Temperate ice in the shear margins of the Antarctic Ice Sheet: Controlling processes and preliminary locations

The flux of grounded ice from the Antarctic Ice Sheet (AIS) primarily occurs through narrow, fast-flowing outlet glaciers and ice streams. Shearing generates heat in the lateral glacier margins, where there is a transition from fast-flow to near-stagnant ice or rock. This heat warms the ice and can form zones of water-saturated porous ice at the melting temperature, known as temperate ice. Here we derive a one-dimensional thermomechanical model to infer which AIS shear margins may contain temperate ice. Our model provides expressions for the critical shear strain rate at which a zone of temperate ice initiates and the thickness of the temperate zone. Both of these quantities are described by two nondimensional numbers-the Brinkman and Péclet numbers-that are functions of observable parameters such as shear strain rate, surface temperature, surface accumulation rate, and ice thickness. The development of temperate zones is incited by shear strain rates (Brinkman number) and suppressed by the advection of cold ice from the surface (Péclet number), which scales with surface accumulation rate. We also include a parametrization for lateral advection, which can suppress the formation of temperate ice. Applying recent observations and outputs from a regional climate model, we show that many active glacier shear margins could contain temperate ice. The spatial distribution and thickness of temperate zones are controlled largely by shear strain rates and surface accumulation rates.