| Summary: | 碩士 === 國立臺灣海洋大學 === 應用地球科學研究所 === 101 === The East China Sea (ECS) is one of the marginal seas of the Western Pacific. The surface climate and hydrologies of the ECS are dominated by the Asian Monsoon (AM) and Kuroshio. In this study, I used organic biomarkers, the TEXH86 (tetraether index of tetraethers consisting of 86 carbon atoms) and BIT (branched and isoprenoid tetraether) indices to reconstruct climate changes over the past 8000 years based on a sediment core MZ01 (120°50.94’E, 26°32.82’N) from the inner shelf of the ECS (near Ming River Mouth). The TEXH86 index is a sea surface temperature (SST) proxy which is developed based on ratios of isoprenoid GDGTs (glycerol dibiphytanyl glycerol tetraethers). The isoprenoid GDGTs are in the membrane lipids of marine crenarchaeota that vary with SSTs. The BIT index is based on the relative abundance of branch GDGTs from the soil bacterial versus isoprenoid GDGTs from the marine crenarchaeota and serves as a proxy for terrestrial organic carbon in marine sediments. The BIT values in core MZ01 range from 0.02 to 0.09, indicating a low contribution of terrestrial organic matter to the studied site. The estimated TEXH86 SST of MZ01 coretop sample is 20.6°C, which is ~2°C lower than the observed mean annual SST at the studied site. The estimated SST is considered to reflect temperatures at 50 to 60 m water depth, and the reasoning based on that suggests that the TEXH86 SST is biased toward subsurface water conditions. Therefore I used the differences between TEXH86 and UK’37 SSTs of core MZ01 to reflect changing water stratifications, which maybe in turn controlled by the frontal movement of the southward China Coastal Current (CCC) and northward Taiwan Warm Current (TWC) on the inner shelves of the ECS. While the water stratification on the inner shelves of the SCS is mainly governed by the relatively freshening surface water of the CCC overlying on the TWC, the MZ01 SST records suggest strong mixing at intervals near ~7.6, 6.1, 5.8 and 0.4 kyr (B.P.), and noticeable stratification at ~6.4, 5.9, 5.3, 3 - 4, 2.5, 1.0 kyr (B.P.). The results suggest a rapid frontal movement in ECS surface waters driven by the AM during the Holocene.
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