Seawater Dimethylsulfide Research Articles

Dimethylsulfide in the South China Sea

Measurements of dimethylsulfide (DMS) concentrations in surface seawater and vertical profiles at sixteen stations in the Nansha Islands waters of the South China Sea showed that surface seawater DMS concentrations ranged from S 52 to 122 ng/L, average of 82 ng/L. DMS distribution tendency coincided with that of primary productivity observed during the same cruise. In vertical profiles, the DMS distribution was influenced by factors such as algal biomass, as indicated by chlorophyll a, particular algal species, consumption by photochemical oxidation, etc. Maximal DMS concentrations appeared at 30–75 m depths. DMS concentration was significantly correlated to seawater temperature. The sea-to-air DMS flux from this sea area was estimated to be 5.95 μmol/(m2·d).

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.

Oceanographic context of the First Aerosol Characterization Experiment (ACE 1): A physical, chemical, and biological overview

The First Aerosol Characterization Experiment (ACE 1) intensive experiment, conducted between November 14 and December 15, 1995, covered an oceanographically complex region, including the subtropical (ST), Subtropical Convergence Zone (STCZ), Subantarctic (SA), and polar water masses. Oceanographic and atmospheric sampling to identify the chemical and biological communities that might affect biologically produced, aerosol precursors in these water masses was carried out from the RV Discoverer and FRV Southern Surveyor. Sea surface temperature was not a good indicator of water mass during ACE 1. The physical structure east of 147.5°E was more complex than west of this longitude. Nutrient concentrations (nitrate, silicate) in the mixed layer increased, but ammonia concentrations decreased from ST to polar waters. Ammonia concentrations in surface waters exceeded >5 μM, and ammonia fluxes peaked at 12 μM m−2 d−1 in ST water near Cape Grim between November 27 and 30. Seawater dimethyl sulfide (DMSSW) concentrations averaged 1.7±1.1 nM with maximum values near 6 nM in ST waters. The flux of dimethyl sulfide to the atmosphere averaged 4.7±5.0 μM m−2 d−1, with peak fluxes (>40 μM m−2 d−1) in SA water. DMSSW increased significantly only in SA waters during the experiment. Surface chlorophyll‐a concentrations measured from the FRV Southern Surveyor ranged between 0.3 and 0.6 mg m−3. Surface chlorophyll‐a concentrations along the Discoverer cruise track were similar, but 5 phytoplankton blooms (>1 mg m−3) were found. Integrated column chlorophylls ranged from 29.4 mg m−2 in SA water to 53.2 mg m−2 in ST water. Modeled primary production rates were ranged between 409 mg carbon m−2 d−1 in the polar front to 3180 mg carbon m−2 d−1 in ST water near Cape Grim. Mixed layer phytoplankton growth rates, estimated from net primary production, were 0.31 d−1 in the SAF to 1.07 d−1 in STCZ water east of Tasmania. Grazing dilution experiments showed microzooplankton grazing and phytoplankton growth rates were tightly coupled, with net growth rates ranging from ‐ 0.13 d−1 to 0.22 d−1. During the ACE 1 intensive period, the surface waters were in transition from the deeply mixed, winter conditions to the shallowly stratified, spring conditions. The spring phytoplankton bloom was just beginning in the northern water masses, and isolated blooms were present at several locations in SA surface waters. The low standing stocks of chlorophyll and tightly coupled grazing rates may have been responsible for the low concentrations of DMS and NH3 in the region, and the generally low fluxes of these compounds to the atmosphere during the ACE 1 intensive experiment.

One‐dimensional modeling of sulfur species during the First Aerosol Characterization Experiment (ACE 1) Lagrangian B

A one‐dimensional Lagrangian model is used to simulate vertical profiles and temporal evolution of dimethylsulfide (DMS), sulfur dioxide (SO2), aerosol methane sulfonate, and non‐sea‐salt sulfate (nss sulfate) that were measured during the three flights of the second First Aerosol Characterization Experiment (ACE 1) Lagrangian (Lagrangian B) experiment. Entrainment rate, mixing heights, and cloud occurrence are calculated prognostically in this type of model. The model is forced by geostrophic winds and large scale subsidence from European Centre for Medium‐Range Weather Forecasts (ECMWF) analysis and sea surface temperature measured on board Research Vessel Discoverer. Gas phase oxidation and heterogeneous oxidation of SO2 to nss sulfate in clouds and sea‐salt particles are considered. The evolution of dynamical variables in the column is found to be well reproduced by the model. The model captures 82% of the variance of observed DMS assuming OH is the only oxidant and a DMS flux term calculated from Liss and Merlivat [1986] parameterization and seawater DMS concentrations measured aboard R/V Discoverer. However, uncertainties in DMS oxidation rates and regional seawater concentrations are too great to identify a best fit wind speed‐transfer velocity relationship. SO2 mixing ratios are correctly represented in the model (least squares correlation coefficient r2 = 75%) using a DMS to SO2 conversion efficiency of about 70%. Oxidation of SO2 in sea‐salt particle appears to be a dominant process and controls SO2 lifetime during the Lagrangian B at least in the well mixed lower layer. Removing heterogeneous loss of SO2 in sea salt significantly deteriorates the simulation (r2 = 50%). Under cloudy conditions, heterogeneous loss in cloud droplets and in sea‐salt particles are competitive (relative rates are 35% and 41%, respectively, during flight 26). Model‐generated aerosol methane sulfonate mixing ratios agree with the observations (r2 = 62.5%) when high branching ratio for an addition oxidation pathway is used. The model estimates nss sulfate mixing ratios with little bias (median simulated‐to‐observed concentration ratio 1.03 and slope of the regression line 0.7) but captures only one third of the observed variance of nss sulfate. Part of the discrepancy could be due to the assumption of a decrease of nss sulfate mixing ratios with altitude in the model, whereas observations revealed high concentrations at 4500 m during the last two flights suggesting that horizontal transport could be more important than vertical mixing in this region. Nss sulfate is found to be produced photochemically under non cloudy, low wind speed conditions encountered during the first flight. During the last two flights, nss sulfate is produced mainly by oxidation in cloud droplets (48% during flight 25 and 69% during flight 26) and sea‐salt particles (50% during flight 25 and 22% during flight 26).

Summertime Seawater Concentrations of Dimethylsulfide in the Western Indian Ocean: Reconciliation of Fluxes and Spatial Variability with Long-Term Atmospheric Observations

Dimethylsulfide (DMS) measurements in the seawater of the subtropical and the temperate western Indian Ocean were conducted for the first time from 3 December to 20 December 1997. In total, 443 surface seawater DMS determinations were performed between 24°–49° S and 50° E–77° E with a frequency of 1 sample every 10 km. An important spatial variability was observed in seawater DMS concentrations with values ranging from 0.9 to 35.8 nM. DMS maxima coincided in most cases with thermal fronts and were in reasonable agreement with mean pigment figures obtained from satellite observations. The deduced DMS fluxes are consistent with long-term observations of atmospheric DMS and rainwater concentrations of nss- SO4= and MSA measured at Amsterdam island (37° S, 77° E); then account for the differences observed in atmospheric DMS concentrations between Amsterdam island and Cape Grim, Indian Ocean monitoring stations.

Bidirectional mixing in an ACE 1 marine boundary layer overlain by a second turbulent layer

In the Lagrangian B flights of the First Aerosol Characterization Experiment (ACE 1), the chemistry and dynamics of the postfrontal air mass were characterized by tracking a constant‐level balloon launched into the air mass for three consecutive 8‐hour flights of the instrumented National Center for Atmospheric Research C‐130 aircraft during a 33‐hour period. The boundary layer extended to a height of 400 to 700 m during this period, with its top defined by changes in the amount of turbulent mixing measured rather than by an inversion. Above the planetary boundary layer to a height of 1400 to 1900 m, a second layer was capped with a more pronounced temperature inversion and contained only intermittent turbulence. Since this layer served as a reservoir and mixing zone for boundary layer and free tropospheric air, we have called it a buffer layer to emphasize its differences from previous concepts of a residual or intermediate layer. Estimates of the entrainment rate of dimethyl sulfide (DMS) and aerosol particles between the boundary layer and the buffer layer demonstrated that exchange occurred across the interface between these two layers in both upward and downward directions. In situ measurements of aerosol particles revealed highly concentrated, nucleation‐mode aerosol particles between 10 and 30 nm diameter at the beginning of the first Lagrangian B flight in the buffer layer, while few were present in the boundary layer. Observations during the second and third flights indicate that aerosol particles of this size were mixing downward into the boundary layer from the buffer layer while DMS was transported upward. This fortuitous enhancement of aerosol particles in the buffer layer allowed simultaneous use of DMS and aerosol particle budgets to track the bidirectional entrainment rates. These estimates were compared to those from measurements of mean vertical motion and boundary layer growth rate, and from estimates of the fluxes and changes in concentration across the layer interface. In addition, three different techniques were used to estimate DMS emission rates from the ocean surface and showed good agreement: (1) evalulation of the DMS and aerosol mean concentration budgets, (2) seawater DMS concentrations and an air‐sea exchange velocity, and (3) the mixed‐layer gradient technique.

Shipboard measurements of dimethyl sulfide and SO2 southwest of Tasmania during the First Aerosol Characterization Experiment (ACE 1)

Measurements of seawater dimethylsulfide (DMS), atmospheric dimethylsulfide, and sulfur dioxide (SO2) were made on board the R/V Discoverer in the Southern Ocean, southeast of Australia, as part of the First Aerosol Characterization Experiment (ACE 1). The measurements covered a latitude range of 40°S–55°S during November‐December 1995. Seawater DMS concentrations ranged from 0.4 to 6.8 nM, with a mean of 1.7±1.1 nM (1σ). The highest DMS concentrations were found in subtropical convergence zone waters north of 44°S, and the lowest were found in polar waters south of 49°S. In general, seawater DMS concentrations increased during the course of the study, presumably due to the onset of austral spring warming. Atmospheric DMS concentrations ranged from 24 to 350 parts per trillion by volume (pptv), with a mean of 112±61 pptv (1σ). Atmospheric SO2 was predominantly of marine origin with occasional anthropogenic input, as evidenced by correlation with elevated 222Rn and air mass trajectories. Concentrations ranged from 3 to 1000 pptv with a mean of 48.8± 49 pptv (1σ) and a median 15.8 pptv. The mean SO2 concentration observed in undisturbed marine air was 11.9±7.6 pptv (1σ), and the mean DMS to SO2 ratio in these conditions was 13±9 (1σ). Diurnal variations in SO2 were observed, with a daytime maximum and early morning minimum in agreement with model simulations of DMS oxidation in the marine boundary layer. Steady state calculations and photochemical box model simulations suggest that the DMS to SO2 conversion efficiency in this region is 30–50%. Comparison of these results with results from warmer regions suggests that the DMS to SO2 conversion efficiency has a positive temperature dependence.

Processes controlling dimethylsulfide over the ocean: Case studies using a 3‐D model driven by assimilated meteorological fields

This study investigates the processes that influence dimethylsulfide (DMS) concentrations over the ocean using a global three‐dimensional chemistry and transport model (CTM). The model is driven by assimilated meteorological data from the Goddard Earth Observing System Data Assimilation System (GEOS‐I DAS). Results from the model are compared with DMS measurements from two marine sites, a ship cruise, and an aircraft campaign. When observed seawater DMS concentrations and meteorological conditions are used, the model reproduces the observed daily and diurnal variations of DMS concentrations at a tropical Pacific station. The model also predicts the observed changes of DMS concentrations across the Atlantic, although it overestimates the DMS level by a factor of 2. The calculated vertical DMS concentrations off Tasmania are more than 4 times higher than the measured data. The model simulates day‐to‐day fluctuations and interannual variations observed at Amsterdam Island but underpredicts the magnitude of the variations. Sensitivities for DMS concentrations to the parameters used in DMS emission, oxidation, boundary layer mixing, and cloud convective transport are tested. The limitations of the current model in interpreting the observations are due to (1) the uncertainties in parameterization of DMS emission from the ocean, (2) the simplistic boundary layer mixing scheme, (3) the inaccurate spatial distribution and intensity of deep convective clouds in the GEOS‐I DAS, and (4) the uncertainties in DMS oxidation rates.

Measurements of dimethyl sulfide, dimethyl sulfoxide, dimethyl sulfone, and aerosol ions at Palmer Station, Antarctica

In January and February 1994, measurements of dimethylsulfide (DMS) in air and seawater were conducted at Palmer Station, Antarctica, during project SCATE (Sulfur Chemistry in the Antarctic Troposphere Experiment). Corresponding values ranged between 6 and 595 pptv (median: 94 pptv) and 0.7 and 3.7 nM (median: 2 nM), respectively. Atmospheric DMS levels were significantly enhanced during a storm episode in connection with large‐scale low‐pressure systems passing through the study area. DMS sea‐to‐air fluxes ranged between 0.03 and 19 (median: 1.1) μmol m−2 d−1 based on seawater DMS and wind speed measurements. The atmospheric DMS lifetime is estimated to be 9 days based on a 24‐hour averaged OH concentration of 1.1 × 105 cm−3. Atmospheric dimethylsulfoxide (DMSO) and dimethylsulfone (DMSO2) mixing ratios varied mostly between <0.2 and 15 pptv. These variations consisted of many short‐term spikes which may be explained by downward mixing of these compounds from the free troposphere [Davis et al., this issue]. The DMSO photochemical lifetime with respect to the 24‐hour average OH concentration is approximately 25 hours in the coastal Antarctic troposphere in summer. However, present calculations show that the dominant sink of both DMSO and DMSO2 could be surface loss, yielding atmospheric lifetimes of a few hours for both compounds [see also Davis et al., this issue]. A good correlation was found between DMSO and DMSO2. Aerosol MSA and excess sulfate concentrations also showed a good correlation, with a slope of 0.73. However, DMS was not correlated with any of its measured oxidation products, probably because of its long atmospheric residence time over Antarctica.

Effect of UV- radiation on DMSP content and DMS formation of Phaeocystis antarctica

DMSP (dimethyl sulphonium propionate) contents produced by an Antarctic marine phytoplankton species, Phaeocystis antarctica (Prymnesiophyta), which were incubated under light conditions with radiations of different UV wavebands, were measured by gas chromatography after various exposure times. Full light (UV-B + UV-A + PAR) caused the strongest decrease in the production of DMSP in the alga. A marked depression of DMSP content was also observed with short UV-B and UV-A wavebands after 3 h. It was therefore hypothesised that DMSP production in Phaeocystis antarctica was inhibited by UV radiation. There was a negative correlation on change of DMSP contents under UV radiation. There was a negative correlation on change of DMSP contents under UV radiation with exposure times. The conversion rate of DMSP dissolved to DMS (dimethyl sulphide) was significantly increased with UV radiation. The possibility could not be excluded that a high concentration of free chemical radicals in seawater due to UV radiation resulted in an increase of DMSP cleavage in seawater. The oxidation of DMS in seawater due to UV-B radiation could result in a decrease of its flux to the atmosphere. The effect of UV radiation on DMSP production and oxidation of DMS may be an important factor in the variability of DMSP and the global flux of DMS from ocean to atmosphere.

Determination of the Henry's law constant for dimethyl sulfide in seawater

This study describes a modified method to measure the Henry's law constant (Hc) of dimethyl sulfide (DMS) across air-water interface. A fixed amount of DMS was added into a 50 ml gas-tight glass syringe with air-water (seawater or distilled water) and equilibrated twice with different volumes of air but identical volume of water. The He of DMS in water could be determined by measuring the concentrations of DMS in the air phases of two equilibrium by gas chromtography. The He of DMS in seawater and distilled water determined by the modified method at 18°C were 0.069 and 0.056, respectively, and the relative standard deviation was less than 5%. The modified method was used to determine the effects of temperature on He of DMS in seawater and concentration of NaCl on He of DMS in freshwater.

Dimethylsulfide (DMS) in the equatorial Pacific Ocean (1982 to 1996): Evidence of a climate feedback?

Oceanic dimethylsulfide (DMS) is the major natural source of sulfur to the atmosphere. The equatorial Pacific Ocean is a region of relatively high DMS emissions that persist throughout the year. Measurements from 11 cruises between 1982 and 1996 show that the mean surface seawater DMS concentration in this region (15°N to 15°S) is relatively constant both seasonally and interannually (2.7±0.7 nM). The large interannual variations in oceanic and atmospheric properties associated with El Niño‐Southern Oscillation (ENSO) events appear to have little effect on the concentration of DMS in surface ocean waters.

Bacterial chemotaxis and its potential role in marine dimethylsulfide production and biogeochemical sulfur cycling

Dimethylsulfide (DMS) gas constitutes 90% of biogenic sulfur emissions from oceans and is an important agent in climate regulation. DMS in seawater arises primarily via lyase degradation of dimethylsulfoniopropionate (DMSP), an osmolyte produced in high concentrations by some marine phytoplankton. After being induced to synthesize DMSP lyase, cells of a marine bacterium (Alcaligenes strain M3A) significantly reduce their rate of change in direction and tumbling frequency, and they are attracted to DMSP at levels similar to those occurring near senescing phytoplankton cells (10‒7–10‒6 M). In contrast, genetically identical bacteria without lyase induction are not attracted to DMSP. Combined with lyase activity, bacterial chemotaxis to DMSP could increase the rate of DMS production and therefore play a critical role in biogeochemical sulfur cycling between dissolved organic matter in seawater and the atmosphere.

Dimethylsulfide in coastal zone of the East China Sea

Dimethylsulfide (DMS) in seawater were observed four times from February 1993 to August 1994 along a fixed section (PN line) in the East China Sea. The DMS concentrations showed remarkable temporal and spatial variations. The DMS concentrations were generally higher in the upper euphotic layer of the continental shelf zone in summer. The spatial variation, however, was more pronounced even in well mixed winter water, where the concentration of DMS varied widely from 3 to 106 ng-S/l in the continental shelf zone while the salinity was vertically almost uniform. This means that DMS in seawater is rapidly produced and decomposed with a time scale less than one month in the water column. The largest value of 376 ng-S/l was obtained at 5 m depth near the mouth of Changjiang River in August 1994. The mean concentrations in the surface 30 m layer in the continental shelf zone were 21, 54, 126 and 57 ng-S/l in February, October, June and August, respectively, which were about twice as large as those in the Kuroshio region. The mean fluxes of DMS from the East China Sea to the atmosphere are estimated to be 49 μg-S/m2/day in winter and 194 μg-S/m2/day in summer in the continental shelf zone, and to be 32 and 107 μg-S/m2/day in the Kuroshio region.

Impact of dimethylsulfide photochemistry on methyl sulfur cycling in the equatorial Pacific Ocean

Shipboard experiments were conducted in the equatorial Pacific Ocean to ascertain the relative importance of atmospheric ventilation, biological consumption, and photolysis in the removal of dimethylsulfide (DMS) from seawater. Comparisons were made at a series of sampling locations in a transect from 12°N 140°W to 12°S 135°W, as part of the International Global Atmospheric Chemistry project's Marine Aerosol and Gas Exchange cruise in February–March 1992. Turnover rate constants for DMS were used to compare the different removal pathways over three depth intervals (0–1 m, 0–20 m, and 0–60 m). In the surface mixed layer (0–60 m), the DMS turnover rate constants ranged from 0.02 to 0.19 day−1 for atmospheric ventilation, 0.04 to 0.66 day−1 for biological consumption, and 0.05 to 0.15 day−1 for photolysis. When all three processes are considered, the corresponding turnover time for DMS ranges from 1 to 4 days, with photolysis accounting for 7%–40% of the total turnover of DMS. Laboratory irradiations were conducted with stored seawater samples to study the kinetics and wavelength dependence of DMS photolysis. Salient results were (1) the photolysis of DMS followed pseudo first‐order kinetics, (2) dimethylsulfoxide was a minor (14%) product of DMS photolysis, and (3) the photolysis of DMS in seawater under natural light conditions occurred primarily at wavelengths between 380 and 460 nm. On the basis of these results, we predict that the photolysis of DMS will occur at appreciable depths in the photic zone in oligotrophic marine environments (∼60 m). An important finding of this study is that atmospheric loss, biological consumption, and photolysis are all important removal pathways for DMS in the photic zone of the equatorial Pacific Ocean. The relative importance of each pathway is a function of the depth interval considered, sampling location, and meteorological conditions.

Production and fate of dimethylsulfide and dimethylsulfoniopropionate in pelagic mesocosms:the role of sedimentation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 131:275-286 (1996) - doi:10.3354/meps131275 Production and fate of dimethylsulfide and dimethylsulfoniopropionate in pelagic mesocosms: the role of sedimentation Osinga R, Kwint RLJ, Lewis WE, Kraay GW, Lont JD, Lindeboom HJ, van Duyl FC Elevated concentrations of dimethylsulfide (DMS) sometimes occur in sea water during phytoplankton blooms. To determine the factors controlling the concentration of DMS in sea water, the development and fate of a bloom dominated by Phaeocystis sp. was studied in relation to the production and fate of DMS and its precursor beta-dimethylsulfoniopropionate (DMSP) in a pelagic mesocosm experiment. The part of this study described here focused on the role of sedimentation of algae as a loss factor for DMSP and as a trigger mechanism for DMS production. A hypothesis tested was that high DMS concentrations occur after a mass release of DMSP from algae due to mass sedimentation followed by cell lysis on the mesocosm floor. This was studied by monitoring Phaeocystis cell numbers, chlorophyll a, particulate DMSP, dissolved DMSP and DMS in the water column, and by daily measurements of the sedimentation of Phaeocystis cells. We evaluated a technique for measuring DMSP indirectly as acrylate by high-performance liquid chromatography (HPLC). This method seemed to be hampered by DMSP-lyase activity of Phaeocystis sp. during sample processing, but gave good results when Phaeocystis was not dominant. Sedimentation rates of Phaeocystis sp. were found to be high and constantly related to the standing stock in the water column. The average sinking velocity of Phaeocystis cells was 1.4 m d-1. At the decline of the bloom, sedimentation accounted for approximately 50% of the observed loss of Phaeocystis biomass, which indicates that cell lysis may have been important as well at this time. The decline of the bloom did not result in an elevated DMS concentration. However, a significant peak in DMS was observed at the end of the exponential growth phase of the Phaeocystis bloom. It was concluded that the decline of a Phaeocystis bloom does not lead to an elevated DMS concentration in the water column. The continuously high sedimentation of living Phaeocystis cells suggests that, in these mesocosms, lysis after sedimentation was an important mechanism for release of DMSP from cells and, hence, production of DMS. Nevertheless, this mechanism in itself can not explain the strong fluctuations in the DMS concentration observed in this experiment. Phaeocystis . Sedimentation . DMS . DMSP Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 131. Publication date: February 08, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

The central Arctic Ocean as a source of dimethyl sulfide Seasonal variability in relation to biological activity

Seawater dimethyl sulfide (DMS) and distribution of phytoplankton biomass were investigated in relation to sea ice conditions, hydrography and nutrients, onboard the Swedish icebreaker Oden as a part of the International Arctic Ocean Expedition, 1991. The expedition lasted from the beginning of August until the middle of October and covered sampling between 75° to 90° N in the open waters and along the ice edge zone in the Greenland Sea-Fram Strait area as well as in the pack ice of the western part of the Nansen and Amundsen basins and in the Makarov basin. Surface seawater DMS concentrations showed a clear seasonal progression related to biological activity, ranging from 0.04 to 12 nmol dm −3 . The highest values were found in open waters along the ice edge in the beginning of August, while the lowest concentrations were measured beneath heavy pack ice in late September. On average DMS fell about 30% per week in the open waters south of and within the ice edge zone whereas a significant higher seasonal decline, about 45% per week, was observed in the pack ice during freeze-up. The importance of the phytoplankton bloom and zooplankton abundance both at the ice edge zone and in the pack ice during summer ice-melt to DMS concentrations in seawater has been demonstrated. We also demonstrated a potential for intense DMS production in the open waters in the wake of the receding ice. The extremely low surface concentrations of DMS during the freeze-up of the pack ice were probably primarily controlled by removal processes within the water column. The turnover time of DMS in the pack ice water column was calculated to be of the order of 13 days with the most effective sink seemingly of micro-biological origin. Although, our limited set of data indicated the likelyhood of a relationship between DMS and degraded phytoplankton material (phaeopigments), seawater DMS showed no simple correlation with phytoplankton standing stock over the large areas and different seasons covered. The area weighed summer and winter fluxes of DMS from the Arctic Polar Ocean to the atmosphere were estimated to be 2.0 and 0.03 μ mol m −2 day −1 , respectively. On an annual basis, winter biogenic sulfur emissions are negligible compared to the summer emissions in the region. The total emissions of marine biogenic sulfur from the Northern Hemispheric high latitudes was estimated to be approximately 4 Gmol yr −1 . DOI: 10.1034/j.1600-0889.1996.t01-1-00003.x

Overview of the atmospheric research program during the International Arctic Ocean Expedition of 1991 (IAOE-91) and its scientific results

The broad aim of the Atmospheric program of the International Arctic Ocean Expedition (IAOE-91) was to test the hypothesis that marine biogenically produced dimethyl sulfide (DMS) gas can exert a significant global climatic control. The hypothesis states that DMS is transferred to the atmosphere and is oxidised to form airborne particles. Some of these grow large enough to act as cloud condensation nuclei (CCN) which help determine cloud droplet concentration. The latter has a strong influence on cloud albedo and hence on the radiation balance of the area affected. In summer, the central Arctic is a specially favourable region for studying the natural sulfur cycle in that the open waters surrounding the pack ice are the only significant sources of DMS and there are almost no anthropogenic particle sources. Concentrations of seawater and atmospheric DMS decreased at about the same rate during the period of measurements, (1 August to 6 October, latitudes 75°N to 90°N) spanning about three orders of magnitude. Methane sulfonate and nonsea salt sulfate in the submicrometer particles, which may be derived from atmospheric DMS, also decreased similarly, suggesting that the first part of the hypothesis under test was true. Influences on cloud droplet concentration and radiation balance could not be measured. Size-resolved aerosol chemistry showed a much lower proportion of methane sulfonate to be associated with supermicrometer particles than has been found elsewhere. Its molar ratio to nonsea salt sulfate suggested that the processes controlling the particulate chemistry do not exhibit a net temperature dependence. Elemental analysis of the aerosol also revealed the interesting possibility that debris from Siberian rivers transported on the moving ice represent a fairly widespread source of supermicrometer crustal material within the pack ice. Highly resolved measurements of aerosol number size distributions were made in the diameter range 3 nm to 500 nm. 3 distinct modal sizes were usually present, the “ultrafine”, “Aitken” and “accumulation” modes centred on 14, 45 and 170 nm diameter, respectively. The presence of ultrafine particles, implying recent production, was more frequent than has been found in lower latitude remote marine areas. Evidence suggests that they were mixed to the surface from higher levels. Sudden and often drastic changes in aerosol concentration and size distribution were surprisingly frequent in view of the relatively slowly changing meteorology of the central Arctic during the study period and the absence of strong pollution sources. They were most common in particles likely to have taken part in cloud formation (> 80 nm diameter). 2 factors appear to have been involved in these sudden changes. The 1st was the formation of vertical gradients in aerosol concentration due to interactions between particles and clouds or favoured regions for new particle production during periods of stability. The 2nd was sporadic localised breakdowns of the stability, bringing changed particle concentrations to the measurement level. Probable reasons for these sporadic mixing events were indicated by the structure of the Marine Boundary Layer (MBL) investigated with high resolution rawinsondes. Low level jets were present about 60% of the time, producing conditions conductive to turbulence and shear-induced waves. It is concluded that an even more detailed study of meteorological processes in the MBL in conjunction with more highly time-resolved measurements of gas-aerosol physics and chemistry appears to be essential in any future research aimed at studying the indirect, cloud mediated, effect of aerosol particles. DOI: 10.1034/j.1600-0889.1996.t01-1-00002.x

Determination of trace quantities of volatile sulfur compounds in aqueous solutions by gas chromatography after purge and trap isolation and cryogenic focusing

AbstractA method for the determination of volatile organic sulfur compounds, such as dimethylsulfide (DMS), at the nanogram level in aqueous samples is described. A purge and trap technique was used to remove and preconcentrate DMS and other sulfur compounds from aqueous solutions. Trapping of the isolated compound was performed on Tenax TA and Carbosieve III S. The water vapor from the purging stream was removed by a commercially available Nafion tube inserted in a plastic container packed with molecular sieve 5A. Analytes, after thermal desorption, were recollected in a short fused silica capillary tube cooled with the vapors of liquid nitrogen to a temperature ca. −150°C. Next, sulfur compounds were revolatilized and directly transferred to the analytical capillary column for analysis. Detection was performed with a flame photometric detector. The whole procedure was optimized and checked using a homemade valving device easily coupled to any gas chromatograph. The method has been used to measure DMS and other volatile sulfur compounds in seawater of the Baltic Sea and in samples of water from three rivers in the Gdańsk, Poland, region.

Biogenic sulfur emissions and aerosols over the tropical South Atlantic: 1. Dimethylsulfide in sea water and in the atmospheric boundary layer

We measured dimethylsulfide (DMS) in air (DMSa) and surface seawater (DMSw) on board the R/V Meteor during February–March 1991 on the tropical South Atlantic. Samples for the determination of DMSa were taken through a fluorinated ethylene/propylene Teflon inlet ≈33 m above sea level, preconcentrated by adsorption onto gold wool in quartz tubes, and analyzed by gas chromotography with flame photometric detection. The DMSa instrument is fully automated, providing improved precision, and processes up to four samples per hour. Over most of the cruise track, which followed the 19°S parallel between Brazil and Africa, DMSw, was significantly correlated to climatologically averaged chlorophyll concentrations obtained from coastal zone color scanner data, suggesting that remote sensing may be useful for estimating seawater DMS levels at least in some ocean regions. The cruise track proceeded from waters of low roductivity (off the coast of Brazil and in the subtropical gyre) to higher productivity (the Benguela Current and the upwelling region off Namibia and Angola); meteorological conditions were steady with consistent easterly winds. DMS values for air and water were low (≈ 50 ppt and 1–2 nmol L−1, respectively) in the areas of low productivity and increased simultaneously (≈ 100–300 ppt and 3–15 nmol L−1) as productivity increased. DMS sea‐to‐air fluxes (average 7.3 μmol m−2 d−1) were calculated based on different parameterizations; for the study region the differences between the results obtained from the different models were minor. DMSa was strongly correlated to its emission flux from the sea surface as estimated from DMSw and meteorological parameters. This suggests that the air/sea transfer parameterizations used are suitable for providing estimates of DMS flux from the oceans.