[1] Estimates of the DMS sea-air transfer velocity (k DMS ) derived from direct flux measurements are poorly modeled by parameterizations based solely on wind speed and Schmidt number. DMS and CO 2 flux measurements show k CO 2 to be a stronger function of wind speed than k DMS . The NOAA/COARE gas flux parameterization, incorporating the bubble-mediated gas transfer theory of Woolf (1997), appears to do a better job reproducing the observations for both gases, illustrating the importance of trace gas solubility in sea-air exchange. The development of gas transfer parameterizations based on physical principles is still in its infancy, but recent advances in direct flux measurement methods provide an opportunity to evaluate the success of various modeling approaches for this critical geophysical process.

Oceanic dimethylsulfide (DMS) emissions to the atmosphere are potentially important to the Earth's radiative balance. Since these emissions are driven by the surface seawater concentration of DMS, it is important to understand the processes controlling the cycling of sulfur in surface seawater. During the third Pacific Sulfur/Stratus Investigation (PSI-3, April 1991) we measured the major sulfur reservoirs (total organic sulfur, total low molecular weight organic sulfur, ester sulfate, protein sulfur, dimethylsulfoniopropionate (DMSP), DMS, dimethylsulfoxide) and quantified many of the processes that cycle sulfur through the upper water column (sulfate assimilation, DMSP consumption, DMS production and consumption, air-sea exchange of DMS, loss of organic sulfur by particulate sinking). Under conditions of low plankton biomass (<0.4 gg/L chlorophyll a) and high nutrient concentrations (>8 tam nitrate), 250 km off the Washington State coast, DMSP and DMS were 22% and 0.9%, respectively, of the total particulate organic sulfur pool. DMS production from the enzymatic cleavage of DMSP accounted for 29% of the total sulfate assimilation. However, only 0.3% of sulfate-S assimilated was released to the atmosphere. From these data it is evident that air-sea exchange is currently only a minor sink in the seawater sulfur cycle and thus there is the potential for much higher DMS emissions under different climatic conditions. Introduction Oceanic dimethylsulfide (DMS) is currently thought to be the major natural source of sulfur to the atmosphere [Bates et al., 1992; Spiro et al., 1992]. Once in the atmosphere, DMS is oxidized to produce aerosol particles which affect the acidbase chemistry of the atmosphere [Charlson and Rodhe, 1982] and the radiative properties of marine stratus clouds [Charlson et al., 1987; Falkowski et al., 1992]. This latter effect is calculated to have a major impact on the Earth's radiative balance and hence its climate [Charlson et al., 1987]. The starting point in the marine atmospheric sulfur cycle is the air-sea exchange of DMS which is a function of the gas i NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington. transfer velocity and surface seawater DMS concentration. The gas transfer velocity is controlled primarily by surface turbulence, seawater temperature and gas diffusivity and can be modeled as a function of wind speed for various trace gases [Liss and Merlivat, 1986; Wanninkhof, 1992]. The different T. S. Bates, NOAA/Pacific Marine

[1] Updates for the Coupled Ocean-Atmosphere Response Experiment (COARE) physically based meteorological and gas transfer bulk flux algorithms are examined. The current versions are summarized and a generalization of the gas transfer codes to 79 gases is described. The current meteorological version COARE3.0 was compared with a collection of 26,700 covariance observations of drag and heat transfer coefficients (compiled from three independent research groups). The algorithm agreed on average to within 5% with observations for a wind speed range of 2 to 18 m s −1 . Covariance observations of CO 2 and dimethyl sulfide (DMS) gas transfer velocity k were normalized to Schmidt number 660 and compared to an ensemble of gas flux observations from six research groups and nine field programs. A reasonable fit of the mean k 660 versus U 10n values was obtained for both CO 2 and DMS with a new version of the COARE gas transfer algorithm (designated COAREG3.1) using friction velocity associated with viscous (tangential) stress, u * n , in the nonbubble term. In the wind speed range 5 to 16 m s , tracer-derived estimates of k 660 are 10% to 20% lower than the CO 2 covariance estimates presented here.

[1] We report the successful eddy-correlation (EC) measurement of dimethyl sulfide (DMS) fluxes using an atmospheric pressure ionization mass spectrometer (APIMS). Calculated hourly transfer velocities span the range of two widely used parameterizations. The results suggest that factors in addition to wind speed also control the flux, but some of the scatter in each wind speed interval is no doubt due to measurement uncertainties. We can at last measure the flux of a marine biogenic gas on a time scale of tens of minutes, with an accuracy of tens of percent. This enables investigations into the physical controls of air-sea gas transfer common to many important trace gas species. [2] The ocean is a net source (e.g., DMS, CO, CH 4 ) and sink (e.g., CO 2 , CFCs) of many radiatively and chemically important trace gases. Air/sea fluxes of these gases are commonly expressed as a product of the air/water concentration difference and a transfer velocity, k. Liss and Merlivat [1986] (hereinafter LM86), Wanninkhof [1992] (hereinafter W92), and others have parameterized k as a function of wind speed only. However, the scatter in tracerloss experiments reported by Nightingale et al. [2000] (hereinafter N2000) suggests other factors are at least as important as wind velocity in determining k. Prior air-sea exchange studies have been limited to long timescales (days to years) by the averaging requirements of budget-type flux methods. As a consequence, studies of this type do not observe the effects of factors that vary over shorter timescales of an hour or less. Thus, the potential impact of other physical factors such as bubble and wave spectra, wave slope, wind speed variability, and surface films have been unconstrained by observations.[3] The most direct technique for measuring gas fluxes is eddy-correlation [Fairall et al., 2000], since it utilizes the covariance of scalar concentrations (or mixing ratios) and vertical wind velocity. EC requires measurements at a sufficient rate (10 -20 Hz) to adequately capture all turbulence frequencies contributing to the flux. On moving platforms, apparent wind velocities must be corrected both for flow distortion by the platform and for contamination of measured wind velocity by platform motion. Lenschow et al. [1981] made airborne EC measurements of the marine ozone flux in 1981. Since then, several groups [Oost, 1998;McGillis et al., 2001] have demonstrated the ability to measure CO 2 fluxes from ships by EC, but the method is only applicable to those regions of the ocean surface with a combination of strong winds and relatively high air-sea concentration gradients (about a third of the worlds oceans). Until now there have been few demonstrations of other suitably fast analytical instruments.[4] Bandy et al. [2002] recently developed the APIMS isotopically labeled standard (APIMS-ILS) technique for DMS and demonstrated its utility for measuring DMS fluxes from aircraft [Stevens et al., 2003]. With this method ionization of DMS is only efficient when ambient air is dried and h...

[1] In the Southern Ocean Gas Exchange Experiment (SO GasEx), we measured an atmospheric dimethylsulfide (DMS) concentration of 118 ± 54 pptv (1s), a DMS sea-to-air flux of 2.9 ± 2.1 mmol m −2 d −1 by eddy covariance, and a seawater DMS concentration of 1.6 ± 0.7 nM. Dividing flux by the concurrent air-sea concentration difference yields the transfer velocity of DMS (k DMS ). The k DMS in the Southern Ocean was significantly lower than previous measurements in the equatorial east Pacific, Sargasso Sea, northeast Atlantic, and southeast Pacific. Normalizing k DMS for the temperature dependence in waterside diffusivity and solubility results in better agreement among various field studies and suggests that the low k DMS in the Southern Ocean is primarily due to colder temperatures. The higher solubility of DMS at a lower temperature results in greater airside control and less transfer of the gas by bubbles formed from breaking waves. The final normalized DMS transfer velocity is similar to k of less soluble gases such as carbon dioxide in low-to-moderate winds; in high winds, DMS transfer velocity is significantly lower because of the reduced bubble-mediated transfer.

In the troposphere, methanol (CH 3 OH) is present ubiquitously and second in abundance among organic gases after methane. In the surface ocean, methanol represents a supply of energy and carbon for marine microbes. Here we report direct measurements of airsea methanol transfer along a ∼10,000-km north-south transect of the Atlantic. The flux of methanol was consistently from the atmosphere to the ocean. Constrained by the aerodynamic limit and measured rate of air-sea sensible heat exchange, methanol transfer resembles a one-way depositional process, which suggests dissolved methanol concentrations near the water surface that are lower than what were measured at ∼5 m depth, for reasons currently unknown. We estimate the global oceanic uptake of methanol and examine the lifetimes of this compound in the lower atmosphere and upper ocean with respect to gas exchange. We also constrain the molecular diffusional resistance above the ocean surface-an important term for improving air-sea gas exchange models.trace gas cycling | air-sea exchange | eddy covariance | environmental chemistry | marine micrometeorology Background Atmospheric methanol affects tropospheric oxidative capacity and air pollution by participating in the cycling of ozone and the hydroxyl radical (OH). Methanol is primarily released to air from terrestrial plants (during growth and decay); other identified sources include industrial emissions, biomass and biofuel burning, and atmospheric production (1-5). Methanol reacts with OH in the troposphere with a photochemical lifetime of ∼10 d, leading to formaldehyde (6) and carbon monoxide (7), among other products. Observations suggest that methanol can be further removed from air via deposition to land (8) and to the sea surface (9, 10). In the upper ocean, methanol supports the growth of methylotrophic bacteria (11) and has recently been found to be consumed by SAR11 alphaprotoeobacteria, the most abundant marine heterotrophs (12). The turnover time of seawater methanol is thus quite short, on the order of a few days (13,14). However, significant oceanic concentrations of methanol have been detected in the range of 50∼400 nM (9, 15-17), leading to questions about its source.To understand the global cycling of methanol, it is imperative to quantify its transport between the ocean and the atmosphere. (17) recently calculated a net oceanic emission of 12 Tg·y −1 , but saw evidence for both oceanic production and uptake.

Emerging application areas such as air pollution in megacities, wind energy, urban security, and operation of unmanned aerial vehicles have intensified scientific and societal interest in mountain meteorology. To address scientific needs and help improve the prediction of mountain weather, the U.S. Department of Defense has funded a research effort—the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program—that draws the expertise of a multidisciplinary, multi-institutional, and multinational group of researchers. The program has four principal thrusts, encompassing modeling, experimental, technology, and parameterization components, directed at diagnosing model deficiencies and critical knowledge gaps, conducting experimental studies, and developing tools for model improvements. The access to the Granite Mountain Atmospheric Sciences Testbed of the U.S. Army Dugway Proving Ground, as well as to a suite of conventional and novel high-end airborne and surface measurement platforms, has provided an unprecedented opportunity to investigate phenomena of time scales from a few seconds to a few days, covering spatial extents of tens of kilometers down to millimeters. This article provides an overview of the MATERHORN and a glimpse at its initial findings. Orographic forcing creates a multitude of time-dependent submesoscale phenomena that contribute to the variability of mountain weather at mesoscale. The nexus of predictions by mesoscale model ensembles and observations are described, identifying opportunities for further improvements in mountain weather forecasting.

We report simultaneous, underway eddy covariance measurements of the vertical flux of isoprene, total monoterpenes, and dimethyl sulfide (DMS) over the Northern Atlantic Ocean during fall. Mean isoprene and monoterpene sea‐to‐air vertical fluxes were significantly lower than mean DMS fluxes. While rare, intense monoterpene sea‐to‐air fluxes were observed, coincident with elevated monoterpene mixing ratios. A statistically significant correlation between isoprene vertical flux and short wave radiation was not observed, suggesting that photochemical processes in the surface microlayer did not enhance isoprene emissions in this study region. Calculations of secondary organic aerosol production rates (PSOA) for mean isoprene and monoterpene emission rates sampled here indicate that PSOA is on average <0.1 μg m−3 d−1. Despite modest PSOA, low particle number concentrations permit a sizable role for condensational growth of monoterpene oxidation products in altering particle size distributions and the concentration of cloud condensation nuclei during episodic monoterpene emission events from the ocean.