Sediment Record Of Paleoenvironment Of The Central Mud Of The South Yellow Sea And Its Response To The East Asian Monsoon During Holocene

The South Yellow Sea (SYS), a marginal sea in the northwestern Pacific, is aunique location, accepting huge amount of materials (sediments) from Changjiangand Huanghe Rivers. The changes in this area are influenced by the interactions ofthe Yellow Sea Warm Current (YSWC), the East Asian Monsoon (EAM) and theKuroshio Current (KC); which develops a typical circulation system at the centre,and forms a unique sediment body of fine particles, thereby concealing richinformation on Paleoclimate change. The study of the central mud in SYS is veryimportant, because it elucidates the impact of sea level change and the globalclimate change. Moreover, it reveals Paleoceanology changes that had occurred onthe continental shelf sea of the low latitude. Currently, the Paleoclimate studies ofthe continental seas mainly focus on the East China Sea. However, studies on theSYS are both limited and superficial. Few studies have been carried on theprovenance and evolution stages of marine environment.The YSWC plays a key role in the formation of the central circulation of theSYS and the evolution of marine sediment environment; however, previous studieslacked continuous high-resolution paleoenvironment indicators: mostly limited todiscussions on its formation time. It is very important to mention that dating hasbeen considered a bottleneck due to lack of foraminifera in the central mud of SYS,which results to lack of continuous precise time scale in SYS.Two key scientific questions in studying the SYS are:(1) how does thesedimentary record under unique circulation responds to the EAM change; and (2)what are the factors responsible for the Paleoenvironment and Paleoceanologychanges in the central mud of SYS?Answers are provided to the abovementioned questions in this study. CoreYS01and Core YSZ05are taken and sub-sampled. Analyses of Grain size, XRFelement, BSi, SST and datings, which provides the most precise and continuous dating record when compared with the previous studies in SYS, are carried out. Onthe basis of these analyses, the outcomes are summarized as follows:(1) Using AMS14C dating, Grain-size and XRF-geochemical data for coreYS01to reconstruct the history of the East Asian Winter Monsoon (EAWM) sincethe mid-Holocene, continuous history of the EAWM over the past7300years areprovided; and the EAWM can be divided into four periods: strong and highlyfluctuation during7.3～4.6ka B.P.; moderate and relatively stable during4.6～2.8ka B.P.; weakened during2.8～1.4ka B.P.; and the transfer period during1.4～0kaB.P.(2) The EAM presents cycles of1471a，420～490a，65a，40a，28a，21a,which correspond to the solar activity cycles. During the period between10～3ka,thermohaline circulation in the high latitude controls the paleoclimate change of theEast Asia. During the period between3～0ka, ENSO mainly impacts the EAMevolution.(3) During the period between6.8～2.8ka, SST was mainly affected by globalclimate change, while the YSWC is the controlling factor of SST during the periodbetween2.8～0ka.(4) Nutrient salt, ENSO and EAWM are main factors that impact theproductivity of SYS. Due to lower deposition rate, the productivity record ofYSZ05is limited owing to insufficient supply of nutrients from land sources.Productivity evolutionary record of YS01is controlled by ENSO on millennial timescales, while the productivity improves owing to the strengthened EAWM on shorttime scales. Paleoproductivity is consistent with the modern strengthened ENSOsince3ka, as well as with SST change of the SYS.