| As a new geochemical index, multi-biomarkers have been widely used in reconstructing paleo-ecological environments in several open oceans and marginal seas. Because biomarkers are produced by only a few groups of organism and have relatively stable chemical properties, multi-biomarkers in marine sediments can be used to reconstruct variations of phytoplankton productivity and community structure. However, the application of multi-biomarkers in the Japan Sea is still limited. In order to further study the variations of ecosystem structure in the Japan Sea, this thesis carries out analyses of biomarkers in core ODP 797 (38.620N, 134.540E) of the Japan Sea and discusses the variations of biomarker-based records for the last 166 ka:sea surface temperature (SST), marine productivity and phytoplankton community structure.A sea-surface temperature record was reconstructed for the last 166 ka using alkenone unsaturation ratios (U37K').The U37K' temperature was lower during the glacial periods (MIS 2-4, MIS 6) and higher during the interglacial periods (MIS 1 and MIS 5). The amplitude of temperature fluctuation was large between glacial and interglacial periods (SST oscillated between 3.8 and 21.5℃). The glacial-interglacial SST variation in the Japan Sea is considered to be closely related to changes in the East Asian monsoon system, the volume transport of the Tsushima Warm Current (TWC) and the position of the sub-polar front (SPF). However, U37K'SST has anomalously high values during the LGM, which could be caused by low surface salinity affecting the haptophyte responses to temperature changes or by very low alkenone contents affecting the accurate calculation of U37K'SST.Biomarker records for ODP 797 indicate alkenone content had obvious high values during MIS 5 compared with other stages, but the contents of brassicasterol and dinosterol had high values during both glacial periods and interglacial periods. The ratios of marine biomarkers to terrestrial biomarkers were higher during interglacial periods (MIS 1, MIS 5) compared with glacial periods (MIS 2-4, MIS 6), which suggests higher productivity during the interglaciations in the Japan Sea. These results were consistent with previous studies. During the glacial periods, the influx of TWC was decreased and the productivity was low as a sea-level drop. Some high values of biomarker content were related to the better preservation of organic matters due to strong stratification and bottom water oxygen-deficient. During the interglacial periods, high stands increased the influx of the TWC and resulted in higher primary productivity and high values of biomarker content.Diatom, dinoflagellate and coccolithophorid biomarker content percentages can be used as proxies of phytoplankton community structure. The results show that the relative coccolithophorid contribution increased and the relative diatom and dinoflagellate contributions decreased during interglacials compared with glacials. The shift from a diatom-dominated phytoplankton community during the glaciation to a coccolithophorid-dominated community during the interglaciation was controlled by surface salinity changes. During the glacial periods, both the decrease of the TWC influx and increased contribution of low salinity East China Sea coastal waters (ECSCW) and terrestrial freshwater resulted in lower salinity conditions in the Japan Sea. Glacial low-salinity environments unfavored coccolithophorids competition. During the interglacial periods, the increase of the TWC influx led to enhanced seawater salinity and increased contribution of coccolithophorids. This glacial-interglacial phytoplankton community structure pattern is in contrast with previous studies using microfossils method. One possible explanation is that the biogenic silica and biogenic carbonate microfossils are controlled by different dissolution processes, which affected the use of their ratios as phytoplankton community structure proxies.
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