Ice flow field over Lake Vostok, East Antarctica inferred by structure tracking

Here, we present a flow field for the East Antarctic ice sheet over Lake Vostok based on tracking structures across the lake inherited from the western, upstream shoreline. The structures, distinctive peaks and troughs identified in the ice sheet internal layers, are imaged in ice-penetrating radar data collected in a systematic grid over the lake. These structures are resolved in three distinct internal layers at depths between 900 and 3750 m. Ridges in the internal layers are associated with prominent topographic highs along the western shoreline, and troughs are correlated with shoreline topographic lows. Lake Vostok is bisected by a topographic ice divide; south of this topographic divide the ice flow is dominantly NNW to SSE and north of the divide the ice flow is W to E. The flow over the lake is also deflected by the small (∼0.02%) southward lake surface slope. Accretion ice, lake water frozen to the bottom of the ice sheet, is preferentially imaged along flowlines emanating from topographic ridges. The coincidence of the accretion ice reflector with our flowlines both provides independent support for our new flow field, and suggests focused accretion along the western shoreline. Global positioning system (GPS) data provide additional independent support for our new flow field in the southern lake. The new flow field will be crucial for subsequent analyses of mass exchange between the ice sheet and the lake, identifying areas of melting above the lake and estimating residence times.