The reason previous studies could not answer this question is technical as much as scientific. Most global climate models do not include an interactive Antarctic Ice Sheet; instead, they prescribe where and how much ice flows into the ocean, which means they cannot capture the slow, centennial-to-millennial feedbacks between ocean temperatures and ice dynamics. Höse and her team broke new ground by coupling the CM2Mc Earth system model, developed at the Geophysical Fluid Dynamics Laboratory and modified at Potsdam, to the Parallel Ice Sheet Model, or PISM, which simulates the entire Antarctic Ice Sheet at a horizontal resolution of 16 kilometers. The two models exchange information through the Potsdam Ice-shelf Cavity model, known as PICO, which calculates how fast ice melts from below based on the temperature and salinity of water entering 19 Antarctic drainage basins. Crucially, the meltwater and heat released by the ice sheet are fed back into the ocean model, closing the loop between the two components.

To force an AMOC collapse, the team followed the protocol of the North Atlantic Hosing Model Intercomparison Project, adding artificial freshwater at a rate of 0.3 Sverdrups, roughly 300,000 cubic meters per second, to the surface of the North Atlantic and Arctic Oceans. This deluge of freshwater stratifies the subpolar North Atlantic, suppressing the deep convection that drives the overturning circulation. Within 100 years, the simulated AMOC weakened from about 21.5 Sverdrups to just 5 Sverdrups, a state the researchers treat as a collapse. They then let the coupled model run for another 1,400 years, long enough for the deep ocean and the ice sheet to respond on their own sluggish timescales, while a parallel control run without freshwater forcing provided a baseline against which every anomaly could be measured.

The immediate consequences of the collapse matched what earlier modeling work had established. Northern Hemisphere surface temperatures dropped sharply, by up to 9 degrees Celsius over the North Atlantic, while the Southern Hemisphere warmed as the oceanic heat transport reversed its imbalance. The Intertropical Convergence Zone shifted southward, the mid-latitude westerly winds over the Southern Ocean strengthened, and the Antarctic Circumpolar Current intensified by roughly 20 Sverdrups. Heat accumulated in the subsurface South Atlantic north of 40 degrees south, exactly as the bipolar seesaw theory, developed to explain the antiphased temperature oscillations recorded in Greenland and Antarctic ice cores, would predict. On the surface, then, everything pointed toward trouble for Antarctica.

But the surface is not where the ice sheet lives. What matters for basal melting, the erosion of ice shelves from below, is the temperature of water at depths of 500 to 1,000 meters, near the cavities beneath floating ice. And here the simulation delivered its first counterintuitive finding: for the first eight centuries after the AMOC collapse, subsurface temperatures along most of the Antarctic margin did not warm at all. In fact, they cooled slightly, by around 0.15 degrees Celsius on average, because residual North Atlantic Deep Water, chilled by the collapsed overturning, was carried southward and upwelled near the continent before being swept around the coast by the Circumpolar Current. As a result, basal melt rates actually declined, by up to 100 gigatonnes per year in some periods, and the total Antarctic ice volume barely changed, remaining within the range of natural variability seen in the control run.

The story took another turn around model year 830, when the Southern Ocean underwent a dramatic regime shift. Deep convection, the vertical mixing of the water column, intensified in the Ross Sea and later spread to coastal regions east of the Weddell Sea, releasing centuries of accumulated heat from the deep ocean to the surface. Antarctic Bottom Water formation surged by more than 10 Sverdrups, maximum sea ice extent abruptly shrank by about 40 percent, and sea surface temperatures around the continent rose roughly four times more than they had in the immediate aftermath of the AMOC collapse. Yet paradoxically, this convective heat release cooled the subsurface waters at ice-shelf cavity depths, producing average negative temperature anomalies of 1.4 degrees Celsius along the continental slope. Basal melting dropped further, with a mean decline of 160 gigatonnes per year, and ice shelves grew thicker.

Herein lies the elegant compensating mechanism that kept the ice sheet stable. As reduced basal melting allowed the ice shelves to expand, their calving fronts extended into deeper water and became more prone to fracturing, so the calving flux increased by an average of 170 gigatonnes per year, almost exactly offsetting the reduction in melt. The net change in sea-level-rise potential after 1,500 years was a decrease of only about 2.5 centimeters, a trivial amount compared with the several meters locked in the West Antarctic Ice Sheet. The authors conclude that the widely assumed positive feedback, in which an AMOC shutdown destabilizes Antarctica through surface warming, is not supported when the full ocean-ice interaction is simulated: it is the subsurface temperature at cavity depths, not the sea surface temperature, that governs the ice sheet’s fate.

The researchers are careful to spell out the limitations of their approach. The coupling between the climate and ice-sheet models is restricted to the ocean-ice interface, so atmospheric changes over Antarctica, including warming of 0.5 to 5 degrees Celsius and increased coastal precipitation, were not transmitted to the ice sheet surface. The artificial freshwater hosing, maintained continuously for 1,500 years, freshened the global ocean without compensation, an amount of water roughly seven times the current freshwater flux from Greenland, and the coarse ocean model does not resolve the Antarctic continental shelf, so bottom water forms through open-ocean convection rather than shelf processes, a known bias shared by about 80 percent of CMIP6 models. The timing of the convective regime shift, and therefore of the subsurface cooling, may also be model-specific, and the authors emphasize that repeating the experiment with other coupled models is essential before general conclusions can be drawn.

Nevertheless, the study marks a milestone: the first freshwater hosing experiment ever conducted with an interactively coupled climate-ice sheet model capable of resolving the millennial response of Antarctica. Its message cuts both ways for the climate conversation. On one hand, it suggests that a collapsing AMOC would not, at least through the ocean pathway alone, immediately push the West Antarctic Ice Sheet over its tipping point, which previous work places at an oceanic warming of about 1.5 degrees Celsius above preindustrial levels. On the other hand, it warns that simple assumptions about tipping cascades, in which one tipping element triggers another through a single variable such as sea surface temperature, may be dangerously oversimplified in a system where deep convection can invert the sign of a temperature anomaly within a few centuries. As freshwater pours from Greenland and Antarctic ice shelves melt at accelerating rates, understanding these cross-hemispheric connections has never mattered more, and this first coupled glimpse suggests the true dynamics are far stranger than the seesaw metaphor implies.

Subject of Research: The impact of an AMOC collapse on the stability of the Antarctic Ice Sheet simulated with a coupled climate-ice sheet model

Article Title: Simulating the impact of an AMOC weakening on the Antarctic Ice Sheet using a coupled climate and ice-sheet model

Article References: Höse, A., Kreuzer, M., Huiskamp, W., Petri, S., & Feulner, G. (2026). Simulating the impact of an AMOC weakening on the Antarctic Ice Sheet using a coupled climate and ice-sheet model. Earth System Dynamics, 17(4), 1025-1059. https://doi.org/10.5194/esd-17-1025-2026

Image Credits: AI Generated

DOI: 10.5194/esd-17-1025-2026

Keywords: AMOC, Antarctic Ice Sheet, climate tipping points, bipolar seesaw, Southern Ocean, ice sheet modeling, basal melt, Antarctic Bottom Water, deep convection, sea level rise, PISM, freshwater hosing

The stakes are considerable. Antarctic Bottom Water forms when dense shelf water, chilled by contact with Antarctic air and ice, spills off the continental shelf around Antarctica, plunging down the slope and mixing with overlying deep water. In the Weddell Sea, this process produces Weddell Sea Deep Water and the even colder Weddell Sea Bottom Water. The deep water overflows the South Scotia Ridge into the Scotia Sea, threads through passages around South Georgia, and pools in the Argentine Basin, where its core properties hover near a potential temperature of −0.10 °C and a salinity of 34.67. From there, the only significant exit toward the equator is the Vema Channel, a narrow, deep trench near 31° S that funnels the coldest bottom water into the Brazil Basin and, eventually, toward the North Atlantic. Every link in this chain matters for the Atlantic Meridional Overturning Circulation, yet direct observations of the abyssal limb remain sparse, limited to a handful of trans-basin moored arrays and repeated shipboard sections.

That observational scarcity is precisely why ocean models and reanalyses carry so much weight. Reanalyses such as ECCO, SODA, and GLORYS blend observations into a numerical simulation to produce a continuous picture of the ocean, while forward models like OFES evolve freely under prescribed atmospheric forcing. Santos and his colleagues began by auditing four such products against the World Ocean Atlas 2018 climatology and against in situ measurements, including thirteen years of conductivity–temperature–depth casts along the SAMBA-West line at 34.5° S and temperature records from three moorings deployed within the Vema Channel. The verdict was sobering. All four simulations broadly captured the large-scale distribution of abyssal water masses, but each displayed persistent warm biases in the deep ocean, and none clearly reproduced the cascading of dense shelf water down the Antarctic continental slope. Most tellingly, all of them showed a discontinuity in abyssal properties between the Argentine and Brazil Basins, as if the cold water simply failed to make it through the Vema Channel.

The temperature–salinity diagrams told the story in stark terms. In the Argentine Basin, the reference climatology shows a well-defined curve extending to waters colder than −0.5 °C. In the Brazil Basin, that curve shifts toward warmer, lighter values, because sills along the Vema Channel block the coldest water and mixing erodes what passes through. The models, however, exaggerated this transition artificially. ECCO, SODA, and OFES shifted their entire deep temperature–salinity curves toward lighter densities north of the channel, while GLORYS lost a striking fraction of its densest water classes. In the channel itself, the picture was even worse: ECCO represented the passage with a single column of grid points, SODA contained no points there at all, and even the higher-resolution products misaligned, widened, or shallowed the trench, leaving no water colder than 0.0 °C inside it.

Because the four simulations differed in so many respects—atmospheric forcing, data assimilation schemes, bathymetry, and sea-ice representation—the intercomparison alone could not pin the blame on any single culprit. So the team turned to the Finite-volumE Sea ice–Ocean Model, FESOM 2, an unstructured-mesh model developed at the Alfred Wegener Institute that is at least nine times faster than its finite-element predecessor. They built a reference configuration, FESOM R, designed to mimic the vertical grid of OFES, with 105 vertical levels and horizontal spacing of about 30 kilometers over most of the globe, refined to 10 kilometers in the South Atlantic. Then they ran three targeted variants, changing nothing else: FESOM V added twenty vertical levels concentrated between 3800 and 5350 meters, bringing the spacing near the seafloor down to roughly 50 meters; FESOM H refined the horizontal grid to 7.5 kilometers in the South Atlantic and 4 kilometers around the Vema Channel; and FESOM VH combined both refinements.

The results were unambiguous. FESOM V, the vertically refined experiment, delivered the largest basin-scale improvement. Cold waters below −0.7 °C spread across a broader swath of the central Weddell Sea, waters at or below 0.0 °C filled the entire Argentine Basin, and a colder class of bottom water finally flowed through the Vema Channel into the Brazil Basin. The warm bias that plagued every configuration shrank and became spatially uniform, without the abrupt basin-to-basin discontinuities seen in the reference run. The density evolution of the deep basins also became more coherent: in FESOM R and FESOM H, entire density classes of abyssal water vanished from the Argentine and Brazil Basins within decades of the simulation, whereas the vertically refined runs retained them. The mechanism is physical rather than numerical sleight of hand. Colder abyssal layers extend upward through the lower water column, allowing the coldest water to reach the depth of the Vema Channel sill and spill northward, instead of being trapped below the deepest model level connected through the passage.

FESOM H, by contrast, was the weakest performer of the four. Refining the horizontal grid alone produced warmer abyssal layers, erased the coldest waters from the central Weddell Sea, and left the Argentine Basin without any water below 0.0 °C. The likely explanation lies in the delicate balance between resolved and parameterized turbulence. The Gent–McWilliams eddy parameterization, which stands in for mesoscale eddies the model cannot explicitly resolve, scales its diffusivity with grid spacing. When the grid becomes fine enough to partially resolve eddies but the parameterization is not retuned, the model can end up double-counting eddy effects, distorting the very mixing that shapes abyssal water masses. The authors caution that this interpretation remains speculative, since they deliberately kept all parameterizations unchanged to isolate the effect of resolution, but the lesson is clear: horizontal refinement without recalibration of mixing schemes can be actively harmful in the deep ocean.

The combined experiment, FESOM VH, offered a more nuanced picture. At the basin scale it did not outperform vertical refinement alone, and its abyssal waters ran slightly warmer than FESOM V’s. But in the Vema Channel it achieved something no other configuration could: a realistic representation of the channel’s geometry, complete with a cold bottom-intensified core deflected toward the eastern wall. That eastward deflection is a genuine dynamical feature, attributed to Ekman transport driven by bottom friction, and it is consistently observed in moored measurements and regional simulations of Antarctic Bottom Water flow. Capturing it required sufficient resolution in both dimensions—vertical refinement to cool the water column and horizontal refinement to resolve the narrow trench—demonstrating that the two grid directions play complementary roles.

Comparisons with the moorings and CTD stations reinforced the hierarchy. Across three historical mooring periods in the Vema Channel, the vertically refined configurations FESOM V and FESOM VH systematically reduced warm biases and reproduced the observed variability more faithfully, while FESOM H consistently produced the largest warm biases. Along the SAMBA-West line, FESOM V again provided the closest match to observed mean temperatures at Sites C and D, though all configurations overestimated the observed warming trend. Correlations with individual mooring time series remained modest across the board, a reminder that even a well-resolved global model cannot be expected to nail phase agreement at single points in the abyss. What vertical resolution reliably controls is the mean state and variance of deep temperature—the very quantities that determine whether cold bottom water survives its journey across bathymetric barriers.

The implications reach well beyond the South Atlantic. Global ocean models feed climate projections, sea-level estimates, and carbon budgets, and the abyssal ocean absorbs a substantial share of the excess heat that the climate system accumulates. If the deep thermal structure is systematically too warm because the vertical grid is too coarse, those biases propagate into every downstream product. Previous studies had hinted that enhanced vertical resolution improves the representation of dense water masses and baroclinic modes, but this study provides an unusually clean demonstration, holding everything constant except the grid. Its message to model developers is direct: before spending scarce computing resources on ever-finer horizontal meshes, invest in the vertical grid near the seafloor, and when horizontal resolution does increase, retune the mixing parameterizations that quietly govern the deep ocean. The coldest waters on the planet, it turns out, live or die in the last fifty meters of a model’s water column.

Subject of Research: The effect of horizontal and vertical grid resolution on the representation of Antarctic Bottom Water and abyssal ocean properties in global numerical ocean models

Article Title: Impact of grid resolution on the abyssal ocean representation in numerical models

Article References: Santos, D. M. C., Van Caspel, M., Timmermann, R., & Sato, O. T. (2026). Impact of grid resolution on the abyssal ocean representation in numerical models. Ocean Science, 22(5), 3079-3104. https://doi.org/10.5194/os-22-3079-2026

Image Credits: AI Generated

DOI: 10.5194/os-22-3079-2026

Keywords: Antarctic Bottom Water, ocean modeling, grid resolution, FESOM 2, Vema Channel, Weddell Sea, Atlantic Meridional Overturning Circulation, abyssal ocean, ocean reanalysis, vertical resolution, Argentine Basin, deep ocean warming

The scale of sea ice’s fingerprints on the Southern Ocean is staggering. The annual freeze-melt cycle moves more freshwater than precipitation minus evaporation and glacial melt combined, and it does so across a zone where the atmosphere and deep ocean exchange heat, salt and carbon. During the Last Glacial Maximum, roughly 19,000 to 23,000 years ago, winter sea ice expanded to approximately twice its modern extent while sea surface temperatures ran about 3.9 degrees Celsius colder than today. Conversely, during the last interglacial around 130,000 to 116,000 years ago, ice core records suggest winter sea ice contracted by as much as 36 percent relative to the Holocene, with models indicating reductions of 40 to 60 percent. These two climate states — one much icier, one much warmer — provide natural experiments for testing how sea ice couples to the rest of the planet.

The first and perhaps most fundamental coupling involves ocean circulation. Deep water from the world’s basins, collectively known as Circumpolar Deep Water, upwells in the Southern Ocean and splits into two branches. The northern branch is freshened by sea-ice melt and subducts to form Antarctic Intermediate Water, while the southern branch loses buoyancy through cooling and brine rejection during ice formation, ultimately producing the dense Antarctic Bottom Water that ventilates the abyss. Proxy evidence shows that during glacial periods Antarctic Intermediate Water shoaled in the southwest Pacific, consistent with expanded sea ice, while the deep Atlantic was filled to a greater volume by poorly ventilated southern-sourced water. Intriguingly, manganese peaks in sediments offshore major bottom-water production sites suggest that the rate of Antarctic Bottom Water formation may actually have been lower during the Last Glacial Maximum, even as its volume expanded — a paradox that highlights how much remains unknown.

Sea ice also acts as a physical guardian of the Antarctic ice sheet itself. A sea-ice barrier dampens ocean swell that would otherwise batter ice shelf fronts, and landfast ice can bond the debris-laden melange that stabilises calving glacier fronts. The disintegration of ice shelves over recent decades, driven by warm currents and rising air temperatures, has drawn attention to this protective role because ice shelves buttress the grounded glaciers behind them and thus regulate sea level rise. The review documents a darker feedback loop: declining summer sea ice exposes ocean surfaces to solar heating, and that warmed water can be advected beneath ice shelves, accelerating basal melt. Reduced winter ice formation likewise weakens stratification in ways that allow warm Circumpolar Deep Water to intrude onto the shelf. In the paleo record, a mid-Holocene expansion of sea ice off Wilkes Land has even been linked to the retreat of the Ross Sea grounding line, whose meltwater outflow cooled downstream waters and promoted ice growth downstream.

The atmosphere is not spared. Sea ice sits directly beneath the polar frontal zone, so even modest shifts in its edge can reorganise atmospheric circulation. Most modelling studies find that shrinking sea ice weakens and shifts the Southern Hemisphere westerly winds equatorward, because a warmer polar region flattens the temperature gradient that drives the jet. This sea-ice effect runs opposite to the poleward wind shift expected from greenhouse warming itself, meaning the two influences partially offset each other. So-called ghost flux experiments, which inject artificial heat fluxes to isolate sea-ice impacts, reveal responses that ripple pole to pole — warming the Antarctic interior, altering katabatic winds, slowing the Antarctic Circumpolar Current, warming equatorial Pacific sea surface temperatures and even thinning Arctic sea ice.

Yet the paleo evidence complicates this tidy picture. Reconstructions of past winds suggest that during the last deglaciation the westerlies shifted poleward by more than four degrees of latitude — more than any model predicts — implying that the sea-ice effect on winds may be overcompensating in simulations. Even more strikingly, millennial-scale Antarctic warming events recorded in ice cores show abrupt sea-ice declines that were not matched by corresponding wind shifts; instead, the winds responded to Northern Hemisphere warming. The review concludes that over millennial timescales, the direct influence of sea ice on atmospheric circulation appears to be a second-order process compared with other climate feedbacks — a humbling result for a variable often assumed to be climatically dominant.

Biology adds another layer of complexity. Sea ice structures Southern Ocean ecosystems into distinct zones, seeding phytoplankton blooms at the retreating ice edge and releasing a springtime pulse of iron that triggers algal growth. Sea ice hosts its own microbial communities, and its melt releases dimethyl sulphide, a sulphur compound that seeds cloud formation and influences albedo. But the glacial record delivers conflicting messages. Sediment cores south of the Antarctic Polar Front show lower productivity during ice ages, which might seem like straightforward light limitation under expanded ice. Yet nitrogen isotope data reveal more complete nutrient consumption during glacials — the opposite of what light limitation would produce. The proxies instead point to reduced upwelling of nitrate-rich deep water, meaning sea ice influenced productivity indirectly through stratification and circulation rather than simply by blocking sunlight.

The carbon cycle is where the stakes are highest. Sea ice caps the ocean, suppressing the release of carbon dioxide from carbon-rich deep waters that upwell in the Southern Ocean. Early box models suggested this capping alone could explain the roughly 80 parts per million drop in glacial atmospheric CO2, but subsequent work showed the mechanism requires implausibly permanent ice cover and is offset by reduced biological uptake. The emerging consensus is subtler: sea ice matters most when it acts in concert with circulation changes. Idealised models show that atmospheric cooling can lower CO2 by about 40 parts per million, but only because expanded ice forces upwelling carbon-rich water to reach the surface beneath the ice, where gas exchange is suppressed — a strengthening of the so-called disequilibrium pump. Proxy timing supports this coupling: during the glacial inception around 115,000 years ago, Antarctic temperatures and sea ice shifted roughly 3,000 years before CO2 began to fall, suggesting that sea ice alone cannot drive atmospheric carbon change without accompanying circulation reorganisation.

The review’s most sobering conclusion is that the relationships are bidirectional, state-dependent and incompletely captured by models. Most global ocean models cannot resolve the coastal polynyas where dense shelf water forms today, instead representing bottom-water formation as an open-ocean process. Summer sea-ice extent during glacial periods remains poorly constrained, and no sediment records exist south of the current summer ice limit. If the net effect of Antarctic sea ice is to enhance ocean carbon storage, its ongoing decline could weaken the ocean’s sink for anthropogenic carbon and shrink humanity’s remaining carbon budget. The past 130,000 years show that sea ice has repeatedly coordinated sweeping changes across the cryosphere, atmosphere, ocean and biosphere — and that understanding its demise requires reading the deep archive of Earth’s climate history with far greater resolution than we currently possess.

Subject of Research: The role of Antarctic sea ice in ocean circulation, ice shelves, atmospheric circulation, marine productivity and the carbon cycle over the past 130,000 years

Article Title: Antarctic sea ice over the past 130 000 years – Part 2: A review of its role in the Earth system

Article References: Antarctic sea ice over the past 130 000 years – Part 2: A review of its role in the Earth system. (n.d.). https://doi.org/10.5194/cp-22-1881-2026

Image Credits: AI Generated

DOI: 10.5194/cp-22-1881-2026

Keywords: Antarctic sea ice, Southern Ocean, paleoclimate, Last Glacial Maximum, last interglacial, ocean circulation, Antarctic Bottom Water, ice shelves, carbon cycle, atmospheric CO2, westerly winds, climate models

The basin’s vulnerability stems from its bathymetry. Much of the bedrock beneath the Wilkes Subglacial Basin sits below sea level and deepens inland, a configuration known as a retrograde bed slope. That geometry is the essential ingredient for what glaciologists call marine ice-sheet instability. When the grounding line, the boundary where grounded ice begins to float, retreats onto such a slope, the ice at the grounding line becomes progressively thicker, increasing the outward flux of ice and driving further retreat. The result is a positive feedback that can continue even if the climate forcing that triggered it stabilises. Classic theoretical work on grounding-line dynamics, notably the stability analysis published by Christian Schoof in 2007, formalised this behaviour, and the Wilkes Subglacial Basin is now recognised as one of the largest marine-grounded basins in East Antarctica where the feedback could operate at scale.

The review’s synthesis of palaeoclimate evidence is perhaps its most striking element. Marine sediment cores recovered from the continental shelf offshore Wilkes Land, together with ice-sheet model simulations, indicate that substantial retreat of the basin’s ice occurred during past warm periods, most notably during the Pliocene epoch roughly three to five million years ago, when atmospheric carbon dioxide concentrations were comparable to today’s. Geochemical proxies in deep-sea sediments record deglacial events with clear biogeochemical responses downstream of the basin, and iceberg-rafted debris in Southern Ocean sediments testifies to episodes of enhanced ice discharge. Model reconstructions of specific Pleistocene interglacials, including Marine Isotope Stages 31, 11 and 5e, suggest repeated episodes of ice loss from the basin, although the review is careful to note that the precise temperature thresholds at which such retreat was triggered remain uncertain.

That uncertainty matters because it bears directly on the question of commitment. If the basin retreated substantially during interglacials only modestly warmer than the pre-industrial climate, then the margin of safety under current warming trajectories may be thin. Recent analyses of Pliocene sea level, drawing on geographically diverse geological archives, imply global mean sea levels several metres above present during that epoch, and the Wilkes Subglacial Basin is one of the few sectors of East Antarctica with sufficient ice volume to account for a meaningful share of that rise. The review’s authors, an international team led by Matt King of the University of Tasmania and including specialists spanning glaciology, oceanography, geophysics and palaeoceanography, argue that reconciling sedimentary archives with model simulations is essential to pin down how much warming the basin can absorb before retreat becomes self-sustaining.

Observations of the present-day ice sheet add a further layer of concern. Satellite altimetry, gravimetry and interferometric synthetic aperture radar measurements reveal multidecadal retreat of the grounding line in parts of the Wilkes Land sector, along with thinning and, in places, collapse of key fringing ice shelves. The Cook Ice Shelf and the Ninnis and Mertz glacier systems, which drain large portions of the basin, have shown measurable change, including velocity increases at Cook Glacier linked to ice-shelf loss and a documented subglacial flood event. Intriguingly, the review highlights that this retreat has not yet been accompanied by clear upstream surface lowering across the basin interior, leaving the ultimate cause of the observed changes unattributed. Whether the signal reflects ocean-driven melt at the ice front, atmospheric variability, or internal ice-sheet dynamics remains an open and pressing question.

The oceanographic context is shifting in ways that favour further change. Relatively warm, salty circumpolar deep water, which can melt ice shelves from below, has been shifting poleward in the Australian-Antarctic sector, increasing the risk of warm-water intrusions onto the continental shelf through the deep glacial troughs that dissect the Wilkes Land margin. At the same time, meltwater from Antarctic ice shelves is freshening the surface ocean, suppressing the formation of dense Antarctic bottom water that drives global deep-ocean circulation. Recent studies have documented reduced abyssal overturning and ventilation in the Australian-Antarctic Basin, and modelling suggests that sustained Antarctic meltwater release could slow the abyssal ocean’s overturning circulation within decades. A major retreat of the Wilkes Subglacial Basin would amplify this meltwater flux, with consequences that ripple through ocean circulation, carbon cycling and marine ecosystems far beyond the Southern Ocean.

Projections of the basin’s future under different emissions scenarios reveal the potential speed of change. Ice-sheet model simulations indicate that, once the grounding line retreats beyond key bedrock pinning points, retreat rates of up to roughly one kilometre per year are possible, an extraordinary pace for a continental ice sheet. The timing of such events is deeply uncertain, but the review stresses a more troubling point: decisions taken this century, in effect the emissions pathway the world follows over the coming decades, may commit the basin to multimillennial change. Because the retreat feedback operates on timescales far longer than human political and economic planning horizons, the full sea-level consequences of near-term warming would unfold over centuries to millennia, locking in losses that later mitigation cannot reverse. Sea-level feedbacks, including the gravitational and solid-Earth responses to changing ice load, modulate but do not eliminate this risk.

The review also identifies the processes that remain poorly constrained and that dominate projection uncertainty. Subglacial hydrology is one: the basin sits atop thick sedimentary sequences, and groundwater systems beneath the ice can amplify sliding and mass loss through basal water feedbacks. Geothermal heat flux, which softens the ice base and feeds subglacial lakes and drainage networks, is poorly mapped across the region. The stability of fringing ice shelves, which buttress upstream flow, depends on basal melt rates, calving dynamics and the protective role of land-fast sea ice, all of which are changing. Surface melt and meltwater ponding, historically rare in East Antarctica, are becoming more sensitive to atmospheric warming, raising the possibility of hydrofracturing-driven ice-shelf disintegration analogous to events observed on the Antarctic Peninsula. Improving the representation of these processes in ice-sheet models, and grounding them in field observations, is central to narrowing the spread of sea-level projections.

The authors’ prescription is unambiguous: a coordinated, multinational and multiyear programme of fieldwork and modelling focused specifically on the Wilkes Subglacial Basin. Such a programme would combine airborne geophysics to refine bed topography and subglacial geology, seismic surveys to characterise sediment properties and mantle structure, oceanographic moorings to monitor warm-water intrusions onto the shelf, sediment coring to extend the palaeo-archive, and targeted ice-core records to constrain past ice extent. It would also feed directly into model intercomparison efforts such as ISMIP6 and its successors, which currently struggle to agree on the basin’s response to given levels of warming. The review notes that planning for such coordinated fieldwork is already under way through international scientific committees, but the scale of the challenge, in one of the most remote and logistically demanding environments on Earth, demands sustained investment across multiple national Antarctic programmes.

What emerges from the synthesis is a picture of an ice sheet sector that is neither doomed imminently nor safely stable, but poised in a state whose trajectory depends on choices made now. The Wilkes Subglacial Basin has retreated before under natural warmth, its fringing ice is already showing signs of stress, and the ocean around it is warming and freshening in ways that erode its natural defences. With three to four metres of potential sea-level rise at stake, alongside far-reaching consequences for ocean circulation and Southern Ocean ecosystems, the basin has moved from a scientific curiosity to a first-order question for climate policy. The review’s central message is that the window for reducing uncertainty through observation is open, but narrowing, and that understanding this sleeping giant of East Antarctica is no longer optional.

Subject of Research: Climate vulnerability and dynamic instability of the marine-based Wilkes Subglacial Basin Ice Sheet in East Antarctica

Article Title: Dynamic instability of the Wilkes Subglacial Basin Ice Sheet, East Antarctica

Article References: King, M. A., Bertler, N. A. N., Anandakrishnan, S., Barruol, G., Bentley, M. J., Crosta, X., Christoffersen, P., Colleoni, F., De Santis, L., Escutia, C., Etourneau, J., Evangelinos, D., Ferraccioli, F., Golledge, N. R., Harris, M., Heil, P., Hill, N. A., Hodgson-Johnston, I., Hofstede, C., … Zhao, C. (2026). Dynamic instability of the Wilkes Subglacial Basin Ice Sheet, East Antarctica. Nature Reviews Earth & Environment. https://doi.org/10.1038/s43017-026-00827-6

Image Credits: AI Generated

DOI: 10.1038/s43017-026-00827-6

Keywords: Wilkes Subglacial Basin, East Antarctic Ice Sheet, marine ice-sheet instability, sea-level rise, grounding line retreat, ice shelves, circumpolar deep water, Pliocene, palaeoclimate, ice-sheet modelling, Antarctic bottom water, subglacial hydrology

Tracking glacial melt in the ocean is deceptively difficult. When ice shelves and glacier termini discharge freshwater, whether as basal melt from floating ice or as subglacial outflow at grounding lines, that water mixes almost immediately with ambient seawater. Oceanographers traditionally quantify the meltwater fraction using tracer-based calculations that require predefined source water types, known as end members. In the classic approach, an analyst assumes the ocean can be described as a mixture of a small number of pure inputs, for example warm deep water, winter-modified shelf water, and pure glacial melt, each with known temperature and salinity. The meltwater fraction is then inferred from the leftover properties that cannot be explained by the mixing of those assumed sources.

The problem is that the answers depend heavily on the choices made. Pick a different deep-water definition, adjust the salinity of the meltwater end member, or allow a glacial ice end member in addition to liquid melt, and the estimated freshwater fractions can shift substantially. In regions with complex hydrography, where Antarctic Bottom Water formation, modified Circumpolar Deep Water intrusions, and seasonal sea-ice processes all compete to shape water properties, the ambiguity grows worse. East Antarctica, with its thousands of kilometers of ice front and sparse observations, has been especially vulnerable to these methodological uncertainties, leaving the meltwater budget of the region poorly constrained.

The new study sidesteps the end-member problem entirely. Rather than prescribing source water types and solving for their proportions, the researchers developed a parameterization that identifies glacier-derived freshwater directly from the structure of the hydrographic data itself. The technique exploits the fact that glacial melt alters temperature and salinity along characteristic lines in property space: because meltwater enters the ocean at the freezing point and carries negligible salt, its addition moves water masses in predictable directions in temperature-salinity coordinates. By parameterizing these trajectories without fixing the end points, the method estimates the freshwater contribution at every measured depth, producing not just a surface map but a three-dimensional reconstruction of the meltwater field.

The reconstruction is built from the vast archive of hydrographic observations collected across the East Antarctic shelf and slope, including conductivity-temperature-depth profiles, seal-mounted sensor data, and ship-based measurements gathered over multiple decades. Each profile is processed to separate the meltwater signal from other processes that also modify salinity, such as sea-ice formation and melting, precipitation, and the intrusion of off-shelf water masses. The end-member-independent framework then assembles these individual column estimates into a continuous three-dimensional field, resolved in longitude, latitude, and depth, that captures the horizontal pathways and vertical distribution of glacier-derived freshwater around the continent’s eastern half.

The resulting picture is striking. Meltwater is not distributed uniformly along the coast. Instead, the reconstruction shows concentrated lenses and layers of freshwater that accumulate at intermediate depths, typically well below the surface, where melt-laden water spreads neutrally according to its density. Along several major glacier systems, plumes of meltwater extend tens to hundreds of kilometers offshore, following the contours of shelf banks and canyon systems that steer the flow. In some locations the freshwater signal reaches the upper slope, hinting that glacial melt from East Antarctica may be exported into the broader Southern Ocean circulation rather than being trapped locally over the shelf, as older, two-dimensional assessments often implied.

These vertical details carry significant implications for ocean physics and climate. Freshwater stabilizes the water column by reducing surface density, which suppresses vertical mixing and can alter the formation of dense shelf waters that ultimately feed Antarctic Bottom Water, a key component of the global overturning circulation. By quantifying where melt accumulates at depth, the reconstruction allows scientists to test whether meltwater is interfering with bottom-water formation sites, potentially weakening the engine that ventilates the deep ocean and stores carbon and heat on centennial timescales. The three-dimensional view also provides essential validation data for ocean and coupled climate models, which historically have struggled to represent meltwater pathways realistically and often rely on crude runoff schemes at the ice-ocean boundary.

The methodological advance is as important as the observational findings. Because the parameterization does not require users to specify source water properties, it can be applied consistently across regions and through time, enabling fair comparisons between sectors of Antarctica and between different observational eras. Consistency is precisely what large-scale budget studies need: aggregating meltwater estimates produced with different end-member choices has been a persistent obstacle to constructing a continent-wide picture. An end-member-independent approach also reduces the risk of circular reasoning, in which assumptions about meltwater properties determine the meltwater fraction that is then used to infer melt rates. The authors show that their framework yields robust meltwater distributions under a range of environmental conditions, offering a template that can be transferred to other glacier-influenced seas.

For East Antarctica specifically, the study arrives at a pivotal moment. Long considered more stable than the marine-terminating glaciers of West Antarctica, the eastern ice sheet is increasingly showing signs of change, with warm modified deep water reaching the flanks of some major ice shelves and several basins identified as potential candidates for future accelerated retreat. A reliable reconstruction of where glacier-derived freshwater already enters the ocean provides both a baseline against which future change can be measured and a diagnostic of which systems are presently discharging melt at elevated rates. If meltwater export from the region strengthens, the three-dimensional fields produced by this method will help determine how quickly that signal propagates into the abyssal circulation.

The work also demonstrates how reanalysis of existing observations can yield new science without new expeditions. Decades of shipboard hydrography and the growing record of instrumented seals have created an underexploited treasure trove for the Southern Ocean; the challenge has been extracting subtle signals, like glacial freshwater, from noisy, unevenly sampled data. By turning a long-standing methodological weakness, the dependence on assumed source waters, into a solved problem, the researchers have converted scattered profiles into a coherent, multidimensional dataset of one of climate science’s most consequential tracers. As observations accumulate and parameterization techniques mature, the approach promises continuously updated maps of Antarctic meltwater, giving scientists and policymakers a clearer view of how the ice sheet, the ocean, and the global climate system are entangling beneath the surface of the far South.

Subject of Research: Three-dimensional mapping of glacier-derived freshwater in East Antarctic coastal waters using an end-member-independent hydrographic method

Article Title: Three-dimensional reconstruction of glacier-derived freshwater in East Antarctica using an end-member-independent hydrographic parameterization

Article References: Watanabe, Y. W., Hirano, D., Ohashi, Y., Sugita, M., Nakano, Y., Makabe, R., & Mizobata, K. (2026). Three-dimensional reconstruction of glacier-derived freshwater in East Antarctica using an end-member-independent hydrographic parameterization. Nature Communications, 17(1), Article 9498. https://doi.org/10.1038/s41467-026-77441-z

Image Credits: AI Generated

DOI: 10.1038/s41467-026-77441-z

Keywords: East Antarctica, glacial meltwater, hydrography, ice shelf melt, Southern Ocean, Antarctic Bottom Water, temperature-salinity analysis, sea-level rise, ocean circulation, water mass analysis, climate change, oceanography