Seafloor Clay Reveals West Antarctica’s Ice Collapsed Repeatedly Over 800,000 Years

Scientists led by the British Antarctic Survey (BAS) found strong evidence from seafloor sediment (clay and mud) cores that West Antarctica’s most vulnerable ice streams, including Thwaites Glacier, repeatedly collapsed and retreated far inland during natural warm periods (interglacial) over the past 800,000 years.

The key signal comes from the clay mineral kaolinite (also known as china clay). This mineral formed under warmer, wetter conditions on Antarctica more than 34 million years ago and is now locked in bedrock beneath the West Antarctic Ice Sheet (WAIS).

Glaciers like Thwaites and Pine Island grind it out and deliver it offshore via icebergs and currents. In sediment cores recovered from ~4,000 m depth on the Amundsen Sea continental margin (IODP Expedition 379 sites U1533 and U1532), the kaolinite signal drops to near-zero during every interglacial in the record. This indicates that marine- based ice in the Amundsen Sea sector retreated far into the continent’s interior, cutting off the supply of that glacigenic debris.⁠

Supporting evidence includes:

• A second clay mineral, smectite (a magnesium- rich variety with a chemical signature from the deep Pacific Ocean floor farther north). Its increased presence at the same times as kaolinite disappearance points to warm deep-water currents (Circumpolar Deep- Water intrusions) carrying it southward while melting the grounded ice.⁠
• Diatom microfossil proxies showing local seawater temperatures in front of the WAIS were about 1- 3°C warmer than today’s near- freezing baseline during those periods, even when global average temperatures were only ~1.0- 1.5°C warmer than pre- industrial levels (or cooler).⁠

The peer- reviewed study, “Repeated loss of the West Antarctic Ice Sheet’s Amundsen Sea sector during late Pleistocene interglacial,” was published in Nature Communications on 9 November 2026 (DOI: 10.1038/s41467-026-77004-2).

Lead author Dr. Claus- Dieter Hillenbrand (BAS) noted that the kaolinite collapse is the only way to explain the cessation of debris delivery and that ocean forcing can drive major West Antarctic deglaciation. Co- author Dr. Rob Larter added that past natural warm periods already saw substantial ice loss, but today’s human- driven warming is “an interglacial on steroids.”⁠

Implications: Complete collapse of Thwaites alone could raise global sea levels by ~65 cm (Pine Island ~51 cm more); broader WAIS loss could contribute 3- 5 m. Under past natural conditions the process likely took thousands of years; current rapid ocean warming could compress it into centuries. The findings strengthen concerns about the WAIS’s vulnerability at temperatures similar to today’s.⁠

Primary sources: BAS press release (“China clay clue to past dramatic ice loss,” 9 November 2026) and the Nature Communications paper.

Over the last 800,000 years, Earth’s climate has followed a roughly 100,000-year cycle of glacial (cold, ice- sheet growth) and interglacial (warmer, ice-sheet retreat) periods. This pattern became dominant after the Mid- Pleistocene Transition.

How many interglacials?

A major scientific review by the Past Interglacial Working Group of PAGES (2016) identified 11 interglacial in the last 800,000 years, using a consistent sea -level definition. This count is robust across alternative definitions.⁠

These include the present- day Holocene (Marine Isotope Stage 1, or MIS 1) and earlier ones such as:

• MIS 5e (Last Interglacial, ~130- 115 ka)
• MIS 11c (~400 ka, one of the strongest and longest)
• MIS 9e, MIS 7e, MIS 13a, MIS 15, MIS 17, MIS 19, and others

Interglacial typically lasted 10,000- 30,000 years.

How many glacial periods?

There are correspondingly about 8–9 major glacial periods in the same interval (the cold phases that separate the interglacial). The most recent full glacial maximum occurred during MIS 2 (~29–14 ka, including the Last Glacial Maximum).

Marine Isotope Stages (MIS) overview

Scientists number these stages using oxygen-isotope records from deep- sea sediments:

• Odd- numbered stages = mostly interglacial (warmer)
• Even- numbered stages = mostly glacial (colder)

The last 800,000 years roughly span from the present (MIS 1) back to around MIS 19- 20 (near the Brunhes- Matuyama magnetic reversal at ~780- 790 ka).

This is the exact time window covered by the recent West Antarctic Ice Sheet study (using seafloor clay minerals). The paper found that the Amundsen Sea sector (including Thwaites Glacier) experienced major ice loss during all previous interglacial in this 800,000- year record.

Sea- level reconstructions and models have long suggested that the vulnerable West Antarctic Ice Sheet (WAIS) experienced major mass losses during late Pleistocene warm periods, contributing several metres to global sea level. Direct near- field evidence had remained inconclusive.

This study examines clay- mineral assemblages and past ocean temperatures in sediments from the West Antarctic continental margin spanning the last 800,000 years (IODP Expedition 379 Sites U1533 and U1532 on the eastern Amundsen Sea continental rise).

Main findings:

• The supply of glacigenic detritus from the main outlet glaciers of the Amundsen Sea sector (especially Thwaites Glacier) ceased almost entirely during all previous interglacial (warm) periods. This documents the loss of their drainage basins.
• Concurrent seawater warming (from a diatom microfossil proxy) is linked to intensified advection of warm deep water toward Antarctica’s Pacific margin. Clay- mineral data corroborate this.
• Ocean forcing alone can drive major deglaciation of West Antarctica and associated global sea- level rise.

Researchers used kaolinite (china clay) as a fingerprint of subglacial erosion under Thwaites Glacier and neighbouring ice streams. Kaolinite- rich bedrock underlies parts of the Amundsen Sea sector; grounded ice grinds it out and delivers it offshore. When the kaolinite signal drops to near- zero in the cores during interglacial, it indicates the ice had retreated far inland and stopped delivering that material.

They also analysed smectite composition. Magnesium- rich “Type- 2” smectites originate from the deep Pacific farther north and are transported south by Circumpolar Deep Water (CDW). Their increased presence during the same intervals supports enhanced warm- water intrusion onto the continental shelf at the same time the local glacigenic (kaolinite) supply collapses.

Broader context and implications

• The Amundsen Sea sector (Thwaites and Pine Island glaciers) drains roughly one- third of the WAIS and is the current focus of rapid mass loss.
• Full loss of this sector (and potential wider WAIS collapse) could raise global sea level by 3.3- 5.3 m.
• Past interglacial often had global temperatures only ~1- 1.5 °C above pre-industrial levels, comparable to today, yet still produced major retreat driven by ocean warming.
• The results strengthen the view that the modern WAIS is highly sensitive to ocean forcing and that ongoing anthropogenic warming increases the risk of substantial, potentially irreversible ice loss.

Lead authors include Claus- Dieter Hillenbrand (British Antarctic Survey) and international collaborators.

The paper provides the strongest proximal geological evidence to date for repeated, major retreat of the Amundsen Sea sector of the WAIS during late Pleistocene interglacials.

You can read the full open- access article (including figures, methods, and supplementary data) directly at the link you provided.

Paper: Repeated loss of the West Antarctic Ice Sheet’s Amundsen Sea sector during late Pleistocene interglacials

Published: Nature Communications, (volume 17, Article 10450)

DOI: 10.1038/s41467-026-77004-2, Open access, (PDF available on the page)

Provided: British Antarctic Survey

Published: 9 November 2026

Authors: Claus-Dieter Hillenbrand,
Werner Ehrmann,
Young Kyu Park,
Jinwook Kim,
Steve M. Bohaty,
Reed P. Scherer,
Joseph A. Ruggiero,
Julia S. Wellner,
Karsten Gohl,
Rebecca L. Totten,
Robert D. Larter,
Mariana Esteves,
Johann P. Klages,
James A. Smith,
Thomas Frederichs,
Keiji Horikawa,
Sandra Passchier,
Joseph R. Mastro,
Thorsten Bauersachs,
Becky A. Hopkins,
Chuang Xuan,
Colm Ó Cofaigh,
Rachel W. Clark,
James W. Marschalek,
Patric Simões Pereira,
Benedict T. I. Reinardy,
Anna Ruth W. Halberstadt,
Li Wu,
Ellen A. Cowan,
Christine S. Siddoway,
Delaney E. Robinson,
Masao Iwai,
Liang Gao,
Sidney R. Hemming,
Michelle L. Penkrot,
Theresa M. King,
Jeremy M. Lloyd &
Denise K. Kulhanek

Abstract

Sea-level reconstructions and numerical models suggest that the vulnerable West Antarctic Ice Sheet underwent major mass losses during the late Pleistocene, raising global sea level by several metres. However, direct evidence from ice-sheet proximal records for such retreat has remained inconclusive. Here we investigate variations in clay mineral assemblages and past ocean temperatures archived in West Antarctic continental margin sediments during the last 800,000 years. Our results demonstrate that the supply of glacigenic detritus sourced from the main outlet glaciers in the Amundsen Sea sector of the West Antarctic Ice Sheet ceased almost entirely during all previous warm periods, documenting the loss of their drainage basins. Concomitant seawater warming, revealed by a microfossil proxy, is attributed to intensified deep-water advection towards Antarctica’s Pacific margin, which is corroborated by the clay mineralogical evidence. Our findings show that ocean forcing can drive major deglaciation of West Antarctica and related global sea-level rise.