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The tipping point for Antarctica is closer than we thought.

Three new studies raise the specter that the great ice platforms of the Antarctic continent are more unstable and susceptible to collapse than previously thought.

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Antarctica holds ninety percent of the world’s store of freshwater and would raise sea levels 230 feet if it all melts.

East Antarctica’s ice is on the ground with no marine extension. That is not true for the majority of Antarctica’s glaciers, which have enormous marine extensions which hold back the land ice from flowing into the ocean. 

Examples are West Antarctica and the peninsula that are vulnerable to warm ocean water eating away at the underbelly of the marine glacier leading to collapse.

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Surface melting occurring on the bitter cold icy surface of the Antarctic peninsula can cause hydrofracturing which collapses ice shelves in the Arctic and Antarctica. According to CIRES-based researchers who have observed the peninsulas Larsen B collapse found that the ice shelf bent “under the weight of ponding meltwater on top.”

But, a new study found that the massive ice shelves have been thinning for three hundred years — the study published in the journal Scientific Reports.

Grist provides a short summary:

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Antarctic ice sheets have been melting rapidly for hundreds of years, much longer than scientists previously thought, according to a study out Thursday. The findings suggest that estimates for global sea-level rise need to be reworked and that we’re even closer to the day that fish start chasing each other through New York City’s subway tunnels.

The scientists behind the new study in Scientific Reports were able to reconstruct a 6,250-year record of how fast Antarctic glaciers slipped into the sea. They did this by drilling the bottom of the Southern Ocean between Antarctica and Tierra del Fuego and analyzing the layers of mud they pulled up.

The story this mud tells between 4300 B.C. and 300 A.D. is uneventful. But around 1400, the skeletons of diatoms — ubiquitous, jewel-like sea creatures often used for dating ocean sediments — suggest that the weather became warmer. More oxygen isotopes that come from fresh (as opposed to saltwater) started showing up, meaning the glaciers were melting. Then around 1706, the ice began to melt even faster than before.

So natural climate change had cued up the massive Antarctic ice shelves to collapse before human-caused climate change turned up the heat. A random shift in wind patterns has been melting the ice caps for the last 300 years, the scientists wrote, “potentially predisposing them to collapse under intensified anthropogenic warming.”

Location of the Weddell Gyre in the Weddell Sea.
Location of the Weddell Gyre in the Weddell Sea. It is the Weddell Gyre was found to warm the ice shelves at Larsen and other east facing peninsular glaciers. –The Weddell Gyre is one of the two gyres that exist within the Southern Ocean. The gyre is formed by interactions between the Antarctic Circumpolar Current and the Antarctic Continental Shelf.  The gyre is located in the Weddell Sea, and rotates clockwise. South of the Antarctic Circumpolar Current (ACC) and spreading northeast from the Antarctic Peninsula, the gyre is an extended large cyclone.

Fabienne Lang writes in Interesting Engineering

The years following the year 1400 saw an increasing amount in glacial meltwater discharge, reaching their peak in 1706.

Another period when the discharge was particularly high was after 1912.

Ultimately, the findings of the research pointed out that the ice shelves in the region have been thinning for around 300 years. This, in turn, may predispose them to collapse more easily when global warming occurs, as it is happening now.

The study authors believe that part of the reason for the thinning ice shelves is due to the Southern Annular Mode (SAM) — a climate driver that can influence rainfall and temperature rise in Australia.

The SAM then led to strong westerly winds, atmospheric warming, and ice shelf melting in the eastern Antarctic peninsula. At the same time, it also directed warmer water to the Weddell Gyre, which could have led to ice shelves melting from underwater.

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