Atmospheric Chemistry and Physics (Jan 2009)
Open ocean DMS air/sea fluxes over the eastern South Pacific Ocean
Abstract
Air/sea fluxes of dimethylsulfide (DMS) were measured by eddy correlation over the Eastern South Pacific Ocean during January 2006. The cruise track extended from Manzanillo, Mexico, along 110° W, to Punta Arenas, Chile. Bulk air and surface ocean DMS levels were also measured and gas transfer coefficients (<i>k</i><sub>DMS</sub>) were computed. Air and seawater DMS measurements were made using chemical ionization mass spectrometry (API-CIMS) and a gas/liquid membrane equilibrator. Mean surface seawater DMS concentrations were 3.8±2.2 nM and atmospheric mixing ratios were 340±370 ppt. The air/sea flux of DMS was uniformly out of the ocean, with an average value of 12±15 μmol m<sup>−2</sup> d<sup>−1</sup>. Sea surface concentration and flux were highest around 15° S, in a region influenced by shelf waters and lowest around 25° S, in low chlorophyll gyre waters. The DMS gas transfer coefficient exhibited a linear wind speed-dependence over the wind speed range of 1 to 9 m s<sup>−1</sup>. This relationship is compared with previously measured estimates of <i>k</i> from DMS, CO<sub>2</sub>, and dual tracer data from the Atlantic and Pacific Ocean, and with the NOAA/COARE gas transfer model. The model generated slope of <i>k</i> vs. wind speed is at the low end of those observed in previous DMS field studies.
