Photochemical oxidation of dimethylsulphide to dimethylsulphoxide in estuarine and coastal waters

Abstract

h i g h l i g h t sWe observed 1:1 M conversion of DMS to DMSO in estuarine waters. This suggests that DMS photo-oxidation occurred via the CDOM sensitised 1 O 2 pathway. Photochemical rate constants decreased~10-fold from river to seawater. Rate constants were strongly correlated with CDOM absorption coefficients (a 350 ). a 350 -normalised rate constants increased~10-fold from river to seawater. a r t i c l e i n f o a b s t r a c tDimethylsulphide (DMS) photo-oxidation and dimethylsulphoxide (DMSO) photoproduction were estimated in 26 laboratory irradiations of coastal samples from NE England (Tyne estuary) and W Scotland (Loch Linnhe and River Nant at Taynuilt). Pseudo-first order rate constants of DMS photo-oxidation (0.038 h À1 to 0.345 h À1 ) and DMSO photo-production (0.017 h À1 to 0.283 h À1 ) varied by one order of magnitude and were lowest in the coastal North Sea. Estuarine samples (salinity S < 30) had a mean DMSO yield of 96 ± 16% (n ¼ 14), consistent with 1:1 M conversion via photosensitised oxidation by singlet oxygen. Photochemical rate constants were strongly correlated with coloured dissolved organic matter (CDOM) absorption coefficients at 350 nm, a 350 . Variations in a 350 explained 61% (R 2 ¼ 0.61, n ¼ 26) and 73% (R 2 ¼ 0.73, n ¼ 17) of the variability in DMS photo-oxidation and DMSO production, respectively. However, CDOM normalised photochemical rate constants increased strongly towards coastal waters exhibiting lowest CDOM absorbance, indicating water samples of marine character (S > 30) to be most reactive with respect to DMS photo-oxidation. Estimates of water column averaged DMS photo-oxidation rate constants, obtained by scaling to mean daily irradiance (July, NE England) and mid-UV underwater irradiance, were 0.012 d À1 , 0.019 d À1 , and 0.017 d À1 for upper estuary (S < 20), lower estuary (20 < S < 30) and coastal waters (S > 30), at the lower end of previous observations. Comparing our water column averaged DMS photo-oxidation rate constants with estimated DMS losses via air-sea gas exchange and previously reported biological consumption implies that DMS photochemical removal is of only minor importance in our study area.

Photochemical Production of Sulfate and Methanesulfonic Acid from Dissolved Organic Sulfur

“…1,9 Other authors showed the formation of dimethylsulfoxide (DMSO) from the photodegradation dimethylsulfide (DMS), a volatile organosulfur compound produced by marine phytoplankton. 1,10 To the authors' knowledge, no direct evidence of the photochemical formation of sulfate from DOS has been reported so far, even if it might be anticipated based on the photochemical behavior of DOC, DON and DOP.…”

Influence of dissolved organic matter on carbonyl sulfide and carbon disulfide formation from dimethyl sulfide during sunlight photolysis

“…One organic sulfur precursor of particular interest is DMS for two key reasons. First, DMS is one of the major marine sources of organic sulfur in the oceans (Andreae, 1990; Bates et al, 1992; Erickson et al, 1990) (~20–35 Tg (S) a −1 released globally; Kloster et al, 2006; Lana et al, 2011; Land et al, 2014; Simó & Dachs, 2002; Uher et al, 2017) and is present in such waters at pM to nM concentrations (Asher et al, 2017; Dacey et al, 1998; Levine et al, 2012; Steiner et al, 2012; Tortell, Long, et al, 2012; Tortell, Merzouk, et al, 2012). Second, DMS can degrade in oceans via indirect photolysis (Bouillon & Miller, 2005; Brugger et al, 1998; Mopper & Kieber, 2002; Toole et al, 2004), thus playing a critical role in the sulfur cycling of these bulk waters.…”

“…Second, DMS can degrade in oceans via indirect photolysis (Bouillon & Miller, 2005; Brugger et al, 1998; Mopper & Kieber, 2002; Toole et al, 2004), thus playing a critical role in the sulfur cycling of these bulk waters. Loss of DMS typically occurs through photooxidation by reacting with 1 O 2 , which is formed via chromophoric photosensitizers (see later discussions for more details), various reactive nitrogen species (RNS), formed via nitrate (NO 3 − ) photolysis, or other species (Uher et al, 2017). One primary product resulting from this photooxidation includes dimethyl sulfoxide (DMSO), although its yields from DMS vary widely depending on water type (Mopper & Kieber, 2002), where 14%, 25%, 39%, and 96 ± 16% conversion to DMSO has been observed in open‐ocean waters, shelf seas, polar waters, and estuarine waters, respectively (Hatton, 2002; Kleber et al, 1996; Toole et al, 2004; Uher et al, 2017).…”

Distribution Characteristics of Dimethylated Sulfur Compounds and Turnover of Dimethylsulfide in the Northern South China Sea During Summer

“…Photochemistry is another important factor affecting the turnover of DMS in surface seawater. DMS photooxidation has been intensively studied in various oceanic environments, particularly in estuarine and coastal waters (Uher et al, ). Under high irradiance conditions typical of summer, photooxidation can be the main removal mechanism for DMS in surface seawater (Galí & Simó, ).…”

“…It was demonstrated that dimethylsulfoxide (DMSO) is an important product of DMS removal (Hanlon et al, 1994;Kieber et al, 1996). Uher et al (2017) even reported that estuarine waters had a DMSO yield of up to 96% from DMS oxidation by singlet oxygen. DMS is oxidized to DMSO through different processes, such as biological consumption and photochemical oxidation (Kieber et al, 1996;Toole & Siegel, 2004).…”