Antarctic ice sheet shed more than 3,000 billion tonnes in 25 years

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The fastest changing region of Antarctica has lost a colossal 3,331 billion tons of ice over the last 25 years, a study has revealed. Located in West Antarctica, the Amundsen Sea Embayment consists of 20 individual glaciers that, in total, cover four times the area of the UK. Loss from these bodies into the sea plays a key role in the continuing global sea level rise. In fact, if the whole embayment were to melt, it would increase sea levels by 3.3 feet. Changes in ocean currents and temperatures are thought to be the most important factors firing the loss of ice from West Antarctica.

In their study, earth scientist Dr Benjamin Davison of the University of Leeds and his colleagues calculated the so-called mass balance of the Amundsen Sea Embayment.

This describes the balance between the increase in snow and ice as a result of snowfall and the mass of the same lost through calving, where icebergs form at the end of the glacier and drift out to sea.

When the rate at which ice is lost via calving is greater than the same is replenished by snowfall, the embayment loses mass overall, and contributes to rising global sea levels.

Similarly, when the rate of snowfall drops, the glaciers also lose ice mass to the sea.

In fact, the team found, the 3,331 billion net tons of ice lost from West Antarctica from 1996–2021 added 0.35 inches to global sea levels as a consequence.

Dr Davison said: “The 20 glaciers in West Antarctica have lost an awful lot of ice over the last quarter of a century.

“There is no sign that the process is going to reverse anytime soon, although there were periods where the rate of mass loss did ease slightly.

“Scientists are monitoring what is happening in the Amundsen Sea Embayment because of the crucial role it plays in sea-level rise.

“If ocean levels were to rise significantly in future years, there are communities around the world who would experience extreme flooding.”

Using climate models that simulate how air currents move around the world, the researchers determined that the Amundsen Sea Embayment experienced several extreme snowfall events over the 25-year study period.

This means there would have been several periods of heavy snowfall and several of little — or what the researchers call a “snow drought.

Considering these, the team found that they contributed to up to half of the ice changes at certain times — and therefore played a key role in the contribution the Amundsen Sea Embayment made to sea level rises and these times.

Between 2009 and 2013, for example, the models indicated that a snow drought “starved” the ice sheet, resulting in a 25 percent increase in ice loss to sea level rise than in average years.

In contrast, the winters of 2019 and 2020 saw very heavy snowfall — reducing the embayment’s contribution to sea level rise by half in comparison to the average level.

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Dr Davison said: “Changes in ocean temperature and circulation appear to be driving the long-term, large-scale changes in West Antarctic ice sheet mass.

“We absolutely need to research those more because they are likely to control the overall sea level contribution from West Antarctica.

“However, we were really surprised to see just how much periods of extremely low or high snowfall could affect the ice sheet over two to five-year periods—so much so that we think they could play an important, albeit secondary role, in controlling rates of West Antarctic ice loss.”

Paper co-author and oceanographer Dr Pierre Dutrieux of the British Antarctic Survey added: “Ocean temperature changes and glacial dynamics appear strongly connected in this part of the world, but this work highlights the large variability and unexpected processes by which snowfall also plays a direct role in modulating glacier mass.”

The full findings of the study were published in the journal Nature Communications.

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