Diatoms In Sediment Of Taiwan Strait And Their Environmental Indications

Diatom is a large group of small eukaryotic unicellular organisms with a wide distribution and a siliceous cell wall.Sedimentary diatoms contain abundant information.By analyzing their population structure,we can study paleoclimate and paleoenvironment well.The Taiwan Strait is an important waterway connecting the East China Sea and the South China Sea,with complex hydrodynamic conditions and frequent typhoons.Based on the study of 32 surface samples in spring,30 surface samples in summer and 33 columnar samples from Y13 core,the main conclusions are as follows:(1)A total of 31 genera and 85 species of diatoms were identified in the surface sediment samples.The abundance of diatom ranges from 5 to 19467 shells/g,with an average of 2740 shells/g.in spring,it ranges from 5 to 9980 shells/g,with an average of 2160 shells/g.in summer,it ranges from 28 to 19467 shells/g,with an average of 3355 grains/g.in summer,it is higher than that in spring,with a decreasing trend from shore to sea,The dominant species are Paralia sulcate,Cyclotella stylorum,Actinoptychus undulatus and Pyxidicula weyprechtii.Most of diatom shells are broken,especially Trachyneis and Coscinodicus,which reflect the strong hydrodynamics in the study area.(2)The correlation analysis shows that there is a weak correlation between the surface diatom abundance and water temperature,salinity,and a strong correlation between the surface diatom abundance and water depth,the average particle size of the bottom material.In spring,the diatom abundance value is low,and the correlation is covered or reduced by other factors.Principal component analysis showed that the distribution of Surface Sediment Diatoms was controlled by temperature,salinity and offshore distance.(3)In spring,the study area can be divided into five types:type ? is obviously affected by coastal runoff,with high content of intertidal and nearshore species,but low content of sea water and ocean species;type ? sediment is mostly sandy silt,with active hydrodynamic force and high temperature and salt depth;type ? sediment has the highest abundance,weak hydrodynamic force,with fine sediment mostly silty sand;The diatom abundance value of ? type sediment is very low,the sediment is sand,and the hydrodynamic force is very strong;The ? type is only at Y23 station,and its abundance value is far lower than that of the adjacent station.Its sand has high component content,deep water and complex hydrodynamic conditions.The results of the study in summer are similar to those in spring.The main difference is that the number of stations in type ? decreases while the number of stations in type ?increases.In the eastern boundary station of the study area,the content of Azpeitia noduliferaa is high,which may indicate the flow path of the branch of Kuroshio.(4)The bottom age of Y13 is about 1040aBP,and the average deposition rate is 1.27mm/a.The lithology of the core is clay sit,featured with tiny particle size,low maturation of texture,extremely positively biased and sharp kurtosis,and the average grain size is positively related to the diatom abundance.(5)A total of 51 species belonging to 24 genera were identified in Y13 porous column samples.The diatom abundance and species diversity of the near surface samples were high,and both of them decreased rapidly below the surface.The total abundance ranges from 452 to 11375 shells/g,with an average of 2163 shells/g.The dominant species are Cyclotella stylorum,Paralia sulcataand Pyxidicula weyprechtii.Most of diatom shells are broken,especially Trachyneis and Coscinodicus,most of the shells of Trachyneis and Coscinodicus diatoms are broken and eroded,which are difficult to identify but have a large number,and the contents of other genera and species are very low.(6)Four diatom zones could be divided in Y13 core sediments:zone ?,132?90cm(976?1071a.D.).The average abundance of diatom is 997 shells/g.The continuity between samples is poor,so it is speculated that deposition disturbance occurred.Corresponding to the period of continuous warming in the early warm period of the middle ages,the sea level should rise slightly and the climate gradually warms,reaching the peak at 1071a.D.,and the boundary with zone ? is the peak period of the warm period of the middle ages.zone ?,120?90cm(1071?1315A.D.)The average abundance of diatom is 1166 shells/g.The abundance of Cyclotella stylorum is high.Corresponding to the period of relatively cold climate after the peak of warm period in the middle ages,the sea level decreased slightly,and the boundary time between zone ? and zone ? was 1315a.D.,which was basically consistent with the end time of warm period in the middle ages,1300A.D.zone ?,90?22cm(1315?1844A.D.)The average abundance of diatom is 1708 shells/g.The abundance of Paralia sulcata isincreased.The change time of diatom assemblage was 1520a.D.,1709a.D.and 1844a.D.respectively,which was basically consistent with the start time of mini ice age 1500A.D.,the peak time of mini ice age 1710a.D.and the end time of mini ice age 1850a.D.and had a good response to climate change.It can be subdivided into three subzones:3.1 subzone 90?63cm(1315?1520a.D.),corresponding to the period from the end of the Middle Ages warm period to the beginning of the mini ice age;3.2 subzone 63?35cm(1520?1709a.D.),corresponding to the beginning of the ice age to the peak of the mini ice age;3.3 subzone 35?22cm(1709?1844a.D.),corresponding to the period from the peak of the ice age to the end of the mini ice age.zone ?,22?0cm(1844A.D.?Now).The average abundance of diatom is the highest,reaching 5288 shells/g.Corresponding to the period of rapid warming since the 20th century,the sea level continued to rise,and the sedimentary environment was a shallow sea environment with high salinity and temperature.