Linearity of DMS transfer coefficient with both friction velocity and wind speed in the moderate wind speed range

In many air-sea gas exchange parameterizations, wind speed is the sole environmental controlling factor for exchange velocity, k. Here we examine also the role of friction velocity (u*) in the mid-range of wind speeds, using data from the 2007 Deep Ocean Gas Exchange Experiment. We measured dimethyl sulfide (DMS) fluxes and divided these by the interfacial concentration difference, ΔCDMS, to derive k. Computed ks are sensitive to spatial gradients in seawater DMS concentration (DMSw). A linear function with either u* or U10N (wind speed) explains 87% of the variance in k. Lower and higher winds will have different physics and curvature in transitions between ranges. This linearity demonstrates that a simple physical model of wind-driven stirring is sufficient for DMS in the wind speed range U10N = 4–12 m/s. A non-linear relationship to wind speed would be superfluous and obscures the physics.