Deep beneath Antarctica’s kilometers-thick layer of glacial ice is a complex network of rivers and lakes. Research suggests that this water may affect the flows of the southern continent’s massive ice streams, though the nature of its effect remains unclear. Adding to scientists’ understanding of Antarctica’s subglacial hydrology, Christoffersen et al. studied five ice streams that flow into the Ross Sea.
Ice streams’ fast flow rates make them Antarctica’s dominant contributors to sea level rise. Ice streams tend to overlay glacial till, loose sediments that create little frictional drag, driving their fast flows. Subglacial water is also thought to contribute, though how and by how much is uncertain.
Using observations of ice motion, bedrock topography, ice thickness, and sediment thickness and an ice sheet model, the researchers estimated the amount of water produced by the ice streams. Comparing these quantities with the amount that flows through pores in the underlying till layer and along the rock surface, they found that the quantity of water produced by each ice stream is surprisingly low and that external hydrological sources are needed to explain the ice streams’ fast motion. For three of the ice streams—Whillans, Mercer, and Kamb—the researchers identified the external source as a large subglacial groundwater reservoir. For the two remaining ice streams, Bindschadler and MacAyeal, the extra water was produced in the ice sheet interior and moved to the ice streams through the regional hydrological network.
The authors found that the amount of water flowing from the ice sheet interior to the Whillans, Mercer, and Kamb ice streams is insufficient to provide sustained fast flows. The recent observed slowdown of these ice streams should be attributed to increasing friction between the ice and the rock bed caused by strengthening and compaction of the underlying glacial till, which is losing water. (Geophysical Research Letters, doi:10.1002/2014GL059250, 2013)
—Colin Schultz, Writer