Dimethylsulfide Consumption Research Articles

Study of heterogeneous reaction of dimethyl sulfide on atmospheric-like particulate TiO2

Dimethyl sulfide (DMS) related to solar radiation and greenhouse effect is one of the most important volatile sulfides and its' oxidation products are also important contributors to acid rain. It is of great importance to study the consumption and reactions of DMS in the atmosphere. In this work, atmospheric-like particulate TiO2 was selected to study the reaction mechanism of DMS on TiO2 with the purpose to explore the possible heterogeneous oxidation of DMS. The results showed that the heterogeneous reaction of DMS with TiO2 occurred under the condition of illumination, which is a first-order-like reaction with the rate constant K = 2.83 × 10−4/s, the initial reaction uptake coefficient and the steady reaction uptake coefficient indicated the occupation of products and by-products on the surface of TiO2. The heterogeneous reaction mechanism of DMS studied by aerosol time-of-flight mass spectrometry (ATOFMS) suggested that DMS underwent a series of complex chemical reactions with sulfate and various sulfur-containing gas products, in which hydroxyl radicals might play an important role.

Methanethiol and Dimethylsulfide Cycling in Stiffkey Saltmarsh.

Methanethiol (MeSH) and dimethylsulfide (DMS) are volatile organic sulfur compounds (VOSCs) with important roles in sulfur cycling, signaling and atmospheric chemistry. DMS can be produced from MeSH through a reaction mediated by the methyltransferase MddA. The mddA gene is present in terrestrial and marine metagenomes, being most abundant in soil environments. The substrate for MddA, MeSH, can also be oxidized by bacteria with the MeSH oxidase (MTO) enzyme, encoded by the mtoX gene, found in marine, freshwater and soil metagenomes. Methanethiol-dependent DMS production (Mdd) pathways have been shown to function in soil and marine sediments, but have not been characterized in detail in the latter environments. In addition, few molecular studies have been conducted on MeSH consumption in the environment. Here, we performed process measurements to confirm that Mdd-dependent and Mdd-independent MeSH consumption pathways are active in tested surface saltmarsh sediment when MeSH is available. We noted that appreciable natural Mdd-independent MeSH and DMS consumption processes masked Mdd activity. 16S rRNA gene amplicon sequencing and metagenomics data showed that Methylophaga, a bacterial genus known to catabolise DMS and MeSH, was enriched by the presence of MeSH. Moreover, some MeSH and/or DMS-degrading bacteria isolated from this marine environment lacked known DMS and/or MeSH cycling genes and can be used as model organisms to potentially identify novel genes in these pathways. Thus, we are likely vastly underestimating the abundance of MeSH and DMS degraders in these marine sediment environments. The future discovery and characterization of novel enzymes involved in MeSH and/or DMS cycling is essential to better assess the role and contribution of microbes to global organosulfur cycling.

Patterns and drivers of dimethylsulfide concentration in the northeast subarctic Pacific across multiple spatial and temporal scales

Abstract. The northeast subarctic Pacific (NESAP) is a globally important source of the climate-active gas dimethylsulfide (DMS), yet the processes driving DMS variability across this region are poorly understood. Here we examine the spatial distribution of DMS at various spatial scales in contrasting oceanographic regimes of the NESAP. We present new high-spatial-resolution measurements of DMS across hydrographic frontal zones along the British Columbia continental shelf, together with key environmental variables and biological rate measurements. We combine these new data with existing observations to produce a revised summertime DMS climatology for the NESAP, yielding a broader context for our sub-mesoscale process studies. Our results demonstrate sharp DMS concentration gradients across hydrographic frontal zones and suggest the presence of two distinct DMS cycling regimes in the NESAP, corresponding to microphytoplankton-dominated waters along the continental shelf and nanoplankton-dominated waters in the cross-shelf transitional zone. DMS concentrations across the continental shelf transition (range < 1–10 nM, mean 3.9 nM) exhibited positive correlations to salinity (r=0.80), sea surface height anomaly (SSHA; r=0.51), and the relative abundance of prymnesiophyte and dinoflagellates (r=0.89). In contrast, DMS concentrations in nearshore coastal transects (range < 1–24 nM, mean 6.1 nM) showed a negative correlation with salinity (r=-0.69; r=-0.78) and SSHA (r=-0.81; r=-0.75) and a positive correlation to relative diatom abundance (r=0.88; r=0.86). These results highlight the importance of bloom-driven DMS production in continental shelf waters of this region and the role of prymnesiophytes and dinoflagellates in DMS cycling further offshore. In all areas, the rate of DMS consumption appeared to be an important control on observed concentration gradients, with higher DMS consumption rate constants associated with lower DMS concentrations. We compiled a data set of all available summertime DMS observations for the NESAP (including previously unpublished results) to examine the performance of several existing algorithms for predicting regional DMS concentrations. None of these existing algorithms was able to accurately reproduce observed DMS distributions across the NESAP, although performance was improved by the use of regionally tuned coefficients. Based on our compiled observations, we derived an average summertime distribution map for DMS concentrations and sea–air fluxes across the NESAP, estimating a mean regional flux of 0.30 Tg of DMS-derived sulfur to the atmosphere during the summer season.

Dimethylsulfide (DMS) fluxes from permeable coral reef carbonate sediments

Dimethylsulfide (DMS) is a biogenic volatile organic compound of high interest as it can influence the Earth's climate by contributing to cloud formation in the atmosphere. Although DMS occurs at high concentrations in coral reef ecosystems, the role of permeable coral reef carbonate sediments as a source and sink of DMS to the surrounding seawater is unknown. Here, we report for the first time fluxes of dissolved DMS from permeable coral reef carbonate sediments over a full diel cycle obtained from benthic chamber deployments on the reef flat of Heron Island, southern Great Barrier Reef. Carbonate coral reef sediments were a substantial net diel source of DMS to the water column (mean 85.4 ± 13.2; range 42.3 ± 5.1 to 114 ± 4.7 nmol m−2 h−1), with rates similar to saltmarsh sediments. DMS effluxes were higher in the light under advective porewater flow, suggesting that DMS production in carbonate coral reef sediments is associated with photosynthesis by benthic microalgae. However, DMS effluxes decreased with advection at night, suggesting either greater DMS consumption or less DMS production under dark conditions. Similarly, dimethylsulfoniopropionate (DMSP), which is generally considered the main precursor of DMS, was mainly produced during the day. Net and dark methane (CH4) effluxes negatively correlated with net DMSP and dark DMS fluxes, respectively; suggesting that CH4 production via methanogenesis could be a sink for DMS and DMSP in carbonate coral reef sediments, especially under dark anoxic conditions. On Heron Island the permeable sands were estimated to contribute from about 22% to 44% of the benthic DMS emitted from the reef to the water column, which could represent an important portion of the yearly sea-to-atmosphere DMS fluxes. Permeable carbonate sediments should be considered further as a source of benthic DMS emitted from coral reefs and the broader continental shelf.

Quantification of dimethyl sulfide (DMS) production in the sea anemone <i>Aiptasia</i> sp. to simulate the sea-to-air flux from coral reefs

Abstract. The production of dimethyl sulfide (DMS) is poorly quantified in tropical reef environments but forms an essential process that couples marine and terrestrial sulfur cycles and affects climate. Here we quantified net aqueous DMS production and the concentration of its cellular precursor dimethylsulfoniopropionate (DMSP) in the sea anemone Aiptasia sp., a model organism to study coral-related processes. Bleached anemones did not show net DMS production whereas symbiotic anemones produced DMS concentrations (mean ± standard error) of 160.7 ± 44.22 nmol g−1 dry weight (DW) after 48 h incubation. Symbiotic and bleached individuals showed DMSP concentrations of 32.7 ± 6.00 and 0.6 ± 0.19 µmol g−1 DW, respectively. We applied these findings to a Monte Carlo simulation to demonstrate that net aqueous DMS production accounts for only 20 % of gross aqueous DMS production. Monte Carlo-based estimations of sea-to-air fluxes of gaseous DMS showed that reefs may release 0.1 to 26.3 µmol DMS m−2 coral surface area (CSA) d−1 into the atmosphere with 40 % probability for rates between 0.5 and 1.5 µmol m−2 CSA d−1. These predictions were in agreement with directly quantified fluxes in previous studies. Conversion to a flux normalised to sea surface area (SSA) (range 0.1 to 17.4, with the highest probability for 0.3 to 1.0 µmol DMS m−2 SSA d−1) suggests that coral reefs emit gaseous DMS at lower rates than the average global oceanic DMS flux of 4.6 µmol m−2 SSA d−1 (19.6 Tg sulfur per year). The large difference between simulated gross and quantified net aqueous DMS production in corals suggests that the current and future potential for its production in tropical reefs is critically governed by DMS consumption processes. Hence, more research is required to assess the sensitivity of DMS-consumption pathways to ongoing environmental change in order to address the impact of predicted degradation of coral reefs on DMS production in tropical coastal ecosystems and its impact on future atmospheric DMS concentrations and climate.

Effect of l-Cysteine and Transition Metal Ions on Dimethyl Sulfide Oxidation.

During malt kilning, significant amounts of dimethyl sulfide (DMS) oxidize leading to the formation of dimethyl sulfoxide (DMSO), a precursor of DMS during fermentation. Yet, knowledge regarding reaction mechanisms of DMSO formation during malt production is limited. The role of thiols in sulfide oxidation is unclear as they possess sulfoxide reducing ability as well as pro- and antioxidative properties. This study investigated the effects of the thiol l-cysteine (Cys), molecular oxygen, transition metal ions, and EDTA on DMS oxidation in aqueous model solutions. Highest oxidative DMS consumption was observed when Cys was combined with iron(II) (∼12%) and copper(II) (∼40%). Response surface modeling (RSM) revealed that Cys together with copper(II) had a strictly prooxidative effect and no antioxidative behavior was found. Hydrogen peroxide, as generated via autoxidation of Cys-Cu(I)-Cys complexes, was supposed to be the primary DMS oxidant in this work. Based on redox kinetics, potential reaction mechanisms, and their impact on oxidative processes in thermal food processing, such as malt and beer production, are discussed.

Vernal distribution and turnover of dimethylsulfide (DMS) in the surface water of the Yellow Sea

AbstractThe spatial and interannual variations of dimethylsulfide (DMS) and its precursors, dissolved and particulate dimethylsulfoniopropionate (DMSP), were discussed on the basis of field observations in the surface waters of the Yellow Sea during spring 2007. Maxima of dimethylated sulfur compounds and low chlorophyll a concentrations were found in the central southern Yellow Sea, whereas low concentrations of DMS and DMSP were detected at the boundary between the northern and southern parts of the Yellow Sea. This frontal region is influenced by active water currents, air‐sea interface exchanges, and biological turnover. The horizontal variations in DMS production and consumption rates showed a decreasing tendency from the coastal to offshore areas mainly due to the complicated biological features. DMS positively correlated with dissolved CH4 and CO2 but negatively correlated with nutrients (nitrite and phosphate). Particulate DMSP concentrations and DMS production rates positively correlated with dinoflagellate abundances but negatively correlated with diatom cell densities. DMS and DMSP concentrations, as well as DMS production and consumption rates, exhibited approximately 2.0–2.8 fold increases from 2005 to 2012. This finding was likely caused by shifts in the phytoplankton communities from diatoms to dinoflagellates and the increases in abundances of zooplankton and bacteria. Average sea‐to‐air DMS fluxes were estimated to be 8.12 ± 1.24 µmol·(m−2·d−1), and DMS microbial consumption was approximately 1.68 times faster than the DMS sea‐air exchange. These findings imply that biological consumption, relative to ventilation, is a predominant mechanism in DMS removal from the surface water.

Revising upper-ocean sulfur dynamics near Bermuda: new lessons from 3 years of concentration and rate measurements

Environmental context Microscopic marine organisms have the potential to influence the global climate through the production of a trace gas, dimethylsulfide, which contributes to cloud formation. Using 3 years of observations, we investigated the environmental drivers behind the production and degradation of dimethylsulfide and its precursor dimethylsulfoniopropionate. Our results highlight the important role of the microbial community in rapidly cycling these compounds and provide an important dataset for future modelling studies. Abstract Oceanic biogeochemical cycling of dimethylsulfide (DMS), and its precursor dimethylsulfoniopropionate (DMSP), has gained considerable attention over the past three decades because of the potential role of DMS in climate mediation. Here we report 3 years of monthly vertical profiles of organic sulfur cycle concentrations (DMS, particulate DMSP (DMSPp) and dissolved DMSP (DMSPd)) and rates (DMSPd consumption, biological DMS consumption and DMS photolysis) from the Bermuda Atlantic Time-series Study (BATS) site taken between 2005 and 2008. Concentrations confirm the summer paradox with mixed layer DMS peaking ~90 days after peak DMSPp and ~50 days after peak DMSPp:Chl. A small decline in mixed layer DMS was observed relative to those measured during a previous study at BATS (1992–1994), potentially driven by long-term climate shifts at the site. On average, DMS cycling occurred on longer timescales than DMSPd (0.43±0.35 v. 1.39±0.76 day–1) with DMSPd consumption rates remaining elevated throughout the year despite significant seasonal variability in the bacterial DMSP degrader community. DMSPp was estimated to account for 4–5% of mixed layer primary production and turned over at a significantly slower rate (~0.2 day–1). Photolysis drove DMS loss in the mixed layer during the summer, whereas biological consumption of DMS was the dominant loss process in the winter and at depth. These findings offer new insight into the underlying mechanisms driving DMS(P) cycling in the oligotrophic ocean, provide an extended dataset for future model evaluation and hypothesis testing and highlight the need for a reexamination of past modelling results and conclusions drawn from data collected with old methodologies.

Ocean acidification has different effects on the production of dimethylsulfide and dimethylsulfoniopropionate measured in cultures of Emiliania huxleyi and a mesocosm study: a comparison of laboratory monocultures and community interactions

Environmental context Approximately 25% of CO2 released to the atmosphere by human activities has been absorbed by the oceans, resulting in ocean acidification. We investigate the acidification effects on marine phytoplankton and subsequent production of the trace gas dimethylsulfide, a major route for sulfur transfer from the oceans to the atmosphere. Increasing surface water CO2 partial pressure (pCO2) affects the growth of phytoplankton groups to different degrees, resulting in varying responses in community production of dimethylsulfide. Abstract The human-induced rise in atmospheric carbon dioxide since the industrial revolution has led to increasing oceanic carbon uptake and changes in seawater carbonate chemistry, resulting in lowering of surface water pH. In this study we investigated the effect of increasing CO2 partial pressure (pCO2) on concentrations of volatile biogenic dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP), through monoculture studies and community pCO2 perturbation. DMS is a climatically important gas produced by many marine algae: it transfers sulfur into the atmosphere and is a major influence on biogeochemical climate regulation through breakdown to sulfate and formation of subsequent cloud condensation nuclei (CCN). Overall, production of DMS and DMSP by the coccolithophore Emiliania huxleyi strain RCC1229 was unaffected by growth at 900μatm pCO2, but DMSP production normalised to cell volume was 12% lower at the higher pCO2 treatment. These cultures were compared with community DMS and DMSP production during an elevated pCO2 mesocosm experiment with the aim of studying E. huxleyi in the natural environment. Results contrasted with the culture experiments and showed reductions in community DMS and DMSP concentrations of up to 60 and 32% respectively at pCO2 up to 3000μatm, with changes attributed to poorer growth of DMSP-producing nanophytoplankton species, including E. huxleyi, and potentially increased microbial consumption of DMS and dissolved DMSP at higher pCO2. DMS and DMSP production differences between culture and community likely arise from pH affecting the inter-species responses between microbial producers and consumers.

Effect of Nanoparticles on DMS Consumption and DMSP Concentration in Aiptasia pallida

Wide use of nanoparticles (NPs) in day-to-day products increases the likelihood of NPs entering and effecting marine organisms as a result of direct emissions and indirect terrestrial runoff. The effects of NPs on dimethylsulfide (DMS) consumption and concentrations of dimethylsulfoniopropionate (DMSP) within the holobiont of cnidarians remain obscure. This study examines the effects of titanium dioxide (TiO2 NP) and capped silver nanoparticles (cAg NP) at 50mg/L concentrations, on the microscopically observations of physiological changes to the tropical sea anemone, Aiptasia pallida (clone CC7), the concentrations of DMS and DMSP of its intracellular symbiont Symbiodinium sp. (A02 and B01) and its surface DMS consuming bacteria. DMS was quantified during NP exposure, and 24 and 96h post exposure using gas chromatography (GC). DMS production was found to be 2.5 fold higher in A02 compared to B01. However, concentrations of particulate DMSP were only observed to increase in the B01 strain when exposed to TiO2 NP (22.90±1.55nmol h-1mg-1) compared to control (11.41±0.05nmol h-1mg-1). A common pattern was identified for the surface DMS consuming bacteria on A. pallida, regardless of Symbiodinium strain or NP treatment. During NP exposure DMS consumption was lower in all NP treatments (0.10±0.05nmol h-1mg-1) in comparison to the controls (0.19±0.19 nmol h-1mg-1). 24h post exposure, DMS consumption was higher (0.27±0.13 nmol h-1mg-1) compared to the controls (0.20±0.22nmol h-1mg-1), with DMS consumption returning to similar rates as controls in NP treatments post 96h exposure. Microscopical observations showed that cAg NP had the greatest adverse effect on both Symbiodinium strains, with approximately 40% decrease in cell density after 24h exposure, and loss of tentacles in A. Pallida being observed only in this NP treatment. This work illustrates the potentially negative impacts of NPs on DMS consumption and concentrations of DMSP in the holobiont of A. pallida, thus emphasising the need for more studies to be conducted on NP effects in the tropical marine environments.

A meta‐analysis of oceanic DMS and DMSP cycling processes: Disentangling the summer paradox

AbstractThe biogenic volatile compound dimethylsulfide (DMS) is produced in the ocean mainly from the ubiquitous phytoplankton osmolyte dimethylsulfoniopropionate (DMSP). In the upper mixed layer, DMS concentration and the daily averaged solar irradiance are roughly proportional across latitudes and seasons. This translates into a seasonal mismatch between DMS and phytoplankton biomass at low latitudes, termed the “DMS summer paradox,” which remains difficult to reproduce with biogeochemical models. Here we report on a global meta‐analysis of DMSP and DMS cycling processes and their relationship to environmental factors. We show that DMS seasonality reflects progressive changes in a short‐term dynamic equilibrium, set by the quotient between gross DMS production rates and the sum of biotic and abiotic DMS consumption rate constants. Gross DMS production is the principal driver of DMS seasonality, due to the synergistic increases toward summer in two of its underlying factors: phytoplankton DMSP content (linked to species succession) and short‐term community DMSP‐to‐DMS conversion yields (linked to physiological stress). We also show that particulate DMSP transformations (linked to grazing‐induced phytoplankton mortality) generally contribute a larger share of gross DMS production than dissolved‐phase DMSP metabolism. The summer paradox is amplified by a decrease in microbial DMS consumption rate constants toward summer. However, this effect is partially compensated by a concomitant increase in abiotic DMS loss rate constants. Besides seasonality, we identify consistent covariation between key sulfur cycling variables and trophic status. These findings should improve the modeling projections of the main natural source of climatically active atmospheric sulfur.

Consistent increase in dimethyl sulfide (DMS) in response to high CO<sub>2</sub> in five shipboard bioassays from contrasting NW European waters

Abstract. The ubiquitous marine trace gas dimethyl sulfide (DMS) comprises the greatest natural source of sulfur to the atmosphere and is a key player in atmospheric chemistry and climate. We explore the short-term response of DMS production and cycling and that of its algal precursor dimethyl sulfoniopropionate (DMSP) to elevated carbon dioxide (CO2) and ocean acidification (OA) in five 96 h shipboard bioassay experiments. Experiments were performed in June and July 2011, using water collected from contrasting sites in NW European waters (Outer Hebrides, Irish Sea, Bay of Biscay, North Sea). Concentrations of DMS and DMSP, alongside rates of DMSP synthesis and DMS production and consumption, were determined during all experiments for ambient CO2 and three high-CO2 treatments (550, 750, 1000 μatm). In general, the response to OA throughout this region showed little variation, despite encompassing a range of biological and biogeochemical conditions. We observed consistent and marked increases in DMS concentrations relative to ambient controls (110% (28–223%) at 550 μatm, 153% (56–295%) at 750 μatm and 225% (79–413%) at 1000 μatm), and decreases in DMSP concentrations (28% (18–40%) at 550 μatm, 44% (18–64%) at 750 μatm and 52% (24–72%) at 1000 μatm). Significant decreases in DMSP synthesis rate constants (μDMSP, d−1) and DMSP production rates (nmol d−1) were observed in two experiments (7–90% decrease), whilst the response under high CO2 from the remaining experiments was generally indistinguishable from ambient controls. Rates of bacterial DMS gross consumption and production gave weak and inconsistent responses to high CO2. The variables and rates we report increase our understanding of the processes behind the response to OA. This could provide the opportunity to improve upon mesocosm-derived empirical modelling relationships and to move towards a mechanistic approach for predicting future DMS concentrations.

Spectral irradiance dependence of sunlight effects on plankton dimethylsulfide production

We investigated the short‐term effects of variable solar irradiance and spectrum on the gross biological production of dimethylsulfide (DMS), a trace gas with potential climatic effects, in eight experiments performed at different times of the year in a northwest Mediterranean coastal site. Experimentally determined net community DMS production, DMS photolysis, and dark microbial DMS consumption rates were used to calculate gross community DMS production by budgeting. In addition, the composition of the bacterioplankton and phytoplankton communities in the initial samples, and the photoinhibition of bulk bacterial heterotrophic activity and phytoplankton photosynthetic efficiency were monitored. Our results show that: (1) gross DMS production is irradiance dependent, with a maximum short‐term stimulation factor of 2‐ to 6‐fold compared to dark incubations; (2) its spectral shape is variable but generally similar to that of phytoplankton photoinhibition or photodamage, with more effective stimulation at shorter ultraviolet wavelengths; and (3) stronger stimulation occurs when samples are overexposed with respect to their prior exposure. Remarkably, the photoresponse of gross DMS production was in most cases strong enough to (at least) compensate the photochemical DMS loss at the water subsurface. Such response would prevent DMS depletion in stratified and highly irradiated waters. Since the initial microbial communities were representative of meso‐ to oligotrophic conditions, our observations should apply to a wide variety of oceanic regimes.

DMS dynamics in the most oligotrophic subtropical zones of the global ocean

The influences of physico-chemical and biological processes on dimethylsulfide (DMS) dynamics in the most oligotrophic subtropical zones of the global ocean were investigated. As metrics for the dynamics of DMS and the so-called ‘summer DMS paradox’ of elevated summer concentrations when surface chlorophyll a (Chl) and particulate organic carbon (POC) levels are lowest, we used the DMS-to-Chl and DMS-to-POC ratios in the context of three independent and complementary approaches. Firstly, field observations of environmental variables (such as the solar radiation dose, phosphorus limitation of phytoplankton and bacterial growth) were used alongside discrete DMS, Chl and POC estimates extracted from global climatologies (i.e., a ‘station based’ approach). We then used monthly climatological data for DMS, Chl, and POC averaged over the biogeographic province wherein a given oligotrophic subtropical zone resides (i.e., a ‘province based’ approach). Finally we employed sensitivity experiments with a new DMS module coupled to the ocean general circulation and biogeochemistry model PISCES to examine the influence of various processes in governing DMS dynamics in oligotrophic regions (i.e., a ‘model based’ approach). We find that the ‘station based’ and ‘province based’ approaches yield markedly different results. Interestingly, the ‘province based’ approach suggests the presence of a ‘summer DMS paradox’ in most all of the oligotrophic regions we studied. In contrast, the ‘station based’ approach suggests that the ‘summer DMS paradox’ is only present in the Sargasso Sea and eastern Mediterranean. Overall, we found the regional differences in the absolute and relative concentrations of DMS between 5 of the most oligotrophic regions of the world’s oceans were better accounted for by their nutrient dynamics (specifically phosphorus limitation) than by physical factors often invoked, e.g., the solar radiation dose. Our ‘model based’ experiments suggest that it is the limitation of phytoplankton/bacterial production and bacterial consumption of DMS by pervasive phosphorus limitation that is responsible for the ‘summer DMS paradox’.

Stimulation of gross dimethylsulfide (DMS) production by solar radiation

Oceanic gross DMS production (GP) exerts a fundamental control on the concentration and the sea‐air flux of this climatically‐active trace gas. However, it is a poorly constrained process, owing to the complexity of the microbial food web processes involved and their interplay with physical forcing, particularly with solar radiation. The “inhibitor method”, using dimethyldisulfide (DMDS) or other compounds to inhibit bacterial DMS consumption, has been frequently used to determine GP in dark incubations. In the work presented here, DMDS addition was optimized for its use in light incubations. By comparing simultaneous dark and light measurements of GP in meso‐ to ultraoligotrophic waters, we found a significant enhancement of GP in natural sunlight in 7 out of 10 experiments. Such stimulation, which was generally between 30 and 80% on a daily basis, occurred throughout contrasting microbial communities and oceanographic settings.

Occurrence and cycling of dimethylated sulfur compounds in the Arctic during summer receding of the ice edge

The distribution and cycling of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) were studied in the Greenland Sea and Arctic Ocean during July 2007. The concentration of these compounds was analyzed in vertical profiles of the top 100 m of the water column, with special emphasis on the subsurface (1 m) and the immediate subsurface waters (0.1 m). Seawater incubations were conducted in order to measure the rates of biological DMS cycling, as well as DMS photolysis rates. DMS ventilation rates were calculated from the hourly meteorological time series. Moderate concentrations of DMS (0.1 to 18.3 nM), DMSP (1.4 to 163.6 nM) and DMSO (9.0 to 84.7 nM) were found, considering that elevated biomasses of the haptophyte Phaeocystis pouchetii dominated in the study area. The overall situation was characterized by a tight coupling of biological DMS production and consumption, and a fast biological turnover of DMS (0.5 to 4 days). Bacterial consumption was the dominant sink for DMS, accounting for 9–73% of its loss in the upper mixed layer (UML). However, the shallow stratification encountered (mixed layer depth between 1.5 and 11 m) enhanced DMS photolysis, which accounted for 12–65% of the total DMS loss and, at some stations, became the dominant sink. DMS production followed phytoplankton biomass (and DMSP concentration) in surface waters, while bacterial DMS consumption was controlled by the depth of the UML (presumably through exposure to solar radiation). Ice melt drove surface stratification, regulating the entrainment of cells and materials into the upper layer from the more productive waters below, and eventually the fraction of DMS escaping to the atmosphere.

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.

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.

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.

Dissolved DMSO production via biological and photochemical oxidation of dissolved DMS in the Ross Sea, Antarctica

Dimethylsulfoxide (DMSO) is an important degradation product of the climate-influencing gas dimethylsulfide (DMS). In the Ross Sea, Antarctica, dissolved DMSO (DMSOd) concentrations exhibited substantial seasonal and vertical variations. Surface water DMSOd concentrations in pre-bloom waters were very low (<1 nM) but increased rapidly up to 41 nM during the spring Phaeocystis antarctica bloom (late November). Increases in DMSOd concentrations lagged by several days increases in DMS concentrations. Although DMSOd concentrations reached relatively high levels during the spring bloom, concentrations were generally higher (36.3–60.6 nM) during summer (January), even though phytoplankton biomass and DMS concentrations had decreased by that time. During both seasons, DMSOd concentrations were substantially higher within the surface mixed layer than below it. DMSOd production from biological DMS consumption (BDMSC) was higher during late November (3.4–5.2 nM d −1) than during the summer (0.7–2.4 nM d −1); therefore, production via BDMSC alone could not explain the higher DMSOd concentrations encountered during the summer. Mixed layer-integrated DMSOd production from BDMSC was 2.5–13.7 times greater than production from dissolved DMS photolysis during the P. antarctica bloom, while photolysis contributed 1.3 times more DMSO than BDMSC before the bloom. The DMSO yield from BDMSC was consistently higher within the upper mixed layer than at depths below. Experimental incubations with water from the mixed layer showed that exposure to full spectrum sunlight for 72 h caused an increase in the DMSO yield whereas exposure to only photosynthetically active radiation did not. This suggests that ultraviolet radiation is a potential factor shifting the fate of biologically consumed DMS toward DMSO. In general, the highest DMSO yields from BDMSC were in samples with slow biological DMS turnover, whereas fast turnover favored sulfate rather than DMSO as a major end-product. This study provides the first detailed information about DMSOd distribution and production in the Ross Sea and points to DMSOd as an important biological and photochemical degradation product of DMS and a major reservoir of methylated sulfur in these polar surface waters.