Antarctic ice volume and contribution to sea-level fall at 20,000 yr BP from raised beaches

Abstract

THE contribution of the Antarctic ice sheets to global sea-level fall at the Last Glacial Maximum (LGM) depends largely on how the extent and thickness of peripheral ice changed. Model studies1–3 suggest that there was widespread thickening (from 500 m to more than 1,000 m) of the ice-sheet margins, sufficient to induce a drop in sea level of at least 25 m. Geological evidence4,5, on the other hand, indicates only limited ice expansion and a sea-level fall of just 8 m. Here we use recent data on the altitudes and ages of raised beaches from the Ross embayment and East Antarctica to investigate the timing and extent of Antarctic deglaciation. These indicate that the ice margin during the LGM was thinner and less extensive than has been formerly thought, and that its contribution to the drop in sea level was only 0.5–2.5 m. Deglaciation was well advanced by 10 kyr BP and was complete by 6 kyr BP. These findings imply either that sea level during the LGM fell less than present estimates suggest, or that an ice volume considerably greater than currently accepted must have been present in the Northern Hemisphere.