Fears over Doomsday glacier as rate of thaw shocks scientists

The rapid retreat of the “Doomsday glacier” in West Antarctica is adding to growing fears of its impact in global sea levels.

The melting of the Thwaites Glacier appears to be driven by different processes under its floating ice shelf than researchers previously understood.

A multi-national team of scientists have used a cutting edge robot to examine the glaciers 600 metres under the sea and found that that while melting beneath much of the ice shelf is weaker than expected, melting in cracks and crevasses is much faster.

Despite the suppressed melting the glacier is still retreating, and the team said these findings provide an important step forward in understanding the glacier’s contribution to future sea-level rise.

The glacier, which is the size of Great Britain or the US state of Florida is one of the fastest changing ice-ocean systems in Antarctica. Results show that although melting has increased beneath the floating ice shelf, the present rate of melting is slower than many computer models currently estimate.

“Thwaites Glacier is one of the fastest changing glaciers in Antarctica: the grounding zone — the point where it meets the seafloor — has retreated 14 km since the late 1990s,” the study stated. “Much of the ice sheet is below sea level and susceptible to rapid, irreversible ice loss that could raise global sea-level by over half a metre within centuries.”

The new data were collected as part of the MELT project, one of the projects in the UK-US International Thwaites Glacier Collaboration, one of the largest international field campaigns ever undertaken in Antarctica. The MELT team undertook observations of the grounding line (where the ice first meets the ocean) beneath the Thwaites Eastern Ice Shelf in order to understand how the ice and ocean interacts in this critical region.

Dr Peter Davis of the British Antarctic Survey (BAS) took ocean measurements through a 600m deep borehole around two kilometres from the grounding line, created by a hot water drill in late 2019. These measurements were compared with melt rate observations taken at five other sites underneath the ice shelf. Over a nine-month period, the ocean near the grounding line became warmer and saltier but the melt rate at the ice base averaged 2-5 m per year: less than previously modelled.

Davis, who’s an oceanographer at BAS and lead author on one of the studies, explained: “Our results are a surprise but the glacier is still in trouble. 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.”

Dr Britney Schmidt, of Cornell University in the US, and a team of scientists and engineers deployed a robot called Icefin through the 600m deep borehole.  The vehicle is designed to access such grounding zones that were previously almost impossible to survey. The observations Icefin made of the seafloor and ice around the grounding zone provide more detail on the picture of how melting varies beneath the ice shelf. They found the staircases, called terraces, as well as crevasses in the ice base are melting rapidly. Melting is especially important in crevasses, as water funnels through them heat and salt can be transferred into the ice, widening the crevasses and rifts.

Schmidt, who is an associate professor at Cornell University and lead author of the second study, added: “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. 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.”

The glacier, which is the size of Great Britain or the US state of Florida is one of the fastest changing ice-ocean systems in Antarctica. Results show that although melting has increased beneath the floating ice shelf, the present rate of melting is slower than many computer models currently estimate.

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