Storing carbon in the Arctic

While the Arctic Ocean is largely a carbon sink, researchers find parts are also a source of atmospheric carbon dioxide.

For the past three decades, as the climate has warmed, the massive plates of sea ice in the Arctic Ocean have shrunk: In 2007, scientists observed nearly 50 percent less summer ice than had been seen in 1980.

Dramatic changes in ice cover have, in turn, altered the Arctic ecosystem — particularly in summer months, when ice recedes and sunlight penetrates surface waters, spurring life to grow. Satellite images have captured large blooms of phytoplankton in Arctic regions that were once relatively unproductive. When these organisms die, a small portion of their carbon sinks to the deep ocean, creating a sink, or reservoir, of carbon.

Now researchers at MIT have found that with the loss of sea ice, the Arctic Ocean is becoming more of a carbon sink. The team modeled changes in Arctic sea ice, temperatures, currents, and flow of carbon from 1996 to 2007, and found that the amount of carbon taken up by the Arctic increased by 1 megaton each year.

But the group also observed a somewhat paradoxical effect: A few Arctic regions where waters were warmest were actually less able to store carbon. Instead, these regions — such as the Barents Sea, near Greenland — were a carbon source, emitting carbon dioxide to the atmosphere.

While the Arctic Ocean as a whole remains a carbon sink, MIT principal research scientist Stephanie Dutkiewicz says places like the Barents Sea paint a more complex picture of how the Arctic is changing with global warming.

“People have suggested that the Arctic is having higher productivity, and therefore higher uptake of carbon,” Dutkiewicz says. “What’s nice about this study is, it says that’s not the whole story. We’ve begun to pull apart the actual bits and pieces that are going on.”

A paper by Dutkiewicz and co-authors Mick Follows and Christopher Hill of MIT, Manfredi Manizza of the Scripps Institute of Oceanography, and Dimitris Menemenlis of NASA’s Jet Propulsion Laboratory is published in the journal Global Biogeochemical Cycles.