The role of biogenic dimethylsulfide from the ocean surface as a source of atmospheric sulfur has so far been largely based on the results of mass balance calculations and on a small number of determinations of DMS in seawater. On a cruise of the R/V Meteor across the Atlantic from Hamburg, F.R.G., to Montevideo, Uruguay, we have sampled the surface ocean at short intervals and analyzed over 300 seawater samples aboard ship immediately after collection. Simultaneously, the atmospheric concentration of DMS has been measured at 13 m above the ocean surface. Biological and chemical oceanographic data have been collected during the cruise to aid in the interpretation of the findings on DMS. A number of vertical profiles to the bottom of the ocean were analyzed for DMS and other parameters. The concentrations of DMS in the surface ocean ranged from 17.7 to 743 ng S(DMS)/1, with a mean of 91 ng S(DMS)/1 (n = 231) for the area traversed. This mean is significantly higher than previous work had suggested. The highest concentrations of DMS were found in productive regions on the continental shelves, in marginal seas and in some estuaries. The vertical distribution of DMS is closely related to the distribution of primary productivity, as measured by chlorophyll and nutrient concentrations. Low concentrations (≤10 ng S(DMS)/1) were found in the deep ocean. From these distributions and from our work on pure cultures of marine algae we conclude that marine primary producers are the dominant source of DMS to seawater and consequently to the atmosphere. The concentrations of DMS in the atmosphere ranged from 2 to 44 ng S(DMS)/m3. The mean concentration of 6.1 ng S(DMS)/m3 is significantly lower than postulated concentrations of 40–200 ng S(DMS)/m3 for marine background atmosphere, thus questioning the rates and mechanisms given for reactions of DMS in this environment. Model calculations for the transfer of DMS across the air‐sea interface, using the data on DMS in seawater and the concentration of DMS in the atmosphere, suggest a global flux of 34–56×1012 g of sulfur in the form of DMS per year from the oceans to the atmosphere.

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An outline is presented here of the Po Valley Fog Experiment 1989, carried out within the EUROTRAC‐GCE project. This experiment is a joint effort by several European research groups from 5 countries. The physical and chemical behaviour of the fog multiphase system was studied experimentally following the temporal evolution of the relevant chemical species in the different phases (gas, droplet, interstitial aerosol) and the evolution of micrometeorological and microphysical conditions, from the pre‐fog situation through the whole fog evolution, to the post‐fog period. Some general results, useful for describing the general features of the fog system, are presented here, while specific scientific questions on the different processes taking place within the system itself will be addressed in other companion papers of this same issue.

During a cruise over the Atlantic from 40øS to 50øN in March-April 1987 the concentrations of dimethylsulfide (DMS) in the ocean and atmosphere were measured as well as the distribution of its precursor, dimethylsulfoniopropionate (DMSP), and of several biological parameters such as chlorophyll, phytoplankton species, and adenosine-5-triphosphate (ATP) in the surface water. The DMS concentration varied in the range 0.2-2 nmol DMS L -1 (surface water) and 0.05-3 nmol DMS m -3 (atmosphere) in the region of the remote tropical and subtropical Atlantic and increased to 2-10 nmol DMS L -1 (surface water) and 1-8 nmol DMS m -3 (atmosphere) north of 40øN and in the English Channel. Based on these results the mean flux of DMS from the Atlantic to the atmosphere is estimated to be 4-4.65 nmol DMS m -2 min -1 . A moderate diurnal variation of atmospheric DMS was found with a minimum during daytime. The DMS concentration in seawater correlated well with the concentration of DMSP and showed a similar trend to ATP, chlorophyll, and some phytoplankton species. Paper number 89JD03776. 0148-0227/90/89 JD-03776505.00 evidence for the role of DMSP as the biogenic precursor of DMS, the major volatile sulfur compound in seawater. EXPERIMENTAL METHODS Sampling of SeawaterSurface water samples were taken 3 times a day (08.30, 12.30, and 16.30 hours) with a 10-L bucket in front of or in the bow wave of the ship. They were used for the analysis of chlorophyll a, salinity, DMSP, and ATP as well as for phytoplankton counting. The seawater samples analyzed for DMS were obtained by means of the ship's pumping system from a depth of 10 m below the surface at 6-hour intervals (0100, 0700, 1300, and 1900).

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