West Antarctic ice streams repeatedly retreated during warm periods, seafloor clay suggests
Sediment cores from the Amundsen Sea show that West Antarctica’s marine-based ice, including Thwaites and Pine Island glaciers, retreated far inland during every interglacial over the past 800,000 years, according to a British Antarctic Survey-led study in Nature Communications. The researchers link the retreats to warm deep-water currents; they say natural retreat could take thousands of years, while current human-driven ocean warming could compress the process into centuries.
Bottom line — Thwaites alone holds enough ice to raise global sea levels by 65 centimetres if it were to melt completely.
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The clue was kaolinite, a clay mineral ground from bedrock beneath the ice: its signal in the cores fell close to zero during each interglacial.
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Researchers also found magnesium-rich smectite with a chemical signature associated with the deep Pacific, which they say warm currents may have carried south.
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Diatom remains indicate that waters off West Antarctica were about 1°C to 3°C warmer than today during past interglacials, even when global temperatures were similar to today or cooler.
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Pine Island Glacier could add another 51 centimetres to sea levels if it melted completely, according to the British Antarctic Survey.
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The study is evidence of past retreat, not a forecast of when either glacier will collapse; co-author Rob Larter said the speed of future sea-level rise remains difficult to predict.