The first geothermal heat flux measurement below the West Antarctic Ice Sheet
Friday, 19 December 2014
The geothermal heat flux is a critical thermal boundary condition that influences the melting, flow and mass balance of outlet glaciers and ice sheets. We measured directly the geothermal heat flux below the West Antarctic Ice Sheet (WAIS), under Subglacial Lake Whillans (SLW), as part of the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project. The one-dimensional, conductive heat flux is the product of thermal gradient and thermal conductivity. We developed and fielded a tool to determine the thermal gradient in lake sediments, after penetrating ~800 m of ice using a hot water drilling system. We used the needle-probe method to measure the thermal conductivity of sediments recovered from the bottom of the lake with a gravity-driven multi-corer. The thermal gradient was determined during two separate deployments of the geothermal tool, which penetrated ~1.1 m into the till below SLW, yielding essentially identical results: 0.21±0.07 °C/m. Fifteen sediment thermal conductivity measurements yield an average value of 1.36±0.12 W/m-K. The heat flux determined from these measurements is 285±85 W/m2. This value is somewhat higher than that estimated from the WAIS-Divide ice core site, 230 mW/m2, ~800 km away, and much higher than regional estimates based on magnetics and a global seismic model, generally ≤100 mW/m2. Elevated heat flux in this area could result from thermal perturbations associated with rifting, crustal thinning, or volcanic activity. Heat flux of this magnitude is likely to cause basal melt rate of a few cm/year. If this value is representative of conditions below this part of the WAIS, it might help to explain the occurrence of active subglacial lakes and fast-moving ice streams and the ice dynamics of WAIS more broadly.