Understanding the future of sea-level rise has been at the forefront of climate scientists’ minds for years now, and new research studying fossilised marine animals found in Antarctica’s seabed sediments are providing new clues as to what we might expect from a melting Antarctica.
The immediate conclusion of the research is that the melting changes observed by satellites over the past 20 years at Pine Island and Thwaites glaciers are very likely exceptional, and are unlikely to have happened more than three or four times over the past 10,000 years.
The research, published in the journal Geology by a team of researchers from British Antarctic Survey (BAS), the Alfred Wegener Institute for Polar and Marine Research (AWI) and the University of Tromsø, presents a timeline for ice loss and glacier retreat in the Amundsen Sea region of West Antarctica.
Research such as this helps improve the accuracy of computer models that are used to predict future global sea level rise. Currently, many of the computer models undertaking this task are lacking huge chunks of data necessary to make complete and accurate predictions.
Already we’ve reached a point where sea level rise will continue through to the year 3000, and if we don’t do something soon that rise will only extend further out.
Meanwhile, other researchers are looking to understand as much as they can about our future sea level increases, by looking back in time. Research published in the journal Nature back in July reported on the work of scientists looking to discover the cause behind two historic sea level rises, again with the hope that it will shine a light on our own future predicament.
Tentative predictions for the last two decades of melting of West Antarctic glaciers suggests that they have contributed up to 0.3 millimetres a year of global sea level increase.
The researchers studied the average rate of glacial retreat since the end of the last Ice Age, which took place 12,000 years ago. They focused their observations on Pine Island and Thwaites glaciers, which drain ice from the West Antarctic Ice Sheet into Pine Island Bay. Their information was gathered during a 2010 expedition on board the German research ship RV Polarstern where the scientists used gravity cores up to ten metres in length to retrieve mud from the sea floor of the continental shelf in the Amundsen Sea.
“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 lead author Dr Claus-Dieter Hillenbrand from BAS. “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. Satellite data are available only for the last 20 years and show that since 1992 the Pine Island and Thwaites glaciers have experienced significant thinning (melting), flow acceleration and rapid landward retreat of their grounding lines, with that of Pine Island Glacier having retreated up to 25 km.
“It’s possible that the grounding lines may retreat even further inland over coming decades. Our study has revealed 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.”
“It was important to get a better understanding of the rapid retreat that we see in the satellite data,” added co-author Dr Gerhard Kuhn from AWI. “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.”
Co-author Dr James Smith, also from BAS, adds, “first we determined the distance between the core locations and the modern position of the grounding line. Then by dating the type of sediment material deposited at a core site in the open ocean (after the grounding line had moved further landward), we were able to calculate the average rate of glacier retreat over time.”