Melting hot spot discovered in East Antarctica | Polarjournal
The research expedition led the Japanese scientists to the Shirase Glacier in Lützow-Holm Bay in East Antarctica. Normally, the bay is inaccessible to ships even in summer, because the sea ice which is connected to the land, also called fast ice, makes it impossible for ships to pass through. Photo: Google Earth (1999)

Scientists at the University of Hokkaido have identified an atypical hot spot of glacier melt in East Antarctica. Their results, published in the journal Nature Communications, contribute to the understanding of sea level rise caused by the mass loss of Antarctic ice sheets and could facilitate its prediction.

The Lützow-Holm Bay in East Antarctica, into which the Shirase Glacier extends, is normally covered by thick sea ice connected to the land and is not accessible for expeditions with research vessels. A few months before the 58th Japanese Antarctic research expedition in the Antarctic summer of 2017, however, large areas of solid ice broke up in the bay and for the first time scientists were able to make ship-based observations near the tip of the Shirase glacier.

During the expedition, Daisuke Hirano, Associate Professor at the Institute of Low Temperature Science at Hokkaido University and lead author of the study, and his collaborators collected data on water temperature, salinity and oxygen content at 31 points in the area. They combined this information with data on currents and wind in the area, with ice radar measurements and computer modeling to understand the ocean circulation under the Shirase glacier tongue at the glacier base.

A deep trough in the seabed leads to the Shirase Glacier, through which warmer water is transported to the glacier tongue. The dots mark the sampling stations. Graphic: Daisuke Hirano et al., Nature Communications, August 24, 2020

“Our data suggests that the ice directly beneath the Shirase Glacier Tongue is melting at a rate of 7–16 meters per year,” Hirano said. “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 10–11 meters per year.”

The scientists suspect that the melting is caused by warm water at depth, which flows towards the base of the Shirase glacier tongue. The warm water moves along a deep underwater trough in the ocean and then flows up along the base of the glacier tongue, heating the ice and melting it. The warm water carrying the melted ice then flows outward and mixes with the glacier melt water.

The team found that this melt occurs throughout the year, but is influenced by coastal easterly winds that vary seasonally. When the winds subside in summer, the influx of deep, warm water increases, accelerating the rate of melting.

“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.

Warmer water flows through the deep-sea trench into Lützow-Holm Bay and causes the ice to melt at the glacier base and, after rising, also at the surface. Graphic: Daisuke Hirano et al., Nature Communications, August 24, 2020

The Antarctic Ice Sheet, which is mostly located in the East Antarctic, is the largest freshwater reservoir on earth. If everything melts, this could lead to a 60-meter rise in global sea level. Current forecasts predict that the global sea level will rise by one meter by 2100 and by more than 15 meters by 2500. It is therefore very important for scientists to understand exactly how the Antarctic continental ice is melting and to predict sea level fluctuations more accurately.

Much more is known about the melting of the West Antarctic ice shelves, since most studies on ocean-ice interactions have been and are being conducted in the Amundsen and Bellinghausen Seas. In contrast, much less attention was paid to the ice shelves in East Antarctica, as it was assumed that the water under most of them, apart from the Totten Ice Shelf, is cold and protects them from melting. In view of the new results, the authors of the study consider the Lützow-Holm Bay to be well suited for observations of the connections between the regional winds, the Southern Ocean and the Antarctic ice sheet against the background of climate change.

Julia Hager, PolarJournal

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