Fine-scale vertical distributions of microbial biomass and activity in California Borderland sediments

Abstract

Vertical distributions of total organic carbon (TOC), porosity, adenosine triphosphate (ATP), and rates of nucleic acid synthesis were measured at millimeter depth intervals in basin sediments from the California Borderland. Within the upper 5 mm, large gradients were measured in sediment microbial biomass (ATP) and nucleic acid synthesis rates, especially deoxyribonucleic acid (DNA) synthesis. A subsurface secondary maximum in specific growth rate (extrapolated from DNA synthesis and ATP biomass measurements) was also observed and may be associated with the onset of sulfate reduction. Carbon production rates integrated over the top 40 mm of the sediment profile in San Pedro Basin (160 to 220 mg carbon m −2 day −1) suggest that the central portion of the basin receives larger inputs of organic carbon than would be predicted from surface water primary production rates and a simple one-dimensional vertical settling model. Lateral transport of carbon from the shallower portions of the basin to the center is the most likely source of this carbon.