A TERRESTRIAL PERSPECTIVE OF THE LGM IN MCMURDO SOUND, ANTARCTICA: IMPLICATIONS FOR MARINE ICE SHEET DYNAMICS, ICE FLOW, AND DEGLACIATION OF THE ROSS SEA EMBAYMENT

During the Last Glacial Maximum (LGM), grounded glacier ice filled the Ross Embayment and deposited glacial drift on volcanic islands and peninsulas in McMurdo Sound, as well as along coastal regions of the Transantarctic Mountains (TAM), including the McMurdo Dry Valleys and Royal Society Range. The flow geometry and retreat history of this ice, however, remains debated. We present terrestrial geomorphologic evidence that enables the reconstruction of former ice elevations, ice-flow paths, and ice-marginal environments in McMurdo Sound with implications for the fundamental dynamics, interaction, and behavior of the East and West Antarctic ice sheets during the late Quaternary. Radiocarbon dates of fossil algae interbedded with ice-marginal sediments provide a coherent timeline for local ice retreat. These data are integrated with multi-beam data and marine-sediment records to reconstruct late glacial dynamics of grounded ice in McMurdo Sound and the western Ross Sea. Grounded glacier ice reached and remained near its maximum extent in McMurdo Sound between 19.6 and 12.3 calibrated thousands of years before present (cal. ka). In combination with allied glacial-marine data from across the wider Ross Embayment, which suggests that deglaciation outside McMurdo Sound did not commence until ~13.1 ka, the implication is that retreat of grounded glacier ice in the Ross Embayment did not add significantly to sea level rise during Meltwater Pulse 1a (14.0-14.5 ka ). In addition, the combined dataset suggests a dominance of ice flow toward the TAM in McMurdo Sound during all phases of glaciation, with no significant advance of locally derived ice from the TAM. The implication is that Late Pleistocene expansion of grounded ice in McMurdo Sound, and throughout the wider Ross Embayment, reflects advance of marine-based outlet glaciers and ice streams in response to lower eustatic sea level and perhaps reduced oceanic heat flux, rather than local increases in precipitation and ice accumulation.