Did meltwater pulse-1a come from Antarctica?: a critical assessment of the near-field geological evidence

Speaker details
Mike Bentley Department of Geography, University of Durham
Event contact
Isobel Howe (isobel.howe@bristol.ac.uk) University of Bristol
Related Research Groups
Sea Level, Ice Sheets and Isostasy

Abstract

Sea-level fingerprinting studies of far-field sites have suggested that meltwater pulse-1a (MWP-1a) was dominantly sourced from Antarctica. This implies a substantial change in ice sheet volume in Antarctica and one that should be detectable in the geological record. Here, I review the geological evidence of former ice sheet extent, thickness and deglacial chronology to assess if such a volume of ice could have been accommodated in the Antarctic ice sheet, and if so the likely location(s) within the ice sheet. There are two key questions I address. One is to quantify total excess ice volume in the different sectors of the Antarctic ice sheet during the Last Glacial Maximum (LGM): this can establish if enough ice existed prior to 14.5 ka to make a significant contribution to the required 15-20m of rapid sea-level rise. A second question is to ask if major changes in ice sheet extent/volume occurred during the MWP-1a interval itself. The geological evidence for former ice sheet extent comes primarily from geological and geophysical techniques, particularly the use of multibeam (swath) bathymetry in the last decade or so.  Onshore investigations of ice sheet thickness have also been ongoing for several decades but have been particularly supplemented in recent years by the use of cosmogenic surface exposure dating. For the West Antarctic Ice Sheet, the areas of significant ice sheet change during the LGM include the Ross Sea embayment, the Weddell Sea embayment, the Amundsen Sea, and the Antarctic Peninsula. For each of these there are now varying degrees of constraint on LGM extent and thickness, with the best-constrained areas being the Ross Sea and Antarctic Peninsula. Available data suggest rather modest LGM excess ice volumes in the West Antarctic Ice Sheet and were unlikely to form the dominant source for MWP-1a. The East Antarctic Ice Sheet is more poorly constrained and for large parts of its marine margin we do not know the LGM extent or thickness. A few locations suggest some marginal thickening and advance, but the wider applicability of these data are not clear, and so total volumes are difficult to assess. There is an urgent need for more glacial geological data around the East Antarctic margin, especially the Queen Maud Land and Wilkes Land sectors. At present, the data-poor East Antarctic Ice Sheet remains the most likely area in which a significant MWP-1a contribution could be accommodated.