Source : the age
Why is a remote glacier in Antarctica that contains enough water to raise global sea levels by 1.5 metres melting twice as fast on one side as the other?
That’s the question facing Australian scientists who have spent the past three summers at a remote outpost in the Bunger Hills, 450 kilometres from Casey research station in East Antarctica.
Dr Sarah Thompson, a glaciologist with the Australian Antarctic Program Partnership, said Denman Glacier was of interest because it contained so much water.
“The Denman Glacier is one of the largest and the fastest, and the one that we’re most concerned about because we think it has around 1.5 metres [of] potential sea level rise contribution – though we don’t really have any idea about when that will happen, either the magnitude or the timing,” Thompson said.
Denman Glacier flows off the side of the continent alongside the Scott Glacier and into the floating Shackleton Ice Shelf. The frozen river is 110 kilometres long, 11-16km wide and at least 3.5km deep, making it one of the deepest places on Earth bar deep ocean trenches.
A 2021 paper in The Cryosphere used satellite imagery to show the “grounding line” – the point at which the ice is no longer grounded on the continent and starts to float on the ocean – had shifted over the past 50 years, suggesting the melting of the glacier was accelerating.
Thompson said once the glacier started to float, it flowed five metres a day – fast by glacial standards.
Thompson said the ice shelves act “like dams by holding back the flow of ice from the Antarctic continent into the ocean”, and the researchers wanted to understand their structure and stability.
“If the ice shelves start to weaken and start to break up, then we’ll get [a] faster flow of ice and a lot more ice delivered from the continent into the ocean that will contribute to sea level rise,” she said.
“We don’t see massive changes in melt at the surface at the moment … but at the base of the ice shelves, we’re getting warmer ocean water … causing melting underneath.”
Last year, the team observed about two metres of melt a year at the base of the Shackleton Ice Shelf side of Denman Glacier. On the Scott Glacier side, it was only one metre a year. Thompson said each side could have different ocean temperatures or currents underneath.
Melt is how much thickness is lost from the base, while flow is how fast the ice is moving downstream. Both melt and faster flow would contribute to sea level rises.
Australian Antarctic Division field leader Simon Cross said this was the final year for the research outpost, so 36 tonnes of equipment needed to be air-lifted out by February 8.
The scientists will leave behind remote monitoring equipment installed at a frozen lake on the edge of Denman and Scott glaciers, near the grounding line, allowing the study to continue for several years.
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