Dimethylsulphoniopropionate Concentrations Research Articles

Variation of biogenic sulphur compounds in the estuarine and coastal waters of Goa, West coast of India

Dimethylsulphide (DMS) originates predominantly from dimethylsulphoniopropionate (DMSP), a metabolite produced by phytoplankton. Through its contribution to the production of new aerosols and cloud condensation nuclei, a high concentration of DMS has the potential to influence the radiation budget of the earth. Estuaries and coastal regions being dynamic may produce significantly high concentrations of DMS and DMSP. The present study aimed to investigate the spatial variation of DMS, its precursor total dimethylsulphoniopropionate (DMSP t ), and its sink total dimethylsulphoxide (DMSO t ) at 7 estuarine locations in 4 rivers and a coastal station in Goa during the North East Monsoon (NEM). Generally, higher concentrations of DMS and DMSP t were observed at the near mouth stations and the coastal station compared to upstream stations. Though a positive correlation was observed between salinity and DMSP t, it was not significant, indicating the involvement of other factors influencing DMSP and DMS concentrations. Diatoms were the most abundant group accounting for > 90 % of the phytoplankton. However, higher fractions of dinoflagellates, nano- and picoplankton probably contributed to the DMSP t , DMS and DMSO t production at the coastal and near mouth stations. As the wind speeds were low, DMS flux was governed by surface DMS concentrations and varied between 0.07 and 2.11 µmoles S m -2 D -1 with an average of 0.92±0.80 µmoles S m -2 D -1 . In comparison to DMSP t and DMS, a relatively higher concentration of DMSO t was observed in the study area. While the high DMSO t concentration at the estuarine mouths may be attributed to the photo- or biological oxidation of DMS, those in the upper reaches point to an unknown source and warrants further investigation.

Different dimethylsulphoniopropionate-producing ability of dinoflagellates could affect the structure of their associated bacterial community

Dinoflagellate plays an important role in the production of dimethylsulphoniopropionate (DMSP) in marine ecosystem. DMSP derived from dinoflagellates is an important reducing sulfur and carbon source for heterotrophic bacterioplankton. Although dinoflagellates have outstanding ability in DMSP biosynthesis, and the inter-specific variation of cellular DMSP concentrations in different species and strains has been well described, the effects of DMSP level on microbial community structure are still unclear. In this study, the ability of seven dinoflagellates to synthesize DMSP and their effects on the composition of associated bacterial community were investigated. Total concentration of DMSP (2397.25 ± 187.17 μM) and single cell DMSP content (34.25 ± 2.67 pmol cell−1) were the highest in Protoceratium reticulatum, while the DMSP contents of Prorocentrum texanum and Amphidinium carterae were significantly lower than those of other dinoflagellates. Bacterial community structure in dinoflagellate culture was determined by cultivation-dependent and cultivation-independent approaches. There were significantly differences in the richness and diversity of bacteria in different dinoflagellate cultures with different DMSP contents. In addition, abundant of Roseobacter-clade bacteria (well-known DMSP degraders) were found in the cultures of six dinoflagellates. Genomic analysis indicated that the Roseobacter-clade bacteria isolated from dinoflagellate could degrade DMSP by cleavage pathway. The results demonstrated that DMSP could be an important factor affecting the abundance and composition of bacterial community in phycosphere of dinoflagellates.

Emissions of biogenic sulfur compounds and their regulation by nutrients during an Ulva prolifera bloom in the Yellow Sea

Three cruises were conducted during an Ulva prolifera bloom in 2018 off the Qingdao coast to observe early-, late-, and after-bloom characteristics. Spatio-temporal changes in dimethylsulfide (DMS), dimethylsulphoniopropionate (DMSP), and acrylic acid (AA) and their relationships with environmental parameters were examined. Mesocosm experiments tested the effect of nutrient on the release of biogenic sulfur compounds during the decline period. Biogenic sulfur concentrations contrasted with those in non-bloom regions and reached their highest values during the late-bloom period. The average sea-to-air DMS flux was about 5 times higher than those of non-bloom regions. The mean concentrations of DMS and DMSP in the enclosures were 3–5 times those of in-situ seawater. Biogenic sulfur release was promoted by the addition of high concentrations of nutrients as U. prolifera was declining. The contribution of the U. prolifera bloom to atmospheric DMS was estimated to be 125 kg S d−1.

Modified VG-CL Detection System for Baseline Assessment of Dimethylsulphide and Dimethylsulphoniopropionate in Tropical Atlantic Seawater

Several studies have been carried out to measure the concentrations of dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP) in coastal and open marine ecosystems. The present study attempted the fabrication of a cost-effective, highly sensitive and portable detection system based on vapour generation and chemiluminescence for a pilot assessment and determination of DMS and DMSP concentrations in tropical Atlantic seawater samples. The Sultan Beach and Badagry parts of the Atlantic Ocean were chosen as designated locations for this study. Vapour generation chemiluminescence (VG-CL) detection system is a device that can measure the concentration (nM) of DMS and DMSP by allowing DMS vapour which in turn reacts with ozone to produce chemiluminescence which can be detected by a photomultiplier (PMT). The mean concentrations of DMS and DMSP in the surface seawater at the sampling location were 5.80±0.71 to 19.40±0.57 nM and 11.00±0.42 to 34.70±1.13 nM, respectively. The average minimum and maximum concentrations of DMS and DMSP across the location were between 0 and 40.91 nM, respectively. This study serves as a baseline measurement of DMS concentrations in the tropical Atlantic Ocean (Lagos).

Field Assessment and determination of concentration levels of Dimethylsulphide in Tropical Seawater

Dimethylsulphide (DMS) is an important climatically reactive trace gas which is emitted from the seawater to the atmosphere. It undergoes various oxidative reactions to produce cloud condensation nuclei, which affect the earth radiation budget. DMS and its precursor dimethylsulphoniopropionate (DMSP) were measured using a modified vapour generation – chemiluminescence (VG-CL) detection system that was designed for this study. The chosen sampling locations used for the measurement were Nigeria Institute of oceanography and marine research (NIOMR) and ELEGUSHI. They are situated along the Gulf of Guinea. The modified VG-CL analyser was used for trace analysis of dimethylsulphide in the study area. The mean concentrations of DMS in the surface seawater at the two sampling locations ranged from 0 to 35.53±2.34 nM, 10.67±0.28 and 44.95±0.27 nM, respectively. The average minimum and maximum concentrations of DMS and DMSP across the two locations were between 0 and 44.95 nM, respectively. The concentrations of DMS and DMSP were compared across the sampling locations, and the observed pattern showed that DMS for ELEGUSHI has a higher concentration than NIOMR. The result further revealed that the concentration of the DMS is a function of the sea surface temperature (SST) of the aquatic ecosystem. The observed DMS concentration data of this study provides a baseline measurement for the tropical Atlantic Ocean (Lagos), thus a significant addition to the global DMS database.

Soft corals are significant DMSP producers in tropical and temperate reefs

Corals synthesise large quantities of the sulphur metabolite dimethylsulphoniopropionate (DMSP), which contributes to key roles in coral reef ecology including the capacity of corals to withstand various stressors. While closely related to scleractinian corals and often occupying similar ecological niche space, it is currently poorly defined to what extent soft corals produce DMSP. We, therefore, examined DMSP content within four key species of soft coral in February and July–August of 2017, including two temperate species from Sydney Harbour (Erythropodium hicksoni, Capnella gaboensis) and two tropical species from the Great Barrier Reef (Sinularia sp., Sarcophyton sp.). We compared DMSP content of these soft coral species to that of commonly occurring temperate (Plesiastrea versipora) and tropical (Acropora aspera) scleractinian coral species. DMSP content was normalised to coral protein content, with soft coral DMSP content highly variable across species and locations [56–539 nmol (mg protein)−1], and lower than for the tropical [1242–4710 nmol (mg protein)−1], but not temperate [465–1984 nmol (mg protein)−1] scleractinian species. Further comparison with previously published values demonstrated that soft coral DMSP content falls within the “low–mid range” of scleractinian corals. Notably, DMSP content was also higher in summer samples than winter samples for the scleractinian corals, but did not differ between seasons for soft corals. Such contrasting dynamics of DMSP production by soft corals compared to scleractinian corals indicates that the regulation of DMSP content differs between these two important benthic cnidarian groups, potentially as a consequence of dissimilar ecophysiological roles for this compound.

Moderate Drought Stress Induces Increased Foliar Dimethylsulphoniopropionate (DMSP) Concentration and Isoprene Emission in Two Contrasting Ecotypes of Arundo donax.

The function of dimethylsulphoniopropionate (DMSP) in plants is unclear. It has been proposed as an antioxidant, osmolyte and overflow for excess energy under stress conditions. The formation of DMSP is part of the methionine (MET) pathway that is involved in plant stress responses. We used a new analytical approach to accurately quantify the changes in DMSP concentration that occurred in two ecotypes of the biomass crop Arundo donax subject to moderate drought stress under field conditions. The ecotypes of A. donax were from a hot semi-arid habitat in Morocco and a warm-humid environment in Central Italy. The Moroccan ecotype showed more pronounced reductions in photosynthesis, stomatal conductance and photochemical electron transport than the Italian ecotype. An increase in isoprene emission occurred in both ecotypes alongside enhanced foliar concentrations of DMSP, indicative of a protective function of these two metabolites in the amelioration of the deleterious effects of excess energy and oxidative stress. This is consistent with the modification of carbon within the methyl-erythritol and MET pathways responsible for increased synthesis of isoprene and DMSP under moderate drought. The results of this study indicate that DMSP is an important adaptive component of the stress response regulated via the MET pathway in A. donax. DMSP is likely a multifunctional molecule playing a number of roles in the response of A. donax to reduced water availability.

Symbiosis-specific changes in dimethylsulphoniopropionate concentrations in Stylophora pistillata along a depth gradient

Scleractinian corals are prolific producers of dimethylsulphoniopropionate (DMSP), but ecophysiological mechanisms influencing cellular concentrations are uncertain. While DMSP is often proposed to function as an antioxidant, interactions between specific host–symbiont genotype associations, plasticity in DMSP concentrations and environmental conditions that can either exert or alleviate oxidative stress are unclear. We used long-term (6 months) reciprocal transplantation of Stylophora pistillata hosting two distinct symbiont phylotypes along a depth gradient, clades A ( 20 m), to assess the effect of change in depth (light intensity) on DMSP concentrations in relation to symbiont genotype and photoacclimation in corals between 3 and 50 m in the Gulf of Aqaba. Bathymetric distribution of total DMSP (DMSPt) per cell varied significantly while particulate DMSP (DMSPp) appeared to be unaffected by depth. Highest DMSPt concentrations in control corals occurred at 20 m. While 3-m transplants showed a significant increase in DMSPt concentration at 20 m and became affiliated with an additional genotype (C72), 50-m transplants largely persisted with their original genotype and exhibited no significant changes in DMSPt concentrations. DMSPt concentrations in transplants at both 3 and 50 m, on the other hand, increased significantly while all corals maintained their original symbiont genotypes. Photoacclimation differed significantly with transplantation direction relative to the controls. Symbionts in 3-m transplants at 20 m exhibited no changes in chlorophyll a (chl a) concentration, cell density or cell diameter while symbiont densities decreased and chl a concentrations increased significantly at 50 m. In contrast, symbiont densities in 50-m transplants remained unaffected across depths while symbiont diameters decreased. Chl a concentrations decreased at 20 m and increased at 3 m. Our results indicate that DMSPt concentrations following changes in depth are not only a function of symbiont genotype but result from different acclimation abilities of both symbiotic partners.

Dimethylsulphoniopropionate (DMSP) as an Indicator of Bleaching Tolerance in Scleractinian Corals

Thermal tolerance tests on Acropora millepora, a common Indo-Pacific hard coral, have shown that adult corals can acquire increased thermal tolerance by shuffling existing type C to type D Symbiodinium zooxanthellae when subjected to increased seawater temperatures. We report here dimethylsulphoniopropionate (DMSP) concentrations in A. millepora and examine links between DMSP concentrations, zooxanthellae clade, and bleaching tolerance. DMSP analysis on native and transplanted corals from three locations in the Great Barrier Reef indicated that the lower thermal tolerance in type C zooxanthellae coincided with variable DMSP concentrations, whilst the more thermal tolerant type D zooxanthellae had more stable areal DMSP concentrations as seawater temperatures increased. Our results suggest this increased thermal tolerance in type D zooxanthellae may reflect the ability of these coral symbionts to conserve their antioxidant DMSP levels to relatively constant concentrations, enabling the coral to overcome the build-up of oxygen free radicals in the cytoplasm of A. millepora. A conceptual diagram illustrates how the antioxidants DMS (P) participate in the bleaching process by scavenging oxygen free radicals and form DMSO, thus moderating coral bleaching and increasing thermotolerance.

Two intertidal, non-calcifying macroalgae (Palmaria palmata and Saccharina latissima) show complex and variable responses to short-term CO2 acidification

Abstract Ocean acidification, the result of increased dissolution of carbon dioxide (CO2) in seawater, is a leading subject of current research. The effects of acidification on non-calcifying macroalgae are, however, still unclear. The current study reports two 1-month studies using two different macroalgae, the red alga Palmaria palmata (Rhodophyta) and the kelp Saccharina latissima (Phaeophyta), exposed to control (pHNBS = ∼8.04) and increased (pHNBS = ∼7.82) levels of CO2-induced seawater acidification. The impacts of both increased acidification and time of exposure on net primary production (NPP), respiration (R), dimethylsulphoniopropionate (DMSP) concentrations, and algal growth have been assessed. In P. palmata, although NPP significantly increased during the testing period, it significantly decreased with acidification, whereas R showed a significant decrease with acidification only. S. latissima significantly increased NPP with acidification but not with time, and significantly increased R with both acidification and time, suggesting a concomitant increase in gross primary production. The DMSP concentrations of both species remained unchanged by either acidification or through time during the experimental period. In contrast, algal growth differed markedly between the two experiments, in that P. palmata showed very little growth throughout the experiment, while S. latissima showed substantial growth during the course of the study, with the latter showing a significant difference between the acidified and control treatments. These two experiments suggest that the study species used here were resistant to a short-term exposure to ocean acidification, with some of the differences seen between species possibly linked to different nutrient concentrations between the experiments.

Dimethylsulphoxide (DMSO) in biological samples: A comparison of the TiCl3 and NaBH4 reduction methods using headspace analysis

Dimethylsulphoxide (DMSO) is a sulphur compound that can result from the oxidation of biogenic dimethylsulphide (DMS) in marine algae and bacteria; with dimethylsulphoniopropionate (DMSP) being the main precursor of DMS. The two most commonly used methods for the analysis of DMSO in seawater and biological samples consist of its chemical reduction to DMS by either titanium trichloride (TiCl3) or sodium borohydride (NaBH4), with subsequent measurement of derived DMS by gas chromatography. Here, these two methods have been compared for the quantitative analysis of DMSO in the zooxanthellate coral Acropora aspera and in two species of marine algae (Ulva intestinalis and Ulva lactuca) using headspace analysis on DMSO-derived DMS. Reduction by NaBH4 or TiCl3 in biological samples yielded highly linear calibrations (R2≥0.99) and excellent repeatability (RSD=6.17% and 4.32% for TiCl3 and NaBH4 respectively, n=10). In coral samples, although a strong linear correlation was generally obtained between the two reduction methods (R2=0.8464, p<0.001, n=72), the regression slope of 0.6 indicated that DMSO concentrations were either underestimated with NaBH4 reduction or overestimated with TiCl3. Reduction with TiCl3 yielded lower values than NaBH4 at DMSO concentrations <0.6μM, whereas TiCl3 gave higher values than NaBH4 when DMSO was >2μM. The reasons for these significant differences remain unclear at this stage and we therefore cannot draw conclusions on the preferential suitability of one reducing agent over the other for coral DMSO analysis. In macroalgae samples, significantly lower DMSO concentrations were obtained with NaBH4 than with TiCl3 for DMSO concentrations averaging 0.6μM and 0.8μM for U. intestinalis and U. lactuca respectively. The difference between reduction methods in the analysis of DMSO across macroalgae and coral samples was interpreted as a difference in taxa or in sample preparation, although this needs to be further investigated. Corals were found to contain more DMSO than macroalgae with similar DMSP concentrations.

Insights into the regulation of DMSP synthesis in the diatom Thalassiosira pseudonana through APR activity, proteomics and gene expression analyses on cells acclimating to changes in salinity, light and nitrogen.

Despite the importance of dimethylsulphoniopropionate (DMSP) in the global sulphur cycle and climate regulation, the biological pathways underpinning its synthesis in marine phytoplankton remain poorly understood. The intracellular concentration of DMSP increases with increased salinity, increased light intensity and nitrogen starvation in the diatom Thalassiosira pseudonana. We used these conditions to investigate DMSP synthesis at the cellular level via analysis of enzyme activity, gene expression and proteome comparison. The activity of the key sulphur assimilatory enzyme, adenosine 5′-phosphosulphate reductase was not coordinated with increasing intracellular DMSP concentration. Under all three treatments coordination in the expression of sulphur assimilation genes was limited to increases in sulphite reductase transcripts. Similarly, proteomic 2D gel analysis only revealed an increase in phosphoenolpyruvate carboxylase following increases in DMSP concentration. Our findings suggest that increased sulphur assimilation might not be required for increased DMSP synthesis, instead the availability of carbon and nitrogen substrates may be important in the regulation of this pathway. This contrasts with the regulation of sulphur metabolism in higher plants, which generally involves up-regulation of several sulphur assimilatory enzymes. In T. pseudonana changes relating to sulphur metabolism were specific to the individual treatments and, given that little coordination was seen in transcript and protein responses across the three growth conditions, different patterns of regulation might be responsible for the increase in DMSP concentration seen under each treatment.

Dynamic photoinhibition exhibited by red coralline algae in the Red Sea.

BackgroundRed coralline algae are critical components of tropical reef systems, and their success and development is, at least in part, dependent on photosynthesis. However, natural variability in the photosynthetic characteristics of red coralline algae is poorly understood. This study investigated diurnal variability in encrusting Porolithon sp. and free-living Lithophyllum kotschyanum. Measured parameters included: photosynthetic characteristics, pigment composition, thallus reflectance and intracellular concentrations of dimethylsulphoniopropionate (DMSP), an algal antioxidant that is derived from methionine, an indirect product of photosynthesis. L. kotschyanum thalli were characterised by a bleached topside and a pigmented underside.ResultsMinimum saturation intensity and intracellular DMSP concentrations in Porolithon sp. were characterised by significant diurnal patterns in response to the high-light regime. A smaller diurnal pattern in minimum saturation intensity in the topside of L. kotschyanum was also evident. The overall reflectance of the topside of L. kotschyanum also exhibited a diurnal pattern, becoming increasingly reflective with increasing ambient irradiance. The underside of L. kotschyanum, which is shaded from ambient light exposure, exhibited a much smaller diurnal variability.ConclusionsThis study highlights a number of dynamic photoinhibition strategies adopted by coralline algae, enabling them to tolerate, rather than be inhibited by, the naturally high irradiance of tropical reef systems; a factor that may become more important in the future under global change projections. In this context, this research has significant implications for tropical reef management planning and conservation monitoring, which, if natural variability is not taken into account, may become flawed. The information provided by this research may be used to inform future investigations into the contribution of coralline algae to reef accretion, ecosystem service provision and palaeoenvironmental reconstruction.

Sulphur compounds, methane, and phytoplankton: interactions along a north–south transit in the western Pacific Ocean

Abstract. Here we present results of the first comprehensive study of sulphur compounds and methane in the oligotrophic tropical western Pacific Ocean. The concentrations of dimethylsuphide (DMS), dimethylsulphoniopropionate (DMSP), dimethylsulphoxide (DMSO), and methane (CH4), as well as various phytoplankton marker pigments in the surface ocean were measured along a north–south transit from Japan to Australia in October 2009. DMS (0.9 nmol L−1), dissolved DMSP (DMSPd, 1.6 nmol L−1) and particulate DMSP (DMSPp, 2 nmol L−1) concentrations were generally low, while dissolved DMSO (DMSOd, 4.4 nmol L−1) and particulate DMSO (DMSOp, 11.5 nmol L−1) concentrations were comparably enhanced. Positive correlations were found between DMSO and DMSP as well as DMSP and DMSO with chlorophyll a, which suggests a similar source for both compounds. Similar phytoplankton groups were identified as being important for the DMSO and DMSP pool, thus, the same algae taxa might produce both DMSP and DMSO. In contrast, phytoplankton seemed to play only a minor role for the DMS distribution in the western Pacific Ocean. The observed DMSPp : DMSOp ratios were very low and seem to be characteristic of oligotrophic tropical waters representing the extreme endpoint of the global DMSPp : DMSOp ratio vs SST relationship. It is most likely that nutrient limitation and oxidative stress in the tropical western Pacific Ocean triggered enhanced DMSO production leading to an accumulation of DMSO in the sea surface. Positive correlations between DMSPd and CH4, as well as between DMSO (particulate and total) and CH4, were found along the transit. We conclude that DMSP and DMSO and/or their degradation products might serve as potential substrates for CH4 production in the oxic surface layer of the western Pacific Ocean.

Contrasting responses of DMS and DMSP to ocean acidification in Arctic waters

Abstract. Increasing atmospheric CO2 is decreasing ocean pH most rapidly in colder regions such as the Arctic. As a component of the EPOCA (European Project on Ocean Acidification) pelagic mesocosm experiment off Spitzbergen in 2010, we examined the consequences of decreased pH and increased pCO2 on the concentrations of dimethylsulphide (DMS). DMS is an important reactant and contributor to aerosol formation and growth in the Arctic troposphere. In the nine mesocosms with initial pHT 8.3 to 7.5, equivalent to pCO2 of 180 to 1420 μatm, highly significant but inverse responses to acidity (hydrogen ion concentration [H&amp;amp;plus;]) occurred following nutrient addition. Compared to ambient [H&amp;amp;plus;], average concentrations of DMS during the mid-phase of the 30 d experiment, when the influence of altered acidity was unambiguous, were reduced by approximately 60% at the highest [H&amp;amp;plus;] and by 35% at [H&amp;amp;plus;] equivalent to 750 μatm pCO2, as projected for 2100. In contrast, concentrations of dimethylsulphoniopropionate (DMSP), the precursor of DMS, were elevated by approximately 50% at the highest [H&amp;amp;plus;] and by 30% at [H&amp;amp;plus;] corresponding to 750 μatm pCO2. Measurements of the specific rate of synthesis of DMSP by phytoplankton indicate increased production at high [H&amp;amp;plus;], in parallel to rates of inorganic carbon fixation. The elevated DMSP production at high [H&amp;amp;plus;] was largely a consequence of increased dinoflagellate biomass and in particular, the increased abundance of the species Heterocapsa rotundata. We discuss both phytoplankton and bacterial processes that may explain the reduced ratios of DMS:DMSPt (total dimethylsulphoniopropionate) at higher [H&amp;amp;plus;]. The experimental design of eight treatment levels provides comparatively robust empirical relationships of DMS and DMSP concentration, DMSP production and dinoflagellate biomass versus [H&amp;amp;plus;] in Arctic waters.

DMS flux over the Antarctic sea ice zone

This study presents concentrations of dimethylsulphide (DMS) and its precursor compound dimethylsulphoniopropionate (DMSP), and chlorophyll a in a variety of sea ice and seawater habitats from pack and fast ice in the Antarctic sea ice zone (ASIZ) of eastern Antarctica. Estimated “hot spot” seawater DMS concentrations released during sea ice melting in October and derived from a total DMSP (DMSPt)-sea ice depth relationship and application of a DMSPt:DMS conversion ratio, predict that sea ice derived DMS of the order of 20–50nM is associated with DMSPt released from melting sea ice of 0.4m thickness. In November and December, melting of large areas of ice less than 0.6m thick could release larger amounts of DMS around 50–80nM and 150–270nM, respectively. In addition, DMSPt released from 1.0 to 1.2m thick ice in December could result in “hot spot” concentrations of DMS of around 100nM. DMS flux in November and mid to late December was highest in pack ice>fast ice>ice edge (pack ice=54μmolm−2d−1; (range 1–325); fast ice=16μmolm−2d−1; (range 10–50); ice edge=12 (range 1.2–26) and 23μmolm−2d−1). In ice-free seawater in the Davis area from January to February, although dissolved DMS concentrations were low, DMS fluxes were high due to high wind speeds (DMS=3nM; DMS flux=27μmolm−2d−1 (range 1–101)). DMS concentrations and flux from a fast ice tide crack (DMS=12nM; DMS flux 6–81μmolm−2d−1), and two days following fast ice breakout from the Davis region DMS concentrations (12nM) and DMS flux (45–84μmolm−2d−1) also indicated that fast ice was a significant source of DMS to the atmosphere of this region. In contrast DMS flux from a fast ice melt-pool was low (DMS flux 0.5–7μmolm−2d−1). These measurements support the suggestion that during sea ice melting during late spring to early summer (November–December), the ASIZ is an area of high DMS (P) production from various sources, leading to very high and variable fluxes of DMS to the atmosphere of this region. As sea ice melts in late November voids in sea ice become larger enabling sea ice to vent DMS directly to the atmosphere, as well as being released from sea ice melting. At most sea ice sites DMS often displayed non-detectable to elevated concentrations of DMS (mean 11nM) in the surface 0–0.1m. Using average DMS concentrations from a range of studies we estimate that DMS flux from ASIZ in November is about 23μmolm−2d−1, much lower than what we have estimated from pack ice using a DMSPt:DMS conversion ratio technique (54μmolm−2d−1). The difference (31μmolm−2d−1) could reflect venting or degassing of DMS directly from pack ice to the Antarctic atmosphere. Depth-integrated sea ice DMS concentrations varied with time of day, with elevated DMS concentrations (18–30nM) in the cores during the later part of the day (i.e. 16.00–20.00h), whilst close to mid-day (11.00–12.00h) concentrations were much lower (2–9nM). The lower depth-integrated DMS concentrations found in pack ice in November could suggest that large amounts of DMS are vented from pack ice close to mid-day when temperatures and wind speeds often increase. Varying DMSPt–chlorophyll a correlations in the sea ice highlight how varying biological activity affects DMSP concentrations, and suggest that variations in biological activity in sea ice also influence DMS flux.

Atmospheric dimethysulphide production from corals in the Great Barrier Reef and links to solar radiation, climate and coral bleaching

Coral zooxanthellae contain high concentrations of dimethylsulphoniopropionate (DMSP), the precursor of dimethylsulphide (DMS), an aerosol substance that could affect cloud cover, solar radiation and ocean temperatures. Acropora intermedia a dominant staghorn coral in the Indo-Pacific region, contain some of the highest concentrations of DMSP reported in the literature but no studies have shown that corals produce atmospheric DMS in situ and thus could potentially participate in sea surface temperature (SST) regulation over reefs; or how production varies during coral bleaching. We show that A. intermedia from the Great Barrier Reef (GBR) produces significant amounts of atmospheric DMS, in chamber experiments, indicating that coral reefs in this region could contribute to an “ocean thermostat” similar to that described for the western Pacific warm pool, where significantly fewer coral reefs have bleached during the last 25 years because of a cloud-SST feedback. However, when Acropora intermedia was stressed with higher light levels and seawater temperatures DMSP production, an indicator of zooxanthellae expulsion, increased markedly in the chamber, whilst atmospheric DMS emissions almost completely shut down. These results suggest that during increased light levels and seawater temperatures in the GBR coral shut-down atmospheric DMS aerosol production, potentially increasing solar radiation levels over reefs and exacerbating coral bleaching.

Concentrations of dimethylsulphoniopropionate and activities of dimethylsulphide-producing enzymes in batch cultures of nine dinoflagellate species

Dinoflagellates are recognised as one of the major phytoplankton groups that produce dimethylsulphoniopropionate (DMSP), the precursor of the marine trace gas dimethylsulphide (DMS) which has climate-cooling potential. To improve the prospects for including dinoflagellates in global climate models that include DMSP-related processes, we increased the data base for this group by measuring DMSP, DMS-producing enzyme activity (DPEA), carbon, nitrogen and Chl a in nine clonal dinoflagellate cultures (1 heterotrophic and 8 phototrophic strains). Growth rates ranged from 0.11 to 1.92 day−1 with the highest value being for the heterotroph Crypthecodinium cohnii. Overall, we observed two orders of magnitude variability in DMSP content (11–364 mM) and detected DPEA in five of the nine strains (0.61–59.73 fmol cell−1 h−1). Cell volume varied between 454 and 18,439 μm3 and whilst C and N content were proportional to the cell volume, DMSP content was not. The first DMSP measurements for a dinoflagellate from Antarctic waters and a species with diatom-like plastids are included. Lower DMSP concentrations were found in three small athecate species and a dinoflagellate with haptophyte-like plastids. The highest concentrations and production rates tended to be in globally distributed dinoflagellates and the heterotroph. Photosynthetic species that are distributed in temperate to tropical waters showed low DMSP concentrations and production rates and the polar representative showed moderate concentration and a low production rate. Estuarine species had the lowest concentrations and production rates. These data should help refine the inclusion of dinoflagellates as a functional group in future global climate models.

Combining cell sorting with gas chromatography to determine phytoplankton group-specific intracellular dimethylsulphoniopropionate

An approach combining flow-cytometric fluorescence-activated cell sorting (FACS) of specific phytoplankton groups and subsequent quantification of dimethylsulphoniopropionate (DMSP) content by gas chromatography (GC) is introduced and applied to cultivated microalgae and natural seawater samples. The FACS-GC based method produces statistically robust estimates of the intracellular DMSP content of a variety of phytoplankton groups ranging from prokaryotic Synechococcus spp. to eukaryotic nanophytoplankton. Comparison between FACS and traditional filtration approaches to determine intracellular DMSP content of cultivated microalgae illustrates variable responses between species to the 2 methods. Natural photosynthetic nanoeukaryote populations contained high intracellular DMSP content; comparable to many cultivated prymnesiophyte taxa. A surprisingly high DMSP content was found in natural populations of Synechococcus spp., in contrast to previous values measured in cultivated strains, but possibly confirming the uptake and retention of DMSP by this photosynthetic prokaryote. When combined, the DMSP contributions of each phytoplankton group amounted to between 40 and 57 % of total DMSP in each water sample, with the bulk of the total comprising nanoeukaryote-DMSP. The approach has high potential to provide information that enables better parameterisation of phytoplankton functional types in mechanistic dimethyl sulphide models and to help elucidate the environmental controls that govern the extent and diversity of DMSP production in the oceans.

Dimethylsulphoniopropionate (DMSP), DMSP-lyase activity (DLA) and dimethylsulphide (DMS) in 10 species of coccolithophore

We investigated dimethylsulphoniopropionate (DMSP) quota (pg DMSP cell(-1)), intracellular DMSP concentration (mM), in vitro and in vivo DMSP-lyase activity (DLA) and dimethylsulphide (DMS) concentration in batch cultures of 10 species of coccolithophore. Species were chosen to span the phylogenetic and size range that exists within the coccolithophores. Our overall objective was to examine if Emiliania huxleyi, considered a `model' coccolithophore species, is representative in terms of DMSP, DLA and DMS, because other coccolithophores contribute substantially to phyto-plankton biomass and carbon fluxes in temperate and tropical waters. DMSP was found in all species, and DMSP quotas correlated significantly with cell volume, reflecting the fundamental physiological role of DMSP as a compatible solute in this group. This DMSP quota-cell volume relationship can be used to calculate the relative contribution of different species to total DMSP. Lowered nutrient availability (batch growth at a 10-fold lower nutrient concentration) did not significantly affect DMSP quota. In contrast to DMSP, DLA and DMS concentration were variable between the subset of species investigated. Coccolithophore DLA is known only in E. huxleyi and Gephyrocapsa oceanica, and we found DLA to be restricted to these closely related species. If DLA is restricted to a subset of coccolithophores, then those species are more likely to emit DMS directly in the sea. Our results indicate that in ecosystems where coccolithophores form stable populations, species other than E. huxleyi can make significant contributions to the particulate DMSP pool and hence to the amount of DMSP potentially available to the microbial loop.