The Characteristics And Provenances Of The Core Sediments In The Middle Okinawa Trough And Their Paleoenvironment Implications Since17Ka

Based on the precise AMS14C dating data, we calculated the dry bulk density with thewater content, and we analyzed the grain size and clay minerals of two sediment cores(OKI03and OKI04), collected from the middle Okinawa Trough. We investigate thesediment provenances of the study area with the clay minerals data. The results showthat terrigenous sediments in the middle Okinawa Trough are mainly from thesediments input into the East China Sea by the large rivers in east China (YangtzRiver and Yellow River) and also the main rivers of the east and west Taiwan.However, the contribution of the two main provenances changes with time andlocation. The Core OKI04records the evolution of the sediments provenance in thesouth of the Middle Okinawa Trough since17ka.17-13.4ka, sediments from Yangtzand Yellow river are dominant in the south of the Middle Okinawa Trough;13.4-11.4ka, sediments from west Taiwan became increase;11.4-7.5ka, the influence of theYangtz and Yellow river’s sediments become stronger;7.5-5.5ka, the sediments in thestudy area are most influenced by the Taiwan source; from5.5ka to now, sedimentswere mainly from the east of Taiwan and the Yangtz River. While the Core OKI03shows that provenances change in the north middle Okinawa Trough since8ka. The records indicate that7.8-6.4ka, sediments in the north middle Okinawa Trough weremainly from the Yangtz and Yellow river, while sediments from the east of Taiwanalso influenced the area;6.4-5.6ka, sediments were influenced by the substancesfrom the Yangtz River and the Yellow River; sediments were mainly from the Yangtzand Yellow River since5.6ka, while sediments of Taiwan also had some affect on thestudy area at the same time. Besides, we applied the standard deviation values VSgrain size class method to analyze the evolution of sedimentary dynamic environment.The environmental sensitive components show that the middle Okinawa Trough wasin a fluctuating dynamic environment since8ka. Our study also recognized that thekaolinite in the middle Okinawa Trough was mainly from the large rivers in the eastChina mainland. We tried to use the content change of the kaolinite as a proxy of theEast Asian winter monsoon evolution. The core OKI04records5strengthen periodsof the winter monsoon since17ka, while the records of the OKI03has improved theresolution of the winter monsoon evolution, and shows5strengthen periods since8ka.