Distribution Of Dimethylsulfide Research Articles

Dimethylsulfide gas transfer coefficients from algal blooms in the Southern Ocean

Abstract. Air–sea dimethylsulfide (DMS) fluxes and bulk air–sea gradients were measured over the Southern Ocean in February–March 2012 during the Surface Ocean Aerosol Production (SOAP) study. The cruise encountered three distinct phytoplankton bloom regions, consisting of two blooms with moderate DMS levels, and a high biomass, dinoflagellate-dominated bloom with high seawater DMS levels (> 15 nM). Gas transfer coefficients were considerably scattered at wind speeds above 5 m s−1. Bin averaging the data resulted in a linear relationship between wind speed and mean gas transfer velocity consistent with that previously observed. However, the wind-speed-binned gas transfer data distribution at all wind speeds is positively skewed. The flux and seawater DMS distributions were also positively skewed, which suggests that eddy covariance-derived gas transfer velocities are consistently influenced by additional, log-normal noise. A flux footprint analysis was conducted during a transect into the prevailing wind and through elevated DMS levels in the dinoflagellate bloom. Accounting for the temporal/spatial separation between flux and seawater concentration significantly reduces the scatter in computed transfer velocity. The SOAP gas transfer velocity data show no obvious modification of the gas transfer–wind speed relationship by biological activity or waves. This study highlights the challenges associated with eddy covariance gas transfer measurements in biologically active and heterogeneous bloom environments.

Small‐scale variability patterns of DMS and phytoplankton in surface waters of the tropical and subtropical Atlantic, Indian, and Pacific Oceans

AbstractHigh‐resolution surface measurements of dimethylsulfide (DMS), chlorophyll a fluorescence, and the efficiency of photosystem II were conducted together with temperature and salinity along five eastward sections in the tropical and subtropical Atlantic, Indian, and Pacific Oceans. Analysis of variability length scales revealed that much of the variability in DMS concentrations occurs at scales between 15 and 50 km, that is, at the lower edge of mesoscale dynamics, decreasing with latitude and productivity. DMS variability was found to be more commonly related to that of phytoplankton‐related variables than to that of physical variables. Unlike phytoplankton physiological data, DMS did not show any universal diel pattern when using the normalized solar zenith angle as a proxy for solar time across latitudes and seasons. The study should help better design sampling and computing schemes aimed at mapping surface DMS and phytoplankton distributions, taking into account latitude and productivity.

Dimethyl sulfide in the Amazon rain forest

AbstractSurface‐to‐atmosphere emissions of dimethyl sulfide (DMS) may impact global climate through the formation of gaseous sulfuric acid, which can yield secondary sulfate aerosols and contribute to new particle formation. While oceans are generally considered the dominant sources of DMS, a shortage of ecosystem observations prevents an accurate analysis of terrestrial DMS sources. Using mass spectrometry, we quantified ambient DMS mixing ratios within and above a primary rainforest ecosystem in the central Amazon Basin in real‐time (2010–2011) and at high vertical resolution (2013–2014). Elevated but highly variable DMS mixing ratios were observed within the canopy, showing clear evidence of a net ecosystem source to the atmosphere during both day and night in both the dry and wet seasons. Periods of high DMS mixing ratios lasting up to 8 h (up to 160 parts per trillion (ppt)) often occurred within the canopy and near the surface during many evenings and nights. Daytime gradients showed mixing ratios (up to 80 ppt) peaking near the top of the canopy as well as near the ground following a rain event. The spatial and temporal distribution of DMS suggests that ambient levels and their potential climatic impacts are dominated by local soil and plant emissions. A soil source was confirmed by measurements of DMS emission fluxes from Amazon soils as a function of temperature and soil moisture. Furthermore, light‐ and temperature‐dependent DMS emissions were measured from seven tropical tree species. Our study has important implications for understanding terrestrial DMS sources and their role in coupled land‐atmosphere climate feedbacks.

Seasonal variation and biogeochemical cycling of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in theYellowSea andBohaiSea

AbstractThe concentrations of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and chlorophylla(Chl‐a) as well as the size distribution of particulate DMSP (DMSPp) were determined in the Yellow Sea (YS) and Bohai Sea (BS) during two cruises from 1 to 20 November 2012 and from 21 June to 11 July 2013. Besides, the biological production and consumption rates of DMS and the degradation rates of dissolved DMSP (DMSPd) were also measured. The concentrations of DMS and DMSP showed a significant seasonal variation with higher values in summer, which corresponded well with the seasonal change of Chl‐ain the study area. Both DMS and DMSPp concentrations were significantly correlated with Chl‐alevels, implying that phytoplankton biomass might play an important role in controlling the distributions of DMS and DMSP in the study area. The size‐fractionation research showed that nanophytoplankton (5–20 μm) contributed to most of Chl‐aand DMSPp in autumn and summer. The average biological production and consumption rates of DMS during summer were 13.35 and 9.80 nmol L−1d−1, respectively, which were much higher than those during autumn. The degradation rates of DMSPd during summer ranged from 7.10 to 21.70 nmol L−1d−1, with an average of 14.71 nmol L−1d−1, which was nearly equal to the average biological production rate (13.35 nmol L−1d−1) of DMS. The average sea‐to‐air flux of DMS in the YS and BS were 12.06 and 20.81 μmol m−2d−1in autumn and in summer, respectively, which were much higher than the values reported in the ocean.

Distribution of dimethylsulfide and dimethylsulfoniopropionate in the Yellow Sea and the East China Sea during spring: Spatio-temporal variability and controlling factors

Spatial distributions of dimethylsulfide (DMS) and total dimethylsulfoniopropionate (DMSP) were determined in the Yellow Sea (YS) and the East China Sea (ECS) during April–May, 2009. The average concentrations of DMS and DMSP in surface water in the study area were 4.91 (1.18–12.6) and 25.2 (5.47–73.7) nmolL−1, respectively. Significant relationships were observed between the sulfur compounds and chlorophyll a concentrations, suggesting that phytoplankton biomass might play an important role in controlling DMS and DMSP distributions in the YS and the ECS. Zooplankton community and complex hydrographic conditions including the Yangtze River effluent and the Kuroshio water might also influence DMS and DMSP spatial variability. The interannual and seasonal variations of DMS distribution were investigated in the study area by comparing the present results with previous data from the past two decades. Collectively these data suggest that more DMS was released after the 2000s likely because of shifts of phytoplankton population caused by the anthropogenic eutrophication in the YS and the ECS. The average flux of DMS from the YS and the ECS to the atmosphere was estimated to be 13.7μmolm−2d−1, implying a significant relative contribution of continental shelf sea areas to global oceanic DMS emissions.

Spatial distribution of pCO2, ΔO2/Ar and dimethylsulfide (DMS) in polynya waters and the sea ice zone of the Amundsen Sea, Antarctica

We report the first simultaneous measurements of surface water pCO2, biological oxygen saturation (ΔO2/Ar) and dimethylsulfide (DMS) concentrations in polynya waters and the sea ice zone of the Amundsen Sea, Antarctica. Across our survey region, we observed large spatial variability in surface water gas concentrations, tied to strong gradients in hydrography and phytoplankton biomass. Variability in sea surface temperature and salinity was attributed to the interacting effects of surface ocean circulation and heat fluxes, sea ice melt and the upwelling of relatively warm, saline and nutrient-rich modified circumpolar deep water. Phytoplankton biomass ranged from <1μgL−1 to ∼40μgL−1 chlorophyll a (Chl a), with the highest values observed in regions of shallow mixed layer depths. Phytoplankton assemblages were dominated by the colonial haptophyte Phaeocystis antarctica at most sampling stations, with lesser abundances of diatoms found throughout the polynya and sea ice zone. Cryptophytes were abundant at a few stations along the continental shelf break. Across the open polynya waters and sea ice zone, ΔO2/Ar ranged from ∼−40% to 40% (mean 8.6%), pCO2 ranged from 80 to 530μatm (mean 250μatm) and DMS concentrations varied from <1nM to ∼350nM. Strong gradients in gas concentrations were observed over short (i.e. <10km) spatial scales. The distribution of pCO2 and ΔO2/Ar across our survey transects reflected the balance between deep water entrainment and net community production, with a significant imprint of air–sea exchange. Chl a concentrations were significantly correlated to both pCO2 and ΔO2/Ar, and the slope of the ΔO2/Ar vs. pCO2 relationship was consistent with photosynthetic stoichiometry (∼1.25molO2 evolved per mol DIC removed). DMS and Chl a concentrations were also correlated in surface waters, but the spatial distribution of DMS was often uncoupled from pCO2 and ΔO2/Ar, likely due to complex microbial cycling processes. Sea surface temperature and salinity were related to surface gas concentrations through their effects on mixed layer depth and as tracers of upwelling. During the time of our cruise, the Amundsen Sea acted as an overall net sink for CO2 (mean sea–air flux=−15.9mmolm−2d−1) and a DMS source (mean sea–air flux=23.1μmolm−2d−1). Sea–air CO2 and DMS fluxes were more than 2-fold higher in open polynya waters relative to the overall cruise means. Simple calculations suggest that the Amundsen Sea contributes ∼5% of total Southern Ocean CO2 fluxes, and ∼1% of DMS fluxes.

Temporal and spatial variations of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in the East China Sea and the Yellow Sea

Temporal and spatial distributions of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) were determined in the East China Sea and the Yellow Sea during June–July, 2006 and January–February, 2007. The concentrations of DMS and total DMSP in surface water in the study area were 5.64 (1.79–12.24) and 28.25 (13.98–44.93) nmol L −1 in summer, and were 1.79 (1.02–3.51) and 11.01 (6.90–17.98) nmol L −1 in winter, respectively. The distributions of DMS and DMSP in the study area were obviously influenced by the Yangtze River effluent and the Kuroshio water. Even under highly variable hydrographic conditions, a significant relationship was observed between DMS and chlorophyll a concentrations in summer as well as in winter, suggesting that phytoplankton biomass might play an important role in controlling DMS distribution in the study area. The summer ratios of DMS/chlorophyll a and DMSP/chlorophyll a were approximately twofold higher than winter values, corresponding with the temporal variation in phytoplankton community structure between summer and winter. The sea-to-air fluxes of DMS were estimated to be 5.32 and 11.92 μmol m −2 d −1 using the equations of Liss and Merlivat (1986) and Wanninkhof (1992), respectively.

Changes in dimethyl sulfide oceanic distribution due to climate change

Dimethyl sulfide (DMS) is one of the major precursors for aerosols and cloud condensation nuclei in the marine boundary layer over much of the remote ocean. Here they report on coupled climate simulations with a state-of-the-art global ocean biogeochemical model for DMS distribution and fluxes using present-day and future atmospheric CO{sub 2} concentrations. They find changes in zonal averaged DMS flux to the atmosphere of over 150% in the Southern Ocean. This is due to concurrent sea ice changes and ocean ecosystem composition shifts caused by changes in temperature, mixing, nutrient, and light regimes. The largest changes occur in a region already sensitive to climate change, so any resultant local CLAW/Gaia feedback of DMS on clouds, and thus radiative forcing, will be particularly important. A comparison of these results to prior studies shows that increasing model complexity is associted with reduced DMS emissions at the equator and increased emissions at high latitudes.

An updated climatology of surface dimethlysulfide concentrations and emission fluxes in the global ocean

[1] The potentially significant role of the biogenic trace gas dimethylsulfide (DMS) in determining the Earth’s radiation budget makes it necessary to accurately reproduce seawater DMS distribution and quantify its global flux across the sea/air interface. Following a threefold increase of data (from 15,000 to over 47,000) in the global surface ocean DMS database over the last decade, new global monthly climatologies of surface ocean DMS concentration and sea‐to‐air emission flux are presented as updates of those constructed 10 years ago. Interpolation/extrapolation techniques were applied to project the discrete concentration data onto a first guess field based on Longhurst’s biogeographic provinces. Further objective analysis allowed us to obtain the final monthly maps. The new climatology projects DMS concentrations typically in the range of 1–7 nM, with higher levels occurring in the high latitudes, and with a general trend toward increasing concentration in summer. The increased size and distribution of the observations in the DMS database have produced in the new climatology substantially lower DMS concentrations in the polar latitudes and generally higher DMS concentrations in regions that were severely undersampled 10 years ago, such as the southern Indian Ocean. Using the new DMS concentration climatology in conjunction with state‐of‐the‐art parameterizations for the sea/air gas transfer velocity and climatological wind fields, we estimate that 28.1 (17.6–34.4) Tg of sulfur are transferred from the oceans into the atmosphere annually in the form of DMS. This represents a global emission increase of 17% with respect to the equivalent calculation using the previous climatology. This new DMS climatology represents a valuable tool for atmospheric chemistry, climate, and Earth System models.

Vertical variability of seawater DMS in the South Pacific Ocean and its implication for atmospheric and surface seawater DMS

Shipboard measurements of atmospheric dimethylsulfide (DMS) and sea surface water DMS were performed aboard the R/V Onnuri across the South Pacific from Santiago, Chile to Fiji in February 2000. Hydrographic profiles of DMS, dissolved dimethylsulfoniopropionate (DMSP d), and particulate DMSP p in the upper 200 m were obtained at 16 stations along the track. Atmospheric and sea surface water DMS concentrations ranged from 3 to 442 pptv and from 0.1 to 19.9 nM, respectively; the mean values of 61 pptv and 2.1 nM, respectively, were comparable to those from previous studies in the South Pacific. The South Pacific Gyre was distinguished by longitudinal-vertical distributions of DMS, DMSP d, and DMSP p, which was thought to be associated with the characteristic modification of biological activities that occurs mainly due to significant change in water temperature. The averaged DMS maximum appeared at 40 m depth, whereas DMSP p and DMSP d maxima coincided with that of dissolved oxygen content at 60–80 m. The sea-to-air fluxes of DMS were estimated to be 0.4–11.3 μmol d −1 m −2 (mean = 2.8 μmol d −1 m −2). A fairly good correlation between atmospheric DMS and sea-to-air DMS flux indicated that atmospheric DMS concentration was more sensitive to change in physical parameters than its photochemical removal process or surface seawater DMS concentrations.

Equilibrator Inlet-Proton Transfer Reaction-Mass Spectrometry (EI-PTR-MS) for Sensitive, High-Resolution Measurement of Dimethyl Sulfide Dissolved in Seawater

We developed an equilibrator inlet-proton transfer reaction-mass spectrometry (EI-PTR-MS) method for fast detection of dimethyl sulfide (DMS) dissolved in seawater. Dissolved DMS extracted by bubbling pure nitrogen through the sample was continuously directed to the PTR-MS instrument. The equilibration of DMS between seawater and the carrier gas, and the response time of the system, were evaluated in the laboratory. DMS reached equilibrium with an overall response time of 1 min. The detection limit (50 pmol L(-1) at 5 s integration) was sufficient for detection of DMS concentrations in the open ocean. The EI-PTR-MS instrument was deployed during a research cruise in the western North Pacific Ocean. Comparison of the EI-PTR-MS results with results obtained by means of membrane tube equilibrator-gas chromatography/mass spectrometry agreed reasonably well on average (R(2) = 0.99). EI-PTR-MS captured temporal variations of dissolved DMS concentrations, including elevated peaks associated with patches of high biogenic activity. These results demonstrate that the EI-PTR-MS technique was effective for highly time-resolved measurements of DMS in the open ocean. Further measurements will improve our understanding of the biogeochemical mechanisms of the production, consumption, and distribution of DMS on the ocean surface and, hence, the air-sea flux of DMS, which is a climatically important species.

Distribution of dimethylsulfide and dimethylsulfoniopropionate and its relation with phytoneuston in the surface microlayer of the western North Atlantic during summer

One of the key steps towards predicting dimethylsulfide (DMS) emission to the atmosphere is to understand the distribution and cycling of biogenic sulfur in the microlayer. In this study, we examined the distribution of DMS and dissolved and particulate fractions of dimethylsulfoniopropionate (DMSPd and DMSPp) in the surface microlayer and bulk water of the western North Atlantic during July 2003. DMS concentrations in the bulk water varied from 0.71 to 7.65 nM. In contrast, DMS concentrations in the surface microlayer were fairly low (0.17-1.33 nM). Average concentrations of DMSPd and DMSPp in the bulk water were 2.09 (1.87-6.25) and 44.1 (8.06-119.8) nM, respectively, and those in the surface microlayer were 15.4 (4.06-54.3) and 29.9 (7.32-97.0) nM. In general, DMS was depleted in the microlayer (mean concentration: 0.60 nM) relative to the bulk water (mean concentration: 2.38 nM) with enrichment factors (the ratio of the microlayer concentration to bulk water concentration) ranging from 0.13 to 0.54. There was no consistent enrichment of DMSPp and chlorophyll a in the microlayer. On the contrary, DMSPd appeared to be highly enriched in the microlayer with an average EF of 4.89. The concentration of phaeopigments was also generally greater in the microlayer than in the bulk water, presumably due to enhanced photo-oxidation of chlorophyll a under high surface light intensities in the microlayer. In the study area, the concentration of DMSPp was significantly correlated with the abundance of dinoflagellates in the microlayer. Moreover, a significant correlation between the distributions of DMS, DMSPp, chlorophyll a and phaeopigment concentrations in the microlayer and the bulk water demonstrated that the biogenic materials in the microlayer come primarily from the bulk water below.

Occurrence and turnover of DMSP and DMS in deep waters of the Ross Sea, Antarctica

High concentrations of the phytoplankton metabolite dimethylsulfoniopropionate (DMSP) and its degradation product dimethylsulfide (DMS) are associated with blooms of Phaeocystis antarctica in the Ross Sea, Antarctica. Episodic and rapid vertical export of Phaeocystis biomass to deep water has been reported for the Ross Sea, therefore we examined the distribution and microbial consumption rates of DMSP and DMS throughout the sub-euphotic water column. Total DMSP (dissolved+particulate; DMSPt) was present at 0.5–22 nM at depths between 70 and 690 m during both the early bloom (November) and the late bloom (January). Sub-euphotic peaks of DMSP were sometimes associated with mid-water temperature maxima, and elevated DMSP below 70 m was found mainly in water masses characterized as Modified Circumpolar Deep Water or Antarctic Shelf Water. Overall, 50–94% of the integrated water-column DMSPt was found below the euphotic zone. At one station during the early bloom, local maxima of DMSPt (14 nM) and DMS (20 nM) were observed between 113 and 240 m and these maxima corresponded with high chlorophyll a concentrations, P. antarctica cell numbers, and Fv/Fm (the quantum yield of photosystem II). During the late bloom, a sub-euphotic maximum of DMSPt (15.8 nM) at 250 m cooccurred with peaks of chlorophyll a concentration, DMSP lyase activity, bacterial production and dissolved DMSP consumption rates. DMSP turnover contributed ∼12% of the bacterial carbon demand between 200 and 400 m. DMS concentrations peaked at 286 m but the maximum concentration (0.42 nM) was far lower than observed during the early bloom, probably because of relatively rapid biological consumption of DMS (1–3 turnovers per day) which, in turn, contributed to elevated dissolved dimethylsulfoxide (DMSO) concentrations. Relatively stable DMSPt distributions at some sites suggest that rapid sinking of Phaeocystis biomass is probably not the major mechanism responsible for mesopelagic DMSP accumulations. Rather, subduction of near-surface water masses, lateral advective transport or trapping of slowly sinking P. antarctica biomass in intermediate water masses are more likely mechanisms. We found that a culture of P. antarctica maintained cellular integrity during 34 days of darkness, therefore the presence of intact cells (and DMSP) at depth can be explained even under a slow sinking/advection scenario. Whatever the mechanism, the large pools of DMSP and DMS below the euphotic zone suggest that export exerts a control on potential DMS emission from the surface waters of the Ross Sea.

Distribution and cycling of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in the sea-surface microlayer of the Yellow Sea, China, in spring

The distributions of dimethylsulfide (DMS) and its precursor, dimethylsulfoniopropionate (DMSP), were examined in the surface microlayer and corresponding subsurface water of the Yellow Sea, China, in April 2006. The average concentrations of DMS and DMSP of dissolved (DMSPd) and particulate (DMSPp) forms were 5.42 (1.78–12.75), 9.22 (2.85–19.73) and 17.50 (4.33–36.09) nmol L −1 in the subsurface water, and those in the surface microlayer were 4.92 (1.69–10.66), 17.08 (3.13–38.82) and 22.54 (4.85–47.24) nmol L −1, respectively. The enrichment factor (EF) of DMS in the microlayer ranged from 0.47 to 2.24 with a mean of 0.98. In contrast, DMSPd and DMSPp appeared to be enriched in the microlayer with average EFs of 1.98 and 1.39, respectively. A close correlation of integrated DMS, DMSPp and chlorophyll a concentrations for compiled data from all stations in the microlayer and the subsurface water indicated that phytoplankton biomass might play an important role in controlling the distributions of biogenic sulfurs in the study area. Moreover, a statistically significant relationship was found between the microlayer concentrations of DMS, DMSP and chlorophyll a and their subsurface water concentrations, suggesting a close linkage between these two water compartments. Interestingly, we observed higher biological production rates and consumption rates of DMS in the microlayer relative to the subsurface water. Furthermore, the DMS production rates were closely correlated both with DMSPd and chlorophyll a concentrations. Our study showed that the major sink of DMS in microlayer was escape into the atmosphere, which greatly exceeded its bacterial consumption. A preliminary estimate for average flux of DMS from the Yellow Sea to the atmosphere was 6.41 μmol m −2 d −1 during spring.

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.

Effect of natural iron fertilisation on the distribution of DMS and DMSP in the Indian sector of the Southern Ocean

Understanding the processes controlling the distribution and fate of dimethylsulphide (DMS) in marine surface waters is critical to quantifying the flux of DMS to the atmosphere. All fertilisation experiments in the Southern Ocean trying to mimic a short-term (several weeks) atmospheric, dust-related, iron supply so far have shown that DMS concentrations increase when iron is added artificially in small patches to iron-limited regions. During the Kerguelen Ocean and Plateau compared Study (KEOPS), we have investigated the impact on surface concentrations of DMS and its precursor, particulate dimethylsulphoniopropionate (DMSPp), of iron supplied by mixing from below. We found that the massive summer phytoplanktonic bloom sustained by naturally enhanced vertical mixing of deep iron-rich seawater above the Kerguelen Plateau is not a substantially larger source of DMS than the surrounding low-primary productivity waters. The sustained enrichment of iron over the Kerguelen Plateau does not translate into an increase in DMS concentration because: (1) the nano-phytoplankton, which is the main producer of DMSPp in the area, is not favoured by the continuous supply of iron in surface waters, (2) the transfer efficiency of DMSP to DMS is probably low due to the higher levels of bacterial production measured over the plateau, which, likely, also stimulate the bacterial removal of DMS, and (3) nitrates and fresh chromophoric dissolved organic matter, supplied in surface waters from enhanced mixing of deep water over the plateau, increase the photodegradation rates of DMS. Thus, artificial short-term iron supplies from above and naturally sustained ones show fundamental differences in their impacts on the distribution and net production of DMS.

Complexation of dimethylsulfide with mercuric ion in aqueous solutions

The tendency of dimethylsulfide (DMS) to form complexes with heavy metal ions in aqueous solutions and the factors that influence it have been investigated. Among five heavy metal ions examined (Cu2+, Cd2+, Zn2+, Pb2+ and Hg2+), only Hg2+ bound significantly with DMS in aqueous solutions in which Hg2+ concentration was increased to much higher levels than that of natural seawater. The complexation capacity of Hg2+ for DMS was influenced by pH and media. The affinity of Hg2+ for DMS was generally lower at high than at low pH, presumably due to the competition of hydroxide ion to form hydroxomercury species. In different solutions, the affinity of Hg2+ for DMS followed the following sequence: ultra-purified water > 35‰ NaCl solution > seawater. It seems apparent that chloride had a negative impact on the complexation of DMS by Hg2+, owing to the competition of chloride with DMS for complexing Hg2+. In addition, the affinity of Hg2+ for DMS in the bulk seawater appeared to be higher than that in the surface microlayer seawater. The tendency of Hg2+ to form complexes with DMS in aqueous solution can be reduced by the presence of 2 mM amino-acid such as glycine, alanine, serine and cysteine, as these ligands give stable mercury complexes. However, the presence of 2 mM acetate in experimental solutions had no significant effect on the complexation of Hg2+ with DMS, even though this ligand has a relatively strong complexing capacity for Hg2+. Although mercury ions appeared to have a strong affinity for DMS, the concentration of mercury in seawater is too low to produce a great effect on the distribution of DMS in oceans.

Distribution of dimethylsulfide and dimethylsulfoniopropionate in the surface microlayer and subsurface water of the Yellow Sea, China during spring

The concentrations of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in the surface microlayer and subsurface water were measured at 21 grid stations and one anchor station in the Yellow Sea, China in March 2005. The average concentrations of DMS and DMSP of dissolved (DMSPd) and particulate (DMSPp) forms were, respectively, 2.31 (1.20–4.54), 6.04 (2.13–9.48) and 7.98 (4.89–13.50) nM in the subsurface water, and those in the microlayer water were 2.26 (0.99–5.14), 9.10 (5.65–13.10) and 9.31 (4.08–15.64) nM. Among the sulfur components investigated, only DMSPd was found to be enriched in the microlayer with an average enrichment factor of 1.70. The concentrations of DMS, DMSPd and DMSPp in the microlayer were closely correlated with those in the corresponding subsurface water, implying that there was a strong exchange effect between the microlayer and subsurface water. The concentrations of DMS were positively correlated with the levels of chlorophyll a in the microlayer as well as in the subsurface water. The chlorophyll a-normalized DMS, DMSPd and DMSPp concentrations were 2.92 (1.47–5.72), 9.63 (2.07–27.88) and 13.10 (3.81–34.60) mmol g − 1 in the subsurface water, and 2.91 (0.77–5.24), 15.86 (1.22–32.34) and 15.95 (2.75–40.10) mmol g − 1 in the microlayer, respectively. A preliminary estimate for average flux of DMS from the Yellow Sea to the atmosphere was 3.14 μmol m − 2 day − 1 .

Spatial variations of DMS, DMSP and phytoplankton in the Bay of Bengal during the summer monsoon 2001

Data on the distribution of dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP) in relation to phytoplankton abundance in different oceanic environments is important to understand the biogeochemistry of DMS, which plays an important role in the radiation balance of the earth. During the summer monsoon of 2001 measurements were made for DMS and DMSPt (total DMSP) together with related biological parameters in the Bay of Bengal. Both DMS and DMSPt were restricted to the upper 40 m of the water column. Diatoms accounted for more than 95% of the phytoplankton and were the major contributors to the DMS and DMSPt pool. The mean concentration of DMS in the upper 40 m was observed to be around 1.8+/-1.9 nM in the study area, while DMSPt concentrations varied between 0.7 nM and 40.2 nM with a mean of 10.4+/-8.2 nM. The observed lower DMSPt in the northern Bay in spite of higher mean primary productivity, chlorophyll a and phytoplankton cell counts seemed to result from grazing. Though salinity divides the Bay into different biogeochemical provinces there is no relation between salinity and DMS or DMSPt. On the other hand DMS was linearly related to chlorophyll a:phaeopigments ratio. The results suggest the need for deeper insight into the role of diatoms in the biogeochemical cycling of DMS.

Emission of dimethylsulfide from Weddell Sea leads

The distribution of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) was examined in lead water in pack ice of the Weddell Sea. Samples were taken by pulling water into a syringe from a series of depths from 0.002 m to 4 m and deeper. Concentrations of DMS, DMSP and DMSO remained low throughout the water column relative to surface water, which was highly enriched. Concentrations of the major sulfur compounds increased by over an order of magnitude during periods with smooth surface water conditions. This increase coincided with a profound stratification of the water column, caused by a decrease in salinity of near surface water. We estimate that the DMS emission from leads and open water in Antarctic sea ice could contribute significantly to the yearly DMS flux from the Southern Ocean.