May 11, 2009

Plankton carbon doesn’t reach deep ocean

U.S. government oceanographers say they've determined plankton carbon particles in the Southern Ocean never reached the deep ocean.

Jim Bishop and Todd Wood of the U.S. Department of Energy's Lawrence Berkeley National Laboratory studied the fate of carbon particles originating in plankton blooms using data deep-diving Carbon Explorer floats collected around the clock for more than a year.

The discovery that most of the carbon never reaches the deep ocean deals a blow to the simplest version of the Iron Hypothesis, which posits global warming can be slowed or even reversed by fertilizing plankton with iron in regions that are iron-poor, but rich in other nutrients such as nitrogen, silicon and phosphorus.

Just adding iron to the ocean hasn't been demonstrated as a good plan for storing atmospheric carbon, said Bishop."What counts is the carbon that reaches the deep sea, and a lot of the carbon tied up in plankton blooms appears not to sink very fast or very far.

The study is to be reported in a forthcoming issue of the journal Global Biogeochemical Cycles.