January 16, 2013
Sea Level Predictions Aided By New Antarctic Geological Timeline
Alan McStravick for redOrbit.com — Your Universe Online
The uncertainty of future sea level rise is getting a little clearer thanks to research being conducted by a team comprised of scientists from the British Antarctic Survey (BAS), the Alfred Wegner Institute for Polar and Marine Research (AWI) and the University of TromsÃ¸. Their study, entitled ℠Grounding-line retreat of the West Antarctic Ice Sheet from inner Pine Island Bay´, is being published in this month´s edition of the journal Geology. Their research involves using the process of radiocarbon dating of tiny fossilized marine animals found in the Antarctic seabed sediments to explore the recent rapid ice loss from the West Antarctic Ice Sheet. The team believes their work will assist scientists in making better predictions of the future of global sea-level rise. The team selected this area of the Antarctic continent as it is believed this region is more vulnerable to regional climate warming and also to changes in ocean circulation.
The method of radiocarbon, or Carbon-14, dating is perhaps the best known and most widely used absolute dating method. Developed in 1949 by J.R. Arnold and W.F. Libby, this method is very widely used among archaeologists because it is able to provide an accurate dating model of deposits, independent of artifacts and local stratigraphic sequences. The establishment of radiocarbon dating as a scientifically viable method has allowed for the development of world-wide chronologies.
The team focused their study on the Amundsen Sea region of West Antarctica. Their findings, they believe, offer conclusive proof that the rapid changes we have witnessed thanks to satellite imaging over the previous 20 years at both the Pine Island and Thwaites glaciers are, most likely, highly exceptional and are unlikely to have occurred more than three or four times over the past 10,000 years. Pine Island and Thwaites were selected for study because they drain ice from the West Antarctic Ice Sheet into Pine Island Bay.
According to the lead author of the study, Dr. Claus-Dieter Hillenbrand of the BAS, "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. 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 goes on to explain, “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."
The study, itself, was conducted in 2010 during an expedition aboard the German research vessel R/V Polarstern. In order to extract samples for the radiocarbon dating process, the team employed the used of gravity corers that were up to ten meters in length. These corers were able to extract mud from the sea floor of the continental shelf in the Amundsen Sea. Some of the radiocarbon dating work was undertaken at the Natural Environment Research Council Radiocarbon Facility.
Dr. Gerhard Kuhn of the AWI and co-author on the study stated, "It was important to get a better understanding of the rapid retreat that we see in the satellite data. As coring targets we selected three relatively shallow undersea ridges that lie within 110 [kilometers] 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.” He goes on to say, “ 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."
Adding to Kuhn´s comments, Dr. James Smith of the BAS stated, "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."
The team hopes that with their new research they will be able to improve the accuracy of computer modeling that is essential in the prediction of future ice loss in the Amundsen Sea sector of the West Antarctic Ice Sheet. They contend that more accurate models will point to the factors that are contributing to a global rise in sea-level. Data collected from satellite imagery over the past two decades shows that the melting of the West Antarctic glaciers has significantly contributed to rises in sea level we have seen around the globe.
The research was funded by the Natural Environment Research Council and the Alfred Wegener Institute.