Process‐Specific Effects of Sulfide on Nitrogen Cycling in Marine Oxygen Minimum Zones

Abstract Marine oxygen minimum zones (OMZs) harbor a variety of nitrogen cycling processes and act as hotspots of fixed nitrogen loss and nitrous oxide (N 2 O) emissions, thereby influencing nitrogen availability and the Earth's climate system. Sulfide occasionally accumulates in OMZs due to in situ production or release from the sediments, but its impact on nitrogen cycling is not fully understood. Using nitrogen tracer incubations in the Eastern Tropical South Pacific OMZ and meta‐analysis of previous observations in other low oxygen environments, we found that sulfide addition generally inhibited nitrification and anammox while enhancing denitrification. These results illustrated the role of sulfide in determining the importance of different nitrogen cycling processes and changing the fate of nitrogen species, for example, increasing the contribution of denitrification to nitrogen loss compared to anammox and causing a stronger N 2 O accumulation in OMZs. Improved understanding of sulfide impacts on nitrogen cycling in marine OMZs strengthens our capacity to predict changes in nitrogen availability and N 2 O emissions during sulfidic events, whose frequency, duration and spatial extent are expected to change under future climate scenarios.