RAPID: Does dinitrogen fixation occur in oxygen minimum zones?

Old Dominion University Research Foundation, Norfolk VA

Investigators

Abstract

Recent and multiple lines of evidence suggest that dinitrogen (N2) fixation and denitrification may be more closely coupled in space than previously suggested and nifH genes and their expression have been identified from within the oxygen minimum zone (OMZ) of the Arabian Sea. In this OMZ, isotopic evidence and N2 supersaturation suggests N2 fixation is a significant process. However, despite the geochemical inferences regarding the location and magnitude of N2 fixation in the Arabian Sea, and the importance of this basin in removing fixed N from the ocean via denitrification, it is thought that OMZs do not harbour diazotrophs (nitrogen fixing bacteria). A team of researchers at Old Dominion University believe that OMZs may be sites of active N2 fixation, and with funding from this Rapid Response Research Grant (RAPID) they will participate in a cruise of opportunity in the Eastern Tropical North Pacific (ETNP) to determine whether N2 fixation is an important process within or adjacent to this OMZ. They expect to achieve a better understanding of where N2 fixation occurs with respect to the OMZ and areas of active denitrification. In collaboration with other marine nitrogen cycle colleagues onboard, they expect to be able to simultaneously compare rates of denitrification and N2 fixation while also examining the diversity, community structure, and juxtaposition of denitrifying and N2 fixing organisms within the ETNP OMZ. Armed with this more comprehensive understanding of the distribution of denitrification and N2 fixation with respect to the OMZ, a more realistic view of the N cycle within should be gained. Broader Impacts. Results will contribute to current understanding of the controls on marine N2 fixation in general, as well as the balance between N inputs and losses from OMZs. IT is reasonable to think that this project will be transformative in shaping our view of the marine N cycle, particularly as regards to N inputs.