Temperate ice develops at topographic highs beneath Thwaites Glacier

Thwaites Glacier is the largest marine-terminating glacier draining the Western Antarctic Ice Sheet. Ice loss from Thwaites is of global importance because it currently contributes ~4% of global sea level rise and is thought to serve as an indicator of how WAIS responds to climate change. Even though Thwaites is well-studied, our understanding of ice-motion near the bed remains enigmatic. Specifically, it is uncertain how subglacial topographic highs interact with ice flow, and this challenges efforts to predict changes in flow and understand subglacial landform development. We present a 3D thermo-mechanically coupled model to investigate ice motion over high-resolution bed topography of Thwaites Glacier. We show that basal slip rates vary considerably at topographic rises where inferred basal traction is high, and landforms are interpreted to be predominantly erosive. Simulations show temperate ice is locally present at these topographic highs, where it can sensitively influence flow resistance. In contrast, basal slip rates are high and uniform in topographic basins where inferred basal traction is low, and landforms are interpreted to be predominantly depositional. Flow-parallel lineations in these depositional settings did not greatly influence ice motion compared to uniform beds in our simulations. Preexisting geology is the crucial decider of landform morphology and ice flow, particularly at erosive topographic highs. The millennial lifespan of structural topographic highs suggests that patterns of basal traction beneath Thwaites Glacier are largely controlled by subglacial topography, not subglacial drainage.