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article imageIce melting fast below East Antarctica's Shirase Glacier tongue

By Karen Graham     Aug 24, 2020 in Science
Ice is melting at a surprisingly fast rate underneath the Shirase Glacier Tongue in East Antarctica due to the continuing influx of warm seawater into the Lützow-Holm Bay.
The Shirase Glacier is a large glacier entering Havsbotn, the bay that forms the head of Lutzow-Holm Bay in Antarctica. The area occupied by this feature was first mapped as a bay and named Instefjorden (the innermost fjord) by the Lars Christensen Expedition (LCE) of 1936–37.
Surveys by the Japanese Antarctic Research Expedition (JARE) of 1957–62, revealed the large glacier in this position which they named after Lt. Nobu Shirase, leader of the Japanese Antarctic Expedition of 1911–12.
In the 58th Japanese Antarctic Research Expedition, scientists from Hokkaido University identified an unusual hot-spot of sub-glacier melting in East Antarctica. Their findings, published in the journal Nature Communications, could further understandings and predictions of sea level rise caused by mass loss of ice sheets from the southernmost continent.
This view below is from the Multi-angle Imaging SpectroRadiometer (MISR) portray the Lutzow-Holm Bay region of Queen Maud Land, East Antarctica, on September 5, 2002. Although Queen Maud Land remains one of the least studied regions of Antarctica, Lutzow-Holm Bay is an exception. Syowa (pronounced 'Showa') Station is the Japanese Antarctic Research Expedition base situated on Ongul Island, just off the eastern coast of the Bay (in the top right-hand portion of these views). Scientists there have studied changes in the ice sheet and sea level for several decades.
s. Large outlet glaciers  such as the fast-flowing Shirase Glacier in the lower right-hand corner of...
s. Large outlet glaciers, such as the fast-flowing Shirase Glacier in the lower right-hand corner of these images, are the primary drainage systems for the Antarctic ice sheet.
NASA/GSFC/LaRC/JPL, MISR Team
During the expedition, the research team was able to conduct ship-based observations near the tip of East Antarctica's Shirase Glacier when large areas of heavy sea ice broke up. This gave them access into the frozen Lützow-Holm Bay into which the glacier's tongue protrudes.
"Our data suggests that the ice directly beneath the Shirase Glacier Tongue is melting at a rate of seven to 16 meters (23 - 52 feet) per year," says Assistant Professor Daisuke Hirano of Hokkaido University's Institute of Low Temperature Science, reports Science Daily.
"This is equal to or perhaps even surpasses the melting rate underneath the Totten Ice Shelf, which was thought to be experiencing the highest melting rate in East Antarctica, at a rate of 10 to 11 (33 to 36 feet) meters per year."
Antarctica's ice sheet - most of it being in Eastern Antarctica - is the largest freshwater reservoir on Earth. Should it ever all melt, it would cause a rise in sea levels approaching 60 meters or close to 197 feet. It is estimated that sea levels will rise about one meter (3.3 feet) by 2100.
So you can see why it is important to get all the information we can on ocean-ice interaction, especially in East Antarctica because the Ice shelves there have received much less attention because they were always thought to have very cold water cavities beneath them that kept them stable.
Warm water flows into Luetzow-Holm Bay along a deep underwater ocean trough and then flows upwards a...
Warm water flows into Luetzow-Holm Bay along a deep underwater ocean trough and then flows upwards along the tongue's base, warming and melting the base of Shirase Glacier Tongue.
Daisuke Hirano et al., Nature Communications, August 24, 2020) Credit: Daisuke Hirano et al., Nature
Daisuke Hirano and his team collected data on water temperature, salinity and oxygen levels from 31 points in the area between January and February 2017. They then combined the data with data on the area's currents and wind, ice radar measurements, and computer modeling to understand ocean circulation underneath the Shirase Glacier Tongue at the glacier's inland base.
The research team concluded that warm ocean water moves along a deep underwater ocean trough and then flows upward along the tongue's base. The melting is occurring as a result of the upflowing current of warm water. The warm waters then carry the melted ice as it flow outwards, mixing with the glacial melt-water.
According to Phys.org., this melting is occurring year-round, and when the winds slow in the summer, the influx of warm water increases, and the melting speeds up.
"We plan to incorporate this and future data into our computer models, which will help us develop more accurate predictions of sea level fluctuations and climate change," says Daisuke Hirano.
More about Shirase Glacier Tongue, subglacier melting, LtzowHolm Bay, 7 16 meters per year, underwater ocean trough
 
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