Accelerated loss of Antarctic ice contributing to faster sea level rise

Melting icebergs

BRISTOL, England, Tuesday May 26, 2015 – A new British study has recorded an abrupt and rapid thinning of once-stable glaciers along the southern Antarctic Peninsula, indicating that significant changes in glacier mass can occur surprisingly quickly as ocean and air temperatures rise.

The new study, published in the journal Science, points to a common cause among the glaciers it studied: Warm water is melting away the underside of the glaciers where they meet the sea floor, weakening the ice shelves that slow the glaciers’ slide into the ocean.

The research, which effectively pinpointed the major driver of the changes, also pointed to the speed with which these changes are taking place.

According to Jonathan Bamber, a glaciologist at Britain’s Bristol University and a member of the team conducting the study: “It’s like a switch was flipped for a pretty extensive region of the peninsula.

“That isn’t something that you would necessarily expect based on the modelling studies that people have done.”

As Antarctica’s ice shelves collapse, the glaciers they buttress will contribute to sea level rise. Currently, the glaciers in the study, which lie along 500 miles of the southern Antarctic Peninsula coast, are losing some 56 billion tons of ice a year to the ocean, the researchers say.

The losses, which started suddenly in 2009, come in addition to losses from the West Antarctic Ice Sheet, which is shedding 80 billion to 110 billion tons of ice a year, according to the study.

The latest findings came about as part of a larger study by a team led by Ben Wouters, also of Bristol University.

The team found a “quite remarkable signal” that the glaciers of the Antarctic Peninsula’s southern coast were losing height over time, Dr Bamber said. Other researchers had noticed the changes as well, he added, but they in essence wrote off the changes to processes on the glaciers’ surfaces, such as continued settling of partially compacted snow.

The Bristol team tested that theory and found that such surface processes couldn’t account for the height losses. That suggested that the flow of the glaciers was speeding up, which would tend to thin them vertically.

This thinning coincided with record high water temperatures measured along the bed of the Bellingshausen Sea, which laps at this region of the Antarctic coast.

The combined evidence pointed to this warm water melting away the glaciers where their undersides meet the sea floor – the so-called grounding line. The melting forces the grounding line to retreat toward the coast, weakening the shelves and reducing their ability to slow the glaciers’ advance to the sea.

Recent modelling work implies that as global warming leads to warmer air temperatures, melting from below and above likely would work in tandem, accelerating ice losses beyond the rates researchers have previously estimated.

The findings of the new study support what researchers have been seeing in other parts of Antarctica, with scientists warning last year that four key glaciers on the West Antarctic Ice Sheet appear to be on the verge of irreversible retreat.

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