资源环境科技发展态势分析平台

The Holocene hydrological regime on the Heixiazi Island is critical for understanding the evolution of the East Asian summer monsoon (EASM) for the island's climate-sensitive location on the northern fringe of the EASM domain. In this paper, a marsh depression on the central island was selected to reconstruct the locally hydrological variation and to discuss its indications for the Holocene EASM evolution. This work is based on multi-proxy (magnetic susceptibility, grain size, loss-on-ignition, and carbonate content) analyses of 22 modern sedimentary samples with a water-level gradient of 0-66cm and 100 cored sedimentary samples covering last similar to 9.0ka BP. The proxies' hydrological significance was previously interpreted by the 22 modern samples using linear regression equations to construct their relationships to water-level changes. Among these proxies, the magnetic susceptibility, carbonate content, as well as the Md and sand fraction of grain size exhibit high-level relationships against the water-level changes with R-2>0.6. Thus, these four proxies' linear-regression equations were selected and used on the 100 cored samples, and the Holocene water-level changes in the studied depression were quantitatively reconstructed. It shows that two relatively high water-level stages with strengthened EASM occurred during 8.0-4.5ka BP and 3.0-1.4ka BP, which were alternated by three low water-level stages with declined EASM during similar to 9.0-8.0ka BP, 4.5-3.0ka BP, and 1.4-0ka BP, respectively. Among these fluctuations, the highest water-level stage with most strengthened EASM which is defined as the Holocene Monsoon Maximum occurred during 6.4-4.5ka BP. Such a new evolution pattern of the EASM can be further supported by a large variety of records from monsoon-margin regions. We suggest the Holocene EASM evolution was generally associated with the thermal conditions in both the inner Eurasia landmass and the West Pacific Ocean, with an exception of the weak EASM before 8.0ka BP due to the enhanced Siberia High with the dominance of the Eurasia ice sheet in the early Holocene.