Jun 29, 2007
Antarctic icebergs become hotspots for ocean life
As global temperatures rise, Antarctic ice shelves are shrinking and splitting to produce thousands of free-drifting icebergs. A study has now shown that these icebergs have a major impact on the ecology of the Southern Ocean and are becoming areas that enhance the production and storage of organic carbon.
The icebergs are essentially ecological "hotspots" for ocean life, supporting flourishing communities of seabirds, phytoplankton, krill and fish.
"Our preliminary studies suggest that free-drifting icebergs and their associated communities could serve as areas of increased production and sequestration of organic carbon to the deep sea," Kenneth Smith of the Monterey Bay Aquarium Research Institute in California, US, told environmentalresearchweb. "While the melting of Antarctic ice shelves is contributing to rising sea levels and other climate-change dynamics, this additional role of removing carbon from the atmosphere may have implications for global climate models that need to be further studied."
Free-drifting icebergs can be as small as a few metres across or as large as hundreds of kilometres in diameter. To investigate their effects on the open ecosystem of the sea, Smith and colleagues studied two drifting icebergs in the northwest Weddell Sea in 2005, sampling the area immediately around the icebergs and up to 10 km out. The icebergs were up to 20 km long, 40 m high and extended more than 300 m below the surface.
The team found that species such as predatory seabirds, chlorophyll and krill were more abundant around the icebergs and up to about 4 km away than in areas with no icebergs.
Smith and co-workers attribute this "halo" effect to the fact that icebergs release trapped terrestrial material far out to sea as they melt, so "fertilizing" the surrounding waters. The material contains iron, among other elements, which stimulates the growth of phytoplankton. These plants take in carbon dioxide from the atmosphere for photosynthesis, producing organic carbon that is fed upon by krill and other species. "This trophic transfer can lead to some of this organic carbon sinking and becoming sequestered into the deep sea," explained Smith.
The researchers detected 89 icebergs, similar in size to those studied, in the surrounding area and calculated that the icy structures may be increasing the biological productivity of the Weddell Sea by almost 40%.
The team says that the effect will become more widespread as global warming continues.
To obtain their results, the researchers used methods such as towing opening–closing trawls for collecting krill and other planktonic species and a CTD and fluorometer for profiling the water column to obtain data on nutrient concentrations and phytoplankton abundance. Making these measurements was risky because the icebergs can shed huge chunks or overturn without warning.
The team also deployed a remote-operated vehicle under the iceberg to examine communities of organisms either attached to or close to the ice surface. Finally, the team used satellite images to estimate the population of icebergs in the surrounding area.
Now the plan is to undertake a more detailed study of the micronutrient release from the icebergs and measure sinking particulate matter exported to the deep sea around the structures.
The researchers reported their work in Science.
About the author
Belle Dumé is a freelance science and technology writer based in Paris, France.