Microbial plankton abundance and heterotrophic activity across the Central Atlantic Ocean

12 pages, 4 tables, 6 figures.-- Printed version published Oct 2008.-- Supporting information (Suppl. tables S1-S2 + references) available at: https://doi.org/10.1016/j.pocean.2008.08.002The role of microorganisms in the transfer of carbon of marine systems is very important in open oligotrophic oceans. Here, we analyze the picoplankton structure, the heterotrophic bacterioplankton activity, and the predator–prey relationships between heterotrophic bacteria and nanoflagellates during two large scale cruises in the Central Atlantic Ocean (~29°N to ~40°S). Latitud cruises were performed in 1995 between March–April and October–November. During both cruises we crossed the regions of different trophic statuses; where we measured different biological variables both at the surface and at the deep chlorophyll maximum (DCM). The concentration of chlorophyll a varied between 0.1 and 0.8 mg m−3, the abundance of heterotrophic bacteria varied between 1.0 × 106 cells ml−1, and that of heterotrophic nanoflagellates between 1.0 × 104 cells ml−1. The production of heterotrophic bacteria varied more than three orders of magnitude between 3 × 105 cells ml−1, Synechococcus between 1.0 × 104 cells ml−1, and picoeukaryotes between 104 cells ml−1.Two empirical models were used to learn more about the relationship between heterotrophic bacteria and nanoflagellates. Most bacterial production was ingested when this production was low, the heterotrophic nanoflagellates could be controlled by preys during Latitud-I cruise at the DCM, and by predators in the surface and in the Latitud-II cruise. Our results were placed in context with others about the structure and function of auto- and heterotrophic picoplankton and heterotrophic nanoplankton in the Central Atlantic OceanThis work was supported by grant AMB94-0739 to S. Agustí. Final writing of the manuscipt has been supported by an I3P felow (CSIC) to E.V.-D.Peer reviewe