# Ocean heat forced West Antarctic Ice Sheet retreat after the Last Glacial Maximum

## TL;DR

Warm ocean water, not atmospheric warming, caused the West Antarctic Ice Sheet to retreat after the last ice age.

## Contribution

New evidence shows ocean heat, not air temperature, was the main driver of ice sheet retreat in West Antarctica.

## Key findings

- Warm Circumpolar Deep Water caused major WAIS retreat from 18,000 to 10,000 years ago.
- Cooling ocean waters after 10,000 years ago stabilized the ice sheet's grounding line.
- Atmospheric warming alone did not cause further ice retreat after ocean temperatures stabilized.

## Abstract

The West Antarctic Ice Sheet (WAIS) is thinning at an accelerating rate, driven by melting at its margins by warm Circumpolar Deep Water (CDW). However, this understanding is largely based on observations from recent decades, leaving the long-term influence of ocean temperature on WAIS stability uncertain. Here we reconstruct bottom water temperatures and water mass properties over the past 18 kyr using benthic foraminiferal Mg/Ca and δ¹³C records from sediment cores in the Amundsen Sea. Our data indicate that warm CDW occupied the continental shelf between ~ 18.0 and 10.1 kyr BP, coincident with major WAIS retreat from the shelf break to near its present-day grounding-line position along the Marie Byrd Land coast. Bottom waters cooled after ~ 10.1 kyr BP and remained relatively stable thereafter, with no evidence for substantial grounding-line migration. Continued atmospheric warming across West Antarctica until a mid-Holocene thermal maximum (~6–3 kyr BP) without further retreat indicates that ocean heat was the primary driver of WAIS variability since the Last Glacial Maximum.

Amundsen Sea records show warm Circumpolar Deep Water drove major West Antarctic Ice Sheet retreat from 18,000–10,000 years ago. Subsequent cooling stabilized the grounding line, indicating ocean heat—not atmospheric warming—controlled long-term WAIS change.