GLACIAL GEOMORPHOLOGIC MAP OF MCMURDO SOUND, ANTARCTICA (78°S): A TERRESTRIAL RECORD OF LATE PLEISTOCENE GLACIATIONS IN THE ROSS SEA WITH IMPLICATIONS FOR FORMER ICE SHEET VOLUME AND CONTRIBUTION TO DEGLACIAL SEA LEVEL RISE

Antarctica’s recent glacial history provides important geologic constraints on potential sea level rise (SLR) from the burning of fossil fuels. However, as almost 98% of the continent is covered with glacial ice, terrestrial archives for ice advance and retreat are rare. The ice-free oasis of the McMurdo region (78°S) offers a unique terrestrial record for Quaternary changes in ice derived from both East and West Antarctica. During three Antarctic field seasons, we mapped the distribution of glacial deposits at key sites on volcanic islands in McMurdo Sound (1:20,000 scale). We developed a drift chronology using radiocarbon-dated algae recovered from ice-marginal deposits and cosmogenic nuclide exposure ages of glacial erratics. Field observations were traced onto aerial photographs and digitally mapped in ArcGIS. We complemented field mapping with image analysis of LandSat (30m/pxl) and DigitalGlobe (<2m/pxl) scenes and geomorphometric analysis of stereo-photogrammetric digital elevation models (2m/pxl) produced by the Polar Geospatial Center. We present a compiled glacial geomorphologic map (1:100,000) of the McMurdo Sound region that is integrated with local data from marine multi-beam bathymetry and sediment records. The combined results show that glacial ice advanced and grounded throughout McMurdo Sound at least twice during the Late Pleistocene. The earliest and most extensive glaciation occurred during Marine Isotope Stage (MIS) 8, and reached a local maximum of ~770 m elevation on Mount Discovery. During MIS 2, grounded ice advanced to at least ~510 m elevation on Mount Discovery and remained at local maxima throughout McMurdo Sound from ~19.6 to ~12.3 ka. Combined with allied data across the wider Ross Embayment, which show that widespread deglaciation outside McMurdo Sound did not commence until ~13.1 ka, these data suggest that deglaciation in the Ross Embayment did not add significantly to SLR during Meltwater Pulse 1a (14.0-14.5 ka). Our data also show no significant advance of locally derived ice during glacial periods, consistent with the assertion that Late Pleistocene expansion and retreat of grounded ice in the Ross Embayment occurs in response to changing eustatic sea level and oceanic heat fluxes, rather than local changes in precipitation and ice accumulation.