Moisture generation and transport at ice stream margins

Alterations to glacial mass balance brought about by dynamic changes in ice ow play a key role in the global climate system via sea-level rise, diminishing albedo and alterations to atmospheric circulation. A detailed understanding of these dynamics is therefore a prerequisite to making accurate predictions of future global ice extent and quantifying its feedbacks on the changing climate. Temperate zones are predicted to exist deep within the Antarctic ice sheet due to intense shear heating at ice stream margins. These are the lateral boundaries of fast- owing regions known as ice streams: rivers of ice which may account for up to 90% of the ow into ice shelves and the surrounding oceans. Thus understanding how ice streams and their margins evolve under temperate ice-water dynamics is of great importance in the climate science community. However, current efforts to include meltwater in glaciological models do not fully couple the dynamic ows of ice and water necessary in describing the full physics in these temperate zones and hence the physics of ice stream margins. We suggest using a two-phase uid dynamical model to describe the movement of water through viscously deforming polycrystalline ice. We investigate the application of this theory to a planned experiment, designed to mimic glacial conditions and reproduce ice deformation in order to infer its rheology. Introducing the mathematics of two-phase ows, originally intended for applications in magma-mantle dynamics, we explain how these equations may equally be applied to ice-water mixtures. More speciffically, we explain how they apply to an experimental setup, drawing inferences on the evolution of ice stream margins. Solutions are identified under constant stress boundary conditions, achieving a stable steady-state porosity φ of 2% assuming a viscosity constant λ much larger than that used from analogy with mantle rocks. That is, we predict that the viscosity of glacier ice is much more sensitive to changes in porosity than that of the mantle. Using this model, the total drainage from Dragon Margin of Whillans Ice Stream, in the Ross Ice Shelf, West Antarctica, due to englacial melting is 36 m3yr-1 per metre downstream. We also lay the groundwork for a two-phase 1D numerical model, and provide recommendations for further modelling and experimentation based on our results.