Ocean to atmosphere carbon monoxide flux: Global inventory and climate implications

Abstract

The global ocean to atmosphere flux of carbon monoxide (CO) is simulated with 4.5° × 7.5° latitude‐longitude spatial resolution using global data fields derived from an atmospheric general circulation model. The cloud and radiation package in the National Center for Atmospheric Research Community Climate Model is used to estimate the solar energy at the Earth's surface. This quantity is empirically related to photochemical interaction with dissolved organic matter, and the global concentration field of CO in surface seawater is estimated. Areas associated with the Intertropical Convergence Zone and mid‐ to high‐latitude winter hemisphere regions have relatively low climatological CO surface ocean concentrations on a local scale. The global surface wind and temperature fields are simultaneously used to calculate the global transfer velocity field of CO. Coupling these two computed fields, a global ocean to atmosphere CO flux of 165± 80 Tg yr−1 is proposed. The CO flux rates vary globally from 0.1 to 12 ug cm−2 month−1. The fluxes are largest in the mid‐latitude summer hemispheres, with a maximum at 40° S during the austral summer that is 40% larger on a zonal average than at any northern hemisphere latitude. Relatively small continental sources of CO to the southern hemisphere atmosphere and the short atmospheric residence time of this trace gas indicate that ocean‐derived CO may influence the local photochemical dynamics in the remote marine boundary layer of this region. A possible climate feedback scenario involving UV radiation, ozone, OH, and the air‐sea exchange of CO is proposed. The global ocean to atmosphere CO flux proposed here is at the high end of those used in previous atmospheric CO budgets. This estimate however must be considered a lower limit because no explicit simulation of global oceanic primary productivity is presently in the model.