An atmospheric constraint on the seasonal air-sea exchange of oxygen and heat in the extratropics

The air-sea exchange of oxygen (O-2) is driven by changes in solubility, biological activity, and circulation. The total air-sea exchange of O-2 has been shown to be closely related to the air-sea exchange of heat on seasonal timescales, with the ratio of the seasonal flux of O-2 to heat varying with latitude, being higher in the extratropics and lower in the subtropics. This O-2/heat ratio is both a fundamental biogeochemical property of air-sea exchange and a convenient metric for testing earth system models. Current estimates of the O-2/heat flux ratio rely on sparse observations of dissolved O-2, leaving it fairly unconstrained. From a model ensemble we show that the ratio of the seasonal amplitude of two atmospheric tracers, atmospheric potential oxygen (APO) and the argon-to-nitrogen ratio (Ar/O-2), exhibits a close relationship to the O-2/heat ratio of the extratropics (40-70 degrees). The amplitude ratio, A(APO)/A(ArN2), is relatively constant within the extratropics of each hemisphere due to the zonal mixing of the atmosphere. A(APO)/A(ArN2) is not sensitive to atmospheric transport, as most of the observed spatial variability in the seasonal amplitude of delta APO is compensated by similar variations in delta(Ar/N-2). From the relationship between O-2/heat and A(APO)/A(ArN2) in the model ensemble, we determine that the atmospheric observations suggest hemispherically distinct O-2/heat flux ratios of 3.3 +/- 0.3 and 4.7 +/- 0.8 nmol J(-1) between 40 and 70 degrees in the Northern and Southern Hemispheres respectively, providing a useful constraint for O-2 and heat air-sea fluxes in earth system models and observation-based data products.