Repeated major inland retreat of Thwaites and Pine Island glaciers (West Antarctica) during the Pliocene

Sep 29, 2026

Significant melting of the Thwaites and Pine Island glaciers in the Amundsen Sea sector threatens the stability of the West Antarctic Ice Sheet (WAIS). Geochemical provenance data from an Amundsen Sea sediment core were used to reconstruct WAIS configurations during the Pliocene, when global temperatures were several degrees warmer than today. The results reveal repeated major inland retreat events across glacial–interglacial cycles, demonstrating strong sensitivity to warm ocean forcing.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages11

Reading Time28 min

AccessFree to download

Significance

Repeated major inland retreat evidence

Scientific background

Pacific sector melting and WAIS vulnerability

Pliocene climate context

Methods and data source

IODP Expedition 379 and Site U1532 provenance isotopes

Findings interpretation

High Pb/low εNd signature and retreat mechanisms

Implications

Risk of partial or complete WAIS collapse

RESEARCH ARTICLE EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES OPEN ACCESS Repeated major inland retreat of Thwaites and Pine Island glaciers (West Antarctica) during the Pliocene Keiji Horikawaa,1, Masao Iwaib , Claus-Dieter Hillenbrandc , Christine S. Siddowayd , Anna Ruth Halberstadte , Ellen A. Cowanf, Michelle L. Penkrotg, Karsten Gohlh , Julia S. Wellneri , Yoshihiro Asaharaj , Ki-Cheol Shink , Masahiro Nodal, Miyu Fujimotol, and Expedition 379 Science Party2 Affiliations are included on p. 10. Edited by Eric Rignot, University of California, Irvine, CA; received April 8, 2025; accepted November 10, 2025 The stability of the West Antarctic Ice Sheet (WAIS), crucial for predicting future sea-level rise, is threatened by ocean-forced melting in the Pacific sector of the Southern Ocean. While some geological records and ice-sheet models suggest WAIS retreat during past warm periods, reliable data constraining the extent of retreat are lacking. Detrital Nd, Sr, and Pb isotope data of sediments recently drilled at International Ocean Discovery Program (IODP) Site U1532 on the Amundsen Sea continental rise manifest repeated alternations in sediment provenance during glacial–interglacial cycles ofthe Pliocene (5.33 to 2.58 Mya), a time warmer than present. The variations reflect large fluctuations in WAIS extent on the Antarctic continent. A unique high Pb/low εNd signature of sediments found at the onset of glacial intervals (3.88, 3.6, and 3.33 Ma) is attributed to the supply of detritus sourced from plutonic rocks located in the West Antarctic interior. Its isotopic signature at Site U1532 indicates major inland retreat of the WAIS during the preceding interglacials. During peak interglacials, the ice margin had retreated inland, and icebergs rafted and deposited inland-sourced detritus over 500 km across the Amundsen Sea shelf. Subsequent readvance of grounded ice then “bulldozed” these inland-derived fine-grained sediments from the shelf down to the continental slope and rise, resulting in a high Pb/low εNd peak in the rise sediments. Our continuous Pliocene records provide conclusive evidence for at least five major inland retreat events of the WAIS, highlighting the significant vulnerability of the WAIS to ongoing warming. IODP Expedition 379 | Pliocene | West Antarctic Ice Sheet | Amundsen Sea | glacial history The Amundsen Sea drainage sector of the West Antarctic Ice Sheet (WAIS), particularly the catchments ofthe marine-terminating Thwaites Glacier and Pine Island Glacier (TG– PIG; Fig. 1A), is losing ice faster than other parts of Antarctica (1) due to inflow of warm Circumpolar Deep Water (CDW; ~ 0.5 to 1.2 °C, located below 300 to 500 m water depth) (2). The CDW melts ice shelves from below (2, 3), thus weakening their buttressing effect, and can possibly intrude far under the base of a glacier during high tides (4) . The situation of the subglacial bed below sea level together with its inland sloping that exceeds 2,000 m water depth in the Byrd Subglacial Basin (5) makes grounded ice of this sector, especially TG, susceptible to run-away retreat (6, 7) (Fig. 1A) . Ice-sheet models suggest that CDW incursion beneath TG can trigger self-sustaining WAIS recession, associated with grounding-line retreat far inland and resulting in rapid, widespread ice-sheet loss (8, 9) . This scenario raises concerns about large-scale and potentially rapid, future global sea-level rise from the WAIS (9). Despite these concerns, our understanding of the response of the TG–PIG to past warming events remains incomplete based on geological evidence. Sediment records from the Amundsen Sea spanning the Pliocene Epoch (5.33 to 2.58 Mya) may reveal a harbinger for WAIS response to future warming since global mean sea-surface temperatures (SSTs) between 4.5 Ma and 3.2 Ma were 3 to 4 °C higher than late Holocene values (16), equivalent to projected future temperature increases (17) . Ice-sheet models and far-field sea-level

FAQs

What problem does the study address about the WAIS?

The study addresses how ocean-forced melting in the Pacific sector of the Southern Ocean threatens the stability of the WAIS and how much retreat occurred during past warm periods.

What data did the authors analyze to constrain Pliocene WAIS behavior?

The authors analyzed detrital Nd, Sr, and Pb isotope data from sediments drilled at IODP Site U1532 on the Amundsen Sea continental rise.

What do the isotope records show about inland retreat events?

The records show repeated alternations in sediment provenance and provide conclusive evidence for at least five major inland retreat events of the WAIS during the Pliocene.

Sep 29, 2026

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