Melting glacial ice from below: from volcanoes to ice shelves
Antarctica is a major source of potential sea level rise, holding 58 meters of sea level equivalent in the Antarctic Ice Sheet. The Antarctic Ice Sheet’s mass balance is governed indirectly by melting from below, which determines the rate at which ice flows from the interior of the continent to the ocean. My thesis addresses three sources of heat which contribute to basal melting: oceanic heat flux, geothermal heat flux, and heat from subglacial volcanism. I measured oceanic heat flux and geothermal heat flux at a location in West Antarctica where the ice sheet transitions from grounded on the continent to floating over the ocean. Oceanic heat flux and thus ice-shelf basal melt rates were low at this site (0.7 W m-2 or 7 cm yr-1) as a result of slow currents and stable stratification of colder and fresher water near the ice base. On the other hand, geothermal heat flux was moderately high at this site (0.09 W m-2), though lower than the oceanic heat flux. Another measurement of geothermal heat flux only 100 km away revealed a much higher value (0.3 W m-2); this spatial variability in geothermal heat flux could be explained by magmatic intrusions and/or advection of heat by flowing crustal fluids. In a separate investigation, I assess whether the magmatic history in Antarctica and elsewhere might have been influenced by the glacial history of these regions. Using a thermomechanical magma reservoir model, I show that ice thinning can increase the frequency of eruptions from ice-covered volcanoes and thus increase basal melting. The results from these three projects can improve the representation of basal melting sources in ice-sheet models and thus improve the accuracy of sea level projections.