Pelagic-benthic coupling of nucleic acids in an abyssal location of the northeastern Atlantic ocean

Spatial and temporal changes in sedimentary nucleic acid concentrations in an abyssal locality of the northeastern Atlantic Ocean were investigated in relation to fluxes of nucleic acids produced in the photic layer. Sediment trap material, collected between 1996 and 1998 at depths of 1,000, 3,000, and 4,700 m, and sediment samples were analyzed for DNA and RNA content. Nucleic acid concentrations in the sediments were very high and displayed significant temporal changes, whereas mesoscale variability was low. DNA and RNA concentrations generally displayed opposite temporal patterns, which are likely to be dependent on the nature and characteristics of DNA and RNA molecules. Nucleic acid fluxes were high and displayed clear seasonal changes apparently coupled with seasonal pulses of primary production. However, while median values of DNA fluxes were relatively similar in all sediment traps, median values of RNA fluxes almost doubled from the 1,000- to the 4,700-m depth, suggesting differences in the metabolic activity of microbes associated with sinking particles. Significant relationships between DNA concentrations in the sediments and DNA fluxes and between RNA concentrations and RNA fluxes, indicating the presence of a clear pelagic-benthic coupling of particulate nucleic acids, were observed. The benthic system investigated was not steady state since we estimated that, from September 1996 to October 1998, nucleic acid concentration in the sediments decreased by about 165 mg of DNA m(-2). Vertical profiles revealed a significant decrease in DNA concentration with depth in the sediments, reaching an asymptotic value of about 5 mu g g(-1). This DNA fraction constitutes a pool of potentially refractory DNA (accounting for 16 to 40% of the total DNA pool) that might be buried in the sediments.