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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. Plain Language Summary: 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. Key Points: 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 facto western boundary of the Bellingshausen Sea [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: 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. Key Points: 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 [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: 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. Key Points: 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 [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: 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. Key Points: 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 [ABSTRACT FROM AUTHOR]

The subpolar gyres of the Southern Ocean form an important dynamical link between the Antarctic Circumpolar Current (ACC) and the coastline of Antarctica. Despite their key involvement in the production and export of bottom water and the poleward transport of oceanic heat, these gyres are rarely acknowledged in conceptual models of the Southern Ocean circulation, which tend to focus on the zonally averaged overturning across the ACC. To isolate the effect of these gyres on the regional circulation, we carried out a set of numerical simulations with idealized representations of the Weddell Sea sector in the Southern Ocean. A key result is that the zonally oriented submarine ridge along the northern periphery of the subpolar gyre plays a fundamental role in setting the stratification and circulation across the entire region. In addition to sharpening and strengthening the horizontal circulation of the gyre, the zonal ridge establishes a strong meridional density front that separates the weakly stratified subpolar gyre from the more stratified circumpolar flow. Critically, the formation of this front shifts the latitudinal outcrop position of certain deep isopycnals such that they experience different buoyancy forcing at the surface. Additionally, the zonal ridge modifies the mechanisms by which heat is transported poleward by the ocean, favoring heat transport by transient eddies while suppressing that by stationary eddies. This study highlights the need to characterize how bathymetry at the subpolar gyre–ACC boundary may constrain the transient response of the regional circulation to changes in surface forcing. Significance Statement: This study explores the impact of seafloor bathymetry on the dynamics of subpolar gyres in the Southern Ocean. The subpolar gyres are major circulation features that connect the Antarctic Circumpolar Current (ACC) and the coastline of Antarctica. This work provides deeper insight for how the submarine ridges that exist along the northern periphery of these gyres shape the vertical distribution of tracers and overturning circulation in these regions. These findings highlight an underappreciated yet fundamentally important topographical constraint on the three-dimensional cycling of heat and carbon in the Southern Ocean—processes that have far-reaching implications for the global climate. Future work should explore how the presence of these ridges affect the time-evolving response of the Southern Ocean to changes in surface conditions. [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: 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. Key Points: 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 [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: 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. Key Points: 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 [ABSTRACT FROM AUTHOR]

The last glacial period is punctuated by abrupt changes in Northern Hemisphere temperatures that are known as Dansgaard–Oeschger (DO) events. A striking and largely unexplained feature of DO events is an interhemispheric asymmetry characterized by cooling in Antarctica during periods of warming in Greenland and vice versa—the bipolar seesaw. Methane-synchronized ice core records indicate that the Southern Hemisphere lags the Northern Hemisphere by approximately 200 years. Here, we propose a mechanism that produces observed features of both the bipolar seesaw and the phasing of DO events. The spatial pattern of sea ice formation and melt in the Southern Ocean imposes a rigid constraint on where water masses are modified: waters are made denser near the coast where ice forms and waters are made lighter farther north where ice melts. This pattern, coupled to the tilt of density surfaces across the Southern Ocean and the stratification of the ocean basins, produces two modes of overturning corresponding to different bipolar seesaw states. We present evolution equations for a simplified ocean model that describes the transient adjustment of the basin stratification, the Southern Ocean surface density distribution, and the overturning strength as the ocean moves between these states in response to perturbations in North Atlantic Deep Water formation, which we take as a proxy for Greenland temperatures. Transitions between different overturning states occur over a multicentennial time scale, which is qualitatively consistent with the observed Southern Hemisphere lag. The volume of deep density layers varies inversely with the overturning strength, leading to significant changes in residence times. Evidence of these dynamics in more realistic circulation models is discussed. [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: 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. Key Points: 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 [ABSTRACT FROM AUTHOR]

Along various stretches of the Antarctic margins, dense Antarctic Bottom Water (AABW) escapes its formation sites and descends the continental slope. This export necessarily raises the isopycnals associated with lighter density classes over the continental slope, resulting in density surfaces that connect the near-freezing waters of the continental shelf to the much warmer circumpolar deep water (CDW) at middepth offshore. In this article, an eddy-resolving process model is used to explore the possibility that AABW export enhances shoreward heat transport by creating a pathway for CDW to access the continental shelf without doing any work against buoyancy forces. In the absence of a net alongshore pressure gradient, the shoreward CDW transport is effected entirely by mesoscale and submesoscale eddy transfer. Eddies are generated partly by instabilities at the pycnocline, sourcing their energy from the alongshore wind stress, but primarily by instabilities at the CDW-AABW interface, sourcing their energy from buoyancy loss on the continental shelf. This combination of processes induces a vertical convergence of eddy kinetic energy and alongshore momentum into the middepth CDW layer, sustaining a local maximum in the eddy kinetic energy over the slope and balancing the Coriolis force associated with the shoreward CDW transport. The resulting slope turbulence self-organizes into a series of alternating along-slope jets with strongly asymmetrical contributions to the slope energy and momentum budgets. Cross-shore variations in the potential vorticity gradient cause the jets to drift continuously offshore, suggesting that fronts observed in regions of AABW down-slope flow may in fact be transient features. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the modern climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleoproxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum, resulting in an expansion of the volume occupied by Antarctic origin waters. In this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around Antarctica. A simple theory further suggests that these deep waters only came to the surface under sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. This unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean's role in regulating atmospheric carbon dioxide on glacial-interglacial timescales. Previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide. Here it is shown that many of these changes are dynamically linked and therefore must co-occur. [ABSTRACT FROM AUTHOR]

An array of 40 surface drifters, drogued at 15-m depth, was deployed in February 2007 to the east of the tip of the Antarctic Peninsula as part of the Antarctic Drifter Experiment: Links to Isobaths and Ecosystems (ADELIE) project. Data obtained from these drifters and from a select number of local historical drifters provide the most detailed observations to date of the surface circulation in the northwestern Weddell Sea. The Antarctic Slope Front (ASF), characterized by a ∼20 cm s-1 current following the 1000-m isobath, is the dominant feature east of the peninsula. The slope front bifurcates when it encounters the South Scotia Ridge with the drifters following one of three paths. Drifters (i) are carried westward into Bransfield Strait; (ii) follow the 1000-m isobath to the east along the southern edge of the South Scotia Ridge; or (iii) become entrained in a large-standing eddy over the South Scotia Ridge. Drifters are strongly steered by contours of f /h (Coriolis frequency/depth) as shown by calculations of the first two moments of displacement in both geographic coordinates and coordinates locally aligned with contours of f /h. An eddy-mean decomposition of the drifter velocities indicates that shear in the mean flow makes the dominant contribution to dispersion in the along-f /h direction, but eddy processes are more important in dispersing particles across contours of f /h. The results of the ADELIE study suggest that the circulation near the tip of the Antarctic Peninsula may influence ecosystem dynamics in the Southern Ocean through Antarctic krill transport and the export of nutrients. [ABSTRACT FROM AUTHOR]

The modern Indo-Pacific oceans absorb more heat from the atmosphere than they release. The resulting energy surplus is exported from the Indo-Pacific by the ocean circulation and lost to the atmosphere from other ocean basins. This heat transport ultimately sustains much of the buoyancy lost to deep water formation at high latitudes, a key component of the global overturning circulation. Despite the fundamental link between inter-basin ocean heat transport and global overturning in today's climate, there is no general understanding of how these phenomena vary with climate state. Here, we use an unprecedented suite of fully-coupled climate model simulations, equilibrated for thousands of years to a wide range of CO 2 levels, to demonstrate that major differences in overturning between climates are related to systematic shifts in ocean heat transport between basins. Uniformly, equilibration to higher CO 2 levels strengthens inter-basin ocean heat transport and global deep water formation. These changes are sustained by increased surface heat uptake within the Indo-Pacific oceans, and increased high-latitude heat loss outside of the Indo-Pacific oceans as the climate warms. However, poleward heat transport and high-latitude heat loss do not increase symmetrically between hemispheres. Between glacial and modern-like states, North Atlantic heat loss intensifies and overturning in the Atlantic strengthens. In contrast, between modern-like and hot climates, heat loss and overturning strengthens in the Southern Ocean. We propose that these differences are linked to a shift in the relative efficiency of northward and southward ocean heat transport — dominated by advection in the North Atlantic and eddy diffusion in the Southern Ocean — with climate state. Our results suggest that, under high CO 2 , future ocean heat transport towards Antarctica would increase disproportionately compared to its changes since the last ice age. • Total ocean heat uptake over the Indo-Pacific increases monotonically in warmer climate states. • Cooling from Atlantic and Southern polar regions increases asymmetrically with climate warming. • Reconfigurations in heat-driven global ocean overturning evolve with polar cooling changes. • Polar-amplified warming accompanies asymmetric overturning changes in each hemisphere. [ABSTRACT FROM AUTHOR]

The article discusses the documentation of the spatial distribution of long-term large-scale trends in temperature, salinity, and core depth over the Antarctic continental shelf and slope. Topics include the role of ice shelf basal melt in Antarctic ice sheet mass loss, circulation of Circumpolar Deep Water (CDW), hydrographic properties of the Antarctic Continental Shelf Bottom Water (ASBW) temperature, and factors contributing to warming at the seabed in the Bellingshausen and Amundsen seas.