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 in 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 fluid shear. Microbial activities and concentrations of various parameters 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 14C-amino acids appeared to be independent of POC and PON concentration, but was related to the contribution of phytogenic material to the POC. The higher microbial activities in the turbulent BBL than in the comparatively stagnant water column could be accounted for by the potential enhancement of nutrient flux due to fluid shear, assuming tight particle association of the bacterial community in the BBL.