An experiment to study the effects of naturally deposited iron in the Southern Ocean has filled in a key piece of the puzzle surrounding iron's role in locking atmospheric carbon dioxide (CO2) in the ocean. The research, conducted by an international team led by Raymond Pollard of the National Oceanography Centre, Southampton, and included Matthew Charette, a marine chemist at the Woods Hole Oceanographic Institution (WHOI), found that natural iron fertilization enhanced the export of carbon to the deep ocean. The research was published January 29, 2009, in the journal Nature.
Scientists have generally accepted the fact that biological productivity in large areas of the Southern Ocean is limited by the supply of iron, an important micronutrient for phytoplankton. However, downstream of ocean islands in this study area, massive phytoplankton blooms have been observed, leading to the idea that the islands themselves are somehow fertilizing the ocean with iron. The team showed that this natural iron fertilization enhanced phytoplankton growth and productivity and the amount of carbon exported from the surface layer (100 meters) by two to three times. Moreover, they found that the amount of carbon stored at 3,000 meters and in the sediment was similarly two to three times higher beneath the natural fertilized region than for the nearby iron-poor region.
"This work demonstrated for the first time that Southern Ocean phytoplankton blooms fueled by natural sources of iron have the potential to sequester carbon in the deep ocean," said Charette.
The team conducted their experiment in 2004-2005 on the seas around the Crozet Islands and Plateau at the northern boundary of the Southern Ocean, about 1,400 miles (2,200 kilometers) southeast of South Africa. These seas provided a natural laboratory, because each spring the waters north of Crozet experience an enormous bloom containing billions of individual phytoplankton and covering 120,00
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Woods Hole Oceanographic Institution