Published January 17, 2013 03:15 PM
West Antarctica Vulnerability
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
future predictions about sea-level rise. This region of the icy
continent is thought to be vulnerable to regional climate warming and
changes in ocean circulation. Reporting this month in the journal
Geology 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. The team
concludes that the rapid changes observed by satellites over the last 20
years at 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.
Lying on the Pacific Ocean side of the Transantarctic Mountains, West
Antarctica comprises the Antarctic Peninsula (with Graham Land and
Palmer Land) and Ellsworth Land, Marie Byrd Land and King Edward VII
Land, offshore islands such as Adelaide Island, and ice shelves, notably
the Filchner-Ronne Ice Shelf on the Weddell Sea, and the Ross Ice Shelf
on the Ross Sea. West Antarctica is separated from the main land mass of
the continent by the icy waters of the Ross Sea and Weddell Sea, and
resembles a giant peninsula that stretches roughly from the South Pole
towards the southern tip of South America.
The team studied the average rate of glacial retreat since the end of
the last Ice Age around 12,000 years ago. Their work centered on Pine
Island and Thwaites glaciers, which drain ice from the West Antarctic
Ice Sheet into Pine Island Bay.
Lead author Dr Claus-Dieter Hillenbrand from BAS says, "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. 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 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 meters long to extract mud from the sea floor of the
continental shelf in the Amundsen Sea.
Co-author Dr Gerhard Kuhn from AWI explains, "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. 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."
This new research will be used to improve the accuracy of computer
models that are essential to predict future ice loss in the Amundsen Sea
sector of the West Antarctic Ice Sheet and its likely contribution to
global sea-level rise. Over the last two decades the melting of West
Antarctic glaciers has contributed significantly to sea-level rise
(recent studies have suggested that continued melting would raise global
sea level by up to 0.3 mm a year).
For further information see
Antarctica Timeline.
Ice Floe image via Wikipedia.
©2013. Copyright Environmental News Network To
subscribe or visit go to: http://www.enn.com
|