| Dimethylsulfide (DMS) is a climatically active biogenic gas emitted from the ocean surface to atmosphere. Emissions of DMS from the ocean are a significant source of sulfate aerosol in the marine boundary layer. There are approximately 28.1 (17.6-34.4) Tg sulfur transferred from the oceans into the atmosphere annually in the form of DMS. DMS emissions not only balance the global sulfur budget, but also impact climate of the Earth due to its oxidation products in the atmosphere. When DMS diffuses into the atmosphere, it can be oxidized rapidly by OH (by day) and NO3 (by night) radicals to form various sulfur containing products, such as sulfur dioxide (SO2), methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO42-). Sulfate produced by this process not only increases the natural acidity of atmospheric deposition, but also contributes to the condensation nuclei (CN) and eventually cloud condensation nuclei (CCN) in remote marine environments. Changes in CCN concentration affect the cloud droplet number concentration, which influences the cloud albedo and subsequently the climate.The eastern marginal seaes of China are located on the margin of the Northwest Pacific Ocean, which is one of the largest continental shelves in the world. These shelves act as a transition zone between land and ocean, and provide an important conduit channeling terrigenous and anthropogenic materials from the northern Asia mainland to the Northeast Pacific. The spatial and temporal variations of distributions of DMS and DMSP, sea-to-air fluxes of DMS, factors influencing them and its contribution to atmospheric sulphate aerosol are studied. In addition, two sites in ECS were chosed to measured DMSP and DMS concentration, phytoplankton community, and using culture-dependent and culture-independent methods to select bacterial members and genes involved in DMSP degradation. Furthermore, the molecular mechanism of DMS production through DMSP cleavage was revealed by structural analyses.(1) The distributions of DMS and DMSP are determined in eastern marginal seas of China during Jun-Jul,2011 (Summer), Sep-Oct,2011 (Fall) and Dec,2011～Jan,2012 (Winter). The concentrations of DMS, DMSPd and DMSPp in summer ranged from 0.63 to 41.19 nmol L-1, from 1.38 to 27.23 nmol L-1 and from 6.23 to 207.73 nmol L-1,respectively, with average values of 5.30,5.23 and 27.13 nmol L-’. Concentrations of DMS, DMSPd and DMSPp in surface seawater during fall were 3.39 (0.83～6.77),3.59 (0.86～12.71) and 15.72 (4.75～44.63) nmol L-1. Concentrations of DMS, DMSPd and DMSPp in surface seawater in winter were 2.20 (0.58～ 4.14),2.12 (0.37～7.86) and 11.98 (4.29～25.76) nmol L-1. DMS and DMSP showed a notable variation:Smmer> Fall> Winter. Their spatial distributions were obviously influenced by Yangtze River and the oligotrophic Kuroshio. The distribution patterns were different in different seasons, during summer and fall, they decreased from inshore to offshore sites. In addition, the distributions of DMS and DMSP are determined in Bohai and North Yellow Sea during Novermber,2011. The concentrations of DMS, DMSPd and DMSPp in surface seawater ranged from 0.75 to 6.69 nmol L-1,from 0.888 to 12.883 nmol L-1 and from 7.56 to 42.28 nmol L-1 respectively, with average values of 2.15,2.82 and 17.76 nmol L-1.(2) Phytoplankton is the main source of DMS and DMSP and Chl-a can be considered as an indicator of phytoplankton biomass. In our study area, the concentrations of Chl-a were significantly correlated with the concentrations of DMPPp, indicating that phytoplankton biomass was a main factor controlling the distributions of DMS and DMSP in the study area. Principal component analysis (PCA) was used to analyze the controlling factors of samples and to research the correlations of measured parameters and significant correlation was observed between DMSPp and silicate whereas no relationship was found between DMSPp and phosphate or nitrate in the BS and NYS. This result showed that diatoms, despite being low DMSP producer, may become the most important sources of DMSP when they are dominant in seawater.(3) The study of size distributions of Chl-a and DMSPp were conducted in the eastern seas of China. The particulates in the surface water were size-fractionated into the classes>20μm (microplankton),5～20μm (larger nanoplankton),2～5μm (smaller nanoplankton), and 0.2～2 μm (picoplankton). At most stations, DMSPp and Chl-a were contributed mainly by larger nanoplankton, which accounted for about 80%. Skeletonema costatum and Paralia sulcata were the main contributor of DMSPp and Chl-a. However, in the peripheral area of the Yangtze River estuary during summer, microplankton became the primary source of DMSPp. At this station the phytoplankton size larger than 20μm mainly was comprised of Ceratium tripos (belonging to dinoflagellates), which is considered to be a primary contributor of DMSPp.(4) In this research, the sea-to-air fluxes of DMS were calculated using the parameterization of Nightingale et al. (2000) (N2000), which is best fit lies between LM86 and W92 and the sea-to-air fluxes of DMS vary widely in different seasons. The sea-to-air fluxes of DMS observed in summer ranged from 0.03 to 102.4μmol m-2 d-1, with an average of 16.73μmol m-2 day-1. The sea-to-air fluxes of DMS during fall ranged from 0.74 to 74.41μmol m-2 d-1, with an average of 12.10μmol m-2 d-1. The sea-to-air fluxes of DMS during winter ranged from 0.61 to 25.52 μmol m-2 d-1, with a mean of 8.30μmol m-2 d-1. The sea-to-air fluxes of DMS observed in BS and NYS during late fall ranged from 0.05 to 27.4μmol m-2 d-1, with an average of 4.21μmol m-1 d-1. In addition, we used the typical nss-SO42-/MSA ratio of 19 to evaluate the biogenic contribution to the total nss-SO42- over the eastern seas of China. The biogenic nss-SO42- over the ECS and SYS during summer contribution to the measured total nss-SO42- ranged from 1.42% to 30.98% with an average of 8.2%, while only 0.8% during winter. Throughout the BS and NYS dring fall, the concentrations of MSA ranged from 0.006 to 0.029μg m-3 with a mean of 0.013μg m-3. The biogenic SO42- contribution to the total nss-SO42- ranged from 0.46% to 5.49% with an average of 1.40%. Considering that the reaction of DMS and NO3- can change the ratio of nss-SO42-/MSA and the high NO3- concentration was observed in our study, the contribution of DMS to sulfate in aerosol might be overestimated. Our results imply that over the eastern seas of China, the contribution of biogenic SO42- to total nss-SO42- in aerosols was not pronounced due to strong influence of anthropogenic source.(6) Among the 211 single colonies,53 differential species assigned to 36 genera were obtained from the surface and bottom water of the two sites Representative strains (91 isolates) belonging to different species were selected for testing their DMSP catabolism activity in MAMS media supplied with mixed "regular" carbon source (4.5%(w/v) glucose and 0.5%(v/v) glycerol).37 isolates demonstrated DMSP-dependent DMS (Ddd+) phenotype. In addition, a proposed mechanism for DMSP cleavage to generate DMS and acrylate by DddQ was conducted. |
PDF Full Text Request