二甲基硫的海洋化学研究

二甲基硫（ＤＭＳ） 是海洋排放到大气中的最主要的生源硫化物。作者综述了ＤＭＳ在海洋中的分布特征、影响ＤＭＳ转化的因素、ＤＭＳ的海空扩散及其对环境的影响等。ＤＭＳ在海洋中存在很大程度的时空变化,这一变化不仅与海洋初级生产力水平有关,而且还与浮游植物的种类组成密切相关。微生物的降解、光化学的氧化以及海空扩散是ＤＭＳ在海洋中迁移变化的三个最重要的途径。ＤＭＳ的海－ 空扩散也存在较大的时空变化。ＤＭＳ的释放会对全球的气候变化和酸雨的形成产生重要的影响。本文同时就国内外的研究现状和今后的研究方向进行了分析和总结。     

黄、渤海二甲基硫化物的浓度分布与迁移转化速率研究

于2015年8-9月对黄、渤海海域进行现场调查，研究了海水中二甲基硫（DMS）、β-二甲巯基丙酸内盐（DMSP）、二甲亚砜（DMSO）的浓度分布、相互关系及影响因素，测定了DMS的生物生产与消耗、光化学氧化和海-气扩散速率，对DMS的迁移转化速率进行综合评价。结果表明:表层海水中DMS、溶解态DMSP（DMSPd）、颗粒态DMSP（DMSPp）、溶解态DMSO（DMSOd）和颗粒态DMSO（DMSOp）浓度的平均值分别为（6.12±3.01）nmol/L、（6.03±3.45）nmol/L、（19.47±9.15）nmol/L、（16.85±8.34）nmol/L和（14.37±7.47）nmol/L，整体呈现近岸高远海低，表层高底层低的趋势。DMS、DMSPd和DMSOp浓度与叶绿素（Chl a）浓度存在显著的相关性。表层海水中DMS光氧化速率顺序为:k_UVA > k_UVB > k_可见，其中UVA波段占光氧化的70.8%。夏季黄、渤海微生物消耗、光氧化及海-气扩散对DMS去除的贡献率分别为32.4%、34.5%和33.1%，表明3种去除途径作用相当。黄、渤海DMS海-气通量变化范围为0.79~48.45 μmol/（m2·d），平均值为（11.87±11.35）μmol/（m2·d）。     

海洋中二甲基亚砜的来源、分布及迁移转化

二甲基亚砜(DMSO)是海水中的主要溶解态甲基硫化物,DMSO在二甲基硫(DMS)的生物地球化学循环中起着重要的作用。它能通过DMS的光化学氧化和细菌氧化生成,可作为DMS的1个汇,也可以通过生物直接合成或其它途径产生。DMSO同时又可以被酶、细菌、植物等还原为DMS,因此,DMSO又可充当DMS的1个源。DMSO除了能被还原为DMS外,还可能会被细菌氧化为SO42-,在氯过氧化物酶作用下被H2O2氧化为DMSO2等。海洋中DMSO的测定通常采用还原剂NaBH4将其还原为DMS后,再利用气相色谱进行测定。海水中DMSO的分布不均匀,高浓度区是那些温度较高,光照充足、浮游植物较多、生物活性较高的表层水或近岸水。     

离子迁移谱现场观测渤海和北黄海二甲基硫的研究

渤海、黄海是高产二甲基硫(Dimethyl Sulfide,DMS)的大陆架海区.该海区DMS的现场调查研究有助于准确评估海洋DMS释放量及其对全球气候变化的负反馈作用.目前,无论是基于模型还是直接测量法的通量估算均以表层海水或低层大气DMS浓度为基础,因此,先进的检测技术对其通量估算的准确度具有决定性作用.气相色谱法...     

互花米草入侵对海岸盐沼二甲基硫及氧化亚氮气体释放的影响

为探讨互花米草(Spartina alterniflora)入侵对我国沿海生态系统的影响,采用静态采样箱法,研究了互花米草入侵滩涂和临近未入侵滩涂在二甲基硫(DMS)、氧化亚氮(N2O)气体通量上的差异及其相关因素.结果显示,互花米草滩DMS和N2O释放量均显著高于临近光滩、盐蒿滩和芦苇滩.该两种气体释放量同植被地下生物量、总生物量以及土壤有效氮含量均呈显著正相关,DMS气体通量还与植被地上生物量有关,但两种气体通量与土壤有机质含量均无直接相关性.研究说明互花米草生物入侵不仅改变了生态系统结构,还能通过改变区域温室气体排放通量进而影响到全球气候变化.     

Responses of DMS in the seawater and atmosphere to iron enrichment in the subarctic western North Pacific (SEEDS-II)

Simultaneous measurements of dimethylsulfide (DMS) in the seawater and atmosphere were conducted during SEEDS-II to investigate the responses of DMS to iron (Fe) fertilization in the subarctic North Pacific. No significant increases in the seawater DMS (DMSw) concentration were observed inside the fertilized patch compared to those outside the patch, while particulate dimethylsulfoniopropionate (DMSPp) concentration inside the patch increased 2-fold compared to those outside the patch in the phytoplankton bloom of major DMSP producers such as prasinophytes, cryptophytes, diatoms and prymnesiophytes. In the decline phase of the bloom, maximum DMSw was observed both inside the patch (ca. 6.2 nM) and outside the patch (ca. 9.3 nM). In this period, increases in mesozooplankton and decreases in the DMSP producers (prymnesiophytes and diatoms) were observed both sides of the patch, but larger inside the patch than outside the patch. Large decreases in the DMSPp inside the patch, which was probably related to the large increases in mesozooplankton inside the patch, did not result in increases in the DMSw concentration. Considering biological and nonbiological parameters, we discussed these results, although they could not be completely explained. Unfortunately, the impact of Fe fertilization on the atmospheric DMS (DMSa) concentration was not detected due to no significant changes in DMSw. However, it is noted that DMSa concentrations were dependent on the sea–air DMS flux in the air from higher latitudes and/or the Eurasian continent, though the DMS flux was a minor role to the budget of DMSw. Therefore if DMSw were significantly changed by Fe fertilization, DMSa might be affected through changes in the sea-air flux in this condition.     

格陵兰海气溶胶光学深度、海冰、浮游植物与二甲基硫的关系及其对未来气候的影响

dimethylsulphide (DMS)的海空通量是海洋生物气溶胶的主要来源之一,对气候（特别是北冰洋的气候）具有重要的辐射影响。利用卫星数据得到的气溶胶光学深度(AOD)作为气溶胶负荷的代表,在夏季和秋季表现的尤其明显。春季海冰的融化是北极气溶胶前体的重要来源。然而,早春的高浓度气溶胶可能与南方大陆污染的平流有关(北极霾)。更高的AOD通常在研究区域的南部出现。海冰浓度(SIC)和AOD呈正相关,而云盖(CLD)和AOD则呈负相关。SIC和CLD的季节性峰值均在AOD峰值的前一个月。AOD与SIC之间存在强烈的正相关关系。融冰与叶绿素（CHL)几乎在3月至9月呈正相关,但与春季和初夏的AOD呈负相关。春季和初夏较高的AOD有可能是由融冰和春季强风在该地区的结合影响。由于春季风的升高和冰的融化,在春季出现了DMS通量的峰值。从3月到五月,DMS浓度和AOD及融冰都呈正相关。早秋季升高的AOD可能与浮游植物合成的生物气溶胶的排放有关。到2100年，格陵兰海的DMS通量将增加3倍以上。生物气溶胶的显著增加可以部分抵消格陵兰海的增温现象。     

DMS and its oxidation products in the remote marine atmosphere: implications for climate and atmospheric chemistry

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

The concentration and distribution of dimethyl sulfide in the marine atmospheric boundary layer near the equator

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Temporal variations in dimethylsulphoniopropionate and dimethyl sulphide in the Zuari estuary,Goa (India)

Despite tropical estuarine systems representing important sites for active biogeochemical processes, studies on dimethyl sulphide (DMS) in these systems are sparse. Here we report on DMS and dimethylsulphoniopropionate (DMSP) variability in relation to physicochemical and biological parameters for a period of 14 months in a tropical estuarine environment. DMS and DMSP showed high temporal variations with maximal concentrations during the southwest monsoon coinciding with a dinoflagellate bloom. Dinoflagellates appear to be the major contributors to the DMSP pool. Average DMS and DMSP concentrations (surface and bottom) suggested that much of the DMSP produced is converted to forms other than DMS. Surface DMS varied between 0.3 and 15.4 nmol dm(-3) while DMSP ranged from 0.8 to 419.5 nmol dm(-3). The DMS flux was 0.03-1.9 microM m(-2) d(-1) (average=0.6 microM m(-2) d(-1)) during the study period, that concurs well with the values reported for temperate estuaries.     

Photochemical oxidation of dimethylsulfide in seawater

Dimethylsulfide(DMS) is generally thought to be lost from the surface oceans by evasion into the atmosphere as well as consumption by microbe.However,photochemical process might be important in the removal of DMS in the oceanic photic zone.A kinetic investigation into the photochemical oxidation of DMS in seawater was performed.The photo-oxidation rates of DMS were influenced by various factors including the medium,dissolved oxygen,photosensitizers,and heavy metal ions.The photo-oxidation rates of DMS were higher in seawater than in distilled water,presumably due to the effect of salinity existing in seawater.Three usual photosensitizers(humic acid,fulvic acid and anthroquinone),especially in the presence of oxygen,were able to enhance the photo-oxidation rate of DMS,with the fastest rate observed with anthroquinone.Photo-oxidation of DMS followed first order reaction kinetics with the rate constant ranging from 2.5×10-5 to 34.3×10-5 s-1.Quantitative analysis showed that approximately 32% of the photochemically removed DMS was converted to dimethylsulfoxide.One of the important findings was that the presence of Hg2 could markedly accelerate the photo-oxidation rate of DMS in seawater.The mechanism of mercuric catalysis for DMS photolysis was suggested according to the way of CTTM(charge transfer to metal) of DMS-Hg2 complex.     

Spatial variations of dimethylsulfide and dimethylsulfoniopropionate in the surface microlayer and in the subsurface waters of the South China Sea during springtime

Spatial variations in dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) were surveyed in the surface microlayer and in the subsurface waters of the low productivity South China Sea in May 2005. Overall, average subsurface water concentrations of DMS and DMSP of dissolved (DMSPd) and particulate (DMSPp) fractions were 1.74 (1.00-2.50), 3.92 (2.21-6.54) and 6.06 (3.40-8.68) nM, respectively. No enrichment in DMS and DMSPp was observed in the microlayer. In contrast, the microlayer showed a DMSPd enrichment, with an average enrichment factor (EF, defined as the ratio of the microlayer concentration to subsurface water concentration) of 1.40. In the study area, none of the sulfur components were correlated with chlorophyll a. An important finding in this study was that DMS, DMSP and chlorophyll a concentrations in the surface microlayer were respectively correlated with those in the subsurface water, suggesting a close linkage between these two water bodies. The ratios of DMS:Chl-a and DMSPp:Chl-a showed a gradually increasing trend from North to South. This might be due to changes in the proportion of DMSP producers in the phytoplankton community with the increased surface seawater temperature. A clear diurnal variation in the DMS and DMSP concentrations was observed at an anchor station with the highest concentrations appearing during the day and the lowest concentrations during the night. The higher DMS and DMSP concentrations during daytime might be attributed to the light-induced increase in both algal synthesis and exudation of DMSP and biological production of DMS. The mean flux of DMS from the investigated area to the atmosphere was estimated to be 2.06 micromo lm(-2)d(-1). This low DMS emission flux, together with the low DMS surface concentrations was attributed to the low productivity in this sea.     

A model of dimethylsulfide dynamics for the subtropical North Atlantic

Dimethylsulfide (DMS) is a volatile sulfur compound produced by the marine biota. The flux of DMS to the atmosphere may act on climate via aerosol formation. It is therefore important to improve our understanding of the processes that regulate sea surface DMS concentrations for eventual inclusion into climate models. In order to simulate the dynamics of DMS concentrations in the mixed layer, a model of DMS production was developed and calibrated against a 1 year time-series of DMS and DMSP (dissolved and particulate) data collected in the Sargasso Sea at Hydrostation ‘S’. The model reproduces the observed divergence between the seasonal cycles of particulate DMSP, the DMS precursor produced by algae, and DMS produced through the microbial loop from the cleavage of dissolved DMSP. DMSP_p (particulate) reaches its maximum in the spring whereas DMSP_d (dissolved) and DMS reach maximum concentrations in summer. Several parameters had to vary seasonally and with depth in order to reproduce the data, pointing out the importance of physiological and structural changes in the plankton food web. These parameters include the intracellular S(DMSp):N ratio, the C:Chl ratio and the sinking rates of phytoplankton and detritus. For the Sargasso Sea, variations in the solar zenithal angle, which co-vary with the seasonal variations in the depth of the mixed layer, proved to be a convenient signal to drive the seasonal variation in the structure and dynamics of the plankton. Variations of the temperature and photosynthetically active radiation also help to reproduce the short-term variability of the annual S cycle. Results from a sensitivity analysis show that variations in DMSP_p are dependent mostly on parameters controlling phytoplankton biomass, whereas DMS is dependent mostly on variables controlling phytoplankton productivity.     

Dimethyl sulfide in the atmospheric surface layer of the Equatorial Pacific Ocean

This paper reports a case study of atmospheric stability effect on dimethyl sulfide(DMS) concentration in the air. Investigation includes model simulation and field measurements over the Pacific Ocean. DMS concentration in surface sea water and in the air were measured during a research cruise from Hawaii to Tahiti. The diurnal variation of air temperature over the sea surface differed from the diurnal cycle of sea surface temperature because of the high heat capacity of sea water. The diurnal cycle of average DMS concentration in the air was studied in relation to the atmospheric stability parameter and surface heat flux. All these parameters had minima at noon and maxima in the early morning. The correlation coefficient of the air DMS concentration with wind speed (at 15 m high) was 0. 64. The observed concentrations of DMS in the equatorial marine surface layer and their diurnal variability agree well with model simulations. The simulated results indicate that the amplitude of the cycle and the mean     

Determinations of dimethylsulphoniopropionate (DMSP) lyase activity using headspace analysis of dimethylsulphide (DMS)

The osmolyte dimethylsulphoniopropionate (DMSP) can be enzymatically cleaved to dimethylsulphide (DMS), acrylate and a proton. The enzyme involved in this reaction is dimethylpropiothetin dethiomethylase (DMSP lyase; enzyme classification number 4.4.1.3.). Although the importance of this reaction for the global sulphur cycle, the influence of DMS on atmospheric acidity and the possible effect on climate regulation have been widely recognised, our knowledge of DMSP lyases is limited to just a few studies. Activity measurements of DMSP lyases offer an important step towards a better understanding of the conditions under which DMS is produced. In the available published data somewhat similar methods have been used before, but a critical examination of the method limitations has not been reported. To encourage further research on this enzyme, we suggest and detail two protocols for measurements of DMSP lyase activity: An in vitro assay for crude cell extracts or purified enzyme and an in vivo method for whole cells, which we recently started to use. After addition of DMSP, samples incubated in a gas tight vial may produce DMS from enzymatic cleavage under suitable conditions, and a DMS production rate can be estimated from time-series measurements of DMS in the headspace of the vial. Headspace analysis of DMS is a useful and rapid technique to estimate and compare DMSP lyase activities from different sources. The relative rates of DMS production in the liquid and of the gas transfer between liquid and headspace, determine the rate of DMS production measured via headspace analysis. If DMS production in the liquid is higher than the rate of transfer, headspace measurements will not reflect the actual amount of DMS produced in the liquid. In this case, extracts have to be diluted to a level that ensures linearity between dilution factor and reduction of enzyme activity. Additionally, incubation volumes and vials should be selected to provide a high surface-to-volume ratio to ensure maximum flux of DMS from the aqueous phase into the headspace. The methods can be adapted to further investigate species- and strain-specific activities, biogeographical distribution, cellular location and biochemical properties of various DMSP lyases.     

Photo-oxidation of dimethylsulphide in aqueous solution

Dimethylsulphide (DMS) is readily photo-oxygenated in the presence of micromolar amounts of photosensitizers such as methylene blue, rose bengal, anthroquinone and humic acid. Two moles of DMS are oxidized for every mole of molecular oxygen utilized consistent with dimethyl-sulphoxide being the oxidation product. Coastal seawater samples examined contained sufficient naturally occurring photosensitizer to photo-oxygenate DMS in sunlight with a first order rate constant of 2.4 × 10⁻⁵ s⁻¹. This rate is rapid enough to imply that DMS is oxidized at approximately the same rate as it is lost to the atmosphere.     

Atmospheric trace gas measurements during SEEDS-II over the northwestern pacific

Atmospheric trace gas measurements were conducted during SEEDS-II. Atmospheric dimethylsulfide (DMS) was continuously measured by GC-MS during the R/V Hakuho cruise. Further, ambient air was sampled into canisters (42 samples) and analyzed by GC-MS and GC-FID for various biogenic and anthropogenic volatile organic compounds (VOCs) after the cruise. CO, O₃, SO₂, and NOx were monitored continuously aboard the ship.A fertilization experiment was conducted in a high-nitrate, low-chlorophyll (HNLC) region (48°N, 165°E). The atmospheric concentrations inside a patch (fertilized area) were compared with those outside it (natural area); however, clear differences were not observed for biogenic trace gasses (DMS, CH₃Cl, CH₃I, isoprene, and alkenes) in the atmosphere. However, a high DMS concentration was observed over the northwestern Pacific Ocean. The fertilized area was also observed by R/V Kilo Moana, and DMS was measured by GC-FPD. A good agreement was observed between the results of the measurements made aboard the two independent ships by different measurement methods.The atmospheric SO₂ concentration was compared with the atmospheric DMS concentration. The SO₂ concentration was found to vary with the atmospheric DMS concentration. A diurnal variation of the atmospheric DMS concentration was observed around the fertilized region. The DMS content tends to increase during the night and decrease during the day. A box model calculation was conducted to explain the diurnal variation of the atmospheric DMS. Since there was no diurnal variation of the wind speed, a constant DMS flux from the ocean surface was assumed. Further, the atmospheric OH radical concentration was assumed to be dependent on sunlight. The box model can roughly reproduce the atmospheric DMS diurnal variation mainly caused by its removal reaction with OH radicals.     

Spatial distributions of dimethylsulfide in the South China Sea

The concentration of dimethylsulfide (DMS) and supporting parameters were determined in surface seawater and vertical profiles at 26 stations in the South China Sea. The concentrations of DMS in surface seawater ranged from 61 to 148 ng S/l, with a mean of 82 ng S/l. High concentrations of DMS were found in the productive regions. The vertical profiles of DMS were characterized by a maximum at depths typically between 20 and 75 m. The concentrations of DMS were correlated with the levels of chlorophyll a both in the surface seawater and in the vertical distribution. The concentrations of DMS were higher than expected for this chlorophyll-poor tropical sea, as indicated by markedly high DMS (ng S/l)/chlorophyll a (μg/l) ratios ranging from 315 to 3524 with a mean of 1768 for all the surface seawater samples. DMS concentration was significantly correlated with seawater temperature and dissolved oxygen, but it showed an inverse relationship to nutrients (including nitrate, phosphate and silicate). On the basis of sea surface concentrations of DMS and gas exchange calculations, the mean flux of DMS from the South China Sea to the atmosphere was estimated to be 5.5 μmol m⁻² d⁻¹.     

Reconstruction of sea surface dimethylsulfide in the North Pacific during 1970s to 2000s

We proposed an empirical equation of sea surface dimethylsulfide (DMS, nM) using sea surface temperature (SST, K), sea surface nitrate (SSN, μM) and latitude (L, °N) to reconstruct the sea surface flux of DMS over the North Pacific between 25°N and 55°N: ln DMS = 0.06346 · SST − 0.1210 · SSN − 14.11 · cos(L) − 6.278 (R² = 0.63, p < 0.0001). Applying our algorithm to climatological hydrographic data in the North Pacific, we reconstructed the climatological distributions of DMS and its flux between 25 °N and 55 °N. DMS generally increased eastward and northward, and DMS in the northeastern region became to 2–5 times as large as that in the southwestern region. DMS in the later half of the year was 2–4 times as large as that in the first half of the year. Moreover, applying our algorithm to hydrographic time series datasets in the western North Pacific from 1971 to 2000, we found that DMS in the last three decades has shown linear increasing trends of 0.03 ± 0.01 nM year^− 1 in the subpolar region, and 0.01 ± 0.001 nM year^− 1 in the subtropical region, indicating that the annual flux of DMS from sea to air has increased by 1.9–4.8 μmol m^− 2 year^− 1. The linear increase was consistent with the annual rate of increase of 1% of the climatological averaged flux in the western North Pacific in the last three decades.     

Seasonal variations of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in the sea-surface microlayer and subsurface water of Jiaozhou Bay and its adjacent area

The distributions of DMS and its precursor dimethylsulfoniopropionate, in both dissolved (DMSP_d) and particulate fractions (DMSP_p) were determined in the seasurface microlayer and corresponding subsurface water of the Jiaozhou Bay, China and its adjacent area in May and August 2006. The concentrations of all these components showed a clear seasonal variation, with higher concentrations occurring in summer. This can be mainly attributed to the higher phytoplankton biomass observed in summer. Simultaneously, the enrichment extents of DMSP_d and DMSP_p in the microlayer also exhibited seasonal changes, with higher values in spring and lower ones in summer. Higher water temperature and stronger radiant intensity in summer can enhance their solubility and photochemical reaction in the microlayer water, reducing their enrichment factors (the ratio of concentration in the microlayer to that in the corresponding subsurface water). A statistically significant relationship was found between the microlayer and subsurface water concentrations of DMS, DMSP and chlorophyll a, demonstrating that the biogenic materials in the microlayer come primarily from the underlying water. Moreover, our data show that the concentrations of DMSP_p and DMS were significantly correlated with the levels of chlorophyll a, indicating that phytoplankton biomass might play an important role in controlling the distributions of biogenic sulfurs in the study area. The ratios of DMS/chlorophyll a and DMSP_p/chlorophyll a varied little from spring to summer, suggesting that there was no obvious change in the proportion of DMSP producers in the phytoplankton community. The mean sea-to-air flux of DMS from the study area was estimated to be 5.70 μmol/(m²·d), which highlights the effects of human impacts on DMS emission.