The heterotrophic bacterial response during a mesoscale iron enrichment experiment (IronEx II) in the eastern equatorial Pacific Ocean

The response of the heterotrophic bacterial community to iron addition was determined during the mesoscale iron-enrichment experiment conducted in the eastern equatorial Pacific during May-June 1995 (IronEx II). Bacterial abundance and H-3-leucine incorporation rates were measured for samples collected from the middle of the mixed layer (15 m) over the course of the iron-induced phytoplankton bloom and its decline. Bacterid abundance and productivity increased 1.7- and threefold, respectively, compared to un-enriched waters. Specific growth rates of heterotrophic bacteria increased three- to fourfold. These results demonstrate that iron addition to this high-nitrate, low-chlorophyll region affects both autotrophic and heterotrophic microorganisms and that bacterial carbon demand can be potentially met by the fivefold increase in photosynthetic productivity in the mixed layer.