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 3H‐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. Bacterial 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.