Japanese Expedition Finds Unexpected Hot Spot in East Antarctica

Adélie penguins in Lützow-Holm Bay, Antarctica, enjoy easy access to food and increase body weight and breeding success in ice-free summer. (Yuuki Watanabe / National Institute of Polar Research, Japan)

(CN) — Scientists from Hokkaido University announced Monday they have discovered a region of high melting activity beneath Shirase Glacier Tongue in East Antarctica responsible for an alarming rate of ice loss, which will give them better insight into predicting sea-level rise from glacial melting.

In a study published in the journal Nature Communications, members of the 58th Japanese Antarctic Research Expedition studied bedrock in Antarctica and are a part of the Asian Forum for Polar Sciences. 

The Shirase Glacier Tongue sits where the glacier flows toward the ocean, and although smaller than other ice structures in the area, researchers have discovered a much more rapid melting rate. Normally it is tremendously difficult to travel through the Lützow-Holm Bay for research due to the vast amount of ice, but in 2017 the team was granted access to this area, where they were able to observe the Shirase Glacier and witness the deterioration of the ice.

“Our data suggests that the ice directly beneath the Shirase Glacier Tongue is melting at a rate of 7-16 meters [23-52 feet] per year,” said assistant professor Daisuke Hirano of Hokkaido University’s Institute of Low Temperature Science. “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 [32-36 feet] per year.”

Ice sheet melting is one of the two largest causes for sea level increase, second only to thermal expansion. Glaciers hold a large fraction of Earth’s freshwater within them, and when pieces of them break off, they can contribute to the rise, with the biggest contributors coming from Antarctica and Greenland. The authors say that by the most recent estimations, global sea levels are on track to rise by around three feet by 2100, and close to 50 feet by 2500.

NASA is continuously observing and collecting data on the states of these ice sheets; its satellites have all observed them shrinking. With the continued progression of climate change, it is becoming increasingly important to get an accurate read on these icy conditions.

Previous sea level research concerning glacial melt has primarily been focused on West Antarctica, as ice sheets here have already been affected by human activity and have the potential to raise sea levels by as much as 10 feet. 

The authors say that although the larger of the two, the East Antarctic ice sheets have been researched much less than their counterpart because they were thought to be more stable. They sit on bedrock high above sea level and contain water cavities that were thought to be chilled enough to prevent excessive melting.

The study took place in January and February 2017 during an observation project called ROBOTICA, where Hirano and his team combed through 31 different points throughout the region and obtained figures on water temperature, salinity and oxygen levels. 

Taking into consideration the impact that global warming and wind patterns have on the stability of these structures, they then compared their findings with existing statistics like wind, ice radar measurements and computer modelling.

Now, with a solid understanding of the oceanic conditions surrounding the Shirase Glacier Tongue, the team concluded that this unprecedented rate of melting has been caused by warm water flooding the tongue’s base. They found an oceanic trough, a depression in the seafloor similar to a trench, that carries warm water through to the tongue’s base where it takes melted ice with it.

A similar phenomenon occurs within ice shelves, which are free-floating ice sheets that are pinned by obstructions on the seafloor and act as a barrier to keep ice from flowing too quickly to the ocean. 

When ice flows too quickly, it begins to form cracks along the shear margins which then become weak points for water to enter, and form what is called upside-down rivers, also known as basal channels. Since warm freshwater is more buoyant than cold saltwater, it makes its way into these cracks and compromises the integrity of the ice shelves from underneath.

Furthermore, they deduced that this is an annual phenomenon that becomes stronger or weaker with the seasons, with the most harmful effects in the summer when easterly winds falter. Previous research has shown that human activity has actually altered characteristics of the oceanic winds that blow over these glaciers, further aggravating this occurrence.

“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,” Hirano said.

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