DMS cycle in the marine ocean-atmosphere system – a global model study

A global coupled ocean-atmosphere modeling system is established to study the production of dimethylsulfide (DMS) in the ocean, the DMS flux to the atmosphere, and the resulting sulfur concentrations in the atmosphere. The DMS production and consumption processes in the ocean are simulated in the marine biogeochemistry model HAMOCC5, embedded in a ocean general circulation model (MPI-OM). The atmospheric model ECHAM5 is extended by the microphysical aerosol model HAM, treating the sulfur chemistry in the atmosphere and the evolution of the microphysically interacting internally- and externally mixed aerosol populations. We simulate a global annual mean DMS sea surface concentration of 1.8 nmol l⁻¹, a DMS emission of 28 Tg(S) yr⁻¹, a DMS burden in the atmosphere of 0.077 Tg(S), and a DMS lifetime of 1.0 days. To quantify the role of DMS in the atmospheric sulfur cycle we simulate the relative contribution of DMS-derived SO₂ and SO₄²⁻ to the total atmospheric sulfur concentrations. DMS contributes 25% to the global annually averaged SO₂ column burden. For SO₄²⁻ the contribution is 27%. The coupled model setup allows the evaluation of the simulated DMS quantities with measurements taken in the ocean and in the atmosphere. The simulated global distribution of DMS sea surface concentrations compares reasonably well with measurements. The comparison to SO₄²⁻ surface concentration measurements in regions with a high DMS contribution to SO₄²⁻ shows an overestimation by the model. This overestimation is most pronounced in the biologically active season with high DMS emissions and most likely caused by a too high simulated SO₄²⁻ yield from DMS oxidation