 "Melting of Antartica's Thwaites Glacier observed by underwater robot: Study")
Widespread cracks and crevasses were revealed in observations beneath the floating shelf of the vulnerable Thwaites Glacier of the Antarctic, where melting occurs more rapidly, contributing to its retreat and potentially to sea-level rise, according to a new study.
The first-of-their-kind observations of the Florida-sized glacier was obtained by deploying the remotely operated Icefin underwater robot through a nearly 2,000-foot-deep borehole drilled in the ice, the study said.
The research team from Cornell University, US, and international collaborators, captured the first close-up views of the critical point near the grounding line where Thwaites Glacier in western Antarctica - one of the continent's fastest changing and most unstable glaciers - meets the Amundsen Sea, the study said.
From that area, the researchers concluded that Thwaites has retreated smoothly and steadily up the ocean floor since at least 2011.
They found that flat sections covering much of the ice shelf's base were thinning, though not as quickly as computer models had suggested.
Meanwhile, the walls of steeply sloped crevasses and staircase-like features were melting outward at much faster rates, the study said.
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The findings, reported in the journal Nature, provided new insight into melting processes at glaciers exposed to relatively warm ocean water, and promised to improve models predicting Thwaites' potentially significant contribution to sea-level rise.
Icefin, developed by Schmidt's team, is a small robotic oceanographer that allows researchers to study ice and water around and beneath ice shelves and develop the technology to explore other oceans in our solar system, according to the study.
"These new ways of observing the glacier allow us to understand that it's not just how much melting is happening, but how and where it is happening that matters in these very warm parts of Antarctica," said Britney Schmidt, associate professor of astronomy and earth and atmospheric sciences at Cornell.
"We see crevasses, and probably terraces, across warming glaciers like Thwaites. "Warm water is getting into the cracks, helping wear down the glacier at its weakest points," said Schmidt.
"Icefin is collecting data as close to the ice as possible in locations no other tool can currently reach," said Peter Washam, co-researcher on Schmidt's team, who led analysis of Icefin data used to calculate melt rates.
"It's showing us that this system is very complex and requires a rethinking of how the ocean is melting the ice, especially in a location like Thwaites," said Washam.
The robotic under-ice observations were collected in early 2020 as part of the International Thwaites Glacier Collaboration (ITGC), the largest international field campaign ever undertaken in Antarctica, funded by the National Science Foundation and the UK's Natural Environment Research Council.
Since the 1990s, the Thwaites grounding line has retreated nearly 9 miles, or 14.5 kilometres (kms), and the amount of ice flowing out of the 75-mile-wide, or 120-km-wide, region has nearly doubled, according to ITGC, the study said.
Because much of the glacier sits below sea level, it is considered susceptible to rapid ice loss that could raise sea levels by more than 1.5 feet, or about half a metre, the study said.
Collapse of the ice sheet behind Thwaites could add substantially more, "with profound consequences for humanity," according to BAS.
The BAS team, which used hot water to drill the borehole Icefin accessed about 1 mile, 1.6 kms, from the Thwaites grounding line, reported that over a nine-month period, the ocean in that area became warmer and saltier.
Surprisingly, the vertical melt rate over much of the ice was less than previously modelled, averaging 6 feet to 18 feet per year, the study said.
"Our results are unexpected, but the glacier is still in trouble," said Peter Davis, an oceanographer at the BAS.
"If an ice shelf and a glacier is in balance, the ice coming off the continent will match the amount of ice being lost through melting and iceberg calving.
"What we have found is that despite small amounts of melting, there is still rapid glacier retreat, so it seems that it doesn't take a lot to push the glacier out of balance," said Davis.
Covering an area larger than Florida or Britain, collapse of the Thwaites Glacier in western Antarctica could contribute significantly to sea-level rise, according to the ITGC.
The researchers attributed the varying melt rates in different topography to water stratification and mixing.
Along flat sections of ice, a thin layer of melted freshwater acts as a barrier to warmer ocean currents, suppressing upward melting, they said.
In contrast, water funnelling through sloped crevasses and scalloped terraces transfers heat that promotes faster sideways melting, at estimated rates of up to 140 feet per year, they said.