The Climate And Environmental Records Of Late Mid-Holocene In Sediments From South China Sea And East Antarctica

As the deterioration of the environment, especially the frequent occurance of the extreme weather events, scientists have paid more and more attention on the reconstruction of the paleoclimate and palaeoenvironmental, and hoped to understand the mechanisms of climate changes, and then to predict the future climate changes and provide counter plan. The research of the Past Global Changes is part of the core program of the International Geosphere-Biosphere Program. The glacial/interglacial cycles (Milankovic cycle) caused by changes in the Earth’s orbital parameters had been proved by paleoclimate study. However, compared with climate changes in Earth’s orbital parameters scale, people tend to focus on the climate variations in shorter time scales. Therefore, the research emphasis was laid on obtaining and explaining high-resolution paleoclimate records.In this thesis, we concerned paleoclimate and palaeoenvironmental changes in mid-to late-Holocene, which is closely associated with the developments of human civilization. Lacustrine sediment cores were collected from Xisha Islands in South China Sea (SCS) and Larsemann Hill in East Antarctic. Variety of research methods were performed to obtain reliable indicators and explore the paleoclimate and palaeoenvironmental changes. Main contents and research results are listed as follows:1. Terrigenous dust records from coral island in South China Sea over last1400years.Lacustrine sediment core (DY6) from the "Cattle Pond" on Dongdao Island provided high-resolution paleoclimate records of the South China Sea. The results of inorganic elements showed that the concentrations of Ti and Al in the sediment samples were much higher than their background values in the island. The acid insoluble particles in the sediments showed similar morphological characters with Aeolian in spring in East China by examining under optical microscope and Scan Electric Microscope (SEM). Ti and Al in the sediment core were mainly from those particles. As the south branch of East Asian Winter Monsoon (EAWM) is the potential transporting force of terrigenous dust in the west tropical pacific, dust in the cattle pond sediment might be transported by south branch of EAWM from Asian inland. Based on AMS-14C dates of caryopsis remains and210Pbex of top15cm sediments, the chronology was established. The continuous dust records for the past1400years in north SCS were presented with Ti flux, which showed opposite trend with the variations of EAWM for the past50years. The composite difference of wind fields between cold winter years and warm winter years showed that the surface north wind (1000hPa) in south-east China was strong in cold years, while the850hPa wind vector along the east coast of China, the key level wind of the long distance dust transmission, weakened in cold years rather than warm years. We recognized differences of EAWM records attributed to the850hPa wind pattern characters in different areas. Furthermore, wind patterns also revealed a different cyclone on Philippines Sea, which indicated convections were stronger in the cold winter and spring.2. biomarkers records from lacustrine sediments, larsemann hills, East AntarcticaBiomarker records from Mochou Lake sediments, Larsemann Hills (69°22.3’S,76°22.0’E), East Antarctica reveals the mid-to late-Holocene climate history in the region. The long chain alkenones (LCAs) was detected in the sediment core at depth of30-36cm and68-111cm. By compareing the proportion and composition of LCAs from Mochou Lake with other regions, we recognized the source algae as some haptophytes, which was favored on cold and high salinity water. The LCAs were detected at6450-4800cal. yr. BP, a period with high relative sea level. Trace amounts of LCAs were found at3700-3500cal. yr. BP, which reflected change of lake salinity caused by cold climate with fewer ice melt water and higher evaporation. The absence of LCAs about4800cal. yr. BP was consistent with the climate switching from cold to warm and gradually dropping of relative sea level, resulting in more glacial melting water and less intrusion of sea water. According to Zink’s Uk37empirical formula, we reconstruct the temperature at the period of6450-4800cal. yr. BP.The evolution of n-alkanes (C19-C33) showed the climate in Larsemann hills was cold and aridity during3700-3500cal yr B.P,4900-4700cal yr BP and6000-5600cal yr BP.