Walking on thin ice: New find could force change in ice flow understanding

A new discovery deep beneath one of Antarctica’s rivers of ice could change scientists’ understanding of how the ice flows, with important implications for estimating future sea level rise. This assumes special significance since the Earth’s southernmost continent contains 187ft of sea level rise potential. A report about the study was published in the journal Science last Thursday. The groundwater system, found in deep sediments in Whillans Ice Stream on the West Antarctic Ice Sheet, reveals an unexplored part of the region and may have implications for how the frozen continent reacts to the climate crisis. The study is based on a 61-day field exercise in 2018 by glacier scientists Matthew Siegfried from Colorado School of Mines, Chloe Gustafson from Scripps Institution of Oceanography and their colleagues.The 96.6km-wide Whillans Ice Stream is one of a half-dozen streams feeding the Ross Ice Shelf, the world’s largest, at about the size of Canada’s Yukon Territory. The research team used geophysical instruments placed directly on the surface to execute a technique called magnetotelluric imaging. The technique can detect the differing degrees of electromagnetic energy conducted by ice, sediment, bedrock fresh water and salt water and create a map from these different sources of information. “We imaged from the ice bed to about 5km and even deeper,” said coauthor Kerry Key, an associate professor of earth and environmental sciences at Columbia University.The researchers calculated that if they could squeeze the groundwater from the sediments in the 100sq km they mapped onto the surface, it would form a lake that ranged from 220 to 820m deep. The ice cap that covers Antarctica isn’t a rigid whole. Researchers in Antarctica have discovered in recent years hundreds of interconnected liquid lakes and rivers cradled within the ice itself. But this is the first time the presence of large amounts of liquid water in below-ice sediments has been found.While glaciers cover only 10% of Earth, the glaciers in Antarctica account for 85% of that coverage. Depending on how this groundwater behaves, it could help ice flow faster or slower into the ocean. The researchers suggest that when the system is stable, groundwater will drain into the Southern Ocean as more meltwater infiltrates the sediments. But if the ice streams were to lose mass under the rising temperatures of climate change, their reduced pressure on the sediments beneath them could allow more groundwater to rise to the surface, further lubricating the base of the stream and increasing its velocity, threatening the future of the continent’s ice cover.The researchers said more work needed to be done understand the implications of the groundwater discovery, particularly in relation to climate crisis and rising sea levels. It was possible that the slow draining of water from the ice into the sediment could prevent water from building up at the base of the ice – acting as a brake for the ice’s forward motion toward the sea.However, if the surface ice cap were to thin, the reduction in pressure could allow this deep water to well up. This upward movement would lubricate the base of the ice and accelerate its flow.“This finding highlights groundwater hydrology as a potentially critical piece in understanding the effect of water flow on Antarctic ice sheet dynamics,” Winnie Chu, an assistant professor at the Georgia Institute of Technology, wrote in a commentary on the research that was published in Science. She was not involved in the study.