Increased Ocean Access to Totten Glacier, East Antarctica

Monday, 14 December 2015: 09:30
3007 (Moscone West)
Donald D Blankenship1, Jamin Stevens Greenbaum2, Duncan A Young2, Thomas G Richter3, Jason L Roberts4, Alan Aitken5, Benoit Legresy4, Roland Charles Warner6, Tas D van Ommen4 and Martin J Siegert7, (1)University of Texas at Austin, Austin, TX, United States, (2)University of Texas, Institute for Geophysics, Austin, TX, United States, (3)University of Texas at Austin, Institute for Geophysics, Austin, TX, United States, (4)Australian Antarctic Division, Kingston, Australia, (5)University of Western Australia, School of Earth and Environment, Crawley, WA, Australia, (6)Australian Antarctic Division, Kingston, TAS, Australia, (7)Imperial College London, London, United Kingdom
The Totten Glacier is the largest ice sheet outlet in East Antarctica, draining 3.5 meters of eustatic sea level potential from the Aurora Subglacial Basin (ASB) into the Sabrina Coast. Recent work has shown that the ASB has drained and filled many times since largescale glaciation began including evidence that it collapsed during the Pliocene. Steady thinning rates observed near Totten Glacier’s grounding line since the beginning of the satellite altimetry record are the largest in East Antarctica and the nature of the thinning suggests that it is driven by enhanced basal melting due to ocean processes. Warm Modified Circumpolar Deep Water (MCDW), which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the Sabrina Coast continental shelf in the 400-500 m depth range. Using airborne geophysical data acquired over multiple years we delineate seafloor valleys connecting the inner continental shelf to the cavity beneath Totten Glacier that cut through a large sill centered along the ice shelf calving front. The sill shallows to depths of about 300 mbsl and was likely a grounding line pinning point during Holocene retreat, however, the two largest seafloor valleys are deeper than the observed range of thermocline depths. The deeper of the two valleys, a 4 km-wide trough, connects to the ice shelf cavity through an area of the coastline that was previously believed to be grounded but that our analysis demonstrates is floating, revealing a second, deeper entryway to ice shelf cavity. The previous coastline was charted using satellite-based mapping techniques that infer subglacial properties based on surface expression and behavior; the new geophysical analysis techniques we use enable inferences of subglacial characteristics using direct observations of the ice-water interface. The results indicate that Totten Glacier and, by extension, the Aurora Subglacial Basin are vulnerable to MCDW that has been observed on the nearby Sabrina Coast continental shelf by multiple shipborne expeditions beginning in 1996.