An improved comparison of atmospheric Ar/N2 time series and paired ocean-atmosphere model predictions

Ar/N-2 variations in the atmosphere reflect ocean heat fluxes, air-sea gas exchange, and atmospheric dynamics. Here atmospheric Ar/N-2 time series are compared to paired ocean-atmosphere model predictions. Agreement between Ar/N-2 observations and simulations has improved in comparison to a previous study because of longer time series and the introduction of automated samplers at several of the atmospheric stations, as well as the refinement of the paired ocean-atmosphere models by inclusion of Ar and N-2 as active tracers in the ocean component. Although analytical uncertainties and collection artifacts are likely to be mainly responsible for observed Ar/N-2 outliers, air parcel back-trajectory analysis suggests that some of the variability in Ar/N-2 measurements could be due to the low-altitude history of the air mass collected and, by extension, the local oceanic Ar/N-2 signal. Although the simulated climatological seasonal cycle can currently be evaluated with Ar/N-2 observations, longer time series and additional improvements in the signal-to-noise ratio will be required to test other model predictions such as interannual variability, latitudinal gradients, and the secular increase in atmospheric Ar/N-2 expected to result from ocean warming.