Short-Term Variability of Atmospheric DMS and Its Oxidation Products at Amsterdam Island during Summer Time

A one-month experiment was performed at Amsterdam Island in January 1998, to investigate the factors controlling the short-term variations of atmospheric dimethylsulfide (DMS) and its oxidation products in the mid-latitudes remote marine atmosphere. High mixing ratios of DMS, sulfur dioxide (SO₂) and dimethylsulfoxide (DMSO) have been observed during this experiment, with mean concentrations of 395 parts per trillion by volume (pptv) (standard deviation, = 285, n = 500), 114 pptv ( = 125, n = 12) and 3 pptv ( = 1.2, n = 167), respectively. Wind speed and direction were identified as the major factors controlling atmospheric DMS levels. Changes in air temperature/air masses origin were found to strongly influence the dimethylsulfoxide (DMSO)/DMS and SO₂/DMS molar ratios, in line with recent laboratory data. Methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO₄ ^2–) mean concentrations in aerosols during this experiment were 12.2± 6.5 pptv (1, n=47) and 59 ± 33 pptv (1, n=47), respectively. Evidence of vertical entrainment was reported following frontal passages, with injection of moisture-poor, ozone-rich air. High MSA/ nss-SO₄ ^2– molar ratios (mean 0.44) were calculated during these events. Finally following frontal passages, few spots in condensation nuclei (CN) concentration were also observed.     

Dimethylsulphide production in the Southern Ocean using a nitrogen-based flow network model and field measurements from ACE-1

Dimethylsulphide (DMS) has been implicated in climate change as a possible negative feedback to global warming, and several Models have been developed that simulate the production of DMS in the marine environment. The focus of this study is to improve the nitrogen based Gabric Model, using field data collected during the Southern Hemisphere First Marine Aerosol Characterisation Experiment (ACE-1) in the Southern Ocean in 1995. Two Model Runs (Series A and B) were carried out with six simulations of varying biotic and abiotic inputs applied over the voyage transect (41-48°S), reflecting Model default values or field values from the experiment. The abiotic inputs were time-step, dissolved dimethylsulphoniopropionate (DMSP) and DMS, and the biotic nitrogen inputs were from phytoplankton, bacteria, zooflagellates, large protozoa, micro and mesozooplankton. The focus of the abiotic assessment was nutrient (nitrate) uptake and dissolved DMSP and DMS output. Model output of the biotic compartments was assessed for congruence with predicted ecological patterns of succession.

Despite a limited data set the study provides a good insight into the utility of the Model, which functioned as a heuristic rather than predictive tool. In simulation 1 (Series A) where the only field value was nitrate, all latitudes from 41-48°S concurred with the ecological succession predicted by the Model authors and the successional pattern predicted by other researchers, with a double phytoplankton peak indicating remineralisation of nitrogen via the microbial loop. In many simulations the Model produced lower values of dissolved DMS than were measured, and production of DMS in the Model appears constrained. However, in simulation 5 (Series A) DMS model outputs were closest to the mean dissolved DMS levels reported on RV Discoverer. In this simulation, field values were used for phytoplankton, nitrate, dissolved DMSP and DMS, with bacterial abundance and micro and mesozooplankton increased over their Gabric default values. Also, the phytoplankton double peak occurred earlier, as did the peaks in bacteria, zooflagellates, and large protozoa. Simulations that deviated more significantly from the predicted successional patterns were characterised by single peaks in phytoplankton growth and delayed bacterial growth. Series C simulations at latitude 43°S, in an attempt to reduce phytoplankton predation by bacteria, increased DMS output reasonably successfully. However, significant recalibration of the Model is recommended in conjunction with field studies to gather vital background biological data - particularly in the areas of nutrient limitation, phytoplankton speciation, and the cellular content of the DMS precursor compound, DMSP.     

Production of dimethylsulfide and acrylic acid from dimethylsulfoniopropionate during growth of three marine microalgae

We measured the concentrations of dimethylsulfide （DMS）, acrylic acid （AA）, and dimethylsulfoniopropionate （DMSP） during growth of three microalgae： Prorocentrum micans, Gephyrocapsa oceanica, and Platymonas subcordiformis. The DMSP, AA, and DMS concentrations in culture media varied significantly among algal growth stages, with the highest concentrations in the late stationary growth stage or the senescent stage. In the stationary growth stage, the average DMSP concentration per cell in P. micans （0.066 5 pmol/cell） was 1.3 times that in G. oceanica （0.049 5 pmol/ cell） and 20.2 times that in P. subcordiformis （0.003 29 pmol/cell）. The average concentrations of AA were 0.044 6, 0.026 9, and 0.003 05 pmol/cell in P. micans, G. oceanica, and P. subcordiformis, respectively, higher than the concentrations of DMS （0.272, 0.497, and 0.086 2 fmol/cell, respectively）. There were significant positive correlations between cell density and AA, DMSP, and DMS concentrations. The ratios of DMS/AA and AA/（DMSP＋AA） in the three algae differed significantly over the growth cycle. In all three microalgae, the DMS/AA ratios were less than 25% during the growth period, suggesting that the enzymatic cleavage pathway, which generates DMS, was not the main DMSP degradation pathway. The changes in the DMS/AA ratio indicated that there was a higher rate of enzymatic breakdown of DMSP in the early growth period and a lower rate during senescence. In all three microalgae, the AA/（DMSP＋AA） ratio （degradation ratio of DMSP） decreased during the exponential growth phase, and then increased. The variations in these ratios can approximately indicate the cleavage mechanism of DMSP at different stages of algal growth.     

DMSP and DMS in coastal fast ice and under-ice water of Lützow-Holm Bay, eastern Antarctica

The combined concentration of total dimethylsulfoniopropionate and dimethylsulfide (DMSP+DMS) were measured in Antarctic fast ice on the coast of Lützow-Holm Bay, eastern Antarctica. High bulk-ice DMSP+DMS and chlorophyll a concentrations were found at the bottom of the sea ice, and these concentrations were higher than those in the under-ice water. The bulk-ice DMSP+DMS and chlorophyll a concentrations were highly correlated (r²=0.68, P<0.001), suggesting that the high bulk-ice DMSP+DMS concentrations were caused mainly by the presence of algae assemblages in the ice. The calculated brine DMSP+DMS concentrations were as high as 1100 nM in the bottom ice layer, and the vertical profile patterns of brine DMSP+DMS concentrations were almost the same as for the bulk ice, mainly because of the small amount of variability in the vertical brine volume fraction. DMSP+DMS and chlorophyll a concentrations in the under-ice water increased, whereas the salinity of the under-ice water decreased, during the sampling period. These results reflect the supply of freshwater containing high levels of DMSP+DMS to the water just under the ice as the ice melted. These results suggest that sea-ice melting could be important to sulfur cycling in coastal ice-covered regions of the polar oceans.     

胶州湾海水中DMS和DMSP的分布及其影响因素

为了解人为活动对二甲基硫(DMS)和二甲巯基丙酸(DMSP)生物生产的干扰,分别于2005年8月、11月对胶州湾海域进行采样。测定结果表明:胶州湾海水中8月DMS、DMSPd和DMSPp在次表层的平均含量分别为4.89,17.9和23.93nmol·L-1,在微表层中的平均含量分别为4.58,19.98和21.49nmol·L-1,11月DMS、DMSPd和DMSPp在次表层的平均含量分别为2.07,12.99和16.74nmol·L-1,在微表层中的平均含量分别为1.44,16.13和19.62nmol·L-1。DMS和DMSP的水平分布由于受到陆源输入的影响,呈现出自湾内向湾外递降的趋势。DMS和DMSP的含量夏季高于秋季。DMS和Chl-a在每个季节具有一定的相关性。DMS浓度的增加导致DMS通量增加。对海水微表层和次表层的研究表明,DMS和DMSPp并未在微表层中富集,而DMSPd有一定程度的富集。DMS,DMSP,Chl-a在海水微表层和次表层之间浓度分布的相关性体现了2层水体之间存在强烈的交换作用。     

Biological control of short-term variations in the concentration of DMSP and DMS during a Phaeocystis spring bloom

In the spring of 1995, short-term variations in the concentration of particulate and dissolved dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) were monitored in the western Wadden Sea, a shallow coastal region in open connection with the North Sea. Significant correlations were found between abundance of Phaeocystis globosa and particulate DMSP; concentrations increased rapidly from 100 to 1650 nM in the middle of April. Highest DMS concentrations were found during the initial phase of the exponential growth of the bloom. DMS production and loss rates of DMSP and DMS were estimated experimentally during various phases of the bloom. DMS production and consumption were roughly in balance, with production only slightly exceeding consumption at the start of the bloom. Rates of production and consumption were highest during the exponential growth phase of Phaeocystis and declined in the course of the bloom (from 300–375 to less than 5 nmol dm⁻³ d⁻¹). Demethylation of DMSP increased during the bloom (from 11 to 1300 nmol dm⁻³ d⁻¹); it accounted for up to 100% of the DMSP loss at the end of the bloom. The shift from DMSP cleavage to demethylation in the course of a Phaeocystis bloom implies that DMS concentrations are not necessarily highest at the peak or towards the end of blooms.     

紫外辐射对南极棕囊藻细胞DMSP合成和DMS释放率的影响

在不同紫外辐射波段下,南极棕囊藻(Phaeocystis antarctica)细胞的生长率、叶绿素a、细胞内DMSP含量和DMS释放量变化的测定结果表明;UV-B对南极棕囊藻细胞生长率和叶绿素a含量有抑制效应,UV-B还可加快DMSP分解成DMS和丙烯酸的分解速率,而UV-A对该藻细胞的DMSP合成有强烈的抑制效应。鉴于在每年春季极地海洋浮游植物繁殖期间,南极棕囊藻在南极海冰带海洋浮游植物种群结构中占有的优势地位,以及该藻是极地海洋浮游植物中DMS的主要释放者,推测南极“臭氧空洞”所增加的紫外辐射可能会对南极海域的DMS释放率产生一定的影响。     

The Role of Multiphase Chemistry in the Oxidation of Dimethylsulphide (DMS). A Latitude Dependent Analysis

A kinetic model for the OH-initiated homogeneous gas phase oxidation of dimethylsulfide (DMS) in the atmosphere (Saltelli and Hjorth, 1995), has been extended here to include the liquid phase chemistry. The updated model has then been employed to predict the temperature dependency of the MSA/nss-SO42- ratio. Model predictions have been compared with observational data reported in Bates et al. (1992). Sensitivity and uncertainty analysis has been performed in a Monte Carlo fashion to identify which are the important uncertainties on the input parameters and which are the possible combinations of parameter values that could explain the field observations. Results of the analysis have indicated that the temperature dependencies of the interactions between gas phase and liquid phase chemistry may to a large extent explain the observed T-dependence of the MSA/nss- SO42- ratio. The potential role of multi-phase atmospheric chemistry, not only in the case of SO2 but also of other oxidation products of DMS and, particularly, of DMS itself, has been highlighted.     

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.