Hydrodynamic and Environmental Controls on the Nitrogen Isotope Effect of Benthic N2 Production
Abstract:
The benthic redox conditions were found to control the N isotope effect, which under reducing conditions is driven by fractionation during nitrification and anaerobic ammonium oxidation and under oxidizing conditions by fractionation during denitrification. The mineralization rate, the bioirrigation intensity, and chemical composition of the overlying water affect the benthic redox zonation and therefore also the benthic N isotope effect.
With increasing water-depth the mineralization rate and the advective nitrate supply to the sediment both decrease, constraining most benthic N cycling to the continental shelf. Simulations that reproduce observed trends of sediment O2 uptake and N2 fluxes with water depth, combined with ocean bathymetry yield an average benthic N isotope effect of -3‰, in line with independent estimates from global circulation models coupled to N cycle models (Somes et al., 2013. Biogeosciences 10, 5889-5910).