As one of the three regions of the world ocean that contains a permanent Oxygen Deficient Zone (ODZ), the Arabian Sea is disproportionately more important to the loss of fixed N from the ocean and to the oceanic flux of nitrous oxide (N2O) to the atmosphere than its size would predict. The generally accepted paradigm that canonical denitrification is responsible for both of these fluxes has recently been challenged by the finding that anaerobic ammonium oxidation (anammox) may even dominate denitrification for N2 production. Because the two processes are performed by different organisms with completely different physiologies that respond differently to environmental factors, it is necessary to accurately resolve their respective contributions in order to understand and predict fluxes in the N cycle. Although conventional anammox incubations suggest that anammox is the sole pathway of N2 production in the ODZ, this cannot be reconciled with stoichiometric constraints or with observed distributions of nitrite and N2O in the ODZ, which strongly suggest denitrification. Additionally, community composition and dynamics derived from molecular data suggest that denitrifiers must play an important role.
In this research, researchers from Princeton and University of Washington hypothesize that the conventional incubation methods tend to artificially favor one or the other process because they alter the concentrations of their respective limiting factors. To test this hypothesis, they will investigate the response of anammox and denitrification to oxygen, ammonium, nitrite and organic carbon using large volume incubations in gas impermeable bags to obtain realistic estimates of the true rates of anammox and denitrification. The experiments will be carried out on a cruise in the Arabian Sea in collaboration with Indian colleagues.
An important component of the broader impacts of the research is a strong collaboration between the Princeton and UW groups and their collaborators in India. This cooperation will provide opportunities to engage in a certain amount of technology transfer in stable isotope and molecular ecological techniques. At Princeton, the project will employ and provide summer and senior thesis research opportunities for undergraduates, and will translate into the classroom by experience and example in the undergraduate oceanography curriculum. Both institutions support department and institutional level outreach programs for teacher training and student research, and all the PIs will continue to participate in these at their respective institutions.
