| The South China Sea,located in the western Pacific and East Asian monsoon regions at low latitudes,is an important area for studying global change.The records of dinoflagellate cysts in the surface sediments of the South China Sea are closely related to surface temperature,salinity,primary productivity and upwelling in the paleomarine environment,which can provide a high-resolution environmental evolution history.In this study,28 surface sediments from the southern South China Sea were used to analyze the concentration and percentage of dinoflagellate in order to reveal the composition and distribution of dinoflagellate species and genera,and the correlation between surface temperature,salinity,chlorophyll a content,primary productivity,upwelling and soil properties in the southern South China Sea during the hottest and coldest months.The results of the analysis can explain the correlation between the composition and distribution patterns of dinoflagellates and the marine environment.The results show that:(1)Distribution of dinoflagellate concentration in the southern South China Sea is mainly affected by surface temperature,salinity,primary productivity and upwelling,showing obvious regional distribution characteristics.The northern continental shelf of Kalimantan Island has high temperature,low salinity,high primary productivity,active upwelling and high nutrient concentration,so the concentration of dinoflagellates in this area is higher;while the concentration of dinoflagellates in Sunda continental shelf is lower and decreases from southeast to northwest,mainly because of the surface temperature of sea water,salinity and chlorophyll a concentration in this area presents southeast.The trend towards the northwest is the result.(2)From the percentage content of dinoflagellate species,the dominant combination of dinoflagellate cysts in surface sediments of the southern South China Sea is S.ramosus,O.centrocarpum,Spiniferites spp.(half or fold),Brigantedinium spp.,Hetertrophic type A(small),O.longispinigerum,S.hyperacanthus,S.pachydermus,T.applanatum and S.mirabilis.In addition,35 species of dinoflagellate can be classified according to their biological names and divided into seven major groups,namely Gonyaulax sp.Indet.,Lingulodinium polyedrum,Gonyaulax spinifera complex,Protoceratium,Protoperidiaceae,Diplopsalid group and Unknown group.(3)Consistent with the distribution of dinoflagellates in other parts of the world,the distribution of dinoflagellate cysts in the southern South China Sea is closely related to marine environmental factors.According to CCA analysis,the genera of dinoflagellates in the southern South China Sea can be divided into three groups: marine type controlled by WD,high productivity controlled by TOC and TN and tropical type affected by surface water temperature in January and surface chlorophyll a in January.(4)The dominant species of dinoflagellates in the surface sediments of the southern South China Sea are mainly tropical.The abundance of autotrophic dinoflagellates in the southern South China Sea is closely related to the high primary productivity in the study area.The TOC/TN ratio of most sediment samples is low and the value of delta 13 C is high.It reveals that the main source of organic matter in marine organisms is high primary productivity,which is the main reason for the high concentration of autotrophic dinoflagellates in the study area.Secondly,the dominant species of heterotrophic dinoflagellates are mainly distributed on the northern continental shelf of Kalimantan Island,which is close to the mainland,and has a large amount of river water input.In addition,the frequent upwelling along the coast leads to an increase in nutrients and a decrease in surface salinity of the sea,which is beneficial to the growth and development of heterotrophic dinoflagellates.At the same time,the distance from the mainland is also an important factor affecting the distribution of heterotrophic dinoflagellates. |
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