MICROBIAL ACTIVITY IN THE BENTHIC BOUNDARY-LAYER - SMALL-SCALE DISTRIBUTION AND ITS RELATIONSHIP TO THE HYDRODYNAMIC REGIME

New information is presented on activity, abundance, and size spectra of bacteria as well as on concentration and composition of particles i n the benthic boundary layer (BBL) and in the lower water column. The distribution of these parameters is related to the hydrodynamic regime close to the seafloor. Particular focus is on modelling the potential increase in nutrient access of particle-associated bacteria due to fl uid shear. Microbial activities and concentrations of various paramete rs displayed distinct distribution patterns In the BBL and were up to a factor of 7.5 higher than in the adjacent water column. Utilization of C-14-amino acids appeared to be independent of POC and PON concentr ation, but was related to the contribution of phytogenic material to t he POC. The higher microbial activities in the turbulent BBL than in t he comparatively stagnant water column could be accounted for by the p otential enhancement of nutrient flux due to fluid shear, assuming tig ht particle association of the bacterial community in the BBL.