Shipboard experiments were conducted in the equatorial Pacific Ocean to ascertain the relative importance of atmospheric ventilation, biological consumption, and photolysis in the removal of dimethylsulfide (DMS) from seawater. Comparisons were made at a series of sampling locations in a transect from 12øN 140øW to 12øS 135øW, as part of the International Global Atmospheric Chemistry project's Marine Aerosol and Gas Exchange cruise in February-March 1992. Turnover rate constants for DMS were used to compare the different removal pathways over three depth intervals (0-1 m, 0-20 m, and 0-60 m). In the surface mixed layer (0-60 m) the DMS turnover rate constants ranged from 0.02 to 0.19 day -• for atmospheric ventilation, 0.04 to 0.66 day -• for biological consumption, and 0.05 to 0.15 day -• for photolysis. When all three processes are considered, the corresponding turnover time for DMS ranges from 1 to 4 days, with photolysis accounting for 7%-40% of the total turnover of DMS. Laboratory irradiations were conducted with stored seawater samples to study the kinetics and wavelength dependence of DMS photolysis. Salient results were (1) the photolysis of DMS followed pseudo first-order kinetics, (2) dimethylsulfoxide was a minor (14%) product of DMS photolysis, and (3) the photolysis of DMS in seawater under natural light conditions occurred primarily at wavelengths between 380 and 460 nm. On the basis of these results, we predict that the photolysis of DMS will occur at appreciable depths in the photic zone in oligotrophic marine environments (-60 m). An important finding of this study is that atmospheric loss, biological consumption, and photolysis are all important removal pathways for DMS in the photic zone of the equatorial Pacific Ocean. The relative importance of each pathway is a function of the depth interval considered, sampling location, and meteorological conditions. precursor of aerosols and cloud condensation nuclei and thus affects the Earth's radiation balance and climate [Bonsang et al., 1980; Bigg et al., 1984; Chadson et al., 1987; Prospero et al., 1991; Ayers and Gras, 1991; Berresheim et al., 1993]. Oceanic DMS emissions are partly a function of surface concentrations of DMS in seawater, which, in turn, are regulated by imbalances in the rates of biological, physical, and chemical sources and removal processes for DMS in the water column. Currently, we have a poor understanding of the dynamics of these processes in seawater. The primary source of DMS in seawater is through the enzy-Paper number 95JC03624. 0148-0227/96/95 JC-03624505.00 matic decomposition of dimethylsulfoniopropionate (DMSP), which is derived from algae in the photic zone [Burgermeister et al., 1990, and references therein]; abiotic decomposition of DMSP is negligible [Dacey and Blough, 1987]. Culture studies support the supposition of a biological source of DMS in seawater [Vairavamurthy et al., 1985; Dickson and Kirst, 1986, 1987a, b; Keller et al., 1989], but often DMS concentrations are poorly correlated with algal parameters...

The chemical and physical characteristics of the particles of the near-surface waters of polluted, hypereutrophic, Onondaga Lake, NY, were observed by individual particle analysis techniques for the spring to fall interval of 1987. Strong temporal variations were documented for the projected particle area per unit volume (PAV), and the relative contribution that six chemical groupings of particles made to the overall assemblage of particles. These dynamics were regulated largely by ( 1) the composition and level of phytoplankton growth, (2) tributary loading of particles, particularly after runoff events, and (3) the precipitation of calcium carbonate. Approximately 85% of the PAV was associated with in-lake processes and 15% was derived from tributary transport. Approximately 25% of the internally produced PAV was related to calcium carbonate precipitation; the remainder was associated with biological production. A once in 7-year runoff event caused a 5-fold increase in the concentration of suspended particles. Much of the increase was due to calcium carbonate precipitation that coated various nuclei particles. 20-30 variables, depending upon the analytical hardware/software configuration. Rapid computer access to this vast array of raw data makes the information Contribution No. 85 of the Upstate Freshwater Institute; Contribution No.

The degradation of the optical aesthetics in the mouth of Onondaga Creek, New York, that occurs during high flow periods as a result of the influx of large quantities of suspended solids, is documented. Features of the degradation include very low clarity (Secchi disc minimum of approximately 0.1 m) and a brown ‘muddy’ appearance. The reduced clarity is mostly a result of increased light scattering. Loading and concentration profiles obtained for an approximately 35 km interval above the creek mouth over a wide range of flow indicates most of the suspended solids received during runoff events is resuspended stream sediment and eroded bank material. Application of microscopy‐based individual particle analysis techniques indicates that the origin of most of these deposits and much of the suspended solids during runoff events is point source inputs, termed ‘mud boils,’ located approximately 32 km upstream of the creek mouth.

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