Summary of Abstract Submission

Abstract Submission No. IO50-09-0055PresentationPoster


Bo Thamdrup*1, Laura A. Bristow1

1 Department of Biology, University of Southern Denmark, Denmark


The Bay of Bengal houses a well-developed oxygen minimum zone (OMZ), where oxygen drops to levels so low, that an induction of anaerobic nitrate respiration ┐ and thereby the removal of reactive nitrogen through N2 production ┐ might be expected. Nonetheless, the Bay does not appear to contribute substantially to reactive nitrogen removal from the oceans. In January 2014 we tested the potential for N2 production through denitrification and anaerobic ammonium oxidation (anammox) in waters from several sites within the core of the OMZ, using batch incubations amended with 15N-labeled substrates and with manipulation of oxygen concentrations. Both pathways of N2 formation were active at oxygen concentrations below 1 ÁM at rates within the range observed in other OMZs. Rates decreased at higher oxygen concentrations and denitrification was inhibited at ~5 ÁM oxygen while anammox was detected to ~10 ÁM. These oxygen sensitivities agree broadly with results from other OMZs, and indicate that N2 production could be active at the oxygen levels found in the Bay of Bengal. This implies that the removal of reactive nitrogen in the Bay is not limited by oxygen directly but rather by substrate availability. We suggest that nitrite concentrations are kept low by efficient aerobic microbial nitrite oxidation even at sub-micromolar oxygen levels, such that denitrification and anammox are controlled indirectly by oxygen. Nonetheless our results imply that anammox bacteria are present in the Bay of Bengal OMZ and thereby that, at least occasionally, conditions must be conducive to the growth of these obligate anaerobes.