Study of ocean currents under the "Doomsday Glacier"

Photo of an unlit Ran submarine. Photo: Philip Stidt
Photo of an unlit Ran submarine. Photo: Philip Stidt

For the first time, researchers were able to get data from under the Thwaites Glacier, also known as the "Doomsday Glacier". They believe that the supply of warm water to the glacier is greater than previously thought, raising fears of faster melting and faster ice flow.

With the help of an unlit Ran submarine that sailed under the Thwaites ice front, researchers have made a number of new discoveries. Professor Karen Heywood from the University of East Anglia commented::

"This was the first venture of the Russian Academy of Sciences in the polar regions, and its exploration of the waters under the ice shelf was much more successful than we dared to hope. We plan to build on these exciting findings with further missions under the ice next year."

The underwater vehicle, among other things, measured the strength, temperature, salinity, and oxygen content of the ocean currents that go under the glacier.

Global sea level depends on how much ice there is on land, and the biggest uncertainty in the projections is the future evolution of the West Antarctic Ice Sheet, says Anna Velin, professor of oceanography at the University of Gothenburg and lead author of a new study published now in Science Advances.

Impact of global sea level

The ice cover in West Antarctica accounts for about ten percent of the current rate of sea-level rise; but also the ice in West Antarctica has the greatest potential to increase this rate because the fastest changes worldwide occur in Thwaites Glacier. Due to its location and shape, Thwaites are particularly sensitive to the warm and salty ocean currents that find their way beneath them.

This process can lead to accelerated melting occurring at the bottom of the glacier, and to move to the interior of the so-called grounding zone, where the ice moves from resting on the seabed to floating in the ocean.

Due to its inaccessible location, away from research stations, in an area that is usually blocked by thick sea ice and many icebergs, there is a large shortage of on-site measurements from this area. This means that there are large gaps in knowledge for the boundary processes of the ice-ocean in this region.

Photo: University of Gothenburg, Rob Larter.
Photo: University of Gothenburg, Rob Larter.

First measurements made

In the study, the researchers present the results of underwater hardware that measured the strength, temperature, salinity, and oxygen content of the ocean currents that go under the glacier.

"These were the first measurements ever made under Thwaites Glacier," says Anna Velin.

The results were used to map the ocean currents under the floating part of the glacier. The researchers found that there is a deep connection to the east through which deepwater flows from Pine Island Bay, a connection that was previously thought to be blocked by an underwater ridge.

The research team also measured heat transport in one of the three channels that lead warm water to Thwaites Glacier from the north. "Channels for warm water to access and attack Thwaites were not known to us prior to the study. Using sonar on the ship, embedded with very high-resolution ocean mapping from the Ran, we were able to discover that there are different paths that water takes in and out of the ice shelf cavity, influenced by the geometry of the ocean floor, " says Dr. Alastair Graham, University of South Florida.

The value measured there, 0.8 TW, corresponds to a net melting of 75 km3 of ice per year, which is almost as large as the total basal melting over the entire ice shelf. Although the amount of ice that melts as a result of hot water is not much compared to other global sources of freshwater, heat transport has a large effect locally and may indicate that the glacier is not stable over time.

Not sustainable over time

The researchers also noted that a large amount of meltwater flowed north from the front of the glacier.

Differences in salinity, temperature, and oxygen content indicate that the area under the glacier is a previously unknown active zone where different water masses meet and mix with each other, which is important for understanding the melting processes at the base of the ice.

Observations show that warm water approaches from all sides to anchorage points, critical places where the ice is connected to the seafloor and gives stability to the ice shelf. Melting around these anchorage points can lead to instability and retreat of the ice shelf, and then cause the glacier upstream to drain away from the land. Dr. Rob Larter, from the British Antarctic Survey, said: "This work highlights that how and where warm water affects Thwaites Glacier is influenced by the shape of the seafloor and shelf base, as well as the properties of the water itself. The successful integration of new data from the seabed survey and water properties observations in the Ras missions shows the benefits of an interdisciplinary spirit within the framework of International Cooperation on the Thwaites Glacier."

"The good news is that we are now collecting the data needed to model the dynamics of the Thwaite Glacier for the first time. This data will help us better calculate the melting of ice in the future. With new technologies, we can improve models and reduce the large uncertainty that currently prevails around global sea-level fluctuations, " says Anna Velin.

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