Archer, SD; Stelfox-Widdicombe, CE; Malin, G; Burkill, PH

Journal of Plankton Research [J. Plankton Res.]. Vol. 25, no. 2, pp. 235-242. Feb 2003.

Microzooplankton herbivory is considered to be a key process by which dimethylsulphoniopropionate (DMSP) in phytoplankton is transformed to climatically active dimethyl sulphide (DMS). However, there is little firm evidence to show that this occurs in natural waters. We used direct measurements of microzooplankton grazing rates and net DMS production in the southern North Sea to examine the impact of herbivory on DMS production. Estimates of the particulate DMSP ingested by microzooplankton in the form of Phaeocystis sp. were found to account for the DMS production rates observed.

Wolfe, GV*; Strom, SL; Holmes, JL; Radzio, T; Olson, MB

Journal of Phycology [J. Phycol.]. Vol. 38, no. 5, pp. 948-960. Oct 2002.

Several bloom-forming marine algae produce concentrated intracellular dimethylsulfoniopropionate (DMSP) and display high DMSP cleavage activity in vitro and during lysis after grazing or viral attack. Here we show evidence for cleavage of DMSP in response to environmental cues among different strains of the haptophyte Emiliania huxleyi (Lohmann) Hay et Mohler and the dinoflagellate Alexandrium spp. (Halim). Sparging or shaking live cells of either taxon increased dimethyl sulfide (DMS), especially in dinoflagellates, known to be very sensitive to shear stresses. Additions of polyamines, known triggers of exocytosis in some protists, also stimulated DMSP cleavage in a dose-responsive manner. We observed DMS production by some algae after shifts in light regime. When most exponential-phase E. huxleyi were transferred to continuous darkness, cells decreased in volume and DMSP content within 24 h; DMSP content per unit cell volume remained relatively steady. DMS accumulated as long as cells remained in the dark, but on returning to a light:dark cycle DMS accumulation ceased within 24 h. However, E. huxleyi strain CCMP 373, containing highly active in vitro DMSP lyase, produced only transient accumulations of DMS in the dark. This was apparently due to production and concomitant oxidation or uptake of DMS, because cells of this strain rapidly removed DMS added to cultures. Three strains of the dinoflagellate Alexandrium tamarense containing high in vitro DMSP lyase activity showed no DMS production in the dark, and all appeared to remove additions of DMS. Alexandrium tamarense strain CCMP 1771 also removed dimethyl disulfide, an inhibitor of bacterial DMS consumption. These data suggest that physical or chemical cues can trigger algal DMSP cleavage, but DMS production may be masked by subsequent oxidation and/or uptake.

Hay, ME; Kubanek, J

Journal of Chemical Ecology [J. Chem. Ecol.]. Vol. 28, no. 10, pp. 2001-2016. Oct 2002.

Aquatic organisms produce compounds that deter consumers, alter prey behavior, suppress or kill target and nontarget species, and dramatically affect food-web structure, community composition, and the rates and pathways of biogeochemical cycles. Toxins from marine and freshwater phytoplankton create health hazards for both aquatic and terrestrial species and can significantly affect human activities and the economic vitality of local communities. A reasonable case can be made that phytoplankton metabolites such as dimethyl sulfide (DMS) link interaction webs that span hundreds to thousands of kilometers and connect production from oceanic phytoplankton to desert cacti and coyotes via zooplankton, fishes, and sea birds. The possible role of DMS in global heat budgets expands this effect even further. The ecosystem-wide and potentially global consequences of aquatic chemical cues is an underappreciated topic that warrants additional attention.

Sunda, W; Kieber, DJ; Kiene, RP; Huntsman, S

Nature [Nature]. Vol. 418, no. 6895, pp. 317-320. 18 Jul 2002.

The algal osmolyte dimethylsulphoniopropionate (DMSP) and its enzymatic cleavage product dimethylsulphide (DMS) contribute significantly to the global sulphur cycle, yet their physiological functions are uncertain. Here we report results that, together with those in the literature, show that DMSP and its breakdown products (DMS, acrylate, dimethylsulphoxide, and methane sulphinic acid) readily scavenge hydroxyl radicals and other reactive oxygen species, and thus may serve as an antioxidant system, regulated in part by enzymatic cleavage of DMSP. In support of this hypothesis, we found that oxidative stressors, solar ultraviolet radiation, CO sub(2) limitation, Fe limitation, high Cu super(2+) and H sub(2)O sub(2) substantially increased cellular DMSP and/or its lysis to DMS in marine algal cultures. Our results indicate direct links between such stressors and the dynamics of DMSP and DMS in marine phytoplankton, which probably influence the production of DMS and its release to the atmosphere. As oxidation of DMS to sulphuric acid in the atmosphere provides a major source of sulphate aerosols and cloud condensation nuclei, oxidative stressors--including solar radiation and Fe limitation--may be involved in complex ocean--atmosphere feedback loops that influence global climate and hydrological cycles.

Kouvarakis, G; Bardouki, H

Tellus. Series B: Chemical and Physical Meteorology [Tellus (B Chem. Phys. Meteorol.)]. Vol. 54B, no. 3, pp. 201-212. Jul 2002.

To access the relative contribution of anthropogenic and biogenic sulfur sources to the sulfur budget in the Eastern Mediterranean, an area characterized by very high nss- [formula] levels, measurements of both wet and dry deposition of sulfur were performed at a remote area on the island of Crete (Finokalia) during a 3-yr period (1996-1999). The estimation of dry deposition is based on both gaseous sulfur dioxide (SO sub(2)) and particulate phase non-sea-salt sulfate (nss- [formula]) and methane sulfonate (MSA) measurements. During the dry period, deposition of SO sub(2) from long-range transport is the main component of anthropogenic sulfur deposition in the area. The results of the wet and dry deposition obtained at Finokalia have been compared with DMS emission from seawater obtained during two yearly surveys (1997-1998) in the Cretan Sea. Our results indicate that the contribution from biogenic sources to the sulfur budget in the Eastern Mediterranean, although negligible during winter, can account for up to 26% during summer.

Aumont, O; Belviso, S; Monfray, P

Journal of Geophysical Research. C. Oceans [J. Geophys. Res. (C Oceans)]. Vol. 107, no. C4, p. 4. 15 Apr 2002.

A global model for surface dimethylsulfide (DMS) and particulate dimethylsulfoniopropionate (DMSP) (pDMS) distributions is presented. The main goals of this work were to be able to predict the regional distribution of the air-sea fluxes of DMS and to predict eventually their future evolution with climate change. Diagnostic relationships have been established from data sets obtained during the ALBATROSS and EUMELI cruises carried out in the Atlantic Ocean. These equations nonlinearly relate DMS and pDMSP concentrations to chlorophyll concentrations and to the trophic status of surface waters. This model has been embedded in the global ocean carbon cycle model Institut Pierre et Simon Laplace-Ocean Carbon Cycle Model version 2 (ISPL-OCCM2), a simple plankton model coupled to a global three-dimensional ocean general circulation model. Predicted global distributions and seasonal variations of surface chlorophyll are in good agreement with the observations, except in the equatorial Pacific Ocean and, to a lesser extent, in the Southern Ocean. In these regions, simulated surface chlorophyll concentrations are strongly overestimated, most likely because limitations of the biological production by nutrients like iron or silicate are not considered. The model predicts surface DMS and pDMSP concentrations, which compare reasonably well with the observations. However, in the high latitudes, seasonal variations are underestimated, especially in the Ross and Weddell Seas where observed very elevated concentrations of DMS due to spring and summer blooms of Phaeocystis cannot be reproduced by the model. The global annual flux of DMS predicted by 1PSL-OCCM2 ranges from 17 to 26.7 Tg S yr super(-1) depending on the formulation for gas exchange coefficient. About one third of this flux is located in the subtropical/subpolar frontal zone of the Southern Ocean, which plays a critical role in the sulfur cycle. Furthermore, model results suggest that the Southern Ocean, south of the Polar Front, could be a rather modest source of DMS for the atmosphere.

Scarratt, MG; Levasseur, M; Michaud, S; Cantin, G; Gosselin, M; de Mora, SJ

Marine ecology progress series [Mar. Ecol. Prog. Ser.]. Vol. 244, pp. 49-61. 2002.

Distributions of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) were surveyed in surface waters of the NW Atlantic in May 1998, a few weeks after the spring bloom. A triangular transect extending from Nova Scotia to Bermuda and northeast toward Newfoundland encompassed 4 major oceanic biogeochemical provinces: Northwest Atlantic Continental Shelves (NWCS), Gulf Stream (GFST), North Atlantic Subtropical Gyre (NAST) and the North Atlantic Drift (NADR). Surface concentrations of DMS and DMSP were highest in the NADR, with peaks up to 8.9 nM DMS, 44.1 nM dissolved DMSP (DMSP sub(d)) and 240 nM particulate DMSP (DMSP sub(p)). The phytoplankton assemblage throughout the study area was dominated by dinoflagellates and prymnesiophytes. Statistically significant correlations were observed between the abundance of dinoflagellates and prymnesiophytes and the concentrations of DMS and DMSP along the transect. Size-fractionation of DMSP sub(p) revealed the 2 to 11 mu m fraction to be the most important contributor to total DMSP (mean 72%, range 27% to 91% of total). In the region of the highest DMS(P) concentrations, the phytoplankton assemblage was dominated by prymnesiophytes and dinoflagellates, with Chrysochromulina and Gyrodinium flagellare being the most abundant. The abundance of these taxa showed a marked correlation with total DMSP sub(p) and with the 2 to 11 mu m size fraction of DMSP in which these cells are found. This plankton assemblage was observed both early and late in the transect, which may indicate that it is a persistent feature along the northern side of the Gulf Stream at this time of year. Sea-air flux of DMS was calculated based on 2 different models. The results showed peaks in flux corresponding to the peaks in DMS concentration in surface water. Pooling and averaging the values for each biogeochemical province reveals DMS concentrations lower than the average values of an existing global DMS database for the same regions and times.

Simo, R; Archer, SD; Pedros-Alio, C; Gilpin, L; Stelfox-Widdicombe, CE

Limnology and Oceanography [Limnol. Oceanogr.]. Vol. 47, no. 1, pp. 53-61. Jan 2002.

Oceanic dimethylsulfide (DMS), the main natural source of sulfur to the global atmosphere, is suggested to play a key role in the interaction between marine biota and climate. Its biochemical precursor is dimethylsulfoniopropionate (DMSP), a globally distributed, intracellular constituent in marine phytoplankton. During a multidisciplinary Lagrangian experiment in the subpolar North Atlantic, we determined the fluxes of DMSP and DMS through phytoplankton, microzooplankton, and bacterioplankton and compared them with concurrent carbon and sulfur fluxes through primary and secondary productions, grazing, and release and use of dissolved organic matter. We found that DMSP and derivatives contributed most (48-100%) of the sulfur fluxes and 5-15% of the carbon fluxes. Our findings highlight DMSP as a prominent player in pelagic biogeochemical pumps, especially as a major carrier in organic sulfur cycling. Also, our results illustrate the key role played by microzooplankton and heterotrophic bacteria (hence the microbial food web) in controlling the amount of phytoplanktonic DMSP that ultimately vents to the atmosphere in the form of DMS.

Kumar, MD; Shenoy, DM; Sarma, VVSS; George, MD; Dandekar, M

Geophysical Research Letters [Geophys. Res. Lett.]. Vol. 29, no. 2, pp. 8-1. Jan 2002.

Dimethylsulfide (DMS) results from the decomposition of dimethylsulfoniopropionate (DMSP), a biogenic product, in seawater. Diffusive transfer of DMS from sea-to-air is known to be the most important source of natural non- seasalt sulfur (NSS) in the atmosphere. Here, we report on the wider occurrence of DMSP in marine aerosols for the first time. We found DMSP (to about 4.7 pmol m super(-3)) and DMS (up to 5.8 pmol m super(-3)) in marine aerosols, over the Indian Ocean, wherein DMSP abundance appears to be a function of its concentration in surface seawater and wind speeds. An experiment on board revealed rapid loss (90%) of loaded DMSP from filters exposed to marine atmosphere. Hence, a photochemical or other mode of formation of NSS gases from DMSP in aerosols or in surface microlayer, not considered hitherto, can directly contribute to sulfur efflux. Although our computations suggest the DMSP fluxes from these sources to be much smaller (3.4 x 10 super(10) g S y super(-1)) compared to DMS diffusive flux (16-25 x 10 super(12) g S y super(-1)) the former could be significant in rough weather conditions similar to trends in water export.

Steinke, M; Malin, G; Archer, SD; Burkill, PH; Liss, PS

Aquatic Microbial Ecology [Aquat. Microb. Ecol.]. Vol. 26, no. 3, pp. 259-270. 18 Jan 2002.

During an experiment in the North Atlantic in June 1998, water samples were collected approximately 400 km south of Iceland inside and outside of a bloom of the coccolithophorid Emiliania huxleyi. In vitro dimethylsulphoniopropionate (DMSP) lyase activity (DLA) was quantified using gas chromatography and found to vary from 0.1 to 142.3 nM dimethyl sulphide (DMS) h super(-1). Inside the bloom area the majority of DLA (>74%) occurred in particles >10 mu m, indicating that E. huxleyi (5 to 7 mu m diameter) made only a minor contribution to total DLA. In surface waters, phototrophic dinoflagellates (>10 mu m) made up a high proportion of the total phytoplankton biomass ( approximately 27%) towards the end of the coccolithophorid bloom and may have been the source of most of the DLA. This was also indicated by a significant correlation (p < 0.02) between DLA and the concentration of peridinin, a pigment used as a chemotaxonomic marker for dinophytes. The data presented here are the first field measurements of DLA in a coccolithophorid bloom and suggest that even a relatively low concentration of photosynthetic dinoflagellates larger than 10 mu m (during our study 18 to 105 cells ml super(-1)) may contribute significantly to DMS production. Although dinoflagellates are recognised as an important source of particulate DMSP, recognition of their significance for DMS production in the field has previously been limited to a few observations in highly concentrated coastal and shelf blooms. Very little information exists on DLA in dinophytes and further investigations are warranted in order to improve our understanding of the biogeochemical and ecophysiological significance of DMSP lyases in this group of phytoplankton.

Archer, SD; Smith, GC; Nightingale, PD; Widdicombe, CE; Tarran, GA; Rees, AP; Burkill, PH

Deep-Sea Research (Part II, Topical Studies in Oceanography) [Deep-Sea Res. (II Top. Stud. Oceanogr.)]. Vol. 49, no. 15, pp. 2979-2999. 2002.

One of the key steps towards predicting dimethyl sulphide (DMS) emissions to the atmosphere is to understand the production and fate of its precursor, dimethylsulphoniopropionate (DMSP). This study used the framework of a SF sub(6)-Lagrangian experiment lasting 6 days, to examine the production and turnover of particulate DMSP (DMSPp) within a developing phytoplankton bloom characterised by abundant Emiliania huxleyi. Detailed information on the composition of the phytoplankton community and literature-derived estimates of cell DMSP content were used to partition DMSPp between 6 taxonomic groups. E. huxleyi was estimated to contribute an average of only 16% and 9% of the DMSPp standing stocks in surface and subsurface layers of the water column, respectively. Other phototrophs, including non-lithed nanoflagellates and dinoflagellates, in particular Prorocentrum minimum, made up a substantial proportion of the DMSPp, especially in the subsurface layer. The Lagrangian approach allowed a direct estimate of the net production of DMSPp, chlorophyll a and the 6 phytoplankton taxonomic groups in the surface layer. The net specific accumulation rate of DMSPp was 0.129 day super(-1), equivalent to a net production of DMSPp over the 6 days of 37.3 nM averaged through the surface-layer depth. The net phytoplankton growth rate in terms of chlorophyll a was similar, at 0.108 day super(-1). However, not all the phytoplankton showed a net growth during the 6 days, indicating that only certain taxa were responsible for the increases in DMSP and chlorophyll a. A significant relationship between super(14)C primary production measurements and the potential production of DMSPp derived from dilution experiments was used to estimate an integrated `gross' production and loss rate of DMSPp for the surface mixed layer. High DMSPp production rates were closely matched by high DMSPp loss rates. Ingestion by microzooplankton appeared to be the major cause of DMSPp loss, accounting for an average of 91% of the DMSPp disappearance. A large proportion of the ingested DMSPp was thought to be released as dissolved DMSP rather than DMS. An estimate of the total DMS flux to the atmosphere was equivalent to only 1.3% of the `gross' DMSPp production in the surface layer during the developing phase of the phytoplankton bloom covered by this experiment. Other processes known to cause DMSP release from phytoplankton, such as viral lysis and senescence, may have become more important if the phytoplankton community had reached higher concentrations and/or encountered more growth-limiting conditions. However, in the present experiment horizontal and vertical mixing appeared to play a major role in determining the fate of the SF sub(6)-labelled water, and hence the progression of the phytoplankton community.

Steinke, M; Malin, G; Gibb, SW; Burkill, PH

Deep-Sea Research (Part II, Topical Studies in Oceanography) [Deep-Sea Res. (II Top. Stud. Oceanogr.)]. Vol. 49, no. 15, pp. 3001-3016. 2002.

The climatically relevant trace gas dimethyl sulphide (DMS) is produced within the microbial food-web from the algal metabolite dimethylsulphoniopropionate (DMSP). The presence of DMSP lyase isozymes is necessary for this process. Measurements of in vitro DMSP lyase activity (DLA) were conducted in the northern North Sea in June 1999 in order to investigate the vertical and temporal variability of activity in a Lagrangian time-series process study. DLA ranged from 4 to 207 nM h super(-1), with maximum values close to the surface and between 30 and 50 m depth. DLA increased towards the surface relative to chlorophyll a, as did the non-photosynthetic but photoprotective pigment diadinoxanthin, DMS and dissolved dimethylsulphoxide, a likely oxidation product of DMS. These observations support the hypothesis that DMSP lyases can be affected by irradiance levels, and that DMSP and its cleavage products could be involved in scavenging oxygen radicals; hence, they may function as antioxidants in marine algae. Linear regression analysis of our field data showed reduced biomass of some oligotrich and non-oligotrich ciliates at higher levels of DLA, a finding that could be supportive of a role for phytoplankton DMSP lyases in chemical defence.

Zubkov, MV; Fuchs, BM; Archer, SD; Kiene, RP; Amann, R; Burkill, PH

Deep-Sea Research (Part II, Topical Studies in Oceanography) [Deep-Sea Res. (II Top. Stud. Oceanogr.)]. Vol. 49, no. 15, pp. 3017-3038. 2002.

Bacterioplankton-driven turnover of the algal osmolyte, dimethylsulphoniopropionate (DMSP), and its degradation product, dimethylsulphide (DMS) the major natural source of atmospheric sulphur, were studied during a Lagrangian SF sub(6)-tracer experiment in the North Sea (60 degree N, 3 degree E). The water mass sampled within the euphotic zone was characterised by a surface mixed layer (from 0 m to 13-30 m) and a subsurface layer (from 13-30 m to 45-58 m) separated by a 2 degree C thermocline spanning 2 m. The fluxes of dissolved DMSP (DMSPd) and DMS were determined using radioactive tracer techniques. Rates of the simultaneous incorporation of super(14)C-leucine and super(3)H-thymidine were measured to estimate bacterioplankton production. Flow cytometry was employed to discriminate subpopulations and to determine the numbers and biomass of bacterioplankton by staining for nucleic acids and proteins. Bacterioplankton subpopulations were separated by flow cytometric sorting and their composition determined using 16S ribosomal gene cloning/sequencing and fluorescence in situ hybridisation with designed group-specific oligonucleotide probes. A subpopulation, dominated by bacteria related to Roseobacter-( alpha -proteobacteria), constituted 26-33% of total bacterioplankton numbers and 45-48% of biomass in both surface and subsurface layers. The other abundant prokaryotes were a group within the SAR86 cluster of gamma -proteobacteria and bacteria from the Cytophaga-Flavobacterium--cluster. Bacterial consumption of DMSPd was greater in the subsurface layer (41 nM d super(-1)) than in the surface layer (20 nM d super(-1)). Bacterioplankton tightly controlled the DMSPd pool, particularly in the subsurface layer, with a turnover time of 2 h, whereas the turnover time of DMSPd in the surface layer was 10 h. Consumed DMSP satisfied the majority of sulphur demands of bacterioplankton, even though bacterioplankton assimilated only about 2.5% and 6.0% of consumed DMSPd sulphur in the surface and subsurface layers, respectively. Bacterioplankton turnover of DMS was also faster in the subsurface layer (12 h) compared to the surface layer (24 h). However, absolute DMS consumption rates were higher in the surface layer, due to higher DMS concentrations in this layer. The majority of DMS was metabolised into dissolved non-volatile products, and bacteria could satisfy only 1-3% of their sulphur demands from DMS. Thus, structurally similar bacterioplankton communities exerted strong control over DMSPd and DMS concentrations both in the subsurface layer and surface mixed layer.

Hatton, AD

Deep-Sea Research (Part II, Topical Studies in Oceanography) [Deep-Sea Res. (II Top. Stud. Oceanogr.)]. Vol. 49, no. 15, pp. 3039-3052. 2002.

Shipboard experiments were conducted in the northern North Sea to assess the rate of removal of dimethylsulphide (DMS) and the rate of production of DMSO due to both UVB and UVA/visible light. Experiments were conducted using 0.2- mu m filtered seawater and natural light conditions. The DMS photolysis rate constant was determined to be between 0.03 and 0.07 h super(-1), and initial photolysis rates were between 1.3 and 2.5 nmol dm super(-3) d super(-1). Using these rates, the in situ profiles for downward irradiance, and the DMS concentration in the water column, a photochemical turnover rate constant of between 0.1 and 0.37 d super(-1) was determined for the upper 20 m of the water column, with a photochemical turnover time of between 2.5 and 9.5 days. DMSO photoproduction rates were up to 1.20 nmol dm super(-3) d super(-1). Furthermore, results indicate that under UVA/visible light most of the DMS is photo-oxidised to form DMSO, whereas under UVB radiation DMS may be removed via a second photolysis pathway.

Archer, SD; Gilbert, FJ; Nightingale, PD; Zubkov, MV; Taylor, AH; Smith, GC; Burkill, PH

Deep-Sea Research (Part II, Topical Studies in Oceanography) [Deep-Sea Res. (II Top. Stud. Oceanogr.)]. Vol. 49, no. 15, pp. 3067-3101. 2002.

This study describes the routes and rates of transformation of dimethylsulphoniopropionate (DMSP) to dimethyl sulphide (DMS) in a phytoplankton bloom in the northern North Sea (59 degree N 2 degree E). A region on the edge of the high reflectance waters that characterised the bloom was labelled with SF sub(6)-tracer and tracked for 6 days. Within the framework of this Lagrangian experiment, it was possible to compile a comprehensive budget of the transformation of DMSP to DMS in the surface mixed layer of 15-30 m depth and a subsurface layer that extended to greater than or equal to 40 m. As a basis to the synthesis of the DMS(P) biogeochemistry, an attempt was made to accurately constrain DMS emissions from the Lagrangian water mass. Included in the study is a comparison of estimates of the transfer velocity and DMS sea to air flux derived from two well established and two recently introduced parameterisations. The two recent approaches encouragingly gave similar rates of total DMS sea to air flux of 1.60 mg S m super(-2) over the 6-day experimental period, and this value was intermediate to values derived from the two more routinely used approaches. The DMS sea to air flux was equivalent in terms of sulphur, to 10% of the DMS production and 1.3% of the particulate DMSP (DMSPp) production in the surface layer over the 6 days. Bacterial consumption accounted for the majority of DMS removal in both surface (62-82%) and subsurface layers (average 98%) and DMS concentrations decreased over the 6 days, despite increasing DMS production. Microzooplankton were the main agents of the transformation of DMSPp to the dissolved phase but little DMS appeared to be produced directly by the grazers. Instead, bacteria rapidly turned over the dissolved DMSP (DMSPd) made available by the grazers. An upper limit of 17% of the DMSPd consumed by bacteria in the surface layer was cleaved to DMS over the 6 days. Lower transformation efficiencies of AA6% were estimated for the subsurface layer. An ecosystem model incorporating DMS(P) biogeochemistry was developed on the basis of the empirical data. Simple sensitivity analyses were employed to demonstrate the importance of both microzooplankton and bacterial metabolism in controlling the yield of DMS from DMSP production and hence, the DMS sea to air flux. Greater yields of DMS are likely to occur when DMSPp is transformed directly to DMS, in this case due to grazing, than when transformed to DMSPd and subsequently cleaved to DMS by bacterial activity.

Yamamoto, H; Yokouchi, Y; Otsuki, A; Itoh, H

Chemosphere [Chemosphere]. Vol. 45, no. 3, pp. 371-377. Oct 2001.

Measurements were made of bromocarbons (CHBr sub(3) and CH sub(2)Br sub(2)), iodocarbons (CH sub(2)I sub(2) and CH sub(2)ClI), and dimethylsulfide (DMS, CH sub(3)SCH sub(3)) in seawater collected from the Bay of Bengal under tropical stratified conditions. These compounds showed different depth profiles, characteristic of each group. CH sub(2)I sub(2) and CH sub(2)ClI showed very similar depth profiles to chlorophyll-a, suggesting their production by phytoplankton followed by rapid decay in seawater. The CH sub(2)I sub(2) maximum at a depth a little below the CH sub(2)ClI maximum was consistent with its more significant photolytic decay. The bromocarbons were less localized in their distributions than were the iodocarbons, suggesting their longer residence time in seawater after their release from phytoplankton. Both of these profiles were different from the pattern of DMS, which had its maxima above the chlorophyll-a maximum layer near the surface.

Archer, SD; Widdicombe, CE; Tarran, GA; Rees, AP; Burkill, PH

Aquatic Microbial Ecology [Aquat. Microb. Ecol.]. Vol. 24, no. 3, pp. 225-241. 18 Jul 2001.

Dimethylsulphoniopropionate (DMSP) synthesised by phytoplankton is the principal precursor of the climatically active gas dimethyl sulphide (DMS). The rates of production of particulate DMSP (DMSPp) and turnover by microzooplankton were determined in surface waters of the northern North Sea, using a dilution approach. The phytoplankton communities were characterised by DMSP-rich taxa including Emiliania huxleyi and Prorocentrum minimum and DMSPp:chlorophyll a (chl a) ratios of 64 to 162 nM mu g super(-1). Microzooplankton biomass varied from 25.5 to 56.7 mu g C l super(-1) and was dominated by oligotrich ciliates and heterotrophic dinoflagellates. DMSPp production rates ranged from 14.8 to 45.6 nM d super(-1) and represent a doubling time of the ambient DMSPp pool of between 1.2 and 3.1 d. Consumption rates of DMSPp by microzooplankton varied between 11.4 and 59.9 nM d super(-1) and were equivalent to turnover rates of the ambient DMSPp pool of between 16 and 43 % d super(-1). In general, production rates of DMSPp were lower than those of chl a and E. huxleyi, with respective mean doubling times of 1.9, 1.5 and 1.3 d. Loss rates due to grazing were similar for DMSPp and E. huxleyi but generally significantly lower than those of the bulk phytoplankton, with mean turnover rates of 31, 30 and 40 % d super(-1) of the standing stock of DMSPp, E. huxleyi and chl a, respectively. E. huxleyi contributed an estimated 2 to 25 % of the total DMSPp production and 6 to 23 % of the DMSPp ingested by microzooplankton, indicating the importance of other phytoplankton to DMSPp dynamics in `E. huxleyi blooms'. At the depths sampled, DMSPp production was closely coupled to primary production and was equivalent to approximately 11 % of the carbon fixation. DMSPp may be an important component of the diets of microzooplankton.

Legrand, M; Sciare, J; Jourdain, B; Genthon, C

Journal of Geophysical Research. D. Atmospheres [J. Geophys. Res. (D Atmos.)]. Vol. 106, no. D13, pp. 14,409-14,422. Jul 2001.

A study of atmospheric dimethylsulfide (DMS) and dimethylsulfoxide (DMSO) was conducted on a subdaily basis during austral summer months (450 samples from mid-December 1998 to late-February 1999) at Dumont d'Urville, a coastal Antarctic site (66 degree 40'S, 140 degree 01'E). In addition, subdaily aerosol samplings were analyzed for particulate methanesulfonate (MSA) and non-sea-salt sulfate (nssSO super(2) sub(4) super(-)). During these summer months, DMS and DMSO levels fluctuated from 34 to 2923 pptv (mean of 290 plus or minus 305 pptv) and from 0.4 to 57 pptv (mean of 3.4 plus or minus 4.4 pptv), respectively. Mean MSA and non-sea-salt sulfate (nssSO super(2) sub(4) super(-)) mixing ratios were close to 12.5 plus or minus 8.2 pptv and 68.1 plus or minus 35.0 pptv, respectively. In two occasions characterized by stable wind conditions and intense insolation, it was possible to examine the local photochemistry of DMS. During these events, DMSO levels tracked quite closely the solar flux and particulate MSA levels were enhanced during the afternoons. Photochemical calculations reproduce quite well observed diurnal variations of DMSO when we assume an 0.8 yield of DMSO from the DMS/OH addition channel and an heterogeneous loss rate of DMSO proportional to the OH radical concentration: 0.5x10 super(-10) [OH] + 5.5x10 super(-5) (in s super(-1)). If correct, on a 24 hour average the heterogeneous loss of DMSO is estimated to be 2 times faster than the DMSO/OH gas phase oxidation in these regions. Very low levels of DMSO were found in the aerosol phase (less than 0.01 pptv), suggesting that an efficient oxidation of DMSO subsequently takes place onto the aerosol surface.

Strom, SL; Wolfe, GV

Journal of Phycology [J. Phycol.]. Vol. 37, no. s3, pp. 47-48. Jun 2001.

Deterrence of herbivores through chemical signaling - plant chemical defense - is known to be widespread throughout terrestrial and marine benthic ecosystems. The occurrence and significance of chemical defenses produced by unicellular marine phytoplankton has not, however, been systematically explored. We are investigating the role of the phytoplankton-produced compounds dimethylsulfo-niopropionate (DMSP) and its cleavage products dimethylsulfide (DMS) and acrylate in reducing herbivory by protist grazers. DMSP is produced in high intracellular concentrations by numerous phytoplankton species, especially notorious bloom-forming dinoflagellates and prymnesiophytes, and is cleaved by the enzyme DMSP lyase during grazing, physiological stress or cell lysis. Using four different strains of Emiliania huxleyi, a coccolithophorid (Prymnesiophyte), we have shown that strains with high DMSP lyase activities experience consistently reduced levels of herbivory in comparison with low lyase strains. Curiously, the products of the cleavage reaction (DMS and acrylate) do not affect rates of herbivory, indicating that this is not an activated chemical defense. Feeding rates are, however, proportionally and substantially reduced by the reaction precursor, DMSP. We also have preliminary evidence that high lyase strains release more DMSP to seawater than do low lyase strains. DMSP, while not evidently toxic to protist grazers, appears to act as a chemical signal that reduces grazing. We hypothesize that these unicellular herbivores may have evolved to recognize and respond to a compound (DMSP) that is a precursor of the potentially deleterious cleavage product acrylate. This and related chemical signaling processes may be important in promoting formation of phytoplankton blooms in the sea.

Van Alstyne, KL; Wolfe, GV; Freidenburg, TL; Neill, A; Hicken, C

Marine Ecology Progress Series [Mar. Ecol. Prog. Ser.]. Vol. 213, pp. 53-65. 2001.

Activated defenses against herbivores and predators are defenses whereby a precursor compound is stored in an inactive or mildly active form. Upon damage to the prey, the precursor is enzymatically converted to a more potent toxin or feeding deterrent. In marine systems, activated defenses are only known to exist in a few species of tropical macroalgae. In this study, we examined an activated defense system in temperate marine macroalgae in which the osmolyte dimethylsulfoniopropionate (DMSP) is converted to acrylic acid or acrylate, depending upon the pH, and dimethyl sulfide (DMS) by the enzyme DMSP lyase upon damage to the alga. We surveyed 39 species of red, green, and brown algae from the Washington and Oregon coasts, and found high concentrations of DMSP in the chlorophytes Acrosiphonia coalita, Codium fragile, Enteromorpha intestinalis, E. linza, Ulva californica, U. fenestrata, and U. taeniata, and in the rhodophyte Polysiphonia hendryi. Concentrations of DMSP ranged from 0.04% of the alga's fresh mass (FM) to 1.8% FM. We found significant DMSP lyase activity in 1 green alga, U. fenestrata, and 1 red alga, P. hendryi, with DMSP cleavage rates approaching 300 mmol/kg FM /min. Loss of DMSP and the production of DMS when the tissues of U. californica and P. hendryi were crushed suggested that physical damage results in DMSP cleavage. In laboratory feeding preference experiments, acrylic acid deterred feeding by the sea urchin Strongylocentrotus droebachiensis at concentrations of 0.1 to 2% FM and by S. purpuratus at 0.25 to 2% FM, while the precursor DMSP functioned as a feeding attractant to both sea urchins. In contrast, feeding by the isopod Idotea wosnesenskii was not deterred by acrylic acid even at concentrations as high as 8% FM. Our data suggest that DMSP may function as a precursor in an activated defense system in diverse species of temperate macroalgae and may possibly contribute to the widespread success of the Ulvophyceae. This chemical system is also found in unicellular phytoplankton, and presents an opportunity to compare and contrast the ecological role of chemical defense among micro- and macroorganisms.

Anderson, TR; Spall, SA; Yool, A; Cipollini, P; Challenor, PG; Fasham, MJR

Journal of Marine Systems [J. Mar. Syst.]. Vol. 30, no. 1-2, pp. 1-20. Aug 2001.

The major difficulty in estimating global sea-air fluxes of dimethylsulphide (DMS) is in interpolating measured seawater DMS concentrations to create seasonally resolved gridded composites. Attempts to correlate DMS with variables that can be mapped globally, e.g. chlorophyll, have not yielded reliable relationships. A comprehensive database of DMS measurements has recently been assembled by Kettle et al. [Global Biogeochem. Cycles 13 (1999) 399]. This database, which contains chlorophyll as a recorded variable, was extended by merging nutrients and light from globally gridded fields. A new equation was developed whereby DMS is predicted from the product of chlorophyll (C, mg m super(-3)), light (J, mean daily shortwave, W m super(-2)) and a nutrient term (Q, dimensionless) using a "broken-stick" regression: DMS = a, log sub(10)(CJQ) less than or equal to s DMS = b[log sub(10)(CJQ) - s] + a, log sub(10)(CJQ) > s where Q = N/(K sub(N) + N), N is nitrate (mmol m super(-3)) and K sub(N) is the half saturation constant for nitrate uptake by phytoplankton (0.5 mmol m super(-3)). Fitted parameter values are: a = 2.29, b = 8.24, s = 1.72. Monthly maps of global DMS were generated by combining these equations with ocean color data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The resulting high DMS concentrations in high latitude, upwelling and shelf areas are consistent with observed patterns. Predicted global seasonally averaged mean DMS is 2.66 nM. The further application of gas transfer equations to these fields leads to estimates of globally integrated DMS fluxes from ocean to atmosphere of 0.86 and 1.01 Tmol S year super(-1) for two formulations of piston velocity. The simplicity of the new relationship makes it suitable for implementation in global ocean general circulation models. The relationship does not however resolve DMS variability in low-DMS areas, which constitute large tracts of the open ocean, and should therefore be used with caution in localized studies.

Wu, Ping; Yang, Guipeng

Mar. Sci. Bull. Vol. 3, no. 2, pp. 38-46. 2001.

Reviews on the current studies on the sea to air flux of dimethyl sulfide (DMS) have been made at home and abroad, pointing out that the flux of DMS is influenced by many factors. There is great difference between the results coming from different models. Besides, this paper focuses on the oxidation mechanisms of DMS by OH and NO sub(3) radicals after it enters the atmosphere, the oxidation products' contribution to acid rain and fog and the relationships among the DMS, CCN and climate system.

Reid, PC; Edwards, M

Encyclopedia of Ocean Sciences - Vol. 4 (N-R). pp. 2194-2200. 2001.

Plankton has two roles with respect to climate: first as an indicator of climate change in present day populations and in the fossil record and second as a factor contributing to climate change through, for example, its role in the CO sub(2) cycle, in cloud formation via dimethylsulfide (DMS) production, and in altering the reflectivity of sea water as a component of suspended particulate matter. Current research on both the contribution of plankton to climate change and its role as an indicator of change are central to predicting potential scenarios that may occur in the future at a time when global mean temperatures are predicted to rise at an unprecedented rate by 1.5-6 degree C within the next 100 years.

Wolfe, GV; Levasseur, M; Cantin, G; Michaud, S

Deep-Sea Research (Part I, Oceanographic Research Papers) [Deep-Sea Res. (I Oceanogr. Res. Pap.)]. Vol. 47, no. 12, pp. 2243-2264. 1 Dec 2000.

We adapted the dilution technique to study microzooplankton grazing of algal dimethylsulfoniopropionate (DMSP) vs. Chl a, and to estimate the impact of microzooplankton grazing on dimethyl sulfide (DMS) production in the Labrador Sea. Phytoplankton numbers were dominated by autotrophic nanoflagellates in the Labrador basin, but diatoms and colonial Phaeocystis pouchetii contributed significantly to phytomass at several high chlorophyll stations and on the Newfoundland and Greenland shelfs. Throughout the region, growth of algal Chl a and DMSP was generally high (0.2--1 d super(-1)), but grazing rates were lower and more variable, characteristic of the early spring bloom period. Production and consumption of Chl a vs. DMSP followed no clear pattern, and sometimes diverged greatly, likely because of their differing distributions among algal prey taxa and size class. In several experiments where Phaeocystis was abundant, we observed DMS production proportional to grazing rate, and we found clear evidence of DMS production by this haptophyte following physical stress such as sparging or filtration. It is possible that grazing-activated DMSP cleavage by Phaeocystis contributes to grazer deterrence: protozoa and copepods apparently avoided healthy colonies (as judged by relative growth and grazing rates of Chl a and DMSP), and grazing of Phaeocystis was significant only at one station where cells were in poor condition. Although we hoped to examine selective grazing on or against DMSP-containing algal prey, the dilution technique cannot differentiate selective ingestion and varying digestion rates of Chl a and DMSP. We also found that the dilution method alone was poorly suited for assessing the impact of grazing on dissolved sulfur pools, because of rapid microbial consumption and the artifactual release of DMSP and DMS during filtration. Measuring and understanding the many processes affecting organosulfur cycling by the microbial food web in natural populations remain a technical challenge that will likely require a combination of techniques to address.

Kiene, RP; Linn, LJ; Bruton, JA

Journal of Sea Research [J. Sea Res.]. Vol. 43, no. 3-4, pp. 209-224. Aug 2000.

The algal osmolyte dimethylsulfoniopropionate (DMSP) is recognised as the major precursor of marine dimethylsulfide (DMS), a volatile sulfur compound that affects atmospheric chemistry and global climate. Recent studies, using super(35)S-DMSP tracer techniques, suggest that DMSP may play additional very important roles in the microbial ecology and biogeochemistry of the surface ocean. DMSP may serve as an intracellular osmolyte in bacteria that take up phytoplankton-derived DMSP from seawater. In addition, DMSP appears to support from 1 to 13% of the bacterial carbon demand in surface waters, making it one of the most significant single substrates for bacterioplankton so far identified. Furthermore, the sulfur from DMSP is efficiently incorporated into bacterial proteins (mostly into methionine) and DMSP appears to be a major source of sulfur for marine bacterioplankton. Assimilatory metabolism of DMSP is via methanethiol (MeSH) that is produced by a demethylation/demethiolation pathway which dominates DMSP degradation in situ. Based on the linkage between assimilatory metabolism of DMSP and bacterial growth, we offer a hypothesis whereby DMSP availability to bacteria controls the production of DMS by the competing DMSP lyase pathway. Also linked with the assimilatory metabolism of DMSP is the production of excess MeSH which, if not assimilated into protein, reacts to form dissolved non-volatile compounds. These include sulfate and DOM-metal-MeSH complexes, both of which represent major short-term end-products of DMSP degradation. Because production rates of MeSH in seawater are high (3-90 nM d super(-1)), reaction of MeSH with trace metals could affect metal availability and chemistry in seawater. Overall, results of recent studies provide evidence that DMSP plays important roles in the carbon, sulfur and perhaps metal and DOM cycles in marine microbial communities. These findings, coupled with the fact that the small fraction of DMSP converted to DMS may influence atmospheric chemistry and climate dynamics, draws attention to DMSP as a molecule of central importance to marine biogeochemical and ecological processes.

Ayers, GP; Gillett, RW

Journal of Sea Research [J. Sea Res.]. Vol. 43, no. 3-4, pp. 275-286. Aug 2000.

DMS emitted into the atmosphere over the global oceans has a range of effects upon atmospheric composition (mediated through various oxidation products) that may be significant with regard to issues as important as climate regulation, and the trace gas oxidation capacity of the marine atmospheric boundary layer. The roles played by DMS oxidation products within these contexts are diverse and complex, and in many instances are not well understood. Here we summarize what is known, and suspected, about the couplings between the marine atmospheric sulfur cycle, other atmospheric chemical cycles, and the dynamics and microphysics of the marine atmospheric boundary layer. This overview focuses heavily on measurements carried out in clean Southern Ocean air masses in association with the Australian Baseline Air Pollution Station located at Cape Grim (40 degree 40' 56"S, 144 degree 41' 18" E), Tasmania. The data confirm that in the remote marine atmosphere, DMS is a central player in a variety of important atmospheric processes, reinforcing the need to understand quantitatively the factors that regulate DMS emissions from the ocean to the atmosphere.

Kiene, RP; Linn, LJ

Limnology and Oceanography [Limnol. Oceanogr.]. no. 4, pp. 849-861. Jun 2000.

We measured the distribution of particulate and dissolved pools of the phytoplankton osmolyte dimethylsulfoniopropionate (DMSP) in the euphotic zone at a series of shelf (<40 m total water depth) and oceanic (>500 m depth) stations in the northern Gulf of Mexico. We also measured turnover rates of the dissolved DMSP pools (DMSPd) with tracer additions of super(35)S-DMSPd and short-term (<1 h) incubations, with the aim of examining the relationship between DMSPd turnover and bacterial production. Particulate DMSP concentrations were relatively low (<25 nM) throughout the study area with about twofold higher mean concentration at the shelf sites (15 nM) compared with the oligotrophic oceanic sites (7 nM). DMSPd concentrations averaged 3.0 nM in shelf waters and 1.3 nM in oceanic waters. Concentrations of dimethylsulfide (DMS), a degradation product of DMSP, also were low throughout the Gulf, averaging 2.0 nM for all depths sampled and 2.5 nM in surface waters. Microbial assemblages metabolized super(35)S-DMSPd with the sulfur being incorporated into biomass, volatile compounds (DMS and methanethiol), and other dissolved products. DMSPd turnover was relatively slow (mean of 3.8 nM d super(-1)) in oligotrophic oceanic waters and averaged 10-fold higher (39 nM d super(-1)) in mesotrophic shelf waters. DMS concentrations ranged from 0.2 to 5.1 nM in oceanic waters and appeared to be weakly related to DMSP turnover. In contrast, DMS concentrations in shelf waters fell within a narrow range (0.8-2.8 nM) and showed no relationship at all with DMSPd turnover. DMSPd turnover rates were high enough to sustain the measured concentrations and estimated turnover of DMS, even if the conversion efficiency of DMSPd into DMS was only 10%. DMSPd turnover was significantly correlated with bacterial production (as measured by super(3)H-thymidine incorporation) and we estimate that DMSPd turnover contributed a mean of 3.4% of the carbon and similar to 100% of the sulfur required for bacterial growth in Gulf of Mexico surface waters. In addition to its role as a precursor of DMS, DMSP deserves attention as an important substrate for bacterioplankton in the euphotic zone.

Nevitt, GA

Biological Bulletin, Marine Biological Laboratory, Woods Hole [Biol. Bull. Mar. Biol. Lab. Woods Hole]. no. 2, pp. 245-253. 2000.

Antarctic procellariiform seabirds forage over vast stretches of open ocean in search of patchily distributed prey resources. These seabirds are unique in that most species have anatomically well-developed olfactory systems and are thought to have an excellent sense of smell. Results from controlled experiments performed at sea near South Georgia Island in the South Atlantic indicate that different species of procellariiforms are sensitive to a variety of scented compounds associated with their primary prey. These include krill-related odors (pyrazines and trimethylamine) as well as odors more closely associated with phytoplankton (dimethyl sulfide, DMS). Data collected in the context of global climatic regulation suggest that at least one of these odors (DMS) tends to be associated with predictable bathymetry, including upwelling zones and seamounts. Such odor features are not ephemeral but can be present for days or weeks. I suggest that procellariiforms foraging over vast distances may be able to recognize these features reflected in the olfactory landscape over the ocean. On the large scale, such features may aid seabirds in navigation or in locating profitable foraging grounds. Once in a profitable foraging area, procellariiforms may use olfactory cues on a small scale to assist them in locating prey patches.

Niki, T; Kunugi, M*; Otsuki, A

Mar. Biol. Vol. 136, no. 5, pp. 759-764. 2000.

Activity of DMSP-lyase, which cleaves dissolved DMSP (henceforth DMSP sub(d)-lyase), was examined in five axenically cultured phytoplankton species, including both DMSP-producing and non-DMSP-producing species. High DMSP sub(d)-lyase activity was found in two DMSP producers, Heterocapsa triquetra strain NIES-7 and Scrippsiella trochoidea strain NIES-369 (Dinophyceae). The DMS production rates at 100 nM DMSP sub(d) were 0.5 fmol/cell/min for H. triquetra and 0.3 fmol/cell/min for S. trochoidea. In a non-DMSP producer, Heterosigma akashiwo strain NIES-6 (Raphidophyceae), the DMSP sub(d)-lyase activity was not found. Two DMSP-producing Prymnesiophyceae species, Isochrysis galbana strain CCMP-1323 and Gephyrocapsa oceanica strain NIES-353, did not show any obvious activity either, in contrary to other authors' findings on Phaeocystis, another DMSP-producing Prymnesiophyceae species. The comparison of the DMSP sub(d)-lyase activity of the two Dinophyceae species with bacterial DMSP consumption and DMS production activity in Tokyo Bay showed that the DMSP sub(d)-lyase activity of H. triquetra and S. trochoidea could be an important mechanism for DMS production during their blooms.

Schultes, S; Levasseur, M*; Michaud, S; Cantin, G; Wolfe, G; Gosselin, M; De Mora, S

Mar. Ecol. Prog. Ser. Vol. 202, pp. 27-40. 2000.

The dynamics of the cleavage of dissolved dimethylsulfoniopropionate (DMSP sub(d)) to dimethylsulfide (DMS) were measured experimentally in the surface waters of the Labrador Sea in spring 1997. At in situ DMSP sub(d) concentrations, DMS production and consumption processes were generally in balance. Two stations in the central Labrador Sea displayed net DMS production of approximately 2 nmol/L /h, DMSP sub(d) net consumption of 3.48 nmol/L/h and a net DMS production yield from DMSP sub(d) of 60% at near in situ DMSP sub(d) concentrations. Similar to general bacterial substrate utilization in cold waters, DMS production in the Labrador Sea seemed to be temperature and substrate limited. Following DMSP sub(d) additions, linear and non-linear net DMS production were observed. The non-linear response was characterized by a lag in DMS production and was associated with the cold, polar waters of the Labrador and West Greenland Currents. Net DMS production rates measured after DMSP sub(d) addition were proportional to the added amount of DMSP sub(d). No saturation of the net DMS production rate was observed for concentrations up to 5000 nmol DMSP sub(d)/L. First order rate constants determined for these DMS production kinetics suggest an average turnover time of DMSP sub(d) by cleavage to DMS of 3.8 d (2.7 to 5.2 d). At water temperatures of -1.3 to 8 degree C, potential net DMS production rates measured following DMSP sub(d) additions were comparable and even higher than those previously published for temperate and warm oceanic and coastal regions. The net DMS production potential varied by 1 order of magnitude. (1.7 to 18.4 nmol DMS/L/h) throughout the study area. Causal links established with path analysis indicate that this potential seemed to be controlled by water temperature and chlorophyll a concentrations.

Simo, R; Pedros-Alio, C; Malin, G; Grimalt, JO

Mar. Ecol. Prog. Ser. Vol. 203, pp. 1-11. 2000.

Speciation and turnover of the methylated sulfur compounds dimethyl sulfide (DMS), dimethylsulfoniopropionate (DMSP) and dimethyl sulfoxide (DMSO) were studied in waters of the open western Mediterranean, the near-coastal North Sea and the subpolar North Atlantic, with chlorophyll a concentrations spanning 2 orders of magnitude (0.12 to 13 mu g/L). Particulate DMSP (DMSP sub(p): 5 to 340 nM) was the predominant pool in most waters. Dissolved and particulate dimethyl sulfoxide were also found at significant concentrations (DMSO sub(d): 2 to 25 nM, DMSO sub(p): 3 to 16 nM). Biological DMSP consumption rates were estimated from the time course of total (dissolved + particulate) DMSP concentration in dark incubations. Dimethyl sulfide production and consumption rates were determined by the 'inhibitor addition' method. High DMS production and consumption rates were found during a bloom of Phaeocystis in North Sea waters. In all samples, turnover time constants for total DMSP and DMS were of the same order, ranging from 0.7 to 5.4 and from 0.3 to 2.1 d, respectively. DMS formation was the fate for 9 to 96% of the DMSP consumed. Use of chloroform as an inhibitor gave estimates of DMS production and consumption rates approximately 70% higher than those obtained with dimethyl disulfide and dimethyl selenide. In some incubation experiments, the time course of DMSO concentration has been followed along with DMS and DMSP for the first time. Evidence for active biological cycling (production and consumption) of DMSO in seawater is presented.

Simo, R; Pedros-Allo, C

Nature [Nature]. Vol. 402, no. 6760, pp. 396-399. 25 Nov 1999.

Marine microbiota are important for the global biogeochemical sulphur cycle, by making possible the transfer of reduced sulphur from the ocean to the atmosphere in the form of dimethyl sulphide, DMS. Subsequent oxidation of DMS to acidic aerosols influences particle nucleation and growth over the oceans, and so has the potential to influence radiative balance and global climate. It has been suggested that this plankton-climate interaction is self-regulated, but tests of this hypothesis have remained elusive as little is known about the feedback effects of climate on the marine DMS cycle. DMS is produced by enzymatic cleavage of the abundant algal component dimethylsulphoniopropionate (DMSP), which suggests a high potential for DMS generation in the ocean. But there are competing processes that utilize DMSP in the food web without producing DMS, and the external controls on these processes are unknown. Here we present data of DMSP consumption, DMS production and mixing-layer depths (which are driven by climate) in the subpolar North Atlantic, and compare these data with published results from other latitudes. We find evidence that the mixing-layer depth has a substantial influence on DMS yield in the short term. This finding, combined with the seasonal effect of vertical mixing on plankton succession and food-web structure, suggests that climate-controlled mixing controls DMS production over vast regions of the ocean.

Wolfe, GV; Levasseur, M; Cantin, G; Michaud, S

Aquatic Microbial Ecology [Aquat. Microb. Ecol.]. no. 2, pp. 197-205. 9 Aug 1999.

We examined microbial production and consumption of dimethyl sulfide (DMS) in Labrador Sea surface waters ranging in temperature from -0.1 to 6.9 degree C. 200 nM dimethyl disulfide (DMDS) was used to inhibit DMS consumption. We also studied DMS consumption kinetics by additions of 5 to 50 nM DMS, DMS production from added dimethylsulfoniopropionate (DMSP), and DMS production and consumption during zooplankton grazing. During the cruise, DMS concentrations were low, ranging from 1 to 7 nM throughout the study area, which included a bloom of the colonial haptophyte alga Phaeocystis pouchetii. DMDS additions often revealed rapid DMS production and consumption (up to 5 nM d super(-1)) and very rapid turnover (<1 to 3 d), similar to rates found in coastal waters at much higher temperatures. There was no clear effect of temperature on DMS consumption; rather, DMS consumption appeared to be tightly coupled with production. Turnover was most rapid at low DMS concentrations, and DMS consumption was stimulated by additions of DMS, or by increased DMS production from additions of dissolved DMSP. DMDS additions to zooplankton grazing incubations revealed rapid gross DMS production and consumption which were nearly balanced, resulting in net steady-state DMS patterns. DMDS did not affect production or grazing of algal pigments or DMSP. DMS consumption saturated at 18 to 32 nM [DMS] and saturation kinetics were similar within the photic zone, but consumption was near-zero at greater depths. We suggest that DMS consumption likely saturates more easily than microbial DMS production from DMSP, and this, combined with temperature limitation on the growth of prokaryotic DMS consumers, may lead to the periodic buildup of high DMS concentrations previously observed in polar and subpolar waters.

Dacey, JWH; Howse, FA; Michaels, AF; Wakeham, SG

Deep-Sea Research (Part I, Oceanographic Research Papers) [Deep-Sea Res. (I Oceanogr. Res. Pap.)]. Vol. 45, no. 12, pp. 2085-2104. Dec 1998.

Vertical profiles of dimethylsulfide (DMS) and beta -dimethylsulfoniopropionate, particulate (pDMSP) and dissolved (dDMSP), were measured biweekly in the upper 140 m of the Sargasso Sea (32 degree 10'N, 64 degree 30'W) during 1992 and 1993. DMS and pDMSP showed strong, but different, seasonal patterns; no distinct intra-annual pattern was observed for dDMSP. During winter, concentrations of DMS were generally less than 1 nmol l super(-1) at all depths, dDMSP was less than 3 nmol l super(-1) and pDMSP was less than 8 nmol l super(-1). In spring, concentrations of both dDMSP and pDMSP rose, on a few occasions up to 20 nmol l super(-1) in the dissolved pool and up to 27 nmol l super(-1) in the particulate pool. These increases, due to blooms of DMSP-containing phytoplankton, resulted in only minor increases in DMS concentrations (up to 4 nmol l super(-1)). Throughout the summer, the concentrations of DMS continued to increase, reaching a maximum in August of 12 nmol l super(-1) (at 30 m depth). There was no concomitant summer increase in dDMSP or pDMSP. The differences among the seasonal patterns of DMS, dDMSP, and pDMSP suggest that the physical and biological processes involved in the cycling of DMS change with the seasons. There is a correlation between the concentration of DMS and temperature in this data set, as required by some of the climate feedback models that have been suggested for DMS. A full understanding of the underlying processes controlling DMS is required to determine if the temperature-DMS pattern is of significance in the context of global climate change.

Andreae, MO; Elbert, W; De Mora, SJ

Journal of Geophysical Research. D. Atmospheres [J. GEOPHYS. RES. (D ATMOS.)], vol. 100, no. D6, 11,335,11,356, 1995

We measured dimethylsulfide in air (DMS sub(a)) and the number concentration, size distribution, and chemical composition of atmospheric aerosols, including the concentration of cloud condensation nuclei (CCN), during February-March 1991 over the tropical South Atlantic along 19 degree S (F/S Meteor, cruise 15/3). Aerosol number/size distributions were determined with a laser-optical particle counter, condensation nuclei (CN) concentrations with a TSI 3020, and cloud condensation nuclei (CCN) with a Hudson-type supersaturation chamber. Aerosol samples were collected on two-stage stacked filters and analyzed by ion chromatography for soluble ion concentrations. Black carbon in aerosols was measured by visible light absorption and used to identify and eliminate periods with anthropogenic pollution from the data set. Meteorological analysis shows that most of the air masses sampled had spent extended periods over remote marine areas in the tropical and subtropical region. DMS sub(a) was closely correlated with the sea-to-air DMS flux calculated from DMS concentrations in seawater and meteorological data. Sea salt made the largest contribution to aerosol mass and volume but provided only a small fraction of the aerosol number concentration. The submicron aerosol had a mean composition close to ammonium bisulfate, with the addition of some methanesulfonate. Aerosol (CN and CCN) number and non-sea-salt sulfate concentrations were significantly correlated with DMS concentration and flux. This suggests that DMS oxidation followed by aerosol nucleation and growth in the marine boundary layer is an important, if not dominating, source of CN and possibly CCN. The degree of correlation between DMS and particle concentrations in the marine boundary layer may be strongly influenced by the different time scales of the processes regulating these concentrations. Our results provide strong support for several aspects of the CLAW hypothesis, which proposes the existence of a feedback loop linking DMS emission from marine plankton to sulfate aerosol and global climate.

Liss, PS; Malin, G; Turner, SM; Holligan, PM

Journal of Marine Systems [J. MAR. SYST.], vol. 5, no. 1, pp. 41-53, 1994

Dimethyl sulphide (DMS) is the dominant sulphur gas found in surface marine waters and there is compelling evidence that it is formed biologically in these environments. In all areas so far investigated the oceans are found to be highly supersaturated (typically by two orders of magnitude) with respect to atmospheric levels of DMS, which indicates a net flux of the gas out of the oceans. In this paper, we first briefly review the environmental importance of the gas and particularly the role of its sea-to-air flux on atmospheric chemistry and physics. Then we discuss what is known of its mode of formation and cycling in seawater, before looking more specifically at the role and significance of Phaeocystis as a producer of DMS.

Malin, G; Turner, SM; Liss, PS

Journal of Phycology [J. PHYCOL.], vol. 28, no. 5, pp. 590-597, 1992

A key process in the global sulfur cycle is the transfer of volatile forms of the element from sea to land via the atmosphere. Early budgets calculated the amount of sulfur required to balance the cycle and generally assumed that this flux was achieved by formation of hydrogen sulfide (H sub(2)S) in coastal waters, mud flats, etc. However, Lovelock et al. (1972) made the first field measurements of dimethylsulfide (DMS) in seawater and suggested that it represented the missing link in the S cycle. In this review we consider processes leading to the formation of DMS in seawater, its emission to the atmosphere, and transformation therein, the possible role of DMS oxidation products in climate regulation as proposed by Charlson et al. (1987), and how global changes might affect DMS production.

Kiene, RP

Applied and Environmental Microbiology [APPL. ENVIRON. MICROBIOL.], vol. 56, no. 11, pp. 3292-3297, 1990

Dimethyl sulfide (DMS) was produced immediately after the addition of 0.1 to 2 mu M beta -dimethyl-sulfoniopropionate (DMSP) to coastal seawater samples. Azide had little on the initial rate of DMS production from 0.5 mu M added DMSP, but decreased the rate of production after 6 h. Filtration of water samples through membrane filters (pore size, 0.2 mu m) greatly reduced DMS production for approximately 10 h, after which time DMS production resumed at a high rate. Acrylate, a product of the enzymatic cleavage of DMSP, was metabolized in seawater samples, and two strains of bacteria were isolated with this compound as the growth substrate. These bacteria produced DMS from DMSP. The sensitivity to inhibitors with respect to growth and DMSP-lyase activity varied from strain. These results illustrate the significant potential for microbial conversion of dissolved DMSP to DMS in coastal seawater.

Andreae, MO

Limnology and Oceanography [LIMNOL. OCEANOGR.], vol. 30, no. 6, pp. 1208-1218, 1985

The concentration of dimethylsulfide (DMS) and supporting parameters were determined on longshore and cross-shelf-traverses in the Peru upwelling area. Vertical DMS profiles were measured at several stations in the marine water column and in the sedimentary porewaters. The rates of DMS production in the water column and its flux into the atmosphere across the air-sea interface are only a small fraction of the rate of sulfate assimilation by the plankton community. The concentrations of DMS in the surface waters of the Peru shelf are similar to those found in other coastal areas; the fluxes of reduced sulfur gases to the atmosphere from this upwelling region do not require special consideration in the global atmospheric sulfur budget.

Andreae, MO; Ferek, RJ; Bermond, F; Byrd, KP; Engstrom, RT; Hardin, S; Houmere, PD; LeMarrec, F; Raemdonck, H; Chatfield, RB

Journal of Geophysical Research. D. Atmospheres [J. GEOPHYS. RES. (D ATMOS.).], vol. 90, no. D7, pp. 12891-900, 1985

Over 900 measurements of atmospheric dimethyl sulfide (DMS) were made in five different marine locations: the equatorial Pacific; Cape Grim, Tasmania; the Bahamas; the North Atlantic; and the Sargasso Sea. At all locations, DMS concentrations were usually in the range of 100-400 ng S m super(-3), with similar average concentrations of 150 ng S m super(-3) (107 ppt by volume). The observed concentrations of DMS in the marine atmosphere and their diurnal variability agree well with model simulations involving OH and NO sub(3) oxidation of DMS and are consistent with a global sea-to-air DMS flux of about 40 plus or minus 20 Tg S yr super(-1). DMS may represent a major sink for NO sub(3) in the marine troposphere.

Andreae, MO; Barnard, WR

Marine Chemistry [MAR. CHEM.], vol. 14, no. 3, pp. 267-279, 1984

Dimethylsulfide (DMS) was determined in surface seawater and vertical hydrographic profiles in the Atlantic Ocean during two cruises from Hamburg to Montevideo (Uruguay), and from Miami (Florida) into the Sargasso Sea. These data cover most of the ecological zones of the Atlantic. DMS concentrations are related to the levels of marine primary production, in agreement with its release by marine phytoplankton in laboratory cultures. The vertical distribution of DMS in the euphotic zone follows that of primary production, with a maximum at or near the ocean surface and a decrease with depth. Below the level of 1% light penetration, DMS levels decline gradually, but DMS remains detectable even in the bottom waters. The mean DMS concentration in surface water is 84.4, and in deep water 3.2 ng S(DMS)l super(-1).

Andreae, MO; Barnard, WR; Ammons, JM

ENVIRONMENTAL BIOGEOCHEMISTRY., 1983, pp. 167-177, ECOL. BULL., vol. 35

It has been suggested that reduced biogenic sulfur compounds, in particular dimethylsulfide (DMS), could account for a significant flux of sulfur from the oceans to the atmosphere. In order to investigate this hypothesis, and to ascertain the biological source of DMS, the authors have determined its concentration in surface and deep sea water at a number of stations, and compared the results with indicators of biological activity, e.g., the concentration of chlorophyll a. They have observed a close correlation between the concentration of DMS in seawater and indicators of algal activity, both in their geographical distribution and in vertical profiles through the water column. Besides DMS, they have observed the presence of other dissolved organosulfur compounds in seawater, among them methylmercaptan, carbon disulfide, and dimethyl disulfide. The authors have found DMS to be produced in pure, axenic cultures of marine planktonic algae. This supports the suggestion (derived from the marine distribution of DMS) that it is produced by marine primary producers. They have also observed the release of very large amounts of DMS from coral organisms, especially under conditions of physiological stress.

Turner, S; Liss, P

Nature, vol. 305, no. 5932, p. 277, 1983

Gaseous sulphur compounds, such as sulphur dioxide (SO sub(2)), dimethyl sulphide (DMS), carbonyl sulphide (COS), carbon disulphide (CS sub(2)) and hydrogen sulphide (H sub(2)S), are thought to be important in two main aspects of atmospheric chemistry. First, they affect the acidity of rain directly. Second, these compounds are reactive in the atmosphere and susceptible to attack by hydroxyl radicals. Applying model calculations, a sea-to-air flux of about 40 x 10 super(12)g per year has been proposed. DMS therefore can account for about 50 per cent of natural emissions. A positive correlation between COS and DMS concentrations was found, suggesting that the presence of COS may also be related to algal productivity. The authors calculate a flux of COS from the oceans to the atmosphere of 0.46 x 10 super(12)g of sulphur per year.

Andreae, MO; Raemdonck, H

Science (Washington) [SCIENCE (WASH.).], vol. 221, no. 4612, pp. 744-746, 1983

Dimethyl sulfide (DMS) has been identified as the major volatile sulfur compound in 628 samples of surface seawater representing most of the major oceanic ecozones. In at least three respects, its vertical distribution, its local patchiness, and its distribution in oceanic ecozones, the concentration of DMS in the sea exhibits a pattern similar to that of primary production. The global weighted average concentration of DMS in surface seawater is 102 nanograms of sulfur (DMS) per liter, corresponding to a global sea-to-air flux of 39 x 10 super(12) grams of sulfur per year. When the biogenic sulfur contributions from the land surface are added, the biogenic sulfur gas flux is approximately equal to the anthropogenic flux of sulfur dioxide. The DMS concentration in air over the equatorial Pacific varies diurnally between 120 and 200 nanograms of sulfur (DMS) per cubic meter, in agreement with the predictions of photochemical models.

Charlson, RJ; Lovelock, JE; Andreae, MO; Warren, SG

Nature, vol. 326, no. 6114, pp. 655-661, 1987

The major source of cloud-condensation nuclei (CCN) over the oceans appears to be dimethylsulphide, which is produced by planktonic algae in sea water and oxidizes in the atmosphere to form a sulphate aerosol. Because the reflectance (albedo) of clouds (and thus the Earth's radiation budget) is sensitive to CCN density, biological regulation of the climate is possible through the effects of temperature and sunlight on phytoplankton population and dimethylsulphide production. To counteract the warming due to doubling of atmospheric CO sub(2), an approximate doubling of CCN would be needed.

Bates, TS; Charlson, RJ; Gammon, RH

Nature, vol. 329, no. 6137, pp. 319-321, 1987

Oceanic dimethylsulphide (DMS) emissions and atmospheric aerosol particle populations (condensation nuclei, CN), resolved by latitude and season, appear to be directly correlated, in that CN, as measured with a condensation nucleus counter, are high (or low) in regions where DMS fluxes and incident solar radiation are high (or low). Although it has been previously hypothesized that CN are produced from DMS, the authors report the first attempt to correlate DMS flux and CN. As the population of cloud condensation nuclei (CCN) in marine air is a subset of the CN population, and CCN in turn control the albedo of marine clouds, DMS could be involved in climate control through a cloud albedo feedback mechanism.