Diazotrophic Cyanobacteria: An Underestimated Source of NewNitrogen in the Oligotrophic Oceans

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This research program is a systematic reassessment of the role of dinitrogen fixation in the upper layers of the open ocean using diazotrophic cyanobacteria. Nitrogen fixation in the open ocean is potentially a major source of nitrogen in seawater, and one of the few ways in which atmospheric nitrogen is transferred to the sea. A procedural redesign of the actylene reduction assay for nitrogenase activity will be undertaken so that unconcentrated seawater samples can be used for study. The new technique has to be perfected, tested and calibrated in the laboratory first. Second the technique will be field tested in local waters near Woods Hole and in a two week field study in the Sargasso Sea. %%% The fixation of nitrogen by marine organisms in the open ocean is one of the few pathways by which nitrogen in the atmosphere is transferred to the sea. Because nitrogen is the fertilizing element most often in short supply in the sea, its concentration often determines the amount of primary production that can take place in the open ocean. In areas of the ocean where nitrogen is especially scarce, microorganisms have been found that convert atmospheric nitrogen to their own tissues. The methods used for measuring nitrogen fixation are old and have problems. An attempt will be made to develop and test new methods that are more sensitive and less invasive than previous approaches.