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"If giant iceberg calving increases this century as expected, this negative feedback on the carbon cycle may become more important than we previously thought," says Grant Bigg. (Credit: Christopher Michel/Flickr)

carbon dioxide

Giant icebergs store high levels of carbon

Satellite images of the Southern Ocean show large icebergs store up to 20 percent of carbon in the ocean.

Melting water from the icebergs, which contains iron and other nutrients, supports unexpectedly high levels of phytoplankton growth. This activity, known as carbon sequestration, contributes to the long-term storage of atmospheric carbon dioxide—helping to slow global warming.

A team of scientists analyzed 175 satellite images of ocean color, which is an indicator of phytoplankton productivity at the ocean’s surface. The images were of a range of icebergs in the Southern Ocean that were at least 18 kilometers (11 miles) long.

The images from 2003 to 2013 showed that enhanced phytoplankton productivity, which has a direct impact on carbon storage in the ocean, extends hundreds of kilometers from giant icebergs and persists for at least one month after the iceberg passes. The findings appear in Nature Geoscience.

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“This new analysis reveals that giant icebergs may play a major role in the Southern Ocean carbon cycle,” says Grant Bigg, a geography professor at the University of Sheffield, who led the team.

“We detected substantially enhanced chlorophyll levels, typically over a radius of at least four to 10 times the iceberg’s length.

“The evidence suggests that assuming carbon export increases by a factor of five to 10 over the area of influence and up to a fifth of the Southern Ocean’s downward carbon flux originates with giant iceberg fertilization.

“If giant iceberg calving increases this century as expected, this negative feedback on the carbon cycle may become more important than we previously thought.”

Source: University of Sheffield

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