The geomorphic and sedimentary record of past subglacial water outbursts, Sabrina Coast, East Antarctica

Abstract:

The drainage basin of Totten Glacier (TG) comprises nearly one-eighth of the East Antarctic Ice Sheet and contains an estimated ice volume equivalent to 6.9 m of eustatic sea level rise, a value greater than the entire West Antarctic Ice Sheet. Adjacent, and partially covering the area presently corresponding to TG drainage basin, is the Aurora Subglacial Basin, a deep trough that reaches more than 1 km below sea level where geophysical data suggest the existence of numerous subglacial water bodies. Such water bodies maintain zero basal shear stress relatively to the overlying ice. It is theorized that subglacial outburst would decrease the shear stress at the bottom of marine ice sheets near the margin, inducing ice acceleration, thinning and ultimately contributing to the collapse of the ice sheet. In this contribution we present part of the preliminary results of the first geological and geophysical marine survey (NBP1402) to the inner continental shelf off the Sabrina Coast in the Totten Glacier/Moscow University Ice Shelf area, East Antarctica. We describe a set of subglacial features that we interpret as representing the sedimentary and geomorphic record of past subglacial water outbursts. These features, which we refer as “feather moraines”, were imaged by high-resolution multichannel seismic (MCS) and CHIRP data to consist of a stack of subglacial sediments separated by erosional unconformities, and were shown in the swath bathymetry to consist of feather-like areas exhibiting cross and cut relationships between different sets, with distinct step-wise borders on the downstream side. They are superimposed on megascale glacial lineations (MSGL) and are elongated in generally the same direction as the MSGLs. The upstream side of the feather moraines coincides with the initiation of the MSGL and an area of drumlins near the limit of the glacial sediments and the outcropping of bedrock. A network of channels carved in bedrock just south of the feather moraines point in the direction of these geomorphic features suggesting a genetic link. The MCS imaged architecture indicate a constructional origin with progradational facies on the downstream side, and complex array of unconformable surfaces separating different growth stages. Ongoing sedimentary analyses of core samples taken from these features will be discussed.