Studies On The Temporal And Spatial Distributions Of DMSO And Influencing Factors In The Eastern China Seas

As the major photochemical and biological oxidation products of dimethysulfide（DMS）, dimethylsulfoxide （DMSO） also can be reduced to DMS by some eukaryotesand prokaryotes in marine environments. Nonvolatile DMSO in seawater can notdirectly influence the global climate. Nevertheless, through its interactions with DMS,DMSO may influence the climate indirectly.In the present dissertation, we choose the Bohai Sea, the Yellow Sea （YS） and theEast China Sea （ECS） as the study areas that are affected seriously by humanactivities. The temporal and spatial distributions of dissolved dimethylsulfoxide（DMSOd） and particulate dimethylsulfoxide （DMSOp） and the factors influencingthem in the study areas were systematically studied, which would be helpful topreliminary understand the possible relationships between DMSO and environmentfactors, and to enrich the researches of marine biogenic sulfur cycle. The mainconclusions were summarized as follows:（1） The distributions of DMSOd and DMSOp and the factors influencing themwere determined in the ECS and the South Yellow Sea during March-April,2011andOctober-November,2011. The results showed that the concentrations of DMSOd andDMSOp in the surface water in spring were20.62（5.13-73.77） and8.90（3.75-29.59）nmol L^-1, respectively. Concentrations in autumn were13.37（4.71-42.73） and8.18（3.44-22.60） nmol L^-1, respectively. Both DMSOd and DMSOp concentrationsrevealed obvious seasonal variations with higher values in spring than in autumn,which correspondence well with the seasonal variation of chlorophyll a （Chl-a）observed in the study areas. The horizontal distributions of DMSOd and DMSOp inspring displayed a general decrease in concentration from inshore to offshore sites,which were obviously affected by anthropogenic activities and terrestrial runoff. Dueto the Yangtze River diluted water, both DMSOd and DMSOp had lower concentrations near the mouth of Yangtze River in autumn.The vertical profiles of DMSOd and DMSOp in the stations of Yangtze estuary inspring and autumn were observed. The maximum DMSOd and DMSOpconcentrations were present at the depth of0-30m. This might mainly attribute to thelight intensity that limited the photochemical oxidation of DMS and the growth ofphytoplankton with the increase of depth, and thus affected the synthesis processes ofDMSOd and DMSOp.DMSOp/Chl-a ratios showed clear seasonal patterns with an average value1.5times higher in autumn than in spring, suggesting that the proportion of dominantspecies in the study area had a strongly seasonal change. A weak relationship wasfound between DMSOp and Chl-a in spring, whereas no relationship was observedbetween them in autumn, indicating that phytoplankton biomass might play a moreimportant role in spring than autumn in controlling the distributions of DMSOp. Asignificant positive correlation was found between DMSOd and DMSOp in autumn,while there was no relationship between DMSOd and DMS, bacteria, implying thatDMSOp was an important factor affecting the concentrations of DMSOd rather thanthe photochemical and biological oxidation of DMS.（2） The temporal and spatial distributions of DMSOd and DMSOp and the factorsinfluencing them were determined in the North Yellow Sea and the Bohai Sea duringJune,2011and November,2011. The concentrations of DMSOd and DMSOp in thesurface water in summer were14.28（6.41-43.80） and12.24（6.89-18.35） nmol L^-1,respectively. Concentrations in autumn were16.23（6.72-52.31） and10.94（6.47-31.13） nmol L^-1, respectively. The concentrations of DMSOp and Chl-arevealed a same seasonal change with higher value in summer than in autumn, whilethe seasonal variation of DMSOd was not distinct with slightly higher values inautumn than in summer. The horizontal distribution of DMSOp in study area wasinfluenced mainly by phytoplankton biomass, with high concentrations of DMSOpappearing in the areas containing high levels of Chl-a. DMSOd concentrations did notshow a significant horizontal distribution pattern due to its complex sources. In summer, the vertical profiles of DMSOd in the stations of YS showed asignificant stratification affected by the Yellow Sea Cold Water Mass, with the highestconcentration appearing in the upper water and lowest value in the thermocline layer.The concentrations of DMSOp and Chl-a revealed a similar vertical profile, with thehighest values in the upper water （0-25m）. However, the concentrations of DMSOd,DMSOp and Chl-a had no obvious stratification phenomenon in autumn due to thedisappearance of the Yellow Sea Cold Water Mass. The maximum DMSOd occurredat the depth of10-25m, where high DMS concentrations existed. The maximumDMSOp concentrations appeared in the surface water containing high levels of Chl-a.DMSOp/Chl-a ratios exhibited obvious seasonal changes with higher values inautumn than in summer, which might due to different phytoplankton species. Apositive correlation was observed in summer between DMSOp/Chl-a and salinity,indicating that intracellular DMSO could act as a cryo-osmoregulator. No relationshipwas found between DMSOp and Chl-a in summer, whereas a significant relationshipwas observed between them in autumn, implying that the concentrations of DMSOpin autumn were strongly influenced by phytoplankton biomass. A significantrelationship was also observed between DMSOd and DMS in summer, while norelationship between DMSOd and bacteria, DMSOp was found, suggesting thatDMSOd was produced mainly through the photochemical oxidation of DMS.However, no relationship between DMSOd and DMS, DMSOp, bacteria was found inautumn, implying that the source of DMSOd was more complex.