Pine Island Glacier and Thwaites Glacier are the most vulnerable ice streams to human induced climate change in Antarctica. Warm ocean water is decaying the marine extensions of these glaciers, causing them to crack and fall apart in ways that have not been seen before. The calved ice eliminates whatever buttressing effect they perform in holding back the land ice from emptying inTO the sea.
Both glaciers combined hold 4 feet of global sea level rise. When the West Antarctic ice shelves collapse it will have catastrophic effects worldwide.
Science Alert reports on the worrisome news that the iceberg itself follows the same lines “along which the iceberg has broken follow the pattern of crevasses developed in the ice shelf that it calved from,"
As the animation above shows – assembled from observations taken by the European Space Agency's Copernicus Sentinel-1 satellite – the iceberg has divided into several discernible fragments of varying size since September 26.
While the fracturing process itself might seem unremarkable, the way the iceberg broke free from the glacier was not, scientists say, and could signal an alarming new precedent in calving processes.
"What we're witnessing on Pine Island Glacier is worrying," explains marine geophysicist Robert Larter from the British Antarctic Survey.
"We're now seeing changes in the calving behaviour of the ice shelf, when for 68 years we saw a pattern of advance and retreat resulting in the calving of a single large iceberg which left the ice front to approximately the same place."
Unlike those events, which effectively replenished the footprint of the up-to-60 metre tall (197 ft) ice front, continued thinning of the glacier as a whole has produced what scientists fear may be evidence of a new era of structural instability.
"What's both interesting and of concern is the lines along which the iceberg has broken follow the pattern of crevasses developed in the ice shelf that it calved from," Larter says.
"This change of behaviour might reflect the crevasses within the ice shelf having an increasing influence on the spacing and pattern of iceberg calving as a result of the thinning that has taken place over the past few decades."
This calving signature – if that's what it is – could foretell a disturbing trend in the Pine Island Glacier, which accounts for about a quarter of all of Antarctica's ice loss, thought to be some 40 billion tonnes of ice each year.
Chris Mooney of the Washington Post writes on the major trouble at Pine Island Glacier which holds 2 feet of sea level rise.
They published a paper last year finding that Pine Island Glacier has developed a troubling new way of losing ice, with rifts forming in the centre of its floating ice shelf from beneath, rather than at the sides, the traditional manner. They suspect this is a function of warmer ocean waters reaching the base of the glacier and weakening it.
"We predicted that the rifting would result in more frequent calving, which is what's happening here," said Howat by email. "If new rifts continue to form progressively inland, the significance to ice shelf retreat would be high."
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