Dinoflagellate Cysts In Sediment Of Taiwan Strait And Their Environmental Indications

Dinoflagellates are ancient marine eukaryotic plankton.About 200 of the 2,000 recorded species can produce resting cysts and deposit in the sediments.Dinoflagellate cysts contain indicator information on sea-level,sea-surface productivity,temperature,salinity,the eutrophication situation and other marine environmental factors.Taiwan Strait is a narrow sea area on the continental marginal crust which connects the East China Sea and the South China Sea.The sediment is mainly from coastal current across the strait and controlled by the complex hydrodynamic condition.At the same time,it's significantly affected by anthropogenic activity.In this paper,the horizontal distribution of dinoflagellate cysts in surface sediment samples of Taiwan Strait was examined from 62 samples collected in spring and summer of 2016.And the vertical variation of dinoflagellate cysts in the Y13 core has been examined from 33 samples.The summary statistics are analyzed by combining with the granularity data,the 14C dating data and the previous research materials.The main conclusions are as follows:(1)58 dinoflagellate cysts species belonging to 19 genera(besiding 3 dinocysts and 2 unidentified species)were identified from surface samples.There are similar cysts assemblages in spring and summer,which is dominated by Protoperidinium avellana,Protoperidinium leonis,Protoperidinium conicum,Protoperidinium spp.,Alexandrium affine,Alexandrium minutum,Gonyaulax scrippsae,Gonyaulax spinifera,Scrippsiella trochoidea and Lingulodinium polyedra.But most cysts were more widespread and the dominant species in each station were more diverse in summer.(2)The dinoflagellate cysts abundance in spring varied from 0 to 516.67 cysts per gram(dry weight),with a mean of 148.32 cysts per gram.The mean abundance of cysts increased by 21%in summer,but in some inshore region the cysts abundances decreased because of the less nutrient.The results show that dinoflagellate cysts abundances is higher in the north than in the south sea area and decreased from inshore region to the middle of the strait.It can be found that the cysts abundance is significantly correlated with granularity.(3)The distribution of dinoflagellate cysts in surface sediments was mainly controlled by nutrient and hydrodynamic condition,and the offshore distance and temperature also had a certain effect to some extent.The sample station can be divided to five classes,three of which are strips almost paralleling to the shoreline,reflecting the distributing characteristics caused by the change of the environment parameters under the different offshore distance.And the other 2 classes reflect local characteristics.(4)Y13 core sediments with a stable lithological variation which belong totally to clayey silt,featured with tiny particle size,low maturation of texture,extremely positively biased and sharp kurtosis.It's located at the fine sediments area in central Taiwan Strait,primarily caused by the hydrodynamic force weakened after Zhejiang-Fujian Coastal Current and Taiwan Warm Current flow together.Above the depth of 50cm the changes of sedimentary environment and the increased sand composition is a response to the intensification of Zhejiang-Fujian Coastal Current.(5)The mean abundance of dinoflagellate cysts in Y13 core sediments was 161.85 cysts per gram(dry weight),contain 45 dinoflagellate cysts species belonging to 16 genera(besiding one unidentified species).Protoperidinium avellana,Protoperidinium leonis,Protoperidinium conicum,Protoperidinium subinerme,Protoperidinium spp.,Gonyaulax scrippsae,Gonyaulax spinifera,Gonyaulax spp.and Scrippsiella trochoidea are the dominant species in the cysts assemblages.The percentage of heterotrophic dinoflagellate cysts above 50%in the whole core except surface sediments indicates the significant impact of water eutrophication.In addition,the percentage of Alexandrium is increasing rapidly in near-surface layer,which may become the initiation factors of algal blooms.(6)4 dinoflagellate cysts assemble zones could be divided in Y13 core sediments:The 130?98cm(1007-1259A.D.)was characterized by eutrophication strengthens,climate cooling and the increase of dinoflagellate cysts abundance.During 98?46cm(1259-1669 A.D.)the climate first cooled and then remained stable,nutrients was stable and the dinoflagellate cysts abundance decreased.The 46?14cm(1669-1921 A.D.)present the stable nutrients,the cold climate and the slight increase of dinoflagellate cysts abundance.The upper from 14cm(1921 A.D.-present)was characterized by climate warming and the increase of superficial water productivity,nutrients,the dinoflagellate cysts abundance,species diversity and evenness.