New 3D bathymetry and sediment distribution in Lake Vostok: Implication for pre-glacial origin and numerical modeling of the internal processes within the lake

Abstract: A new distribution of water and unconsolidated sediments in subglacial Lake Vostok, East Antarctica was developed via inversion of airborne gravity data constrained by 60 seismic soundings. A model was developed for host rock with a density of 2550 kg/m3 that was inferred from prior 2D modeling. Our 3D bathymetry model of Lake Vostok corresponds better with seismic data (RMS of 125 m) than two previous models based on the same gravity dataset. The good match in both water and sediment thicknesses between the gravity model and seismic measurements confirms two major facts about Lake Vostok: (1) the lake is hosted by sedimentary rocks, and (2) the bottom of the lake is covered with a layer of unconsolidated sediments that does not exceed 300 m in the southern basin and thickens almost to 400 m in the northern basin. Our new bathymetry model suggests much shallower water thicknesses (up to twice the previous estimates) in the middle and northern parts of the lake, while the water layer is thicker in the southern basin. Numerical modeling of the internal processes in the lake reveals the relevance of our new bathymetry model to the basal mass balance. A significant decrease in transport is observed in the shallower northern basin, as well as a decrease of 33% in the turbulent kinetic energy. However, only minor differences were observed in the distribution of the calculated freezing and melting zones compared to previous models. Estimates for the sedimentation rates for six possible mechanisms were made. Possible sedimentation mechanisms are: (1) fluvial and periglacial, i.e. those that are active prior to the establishment of a large subglacial lake; (2) deposition due to overlying ice sheet, including melting out of the ice, as well as bulldozering by the overriding ice; and (3) suspended sediments from subglacial water flow including those deposited by periodical subglacial outbursts. The estimates for these mechanisms show that unconsolidated sediments of the observed thickness are most consistent with a lake that existed before glaciation. [Copyright &y& Elsevier]