Biogeosciences (Feb 2008)
Heterotrophic bacterial production in the eastern South Pacific: longitudinal trends and coupling with primary production
Abstract
Spatial variation of heterotrophic bacterial production and phytoplankton primary production were investigated across the eastern South Pacific Ocean (−141° W, −8° S to −72° W, −35° S) in November–December 2004. Bacterial production (<sup>3</sup>H leucine incorporation) integrated over the euphotic zone encompassed a wide range of values, from 43 mg C m<sup>−2</sup> d<sup>−1</sup> in the hyper-oligotrophic South Pacific Gyre to 392 mg C m<sup>−2</sup> d<sup>−1</sup> in the upwelling off Chile. In the gyre (120° W, 22° S) records of low phytoplankton biomass (7 mg Total Chl<i>a</i> m<sup>−2</sup>) were obtained and fluxes of in situ <sup>14</sup>C-based particulate primary production were as low as 153 mg C m<sup>−2</sup> d<sup>−1</sup>, thus equal to the value considered as a limit for primary production under strong oligotrophic conditions. Average rates of <sup>3</sup>H leucine incorporation rates, and leucine incorporation rates per cell (5–21 pmol l<sup>−1</sup> h<sup>−1</sup> and 15–56×10<sup>−21</sup> mol cell<sup>−1</sup> h<sup>−1</sup>, respectively) determined in the South Pacific gyre, were in the same range as those reported for other oligotrophic subtropical and temperate waters. Fluxes of dark community respiration, determined at selected stations across the transect varied in a narrow range (42–97 mmol O<sub>2</sub> m<sup>−2</sup> d<sup>−1</sup>), except for one station in the upwelling off Chile (245 mmol O<sub>2</sub> m<sup>−2</sup> d<sup>−1</sup>). Bacterial growth efficiencies varied between 5 and 38%. Bacterial carbon demand largely exceeded <sup>14</sup>C particulate primary production across the South Pacific Ocean, but was lower or equal to gross community production.
