Biological Sink of Nitrous Oxide in Oxygen Minimum Zones

Xin Sun1, John Tracey2, Colette LaMonica Kelly3, Elizabeth Wallace4, Amal Jayakumar1, Karen L Casciotti5 and Bess B Ward2, (1)Princeton University, Princeton, NJ, United States, (2)Princeton University, Department of Geosciences, Princeton, NJ, United States, (3)Stanford University, Stanford, CA, United States, (4)Princeton University, United States, (5)Stanford University, Stanford, United States
Nitrous oxide (N2O) is a greenhouse gas and an ozone destroyer. Accurately quantifying sources and sinks of N2O is necessary to estimate its impact on global climate. The only biological sink, N2O consumption by microbes possessing N2O reductase genes, is poorly understood. Here we used (15N)2O stable isotope incubation experiments to measure N2O consumption rates at three stations in a marine oxygen minimum zone, a hotspot for N2O cycling. Rates measured in incubations responded to manipulated substrate and oxygen concentrations, so we estimated in situ N2O consumption rates by accounting for the effect of in situ environmental conditions. We also explored N2O consuming communities by quantifying N2O reductase genes. N2O consumption is inhibited by O2, so N2O consumption in oxic environments has been assumed to be negligible. N2O reductase genes, however, were detected at both anoxic and oxic depths, suggesting the potential for N2O consumption even in surface waters. N2O consumption occurred in samples collected from oxygenated surface seawaters, but only after O2 was purged from the incubation bottles. These results indicate that the surface oxygenated layer of oxygen minimum zones has the potential to trap N2O produced at deeper depths if transient or localized anoxia occurs.