Sedimentary Diatoms Records And Paleoenvironmental Implications In The Pearl River Estuary Since The Last 6000 Years

Diatom is a type of single-celled algae living in water and humid environment,from the land to the ocean,from the poles to the equator are distributed,according to the ecological habits of diatom can be very good inversion of environmental changes.The Pearl River Estuary is an ideal place to study the evolution of paleo-environment because of its special geographical location and complex hydrological characteristics.This study through 23 surface samples in pearl river mouth area and CN-PL04 columnar sediment samples were carried out by granularity test,diatom identification,AMS14C dating,combining previous research data that reveals the trend of the ancient climate change and sea level and global climate events of the pearl river mouth area of nearly 5660 years,and the main results are as follows:(1)A total of 34 genera and 72 species of diatoms were identified from the surface sediments;Coscinodicus subtilis,Cyclotella stylorum,Paralia sulcata are three dominant species in surface samples.And the diatom abundance ranged from 110 frustules/g to 3904 frustules/g,the average level is 1655 frustules/g,The Salinity water species in the study area were mainly distributed in the outer side of the bay and decreased towards the inner side.The content of brackish water was higher in the bay.Freshwater species are mainly distributed in the west of the bay.(2)Pearl river mouth area of diatom taxa distribution affected by many factors,brackish water species distribution affected by fresh water,the control of underwater terrain,the content of research zone on the east side and north side is important,the smallest distribution phenomenon to the sea side Influenced by salt water of the sea,from the bay mouth to bay content decreases Freshwater species are mainly distributed in the bay area.(3)The abundance and grain size of diatoms in the Pearl River Estuary area are obviously affected by the hydrodynamic topography,river water and seawater action,river dredging project,sea reclamation and land reclamation project.The comprehensive analysis results of diatoms abundance and grain size data show that the conclusions obtained are basically consistent with the relevant research results of previous studies.(4)The columnar sample was located outside the Pearl River Estuary with a water depth of 14.4 meters.A total of 24 genera and 60 species of diatoms were identified in the sediments,among which Cyclotella stylorum,Paralia sulcata was the dominant diatom species.The variation trend of diatom abundance in the columnar sample was significantly correlated with the grain size composition of the sediments,which was mainly affected by the local hydrodynamics and surrounding climate conditions.(5)Diatom taxa content according to the column samples and abundance of vertical changes were divided into four combination belt,combination of sediment grain size parameters and AMS14C dating and ancient environment to study area is analyzed and divided into four evolution stages.During 5660-4200 cal.yr.BP,hydrodynamics relatively strong and the climate was warm,but in 4200 cal.yr.BP climate events the climate was suddenly cold;During 4200-2250 cal.yr.BP period,the water depth increased,the hydrodynamics was relatively weak,and the climate was mainly cool.However,the study found that during this period,the global climate events were more frequent,which had a great impact on the sediment granularity and the abundance of diatoms in the study area.During 2250-400 cal.yr.BP stage,the water depth gradually became shallower,the hydrodynamics gradually weakened,the influence of human activities was obvious,the temperature was low,and the sea level began to drop.During 400-0 cal.yr.BP,The global climate was in the process of continuous warming,precipitation significantly increased,sea level slowly rising.(6)Comparing the sedimentary column sample curve of diatom abundance,sediment particle size,oxygen isotopic of dongge cave,and curve of Ti of ODP1002 in Cariaco basin,we find the results are good corresponding to this article research conclusion,and reveal the ITCZ monsoon precipitation in different periods of diatom abundance in plots content as well as the impact of sediment particle size.