In this map of the Pacific Ocean, the deep blue areas are the nutrient-poor and thus low-fertility, central gyres of the major ocean basins. Fewer phytoplankton grow here. The lighter blue areas represent more productive regions with higher rates of nutrient input and consequently higher phytoplankton biomass. The continental shelves and upwelling regions (e.g., along the equator) tend to have higher biomass because of nutrient input. Map Courtesy of the National Oceanic and Atmospheric Administration
Large, nutrient-poor expanses of the open ocean are getting a substantial nitrogen influx from an abundant group of unicellular organisms that "fix," or chemically alter, nitrogen into a form usable for biological productivity.
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."
Jane Sanders | EurekAlert!
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