

Melt rates of West Antarctic ice shelves in the Amundsen Sea track large decadal variations in the volume of warm water at their outlets. This variability is generally attributed to wind‐driven variations in warm water transport toward ice shelves. Inspired by conceptual representations of the global overturning circulation, we introduce a simple model for the evolution of the thermocline, which caps the warm water layer at the ice‐shelf front. This model demonstrates that interannual variations in coastal polynya buoyancy forcing can generate large decadal‐scale thermocline depth variations, even when the supply of warm water from the shelf‐break is fixed. The modeled variability involves transitions between bistable high and low melt regimes, enabled by feedbacks between basal melt rates and ice front stratification strength. Our simple model captures observed variations in near‐coast thermocline depth and stratification strength, and poses an alternative mechanism for warm water volume changes to wind‐driven theories. Ice loss from the West Antarctic Ice Sheet contributes significantly to current and projected rates of global sea‐level rise. The ice sheet is primarily losing mass via glaciers that flow from the Antarctic continent into the Amundsen Sea, where floating ice shelves are exposed to much warmer ocean waters than elsewhere around Antarctica. In this work we present a simplified mathematical model for the volume of warm water at Amundsen Sea ice shelf fronts that reproduces observed patterns of warm water variability. The modeled variability relies on interactions between ice shelf melt and coastal polynyas, regions where enhanced wintertime sea‐ice production can trigger mixing that diverts heat carried by warm waters away from the ice shelf and into the atmosphere. Higher melt rates inhibit polynya convection, allowing more warm water into the ice shelf cavity and reinforcing a high melt state, whilst lower melt rates facilitate polynya convection, diverting heat away from the ice shelf and reinforcing a low melt state. Interannual variations in polynya sea‐ice production trigger shifts between these reinforcing states. Our results promote the importance of coastal processes in explaining observed variations in Amundsen Sea ice shelf melt, which have previously been attributed to remote wind patterns. Rates of ocean‐driven Amundsen Sea ice shelf melt respond to variations in warm water transport to the coast and modification at the coastA simple Amundsen Sea continental shelf overturning model, based on water mass transformation, reveals bistable high and low melt regimesFeedbacks between glacial melt and polynya convection are central to the bistability and produce variability consistent with observations Rates of ocean‐driven Amundsen Sea ice shelf melt respond to variations in warm water transport to the coast and modification at the coast A simple Amundsen Sea continental shelf overturning model, based on water mass transformation, reveals bistable high and low melt regimes Feedbacks between glacial melt and polynya convection are central to the bistability and produce variability consistent with observations

Mesoscale eddies are a dominant source of spatial variability in the surface ocean and play a major role in the biological marine carbon cycle. Satellite altimetry is often used to locate and track eddies, but this approach is rarely validated against in situ observations. Here we compare measurements of a small (under 25 km radius) mode water anticyclonic eddy over the Porcupine Abyssal Plain in the northeastern Atlantic Ocean using CTD and Acoustic Doppler Current Profiler (ADCP) measurements from three ships, two gliders, two profiling floats, and one Lagrangian float with those derived from sea level anomaly (SLA). In situ estimates of the eddy center were estimated from maps of the thickness of its central isopycnal layer, from ADCP velocities at a reference depth, and from the trajectory of the Lagrangian float. These were compared to three methods using altimetric SLA: one based on maximizing geostrophic rotation, one based on a constant SLA contour, and one which maximizes geostrophic velocity speed along the eddy boundary. All algorithms were used to select CTD profiles that were within the eddy. The in‐situ metrics agreed to 97%. The altimetry metrics showed only a small loss of accuracy, giving >90% agreement with the in situ results. This suggests that current satellite altimetry is adequate for understanding the spatial representation of even relatively small mesoscale eddies. Rotating water masses called eddies are ubiquitous features in the ocean and are important because they can transport nutrients and heat and are often associated with enhanced biological activity. Eddies are accompanied by sea level anomalies (SLA), in the same way that atmospheric weather systems are associated with high or low pressure systems, and can therefore be observed and monitored by satellite altimeters. However, observations of SLA from satellite are relatively coarse compared with the spatial scales of eddies, and satellite‐based algorithms are rarely rigorously tested against “ground truth” observations. We use data from a dense network of observations in the vicinity of a relatively small eddy in the northeastern Atlantic Ocean to track this eddy for several weeks from direct ocean measurements and satellite algorithms. We find widespread agreement between the in situ metrics and the satellite altimetry results, suggesting that satellite‐based eddy tracking is sufficient to track even eddies that are relatively small compared with the resolution of SLA products. Ship‐based, autonomous, and remote sensing observations were combined to identify, characterize, and track a coherent anticyclonic eddyEstimates of the eddy center and spatial extent derived from altimetry and in situ observations had similar accuracyConstant or smoothly varying sea level anomaly thresholds better represent eddy spatial extent than other satellite‐based methods Ship‐based, autonomous, and remote sensing observations were combined to identify, characterize, and track a coherent anticyclonic eddy Estimates of the eddy center and spatial extent derived from altimetry and in situ observations had similar accuracy Constant or smoothly varying sea level anomaly thresholds better represent eddy spatial extent than other satellite‐based methods

Meltwater content and pathways determine the impact of Antarctica's melting ice shelves on ocean circulation and climate. Using ocean glider observations, we quantify meltwater distribution and transport within the Bellingshausen Sea's Belgica Trough. Meltwater is present at different densities and with different turbidities: both are indicative of a layer's ice shelf of origin. To investigate how ice‐shelf origin separates meltwater into different export pathways, we compare these observations with high‐resolution tracer‐release model simulations. Meltwater filaments branch off the Antarctic Coastal Current into the southwestern trough. Meltwater also enters the Belgica Trough in the northwest via an extended western pathway, hence the greater observed southward (0.50 mSv) than northward (0.17 mSv) meltwater transport. Together, the observations and simulations reveal meltwater retention within a cyclonic in‐trough gyre, which has the potential to promote climactically important feedbacks on circulation and future melting. Recent research has advanced our understanding of interactions between warm ocean waters and the underside of Antarctica's floating ice shelves. But what happens to meltwater that these ice shelves release? Meltwater is fresh: it reduces the salinity of sea water and upsets the delicate balance between salty and fresh water that drives many polar ocean processes ‐ for example, the sinking of cold, salty water to the deepest regions of the ocean, which is of global climatic importance. We use high‐resolution observations and state‐of‐the‐art model simulations to determine the pathways that meltwater takes as it flows in and around the Belgica Trough in the central Bellingshausen Sea, Antarctica. Meltwater is principally confined to the edges of the trough's clockwise gyre circulation. Meltwater from eastern ice shelves is generally found at shallower depths than meltwater from southern ice shelves; this explains evidence of two meltwater layers found in our observations. In addition, meltwater from eastern ice shelves is turbid, while meltwater from southern ice shelves is clear. These results will help us to better predict how Antarctica's coastal seas will respond to a warming climate as ever more meltwater is released into the ocean. Meltwater pathways in the Bellingshausen Sea, Antarctica, are explored using observations from gliders and a high‐resolution regional modelMeltwater observed at different densities originates from different ice shelves: lighter meltwater layers originate from eastern ice shelvesMeltwater from different ice shelves is distinguished by different turbidity signatures, suggestive of different biogeochemical properties Meltwater pathways in the Bellingshausen Sea, Antarctica, are explored using observations from gliders and a high‐resolution regional model Meltwater observed at different densities originates from different ice shelves: lighter meltwater layers originate from eastern ice shelves Meltwater from different ice shelves is distinguished by different turbidity signatures, suggestive of different biogeochemical properties

Submesoscale dynamics O(1–100 km) are associated with enhanced vertical velocities and evolve on a time scale similar to that of biological production (hours to days). Here we consider an annual cycle of submesoscale dynamics and their relation to productivity and export in a small (20 × 20 km) region of the northeast Atlantic Ocean. In this region, a springtime bloom is initiated by restratification of the mixed layer in June, although intermittent shoaling of the mixed layer maintains phytoplankton populations throughout the year. An optical community index suggests a dominance of large species (e.g., diatoms) during spring and picophytoplankton during the winter. We review three types of submesoscale instabilities—mixed layer (baroclinic), gravitational, and symmetric—and consider the impact of each on export of fixed carbon out of the surface layer. Mixed layer instabilities can potentially export material out of the mixed layer during winter, although the vertical velocity across the base of the mixed layer is sensitive to the parameterization scheme. Symmetric instabilities, in contrast, provide a clear mechanism for rapid export out of the mixed layer. A crucial factor determining export potential is the strength of the pycnocline at the base of the mixed layer. Export production is sensitive to the degree of overlap that exists between intense submesoscale activity associated with deep mixed layers in the winter and high productivity associated with the spring restratification, meaning that physically driven export of fixed carbon will likely happen over a short time window during spring. Seaglider measurements captured a full annual cycle of physical and optical data at submesoscale resolutionStratification at the base of the mixed layer plays a critical role in controlling export from submesoscale motionsTemporal offset between peak productivity and submesoscale activity limits physical carbon export in this location

This study combines sea surface height (SSH) estimates of the ice‐covered Southern Ocean with conventional open‐ocean SSH estimates from CryoSat‐2 to produce monthly composites of dynamic ocean topography (DOT) and sea level anomaly (SLA) on a 50 km grid spanning 2011–2016. This data set reveals the full Southern Ocean SSH seasonal cycle for the first time; there is an antiphase relationship between sea level on the Antarctic continental shelf and the deeper basins, with coastal SSH highest in autumn and lowest in spring. As a result of this pattern of seasonal SSH variability, the barotropic component of the Antarctic Slope Current (ASC) has speeds that are regionally up to twice as fast in the autumn. Month‐to‐month circulation variability of the Ross and Weddell Gyres is strongly influenced by the local wind field, and is correlated with the local wind curl (Ross: −0.58; Weddell: −0.67). SSH variability is linked to both the Southern Oscillation and the Southern Annular Mode, dominant modes of southern hemisphere climate variability. In particular, during the strong 2015–2016 El Niño, a sustained negative coastal SLA of up to −6 cm, implying a weakening of the ASC, was observed in the Pacific sector of the Southern Ocean. The ability to examine sea level variability in the seasonally ice‐covered regions of the Southern Ocean—climatically important regions with an acute sparsity of data—makes this new merged sea level record of particular interest to the Southern Ocean oceanography and glaciology communities. New monthly merged sea level record of the ice‐covered and ice‐free Southern Ocean between 2011 and 2016, from CryoSat‐2 radar altimetryAntarctic coastal sea level peaks in autumn, minimum in spring; Antarctic Slope Current speeds regionally up to twice as fast in autumnSouthern Oscillation and Southern Annular Mode drive significant Antarctic coastal sea level response, modulating the ASC strength

Signatures of ocean eddies, fronts, and filaments are commonly observed within marginal ice zones (MIZs) from satellite images of sea ice concentration, and in situ observations via ice‐tethered profilers or underice gliders. However, localized and intermittent sea ice heating and advection by ocean eddies are currently not accounted for in climate models and may contribute to their biases and errors in sea ice forecasts. Here, we explore mechanical sea ice interactions with underlying submesoscale ocean turbulence. We demonstrate that the release of potential energy stored in meltwater fronts can lead to energetic submesoscale motions along MIZs with spatial scales O(10 km) and Rossby numbers O(1). In low‐wind conditions, cyclonic eddies and filaments efficiently trap the sea ice and advect it over warmer surface ocean waters where it can effectively melt. The horizontal eddy diffusivity of sea ice mass and heat across the MIZ can reach O(200 m2s−1). Submesoscale ocean variability also induces large vertical velocities (order 10 m d−1) that can bring relatively warm subsurface waters into the mixed layer. The ocean‐sea ice heat fluxes are localized over cyclonic eddies and filaments reaching about 100 W m−2. We speculate that these submesoscale‐driven intermittent fluxes of heat and sea ice can contribute to the seasonal evolution of MIZs. With the continuing global warming and sea ice thickness reduction in the Arctic Ocean, submesoscale sea ice‐ocean processes are expected to become increasingly prominent. Energetic submesoscale ocean variability forms at marginal ice zones due to mixed‐layer instabilities of ice‐edge meltwater frontsMechanical sea ice‐ocean interactions trap sea ice in cyclonic eddies and filaments—regions with dramatically enhanced ocean heat fluxesThe strength of submesoscale sea ice‐ocean coupling is expected to increase with thinning of Arctic sea ice and marginal ice zone expansion

The ocean’s global overturning circulation regulates the transport and storage of heat, carbon and nutrients. Upwelling across the Southern Ocean’s Antarctic Circumpolar Current and into the mixed layer, coupled to water mass modification by surface buoyancy forcing, has been highlighted as a key process in the closure of the overturning circulation. Here, using twelve high-resolution hydrographic sections in southern Drake Passage, collected with autonomous ocean gliders, we show that Circumpolar Deep Water originating from the North Atlantic, known as Lower Circumpolar Deep Water, intersects sloping topography in narrow and strong boundary currents. Observations of strong lateral buoyancy gradients, enhanced bottom turbulence, thick bottom mixed layers and modified water masses are consistent with growing evidence that topographically generated submesoscale flows over continental slopes enhance near-bottom mixing, and that cross-density upwelling occurs preferentially over sloping topography. Interactions between narrow frontal currents and topography occur elsewhere along the path of the Antarctic Circumpolar Current, which leads us to propose that such interactions contribute significantly to the closure of the overturning in the Southern Ocean.

We investigate statistical properties of surface currents as well as coherent mesoscale eddies in the seasonally ice‐covered Southern Ocean. Based on a recent regional Sea Level Anomaly satellite altimetry data set, we compute Eddy Kinetic Energy (EKE) and detect mesoscale eddies. EKE is about one order of magnitude higher in the northern sector of the subpolar basin and over the continental slope, as compared to the middle of the subpolar gyres. An eddy detection methodology reveals that eddies are distributed evenly in the subpolar Southern Ocean, and their amplitude follows the spatial pattern of EKE. In addition to regional circulation variations, sea ice concentration arises as an important driver of eddy properties. Eddies have low amplitude and density in the pack ice, in particular in the middle of the gyres where the background circulation is unfavorable for instabilities. In contrast, the northern part of the Marginal Ice Zone is favorable for mesoscale eddies, especially cyclonic. There, eddies are stronger and their density is higher than in any other region of the ice‐covered or ice‐free subpolar Southern Ocean. This region is expected to be a site of frontogenesis due to sea ice melt and upwelling generated from interactions between the wind and the sea ice. While many mesoscale eddies will fall below detection level due to the small Rossby radius at high latitudes, these results contribute to understanding the interactions between mesoscale eddies, sea ice, and the background circulation in the subpolar region. Ocean eddies are spatially coherent vortices, ubiquitous in the global oceans, and are central structures contributing to shaping the global ocean circulation. In the Southern Ocean, they have been shown to play a potentially important role in the cross‐front transport of heat and nutrients at mid and high latitudes. Recent improvements in satellite altimetry capabilities in the ice‐covered regions allow for a first description of mesoscale eddies in the ice‐covered Southern Ocean, and the investigation of their interactions with sea ice. The location of the detected eddies is consistent with the main large‐scale circulation features. In addition to the background circulation, the sea ice cover has a strong impact on the size of eddies. While weaker eddies are found in the highly concentrated sea ice areas, the marginal ice zone seems to be a region with enhanced eddy activity, with more and stronger eddies detected. A new satellite altimetry data set allows the detection of mesoscale eddies in the ice‐covered Southern OceanEddy generation and strength are primarily impacted by sea ice concentration and the background circulationWhile the eddy strength is damped under high sea‐ice concentration, the northern edge of the sea‐ice region is a hotspot of large eddies A new satellite altimetry data set allows the detection of mesoscale eddies in the ice‐covered Southern Ocean Eddy generation and strength are primarily impacted by sea ice concentration and the background circulation While the eddy strength is damped under high sea‐ice concentration, the northern edge of the sea‐ice region is a hotspot of large eddies

A high‐resolution satellite image that reveals a train of coherent, submesoscale (6 km) vortices along the edge of an ocean front is examined in concert with hydrographic measurements in an effort to understand formation mechanisms of the submesoscale eddies. The infrared satellite image consists of ocean surface temperatures at ∼390m resolution over the midlatitude North Atlantic (48.69°N, 16.19°W). Concomitant altimetric observations coupled with regular spacing of the eddies suggest the eddies result from mesoscale stirring, filamentation, and subsequent frontal instability. While horizontal shear or barotropic instability (BTI) is one mechanism for generating such eddies (Munk's hypothesis), we conclude from linear theory coupled with the in situ data that mixed layer or submesoscale baroclinic instability (BCI) is a more plausible explanation for the observed submesoscale vortices. Here we assume that the frontal disturbance remains in its linear growth stage and is accurately described by linear dynamics. This result likely has greater applicability to the open ocean, i.e., regions where the gradient Rossby number is reduced relative to its value along coasts and within strong current systems. Given that such waters comprise an appreciable percentage of the ocean surface and that energy and buoyancy fluxes differ under BTI and BCI, this result has wider implications for open‐ocean energy/buoyancy budgets and parameterizations within ocean general circulation models. In summary, this work provides rare observational evidence of submesoscale eddy generation by BCI in the open ocean. Here, we test Munk's theory for small‐scale eddy generation using a unique set of satellite‐ and ship‐based observations. We find that for one particular set of observations in the North Atlantic, the mechanism for eddy generation is not pure horizontal shear, as proposed by Munk et al. ([Munk, W., 2000]) and Munk ([Munk, W., 2001]), but is instead vertical shear, or baroclinic instability. While by itself, this is not a globally important result, taken in the context of mesoscale eddies which are ubiquitous in the World Ocean, this suggests energy exchanges in the more ambient, open ocean are the result of the latter mechanism. In conclusion, submesoscale eddy generation is poorly understood in the ocean and we need to better constrain our geographical and temporal understanding of these processes for representation in coarse‐resolution models. A high‐resolution satellite image reveals an ocean front populated by submesoscale vorticesLinear theory applied to coincident hydrography suggests vortices result not from barotropic but baroclinic instabilityThis study documents rare observational evidence of submesoscale baroclinic instability in the open ocean

Jupiter's moon Europa likely hosts a saltwater ocean beneath its icy surface. Geothermal heating and rotating convection in the ocean may drive a global overturning circulation that redistributes heat vertically and meridionally, preferentially warming the ice shell at the equator. Here we assess the previously unconstrained influence of ocean‐ice coupling on Europa's ocean stratification and heat transport. We demonstrate that a relatively fresh layer can form at the ice‐ocean interface due to a meridional ice transport forced by the differential ice shell heating between the equator and the poles. We provide analytical and numerical solutions for the layer's characteristics, highlighting their sensitivity to critical ocean parameters. For a weakly turbulent and highly saline ocean, a strong buoyancy gradient at the base of the freshwater layer can suppress vertical tracer exchange with the deeper ocean. As a result, the freshwater layer permits relatively warm deep ocean temperatures. Coupling of Europa's ocean circulation and the ice shell impacts global stratificationA low‐latitude freshwater layer may suppress vertical heat and tracer transportParameter space is explored based on properties observed by future missions

Drake Passage is a key region for transport between the surface and interior ocean, but a mechanistic understanding of this exchange remains immature. Here, we present wintertime, submesoscale‐resolving hydrographic transects spanning the southern boundary of the Antarctic Circumpolar Current and the Polar Front (PF). Despite the strong surface wind and buoyancy forcing, a freshwater lens suppresses surface‐interior exchange south of the PF; ventilation is instead localized to the PF. Multiple lines of the analysis suggest submesoscale processes contribute to ventilation at the PF, including small‐scale, O(10 km), frontal structure in water mass properties below the mixed layer and modulation of a surface eddy diffusivity at sub‐50 km scales. These results show that ventilation is sensitive to both submesoscale properties near fronts and non‐local processes, for example, sea‐ice melt, that set stratification and mixed layer properties. This highlights the need for adaptive observing strategies to constrain Southern Ocean heat and carbon budgets. Drake Passage is a region of the Southern Ocean between the southern tip of South America and the Antarctic Peninsula. Due to its relative accessibility as compared to the rest of the polar ocean, it is the most frequently occupied region of the Southern Ocean. Most occupations by ships in Drake Passage acquire measurements at 20–100 km spacing or “mesoscale” resolution. Here, we present data collected by piloted robotic underwater vehicles that sampled across the southern section of Drake Passage with submesoscale, or 1–10 km, resolution in wintertime. These novel observations indicate that while the southernmost region of Drake Passage is strongly stratified in density, the Polar Front (PF), one of the major dynamical features of the Southern Ocean, is more weakly stratified. The reduced stratification at the PF presents a pathway for the localized exchange of water between the surface and interior ocean. In addition, this study finds that the PF is eddy‐suppressing, meaning that the mean flow of the PF can transport oceanic properties away before they can be stirred. These findings have implications for the estimation of carbon fluxes between the atmosphere and the Southern Ocean, a vital part of the climate system. High‐resolution hydrographic sections across the Drake Passage provide insight into spatial variability in surface‐interior exchangeWintertime observations suggest ventilation is spatially localized to the Polar Front and influenced by submesoscale processesA mixing length estimate shows modulation at submesoscales and mixing suppression in the upper layers of the Polar Front High‐resolution hydrographic sections across the Drake Passage provide insight into spatial variability in surface‐interior exchange Wintertime observations suggest ventilation is spatially localized to the Polar Front and influenced by submesoscale processes A mixing length estimate shows modulation at submesoscales and mixing suppression in the upper layers of the Polar Front

The Bellingshausen Sea hosts heat transport onto the continental shelf, potentially enhancing ice shelf basal melt. Here, we use the GLORYS12V1 1993–2018 reanalysis to identify physical processes that set seasonal and interannual variability of water mass properties in the Eltanin and Latady Bays on the southern Bellingshausen Sea continental shelf. Annual means of potential temperature from 300 m to the seabed reveal interannual variability and allow separation into warm and cold regimes. The Amundsen Sea Low (ASL) is more intense and extends further east during the warm regime than the cold regime. In the warm regime, a wind‐induced reduction of sea ice concentration near the coast increases surface heat loss, convection, and formation of cold dense water in winter, associated with a decrease in heat content of the southern Bellingshausen Sea over time and a net northward heat transport. In contrast, in the cold regime, increased sea ice concentration reduces surface heat loss and thus formation of cold, dense water. Combined with an increase in heat content over time and a net southward heat transport, this results in a warming of the southern Bellingshausen Sea. This suggests that variability in the deep water temperature in the southern Bellingshausen Sea is primarily due to local surface heat fluxes above the shelf. The variability of surface heat fluxes is related to the variability of the ASL and its influence on sea ice extent and local formation of cold, dense water in winter. The stability of the West Antarctic Ice Sheet is a key factor in uncertainty in global sea level predictions on decadal to centennial time scales. Today, melt of West Antarctic ice shelves is dominated by relatively warm (above freezing) ocean waters, and the warmest waters around Antarctica are found in the Bellingshausen Sea. There is a lack of long‐term observations in this inaccessible region so we use a model product to investigate variability of deep water temperatures, identifying warm and cold years. We find a link between sea ice concentration, heat loss to the atmosphere and cold water formation and the wind fields associated with a weather system, the Amundsen Sea Low (ASL). Winds in the southern Bellingshausen Sea are stronger in warm years than in cold years and blow the ice away from the coast more rapidly, allowing more heat loss to the atmosphere, cooling the ocean in winter. Conversely, in cold years increased sea ice cover reduces heat loss to the atmosphere, less cold water is formed, and there is increased southward transport of warm water. We highlight the importance of the ASL's location and intensity for cold water formation and its impacts on temperature. Intensity and location of Amundsen Sea Low (ASL) affect ocean properties of southern Bellingshausen Sea continental shelf in 26‐year reanalysisThe ASL modifies the surface heat flux, warming Bellingshausen Sea shelf when it shifts westward and weakens, and vice versaThe southern Bellingshausen Sea temperature depends more on surface heat fluxes above the continental shelf than southward heat transport Intensity and location of Amundsen Sea Low (ASL) affect ocean properties of southern Bellingshausen Sea continental shelf in 26‐year reanalysis The ASL modifies the surface heat flux, warming Bellingshausen Sea shelf when it shifts westward and weakens, and vice versa The southern Bellingshausen Sea temperature depends more on surface heat fluxes above the continental shelf than southward heat transport

The spatial and temporal variability of upwelling into the mixed layer in the Southern Ocean is studied using a 1/10 °ocean general circulation model. Virtual drifters are released in a regularly spaced pattern across the Southern Ocean at depths of 250, 500, and 1000 m during both summer and winter months. The drifters are advected along isopycnals for a period of 4 years, unless they outcrop into the mixed layer, where lateral advection and a parameterization of vertical mixing are applied. The focus of this study is on the discrete exchange between the model mixed layer and the interior. Localization of interior‐mixed layer exchange occurs downstream of major topographic features across the Indian and Pacific basins, creating “hotspots” of outcropping. Minimal outcropping occurs in the Atlantic basin, while 59% of drifters outcrop in the Pacific sector and in Drake Passage (the region from 140 °W to 40 °W), a disproportionately large amount even when considering the relative basin sizes. Due to spatial and temporal variations in mixed layer depth, the Lagrangian trajectories provide a statistical measure of mixed layer residence times. For each exchange into the mixed layer, the residence time has a Rayleigh distribution with a mean of 30 days; the cumulative residence time of the drifters is 261 ± 194 days, over a period of 4 years. These results suggest that certain oceanic gas concentrations, such as CO2and 14C, will likely not reach equilibrium with the atmosphere before being resubducted. Spatial and temporal variability of Southern Ocean upwelling is studied using virtual driftersUpwelling locations are highly constrained by topographic featuresMean mixed layer residence times are found to be on the order of one month

West Antarctic ice shelves have thinned dramatically over recent decades. Oceanographic measurements that explore connections between offshore warming and transport across a continental shelf with variable bathymetry toward ice shelves are needed to constrain future changes in melt rates. Six years of seal‐acquired observations provide extensive hydrographic coverage in the Bellingshausen Sea, where ship‐based measurements are scarce. Warm but modified Circumpolar Deep Water floods the shelf and establishes a cyclonic circulation within the Belgica Trough with flow extending toward the coast along the eastern boundaries and returning to the shelf break along western boundaries. These boundary currents are the primary water mass pathways that carry heat toward the coast and advect ice shelf meltwater offshore. The modified Circumpolar Deep Water and meltwater mixtures shoal and thin as they approach the continental slope before flowing westward at the shelf break, suggesting the presence of the Antarctic Slope Current. Constraining meltwater pathways is a key step in monitoring the stability of the West Antarctic Ice Sheet. Warm but modified CDW floods the continental shelf of the Bellingshausen SeaA cyclonic trough circulation that carries heat toward the coast is detectedThe mCDW flows westward at the shelf break, suggesting the Antarctic Slope Current

This study presents the characterization of variability in temperature, salinity and oxygen concentration, including the vertical structure of the variability, in the upper 1000 m of the ocean over a full year in the northeast Atlantic. Continuously profiling ocean gliders with vertical resolution between 0.5 and 1 m provide more information on temporal variability throughout the water column than time series from moorings with sensors at a limited number of fixed depths. The heat, salt and dissolved oxygen content are quantified at each depth. While the near surface heat content is consistent with the net surface heat flux, heat content of the deeper layers is driven by gyre‐scale water mass changes. Below ∼150m, heat and salt content display intraseasonal variability which has not been resolved by previous studies. A mode‐1 baroclinic internal tide is detected as a peak in the power spectra of water mass properties. The depth of minimum variability is at ∼415m for both temperature and salinity, but this is a depth of high variability for oxygen concentration. The deep variability is dominated by the intermittent appearance of Mediterranean Water, which shows evidence of filamentation. Susceptibility to salt fingering occurs throughout much of the water column for much of the year. Between about 700–900 m, the water column is susceptible to diffusive layering, particularly when Mediterranean Water is present. This unique ability to resolve both high vertical and temporal variability highlights the importance of intraseasonal variability in upper ocean heat and salt content, variations that may be aliased by traditional observing techniques. Intraseasonal variability in upper ocean temperature and salinity, not previously reportedMode‐1 baroclinic internal tide detectedDeep variability dominated by intermittent patches of Mediterranean Water, which show evidence of filamentation

A signature of submesoscale flows in the upper ocean is skewness in the distribution of relative vorticity. Expected to result for high Rossby number flows, such skewness has implications for mixing, dissipation, and stratification within the upper ocean. An array of moorings deployed in the Northeast Atlantic for 1 year as part of the experiment of the Ocean Surface Mixing, Ocean Submesoscale Interaction Study (OSMOSIS) reveals that relative vorticity is positively skewed during winter even though the scale of the Rossby number is less than 0.5. Furthermore, this skewness is reduced to zero during spring and autumn. There is also evidence of modest seasonal variations in the gradient Rossby number. The proposed mechanism by which relative vorticity is skewed is that the ratio of lateral to vertical buoyancy gradients, as summarized by the inverse gradient Richardson number, restricts its range during winter but less so at other times of the year. These results support recent observations and model simulations suggesting that the upper ocean is host to a seasonal cycle in submesoscale turbulence. Submesoscale relative vorticity (RV) is estimated for approximately 1 year in the Northeast AtlanticVariance and skewness of RV within the upper ocean are enhanced during winterObservations are consistent with seasonally varying submesoscale turbulence

Marginal ice zones are composed of discrete sea‐ice floes, whose dynamics are not well captured by the continuum representation of sea ice in most climate models. This study makes use of an ocean large eddy simulation (LES) model, coupled to cylindrical sea‐ice floes, to investigate thermal and mechanical interactions between melt‐induced submesoscale features and sea‐ice floes, during summer conditions. We explore the sensitivity of sea‐ice melt rates and upper‐ocean turbulence properties to floe size, ice‐ocean drag, and surface winds. Under low wind conditions, upper ocean turbulence transports warm cyclonic filaments from the open ocean toward the center of the floes and enhances their basal melt. This heat transport is partially suppressed by trapping of ice within cold anticyclonic features. When winds are stronger, melt rates are enhanced by the decoupling of floes from the cold, melt‐induced lens underneath sea ice. Distinct dynamical regimes emerge in which the influence of warm filaments on sea‐ice melt is mitigated by the strength of ice‐ocean coupling and eddy size relative to floe size. Simple scaling laws, which may help parameterize these processes in coarse continuum‐based sea‐ice models, successfully capture floe melt rates under these limiting regimes. At high latitudes, the ocean is often covered by a thin layer of sea ice, which forms in the winter due to the freezing of seawater. Sea ice is typically characterized by a collection of distinct pieces, known as ice floes, which range in size between several meters to tens of kilometers. In the summer, floes melt due to a warm atmosphere above, as well as a warm ocean below. The melting of sea‐ice floes often generates small‐scale (1–10 km) ocean currents at the surface, which in turn affect sea‐ice motion and melt. Here, we study these ice‐ocean interactions, using an idealized sea‐ice model coupled to a regional ocean model that resolves these fine‐scale dynamics. We find that small‐scale oceanic currents and surface winds accelerate the sea‐ice melt rate by allowing warm waters to move into colder regions under the ice floes. Simple relationships, or scalings, involving the floe size, wind speed, and ice‐ocean friction, are able to explain these varying ice floe melt rates across a range of environmental conditions. These scalings, when included in global climate models, may help to improve future predictions of sea‐ice changes by accounting for the impact of small‐scale ocean currents. The relative size of sea‐ice floes and submesoscale eddies controls lateral heat transport to sea iceMechanical coupling shields floes from warm filaments but winds disrupt this coupling and advect ice into warm watersScaling laws capture sea‐ice melt rate dependence on floe size, ice‐ocean drag and wind speed The relative size of sea‐ice floes and submesoscale eddies controls lateral heat transport to sea ice Mechanical coupling shields floes from warm filaments but winds disrupt this coupling and advect ice into warm waters Scaling laws capture sea‐ice melt rate dependence on floe size, ice‐ocean drag and wind speed

Flow‐topography interactions along the path of the Antarctic Circumpolar Current generate standing meanders, create regions of enhanced eddy kinetic energy (EKE), and modify frontal structure. We consider the impact of standing meanders on ventilation based on oxygen measurements from Argo floats and the patterns of apparent oxygen utilization (AOU). Regions of high‐EKE have relatively reduced AOU values at depths 200–700 m below the base of the mixed layer and larger AOU variance, suggesting enhanced ventilation due to both along‐isopycnal stirring and enhanced exchange across the base of the mixed layer. Vertical exchange is inferred from finite‐size Lyapunov exponents, a proxy for the magnitude of surface lateral density gradients, which suggest that submesoscale vertical velocities may contribute to ventilation. The shaping of ventilation by standing meanders has implications for the temporal and spatial variability of air‒sea exchange. The circulation of the Southern Ocean is dominated by the eastward‐flowing Antarctic Circumpolar Current (ACC). The characteristics of the ACC are not uniform around the Southern Ocean. Rather, when the ACC encounters underwater mountain ranges the flow is diverted, which causes these regions to be more energetic through the generation of ocean eddies in a process similar to atmospheric storm tracks. Numerical models have suggested that the exchange of properties, such as heat and carbon dioxide, between the atmosphere and the interior ocean is enhanced in these energetic regions. In this study, data from freely floating robotic floats in the Southern Ocean is used to observe the vertical structure of dissolved oxygen. Transfer of properties between the ocean's surface and the interior ocean preferentially occurs in high energy regions of the ACC. Most previous work has relied on numerical models of the ocean that, due to computational limits, do not represent all aspects of the ACC's energetic regions. This study has implications for how the Southern Ocean's ability to take up excess carbon dioxide from the atmosphere will evolve in the future. The relationship between apparent oxygen utilization (AOU) and eddy kinetic energy (EKE) is assessed in the Antarctic Circumpolar CurrentAOU has relatively reduced values below the mixed layer in high‐EKE standing meanders as compared to low‐EKE regionsModification of the density structure and enhanced meso‐ and submesoscale motions enhance ventilation in standing meanders The relationship between apparent oxygen utilization (AOU) and eddy kinetic energy (EKE) is assessed in the Antarctic Circumpolar Current AOU has relatively reduced values below the mixed layer in high‐EKE standing meanders as compared to low‐EKE regions Modification of the density structure and enhanced meso‐ and submesoscale motions enhance ventilation in standing meanders

The Antarctic Slope Front (ASF) modulates ventilation of the abyssal ocean via the export of dense Antarctic Bottom Water (AABW) and constrains shoreward transport of warm Circumpolar Deep Water (CDW) toward marine‐terminating glaciers. Along certain stretches of the continental shelf, particularly where AABW is exported, density surfaces connect the shelf waters to the middepth Circumpolar Deep Water offshore, offering a pathway for mesoscale eddies to transport CDW directly onto the continental shelf. Using an eddy‐resolving process model of the ASF, the authors show that mesoscale eddies can supply a dynamically significant transport of heat and mass across the continental shelf break. The shoreward transport of surface waters is purely wind driven, while the shoreward CDW transport is entirely due to mesoscale eddy transfer. The CDW flux is sensitive to all aspects of the model's surface forcing and geometry, suggesting that shoreward eddy heat transport may be localized to favorable sections of the continental slope. The Antarctic Slope Front supports a significant shoreward eddy transport of CDWSensitivity to surface forcing and bathymetry points to localized eddy CDW fluxEasterly wind stress particularly shapes ASF and constrains shoreward CDW flux

Icebergs affect local biological production around Antarctica. We used an ocean glider to observe the effects of a large iceberg that was advected by the Antarctic Slope Current along the continental slope in the northwestern Weddell Sea in early 2012. The high‐resolution glider data reveal a pronounced effect of the iceberg on ocean properties, with oxygen concentrations of (13 ± 4) μmol kg−1higher than levels in surrounding waters, which are most likely due to positive net community production. This response was confined to three areas of water in the direct vicinity of the iceberg track, each no larger than 2  km2. Our findings suggest that icebergs have an impact on Antarctic production presumably through local micronutrient injections, on a scale smaller than typical satellite observations of biological production in the Southern Ocean. Glider‐based observations were made of the influence of an icebergSubmesoscale meltwater patches require high‐resolution observationsThe iceberg meltwater stimulates biological productivity

The exchange of water masses across the Antarctic continental shelf break regulates the export of dense shelf waters to depth as well as the transport of warm, mid-depth waters towards ice shelves and glacial grounding lines. The penetration of the warmer mid-depth waters past the shelf break has been implicated in the pronounced loss of ice shelf mass over much of west Antarctica. In high-resolution, regional circulation models, the Antarctic shelf break hosts an energetic mesoscale eddy field, but observations that capture this mesoscale variability have been limited. Here we show, using hydrographic data collected from ocean gliders, that eddy-induced transport is a primary contributor to mass and property fluxes across the slope. Measurements along ten cross-shelf hydrographic sections show a complex velocity structure and a stratification consistent with an onshore eddy mass flux. We show that the eddy transport and the surface wind-driven transport make comparable contributions to the total overturning circulation. Eddy-induced transport is concentrated in the warm, intermediate layers away from frictional boundaries. We conclude that understanding mesoscale dynamics will be critical for constraining circumpolar heat fluxes and future rates of retreat of Antarctic ice shelves.

Oceanic fronts with lateral scales less than 20 km are now known to be one of the major contributors to vertical heat fluxes in the global ocean, which highlights their potential impact on Earth's climate. However, frontal dynamics with time scales less than 1 day, whose contribution to vertical heat fluxes is thought to be significant, are obscured by energetic internal gravity waves (IGWs). In this study, we address this critical issue by separating IGWs and frontal dynamics using an approach based on their respective vertical scales of variability. Results using a numerical model with a horizontal grid spacing of 500 m confirm that it is possible to recover frontal dynamics at short time scales as well as associated intense vertical velocities and vertical heat fluxes. This opens up new possibilities for a more accurate estimation of the vertical exchanges of any tracers between the surface and the ocean interior. Two classes of motions involving large vertical velocities are present in the upper ocean: Those associated with small‐scale fronts (<20 km, also called submesoscale or SBM fronts) and those associated with internal gravity waves (IGWs). SBM fronts are known to explain most of the vertical transport of heat, nutrients, and major gases. IGWs do not transport tracers. Rather, small‐scale IGWs are thought to lead to irreversible mixing through breaking. One issue that arises when analyzing in‐situ observations and numerical simulations is how to discriminate between SBMs and IGWs when both classes of motions are energetic, such as in the California Current System. In this study, we show that SBM fronts and IGWs exhibit different vertical scales, which can be exploited to separate the two classes of motions. Our results confirm that filtering the contribution of large vertical scales to 3‐dimensional velocity fields leads to an almost complete recovery of SBM frontal dynamics at short time scales. The significance of this separation is illustrated by the impact of short‐time‐scale, frontal‐induced vertical velocity on vertical heat fluxes. Vertical transport due to convergence at surface fronts is obscured by internal gravity waves in a model of the California CurrentContamination by low‐mode internal waves can be reduced by filtering large vertical scalesA simple filtering algorithm can effectively remove internal waves with little impact on frontal dynamics in the model Vertical transport due to convergence at surface fronts is obscured by internal gravity waves in a model of the California Current Contamination by low‐mode internal waves can be reduced by filtering large vertical scales A simple filtering algorithm can effectively remove internal waves with little impact on frontal dynamics in the model

We present the results of an experimental study on the formation and propagation of thermohaline intrusions from an initial state that is stably stratified in two diffusing components. The intrusions form in a layer that contains compensating horizontal gradients of the two components and that lies above a denser reservoir layer that is homogeneous. In the initial state, a vertical barrier separates the upper layer into two half layers each with a different concentration but with the same density. Differential diffusion of solute from. the reservoir into the upper layer initiates intrusions that are separated by an interface and that move in opposite directions, The propagation of these intrusions is augmented by double-diffusive fluxes across the interface. Our experiments show that the formation of a diffusive interface between the two intrusions is a robust feature for all experiments that initially have a stable stratification in both diffusing components. A series of contrasting experiments with a fingering interface between the two intrusions was also performed using an initial density profile that favored fingering between part of the upper layer and the reservoir. A simple model is presented for intrusion propagation and density evolution in the intrusions, and the results are compared to measurements from the experiments. These experiments may help illuminate how thermohaline intrusions form in regions of the ocean where both temperature and salinity are stably stratified. [ABSTRACT FROM AUTHOR]

Standing meanders are a key component of the Antarctic Circumpolar Current (ACC) circulation system, and numerical studies have shown that these features may locally enhance subduction, upwelling, as well as lateral and vertical tracer transport. Yet, observational data from these regions remain sparse. Here, we present results based on measurements made by a group of autonomous platforms sampling an ACC standing meander formed due to the interaction of the Polar Front with the Southwest Indian Ridge. Two Seagliders were deployed alongside a Biogeochemical‐Argo float that was advected through the standing meander. In the high eddy kinetic energy region of the standing meander, the glider observations reveal enhanced submesoscale frontal gradients as well as heightened tracer variability at depth, as compared to the more quiescent region further downstream. Vertical gradients in spice and apparent oxygen utilization are reduced in the standing meander despite similarities in the large‐scale vertical stratification, suggesting greater ventilation of the surface ocean. These observations are consistent with numerical studies that highlight standing meanders as hotspots for ventilation and subduction due to enhanced mesoscale stirring and submesoscale vertical velocities. Our results emphasize the need to account for spatial heterogeneity in processes influencing air‐sea exchange, carbon export, and biogeochemical cycling in the Southern Ocean. The Southern Ocean plays a vital role in taking up carbon dioxide and heat from the Earth's atmosphere. Yet, historically, this region has suffered from a lack of direct observations, making it difficult to quantify rates of exchange. In regions where the strongest currents of the Southern Ocean interact with underwater topography turbulence and mixing may be locally enhanced. Data collected from two different types of robotic vehicles, including steerable ocean gliders, were used to study one of these mixing “hotspots.” The instrumented platforms provided expanded data as compared to typical Southern Ocean observational techniques. The results show that these turbulent regions allow water properties, such as temperature and oxygen, to mix vigorously. In particular, at these hotspots the exchange of waters between the ocean surface and interior increases. It is important to document the magnitude and regional patterns of this exchange because only surface waters interact with the atmosphere to take up or release carbon and heat, while interior waters store these properties for centuries or longer. Numerical models of the ocean have indicated that these turbulent regions of the Southern Ocean are particularly influential, and we provide some of the first observational evidence confirming these hotspots' importance. Observations with high spatial and temporal resolution were collected from two ocean gliders following a Biogeochemical‐Argo floatPhysical and biogeochemical tracer variance is enhanced within a standing meander of the Antarctic Circumpolar CurrentThe standing meander shows evidence of heightened exchange of water properties between the ocean surface boundary layer and the interior Observations with high spatial and temporal resolution were collected from two ocean gliders following a Biogeochemical‐Argo float Physical and biogeochemical tracer variance is enhanced within a standing meander of the Antarctic Circumpolar Current The standing meander shows evidence of heightened exchange of water properties between the ocean surface boundary layer and the interior

Hydrographic data are analyzed for the broad continental shelf of the Bellingshausen Sea, which is host to a number of rapidly thinning ice shelves. The flow of warm Circumpolar Deep Water (CDW) onto the continental shelf is observed in the two major glacially carved troughs, the Belgica and Latady troughs. Using ship‐based measurements of potential temperature, salinity, and dissolved oxygen, collected across several coast‐to‐coast transects over the Bellingshausen shelf in 2007, the velocity and circulation patterns are inferred based on geostrophic balance and further constrained by the tracer and mass budgets. Meltwater was observed at the surface and at intermediate depth toward the western side of the continental shelf, collocated with inferred outflows. The maximum conversion rate from the dense CDW to lighter water masses by mixing with glacial meltwater is estimated to be 0.37 ± 0.1 Sv in both depth and potential density spaces. This diapycnal overturning is comparable to previous estimates made in the neighboring Amundsen Sea, highlighting the overlooked importance of water mass modification and meltwater production associated with glacial melting in the Bellingshausen Sea. The Bellingshausen Sea is sandwiched between the Amundsen Sea and the West Antarctic Peninsula continental shelf sea and where warm offshore waters around Antarctica can flow onto the continental shelf and directly melt the floating ice‐shelves. However, in situ observations are historically very sparse in this region due to the heavy sea‐ice cover throughout most of the year. In this study, we present the distribution of temperature, salinity, dissolved oxygen, and the diagnosed meltwater concentration over the broad continental shelf of the Bellingshausen Sea from one of the most comprehensive hydrographic surveys so far. We further infer the velocity and circulation patterns by balancing the input and output rates of tracers (heat, salt, and dissolved oxygen) within selected regions. A clockwise‐flowing boundary current is identified over the shelf, consistent with the meltwater distribution and previous findings. Lastly, we measure the overturning circulation over the Bellingshausen Shelf, which consists of warm water inflow in the lower water column and meltwater outflow near the surface. We conclude that the magnitude of this circulation is comparable to previous estimates made in the neighboring Amundsen Sea where the ice‐shelf melting has drawn much attention recently. Tracer distribution over the Bellingshausen shelf is presented with data from a comprehensive hydrographic surveyMeltwater is present from mid‐depth to surface and is accumulated toward the western shelf, consistent with a cyclonic gyre circulationThe inferred overturning circulation driven by ice‐shelf melting is comparable to previous estimates made in the neighboring Amundsen Sea Tracer distribution over the Bellingshausen shelf is presented with data from a comprehensive hydrographic survey Meltwater is present from mid‐depth to surface and is accumulated toward the western shelf, consistent with a cyclonic gyre circulation The inferred overturning circulation driven by ice‐shelf melting is comparable to previous estimates made in the neighboring Amundsen Sea

Climate models consistently project a robust weakening of the Indonesian Throughflow (ITF) and the Atlantic meridional overturning circulation (AMOC) in response to greenhouse gas forcing. Previous studies of ITF variability have largely focused on local processes in the Indo‐Pacific Basin. Here, we propose that much of the centennial‐scale ITF weakening is dynamically linked to changes in the Atlantic Basin and communicated between basins via wave processes. In response to an AMOC slowdown, the Indian Ocean develops a northward surface transport anomaly that converges mass and modifies sea surface height in the Indian Ocean, which weakens the ITF. We illustrate these dynamic interbasin connections using a 1.5‐layer reduced gravity model and then validate the responses in a comprehensive general circulation model. Our results highlight the importance of transient volume exchanges between the Atlantic and Indo‐Pacific basins in regulating the global ocean circulation in a changing climate. The Indonesian Throughflow (ITF) is a key component of the global ocean circulation. By exchanging water between the low‐latitude Indian Ocean and Pacific Ocean, the ITF has been suggested to play an important role in shaping global warming patterns in response to greenhouse gas forcing. Climate models consistently project the ITF strength to decline in the 21st century. Traditionally, changes in the strength of the ITF have been attributed to local processes, such as changes in precipitation and atmospheric winds. Here, we suggest that remote processes can also have a significant impact on ITF variability. In particular, we show that the projected weakening in the ITF during the 21st century could be tied to changes in the Atlantic meridional overturning circulation (AMOC). Through this transient version of the ocean's conveyor belt circulation, changes in the high‐latitude North Atlantic (e.g., Arctic sea ice melt) can affect the climate in the low‐latitude Indo‐Pacific Ocean. An intriguing corollary is the potential to use the ITF to monitor or interpret long‐term trends in the AMOC. Basin‐scale transient responses of the global ocean overturning circulation are explored with a hierarchy of modelsChanges in AMOC strength can produce a response in ITF volume transport on centennial timescalesITF transport time series may assist in monitoring and interpreting long‐term trends in the AMOC

The rate of ocean heat uptake depends on the mechanisms that transport heat between the surface and the ocean interior. A recent study found that the vertical heat transport driven by motions with scales smaller than 0.5° (submesoscales) and frequencies smaller than 1 day−1is upward. This transport competes with the other major components of the global heat transport, namely, the downward heat transport explained by the large‐scale wind‐driven vertical circulation and vertical diffusion at small scales and the upward heat transport associated with mesoscale eddies (50‐ to 300‐km size). The contribution from motions with small spatial scales (<0.5°) and frequencies larger than 1 day−1, including internal gravity waves, has never been explicitly estimated. This study investigates this high‐frequency (subdaily) submesoscale contribution to the global heat transport. The major result of this study, based on the analysis of a high‐resolution ocean model, is that including this high‐frequency contribution surprisingly doubles the upward heat transport due to submesoscales in winter in the global ocean. This contribution typically concerns depths down to 200–500 m and can have a magnitude of up to 500 W m−2in terms of wintertime heat fluxes at 40‐m depth, which causes a significant upward heat transport of ~7 PW when integrated over the global ocean. Thus, such submesoscale heat transport, which is not resolved by climate models, impacts the heat uptake in the global ocean. The mechanisms involved in these results still need to be understood, which should be the scope of future work. Ocean heat flux is large at high frequencySuch high‐frequency flux is generated at submesoscaleSuch heat flux is a key component of global heat budget

The stability of the West Antarctic Ice Sheet (WAIS) depends on ocean heat transport toward its base and remains a source of uncertainty in sea level rise prediction. The Antarctic Slope Current (ASC), a major boundary current of the ocean's global circulation, serves as a dynamic gateway for heat transport toward Antarctica. Here, we use observations collected from the Bellingshausen Sea to propose a mechanistic explanation for the initiation of the westward‐flowing ASC. Waters modified throughout the Bellingshausen Sea by ocean‐sea‐ice and ocean‐ice‐shelf interactions are exported to the continental slope in a narrow, topographically steered western boundary current. This focused outflow produces a localized front at the shelf break that supports the emerging ASC. This mechanism emphasizes the importance of buoyancy forcing, integrated over the continental shelf, as opposed to local wind forcing, in the generation mechanism and suggests the potential for remote control of melt rates of WAIS' largest ice shelves. The Antarctic Slope Current (ASC) is an ocean current that separates warmer, offshore water from colder waters over the continental shelf. The ASC helps to control the movement of warm water on to the continental shelf and ultimately under floating ice shelves. Warm ocean water has contributed to the melting and thinning of West Antarctic ice shelves in recent decades. This study describes where and how the ASC first forms in West Antarctica. Previous studies have suggested that the ASC responds primarily to atmospheric winds blowing over the current itself, whereas here it is argued that processes occurring over a much larger region of the west Antarctic continental shelf may determine the strength and structure of the ASC. These results contribute to our understanding of the long‐term, for example, decades or longer, evolution of the West Antarctic Ice Sheet. The initiation of a westward Antarctic Slope Current (ASC) occurs in the western Bellingshausen SeaThe ASC arises from the export of waters, modified by ocean‐ice interactions, to the shelf break, rather than from local wind forcingThis mechanism suggests the potential for remote control of shelf properties as well as West Antarctic ice shelf melt rates

Submesoscale flows in the ocean are energetic motions, O(1–10 km), that influence stratification and the distributions of properties, such as heat and carbon. They are believed to play an important role in sea‐ice‐impacted oceans by modulating air‐sea‐ice fluxes and sea‐ice extent. The intensity of these flows and their response to wind forcing are unobserved in the sea‐ice regions of the Southern Ocean. We present the first submesoscale‐resolving observations in the Antarctic marginal ice zone (MIZ) collected by surface and underwater autonomous vehicles, for >3 months in austral summer. We observe salinity‐dominated lateral density fronts occurring at sub‐kilometer scales. Surface winds are shown to modify the magnitude of the mixed‐layer density fronts, revealing strongly coupled atmosphere‐ocean processes. We posture that these wind‐front interactions occur as a continuous interplay between front slumping and vertical mixing, which leads to the dispersion of submesoscale fronts. Such processes are expected to be ubiquitous in the Southern Ocean MIZ. Satellite radar imagery shows evidence of 1–10 km eddies and jets in the ocean adjacent to the sea‐ice edge around Antarctica. We use field observations of temperature, salinity, and wind speed from autonomous robotic platforms deployed in the sea‐ice zone for >3 months. These measurements provide estimates of the surface ocean density fronts which are controlled primarily by lateral variations in salinity. We show that, during high wind speeds, these surface fronts temporarily dissipate, indicating an atmosphere‐ocean coupling occurring at the submesoscale. The fronts strengthen again during low wind speed, which is thought to be because the stirring of the fresher surface layer by mesoscale eddies leads to the generation of the submesoscale fronts. Providing in situ observations of such features improves our understanding of the small‐scale ocean and climate processes at play, such as how heat and carbon may exchange between the atmosphere and the ocean. Using combined surface and underwater robotic observations, we observe haline‐dominated submesoscale fronts in the Antarctic MIZEnhanced wind speeds reduce the magnitude of lateral submesoscale fronts within the surface mixed layerSubmesoscale wind‐front interactions cause a continuous interplay between front slumping and vertical mixing, arresting lateral shear

Surface buoyancy fluxes in the Southern and North Atlantic Oceans are presumed to disproportionately influence the ocean's residual global overturning circulation (GOC) with respect to those in the Indo‐Pacific. Here, this assumption is challenged through an assessment of global buoyancy transport in the Community Earth System Model 1.0, which reveals that the steady state GOC is equally constrained by surface buoyancy flux everywhere. Further, an unacknowledged aspect of the GOC is demonstrated: it transports buoyancy from where it is gained at the surface, predominately in the Indo‐Pacific, to where it is lost, predominately in the Atlantic and Southern Oceans. This global buoyancy transport requires zonal structure in the GOC, linking the Atlantic and Indo‐Pacific within the Southern Ocean, asymmetry and interbasin coupling absent from many conceptual descriptions of overturning dynamics. These results compel a more nuanced appreciation for an Indo‐Pacific influence in GOC evolution. The great conveyor beltof global currents that transit the global ocean—the global overturning circulation—carry with them heat, freshwater, and dissolved gases that are essential to Earth's climate. Changes in heating and cooling of the ocean surface, or changes to patterns of precipitation, are known to influence this global‐scale circulation, but a full understanding of the response remains incomplete. In this study, we develop a new technique to study the global overturning circulation. Our methods use the spatial patterns of ocean surface processes, for example, heating and cooling, precipitation and evaporation, to infer circulation behaviors deep in the ocean's interior. Historically, deep ocean behaviors were thought to be influenced by surface processes occurring at the high latitudes. Here, using this new technique, we find that surface processes at the low latitudes of the Indo‐Pacific Oceans are equally essential in determining the strength and structure of the global overturning circulation. As a consequence, the climate that we experience at Earth's surface may depend far more heavily on the processes occurring at the equatorial Indo‐Pacific Ocean surface than often assumed. Constraints on overturning pathways, based on global surface buoyancy forcing, are tested in comprehensive climate modelIndo‐Pacific air‐sea fluxes require zonal asymmetries in the global overturning circulationActive low‐latitude, Indo‐Pacific surface controls on global overturning dynamics are proposed

We observe surface and subsurface fluorescence‐derived chlorophyll maxima in southern Drake Passage during austral summer. Backscatter measurements indicate that the deep chlorophyll maxima (DCMs) are also deep biomass maxima, and euphotic depth estimates show that they lie below the euphotic layer. Subsurface, offshore and near‐surface, onshore features lie along the same isopycnal, suggesting advective generation of DCMs. Temperature measurements indicate a warming of surface waters throughout austral summer, capping the winter water (WW) layer and increasing off‐shelf stratification in this isopycnal layer. The outcrop position of the WW isopycnal layer shifts onshore, into a surface phytoplankton bloom. A lateral potential vorticity (PV) gradient develops, such that a down‐gradient PV flux is consistent with offshore, along‐isopycnal tracer transport. Model results are consistent with this mechanism. Subduction of chlorophyll and biomass along isopycnals represents a biological term not observed by surface satellite measurements which may contribute significantly to the strength of the biological pump in this region. Surface and subsurface chlorophyll maxima are connected along isopycnalsChlorophyll transport is consistent with down‐gradient potential vorticity fluxModel results confirm mean and eddy pathways for DCM formation