Modeling oceanic nitrate and nitrite concentrations and isotopes using a 3-D inverse N cycle model
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Published:2019-01-24
Issue:2
Volume:16
Page:347-367
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Martin Taylor S.ORCID, Primeau François, Casciotti Karen L.
Abstract
Abstract. Nitrite (NO2-) is a key intermediate in the marine nitrogen (N) cycle
and a substrate in nitrification, which produces nitrate (NO3-),
as well as water column N loss processes denitrification and anammox. In
models of the marine N cycle, NO2- is often not considered as a
separate state variable, since NO3- occurs in much higher
concentrations in the ocean. In oxygen deficient zones (ODZs), however,
NO2- represents a substantial fraction of the bioavailable N,
and modeling its production and consumption is important to understand the N
cycle processes occurring there, especially those where bioavailable N is
lost from or retained within the water column. Improving N cycle models by
including NO2- is important in order to better quantify N
cycling rates in ODZs, particularly N loss rates. Here we present the
expansion of a global 3-D inverse N cycle model to include NO2-
as a reactive intermediate as well as the processes that produce and consume
NO2- in marine ODZs. NO2- accumulation in ODZs is
accurately represented by the model involving NO3- reduction,
NO2- reduction, NO2- oxidation, and anammox. We
model both 14N and 15N and use a compilation of
oceanographic measurements of NO3- and NO2-
concentrations and isotopes to place a better constraint on the N cycle
processes occurring. The model is optimized using a range of isotope effects
for denitrification and NO2- oxidation, and we find that the
larger (more negative) inverse isotope effects for NO2-
oxidation, along with relatively high rates of NO2-, oxidation
give a better simulation of NO3- and NO2-
concentrations and isotopes in marine ODZs.
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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