Title:
Nitrogen fixation by Trichodesmium spp.: An important source of new nitrogen to the tropical North Atlantic Ocean
Nitrogen fixation by Trichodesmium spp.: An important source of new nitrogen to the tropical North Atlantic Ocean
Author(s)
Capone, Douglas G.
Burns, James A.
Montoya, Joseph P.
Subramaniam, Ajit
Mahaffey,
Gunderson, Troy
Michaels, Anthony F.
Carpenter, Edward J.
Burns, James A.
Montoya, Joseph P.
Subramaniam, Ajit
Mahaffey,
Gunderson, Troy
Michaels, Anthony F.
Carpenter, Edward J.
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Abstract
The broad distribution and often high densities of the cyanobacterium Trichodesmium spp. in oligotrophic waters imply a substantial role for this one taxon in the oceanic N cycle of the marine tropics and subtropics. New results from 154 stations on six research cruises in the North Atlantic Ocean show depth-integrated N₂ fixation by Trichodesmium spp. at many stations that equalled or exceeded the estimated vertical flux of NO₃ into the euphotic zone by diapycnal mixing. Areal rates are consistent with those derived from several indirect geochemical analyses. Direct measurements of N₂ fixation rates by Trichodesmium are also congruent with upper water column N budgets derived from parallel determinations of stable isotope distributions, clearly showing that N₂ fixation by Trichodesmium is a major source of new nitrogen in the tropical North Atlantic. We project a conservative estimate of the annual input of new N into the tropical North Atlantic of at least 1.6 X 10 ¹² mol N by Trichodesmium N₂ fixation alone. This input can account for a substantial fraction of the N₂ fixation in the North Atlantic inferred by several of the geochemical approaches.
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2005
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