Nitrogen Fixation Within a Tropical Upwelling Ecosystem: Evidence for a Redfield Budget of Carbon/Nitrogen Cycling by the Total Phytoplankton Community

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Recent measurements and paradigms suggest that (1) the uptake of-dissolved carbon and nitrate by phytoplankton may be greater than the Redfield ratio of 6.6 and (2) the oceans may be loosing nitrogen from an imbalance in the global rates of nitrogen fixation and denitrification. An analysis of concurrent Delta DIC/Delta NO3 depletion ratios within the Venezuelan and Peruvian upwelling ecosystems, indeed, suggests that values of 10.1-28.6 may pertain to these tropical eutrophic habitats. Nitrogen fixation may provide a Redfield balance in at least the former system, with 34-77% of the new production attributed to assimilation of N-2. Independent confirmation of such new production on the Venezuelan shelf is provided by the interannual increases of H2S and DIC within the adjacent Cariaco Trench.

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Journal of Geophysical Research - Oceans, v. 101, no. C9, p. 20607-20616.