Population Characteristics And Environmental Indications Of Dinoflagellate Cysts From The Northern Yellow Sea

Dinoflagellates are unicellular,primarily marine eukaryotic plankton and 10-20%of them can produce resting cysts to get through the hard environment in their life cycle.Dinoflagellate cysts records have paleoenvironmental significance on sea-surface productivity,temperature,salinity,sea-level and the potential for recording eutrophication and forecasting future red tides events.The Yellow Sea is a semi-closed epicontinental sea which surrounded by the China Continent and the Korean peninsula,and its thick sediments caused by receiving a mass of deposits from the Yellow River and the Yangtze River record diverse paleoenvironmental and paleoclimatic information.The horizontal distribution of dinoflagellate cysts in 19 surface sediment samples of the western parts of the North Yellow Sea and the vertical variation of dinoflagellate cysts of the core B07(54 samples)in the eastern of the Shandong Peninsulas have been examined.This paper has analyzed the correlation between the dinoflagellate cysts and environmental conditions combined with the sea surface temperature,salinity and water depth data and discussed the changes in marine environment of the Yellow Sea during the last three hundred years in combination with the chronological age,analysis results of surface sediment and previous studies.The main study results display as follows:(1)Abundances of dinoflagellate cysts in surface sediment from the western parts of the North Yellow Sea vary greatly and decreased towards both directions especially northeastward.Our results shows that dinoflagellate cysts abundances were affected obviously by bottom sediment types and the hydrodynamics condition,in response to red tide event partly and irrelevant to sea surface temperature,salinity and water depth.(2)39 dinoflagellate cysts species belonging to 11 genera(besiding one unidentified species)were identified from surface samples which is based on autotrophic species in kind and quantitative terms.Alexandrium spp.,Gonyaulax spp.,Scrippsiella specaria,Lingulodinium polyedrum and Operculodinium centrocarpum are the dominant species in the dinoflagellate cysts association.P/G values(the ratio of protoperidinioid to gonyaulacoid)indicate high nutrient saline levels and primary production in center of Bohai straits and the southwest of the North Yellow Sea off the coast of Shandong Peninsula.The central part of research area risk the Alexandrium catenella/tamarense red tide among which No.B27 and No.B29 is undergoing cultural eutrophication,in addition,No.B27 risks the Scrippsiella specaria red tide.(3)According to dinoflagellate cysts abundance and community,the surface sedimentary dinoflagellate cysts can be categorized to 3 types.The first type reflects the warm and terrigenous nutrient-rich marine environment.The second type represents the sea area which influenced by the perivous red tide,the Yellow Sea warm current and terrigenous continental input.The third type stands for ocean of which water dybamics was stronger.(4)B07 core sediments with a stable lithological variation which belong mainly to silt,featured with thin particle size,low maturation of texture and smooth to medium kurtosis.Above a depth of 80 cm the increased sand composition and smooth kurtosis is a response to the intensification of East Asian monsoon.(5)43 dinoflagellate cysts species belonging to 13 genera(besiding two unidentified species)were identified from the core sediments which is dominated by Gonyaulax spp.and Lingulodinium polyedrum.Abundance of dinoflagellate cysts were affected obviously by primary production and nutrient saline levels.A red tide accident occurred in the sea area around B07 core at about 1970A.D..(6)2 dinoflagellate cysts assemble zones and 3 sub-zones could be classificated according to abundance and dominant community in B07 core sediment which recorded a series of marine environment changes in the Yellow Sea during the last three hundred years.The 270-180cm(1700-1877A.D.)was characterized by lower temperature water and poorer nutrient.In the 118-68cm(1877-1936A.D.)sea water temperature was increasing but nutrient still fairly poor.Sea water temperature turned to decline but nutrient was the opposite in the 68-3 8cm(1936-1970 A.D.).The upper from 38cm(1970 A.D.-present)was characterized by increased temperature and the trend of eutrophication.