Assessment of dimethylsulfide sea-air exchange rate

International audienceThe concentrations of dimethylsulfide (DMS) in surface seawater and in the atmosphere at three heights above sea level (1, 6, and 20 m) were measured in June 1992 in the Atlantic Ocean south of the Azores Islands (34-37øN, 23-26øW) at stations of the "Surface of Oceans: Fluxes and Interactions With the Atmosphere" cruise (SOFIA). Simultaneous meteorological and micrometeorological measurements were also made. Sea surface temperature and wind speed were used to estimate sea-air exchange coefficients, according to two parameterizafions of the piston velocity K w reported by Liss and Merlivat [1986] and by Smethie et al. [1985]. The Liss and Merlivat's [1986] parameterizafion leads to values of K w smaller by 40% on average than Smethie et al. 's [1985] parameterizafion, the difference depending on wind speed. K w values were used to calculate the DMS flux from an air-sea exchange model, with DMS concentrations measured in and above the seawater. Friction velocity, air temperature and heat flux were used to compute file eddy diffusion coefficient K z as a function of altitude. In file cases where the DMS concentration decreased between 1 and 6 m, DMS flux in the 1-6 m layer was calculated from K z and DMS atmospheric gradients according to the gradient-transfer approach. DMS flux values obtained from the sea-air exchange model and from the gradient-transfer approach appear to be significantly correlated (R=0.7, n= 15). The slopes of regressions suggest that the Liss and Merlivat's [1986] and Smethie et al. 's [1985] parmneterizations of K w both lead to DMS sea-air fluxes lower than that calculated by the gradient-transfer approach by a factor of 1.6 to 1.9 + 0.5 and 1.1 to 1.4 + 0.4, respectively