Tag: Cryospheric science

Antarctic Sea Ice Collapse Triggers Abrupt Reversal in Key Southern Ocean Layer, Threatening Heat and Carbon Storage

New research from the University of Melbourne (with the Indian Institute of Science and University of Southampton), published in Nature Climate Change (October 2026), shows that the Antarctic Intermediate Water (AAIW), a vast, relatively fresh ocean layer spanning much of the Southern Hemisphere, has abruptly reversed long- term trends in salinity, density, and depth since around 2016, linked to major Antarctic sea ice loss.

Illustration depicting the collapse of Antarctic sea ice and its impact on the Southern Ocean, highlighting ocean layer reversal, with labels for fresh, warmer surface layer, denser, saltier deep water, and associated risks to heat and carbon storage.
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New research from the University of Melbourne (with the Indian Institute of Science and University of Southampton), published in Nature Climate Change (October 2026), shows that the Antarctic Intermediate Water (AAIW), a vast, relatively fresh ocean layer spanning much of the Southern Hemisphere, has abruptly reversed long- term trends in salinity, density, and depth since around 2016, linked to major Antarctic sea ice loss.

What is the AAIW and why does it matter?

The AAIW is a layer typically found roughly 500- 1,500 meters (or more specifically ~700- 1,200 m in some descriptions) below the surface. It forms partly from Antarctic surface waters influenced by sea ice melt and spreads northward into the Atlantic, Indian, and Pacific Oceans.

It helps:

  • Store and redistribute heat, freshwater, and carbon.
  • Supply oxygen.
  • Support parts of the global ocean overturning circulation (a key climate regulator).⁠

The ocean absorbs over 90% of excess heat from human activities (mostly in the upper ocean) and a large share of CO₂ emissions, acting as a climate buffer.

The observed shift

  • Pre- 2016 (roughly 1990s and 2004- 2015): Antarctic summer sea ice melt supplied large volumes of freshwater (estimated at ~triple the Amazon River’s annual discharge, or ~17,400 gigatons in some accounts). This made the AAIW progressively fresher, lighter, and shallower.
  • 2016- 2024: Record- low Antarctic sea ice sharply reduced this meltwater input (dropping toward roughly double the Amazon’s flow). The AAIW rapidly became saltier, denser, and deeper across multiple ocean basins. This is the first direct observational evidence of such a change, detected via Argo floats (thousands of robotic ocean profilers), satellite data, and other records.⁠

Researchers note the last comparable major switch in AAIW properties occurred at the end of the previous interglacial period (~130,000 years ago), when Antarctic ice was minimal, but that transition unfolded over thousands of years, not roughly a decade or two.

Implications for heat and carbon storage

  • A denser and weaker or altered AAIW could reduce the effectiveness of the density barrier (pycnocline) that limits vertical mixing, potentially allowing more excess heat to move into deeper ocean layers. Climate models may therefore be underestimating deep-ocean warming, regional sea- level rise, and longer- term surface temperature responses.⁠
  • Changes in how surface water is subducted could affect the ocean’s capacity to lock away atmospheric carbon, though the magnitude and timing remain uncertain.
  • As the altered water mass spreads north, it forms part of the upper limb of the global overturning circulation and could eventually influence systems like the Atlantic Meridional Overturning Circulation (AMOC), as well as Southern Hemisphere atmospheric circulation, storm tracks, rainfall, and weather patterns over years to decades. Effects could cascade more widely.⁠

The lead researchers (including Associate Professor Bishakhdatta Gayen and PhD student Kaushik Mishra) describe this as revealing a critical missing feedback and an urgent signal that the ocean is responding faster than previously appreciated.

Ongoing monitoring (especially Argo data) and improved climate model representation of these processes are highlighted as priorities, particularly while Antarctic sea ice remains at record lows.

In short, the findings raise important questions about whether current projections fully capture the ocean’s evolving role in heat and carbon storage under rapid polar change.

The study itself focuses on the observational reversal rather than detailed future projections or quantified environmental impacts.

A snowy mountain under a blue sky, with a foreground of ice and snow texture.
Sea ice off Victoria Land, Antarctica, with Mount Melbourne in the background. Credit: Alberto C Naveira Garabato

Antarctic Intermediate Water (AAIW) plays a key role in oceanic carbon storage and redistribution as part of the Southern Ocean’s contribution to the global carbon cycle.

AAIW forms in the polar Southern Ocean (primarily in the Polar Frontal Zone, between the Subantarctic and Polar Fronts). Surface waters there are influenced by sea-ice processes, winds, and mixing.

These waters exchange gases with the atmosphere, absorbing substantial amounts of CO₂ (both natural and anthropogenic) through air- sea gas exchange. Cold temperatures enhance CO₂ solubility, aiding uptake.

Once formed, AAIW is subducted (sunk) to intermediate depths, typically around 500–1,500 meters (often cited as ~700– 1,200 m), and spreads northward into the Atlantic, Indian, and Pacific Oceans as part of the upper limb of the global overturning circulation. This process isolates the absorbed carbon from the atmosphere for decades to centuries.

Specific contributions to carbon storage

  • Major anthropogenic CO₂ sink: Modern AAIW is a significant reservoir for anthropogenic carbon. Its associated carbon inventory has been estimated to exceed ~20 Pg C (petagrams of carbon).⁠
  • Redistribution and transport: AAIW acts as a lateral conduit, carrying carbon (along with nutrients and oxygen) from high-latitude Southern Ocean uptake regions to lower latitudes. This links Southern Ocean air- sea CO₂ exchange with biogeochemical processes in subtropical and tropical oceans.⁠
  • Physical and biological pumps: It participates in the solubility pump (temperature- and salinity- driven CO₂ uptake and isolation at depth) and supports aspects of the biological pump by transporting nutrients that fuel productivity elsewhere. Stratification and density structure associated with AAIW help regulate how effectively carbon is retained versus returned to the surface.
  • Broader Southern Ocean context: The Southern Ocean as a whole dominates global oceanic uptake of anthropogenic heat and carbon. AAIW (together with Subantarctic Mode Water) is central to the rate of water- mass formation and subduction that determines how much CO₂ is taken up and sequestered.

Relevance to recent changes

In the context of the recent research (the abrupt post- 2016 shift toward saltier, denser, and deeper AAIW due to reduced Antarctic sea- ice meltwater), scientists note that alterations to AAIW properties or the way surface water is carried into deeper layers could change how much carbon the ocean locks away.

The magnitude and timing of any such effect remain uncertain, but it raises questions about the future efficiency of this carbon storage pathway.⁠

In summary, AAIW functions as both a direct storage reservoir for absorbed atmospheric CO₂ at intermediate depths and a key transporter that redistributes carbon within the global ocean, helping moderate atmospheric CO₂ levels on multi- decadal to centennial timescales.

Its effectiveness depends on formation rates, surface conditions (temperature, salinity, ice melt), stratification, and circulation.

An expanse of icy water with numerous irregularly shaped ice floes floating on its surface, alongside a snowy edge.
Sea ice floes from a marine voyage. Credit: Alberto C Naveira Garabato

Reversal of Antarctic Intermediate Water trends triggered by sea ice decline

Abstract

Antarctic Intermediate Water (AAIW), a key component of the global overturning circulation and a major regulator of pycnocline structure, forms in the polar Southern Ocean, where sea-ice processes shape its properties. Sustained sea-ice expansion over several decades up to 2015 enhanced summertime meltwater input, stratifying the upper polar ocean and freshening AAIW. However, since 2016, repeated record sea-ice losses have reversed these trends. Using Argo-derived ocean observations supplemented by satellite and re-analysis datasets, we reveal that the abrupt post-2015 shift in sea-ice conditions is on course to alter hemispheric-wide water-mass properties. We estimate a net decline in sea-ice meltwater input of nearly 36 mSv per decade, relative to a pre-2016 increase of 14 mSv per decade. This unprecedented sea-ice loss has triggered densification and salinification of AAIW, whose core has salinified at 4.8×10−3±1.7×10−34.8×10−3±1.7×10−3 g kg−1−1 per decade. These changes signal that a hemispheric-scale reconfiguration of the pycnocline is underway.

Key points from the paper

  • Pre- 2016 trend: Decades of Antarctic sea- ice expansion increased summertime meltwater, which freshened and lightened AAIW while helping stratify the upper ocean.
  • Post- 2016 reversal: Record sea- ice losses sharply reduced meltwater input. This caused AAIW (and related Winter Water) to become saltier, denser, and deeper across the Southern Hemisphere.
  • Quantitative estimates:
    • Net decline in sea- ice meltwater input: ~36 mSv per decade (vs. a prior increase of ~14 mSv per decade).
    • AAIW core salinification rate: 4.8×10−3±1.7×10−3 per decade.
  • Methods: Primarily Argo float data (upper-ocean profiles), combined with satellite sea- ice observations, reanalysis products, and supporting datasets (e.g., EN4, IAP, CFC- 11 tracers).
  • Broader implication: The shift indicates an ongoing hemispheric- scale reconfiguration of the ocean’s pycnocline (the density gradient layer that regulates vertical mixing, heat, and carbon exchange).

Figures (titles)

  1. Climatological state of Winter Water (WW) and AAIW
  2. Evolution of Antarctic sea ice and northward transport of sea- ice meltwater
  3. Evolution of WW and AAIW core salinity anomalies
  4. Evolution of WW core density and depth
  5. Evolution of AAIW core density and depth
  6. Schematic of AAIW regime shift linked to changes in Antarctic sea-ice cover

Data and code

The full text is behind a paywall (institutional access, Nature+, or purchase required). The abstract and supporting materials above capture the core findings. This is the primary research paper underlying the University of Melbourne press coverage discussed earlier.

Journal: Nature Climate Change, (2026)

DOI: 10.1038/s41558-026-02758-y

Provided: University of Melbourne

Published: 28 October 2026

Authors: Kaushik Mishra,
Bishakhdatta Gayen&
Alberto C. Naveira Garabato

Comparison of Antarctic sea ice trends before and after 2016, illustrating changes in Antarctic Intermediate Water (AAIW) characteristics and their impact on ocean dynamics.
Antarctic Intermediate Water shifted from freshening before 2016 to becoming saltier, denser and deeper afterward. Credit: Kaushik Mishra

Winds Open Antarctic Ice Holes — Then Waves Shatter Them From the Inside Out

A recent Nature Communications paper by Joey J. Voermans (University of Melbourne) and colleagues shows that locally generated waves in Antarctic coastal polynyas can break up surrounding sea ice from the inside outward.

Katabatic winds are downslope winds driven by gravity acting on denser (usually colder) air.

Cold air near the surface becomes denser than the surrounding air. On elevated terrain, such as a plateau, ice sheet, or mountain slope, this dense air flows downhill under gravity. The term comes from the Greek katabasis (“descent” or “going down”).

Aerial view of cracked ice on a frozen body of water, with dark patches of liquid water, and wisps of mist rising above it under a dramatic sky.
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A recent Nature Communications paper by Joey J. Voermans (University of Melbourne) and colleagues shows that locally generated waves in Antarctic coastal polynyas can break up surrounding sea ice from the inside outward.

Coastal polynyas are recurring open- water areas within sea ice that act as “sea- ice factories”, producing large volumes of new ice. Their formation and persistence have long been attributed mainly to strong offshore (katabatic or synoptic) winds that advect ice away from the coast. The role of waves has been largely unexplored due to the scarcity of in situ observations.

Using rare wave- buoy data from the Vincennes Bay Polynya (East Antarctica, near Casey Station), the researchers found that strong winds generate energetic, short- period wind waves within the open water.

These waves grow across the polynya’s fetch and are steep enough to fracture the surrounding ice cover starting at the polynya edge and propagating outward. This “inside- outward” breakup contrasts with the more familiar “outside- inward” process driven by long- period Southern Ocean swells that approach the ice edge from the open ocean.

The buoy records (from deployments in 2021, 2022, 2024, and 2025) showed sharp increases in wave energy with relatively short dominant wavelengths once the instruments entered the polynya, consistent with fetch- limited local wind- wave growth rather than distant swell (which is strongly attenuated by intervening pack ice).

Analysis of satellite sea- ice concentration records (2003- 2022) showed that extreme wave- induced breakup events are associated with substantial, persistent reductions in sea- ice concentration lasting at least one week, along with increased transitions to active frazil ice (the loose crystals that form in turbulent, supercooled water).

This creates feedback: waves enlarge and help sustain the open- water area, promoting further heat loss, supercooling, and new ice production.

The results highlight a previously overlooked mechanism in polynya dynamics. As Antarctic coastal polynyas change under a warming climate, wave activity may become increasingly important in shaping sea- ice conditions, dense-water formation, and related processes in the polar ocean.

Paper: Voermans, J. J., et al. (2026). “Inside-outward breakup of sea ice by locally generated waves in the Vincennes Bay Polynya.” Nature Communications. DOI: 10.1038/s41467-026-77979-y.

Satellite image comparing sea ice coverage before and after significant thinning on 6 October 2021 and 7 October 2021, respectively.
MODIS satellite images showing sea- ice conditions in the Vincennes Bay Polynya before and after an extreme wind-wave event. Credit: NASA Worldview

Katabatic winds are downslope winds driven by gravity acting on denser (usually colder) air.

Cold air near the surface becomes denser than the surrounding air. On elevated terrain, such as a plateau, ice sheet, or mountain slope, this dense air flows downhill under gravity. The term comes from the Greek katabasis (“descent” or “going down”).

Key characteristics:

  • They are typically cold and dry.
  • Speeds can range from gentle breezes to gale-force or stronger, especially where the terrain funnels or steepens the flow.
  • They often intensify at night or in winter when radiative cooling is strongest.

Katabatic winds are common in polar regions and high mountain areas:

  • Antarctica: Extremely important. Cold air over the high interior ice sheet drains toward the coast, sometimes reaching very high speeds. These winds help create and maintain coastal polynyas by blowing newly formed sea ice offshore.
  • Greenland: Similar drainage flows off the ice sheet.
  • Other locations: Alpine valleys, the Adriatic coast (bora winds have a katabatic component), and various mountainous regions worldwide.

In short, katabatic winds are gravity- driven downslope flows of dense cold air, and they play a major role in polar climate and sea-ice dynamics.

Diagram illustrating wave dynamics in a coastal polynya, showing strong winds generating waves, wave-induced breakup of ice cover, and effects of wind and wave stresses on ice transport and compaction.
Conceptual diagram of wave-driven breakup and redistribution of sea ice around a coastal polynya. Credit: Joey Voermans

Inside-outward breakup of sea ice by locally generated waves in the Vincennes Bay Polynya

Strong offshore winds (including katabatic winds) in the Vincennes Bay Polynya (East Antarctica) generate energetic local wind waves inside the open water. These waves are steep enough to fracture the surrounding sea ice from the inside outward, the opposite of the usual process in which Southern Ocean swells break ice from the outside inward.

Key evidence

  • Rare in- situ measurements from four drifting wave buoys (deployed near Casey Station in 2021, 2022, 2024 and 2025) recorded a sharp rise in wave energy with short dominant periods once the buoys entered the polynya, consistent with fetch- limited local wind- wave growth rather than distant swell.
  • Southern Ocean swell was strongly attenuated by the intervening pack ice and contributed little to the measured wave energy.
  • Satellite records (2003- 2022) show that extreme wave- breakup events coincide with substantial, persistent drops in sea- ice concentration lasting at least one week, plus increased production of active frazil ice.

Coastal polynyas are major “sea- ice factories” and sites of dense- water formation. The study shows that locally generated waves are an important, previously overlooked feedback that helps reshape and sustain these polynyas. As Antarctic conditions change, wave activity may become increasingly significant.

The paper directly links the strong katabatic and synoptic winds that keep the polynya open to the generation of the waves that then break the surrounding ice.

Journal: Nature Communications, 17, Article number: 11224 (2026)

DOI: 10.1038/s41467-026-77979-y

Published: 29 September 2026, Open access

Authors: Joey J. Voermans,
Qingxiang Liu,
Lang Cao,
Josh Kousal,
Petra Heil,
Alexander D. Fraser,
Clarence O. Collins,
Jean Rabault &
Alexander V. Babanin

Abstract

Coastal polynyas are recurring regions of open water within sea ice that serve as sea-ice factories, producing vast amounts of new ice relative to nearby sea-ice-covered regions. Their formation and persistence are commonly attributed to strong offshore winds, while the influence of waves on polynya dynamics remains largely unexplored. Using rare wave-buoy observations from the Vincennes Bay Polynya, we show that strong winds generate energetic waves capable of breaking surrounding sea ice from the inside-outward, contrasting with outside-inward breakup caused by Southern Ocean swells. Satellite records from 2003–2022 reveal that extreme wave-induced breakup events coincide with substantial reductions in sea-ice concentration that persist for at least one week, accompanied by increased transitions to active frazil ice. These findings demonstrate that locally generated waves impact polynya dynamics and reshape surrounding sea-ice conditions. As Antarctic coastal polynyas evolve under a changing climate, wave activity may become increasingly important in shaping their sea-ice conditions and evolution.

Just 3% of glaciers cause over half the world’s ice loss — lakes are key

Just 3% (specifically 3.2%) of the world’s glaciers, those ending in lakes, oceans, or ice shelves, account for more than half of global glacier ice loss.

The 57% faster loss rate refers specifically to lake- terminating glaciers compared with land- terminating glaciers.

As the climate warms, proglacial lakes are becoming more common.

Many currently land- terminating glaciers are expected to start ending in lakes, which could accelerate their mass loss beyond what models that ignore terminus type would predict.

A glacier with blue ice and mountains in the background, featuring the text overlay about ice loss due to glaciers and lakes.
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Just 3% (specifically 3.2%) of the world’s glaciers, those ending in lakes, oceans, or ice shelves, account for more than half of global glacier ice loss.

A study led by researchers from the University of Birmingham and the University of Leeds, published in Nature Communications (23 October 2026), examined 216,502 glaciers worldwide (excluding the Greenland and Antarctic ice sheets). These water- terminating glaciers lost an estimated 134 billion tonnes of ice per year between 2000 and 2019.

Key findings

  • These glaciers represent only about 3.2% of the total number but cover more than half of the world’s glacier area because they tend to be much larger than land- terminating ones.
  • Breakdown of terminus types: ~96.8% end on land, 1.6% in lakes, 1.5% in the ocean, and 0.1% on ice shelves.
  • Mass loss shares (2000–2019): land- terminating glaciers ~49.4%; lake-terminating ~24.0%; marine- terminating ~22.8%; shelf-terminating ~3.9%. The water- contact group therefore contributed slightly over half of total loss.⁠
  • After controlling for climate, size, and elevation, lake- terminating glaciers lost ice ~57% faster (relative to their size) than land– terminating ones. They also flow ~10% faster on average; ocean- terminating glaciers flow ~44% faster.

Why lake- ending glaciers lose ice faster

Possible mechanisms include calving (large ice chunks breaking off as icebergs) and melting of ice below the waterline by lake water. The exact relative contributions of the lakes themselves versus glacier size and shape remain under investigation. Lake- terminating glaciers occur in every major glacier region and, in most regions, lose ice faster than land- or ocean- ending ones.

Implications

Many models used to project glacier change, sea- level rise, water resources, and hazards do not fully account for lake- terminating glaciers.

The study provides a new global classification (freely available) to help improve those projections.

As the climate warms, more glaciers are shifting types: some ocean- ending glaciers in the Arctic are retreating onto land (potentially slowing loss), while growing proglacial lakes are turning land- ending glaciers into lake- ending ones (potentially accelerating loss).⁠

Lead researcher Dr Joe Mallalieu (research done at Birmingham, now at Leeds) noted that lake- ending glaciers “really stand out” for rapid ice loss, and understanding the causes is especially important as glacier lakes become more common. Co-author Dr Nicholas Barrand (University of Birmingham) highlighted the value of combining expanded global datasets to compare glacier behaviour across settings.

Paper: Mallalieu et al. (2026), “Global-scale variability of glacier velocity and mass loss across terminus environments,” Nature Communications (DOI: 10.1038/s41467-026-78654-y).

Bar graph displaying global glaciers by type: Land, Lake, Marine, and Shelf, showing the number of glaciers, glacier area, and mass change rate from 2000 to 2019.
Fig. 1: Global classification of glacier termini by type. | Nature Communications | Nature Communications

The 57% faster loss rate refers specifically to lake- terminating glaciers compared with land- terminating glaciers.

What the number means

After researchers controlled for major confounding factors (climate, glacier size, and elevation), lake- ending glaciers still lost mass ~57% faster relative to their size than land- ending glaciers during 2000- 2019.

In other words:

  • It is not simply that lake glaciers are bigger (though they often are).
  • It is a higher specific mass- loss rate (ice lost per unit area or volume), once size and other variables are accounted for.

How the comparison was made

The team analysed 216,502 glaciers worldwide (excluding the Greenland and Antarctic ice sheets) and classified them by terminus type:

  • Land- terminating
  • Lake- terminating
  • Ocean (marine)- terminating
  • Ice- shelf- terminating

They then compared ice- flow speeds and mass-change rates across these categories.

Statistical controls removed the influence of climate, overall size, and elevation so the remaining difference could be more confidently linked to the terminus environment itself.

Why lake- ending glaciers lose ice faster

Two main physical processes are thought to drive the elevated rates:

  1. Calving: Large blocks of ice break off the glacier front into the lake as icebergs. This removes ice much more rapidly than surface melting alone.
  2. Subaqueous (underwater) melting: Relatively warmer lake water contacts the submerged ice front and melts it from below the waterline, undercutting the glacier and further promoting calving.

These processes are largely absent (or far weaker) for glaciers that end on dry land.

Supporting observations

  • Lake- terminating glaciers flow ~10% faster on average than land- terminating ones (ocean- terminating glaciers flow ~44% faster).
  • Lake- ending glaciers occur in every major glacier region and, in most regions, show higher specific mass- loss rates than both land- and ocean- ending glaciers.

Why this matters

As the climate warms, proglacial lakes are becoming more common.

Many currently land- terminating glaciers are expected to start ending in lakes, which could accelerate their mass loss beyond what models that ignore terminus type would predict.

Conversely, some marine- terminating glaciers that retreat onto land may slow down.

Accurately capturing the ~57% relative difference therefore improves projections of future sea- level rise, regional water resources, and glacier-related hazards.

World map with highlights of various regions, each containing pie charts representing glacier areas, types, and terminus classifications. Regions include Arctic Canada, Greenland, Scandinavia, Iceland, and areas in Asia and South America.
Fig. 2: Distribution of glacier area by terminus type across RGI 6.0 world regions. | Nature Communications | Nature Communications

Global-scale variability of glacier velocity and mass loss across terminus environments

The 57% figure refers to the specific (area- normalised) mass- loss rate of lake- terminating glaciers.

In the paper (Nature Communications, 2026), the authors state:

“specific (area- normalised) mass loss rates at lake- terminating glaciers are 57% greater than those at land- and marine-terminating glaciers.”

Precise meaning

After applying linear mixed- effects statistical models that controlled for climate (temperature and precipitation) plus a range of geometric and topographic factors (elevation, area, debris cover, polar deviation, etc.), lake-terminating glaciers still showed significantly greater specific mass loss than land- terminating glaciers.

The model- predicted difference was −0.162 m water equivalent per year (m w.e. a⁻¹). Relative to the land- terminating baseline, this equates to 57% greater losses.

Raw (uncontrolled) numbers for context

  • Median specific mass- change rate (2000– 2019):
    • Lake- terminating: −0.490 m w.e. a⁻¹
    • Land- terminating: −0.245 m w.e. a⁻¹
    • Marine- terminating: −0.239 m w.e. a⁻¹

So, the raw median for lake glaciers is roughly double that of land or marine glaciers. After statistical controls, the residual difference shrinks to the 57% figure, isolating the association with terminus type itself.

Why “specific” (area- normalised) matters

Total ice loss is dominated by the large size of many non- land glaciers.

The specific rate removes the size effect and shows how rapidly ice is being lost per unit area. The 57% value therefore indicates a higher intensity of loss at lake termini, not merely a size effect.

Note on the comparison

The abstract groups the comparison as “57% greater than those at land- and marine- terminating glaciers” because the land and marine medians are nearly identical.

In the detailed model results the primary contrast is with land- terminating glaciers (the statistical baseline). Marine- and shelf-terminating glaciers actually showed slightly lower specific losses than land-terminating ones after controls.

In short: once climate, size, elevation and other factors are accounted for, lake-ending glaciers still lose mass ~57% faster per unit area than land- ending ones.

Journal: Nature Communications, 17, Article number: 10873 (2026)

DOI: 10.1038/s41467-026-78654-y

Provided: University of Birmingham

Authors: Joseph Mallalieu,
Jonathan L. Carrivick,
Matthias Huss,
Iestyn D. Barr,
Nicholas E. Barrand &
Cassandra L. Raby

Abstract

The environment in which a glacier terminates can strongly influence its behaviour, stability and future evolution, yet the relationship between terminus type and glacier dynamics at the global scale remains poorly constrained. Here we present a globally-complete classification of glacier termini distinguishing between land, lake, marine and shelf environments, and integrate it with datasets of glacier geometry, dynamics and climate. We show that although lake-, marine- and shelf-terminating glaciers comprise only 3.2% of glaciers globally, they account for over half of global glacier area and mass loss. We also show that lake- and marine-terminating glaciers flow, on average, 10% and 44% faster than land-terminating glaciers, respectively. Furthermore, specific (area-normalised) mass loss rates at lake-terminating glaciers are 57% greater than those at land- and marine-terminating glaciers. Our findings underscore the need for improved representation of non-land glacier termini in models of glacier evolution and sea-level rise, and suggest that distinguishing the environmental and geometric controls of termini on glacier dynamics remains an important challenge for future research.

Massive Ice Shelf Once Locked Northern Ice Sheets in Place—Its Collapse Holds Clues for Antarctica’s Future

A massive floating ice shelf in Baffin Bay (west of Greenland) once buttressed three major Northern Hemisphere ice sheets during the Last Glacial Maximum (~20,000 years ago). Its later disappearance helped accelerate glacier retreat and contributed to substantial sea-level rise. The finding offers a paleo-analog for how loss of buttressing ice shelves could affect Antarctica today.

A large, flat-topped iceberg surrounded by floating ice chunks in a calm ocean, with snow-covered mountains in the background under a cloudy sky.
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A massive floating ice shelf in Baffin Bay (west of Greenland) once buttressed three major Northern Hemisphere ice sheets during the Last Glacial Maximum (~20,000 years ago). Its later disappearance helped accelerate glacier retreat and contributed to substantial sea- level rise. The finding offers a paleo-analog for how loss of buttressing ice shelves could affect Antarctica today.

About 20,000 years ago, an enormous ice shelf more than a mile (~1.4- 2.1 km) thick occupied Baffin Bay. It helped restrain the margins of the Greenland Ice Sheet (to the east), the Innuitian Ice Sheet (to the north), and the Laurentide Ice Sheet (to the west).

Researchers describe these ice sheets as resembling a gothic cathedral, with the floating ice shelves acting as flying buttresses that slow the flow of grounded ice into the ocean.

Key findings

  • Scientists from the University of Florida (including co-author Robert Hatfield), University of North Carolina Wilmington, Columbia University, and other institutions mapped the seafloor using multibeam bathymetry and collected sediment cores during a research cruise on the R/V Neil Armstrong. They identified a sharp “Ice Contact Boundary” marking where the ice shelf was grounded versus floating. These features occur at depths up to ~1,800 m, deeper than any previously documented glacial bedforms in the Northern Hemisphere, indicating an unusually thick ice shelf.⁠
  • The shelf was comparable in area to major modern Antarctic ice shelves (larger than most except the Ross and Ronne) and thicker at its grounding zone than typical modern Antarctic shelves.
  • Sediment evidence shows the ice shelf disappeared over roughly 500- 1,000 years. Once the buttressing was lost, the land- based glaciers flowed faster into the sea, melted, and contributed to hundreds of feet of sea- level rise that helped shape modern coastlines.

The results were published on October 21, 2026, in Nature Geoscience. The discovery was unexpected; the team originally aimed to study what destabilized the western Greenland Ice Sheet at the end of the last ice age.

Relevance to Antarctica today

Ice shelves play a critical stabilizing role. When they thin, break up, or disappear, the grounded ice behind them can accelerate, increasing ice discharge and sea- level contribution, exactly the concern for parts of Antarctica (e.g., around Thwaites or Pine Island glaciers).

This ancient Baffin Bay example shows that a large, thick ice shelf on the scale of major Antarctic ones can vanish in centuries, providing a real- world case study of the mechanisms and timescales involved. It supplies new constraints for ice- sheet models, potentially improving projections of how quickly Antarctic ice could respond if buttressing is lost.⁠

In short, the past behavior of this Northern Hemisphere ice shelf underscores the importance of monitoring and understanding Antarctic ice shelves as climate warms, because their loss can unlock much larger volumes of ice on land.

Topographic map of Baffin Bay showing depth contours and features like ridges, benches, and gulleys.
Deep ice-contact features on the Baffin Bay slope. Credit: Nature Geoscience (2026). DOI: 10.1038/s41561-026-02126-7

The Baffin Bay Ice Shelf stabilized three adjacent ice sheets during the last glacial period

The Baffin Bay study is valuable as a paleo- analogue, it shows how the loss of a large, thick ice shelf can destabilize marine- based ice sheets, but it does not imply any direct connection between the northern and southern ice sheets.

Abstract summary

During the Last Glacial Maximum (roughly 26,500- 19,000 years ago), the Laurentide, Innuitian, and Greenland ice sheets coalesced around Baffin Bay, a semi- enclosed basin between Greenland and Canada. The exact configuration of their marine- terminating margins had been unclear.

Using compiled bathymetric data and a geomorphic study of the Baffin Bay continental slope, the authors identify evidence of slope- grounded ice and trace its maximum- depth imprint around most of the bay. They interpret these ice- contact features as the signature of a basin- spanning ice shelf that was ~1,400– 2,100 m thick (after correction for relative sea level). The shelf covered approximately 150,000 km².

This extensive ice shelf, supported by the basin’s geometry, buttressed, mechanically coupled, and promoted thickening of the three adjacent ice sheets. Sediment- core evidence indicates that collapse of the ice shelf triggered rapid ice- sheet retreat, linking abrupt Northern Hemisphere ice-sheet instability to embayment- scale ice- shelf dynamics.

The Baffin Bay Ice Shelf serves as a paleo-analogue showing that ice-shelf loss can rapidly reorganize marine ice sheets, relevant to how weakening buttresses may accelerate future Antarctic ice, stream retreat.

Key supporting details from related coverage

  • Authors include Shannon A. Klotsko (University of North Carolina Wilmington), Robert G. Hatfield (University of Florida), Brendan T. Reilly (Columbia University / Lamont- Doherty), and others.⁠
  • Ice- contact boundary (ICB) features were mapped at water depths up to ~1,800 m, deeper than previously recognized Northern Hemisphere glacial bedforms.⁠
  • The shelf was thicker at its grounding zone than most modern Antarctic ice shelves (which reach similar thicknesses only near major feeder glaciers) and comparable in area to large present- day Antarctic shelves (except the Ross and Ronne).
  • Data (shapefiles of geomorphic mapping, processed bathymetry grids) are publicly available via the Marine Geoscience Data System.

This is the peer- reviewed paper underlying the University of Florida news release discussed previously. The full text beyond the abstract is behind a paywall and institutional access.

Journal: Nature Geoscience

DOI: 10.1038/s41561-026-02126-7

Provided: University of Florida

Authors: Shannon A. Klotsko,
Robert G. Hatfield,
Brendan T. Reilly,
Anne E. Jennings,
Andrew M. W. Newton,
Erin E. Gregory,
Alan C. Mix,
Joseph S. Stoner,
Maureen H. Walczak,
Jacqueline Austermann &
Lauren Lewright

A color-coded topographic map showing the seafloor depth in relation to the ice shelf and sub-ice features.
Geomorphic features and formation schematics. Credit: Nature Geoscience (2026). DOI: 10.1038/s41561-026-02126-7