Mind the Gap: Fluid Flow Along the Ice-Bed Interface

Glaciers and ice sheets move under their own weight, redistributing ice from regions of snowfall at high elevations to regions of ice loss at low elevations. A key driver of glacier movement is sliding at the ice-bed interface. A glacier’s sliding speed depends on the amount of water underneath the ice, with high water pressures typically corresponding to faster sliding. However, for many glaciers where the subglacial bed is soft and permeable, the complexity of water flow and drainage remains poorly understood. This project will investigate the movement of water at the ice-bed interface through a combination of laboratory and theoretical approaches. This project will support several undergraduate and graduate students and offer hands-on training in experimental and numerical techniques. The team will build an improved model of subglacial water flow, which will reduce uncertainty in future ice discharge from polar ice sheets, and ultimately lead to better forecasts of future sea level rise. The fast movement of many West Antarctic ice streams and outlet glaciers is due to slip at the ice-bed interface. Liquid water at the bed reduces the basal resistance to flow and increases slip speed. Experimental and theoretical studies have investigated the relationship between water pressure at the bed and basal resistance to flow, and identified that the effective pressure (the difference between ice overburden pressure and water pressure) is a key quantity. However, water pressure on soft (i.e., deformable and erodible) beds remains poorly modeled. This project will use a range of theoretical, numerical, and experimental techniques to (1) derive a model of distributed water flow in the bed-till aperture and within the till; (2) analyze the conditions that determine whether distributed drainage will occur predominantly within the till or at the ice-bed interface; and (3) solve this model numerically to determine how the system can be parameterized for large-scale simulations of the Antarctic ice sheet. This project will improve our understanding of basal slip and the effective pressure underneath glaciers, one of the main uncertainties in ice flow modeling. This in turn will lead to a better understanding of glacier and ice sheet dynamics, ultimately enhancing projections of future sea level rise and informing planning for coastal communities. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.