Isotopic Constraints on Nitrogen Transformation Rates in the Deep Sedimentary Marine Biosphere
Date of Original Version
Little is known about the nature of microbial community activity contributing to the cycling of nitrogen in organic-poor sediments underlying the expansive oligotrophic ocean gyres. Here we use pore water concentrations and stable N and O isotope measurements of nitrate and nitrite to constrain rates of nitrogen cycling processes over a 34-m profile from the deep North Atlantic spanning fully oxic to anoxic conditions. Using a 1-D reaction-diffusion model to predict the distribution of nitrogen cycling rates, results converge on two distinct scenarios: (1) an exceptionally high degree of coupling between nitrite oxidation and nitrate reduction near the top of the anoxic zone or (2) an unusually large N isotope effect (~60‰) for nitrate reduction that is decoupled from the corresponding O isotope effect, which is possibly explained by enzyme-level interconversion between nitrite and nitrate.
Publication Title, e.g., Journal
Global Biogeochemical Cycles
Buchwald, C., K. Homola, A. J. Spivack, E. R. Estes, R. W. Murray, and S. D. Wankel. "Isotopic Constraints on Nitrogen Transformation Rates in the Deep Sedimentary Marine Biosphere." Global Biogeochemical Cycles 32, 11 (2018). doi: 10.1029/2018GB005948.