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Future sea-level rise projections carry large uncertainties, mainly driven by the unknown response of the Antarctic Ice Sheet to climate change. During the past four decades, the contribution of the East Antarctic Ice Sheet to sea-level rise has increased. However, unlike for West Antarctica, the causes of East Antarctic ice-mass loss are largely unexplored. Here, using oceanographic observations off East Antarctica (80–160° E) we show that mid-depth Circumpolar Deep Water has warmed by 0.8–2.0 °C along the continental slope between 1930–1990 and 2010–2018. Our results indicate that this warming may be implicated in East Antarctic ice-mass loss and coastal water-mass reorganization. Further, it is associated with an interdecadal, summer-focused poleward shift of the westerlies over the Southern Ocean. Since this shift is predicted to persist into the twenty-first century, the oceanic heat supply to East Antarctica may continue to intensify, threatening the ice sheet’s future stability.

Coastal polynyas are key regions of Dense Shelf Water (DSW) formation that ultimately contributes to the ventilation of the ocean abyss. However, not all polynyas form DSW. In this study, we analyse the main drivers of DSW formation in four East Antarctic polynyas: Mackenzie, Barrier, Shackelton and Vincennes Bay from west to east. Mackenzie and Barrier (in lesser extent) were the only two polynyas where DSW formation was observed while it is absent in Shackelton and Vincennes Bay in the particular years when they were best sampled. We analysed the role of Bathymetry, water-mass distribution and transformation, stratification of the water column, sea-ice production rate and associated salt advection. We found that sea ice production was highest in Mackenzie, particularly in early winter, which likely contributed to reach higher salinity than the other polynyas at the beginning of the sea ice formation season. From April to September, the total salinity change in Mackenzie polynya was lower than in the other polynyas, and the strong contribution of the brine rejection was partly offset by freshwater advection. Overall, the preconditioning in early winter in Mackenzie polynya, likely due to strong SIP in February and March was the main driver determining DSW formation in MAckenzie in contrast with the other East Antarctic polynyas.

Coastal polynyas are key formation regions for Dense Shelf Water (DSW) that ultimately contributes to the ventilation of the ocean abyss. However, not all polynyas form DSW. We examine how the physiographic setting, water-mass distribution and transformation, water column stratification, and sea-ice production regulate DSW formation in four East Antarctic coastal polynyas. We use a salt budget to estimate the relative contribution of sea-ice production and lateral advection to the monthly change in salinity in each polynya. DSW forms in Mackenzie polynya due to a combination of physical features (shallow water depth and a broad continental shelf) and high sea-ice production. Sea-ice formation begins early (March) in Mackenzie polynya, counteracting fresh advection and establishing a salty mixed layer in autumn that preconditions the water column for deep convection in winter. Sea-ice production is moderate in the other three polynyas, but saline DSW is not formed (a fresh variety is formed in the Barrier polynya). In the Shackleton polynya, brine rejection during winter is insufficient to overcome the very fresh autumn mixed layer. In Vincennes Bay, a strong inflow of modified Circumpolar Deep Water stratifies the water column, hindering deep convection and DSW formation. Our study highlights that DSW formation in a given polynya depends on a complex combination of factors, some of which may be strongly altered under a changing climate, with potentially important consequences for the ventilation of the deep ocean, the global meridional overturning circulation, and the transport of ocean heat to Antarctic ice shelves. Key Points We determined the physical factors enhancing (or hindering) DSW formation in four East Antarctic polynyas during a well sampled year Relatively high salinity in early winter and high sea-ice formation favor Dense Shelf Water formation in Mackenzie Polynya The properties and volume of DSW formed in a coastal polynya depend on its preconditioning as well as on sea-ice formation Plain Language Summary Coastal polynyas are regions of open water surrounded by sea ice. As sea ice forms, it is pushed offshore by strong winds blowing from the Antarctic continent, keeping the polynya ice-free. Salt is released into the water below as sea ice forms, increasing the salinity and density of the water column. In some polynyas, this water is dense enough to sink from the continental shelf to supply a network of bottom ocean currents that influences global climate. In other polynyas, the water in winter never gets dense enough to reach the ocean abyss. Using data collected by instrumented elephant seals, we investigated the main factors controlling dense water formation in four East Antarctic polynyas. We found that dense water production is related to the strength of sea-ice formation, as expected, but also depends on the salinity at the start of winter. The geographical and physical characteristics of the polynyas and regional circulation also modulate the final water density. Our findings provide insight into how dense water formation in East Antarctic polynyas might respond to future changes in climate and thereby influence the transport of ocean heat to the Antarctic continent and the melt of ice shelves.

We provide a detailed description of the spatial distribution, seasonality and transformation of the main water masses within MacKenzie Polynya (MP) in Prydz Bay, East Antarctica, using data from instrumented southern elephant seals. Dense Shelf Water (DSW) formation in MP shows large spatial variability that is related to the (i) local bathymetry, (ii) water column preconditioning from the presence/absence of different water masses, and (iii) proximity to the Amery Ice Shelf meltwater outflow. MP exhibits sustained sea ice production and brine rejection (thus, salinity increase) from April to October. However, new DSW is only formed from June onward, when the mixed layer deepens and convection is strong enough to break the stratification set by Antarctic Surface Water above and Ice Shelf Water below. We found no evidence of DSW export from MP to Darnley polynya, as previously suggested. Rather, our observations suggest some DSW formed in Darnley Polynya may drain towards the western Prydz Bay. Then, DSW is exported offshore from Prydz Bay through the Prydz Channel. The interplay between sea ice formation, meltwater input, and sea floor topography is likely to explain why some coastal polynyas form more DSW than others, as well as the temporal variability in DSW formation within a particular polynya. Plain Language Summary Coastal polynyas are regions of open water surrounded by sea ice. They form when strong winds from the Antarctic continent push newly-formed sea ice away from the coast, as rapidly as it forms. Polynyas are therefore important sea ice factories. When sea ice forms, salt is released into the water below, increasing its salinity and density. The densest water in the World Ocean can be traced back to a few coastal polynyas along the Antarctic continent. This dense water formed in polynyas supplies the deep limb of a network of ocean currents that influences climate on global scales. Despite their importance, coastal polynyas remain poorly understood as they are difficult to reach and observe. Using data collected by instrumented elephant seals, we investigated seasonal changes in the MacKenzie Polynya in Prydz Bay, East Antarctica. Our study shows that dense water production is regulated by a complex interplay between three factors: strength of sea ice formation, the input of meltwater from ice shelves, and steering of the flow by sea floor topography. These new observations collected by seals contribute to a better understanding of dense water formation and the vulnerability of the global overturning circulation to future change.

The changing supply of warm Circumpolar Deep Water (CDW) to the West Antarctic continental shelf is responsible for the basal melting and thinning of the West Antarctic ice shelves that has occurred in recent decades. Here, we assess the variability in CDW supply, and its drivers, from a multi‐year mooring deployed in, and a regional ocean model spanning, the Getz‐Dotson Trough, Amundsen Sea. Between 2010 to 2015, the CDW within the trough underwent a pronounced cooling and freshening, associated with changes in thermohaline properties on isopycnals. Variability in the rate of CDW inflow is controlled by local wind forcing of a shelf break undercurrent, which determines the hydrographic properties of inflowing CDW via tilting of density surfaces above the continental slope. Local wind is coupled to the Amundsen Sea Low (ASL) low‐pressure system, which is modulated by large‐scale climatic modes via atmospheric teleconnections. For the period analysed, a deeper ASL was associated with westward wind anomaly at the shelf break. Changes in the sea surface slope decelerated the shelf break undercurrent, resulting in less heat accessing the continental shelf and, consequently, a cooling of the Getz‐Dotson Trough. Therefore, the present work suggests that the fate of the West Antarctic ice shelves is closely tied to the future evolution of the ASL.

Mass loss from the Antarctic Ice Sheet to the ocean has increased in recent decades, largely because the thinning of its floating ice shelves has allowed the outflow of grounded ice to accelerate1,2. Enhanced basal melting of the ice shelves is thought to be the ultimate driver of change2,3, motivating a recent focus on the processes that control ocean heat transport onto and across the seabed of the Antarctic continental shelf towards the ice4–6. However, the shoreward heat flux typically far exceeds that required to match observed melt rates2,7,8, suggesting that other critical controls exist. Here we show that the depth-independent (barotropic) component of the heat flow towards an ice shelf is blocked by the marked step shape of the ice front, and that only the depth-varying (baroclinic) component, which is typically much smaller, can enter the sub-ice cavity. Our results arise from direct observations of the Getz Ice Shelf system and laboratory experiments on a rotating platform. A similar blocking of the barotropic component may occur in other areas with comparable ice–bathymetry configurations, which may explain why changes in the density structure of the water column have been found to be a better indicator of basal melt rate variability than the heat transported onto the continental shelf9. Representing the step topography of the ice front accurately in models is thus important for simulating ocean heat fluxes and induced melt rates. The front of the Getz Ice Shelf in West Antarctica creates an abrupt topographic step that deflects ocean currents, suppressing 70% of the heat delivery to the ice sheet.

The response of the subpolar Southern Ocean (sSO) to wind forcing is assessed using satellite radar altimetry. sSO sea level exhibits a phased, zonally coherent, bi‐modal adjustment to circumpolar wind changes, involving comparable seasonal and interannual variations. The adjustment is effected via a quasi‐instantaneous exchange of mass between the Antarctic continental shelf and the sSO to the north, and a 2‐month‐delayed transfer of mass between the wider Southern Ocean and the subtropics. Both adjustment modes are consistent with an Ekman‐mediated response to variations in surface stress. Only the fast mode projects significantly onto the surface geostrophic flow of the sSO, thus the regional circulation varies in phase with the leading edge of sSO sea level variability. The surface forcing of changes in the sSO system is partly associated with variations of surface winds linked to the Southern Annular Mode, and is modulated by sea ice cover near Antarctica.

Assessments of the Antarctic contribution to future sea level rise have generally focused on ice loss in West Antarctica. This focus was motivated by glaciological and oceanographic observations that showed ocean warming was driving loss of ice mass from the West Antarctic Ice Sheet (WAIS). Paleoclimate studies confirmed that ice discharge from West Antarctica contributed several meters to sea level during past warm periods. On the other hand, the much larger East Antarctic Ice Sheet (EAIS) was generally considered to be relatively stable because of being largely grounded above sea level and therefore protected from ocean heat flux. However, recent studies suggest that a large part of the EAIS is grounded well below sea level and that the EAIS also retreated and contributed several meters to sea level rise during past warm periods. We use ocean observations from three ice shelf systems to illustrate the variety of ocean-ice shelf interactions taking place in East Antarctica and to discuss the potential vulnerability of East Antarctic ice shelves to ocean heat flux. The Amery and the Mertz are “cold cavity” ice shelves that exhibit relatively low area-averaged basal melt rates, although substantial melting and refreezing occurs beneath the large and deep Amery Ice Shelf. In contrast, new oceanographic measurements near the Totten Ice Shelf show that warm water enters the sub-ice-shelf cavity and drives rapid basal melting, as is seen in West Antarctica. Totten Glacier is of particular interest because it holds a marine-based ice volume equivalent to at least 3.5 m of global sea level rise, an amount comparable to the entire marine-based WAIS, and recent glaciological measurements show the grounded portion of Totten Glacier is thinning and the grounding line is retreating. Multiple lines of evidence support the hypothesis that parts of the EAIS are more dynamic than once thought. Given that the EAIS contains a volume of marine-based ice equivalent to 19 m of global sea level rise, the potential for ocean-driven melt to destabilize the marine-based ice sheet needs to be accounted for in assessments of future sea level rise.

The Antarctic continental shelf supports a high level of marine primary productivity and is a globally important carbon dioxide (CO2) sink through the photosynthetic fixation of CO2 via the biological pump. Sustaining such high productivity requires a large supply of the essential micronutrient iron (Fe); however, the pathways for Fe delivery to these zones vary spatially and temporally. Our study is the first to report a previously unquantified source of concentrated bioavailable Fe to Antarctic surface waters. We hypothesize that Fe derived from subglacial processes is delivered to euphotic waters through the accretion (Fe storage) and subsequent melting (Fe release) of a marine-accreted layer of ice at the base of the Amery Ice Shelf (AIS). Using satellite-derived Chlorophyll-a data, we show that the soluble Fe supplied by the melting of the marine ice layer is an order of magnitude larger than the required Fe necessary to sustain the large annual phytoplankton bloom in Prydz Bay. Our finding of high concentrations of Fe in AIS marine ice and recent data on increasing rates of ice shelf basal melt in many of Antarctica's ice shelves should encourage further research into glacial and marine sediment transport beneath ice shelves and their sensitivity to current changes in basal melt. Currently, the distribution, volume, and Fe concentration of Antarctic marine ice is poorly constrained. This uncertainty, combined with variable forecasts of increased rates of ice shelf basal melt, limits our ability to predict future Fe supply to Antarctic coastal waters.

Antarctic ice sheet mass loss has been linked to an increase in oceanic heat supply, which enhances basal melt and thinning of ice shelves. Here we detail the interaction of modified Circumpolar Deep Water (mCDW) with the Amery Ice Shelf, the largest ice shelf in East Antarctica, and provide the first estimates of basal melting due to mCDW. We use subice shelf ocean observations from a borehole site (AM02) situated ?70 km inshore of the ice shelf front, together with open ocean observations in Prydz Bay. We find that mCDW transport into the cavity is about 0.22?±?0.06 Sv (1 Sv?=?106 m3 s?1). The inflow of mCDW drives a net basal melt rate of up to 2?±?0.5 m yr?1 during 2001 (23.9?±?6.52 Gt yr?1 from under about 12,800 km2 of the north-eastern flank of the ice shelf). The heat content flux by mCDW at AM02 shows high intra-annual variability (up to 40%). Our results suggest two main modes of subice shelf circulation and basal melt regimes: (1) the “ice pump”/high salinity shelf water circulation, on the western flank and (2) the mCDW meltwater-driven circulation in conjunction with the “ice pump,” on the eastern flank. These results highlight the sensitivity of the Amery's basal melting to changes in mCDW inflow. Improved understanding of such ice shelf-ocean interaction is crucial to refining projections of mass loss and associated sea level rise.

The surface sedimentary record from six cores collected from beneath the Amery Ice Shelf, East Antarctica, provides a unique view of the sedimentary and oceanographic processes in this sub-ice shelf setting. The composition and age of the surface sediments indicate spatial variations in ice shelf cavity–ocean interaction, which are consistent with patterns of ocean inflow and outflow modelled and observed beneath the ice shelf. Sediments within 100 km of the ice shelf front (site AM01) show the greatest open ocean influence with a young surface age and the highest total diatom abundance, compared to older ages and lower diatom abundances at sites deeper in the cavity (AM03–AM06). The variable marine influence between sites determines the nature of benthic communities. Seabed imagery indicates the existence of sessile suspension feeders in areas of strong marine inflow (site AM01b), while grazers, deposit feeders and a few suspension feeders occur at sites more distal from the shelf calving front where the food supply is lower (sites AM03 and AM04). Understanding the sedimentary and oceanographic processes within the sub-ice shelf environment allows better constraint of interpretations of down core sediment records, an improved understanding of the nature of biological communities in sub-ice shelf environments, and a baseline for determining the sensitivity of the system to any future changes in ocean dynamics.

Oceanographic instruments suspended beneath the Amery Ice Shelf, East Antarctica, have recorded sporadic pressure decreases of 10–20 dbar over a few days at three sites where basal marine ice growth is expected. We attribute these events to flotation due to platelet ice accretion on the instrument moorings. Some events were transient, rapidly returning to pre-event pressures, probably through dislodgement of loosely attached crystals. Driven by these pressure changes, temperatures recorded by the shallowest instruments (within 20 m of the shelf base) tracked in situ freezing temperatures during the events. These observations provide indirect evidence for the presence of frazil ice in the sub-ice-shelf mixed layer and for active marine ice accretion. At one site we infer that a dense layer of platelet ice ˜1.5 m thick was accreted to the ice shelf over a 50 day period. Following some permanent abrupt pressure decreases (which we interpret as due to the lodgement of the uppermost instrument at the ice-shelf base), altered background trends in pressure suggest compaction rates of 3–4 m a–1 for the accreted basal platelet layer. Attachment of platelet ice and resulting displacement of moorings has ramifications for project design and instrument deployment, and implications for interpretation of oceanographic data from sub-ice-shelf environments.

[1] Marine ice is an important factor in ice shelf stability. An extensive marine ice layer is present under the Amery Ice Shelf (AIS), East Antarctica. This paper documents observations on the seasonal variability of the AIS-ocean interaction beneath the marine ice layer. We focus on data collected during 2002 through a borehole at AM01, 100 km from the ice shelf calving front, and use additional data from two other boreholes to complement the study. At AM01, the top ∼20 m of the water column is super-cooled almost year round, protecting the marine ice layer and promoting frazil ice formation. The mixed layer thickness varies from ∼50 m in February to at least 160 m by June, as the water column cools and freshens. High Salinity Shelf Water (HSSW) abruptly arrives at AM01 in June–August as an eddy-like flow. We suggest that the flow characteristics are a result of baroclinic instabilities. In addition, the inflow of HSSW results in a steepening of the isopycnals that enhances the upwelling of Ice Shelf Water. This study documents, for the first time, a seasonal signal in the formation of marine ice under the AIS. Our results highlight the vulnerability of the marine ice layer to ocean variability with potential consequences for the overall ice shelf mass balance.

Antarctic Bottom Water fills much of the global abyssal ocean, and is known to form in three main sites in the Southern Ocean. Data from instrumented elephant seals and moorings suggest an additional source of bottom-water formation in the Cape Darnley polynya that is driven by sea-ice production.

A fourth production region for the globally important Antarctic bottom water has been attributed to dense shelf water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011–2013 that provide the first complete assessment of dense shelf water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf water (salinity 34.65–34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley bottom water. Elsewhere, dense water formation is hindered by the freshwater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic bottom water to increased freshwater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic bottom water formation in a warming climate., Antarctic bottom water (AABW) production is critical to the global ocean overturning circulation. Here, the authors show new observations of AABW formation from seal CTD data in Prydz Bay, East Antarctica that highlights its susceptibility to increased freshwater input from the melting of ice shelves.

Despite the Amery Ice Shelf (AIS) being the third largest ice shelf in Antarctica, the seasonal variability of the physical processes involved in the AIS-ocean interaction remains undocumented and a robust observational, oceanographic-based basal melt rate estimate has been lacking. Here we use year-long time series of water column temperature, salinity, and horizontal velocities measured along the ice shelf front from 2001 to 2002. Our results show strong zonal variations in the distribution of water masses along the ice shelf front: modified Circumpolar Deep Water (mCDW) arrives in the east, while in the west, Ice Shelf Water (ISW) and Dense Shelf Water (DSW) formed in the Mackenzie polynya dominate the water column. Baroclinic eddies, formed during winter deep convection (down to 1100 m), drive the inflow of DSW into the ice shelf cavity. Our net basal melt rate estimate is 57.4 ± 25.3 Gt yr−1 (1 ± 0.4 m yr−1), larger than previous modeling-based and glaciological-based estimates, and results from the inflow of DSW (0.52 ± 0.38 Sv; 1 Sv = 106 m3 s−1) and mCDW (0.22 ± 0.06 Sv) into the cavity. Our results highlight the role of the Mackenzie polynya in the seasonal exchange of water masses across the ice shelf front, and the role of the ISW in controlling the formation rate and thermohaline properties of DSW. These two processes directly impact on the ice shelf mass balance, and on the contribution of DSW/ISW to the formation of Antarctic Bottom Water.

In the Southern Ocean, wide-ranging predators offer the opportunity to quantify how animals respond to differences in the environment because their behavior and population trends are an integrated signal of prevailing conditions within multiple marine habitats. Southern elephant seals in particular, can provide useful insights due to their circumpolar distribution, their long and distant migrations and their performance of extended bouts of deep diving. Furthermore, across their range, elephant seal populations have very different population trends. In this study, we present a data set from the International Polar Year project; Marine Mammals Exploring the Oceans Pole to Pole for southern elephant seals, in which a large number of instruments (N = 287) deployed on animals, encompassing a broad circum-Antarctic geographic extent, collected in situ ocean data and at-sea foraging metrics that explicitly link foraging behavior and habitat structure in time and space. Broadly speaking, the seals foraged in two habitats, the relatively shallow waters of the Antarctic continental shelf and the Kerguelen Plateau and deep open water regions. Animals of both sexes were more likely to exhibit area-restricted search (ARS) behavior rather than transit in shelf habitats. While Antarctic shelf waters can be regarded as prime habitat for both sexes, female seals tend to move northwards with the advance of sea ice in the late autumn or early winter. The water masses used by the seals also influenced their behavioral mode, with female ARS behavior being most likely in modified Circumpolar Deepwater or northerly Modified Shelf Water, both of which tend to be associated with the outer reaches of the Antarctic Continental Shelf. The combined effects of (1) the differing habitat quality, (2) differing responses to encroaching ice as the winter progresses among colonies, (3) differing distances between breeding and haul-out sites and high quality habitats, and (4) differing long-term regional trends in sea ice extent can explain the differing population trends observed among elephant seal colonies. Publisher PDF

The subduction and export of subantarctic mode water (SAMW) as part of the overturning circulation play an important role in global heat, freshwater, carbon and nutrient budgets. Here, the spatial distribution and export of SAMW is investigated using Argo profiles and a climatology. SAMW is identified by a dynamical tracer: a minimum in potential vorticity. We have found that SAMW consists of several modes with distinct properties in each oceanic basin. This conflicts with the previous view of SAMW as a continuous water mass that gradually cools and freshens to the east. The circulation paths of SAMW were determined using (modified) Montgomery streamlines on the density surfaces corresponding with potential vorticity minima. The distribution of the potential vorticity minima revealed “hotspots” where the different SAMW modes subduct north of the Subantarctic Front. The subducted SAMWs follow narrow export pathways into the subtropical gyres influenced by topography. The export of warmer, saltier modes in these “hotspots” contributes to the circumpolar evolution of mode water properties toward cooler, fresher and denser modes in the east.

[1] Four repeat hydrographic sections across the eastern Weddell gyre at 30°E reveal a warming (by ~0.1°C) and lightening (by ~0.02–0.03 kg m−3) of the Antarctic Bottom Water (AABW) entering the gyre from the Indian sector of the Southern Ocean between the mid-1990s and late 2000s. Historical hydrographic and altimetric measurements in the region suggest that the most likely explanation for the change is increased entrainment of warmer mid-depth Circumpolar Deep Water by cascading shelf water plumes close to Cape Darnley, where the Indian-sourced AABW entering the Weddell gyre from the east is ventilated. This change in entrainment is associated with a concurrent southward shift of the Antarctic Circumpolar Current's (ACC) southern boundary in the region. This mechanism of AABW warming may affect wherever the ACC flows close to Antarctica.

Subantarctic Mode Water (SAMW) is formed by deep mixing on the equatorward side of the Antarctic Circumpolar Current. The subduction and export of SAMW from the Southern Ocean play an important role in global heat, freshwater, carbon, and nutrient budgets. However, the formation process and variability of SAMW remain poorly understood, largely because of a lack of observations. To determine the temporal variability of SAMW in the Australian sector of the Southern Ocean, we used a 15 year time series of repeat expendable bathythermograph sections from 1993 to 2007, seven repeat conductivity-temperature-depth sections from 1991 to 2001, and sea surface height maps. The mean temperature of the SAMW lies between 8.5 degrees C and 9.5 degrees C (mean of 8.8 degrees C, standard deviation of 0.3 degrees C), and there is no evidence of a trend over the 18 year record. However, the temperature, salinity, and pycnostad strength of the SAMW can change abruptly from section to section. In addition, the SAMW pool on a single section often consists of two or more modes with distinct temperature, salinity, and vertical homogeneity characteristics but similar density. We show that the multiple types of mode water can be explained by the advection of anomalous water from eddies and meanders of the fronts bounding the Subantarctic Zone and by recirculation of SAMW of different ages. Our results suggest that infrequently repeated sections can potentially produce misleading results because of aliasing of high interannual variability.

Sea level rise is one of many expected consequences of climate change, with accompanying complex social and economic challenges. Major uncertainties in sea level rise projections relate to the response of ice sheets to sea level rise and the key role that interactions with the ocean may play. Recognizing that probably no comprehensive curriculum currently exists at any single university that covers this novel and interdisciplinary subject, the Advanced Climate Dynamics Courses (ACDC) team brought together a group of 40 international students, postdocs, and lecturers from diverse backgrounds to provide an overview and discussion of state-of-the-art research into ocean—ice sheet interactions and to propose research priorities for the next decade. Among the key issues addressed were small-scale processes near the Antarctic ice shelves and Greenland outlet glaciers. These are fast changing components in the climate system, often related to large-scale forcings (atmospheric teleconnections and oceanic circulation). Progress in understanding and modeling is hampered by the range of scales involved, the lack of observations, and the difficulties in constraining, initializing, and providing adequate boundary conditions for ice sheet and ocean models.