First identified about five years ago, these organisms about 7 microns in diameter are fixing nitrogen at rates up to three times higher than previously reported for the Pacific Ocean, according to research published in the Aug. 26, 2004 edition of the journal Nature. On a transect from Oahu, Hawaii, to San Diego, Calif., researchers measured some of the highest rates in this study: Seven milligrams of nitrogen an essential nutrient for the growth of many organisms were being injected into the phytoplankton and other organic materials in every square meter of the ocean surface. "To our surprise, these unicellular nitrogen-fixers are broadly distributed spatially and vertically distributed at least down to 100 meters, and they're fixing nitrogen at quite high rates," said lead author Joe Montoya, an associate professor of biology at the Georgia Institute of Technology. "The rates we measured imply a total input of nitrogen that exceeds the rate of nitrogen fixation measured for the cyanobacteria Trichodesmium (traditionally believed to be the dominant marine nitrogen-fixer) in the Pacific Ocean. These unicells are the largest single source of nitrogen entering the water in broad areas of the ocean."

This level of nitrogen fixation in the Pacific Ocean alone accounts for about 10 percent of the total global oceanic new production of biomass, according to the researchers' preliminary calculations published in the Nature paper. "This is globally important because new production in the ocean is one of the key forces that drives the uptake of carbon dioxide from the atmosphere into the ocean," Montoya explained. "This represents a route for trapping and sequestering carbon dioxide and keeping it out of atmospheric circula
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Contact: Jane Sanders
jane.sanders@edi.gatech.edu
404-894-2214
Georgia Institute of Technology Research News
25-Aug-2004