Distribution of microbial biomass and secondary production in a warm-core Gulf Stream ring

Abstract

Microbial biomass, bacterial abundance and secondary production were examined in relation to the changing physiochemical conditions within warm-core Gulf Stream ring 81-F. Highest densities of bacterioplankton (6.14 × 10 8 cells 1 −1) occured at the ring margin in continental shelf and slope water entrained by the ring. Likewise, both total bacterial secondary production (measured as incorporation of [ 3H]thymidine into DNA) and per-cell bacterial secondary production were highest at the ring margin, averaging 291.1 pmoles 1 −1 d −1 and 4.95 × 10 −7 pmoles cell −1 d −1, respectively. In contrast, high concentrations of ATP (mean, 1.45 μg l −1) and chlorophyll α (mean, 2.29 μg l −1) were found both at the periphery and near the center of the ring. A similar distribution pattern was found for the incorporation of [ 3H]adenine into microbial RNA. The elevated values for microbial biomass and activity at the ring margin may reflect the response of microbial populations to new conditions resulting from the juxtaposition of water masses comprising and surrounding the ring. Our results indicate that the distribution of microbial populations and the rates of microbial processes occuring within warm-core ring 81-F were influenced by the age of the ring and the extent of its interaction with continental shelf water, surrounding slope water and Gulf Stream meanders.