A massive iceberg that got stuck and was helping to slow the loss of floating ice from the Thwaites glacier in West Antarctica has come free.
The iceberg, which started out roughly originally broke away from the floating ice shelf formed by the glacier in March 2002, but got caught in a shallow part of the Amundsen Sea around 100 kilometres away.
Its presence had been helping to anchor sea ice 鈥� formed by the freezing of the sea in winter 鈥� in the area behind it, which in turn has helped to hold back the icebergs and remaining ice shelf in this area.
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But in the past few months it has finally come unstuck and is drifting off into the Southern Ocean, as the timelapse satellite images above show.
鈥淭he iceberg was always going to unground and drift away at some point in time,鈥� says at the University of Edinburgh in the UK. As a consequence, 鈥渨e could see some more frequent break-outs of the icebergs in front of Thwaites鈥�, he says. But the drifting away of B22A, as the iceberg is known, won鈥檛 directly increase the discharge of Thwaites glacier or raise sea level, he says.
Antarctica is covered by ice sheets more than 2 kilometres thick on average. Some of this ice flows in glaciers to the sea, at which point it forms floating ice shelves up to a kilometre thick. These ice shelves act as dams, holding back the ice on land behind them.
As a result of global warming, some ice shelves are starting to break up. This means the glaciers behind them are speeding up and pouring more ice into the sea, raising sea levels worldwide.
The Thwaites glacier alone, dubbed the 鈥渄oomsday glacier鈥� for the potential domino effect should it collapse, holds enough water to raise sea levels by 65 centimetres, and is already . The collapse of the associated and much larger West Antarctic ice sheet would raise sea level by more than 3 metres.
The Thwaites glacier has already lost most of its ice shelf, and part of the remaining ice shelf is currently pinned in place by an undersea mountain. It could soon break free.
鈥淭he ice shelf is heavily broken up already,鈥� says Miles. 鈥淭he sea ice is acting a little bit like glue, sticking it together.鈥�
The glacier and the ice sheet are expected to collapse over the following centuries. They are unstable because they sit on land that is below sea level, and further inland that land surface is deeper below sea level. What this means is that as the glacier retreats, more and more water can get under it, a positive feedback leading to accelerating retreat. 鈥淚t鈥檚 the one we鈥檙e most concerned about,鈥� says Miles.
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