An Antarctic Ice Shelf Melting Study Finds A Previously Unknown Factor

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One mechanism that may hasten the demise of Antarctic ice shelves has been identified by scientists. Instability in one ice shelf may contribute to problems in downstream shelves, according to research by an international team of experts. The research team, based out of the University of East Anglia in the United Kingdom, also found that the volume of glacial-meltwater flowing under the Thwaites Ice Shelf may be affected by a tiny ocean gyre nearby. More melting occurs as the gyre weakens because more warm water may reach the regions under the ice shelf.

Buttressing the eastern flank of the Thwaites Glacier, that has been receding quickly over the last 20 years and is the greatest factor contributing to worldwide sea-level rise amongst Antarctic glaciers, lies the Thwaites Ice Shelf, one of the biggest ice shelves in West Antarctica. Using data from sensors placed under the Thwaites Ice Shelf, scientists were able to determine that the ocean’s shallow layers warmed dramatically from January 2020 to March 2021. The waves moving eastward from the Pine Island Ice Shelf, carrying a lot of glacial meltwater, warmed the region just under the Thwaites Ice Shelf.

When the ocean melts the base of ice shelves, the resulting mixture of glacial meltwater and seawater may rise to the surface and trap heat. The Thwaites Ice Shelf is melted at its base by this lighter, somewhat fresher and warmer water.

What affects ice shelves?

Researchers have found another another mechanism that may affect ice shelf stability, highlighting the significance of regional ocean circulation and sea ice. The warm Antarctic seas known as Circumpolar Deep Water play a crucial role in thawing the ice shelf bases. This research, however, demonstrates that seas coming from neighboring melting ice shelves may deliver a significant amount of heat at shallow levels under a single ice shelf.

As a result, the fate of one ice shelf might have repercussions on its neighbor, and so on. Particularly in the Amundsen Sea, where two ice shelves are next to one another and the heat exported from the southernmost shelf may be carried by ocean currents to the northernmost, this mechanism is crucial for explaining the high rates of ice shelf melting in the area.

These connections between the atmosphere, sea, ice, and ocean are significant because they enable warm as well as meltwater-enriched water to enter neighboring ice-shelf cavities, so extending warm periods under ice shelves. More ice shelves may be vulnerable to the strong basal melting linked with protracted warm weather if gyres occur in other places surrounding Antarctica, adding to global sea-level rise.

Colleagues from the United States bore holes in the ice in January 2020 and implanted sensors to measure the temperature, salinity, as well as water currents under the Thwaites Ice Shelf. Over the course of more than a year, these sensors sent data via satellite that was utilized to determine oceanic fluctuations such as temperature and meltwater concentration. Due to the lack of significant melting at the sensor locations, the researchers concluded that the surplus heat could not have emanated locally on the Thwaites Ice Shelf.

With the data and simulations combined, scientists were able to determine that the water escaping Pine Island Ice Shelf may reach the regions under Thwaites Ice Shelf, revealing its role as the heat source. Using data from seal-worn transmitters and computer simulations, scientists have pinpointed the method by which these fluids reach the Thwaites Ice Shelf. Both of these studies demonstrated that throughout the winter months, a gyre close to the Thwaites Ice Shelf weakens, allowing greater heat to get to shallow places under the ice shelf.

Sea ice around the Thwaites Ice Shelf was unusually thick in satellite photographs taken during the 2020/21 summer season in the Southern Hemisphere. The scientists anticipated, based on the models and prior studies, that the gyre was much weaker, leading to the overflow of meltwater from neighboring ice shelves onto the Thwaites Ice Shelf. As a result, the strength of this gyre was further diminished, allowing glacial meltwater-rich water to flow in from below the ice shelf.