Trichodesmium blooms and new nitrogen in the North Pacific gyre

Abstract

In August 1989 the authors encountered a >1×103 km2 Trichodesmium bloom in the North Pacific near the JGOFS Hawaii Ocean Time-Series Station ALOHA. Analyses of particulate matter collected from the densest portion of the bloom showed enrichments of 3375-7787-fold for carbon, nitrogen, adenosine triphosphate and pigments, relative to typical non-bloom concentrations: phosphorus was enriched only 583-fold. Dissolved nitrogen pools were also enriched within the bloom, and in the case of NH4 by 27-fold. Budget estimates based upon seasonally-averaged N imports to and exports from the epipelagic zone suggest that diazotrophic cyanobacterial blooms may be an important source of new nitrogen to the ecosystem. Two models are discussed to account for the initiation of these open ocean blooms, and to explain the uncoupling of N and P concentrations and the selective enrichments of P which are required to favor the growth of diazotrophic microorganisms. -from Authors