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Advances in reconstructing the East Asian monsoon have provided important insights into the natural climate variability in Asia during the pre-instrumental period. However, there are still unresolved paleoclimate issues that necessitate the use of geological proxy data to further our understanding of past climate changes. This study focused on core B13, located in the muddy area of the North Yellow Sea (NYS), to investigate the evolutionary history over the past 1500 years and reconstruct the records of the East Asian summer monsoon (EASM) and Yellow Sea warm current (YSWC). The mean grain size of sediment ranged from 4.2 Φ to 5.6 Φ, with the sorting coefficient ranging from 1.9 to 2.2, indicating poor sorting. The C–M pattern showed a limited range of values, with the M values being between 33 and 83 μm and the C values being between 165 and 287 μm, suggesting uniform-suspension transport. The L* index ranged from 40.41 to 44.12, while the a* and b* indexes ranged from 0.55 to 1.78 and 2.86 to 5.94, respectively. A stable and relatively strong sedimentary environment is indicated through a comprehensive analysis of the C–M plot, triangular plot, the relationship between the mean grain size and sorting, and the changes in grain-size and color parameters. The sedimentary evolution in the muddy area of the NYS over the past 1500 years can be categorized into three distinct stages. In this study, proxies for the EASM and YSWC were extracted using the VPCA method from the sediment grain size and diffuse spectral reflectance (DSR) data, respectively. The reliability of these proxies has been confirmed through comparison with other validated proxies. The results indicated that the strength of the EASM and YSWC also exhibited three stages, corresponding to the Dark Ages Cold Period (DACP), Medieval Warm Period (MWP), and Little Ice Age (LIA), respectively. On a centennial scale, the correlation between the EASM and YSWC was predominantly negative. This research validates the reliability of the VPCA method for paleoclimate reconstruction, contributes important climate records in a special muddy area, and provides a new perspective on how to eliminate temporal errors in verifying the correlation between the two climate systems. [ABSTRACT FROM AUTHOR]

The Laizhou Bay area contains a large amount of Quaternary brine resources, which have been gradually depleted by long-term high-intensity mining. The local brine genesis is still controversial, and the dominant theory of the evaporation of brine formation limits the exploration of brine resources to the land area, while the confirmation of freezing brine formation would greatly expand the brine storage range. In this research paper, the genesis of underground brines was analyzed based on the major ion concentrations of 62 samples of underground brines at different depths at 24 stations along the south coast of Laizhou Bay. The results show that the underground brines originated from seawater; however, their chemical components were changed during the evolution process after formation. The hydrogeochemical modeling results show that the mixing of seawater and fresh groundwater also affects the chemical composition of brines. The large-scale exploitation of brine resources in recent decades has also led to significant changes in the chemical composition of the underground brine in Laizhou Bay compared with the earlier period. The special geographic environment and the development of the brine chemical industry have led to the evolution of underground brines in Laizhou Bay being affected by a variety of factors, which makes the traditional analysis of brine genesis in this region not applicable. Furthermore, although evaporation and concentration are the dominant factors in the formation of brine, there is still a lack of evidence to rule out the existence of the freezing pathway. [ABSTRACT FROM AUTHOR]