An Atmospheric Constraint on the Seasonal Air-Sea Exchange of Oxygen and Heat in the Extratropics

Abstract

© 2021. American Geophysical Union. All Rights Reserved.The air-sea exchange of oxygen (O2) is driven by changes in solubility, biological activity, and circulation. The total air-sea exchange of O2 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 O2 to heat varying with latitude, being higher in the extratropics and lower in the subtropics. This O2/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 O2/heat flux ratio rely on sparse observations of dissolved O2, 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/O2), exhibits a close relationship to the O2/heat ratio of the extratropics (40– (Formula presented.)). The amplitude ratio, (Formula presented.) / (Formula presented.), is relatively constant within the extratropics of each hemisphere due to the zonal mixing of the atmosphere. (Formula presented.) / (Formula presented.) is not sensitive to atmospheric transport, as most of the observed spatial variability in the seasonal amplitude of (Formula presented.) APO is compensated by similar variations in (Formula presented.) (Ar/ (Formula presented.)). From the relationship between (Formula presented.) /heat and (Formula presented.) / (Formula presented.) in the model ensemble, we determine that the atmospheric observations suggest hemispherically distinct (Formula presented.) /heat flux ratios of 3.3 (Formula presented.) 0.3 and 4.7 (Formula presented.) 0.8 nmol (Formula presented.) between 40 and (Formula presented.) in the Northern and Southern Hemispheres respectively, providing a useful constraint for (Formula presented.) and heat air-sea fluxes in earth system models and observation-based data products.