Antarctic glacier robot observations surprise scientists

New observations by an international team of researchers, including Peter Davis of the British Antarctic Survey, David Holland, principal investigator for the Center for Sea Level Change, New York University Abu Dhabi, and other members of the International Thwaites Glacier Collaboration, show that melting beneath much of the ice shelf is weaker than previously modelled. 

The observations were made from a 587-metre-deep hot-water-drilled access hole and a remotely operated underwater robot called Icefin. Ocean measurements were compared with melt rate observations at five different sites underneath the ice shelf. Between January and September 2020, the grounding zone was found to become warmer and saltier, but the melt rate at the ice base was no more than two to 5.4 metres per year, which is less than previously estimated. 

Davis describes the results as “highly surprising”. He explains: “As we had expected, our observations showed that there is plenty of ‘warm’ ocean water (1.5°C above the freezing point) available to drive melting at the ice shelf base. What we did not expect to see was that the ice shelf was largely isolated from this warm water by a layer of very fresh water right beneath the ice. This fresh layer suppresses the transfer of ocean heat into the ice, slowing the basal melt rate.”

He notes that, although the observed melt rate was much smaller than expected, the grounding line beneath Thwaites Glacier is still retreating rapidly, with significant implications for global sea-level rise. “Our results therefore show that rapid grounding line retreat can be driven by much lower rates of basal melting than previously thought, and it doesn’t take much to push Thwaites Glacier out of balance,” he says.    

Ted Scambos at the Earth Science and Observation Center of the Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, who was not involved in the study, says the work reveals “new aspects to the processes affecting the giant Thwaites Glacier and, despite being in a current slow period with respect to melting, earlier melting is still affecting its flow speed. Moreover, the melting we are seeing along the steeper edges of the underside of the ice points to a new style of ice shelf damage and break-up.” 

“I would like to congratulate the team members for their great achievement,” says polar oceanographer, Yoshihiro Nakayama at the Institute of Low Temperature Science, Hokkaido University, Japan, who was also not involved in the study. “They are the only people in the world who can accomplish such crazy observation beneath 500 metres of ice. I am sure this observation will lead to a breakthrough in our scientific community.”

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