Data to help refine sea level rise forecasts
By Summit Voice
FRISCO — After studying the paleoclimate record of West Antarctica, an international team of scientists say some of the recent observed changes in the Pine Island and Thwaites glaciers may well be exceptional and are unlikely to have happened more than three or four times in the last 10,000 years.
Radiocarbon dates of tiny fossilized marine animals found in Antarctica’s seabed sediments offer new clues about the recent rapid ice loss from the West Antarctic Ice Sheet and help scientists make better predictions about future sea-level rise. This region of the icy continent is thought to be vulnerable to regional climate warming and changes in ocean circulation.
The data enabled the researchers to determine the average rate of glacial retreat since the end of the last Ice Age around 12,000 years ago.
“As snow and ice builds up on the vast Antarctic Ice Sheet, the ice flows from the centre of the continent through glaciers towards the sea where it often forms floating ice shelves and eventually breaks off as icebergs,” said Dr. Claus-Dieter Hillenbrand, of the British Antarctic Survey.
“The floating ice shelves hold back the ice on land. A critical issue for us is to understand how the ‘grounding line’ – the position where the ice sitting on land (glaciers) begins to float (ice shelves) – has retreated landward over time,” Hillenbrand said.
Satellite data from the past 20 years shows that the Pine Island and Thwaites glaciers have experienced significant thinning, flow acceleration and rapid landward retreat of their grounding lines, he said, adding that the new study showed that episodes of fast glacier retreat similar to that observed over recent decades can only have occurred very rarely during the previous 10,000 years.
Hillenbrand worked with scientists from the Alfred Wegener Institute for Polar and Marine Research and the University of Tromsø. The study is part of an urgent international effort by polar scientists to understand if the recent rapid changes are unusual in the geological past.
The investigation was carried out in 2010 during an expedition on-board the German research ship RV Polarstern. The science team used gravity corers up to ten metres long to extract mud from the sea floor of the continental shelf in the Amundsen Sea.
“It was important to get a better understanding of the rapid retreat that we see in the satellite data,” said co-author Dr Gerhard Kuhn. “As coring targets we selected three relatively shallow undersea ridges that lie within 110 kilometres of the current grounding line and flank a deep glacial valley which was carved into the sea bed by the glaciers during past ice sheet advances.
“These locations gave us the best chance to collect the tiny skeletons and shells of animals made of calcium carbonate. Such ‘calcareous’ microfossils are critical for using the radiocarbon technique to determine the age of the sediments, but they are normally extremely rare on the Antarctic continental shelf.”
Dating the fossils from the sediment cores at different locations helped the researchers calculate the average rate of glacier retreat over time,” said co-author Dr. James Smith, also with the BAS.
Over the last two decades the melting of West Antarctic glaciers has contributed significantly to sea-level rise, with recent studies have suggested that continued melting would raise global sea level by up to 0.3 mm a year.