Friday, November 5, 2004

Warming In Antarctica: cause for concern

In Antarctica the ocean food chain is crashing due to the loss of ice shelves around the Antarctic peninsula caused by climate warming. The breakup of the Larsen B ice shelf in 2002 has also released several glaciers, increasing their speed eight fold, and dumping their loads into the Weddell Sea contributing to a rising sea level, according to new research.


Ocean Food Chain crashing due to Antarctic Warming

Disappearing sea ice and warmer temperatures in the Southern Ocean around Antarctica are causing an 80 percent drop in the numbers of Antarctic Krill. Krill, a small custacean which feeds on algae under ice sheets, is at the bottom of the food chain. Penguins, seals, fish, sea birds and whales are all dependent on Krill as a food source. This will also impact southern Fisheries. A new study released 3 November in the journal Nature, revealed the extent of the problem.

Angus Atkinson, a marine biologist at the British Antarctic Survey, said "This is the first time that we have understood the full scale of this decline,"

"The Antarctic Peninsula, a key breeding ground for the krill, has warmed by 2.5 degrees Celsius in the last 50 years, with a striking decrease in sea-ice," Atkinson said in a statement. "We don't fully understand how the loss of sea ice here is connected to the warming, but we believe that it could be behind the decline in krill."

The air temperature increase is about five times faster than the global mean rate.

"We're already seeing some effects in certain penguin species at several sites in this area where krill are declining so much," Atkinson said.

Previously, estimates were based on local surveys so scientists had only suspected that stocks of krill were dropping. The latest figures are derived from data between 1926 to 2003 covering 40 Antarctic summers that was gathered by nine countries working in Antarctica.

"We need to understand the mechanisms of these ecosystem interactions to be able to predict what is going to happen in the future. The key thing is the climatic change at the Antarctic Peninsula. It is this particular area that is warming up." said Atkinson

Antarctic Glaciers on the move

Ice shelves are not only important for stocks of Krill. It has been known for sometime that the various Antarctic ice shelves slow down or hold glaciers from dispensing their huge load of ice into the surrounding waters.

Under the influence of global warming, when ice shelves break up, as in the Larsen B ice shelf in 2002, or in 1995, it releases the blocked glaciers, which now flow up to eight times faster than before into the Weddell Sea.

Ice shelves displace their own weight in water, however glaciers rest on land and when they slide off into the water, they instantly affect sea levels.

Studies from climate researchers and the U.S. space agency NASA show the glaciers are flowing into Antarctica's Weddell Sea, freed by the 2002 breakup of the Larsen B ice shelf.

The researchers come from teams at NASA's Jet Propulsion Laboratory in Pasadena, California, the National Snow and Ice Data Center at the University of Colorado in Boulder, and NASA's Goddard Space Flight Center in Greenbelt, Maryland. They claimed that satellite measurements suggest climate warming can lead to rapid sea level rise, and also prove that ice shelves hold back glaciers.

"If anyone was waiting to find out whether Antarctica would respond quickly to climate warming, I think the answer is yes," said Dr Theodore Scambos, a University of Colorado glacier expert who worked on one study.

"We've seen [240 kilometres] of coastline change drastically in just 15 years."

In the past 30 years, ice shelves in the Antarctic peninsula region have lost more than 13,500 square kilometers of area.

"The Larsen area can be looked at as a miniature experiment, showing how warming can dramatically change the ice sheets, and how fast it can happen," Scambos said.

"At every step in the process, things have occurred more rapidly than we expected."

Scambos warned what would happen if climate warming occurs in places like the Ross Ice Shelf: "it is a harbinger of what will happen when the large ice sheets begin to warm," Scambos said. "The much larger ice shelves in other parts of Antarctica could have much greater effects on the rate of sea level rise." If the glaciers held by the Ross Ice Shelf melted completly the sea level could rise by 5 metres in a worst case scenario.

Sources:

* The Breakup of the Antarctic Peninsula Ice Shelves - Greenpeace 1997
* Antarctic species short of food, warming cited - MSNBC 3 Nov 2004
* Antarctic warming killing off fish food - ABC 4 Nov 2004
* Antarctic glaciers going, going, gone - ABC 23 Sept 2004
* Antarctic food chain at risk - The Guardian 4 Nov 2004