Tectonic Influence on Bed-Character Variability under Thwaites Glacier, West Antarctica

Subglacial topography and bed character are important controls on glacier and ice-sheet flow. Previous studies using reflection-seismic data from the upper half of Thwaites Glacier, West Antarctica, have shown variations in the bed character in the along-flow direction with continuous soft bed in the flatter “lowland” areas and a mix of soft and hard bed over more elevated, rugged “highland” areas. Here we use long-offset reflection/refraction seismic and aerogravity data over a ~40-km section 230-km inland of the current grounding line to model the upper-crustal structures and relate them to the previously identified bed-character variability. We identified a sedimentary basin ~11-km long and up to ~400-m deep beneath the lowland area with continuous soft bed. The downstream end of this sedimentary basin aligns with the transition from the lowland to highland area which indicates its existence could be related to the formation of the subglacial topography. The sedimentary basin is a graben or half-graben potentially formed due to rifting associated with the development of the West Antarctic Rift System, suggesting tectonic influence on the bed character variability and, in turn, on the glacier flow. We will further analyze the seismic reflection data and also add aeromagnetic data to model the crustal structures more accurately and clarify the potential tectonic control on bed-character variability.