Atmospheric Chemistry and Physics 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 Pa-cific 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 (kDMS) were com-puted. Air and seawater DMS measurements were made us-ing chemical ionization mass spectrometry (API-CIMS) and a gas/liquid membrane equilibrator. Mean surface seawa-ter 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±15µmol m−2 d−1. 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 lin-ear wind speed-dependence over the wind speed range of 1 to 9 m s−1. This relationship is compared with previ-ously measured estimates of k from DMS, CO2, and dual tracer data from the Atlantic and Pacific Ocean, and with the NOAA/COARE gas transfer model. The model generated slope of k vs. wind speed is at the low end of those observed in previous DMS field studies.