Release Of Dimethylsulfide Research Articles

Microplastics stress alters microorganism community structure and reduces the production of biogenic dimethylated sulfur compounds

AbstractDimethylsulfoniopropionate (DMSP) is a plentiful organic sulfur metabolite and the primary precursor for dimethyl sulfide (DMS), which plays a crucial role in global sulfur cycling, the formation of clouds, and cooling the warming earth. The origin and fate of DMSP are intricately linked to marine microorganisms, making the variation of the microorganism community crucial for DMSP dynamics. Nonetheless, the impact of pervasive marine microplastics on microorganisms and processes related to DMSP synthesis and degradation remains insufficiently investigated. To bridge this gap, a 14‐d deck‐based microcosm experiment was conducted, revealing that microplastics significantly altered the composition of microorganism communities and dramatically inhibited the release of DMS and DMSP. Furthermore, multivariate analysis demonstrated that the variations both in environmental variables and microorganism communities caused by microplastics were forcing factors in reducing DMS and DMSP release. In addition, the predicted function of the bacterial community showed a significant reduction in the presence of dddP and dmdA genes when exposed to microplastics, which directly disrupted both the demethylation and cleavage pathways of DMSP. These results indicate that the release of DMS and DMSP in marine ecosystems can be significantly affected by microplastics through influencing microorganisms. Thus, it is imperative to conduct research on controlling the synthesis and degradation of DMSP in the ocean, particularly in response to these environmental pollution issues. Such research can help discern new patterns from specific phenomena and identify crucial processes.

Dimethylated Sulfur, Methane and Aerobic Methane Production in the Yellow Sea and Bohai Sea

AbstractThis paper presents a comprehensive study of biogenic dimethylated sulfur compounds and methane (CH4) from 27 March to 16 April 2018 (spring) and from 24 July to 10 August 2018 (summer) in the Yellow Sea and Bohai Sea. The overall distributions of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP, precursor of DMS), dimethylsulfoxide (DMSO, oxidation product of DMS) and CH4 in surface waters were characterized by elevated concentrations in summer and in coastal waters, coupled to phytoplankton biomass and terrestrially sourced inputs. Surface waters were oversaturated with CH4. The flux distributions of DMS and CH4 were generally consistent with their concentration distributions. In situ incubation experiments revealed that microbial consumption was the main removal mechanism for DMS, which could remove up to 72.1% of the total DMS compared to sea‐to‐air exchange in the surface layer. High DMS release and enhanced DMS yields (34%–62%) suggested more obvious influence from high DMSP concentrations (1 or 5 μm L−1) on DMS production in oligotrophic waters with lower bacterial sulfur demand in contrast to near‐shore waters. Positive correlations were found between CH4 and DMSP (dissolved) in summer and DMSO (particulate and dissolved) in spring. A DMSP addition experiment suggested that DMSP could act as a precursor for aerobic methanogenesis, and CH4 preferentially occurs under nitrogen‐stressed conditions in the surface layers of the Yellow Sea and Bohai Sea.

Phosphorus accelerate the sulfur cycle by promoting the release of malodorous volatile organic sulfur compounds from Microcystis in freshwater lakes

Volatile organic sulfur compounds (VSCs) released by algae are of great significance in sulfur cycle, climate regulation and biological information transmission, and they also caused taste and odor in freshwaters. However, the categories, sources, and environmental regulatory factors of VSCs in freshwaters were less known. Here, we show that eight common freshwater cyanobacterium Microcystis, which bloom in freshwaters over the world, are found to be important producers of VSCs. Dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and isopropyl methyl sulfide (IPMS) are the main VSCs with the highest concentrations 184.81 nmol/L, 162.01 nmol/L and 101.55 nmol/L, respectively. The amount of VSCs released from those Microcystis varied greatly, M. elabens, M. panniformis and M. flos-aquae released the largest amount of VSCs (1260.52 nmol S/L, 1154.75 nmol S/L and 670.58 nmol S/L), and M. wesenbergii had the smallest release amount. We also found for the first time that phosphorus (P) was one of the important factors for the regulation VSCs from most Microcystis. P can elevate the release of DMS by promoting the biomass and DMS yields of most Microcystis in the range 0.05 mg/L to 0.5 mg/L. Similar results were also found in 16 lakes at three different spatiotemporal scales. Overall, we revealed that the common freshwater Microcystis were able to release diverse thioethers, and the major VSCs were significantly influenced by water P concentrations. In the context of global freshwater eutrophication and Microcystis bloom, freshwater cyanobacteria driven sulfur cycle and water odor will probably be further strengthened.

Natural dimethyl sulfide gradients would lead marine predators to higher prey biomass

Finding prey is essential to survival, with marine predators hypothesised to track chemicals such as dimethyl sulfide (DMS) while foraging. Many predators are attracted to artificially released DMS, and laboratory experiments have shown that zooplankton grazing on phytoplankton accelerates DMS release. However, whether natural DMS concentrations are useful for predators and correlated to areas of high prey biomass remains a fundamental knowledge gap. Here, we used concurrent hydroacoustic surveys and in situ DMS measurements to present evidence that zooplankton biomass is spatially correlated to natural DMS concentration in air and seawater. Using agent simulations, we also show that following gradients of DMS would lead zooplankton predators to areas of higher prey biomass than swimming randomly. Further understanding of the conditions and scales over which these gradients occur, and how they are used by predators, is essential to predicting the impact of future changes in the ocean on predator foraging success.

Production, distribution and flux of dimethyl sulfide in the East China Sea and its contribution to atmospheric sulfate aerosols

Environmental context Dimethyl sulfide is an important biogenic gas, released from ocean to atmosphere, which contributes to aerosol formation and can therefore affect global climate. Studies on dimethyl sulfide in both seawater and atmosphere have linked the atmospheric chemistry of dimethyl sulfide with its circulation in the marine environment. This study showed that these biogenic emissions contribute to the sulfur cycle and particulate production, deepening our understanding of their role in the East China Sea. Abstract Dimethyl sulfide (DMS) is identified as an essential biogenic sulfur compound in the ocean. Its oxidation products are thought to be important contributors to cloud condensation nuclei, thereby influencing the earth’s radiative balance and climate. The concentrations of DMS and its precursor, dimethylsulfoniopropionate (DMSP) were measured in seawater and sediment pore water in the East China Sea (ECS) during summer. In addition, dissolved DMSP (DMSPd) degradation rates, DMS production and consumption rates, and sea-to-air flux of DMS were determined, and the biogenic contribution to atmospheric non-sea-salt sulfate (nss-SO42−) was evaluated in PM2.5 and PM10 aerosols over the study area. The spatial distributions of DMS and DMSP were closely related to that of chlorophyll-a and decreased from the inshore to the offshore. The concentration of DMSPd in sediment pore water was significantly higher than that in bottom water, which indicated that sediment is a net source of DMSPd for bottom water. The biological incubation experiments showed that ~36.0 % of decomposed DMSPd was degraded into DMS, while 78.7 % of produced DMS was consumed by bacteria within the surface water. The sea-to-air flux of DMS varied from 1.30 to 31.84 μmol m−2 day−1, with an average of 7.45 ± 6.30 μmol m−2 day−1. Biogenic contributions of the ECS to total nss-SO42− were estimated to be 13.0 % ± 9.9 % in PM2.5 and 13.5 % ± 5.1 % in PM10 samples respectively, which indicated that marine DMS release cannot be neglected in the ECS during summer.

Effects of microplastics exposure on ingestion, fecundity, development, and dimethylsulfide production in Tigriopus japonicus (Harpacticoida, copepod)

The effects of microplastics pollution on the marine ecosystem have aroused attention. Copepod grazing stimulates dimethylsulfide (DMS) release from dimethylsulfoniopropionate (DMSP) in phytoplankton, but the effect of microplastics exposure on DMS and DMSP production during copepod feeding has not yet been revealed. Here, we investigated the effects of polyethylene (PE) and polyamide-nylon 6 (PA 6) microplastics on ecotoxicity and DMS/DMSP production in the copepod Tigriopus japonicus. The microplastics had detrimental effects on feeding, egestion, reproduction, survival, and DMS and DMSP production in T. japonicus and presented significant dose-response relationships. The 24 h-EC50 for ingestion rates (IRs) of female T. japonicus exposed to PE and PA 6 were 57.6 and 58.9 mg L−1, respectively. In comparison, the body size of the copepods was not significantly affected by the microplastics during one generation of culture. Ingesting fluorescently labeled microplastics confirmed that microplastics were ingested by T. japonicus and adhered to the organs of the body surface. T. japonicus grazing promoted DMS release originating from degradation of DMSP in algal cells. Grazing-activated DMS production decreased because of reduced IR in the presence of microplastics. These results provide new insight into the biogeochemical cycle of sulfur during feeding in copepods exposed to microplastics.

Phytoplankton-derived zwitterionic gonyol and dimethylsulfonioacetate interfere with microbial dimethylsulfoniopropionate sulfur cycling.

The marine sulfur cycle is substantially fueled by the phytoplankton osmolyte dimethylsulfoniopropionate (DMSP). This metabolite can be metabolized by bacteria, which results in the emission of the volatile sulfur species methanethiol (MeSH) and the climate‐cooling dimethylsulfide (DMS). It is generally accepted that bacteria contribute significantly to DMSP turnover. We show that the other low molecular weight zwitterionic dimethylsulfonio compounds dimethylsulfonioacetate (DMSA) and gonyol are also widely distributed in phytoplankton and can serve as alternative substrates for volatile production. DMSA was found in 11 of the 16 surveyed phytoplankton species, and gonyol was detected in all haptophytes and dinoflagellates. These prevalent zwitterions are also metabolized by marine bacteria. The patterns of bacterial MeSH and DMS release were dependent on the zwitterions present. Certain bacteria metabolize DMSA and gonyol and release MeSH, in others gonyol inhibited DMS‐producing enzymes. If added in addition to DMSP, gonyol entirely inhibited the formation of volatiles in Ruegeria pomeroyi. In contrast, no substantial effect of this compound was observed in the DMSP metabolism of Halomonas sp. We argue that the production of DMSA and gonyol and their inhibitory properties on the release of volatiles from DMSP has the potential to modulate planktonic sulfur cycling between species.

Response of Taste and Odor Compounds to Elevated Cyanobacteria Biomass and Temperature.

Taste and odor (T&O) compounds are frequently reported during black blooms, however, their production mechanisms and influencing factors are far from clear. In this study, laboratory simulation experiment was carried out to investigate the formation processes of T&O compounds under the influences of temperature, cyanobacteria biomass and their combined effects. The decay of cyanobacteria blooms caused increased T&O compounds loading to water. Results showed the maximum dimethyl sulfide (DMS) release concentration was observed at 35°C compared with that at 25 and 30°C. DMS release concentration under cyanobacteria biomass of 25000g/m3 demonstrated the highest production, whereas the minimum DMS production were obtained under 7500g/m3. Similar patterns were observed for dimethyl disulfide, dimethyl trisulfide, β-cyclocitral and β-ionone production. Therefore, higher temperature and higher cyanobacteria biomass can enhance the concentration of T&O compounds. Furthermore, there were synergistic effects of cyanobacteria biomass and temperature on the production of T&O compounds.

Biochemical Profiling of DMSP Lyases.

Dimethyl sulfide (DMS) is released at rates of >107 tons annually and plays a key role in the oceanic sulfur cycle and ecology. Marine bacteria, algae, and possibly other organisms release DMS via cleavage of dimethylsulfoniopropionate (DMSP). DMSP lyases have been identified in various organisms, including bacteria, coral, and algae, thus comprising a range of gene families putatively assigned as DMSP lyases. Metagenomics may therefore provide insight regarding the presence of DMSP lyases in various marine environments, thereby promoting a better understanding of global DMS emission. However, gene counts, and even mRNA levels, do not necessarily reflect the level of DMSP cleavage activity in a given environmental sample, especially because some of the families assigned as DMSP lyases may merely exhibit promiscuous lyase activity. Here, we describe a range of biochemical profiling methods that can assign an observed DMSP lysis activity to a specific gene family. These methods include selective inhibitors and DMSP substrate analogues. Combined with genomics and metagenomics, biochemical profiling may enable a more reliable identification of the origins of DMS release in specific organisms and in crude environmental samples.

Volatile organic compounds as markers of quality changes during the storage of wild rocket

The quality of leafy green vegetables changes during storage. Leaves become yellow or disintegrate, and an off-odor may develop. In addition, small amounts of volatile organic compounds (VOCs) are released. In this study, the release of acetone, carbon disulfide, dimethyl sulfide, nitromethane, pentane, 3-methylfuran, 2-ethylfuran, and dimethyl disulfide from wild rocket with different initial qualities was monitored during 8d storage at 10°C and correlated to aerobic bacteria counts, yeast and mold counts, and degree of tissue disintegration. The release of VOCs, except for 3-methylfuran, was influenced by the initial quality of the leaves. The release of pentane and 2-ethylfuran was related to the degree of tissue disintegration, and the release of dimethyl sulfide and dimethyl disulfide was related to the total aerobic bacteria count. The results demonstrated that VOCs can be used as markers for monitoring the complex quality changes taking place in packaged fresh produce during storage.

Effects of environmental changes, tissue types and reproduction on the emissions of dimethyl sulfide from seaweeds that form green tides

Environmental context Dimethyl sulfide (DMS) is released by marine algae and is important to sulfur transfer between the oceans and the atmosphere. We measured DMS emissions from algae that form large blooms, and found that the hydration of the plants, seawater temperatures and salinity affect DMS release, but their effects were species-specific. Thus, the effect of algal blooms on sulfur transfer will depend on the bloom’s species composition and the environmental conditions experienced by the algae. Abstract Bloom-forming ulvoid macroalgae produce dimethylsulfoniopropionate (DMSP), which when cleaved in response to biotic and abiotic stresses results in the emission of dimethyl sulfide (DMS) into the atmosphere. We quantified DMS emission rates from three intertidal seaweeds (Ulva intestinalis, Ulva lactuca and Ulvaria obscura) that form green tide blooms in the Salish Sea. The algae were subjected to different salinities (freshwater to seawater), temperatures (15 to 35°C) and desiccation levels, and DMS emission rates were measured. We also quantified tissue DMSP concentrations and DMS emissions by different life history stages of U. intestinalis. All three species had significantly higher emission rates if the plants were dry, relative to damp or submerged plants, with highest emissions in the high intertidal species and lowest emissions in the low intertidal species. Seawater temperature did not affect emission rates by U. intestinalis or U. lactuca, but emission rates by U. obscura were significantly higher at 35°C. Hyposaline conditions also increased emission rates by U. obscura and U. lactuca but had no effect on emission by U. intestinalis. DMSP concentrations did not differ in sporophytes and gametophytes, but were twice as high in the tips as the bases of sporophytes. Most spores were released from the tips of the blades. Spores had average DMSP concentrations of 258±114 fmol spore–1. Our results demonstrate that the amounts of DMS emitted by green tides will depend on the bloom’s species composition and the environmental conditions experienced by the algae.

Physical and biological controls on DMS,P dynamics in ice shelf-influenced fast ice during a winter-spring and a spring-summer transitions

We report the seasonal and vertical variations of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) in fast ice at Cape Evans, McMurdo Sound (Antarctica) during the spring-summer transition in 2011 and winter-spring transition in 2012. We compare the variations of DMS,P observed to the seasonal evolution of the ice algal biomass and of the physical properties of the ice cover, with emphasis on the ice texture and brine dynamics. Isolated DMS and DMSP maxima were found during both seasonal episodes in interior ice and corresponded to the occurrence of platelet crystals in the ice texture. We show that platelet crystals formation corresponded in time and depth to the incorporation of dinoflagellates (strong DMSP producers) in the ice cover. We also show that platelet crystals could modify the environmental stresses on algal cells and perturb the vertical redistribution of DMS,P concentrations. We show that during the winter-spring transition in 2012, the DMS,P profiles were strongly influenced by the development and decline of a diatom-dominated bloom in the bottom ice, with DMSP variations remarkably following chl a variations. During the spring-summer transition in 2011, the increase in brine volume fraction (influencing ice permeability) on warming was shown to trigger (1) an important release of DMS to the under-ice water through brine convection and (2) a vertical redistribution of DMSP across the ice.

A mechanistic explanation of the Sargasso Sea DMS “summer paradox”

In the Sargasso Sea, maximum dimethylsulfide (DMS) accumulation occurs in summer, concomitant with the minimum of chlorophyll and 2 months later than its precursor, dimethylsulfoniopropionate (DMSP). This phenomenon is often referred to as the DMS “summer paradox”. It has been previously suggested that the main agent triggering this pattern is increasing irradiance leading to light stress-induced DMS release from phytoplankton cells. We have developed a new model describing DMS(P) dynamics in the water column and used it to investigate how and to what extent processes other than light induced DMS exudation from phytoplankton, may contribute to the DMS summer paradox. To do this, we have conceptually divided the DMS “summer paradox” into two components: (1) the temporal decoupling between chlorophyll and DMSP and (2) the temporal decoupling between DMSP and DMS. Our results suggest that it is possible to explain the above cited patterns by means of two different dynamics, respectively: (1) a succession of phytoplankton types in the surface water and (2) the bacterially mediated DMSP(d) to DMS conversion, seasonally varying as a function of nutrient limitation. This work differs from previous modelling studies in that the presented model suggests that phytoplankton light-stress induced processes may only partially explain the summer paradox, not being able to explain the decoupling between DMSP and DMS, which is possibly the more challenging aspect of this phenomenon. Our study, therefore, provides an “alternative” explanation to the summer paradox further underlining the major role that bacteria potentially play in DMS production and fate.

Production of DMS and DMSP in different physiological stages and salinity conditions in two marine algae

Dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) production by Scrippsiella trochoidea and Prorocentrum minimum was investigated to characterize the effects of physiological stage and salinity on DMS and DMSP pools of these two marine phytoplankton species. Axenic laboratory cultures of the two marine algae were tested for DMSP production and its conversion into DMS. The results demonstrated that both algal species could produce DMS, but the average concentration of DMS per cell in S. trochoidea (12.63 fmol/L) was about six times that in P. minimum (2.01 fmol/L). DMS and DMSP concentrations in algal cultures varied significantly at different growth stages, with high release during the late stationary growth phase and the senescent phase. DMS production induced by three salinities (22, 28, 34) showed that the DMS concentrations per cell in the two algal cultures increased with increasing salinity, which might result from intra-cellular DMSP up-regulation with the change of osmotic stress. Our study specifies the distinctive contributions of different physiological stages of marine phytoplankton on DMSP and DMS production, and clarifies the influence of salinity conditions on the release of DMS and DMSP. As S. trochoidea and P. minimum are harmful algal bloom species with high DMS production, they might play an additional significant role in the sulfur cycle when a red tide occurs.

Bacterial Catabolism of Dimethylsulfoniopropionate (DMSP)

Dimethylsulfoniopropionate (DMSP) is a metabolite produced primarily by marine phytoplankton and is the main precursor to the climatically important gas dimethylsulfide (DMS). DMS is released upon bacterial catabolism of DMSP, but it is not the only possible fate of DMSP sulfur. An alternative demethylation/demethiolation pathway results in the eventual release of methanethiol, a highly reactive volatile sulfur compound that contributes little to the atmospheric sulfur flux. The activity of these pathways control the natural flux of sulfur released to the atmosphere. Although these biochemical pathways and the factors that regulate them are of great interest, they are poorly understood. Only recently have some of the genes and pathways responsible for DMSP catabolism been elucidated. Thus far, six different enzymes have been identified that catalyze the cleavage of DMSP, resulting in the release of DMS. In addition, five of these enzymes appear to produce acrylate, while one produces 3-hydroxypropionate. In contrast, only one enzyme, designated DmdA, has been identified that catalyzes the demethylation reaction producing methylmercaptopropionate (MMPA). The metabolism of MMPA is performed by a series of three coenzyme-A mediated reactions catalyzed by DmdB, DmdC, and DmdD. Interestingly, Candidatus Pelagibacter ubique, a member of the SAR11 clade of Alphaproteobacteria that is highly abundant in marine surface waters, possessed functional DmdA, DmdB, and DmdC enzymes. Microbially mediated transformations of both DMS and methanethiol are also possible, although many of the biochemical and molecular genetic details are still unknown. This review will focus on the recent discoveries in the biochemical pathways that mineralize and assimilate DMSP carbon and sulfur, as well as the areas for which a comprehensive understanding is still lacking.

Experimental studies on dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) production by four marine microalgae

The production of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) by marine microalgae was investigated to elucidate more on the role of marine phytoplankton in ocean-atmosphere interactions in the global biogeochemical sulfur cycle. Axenic laboratory cultures of four marine microalgae-Isochrysis galbana 8701, Pavlova viridis, Platymonas sp. and Chlorella were tested for DMSP production and conversion into DMS. Among these four microalgae, Isochrysis galbana 8701 and Pavlova viridis are two species of Haptophyta, while Chlorella and Platymonas sp. belong to Chlorophyta. The results demonstrate that the four algae can produce various amounts of DMS(P), and their DMS(P) production was species specific. With similar cell size, more DMS was released by Haptophyta than that by Chlorophyta. DMS and dissolved DMSP (DMSPd) concentrations in algal cultures varied significantly during their life cycles. The highest release of DMS appeared in the senescent period for all the four algae. Variations in DMSP concentrations were in strong compliance with variations in algal cell densities during the growing period. A highly significant correlation was observed between the DMS and DMSPd concentrations in algal cultures, and there was a time lag for the variation trend of the DMS concentrations as compared with that of the DMSPd. The consistency of variation patterns of DMS and DMSPd implies that the DMSPd produced by phytoplankton cells has a marked effect on the production of DMS. In the present study, the authors’ results specify the significant contribution of the marine phytoplankton to DMS(P) production and the importance of biological control of DMS concentrations in oceanic water.

Dimethyl sulfoniopropionate and dimethyl sulfide production in response to photoinhibition in Emiliania huxleyi

The response in intracellular dimethyl sulfoniopropionate (DMSP) and dissolved DMSP and dimethyl sulfide (DMS) concentrations when Emiliania huxleyi was exposed to acute (1‐h) increases in photon flux densities of photosynthetically active radiation (PAR) and ultraviolet (UV) radiation was examined in cells acclimated to low light (LL, 30 µmol photons m−2 s−1) and high light (HL, 300 vmol photons m−2 s−1). LL‐acclimated cells displayed greater photoinhibition, assessed as a decrease in maximum photochemical efficiency (Fv : Fm). Photoinhibition was increased by exposure to UV wavelengths. LL‐acclimated cells also exhibited more light dissipation through the xanthophyll cycle, evident as changes in de‐epoxidation state. Greater photoinhibition in LL‐acclimated cells corresponded with increased accumulation of DMSP of 21% ± 4% relative to initial concentrations, contrasting with a slight decrease of 5% ± 6% in HL‐acclimated cells. Exposure to UV appeared to decrease the rates of intracellular accumulation of DMSP. Conversely, PAR + UV exposure stimulated the net production of dissolved DMSP and DMS in both HL‐acclimated and LL‐acclimated cultures, compared with high PAR alone. The results indicate a direct link between acute photo‐oxidative stress and DMSP synthesis by E. huxleyi. The physiological basis for increased release of DMSP and DMS from cells due to high PAR + UV exposure is unclear. However, the timescales of changes in intracellular DMSP, dissolved DMSP, and DMS are consistent with variations in light intensity experienced by phytoplankton in a turbulent mixed layer and are similar to rates of change in photosynthetic parameters associated with photoacclimation.

Biological consumption of dimethylsulfide (DMS) and its importance in DMS dynamics in the Ross Sea, Antarctica

We studied the biological consumption of dimethylsulfide (DMS) and its role in controlling DMS concentrations in the Ross Sea, Antarctica, during the spring (Nov) and summer (Jan) of 2005. Surface DMS concentrations, measured with a technique that minimized DMS release from Phaeocystis antarctica, increased rapidly in the spring from 0.3 nmol L−1 to 67.7 nmol L−1, paralleling increases in chlorophyll a and bacterial biomass production. Biological DMS consumption (BDMSC) rates were low (0.02 nmol L−1 d−1) at the start of the bloom, but increased to 8.8 nmol L−1 d−1 at the peak of the bloom. Rate constants for BDMSC (kbc) remained relatively low throughout the spring (0.05‐0.21 d−1) and this slow biological turnover contributed to the buildup of DMS during the early bloom. DMS concentrations in the summer (3.2‐16.8 nmol L−1) were much lower than peak springtime concentrations, partly due to the higher BDMSC rate constants (0.22‐0.98 d−1; i.e., faster biological turnover) in the summer. Kinetic analysis suggested that BDMSC rates were nearly saturated at ambient DMS concentrations in the spring but not in summer. BDMSC was mostly carried out in the size fractions ≪1 µm and ≫8 µm, except in the early spring when the ≪1‐µm fraction (likely free‐living bacteria) dominated BDMSC. BDMSC was the main removal pathway for DMS in the surface mixed layer during both the spring and summer, except during the prebloom, when photolysis dominated. BDMSC exerts a major control on DMS concentrations in the Ross Sea throughout the Phaeocystis antarctica bloom.

Major ionic species in size-segregated aerosols and associated gaseous pollutants at a coastal site on the Belgian North Sea

The chemical composition of airborne particulate matter (PM) was studied at a coastal region near De Haan, Belgium, during a winter-spring and a summer campaign in 2006. The major ionic components of size-segregated PM, i.e. NH(4)(+), Na(+), K(+), Mg(2+), Ca(2+), Cl(-), NO(3)(-), and SO(4)(2-), and related gaseous pollutants (SO(2), NO(2), NH(3), HNO(2), and HNO(3)) were monitored on a daily basis. Air mass backward-trajectories aided in evaluating the origin of the diurnal pollution load. This was characterised with high levels of fine secondary inorganic aerosols (NH(4)(+), NO(3)(-), and non-sea-salt SO(4)(2-)) for continental air masses, and sea-salts as the dominant species in coarse maritime aerosols. Seasonal variations in the level of major ionic species were explained by weather conditions and the release of dimethyl sulfide from marine regions. This species was responsible for an increased sea-salt Cl(-) depletion during summer (56%), causing elevated levels of HCl. Neutralisation ratios for the coarse fraction (0.6-0.8) suggested a depleted NH(4)(+) level, while that for the fine fraction (1.1-1.3) had definitely an excess of NH(4)(+), formed by the neutralisation of HCl. The results of factor analysis and the extent of SO(2) oxidation indicated that the major ionic species originated from both local and remote sources, classifying the Belgian coastal region as a combined source-receptor area of air pollution.

A light‐driven, one‐dimensional dimethylsulfide biogeochemical cycling model for the Sargasso Sea

We evaluate the extent to which dimethylsulfide (DMS) cycling in an open‐ocean environment can be constrained and parameterized utilizing emerging evidence for the significant impacts of solar ultraviolet radiation (UVR) on the marine organic sulfur cycle. Using the Dacey et al. (1998) 1992–1994 Sargasso Sea DMS data set, in conjunction with an offline turbulent mixing model, we develop and optimize a light driven, one‐dimensional DMS model for the upper 140 m. The DMS numerical model is primarily diagnostic in that it incorporates observations of bacterial, phytoplankton, physical, and optical quantities concurrently measured as part of the Bermuda Atlantic Time‐series Study (BATS) and Bermuda Bio‐Optical Project (BBOP) programs. With the exception of sea‐to‐air ventilation, each of the sulfur cycling terms is explicitly parameterized or altered by the radiation field. Overall, the model shows considerable skill in capturing the salient features of the DMS distribution, specifically the observed DMS summer paradox whereby peak summer DMS concentrations occur coincident with annual minima in phytoplankton pigment biomass and primary production. The dominant processes controlling the upper‐ocean DMS concentrations are phytoplankton UVR‐induced DMS release superimposed upon more surface oriented processes such as photolysis and sea‐to‐air ventilation. The results also demonstrate that mixing alone is not enough to parameterize DMS distributions in this environment. It is critical to directly parameterize the seasonal changes in the flux and attenuation of solar radiation in the upper water column to describe the DMS distribution with depth and allow for experimentation under a variety of climate change scenarios.