N2O cycling in the Gulf of Mexico from concentration and stable isotopic data

Melissa Shugart

Collaboration with Laura Bristow (Nordcee, University of Southern Denmark)

Nitrous oxide (N2O) is a trace gas with a warming potential approximately 300 times that of carbon dioxide. N2O is also the primary source of atmospheric nitrogen oxides, which can deplete the stratospheric ozone layer. Marine N2O production from bacterial processes (nitrification and denitrification) represents a significant natural source of N2O to the atmosphere. Different pathways of N2O production and consumption have distinct isotopic signatures due to kinetic isotope fractionation during biological transformations. N2O samples were collected at various locations and depths in the Gulf of Mexico hypoxic zone during the summers of 2015 and 2016 to investigate N2O cycling. We measured N2O concentrations, the stable isotopic composition of N2O (d   N and d   O) and also the site preference (SP), defined as the difference between the d   Na (internal) and the d   Nb (external), to gain further insight into N2O production and consumption processes. N2O concentrations showed interannual variability, ranging from 6 to 16 nM in 2015 and 3 to 37 nM in 2016. Highest N2O concentrations were associated with a relatively low d   N near the oxycline, indicating net N2O production. d   N of N2O as well as SP were elevated under anoxic conditions, indicating N2O consumption. As part of this project, we will interpret spatial and temporal changes in N2O production and consumption in relation to physical and chemical factors.  

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