Global ocean‐to‐atmosphere dimethyl sulfide flux

Abstract

The global ocean‐to‐atmosphere flux of dimethyl sulfide (DMS) is calculated on a monthly basis with 4.5°×7.5° latitude/longitude spatial resolution. An atmospheric general circulation model, the National Center for Atmospheric Research (NCAR) Community Climate Model 1 (CCM1) is used to drive algorithms pertinent to the air‐sea exchange of DMS. The cloud and radiation package in the CCM1 provides estimates of the solar radiation impinging on the surface ocean, which is then related to the flux of DMS from the ocean to the atmosphere on the basis of the empirical data of Bates et al. (1987a). The computed DMS flux values vary globally from 0.5 to 5.5 μmol m−2 d−1. A globally integrated ocean‐to‐atmosphere flux of 15 Tg S yr−1 (as DMS) is computed. This value is probably a lower limit since there is no explicit simulation of global primary productivity presently in the model. The DMS flux is implicitly lower in chronically cloudy regions, such as the Inter‐Tropical Convergence Zone and in low‐radiation regions such as the high‐latitude winter hemispheres. To examine the global applicability of the solar radiation‐DMS flux relationship, the DMS flux fields are scaled by the independently computed transfer velocity fields so as to obtain global maps of surface ocean DMS concentration at the resolution of the model. The computed surface ocean DMS concentrations vary from 2 to 150 nL L−1, with highest values predicted near equatorial regions and adjacent to summer hemisphere polar regions, areas with relatively low climatological wind speeds. The oceanic DMS concentrations computed here agree with the experimental data in those regions not impacted by high biological productivity. In those areas of relatively high oceanic productivity the solar radiation‐DMS flux relationship underestimates the ocean‐to‐atmosphere DMS flux and the subsequently computed surface ocean DMS concentrations.