International Team Recovers Longest Sub-Ice Sediment Core from West Antarctica; Studies Examine Ice Sheet and Sea Ice Dynamics

A 228-meter sediment core, the longest ever drilled from beneath an ice sheet, has been retrieved from West Antarctica, promising a detailed environmental record stretching back millions of years.

An international team of researchers has successfully retrieved a 228-meter sediment core from beneath the West Antarctic Ice Sheet, the longest core ever drilled from under an ice sheet. Analysis of the core is expected to provide a detailed environmental history spanning millions of years. Concurrently, multiple studies published in 2025 and 2026 have investigated recent and rapid declines in Antarctic sea ice and the potential for future ice sheet collapse, based on modeling and observational data.

West Antarctic Ice Sheet Sediment Core Drilling

The sediment core was recovered as part of the Sensitivity of the West Antarctic Ice Sheet to 2°C (SWAIS2C) project, a collaboration involving over 120 scientists from approximately 50 international research organizations. Drilling took place at Crary Ice Rise on the Ross Ice Shelf, a site over 700 kilometers from the nearest Antarctic station.

The team first drilled a 523-meter hole through the ice using a hot-water drill. A geological rig was then used to extract a 228-meter core of rock and mud from the bedrock beneath. The core has been transported from Crary Ice Rise to Scott Base and will be sent to New Zealand for comprehensive analysis at the University of Otago Repository for Core Analysis facility in Dunedin. Drilling concluded in January 2025. Previous drilling efforts during two prior seasons had encountered technical difficulties.

Initial analysis of the core indicates it provides an environmental archive spanning approximately 17 to 23 million years. Researchers have identified layers of sediment and fossilized marine organisms in the core.

• Samples consistent with deposits found under an ice sheet (similar to current conditions at Crary Ice Rise) have been observed.
• Other samples contain shell fragments and remains of marine organisms that require light, such as microscopic algae. These findings are characteristic of an open ocean environment, an ice shelf floating over open water, or the margin of an ice shelf.
• Rob McKay, director of the Antarctic Research Centre at Victoria University of Wellington, stated that changes from glacial to near ice-free conditions have been observed within the first 10 meters of sediment.
• The presence of fossils indicating open water conditions suggests periods in the past without ice sheet cover in the region.

"Changes from glacial to near ice-free conditions have been observed within the first 10 meters of sediment."
— Rob McKay, director of the Antarctic Research Centre at Victoria University of Wellington

Studies on the West Antarctic Ice Sheet's Future

A modeling study published in Communications Earth & Environment in June 2025 examined the potential for irreversible collapse of the West Antarctic Ice Sheet. The study ran simulations extending back 800,000 years.

• The study found that the ice sheet could shift from a stable state to long-term, self-sustaining retreat if deep ocean temperatures around West Antarctica rise by 0 to 0.25°C above current levels.
• The authors state that once triggered, the collapse would contribute approximately four meters to global sea levels over centuries to millennia. The Amundsen Sea and Weddell Sea sectors were identified as key areas where this tipping process could begin.
• The 0.25°C figure refers to ocean warming at depth, not global average surface temperature. The study does not claim this threshold has been crossed. It is one modeling paper and does not represent a settled consensus. Other modeling studies, such as a 2023 paper, have produced varying conclusions. The authors note that ice-sheet models depend on assumptions about ocean forcing, ice physics, and feedbacks.

Studies on Antarctic Sea Ice Decline

Satellite records show that Antarctic sea ice expanded from the late 1970s until approximately 2015, after which it began a sharp and sustained decline. In 2023, winter sea ice extent reached record lows, including in the Bellingshausen Sea, which was largely ice-free in June 2023, missing approximately 650,000 square kilometers of ice compared to the 1991–2020 average. The 2024 winter maximum was the 16th lowest in 46 years of records. These low extents were not predicted by climate models.

Multiple studies, including one published in Science Advances on May 8-11, 2025, describe the processes driving this decline. The research attributes the change to a sequence of events involving wind patterns and ocean heat.

• Phase 1 (pre-2015): Westerly winds around Antarctica, strengthened by the ozone hole and greenhouse gas emissions, intensified. This initially cooled the surface ocean and contributed to sea ice expansion.
• Phase 2 (from ~2015): The strengthening winds began to pull warmer, saltier Circumpolar Deep Water closer to the surface. The barrier between cold surface water and deeper warm water weakened, allowing heat to reach the surface and melt sea ice.
• Phase 3 (from ~2018): A self-reinforcing feedback loop emerged. Reduced sea ice cover exposed the ocean surface to sunlight, causing it to absorb more heat and remain warmer. Higher surface salinity from the upwelled deep water made the surface water denser, which inhibited the formation of a stable cold layer and further prevented new ice formation.

• In East Antarctica, sea ice loss is primarily driven by warm water rising from deeper ocean layers.
• In West Antarctica, atmospheric processes, including warm air and clouds, play a larger role.

• Sea ice loss exposes floating ice shelves and coastal glaciers to waves and warmer water, which can increase melting and the risk of breakup.
• Reduced reflective sea ice cover leads to greater absorption of solar energy by the darker ocean, amplifying local warming.
• Changes in the Southern Ocean's overturning circulation could reduce its ability to store heat and carbon dioxide.
• Sea ice supports ecosystems, including algae, krill, penguins, seals, and whales. Low sea ice has been linked to reduced breeding success in emperor penguins.
• If low sea ice conditions persist, the Southern Ocean could begin to accelerate, rather than mitigate, global warming, according to some researchers.

"If low sea ice conditions persist, the Southern Ocean could begin to accelerate, rather than mitigate, global warming."

Ocean Dynamics Beneath the Ross Ice Shelf

A separate study provided a continuous four-year record of ocean processes beneath the Ross Ice Shelf, the largest of Antarctica's ice shelves. Instruments deployed through a hole in the 320-meter thick ice at the shelf's center operated for over four years.

• The study found that water properties in the central cavity vary systematically throughout the year.
• Persistent horizontal layers of water with different properties were detected, a structure first observed in 1978. This layering acts as a barrier, isolating the ice shelf from deeper, warmer waters.
• Changes to the heat balance in ice-shelf cavities are projected to accelerate sea-level rise.