Geophysical investigations of the coastal evolution of the Totten Glacier System, East Antarctica
The Sabrina Coast is the primary outlet of ice from the Aurora Subglacial Basin, draining more than 3.5 meters of eustatic sea level potential into the Indo-Pacific sector of the Southern Ocean. Recent work has shown that the Aurora Subglacial Basin has drained and filled many times since large scale glaciation began including evidence that it collapsed during the Pliocene. Ice predominantly flows from the interior to the coast through two outlet glaciers, Totten Glacier and the unnamed glacier feeding the Moscow University Ice Shelf. Steady thinning rates near the grounding line of Totten Glacier 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 while thinning rates are modest for the glacier feeding the Moscow University Ice Shelf. 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 300-600 m depth range. Here we show that entrances to the cavity deeper than this range of thermocline depths indicate that the TGIS is vulnerable to intrusions of mCDW. We relate areas of elevated basal specularity and reflectivity (flatness and brightness of the ice-ocean interface, respectively), supported by independent model predictions and ice flow divergence estimates of basal melt, to ice draft and ice thinning rates, demonstrating that the current climatological regime is enhancing melting of ice deeper than 800 mbsl in the cavity, possibly resulting in a bifurcated coastal ice thinning signal. For the first time in East Antarctica, and the first time using ice sounding radar, we identify large basal channels and flat terraces several kilometers wide and several hundred meters deep produced by complex ice-ocean melt processes in the deep, warm cavity waters. Finally, by analyzing new physical oceanographic data recently acquired along the Sabrina Coast, we show that the depths of deep, warm mCDW observed on the continental shelf relative to the coastal bathymetry control the coastal thinning of ice between the Moscow University Ice Shelf and Totten Glacier; moderate shoaling the average depth of the thermocline would allow the observed mCDW to breach this topography and enhance coastal melting. The lack of dense, cool Shelf Water at depth on the continental shelf indicates that that variability in heat content along the Sabrina Coast is driven by far-field oceanic boundary conditions, not to polynya activity as has been proposed. Predicting future change in this important area of the coastline requires improved knowledge of the sub-ice shelf boundary conditions and processes, and controls on continental shelf circulation and heat transfer.