Atmospheric Dimethyl Sulphide and the Natural Sulphur Cycle

Abstract

ALL models of natural processes for the transfer of sulphur on a global scale^1–4 require some volatile or gaseous sulphur compound to complete the cycle by providing a vehicle for the transfer of sulphur from the sea through the air to the land surfaces. In the past, this role has been assigned to H₂S and an average atmospheric concentration of 2×10⁻¹⁰ by volume satisfied the mass transfer needs of the models. Attempts to detect the presence of these concentrations of H₂S have always failed and, more important, the ocean surface waters are much too oxidizing to permit the existence of H₂S at concentrations sufficient to sustain an atmospheric equilibrium concentration of 2×10⁻¹⁰ by volume. Many elements form volatile methyl derivatives; Challenger⁵ reported that many living systems produced dimethyl sulphide (DMS), and that prominent among them were marine algae. Here we suggest that DMS is the natural sulphur compound which fills the role originally assigned to H₂S; that of transferring sulphur from the seas through the air to land surfaces.