Understanding the role of bacteria in the oxygen minimum zone (OMZ) in the carbon cycle

Abstract

In order to understand the role of heterotrophic prokaryotes (hereafter bacteria) in the carbon cycle, we investigated bacterial biomass and production in an oxygen minimum zone (OMZ), the NE equatorial Pacific. Field sampling was conducted over the period from July 10 to August 14, 2011. The OMZ (< 30μmol O2) extended vertically ranging from the depth of 400 to 700m. Bacterial biomass (based on Adenosine tri-phosphate conc.) and production (estimated by the 3H-thymidine incorporation) was very high in the euphotic zone (mean = 36.78 ng L-1 and 1.82 mg C m-3 d-1, respectively) and decreased with the depth (mean = 4.88 ng L-1 and 1.00 mg C m-3 d-1, respectively). Interestingly, the second peak of these values was found in the deeper layer of the OMZ (mean = 17.00 ng L-1 and 2.06 mg C m-3 d-1, respectively). This suggests different types of electron acceptors may be active in the deeper layer of the OMZ. Furthermore, the increased rate of production was higher than that of the biomass in the deeper layer of the OMZ. This discrepancy may be due to the grazing effect by protozoa. These results indicate that bacteria in OMZ could be an important contributor to secondary production and carbon cycling in the ocean. Further genetic investigation will provide more detailed information on diversity and identify key functional groups of bacteria in the OMZ.