Icebergs are 'ecological hotspot'

Melting icebergs release minerals into the surrounding water

Drifting icebergs are "ecological hotspots" that enable the surrounding waters to absorb an increased volume of carbon dioxide, a study suggests.

US scientists found that minerals released from the melting ice triggered blooms of CO2-absorbing phytoplankton.

These microscopic plants were then eaten by krill (shrimp-like organisms), whose waste material containing the carbon sank to the ocean floor.

The findings are published in the online journal Science Express.

The study, carried out in the Southern Ocean's Weddell Sea in December 2005, has helped researchers understand the impact of free-floating icebergs on the marine environment.

Floating feeding stations

The number of icebergs found in waters around Antarctica had increased in recent decades as a result of global warming, the researchers wrote in the paper.

"We got a satellite image that covered roughly 11,000 sq km (4,200 sq miles), and counted the number of icebergs within that area," explained Ken Smith, an oceanographer from Monterey Bay Aquarium Research Institute, California.

We are going to go back and look at smaller icebergs to see how important they are Dr Ken Smith Oceanographer

"We had almost 1,000 icebergs."

The team focused its attention on two icebergs, one measuring 2km by 0.5km (1.2 miles by 0.3 miles) and another 21km in length and 5km wide (13 miles by 3 miles).

Using instruments that included a trawl net and a remotely operated vehicle (ROV) with a video camera, the researchers sampled waters from the ice blocks up to 9km away (5.5 miles).

They found a "substantial enrichment" of minerals, phytoplankton, krill and seabirds in the surrounding water up to 3.7km away (2.3 miles) compared with areas with no icebergs.

"These results suggest that free-drifting icebergs can substantially impact the (open sea) ecosystem of the Southern Ocean and can serve as areas of enhanced production and sequestration of organic carbon to the deep sea," the scientists wrote.

Dr Smith said these findings would be followed up next year by a much more intensive examination.

"Ninety percent [of the icebergs in the area] were smaller than the ones we studied," he told BBC News.

"We are going to go back and look at smaller icebergs to see how important they are, and to see if they also have an associated enrichment of the surrounding water."