Martin/marine1: chemical oceanography; a marine nitrogen cycle inverse model   
                                                                               
A matrix submitted by Taylor Martin, Stanford, discussed the following paper:  
                                                                               
Title: Modeling oceanic nitrite concentrations and isotopes using a 3D         
inverse N cycle model                                                          
Authors: Taylor S. Martin(1), Francois Primeau(2), and Karen L. Casciotti(1)   
(1) Stanford University, Department of Earth System Science                    
(2) University of California, Irvine, Department of Earth System Science       
Received: 05 Sep 2018                                                          
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    
understanding the N cycle processes occurring there, especially those where    
bioavailable N is lost from or retained within the water column. Here we       
present the expansion of a global 3D 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.                               
                                                                               
How to cite: Martin, T. S., Primeau, F., and Casciotti, K. L.: Modeling        
oceanic nitrite concentrations and isotopes using a 3D inverse N cycle model,  
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-397, in review, 2018.