Glaciers from Antarctic peninsula in widespread retreat, Science study says

04/15/05

Global warming link remains elusive

The first comprehensive study of glaciers on Antarctic Peninsula has uncovered widespread glacier retreat and suggests that recent climate change on the peninsula is responsible.

Eighty-seven percent of the 244 marine glaciers have retreated over the last 50 years, a new study says. The widespread glacier retreat began at the northern, warmer tip of the Antarctic Peninsula. As atmospheric temperatures rose along the peninsula -- more than 2.5 degrees Celsius in the last 50 years -- the trend of retreat moved south toward colder mainland Antarctica.

The paper appears in the 22 April, 2005 issue of the journal Science, published by AAAS the nonprofit science society

The research highlights the possibility that inland glaciers are accelerating their descent to the ocean and that the rate of sea level rise could be affected if ice shelves on the peninsula continue their retreat.

"The widespread retreat of the glaciers on the Antarctic Peninsula over the last 50 years was largely caused by climate change. Are humans responsible? We can't say for sure, but we are one step closer to answering this important question," said Science author David Vaughan from the British Antarctic Survey in Cambridge, UK.

Two thousand aerial photos, the oldest of which were shot in the late 1940s, and over 100 satellite images from the Antarctic Peninsula record this glacier retreat. With these photos and satellite images, Alison Cook from the British Antarctic Survey in Cambridge, UK and her team compiled a record of the behavior of glacier-ice shelves and tidewater glaciers along the coasts of the Antarctic Peninsula over the last half-century.

Glacier-ice shelves are floating glaciers still connected to the land-based glacier from which they flowed. Tidewater glaciers rest on rock and break off into the ocean when they reach the water's edge. They do not form floating ice shelves.

The researchers mapped the photos and satellite images onto a Geographical Information System (GIS) that served as a common reference. They report changes in the ebb and flow of glaciers, in meters per year, over five-year intervals.

"This is a unique glacier archive. There is nowhere else in the Antarctic with such good photos dating back to the late 1940s," said Cook, who spent many hundreds of hours wading through piles of photos, historic records and satellite images to create three cartographic-quality maps that will soon be available to researchers and the public around the world from the United States Geological Survey.

"This is the kind of exploration of Antarctica you could never do on site," said Vaughan.

Of the 244 glacier-ice shelves and tidewater glaciers, 212 retreated from their earliest known position, which occurred in 1953, on average. Over this time, the average retreat of each glacier was approximately 600 meters.

A small remainder of glaciers advanced instead of retreated. The 32 advancing glaciers are not clustered in any pattern, but are evenly scattered down the coast. Their advances, 300 meters on average, are generally smaller than the reported retreats of the other glaciers.

Sjogren Glacier, at the northern end of the peninsula, has retreated 13 kilometers since 1993, more than any other glacier in the study. Sjogren Glacier had flowed into the Prince Gustav Ice Shelf and when the ice shelf broke up in 1993, the glacier retreated rapidly.

With the exception of this unique case involving the break up of an ice shelf, Widdowson Glacier on the west coast of the peninsula, close to the Antarctic Circle, demonstrated the greatest retreat seen in a single glacier in any five-year interval 1.1 kilometers per year. This glacier had been advancing at around 200 meters per year in the 1940s but more recently switched to retreat. The highest rate of retreat for Widdowson Glacier occurred in the last five years.

From 1945 until 1954, 62 percent of the glaciers studied advanced and 38 percent retreated. After 1954 the number of glaciers in retreat rose, with 75 percent in retreat from 2000 to 2004.

The authors describe a clear geographical pattern to the glacial retreat with more of the glaciers in the northern part of the peninsula retreating before those in southern, colder regions of the peninsula. In broad terms, this pattern reflects the atmospheric warming that has occurred on the Antarctic Peninsula since the 1940s.

Atmospheric warming is clearly important but cannot be the only cause of the retreat, the authors say.

The Antarctic Peninsula glaciers have a complex response to climate change that may also involve variables such as ocean temperature, for which researchers have little data at present. Future analysis of all environmental conditions at the site of marine glacier retreat may explain the behavior of these glaciers.

To be sure that humans are responsible for the warming that seems to be playing a big role in the retreat of these glaciers, global circulation models need to reproduce the timing and geographic extent of the regional warming that has taken place on the Antarctic Peninsula, a concept that David Vaughan from the British Antarctic Survey in Cambridge, UK and colleagues covered in a "Perspective" article in the 07 September, 2001 issue of Science.

To get to these bigger questions, scientists need to first uncover the patterns of glacial response to climate change.

The new findings suggest that the Antarctic Peninsula's inland glaciers could be accelerating into the ocean and this could lead to increased loss of the Antarctic Peninsula's ice sheet.

In addition, further loss of the ice shelves that restrain inland glaciers and slow the flow of ice into the ocean could contribute to future increases in the rate of sea level rise.

The forthcoming maps highlighting the patterns of glacial change should be of interest to biologists and those choosing new sites for research stations.

Biologists studying colonization in newly ice-free parts of Antarctica may use the maps to locate recently exposed islands. Others may use the maps to study how glacier retreat affects phytoplankton and sea edge communities.

Nations interested in building research stations in Antarctica could consult the maps so as to avoid building near glaciers that have acted with the highest variability in the last 50 years.

Source: Eurekalert & others

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