Satellite observations of Antarctic subglacial hydrology

A series of recent discoveries regarding Antarctic subglacial hydrology have shown that the interaction between an ice sheet and its underlying water system is more active and complex than had been imagined. A better understanding of the physical processes and spatial extent of subglacial hydrologic systems is needed to assess their impact on ice sheet dynamics, and to correctly incorporate subglacial hydrology into ice sheet models. This requires a clearer picture of the locations of subglacial reservoirs, the frequency and quantity of water exchanged between them, and the configuration of subglacial conduits. Datasets for studying subglacial hydrology are, however, limited both in spatial and temporal coverage because the environment is remote and inaccessible. Since 2005, satellite observations (InSAR and radar/laser altimetry) have transformed our understanding of the Antarctic subglacial environment. Before this, most known subglacial lakes were near ice divides, and were thought to be isolated, and exerting only localised influence on the ice flow. By inference from rapid, localised surface elevation changes measured by satellite, subglacial water has been observed to move rapidly between sub-ice reservoirs; refill and drainage can occur via steady flow and/or episodic floods. Mapping of surface slope and ice thickness shows that the reservoirs, and inferred conduits, lie precisely in regions of lower hydropotential. Active lakes have been detected throughout many glacial catchment basins; lakes not only exist under the ice divides, but are also present under upper catchment areas and the fast-flowing ice streams. Complex hydrologic systems consisting of interconnected water bodies have been observed in the lower ice streams, with fill-drain cycles of years to decades. Although in one case (Byrd Glacier) a subglacial flooding event led to a temporary 15% increase in mass flux, the impact of these subglacial water systems on ice dynamics and ice sheet mass balance remains largely unknown.