A paleoenvironmental reconstruction of the last 15 000 cal yr BP via Yellow Sea sediments using biomarkers and isotopic composition of organic matter

摘要

This study is the first reconstruction of the paleoenvironment and paleovegetation during the Holocene (interglacial) and glacial periods of the Yellow Sea. We report the carbon isotopic and biomarker (n-alkane and alkenone) compositions of organic matter from Yellow Sea sediments since the glacial period. Our findings show that the variability of the East Asian Monsoon (EAM) affected the sedimentary profile of total organic carbon (TOC), the stable isotopes of bulk organic carbon (δ13C_org), the atomic ratio of carbon and nitrogen (C/N ratio), and biomarker content. The sedimentary δ13C_org profile along the core exhibited more negative δ13C_org values under cold/dry climatic conditions (Younger and Oldest Dryas). The carbon preference index (CPI), the pristane to phytane ratio (Pr/Ph) and the pristane to n-C₁₇ ratio (Pr-C₁₇) were used to determine the early stages of diagenesis along the sediment core. Two climatic conditions were distinguished (warm/humid and cold/dry) based on an n-alkane proxy, and the observed changes in δ13C of individual n-alkane (δ13C_ALK) between the Holocene and glacial periods were attributed to changes in plant distribution/type. Clear differences were not found in the calculated alkenone sea surface temperature (SST) between those of the Holocene and glacial periods. This anomaly during the glacial period might be attributed to the seasonal water mass distribution in the Yellow Sea or a seasonal shift in the timing of maximum alkenone production as well as the B?lling/Aller?d interstadial.