Abstract
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 (kDMS) 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−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 linear wind speed-dependence over the wind speed range of 1 to 9 m s−1. This relationship is compared with previously 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.
Highlights
The physics, chemistry, and biology of the air/sea interface are not well understood
The water temperatures in the gyre region were similar to the upwelling region, but chlorophyll levels were much lower
Elevated wind speeds were encountered on DOY 21 to 22 and 24, associated with the intersection of the cruise track with westerly low pressure systems
Summary
The physics, chemistry, and biology of the air/sea interface are not well understood. Estimates of air/sea gas transfer rates are usually based on simple parameterizations. Air/sea fluxes (F ) of trace gases are usually described as the product of a gas transfer coefficient (k) and a difference in gas partial pressure between the surface ocean and overlying atmosphere ( C), F =k C (1). The gas transfer coefficient can be estimated from micrometeorological flux measurements, such as eddy covariance, profile, or relaxed eddy accumulation, in conjunction with air/sea concentration measurements. It is clear that many factors which influence turbulence near the air/sea interface affect rates of gas transfer. These include buoyancy effects, surface tension (microlayer effects), whitecap formation and bubble breaking, and wind/wave interactions (Donelan and Wanninkhof, 2002 and references therein). Gas exchange models of increasing sophistication have been developed, based on similarity theory and energy balance considerations, but these are highly parameterized, and based on limited observational data (Fairall et al, 1996a, b, 2000; Hare et al, 2004; Soloviev, 2007; Soloviev and Schlussel, 1994, 1996)
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