Sedimentary Record Of Coccolithophore Assemblages In The Yellow Sea And The East China Sea And Their Response To Climate Changes

Coccolithophores,as the important primary producers in the marine ecosystem,broadly inhabit in the world oceans and respond sensitively to the changes of environmental conditions such as salinity,temperature,nutrient availability.When coccolithophores in the water are died,the calcified plates(coccoiths)they secrete,preserve well the composition of overlying photic-zone communities in sediments.Previous works in the Atlantic and northeast Pacific have proved that these coccolith fossils in the sedement have correlationships with climate changes and can be uesd as indicator in paleoceanographic and paleoclimatic changes sutdy,while the related research is rarely reported in shelf areas of the northwest Pacific.Here a first quantiative investigation and study of coccolith fossils in five box cores from the typical areas in the Yellow Sea and East China Sea was carried out to assess the species composition and abundance variation of coccolith assemblages in the sediment dated from decades to more than two hundred years.The distribution patterns of coccolith fossils and their influencing factors were analyzed.The resluts was expected to provid fundamental information and evidence basis for paleo-oceanographic researches.The main results were as followed:Seventeen species of coccolith fossils were identified in the five cores from the Yellow Sea and East China Sea.Emiliania huxleyi,Gephyrocapsa oceanica,Braarudosphaera bigelowii,Calcidiscus leptoporus,Coronosphaera mediterranea,Helicosphaera carteri,Syracosphaera pulchra and Umbilicosphaera sibogae were the common species in the five cores.The species composition was basically the same,but the absolute abundances were quite different in different cores.The absolute abundance of Core N02 in the coastal of Shandong Peninsula ranged from 5.07 × 106 coccoliths/g to 14.21 × 106 coccoliths/g,with an average value of 9.76 × 106 coccoliths/g.While in the northwest off Jeju Island(Core F10),the average abundance reached up to 382.37 × 106 coccoliths/g,and the abundance throughout the core ranged form 255.25-536.58 × 106 coccoliths/g.The abundances of Core C04 and Core C05 in the central area of Yellow Sea ranged form 6.95-62.82 × 106 coccoliths/g and 49.76-97.47 × 106 coccoliths/g,respectively and the average abundance were respectively 29.16 x 106 coccoliths/g and 69.84 x 106 coccoliths/g.In Core T5 near Yangtze estuary,the abundance was in the medium level(49.77 × 106 coccoliths/g)and ranged from 30.08-77.03 × 106 coccoliths/g.In the study area,the compositions of coccolithophore communities were similar.Both in absolute abundance and relative abundance E.huxleyi and G.oceanic were the predominant species of all the surveyed cores.However,the vertical distribution trends were various in different areas,which due to different areas exhibited different environmental conditions.In the coastal of Shandong Peninsula,the distribution pattern of coccolith absolute abundance in Core N02 was highly correlative with Sea Level High indicating the intensity of East Asian Winter Monsoon(EAWM).And the intensity of Yellow Sea Coastal Current(YSCC)could be controlled by EAWM.Therefore we inferred that coccolithophore assemblage in this area was influenced by YSCC through EAWM.While in the central Yellow Sea,the coccolith distribution has no obvious realtions with neither EAWM and Pacific Decadal Oscillation(PDO),which are the main climatic parameter in the Yellow Sea.In the northwest off Jeju Island(Core F10),increases in coccolith abundance during the positive PDO phase may result from the enhanced input of warm water mass from the YSWC.In Core T5 near Yangtze estuary,the abundance of coccolith had negative correlation with rainfall.Rainfall in Yangtze River effect the transmission of light and light is the basic condition for phytoplankton growth.Therefore illuminaton intensity may be the main factor of coccolithophore distribution in the region.The reason for the different long-term changes of coccolith abundance in different areas of the Yellow Sea and the East China Sea may due to the different responses of coccolithophore community to the global or regional climate changes.Besides,in the shelf seas exhibiting such complicated hydrological conditions,the diversity response of coccolithophore to climate changes should be treated carefully.