Scientists were able to reach the vast floating East Antarctic Totten ice shelf, which provides the backward stress that blocks the ice of the largest glacier in East Antarctica from emptying into the ocean. They were able to take measurements of the water, the depth and the shape of the bedrock.
Jane Qiu writes a compelling post in the journal Nature, where she reports on the scientists and the grim findings that the measurements had revealed below the bitter cold and ice of East Antarctica.
Qiu notes the E Antarctic region is about as big as the entire United States and the majority of it is an ice cap sitting on a high plateau 2 ½ miles above the ocean surface. It is an inhospitable environment where temperatures can plunge to −140F.
The glaciologists confirmed, that like the West Antarctic ice shelves that buttress their glaciers, the East Antarctica shelves are also melting from beneath due to warm ocean temperatures. The warm water is gnawing at the ice forming channels which may some day weaken the shelf from the inside out. It was also determined that a large fraction of the eastern half of Antarctica is below sea level making it very vulnerable to melting. They found evidence that the massive glacier has a history of growth and shrinkage proving that it can retreat once again given the right conditions.
The flights have revealed an astoundingly dramatic landscape hidden beneath the relatively flat ice sheet. Preliminary results from airborne surveys this January, led by glaciologist Sun Bo at the Polar Research Institute of China in Shanghai, confirmed the existence of a 1,100-kilometre-long canyon — the longest in the world, and almost as deep as the Grand Canyon in the United States. In previous flights over Wilkes Land, van Ommen’s team discovered that 21% of the Totten glacier catchment is more than 1 kilometre below sea level — an area 100 times larger than previous estimates. “We really didn’t expect it to be as extensive as it has turned out to be,” says Donald Blankenship, a geophysicist at the University of Texas at Austin and another ICECAP principal investigator.
The team also found underwater troughs that extend all the way from the edge of the Totten Ice Shelf to the grounding line 125 kilometres inland, and as deep as 2.7 kilometres below sea level6. This deeply contoured landscape could allow warming waters from offshore to quickly reach and erode the ice.
The measurements taken show that warm waters of roughly 38F are present year round, and that the warm water flows like a river through the channels directly to the grounding line of Totten.
Threats to ice shelves could also come from the Antarctic interior — from lakes under the ice sheet that periodically send flood waters towards the coast. A decade ago, Lake Cook beneath the ice sheet in Wilkes Land suddenly drained, gushing 5.2 billion cubic metres of flood water — the largest event of this type ever reported in Antarctica. Such floods could be another destabilizing factor, causing faster ice flow and more iceberg calving, says Leigh Stearns, a glaciologist at the University of Kansas in Lawrence.
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Instead, the sea-floor sediments revealed that the ice sheet waxed and waned many times between 5.3 million and 3.3 million years ago7— an epoch called the Pliocene, when air temperatures were up to 2 °C higher than today. “We got a clear signal every time it was warm, suggesting that the ice sheet was sensitive to climate warming,” says van de Flierdt.
The researchers say that they have some intriguing preliminary results from the most recent interglacial period, between 129,000 and 116,000 years ago — when the globe was as warm as it is today. The ice sheet retreated just slightly less at that time than it did during the much warmer Pliocene. “That’s a big surprise,” says van de Flierdt.
I highly suggest reading the excellent prose of Jane Qiu.
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