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Measurements from ‘lost’ sea glider provide new insights into Antarctic ice melting

Gillian Damerel (former UEA) prepares to deploy the Sea Glider Merlin with the Ross Ice Shelf in the background. Credit: Walker Smith

A new study reveals for the first time how rising sea temperatures have accelerated the melting of Antarctica’s major ice shelves over the past 40 years.

Scientists at the University of East Anglia (UEA) say the study, which was the result of the university’s autonomous sea glider accidentally becoming trapped beneath the Ross Ice Shelf, shows that as climate change accelerates ocean warming, This trend suggests that it is likely to increase further.

The glider, named Merlin, was launched into the Ross Sea from the edge of the sea ice in December 2022. It was programmed to travel north into the open ocean, carrying a variety of sensors to collect data on ocean processes important to climate.

However, the marlin got caught in a southerly current and was drawn into a cavity in the ice shelf, where it remained for four days with its sensors on, before reappearing. During this time, the “lost” glider completed 79 dives, measuring water within the cavity to a depth of 200 meters to the base of the ice shelf above.

Researchers from the UEA Faculty of Environmental Sciences recorded a 50-meter-thick “intrusion” of relatively warm water that entered the cavity from the nearby open water surface. Water temperatures ranged from -1.9°C to -1.7°C, which was even warmer under the ice.

A subsequent reanalysis of all available measurements shows that heat transported into the cavity has increased over the past 45 years, likely due to warming of the Ross Sea due to climate change. It’s possible.

The study, “The Ross Ice Shelf front zone exposed to increased melting from sea surface water,” was published Nov. 8 in the journal Science Advances.

“Temperature increases (4/1000 degrees Celsius per year) may not seem like a big deal, but over the 45 years we are studying, they lead to an additional ice loss of about 20 to 80 centimeters per year. “It’s possible,” explained lead author Dr. Donner. Peter Sheehan.

“We found that the invading water was warm enough to melt the underside of the ice shelf, unlike the freezing point water that would have been displaced. What’s new here is that almost that warm water from the open waters of the Ross River “Being able to track the ice front back into the ocean and the cavity. We’ve never seen this kind of intrusion happen directly before.” ”

Dr. Sheehan added: “Travel to the cavity beneath the Ross Ice Shelf is not planned and it is typically impossible to measure this area of ​​the ice shelf. We can’t send equipment in,” he added. , the risk is too great. ”

The ice shelves surrounding Antarctica are exposed to ocean warmth across the extent of their underside, which floats above the ocean on the continental shelf, and ocean-driven melting that occurs at the base of the ice is the largest contributor to Antarctic ice mass. be. loss.

Measurements from 'lost' sea glider provide new insights into Antarctic ice melting

The Sea Glider Merlin was deployed from the sea ice into the Ross Sea. Credit: Walker Smith

Although the melting of floating ice itself does not significantly raise sea levels, ice shelves slow the seaward flow of land ice and stabilize the Antarctic ice sheet. Their thinning and collapse will increase the supply of land ice to the oceans, accelerating global sea level rise.

One of the processes that pushes warm surface water beneath the Ross Ice Shelf is wind. Certain wind patterns cause winds to flow southward across the ocean surface and into ice shelf cavities.

This type of wind-driven current on the sea surface is called the Ekman Current, and like other ocean currents, it involves heat transport. Because this is a process at sea level, this heat is immediately available to melt the ice on top, without having to wait for it to mix upwards to the bottom of the ice.

Ekman heat transport is particularly relevant to climate scientists because the oceans absorb and redistribute much of the Earth’s heat. Changes in this system can have significant effects on weather, sea levels, and global temperature trends.

Dr Sheehan and co-author Professor Karen Heywood used long-term measurements of wind and sea temperatures, combined with models that fill in the spatial and temporal gaps in the record, to predict southward Ekman heat transport over the past 45 years. We calculated the strength of . They found that the Ekman flow increases the amount of heat transported into the cavity.

The year-to-year variation is caused by the wind. However, the trend toward increased heat transport into the cavity is likely linked to warming of the Ross Sea. Because the water has warmed, today’s winds will transport more thermal energy into the cavity than winds of comparable strength in the past.

Professor Heywood said: “It seems reasonable to expect that the Ekman heat flux and the magnitude of the melting it causes will further increase as ocean warming increases due to climate change. This trend is itself a concern. ” he said.

“The effects of surface water intrusion, together with the trends and variability in Ekman dynamics that can drive them, are particularly important given the continuing uncertainty in the response of Antarctic land ice to climate change. It has to be incorporated into climate models.”

This is the first time this process has been investigated using a long-term, multi-decade dataset. Previous understanding of surface water intrusion has primarily come from comparisons of open ocean hydrographs such as ships, observations of tagged seals, and ice moorings deployed within cavities.

Further information: Peter Sheehan, “Ross Ice Shelf front zone exposed to increased melting by sea surface water,” Science Advances (2024). DOI: 10.1126/sciadv.ado6429. www.science.org/doi/10.1126/sciadv.ado6429

Provided by University of East Anglia

Citation: Measurements from ‘lost’ sea glider provide new insights into Antarctic ice melt (November 8, 2024), https://phys.org/news/2024-11- Retrieved November 8, 2024 from lost-seaglider-insights-antarctic-ice. html

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