Abstract

Known collectively as the “weak underbelly of the West Antarctic Ice Sheet’’ owing to their vulnerability to future warming, Thwaites and Pine Island glaciers contain enough ice to raise global sea level by over 1 metre. Understanding the past behaviour of major Antarctic ice streams helps reduce uncertainty when projecting the future of the Antarctic ice sheets under different climate scenarios. To explore the Holocene history of these ice streams, members of the US-UK International Thwaites Glacier Collaboration (ITGC) collected geologic material from both above and beneath ice in the Thwaites and Pine Island glacier catchment. Rare isotopes (in situ-produced cosmogenic nuclides) measured in these rocks show that these glaciers have been thicker and, perhaps most interestingly, thinner than present in the Holocene, with implications for the reversibility of ongoing ice sheet mass loss and grounding line retreat.