Nitrogen fixation, distribution, and production of Oscillatoria (Trichodesmium) spp. in the western Sargasso and Caribbean Seas1

Measurements of Oscillatoria spp. standing crop, primary production, and N 2 fixation were made at 46 stations on three cruises to the Caribbean and western Sargasso Seas. Oscillatoria is a major component of the Caribbean Sea plankton, comprising 60% of the total chlorophyll a in the upper 50 m and about 20% of the primary production. Through N 2 fixation it contributes an average of 1.3 mg N m −2 d −1 to the Caribbean Sea, and this may be a major input of nitrogen to this area. Oscillatoria appears to be of relatively little importance in the western Sargasso Sea.