Seawater Dimethylsulfide Concentrations Research Articles

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.

Elevated production of dimethylsulfide resulting from viral infection of cultures of Phaeocystis pouchetii

The effects of viral lysis on dimethyl sulfide (DMS) and particulate and dissolved dimethylsulfoniopropionate (DMSP) concentrations were studied in batch cultures of Phaeocystis pouchetii infected with a strain‐specific viral isolate. After 20 h, DMS concentration had increased by fourfold over the levels observed in the control cultures, and this increased to eightfold 45 h after addition of viral particles. The results suggest that viral lysis of DMSP‐containing phytoplankton cells should be considered alongside autolysis, grazing, and bacterial activity as a process that can influence DMS concentrations in seawater. Further research will be necessary to determine the importance of viruses in the biogeochemical DMS cycle in the natural environment.

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.

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.

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

Biogenic sulfur compounds in seawater and the atmosphere of the Antarctic region

Shipboard measurements of dimethyl sulfide (DMS), carbonyl sulfide (COS) and carbon disulfide (CS 2 ) in seawater and the marine boundary layer were performed during a cruise between Punta Arenas (Chile) and Cape Town (South Africa) through the Weddell Sea in November/December 1990. The DMS concentrations in seawater averaged to 71 ngS/l, atmospheric DMS mixing ratios showed a range between 2 and 1048 pptv. In the Weddell Sea where DMS mixing ratios as low as 24 pptv on the average were observed, the extensive ice cover seemed to minimize the gas exchange between seawater and the overlying atmosphere. The COS levels in seawater showed a mean of 3.5 ngS/l with minor variability. Atmospheric COS mixing ratios measured over the Weddell Sea averaged to 453 ± 43 pptv. In contrast, COS concentrations during advection processes of continental air masses over the Drake Passage were evidently higher with a mean of 628 ± 42 pptv. The concentrations of CS 2 in the remote marine boundary layer were below the detection limit of 7 pptv, with enhanced concentrations of about 35 pptv observed in air masses influenced by continental inputs. CS 2 values in surface seawater were mostly below the detection limit of 0.43 ngS/l with few exceptions revealing CS 2 values between 0.48 and 1.43 ngS/l. In 91% of all seawater samples taken during this cruise CS 2 were not found in detectable concentrations. DOI: 10.1034/j.1600-0889.1993.t01-1-00005.x

On the biogenic origin of dimethylsulfide: Relation between chlorophyll, ATP, organismic DMSP, phytoplankton species, and DMS distribution in Atlantic surface water and atmosphere

During a cruise over the Atlantic from 40°S to 50°N in March–April 1987 the concentrations of dimethylsulfide (DMS) in the ocean and atmosphere were measured as well as the distribution of its precursor, dimethylsulfoniopropionate (DMSP), and of several biological parameters such as chlorophyll, phytoplankton species, and adenosine‐5‐triphosphate (ATP) in the surface water. The DMS concentration varied in the range 0.2–2 nmol DMS L−1 (surface water) and 0.05–3 nmol DMS m−3 (atmosphere) in the region of the remote tropical and subtropical Atlantic and increased to 2–10 nmol DMS L−1 (surface water) and 1–8 nmol DMS m−3 (atmosphere) north of 40°N and in the English Channel. Based on these results the mean flux of DMS from the Atlantic to the atmosphere is estimated to be 4–4.65 nmol DMS m−2 min−1. A moderate diurnal variation of atmospheric DMS was found with a minimum during daytime. The DMS concentration in seawater correlated well with the concentration of DMSP and showed a similar trend to ATP, chlorophyll, and some phytoplankton species.

Two approaches to determining the sea‐to‐air flux of dimethyl sulfide: Satellite ocean color and a photochemical model with atmospheric measurements

Two estimates of the ocean‐to‐atmosphere flux of dimethyl sulfide (DMS) are presented to determine the feasibility of using remotely sensed data to map the marine sources of a photoreactive trace gas. First, an empirical relationship between chlorophyll a and DMS in surface seawater (Andreae and Barnard, 1984) is used with NASA coastal zone color scanner (CZCS) data for chlorophyll a pigment to derive a mean DMS flux for a region in the tropical North Atlantic for October 1980. This is compared with the sea‐to‐air flux derived from a one‐dimensional photochemical model that reproduces boundary layer concentrations of O3, CO, NO, and hydrocarbons measured on a cruise at the same location and time (Meteor 56/1). Both evaluations of DMS fluxes are in the range (2–7)×109 molecules DMS cm−2 s−1 and agree well with fluxes based on the seawater DMS concentration given by Barnard et al. (1982) for the Meteor cruise. The applicability of the results to strategies for satellite remote sensing of the tropospheric sulfur cycle is discussed. For some species (e.g., DMS) surface sensing of sources is feasible, but only in regions and seasons where phytoplankton pigment is a meaningful marker for biogenic emissions. The general applicability of ocean color to DMS determination awaits the development of an algorithm that can extract distributions of DMS emitting species from the optical signal. For other sulfur constituents (e.g., SO2, COS) atmospheric measurements are appropriate for determining tropospheric distribution. Wind, moisture, cloud, precipitation, and temperature data are also required for complete characterization of the marine sulfur cycle.

The biogeochemical sulfur cycle in the marine boundary layer over the Northeast Pacific Ocean

The major components of the marine boundary layer biogeochemical sulfur cycle were measured simultaneously onshore and off the coast of Washington State, U.S.A. during May 1987. Seawater dimethylsulfide (DMS) concentrations on the continental shelf were strongly influenced by coastal upwelling. Concentration further offshore were typical of summer values (2.2 nmol/L) at this latitude. Although seawater DMS concentrations were high on the biologically productive continental shelf (2–12 nmol/L), this region had no measurable effect on atmospheric DMS concentrations. Atmospheric DMS concentrations (0.1–12 nmol/m3), however, were extremely dependent upon wind speed and boundary layer height. Although there appeared to be an appreciable input of non-sea-salt sulfate to the marine boundary layer from the free troposphere, the local flux of DMS from the ocean to the atmosphere was sufficient to balance the remainder of the sulfur budget.

Seasonal variation of atmospheric dimethylsulfide at Amsterdam Island in the southern Indian Ocean

Daily measurements of atmospheric concentrations of dimethylsulfide (DMS) were carried out for two years in a marine site at remote area: the Amsterdam Island (37°50′S–77°31′E) located in the southern Indian Ocean. DMS concentrations were also measured in seawater. A seasonal variation is observed for both DMS in the atmosphere and in the sea-surface. The monthly averages of DMS concentrations in the surface coastal seawater and in the atmosphere ranged, respectively, from 0.3 to 2.0 nmol l-1 and from 1.4 to 11.3 nmol m-3 (34 to 274 pptv), with the highest values in summer. The monthly variation of sea-to-air flux of DMS from the southern Indian Ocean ranges from 0.7 to 4.4 μmol m-2 d-1. A factor of 2.3 is observed between summer and winter with mean DMS fluxes of 3.0 and 1.3 μmol m-2 d-1, respectively.

Dimethylsulfide and Phaeocystis poucheti in the southeastern Bering Sea

Dimethylsulfide (DMS), a volatile excretion product of marine phytoplankton, was determined in the water column during the spring phytoplankton bloom on the southeastern Bering Sea shelf. In the same samples, a broad range of variables which characterize the biological processes in this region were measured. DMS was correlated with phytoplankton chlorophyll in the outer shelf and oceanic domains, but not in the middle shelf domain. A very strong correlation between the cell density of the haptophyte Phaeocystis poucheti and the DMS concentration in seawater was found, which suggests that this species accounts for most of the DMS present in the study region. We propose that in P. poucheti and certain other phytoplankton species the excretion of DMS is incidental to the release of acrylic acid which serves to inhibit bacterial attack upon the algae.