North Atlantic production of nitrous oxide in the context of changing atmospheric levels

We use transit time distributions calculated from tracer data together with in situ measurements of N 2 O to estimate the concentration of biologically produced N 2 O ([N 2 O] xs ) and N 2 O production rates in the central North Atlantic Ocean. Our approach to estimation of N 2 O production rates integrates the effects of potentially varying production and decomposition mechanisms along the transport path of a water mass. We find that previously used approaches overestimate the oceanic equilibrium N 2 O concentrations by 8–13% and thus underestimate the strength of N 2 O sources in large parts of the water column. Thus the quantitative characteristics of the [N 2 O] xs /AOU relationship used as an indicator of nitrification are distorted. We developed a new parameterization of N 2 O production during nitrification depending linearly on AOU and exponentially on temperature and depth, which can be applied to calculate N 2 O production due to nitrification in the entire ocean including oxygen minimum zones.