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- Title
Modeling oceanic nitrate and nitrite concentrations and isotopes using a 3-D inverse N cycle model.
- Authors
Martin, Taylor S.; Primeau, François; Casciotti, Karen L.
- 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.
- Subjects
NITROGEN; ISOTOPES; NITRIFICATION; OCEANOGRAPHIC research; THERMODYNAMIC state variables
- Publication
Biogeosciences, 2019, Vol 16, Issue 2, p347
- ISSN
1726-4170
- Publication type
Article
- DOI
10.5194/bg-16-347-2019