Time-dependent freshwater fluxes from deep and shallow meltwater sources under Antarctica's large ice shelves

Recent mass loss of Antarctic grounded ice is driven primarily by a decrease in buttressing as the floating ice shelves downstream lose mass by calving and basal melting in excess of steady state values. Large-scale observations of ice shelf melt rates and corresponding freshwater fluxes are difficult to make using in situ techniques, but can be inferred using satellite and airborne observations combined with output from atmospheric and firn models. We estimated height changes from CryoSat-2 radar altimetry (2010-present) for all ice shelves at 1 km resolution averaged over the mission duration, and interpreted these results in the context of estimates of annual basal melt rates at 25 km resolution for ice shelf regions up to 81.5°S from the 25 year record (1994–present) obtained from the ERS-1, ERS-2, Envisat, and CryoSat-2 missions. We converted ice shelf height changes to basal melt rates using vertical strain rates from satellite-derived ice velocity and a new, high-resolution (12.5 km) atmospheric and firn densification model. For the three largest ice shelves (Amery, Filchner-Ronne, and Ross), we partitioned basal melting into deep melting associated with inflows of High Salinity Shelf Water (HSSW) and shallow melting from inflows of modified Circumpolar Deep Water and seasonally warmed Antarctic Surface Water. The deep freshwater sources contribute to Antarctic Bottom Water formation, and the shallow sources feed freshwater into the upper coastal ocean where they affect ocean-atmosphere interactions, sea ice evolution, and primary productivity. The 25-year time series of meltwater production at deep and shallow sources show distinct spatial and temporal signatures that we use to examine oceanic and atmospheric drivers of melting and ocean response.