EXPERIMENTAL-DETERMINATION OF THE DIFFUSION-COEFFICIENT OF DIMETHYLSULFIDE IN WATER

Estimates of the sea-to-air flux of dimethylsulfide (DMS) are based on sea surface concentration measurements and gas exchange calculations. Such calculations are dependent on the diffusivity of DMS (D(DMS)), which has never been experimentally determined. In this study the diffusivity of DMS in pure water was measured over a temperature range of 5-degrees-30-degrees-C. The measurements were made using a dynamic diffusion cell in which the diffusing gas flows over one side of an agar gel membrane and the inert gas flows over the other side. The diffusion coefficient can be estimated from either time dependent or steady state analysis of the data, with an estimated uncertainty of less than 8% (1sigma) in each measurement. A best fit to all the experimental results yields the equation D(DMS) (in cm2 sec - 1) = 0.020 exp (-18.1/RT), where R = 8.314 x 10(-3) kJ mole-1 K-1 and T is temperature in kelvin. The values of D(DMS) obtained in this study were 7-28% larger than estimates from the empirical formula of Hayduk and Laudie (1974) which has previously been used for DMS in gas exchange calculations. Applying these values to seawater results in an increase of less than 5% in the global oceanic flux of DMS.