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Isotopic Constraints on Nitrogen Transformation Rates in the Deep Sedimentary Marine Biosphere
Author(s) -
Buchwald C.,
Homola K.,
Spivack A. J.,
Estes E. R.,
Murray R. W.,
Wankel S. D.
Publication year - 2018
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2018gb005948
Subject(s) - anoxic waters , nitrate , isotopes of nitrogen , nitrite , denitrification , environmental chemistry , nitrogen cycle , nitrogen , cycling , stable isotope ratio , sedimentary rock , chemistry , oceanography , environmental science , geology , geochemistry , physics , organic chemistry , archaeology , quantum mechanics , history
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.