Buchwald C, K Homola, AJ Spivack, ER Estes, RA Pockalny, RW Murray and SD Wankel. 2018. Isotopic constraints on nitrogen transformation rates in the deep sedimentary biosphere. Global Biogeochemical Cycles. doi:10.1029/2018GB005948
Date Published:
November 15, 2018
AJ Spivack, C Buchwald, ER Estes, K Homola, RA Pockalny, RW Murray, SD Wankel,

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 34m profile from the deep North Atlantic spanning fully oxic to anoxic conditions. Using a 1D reactiondiffusion 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.