Vast fossil seawater reservoir found beneath the West Antarctic Ice Sheet

Though direct evidence of a groundwater reservoir lying beneath the subglacial water system along the base of the Antarctic Ice Sheet has been elusive, researchers now present obser­vations of such a reservoir beneath the Whillans Ice Stream in West Antarctica. This reservoir is esti­mated to contain a water volume more than 10 times greater than that in the overlaying subglacial hydrologic system, the researchers say; their finding highlights groundwater hydrol­ogy as a potentially critical piece in understanding the effect of water flow on Antarctic ice sheet dynamics. Subglacial water moves along the base of the Antarctic Ice Sheet through an under-ice plumbing network known as the “subglacial hydrologic sys­tem." Water flow in this system plays an important role in modulat­ing ice motion by providing lubrication between the ice sheet and the bedrock, or by causing the deformation of wet sediments beneath glaciers. Through these two mechanisms, water at the base of the ice sheet controls Antarctica’s ice sheet dynamics and, poten­tially, its contribution to sea level rise. To date, the subglacial hydrologic sys­tem has been considered to be a shallow system in which wa­ter exists either at or very near the base of the ice sheet. Now, Chloe Gustafson et al. use magnetotelluric and passive seismic data from Whillans Ice Stream, West Antarctica, to provide the first observations of deep sub-ice stream groundwater. They show that the subglacial sediments beneath Whillans Ice Stream are saturated with a mixture of fossil seawater and freshwater from the glacier. This groundwater, extending downward for more than a kilometer, contains more than ten times as much fluid volume as the shallow hydrologic system above and actively exchanges with it. Consequently, it has the potential to modulate ice streaming and subglacial biogeochemical reactions. “We expect that similar groundwater systems exist within other marine sedimentary basins that underlie Antarctic ice stream,” say the authors. “Understanding the influence of this groundwater on ice sheet behavior will require its integration into the next generation of ice sheet models.” Winnie Chu discusses the findings in more detail in a related Perspective.