Paleoceanographic records in the sedimentary cores from the middle Okinawa Trough

Two gravity piston cores (Cores 155 and 180)involved in this study were collected from the middle Oki-nawa Trough. Stratigraphy of the two cores was divided andclassified based on the features of planktonic foraminiferaoxygen isotope changes together with depositional sequence,millennium-scale climatic event comparison, carbonate cy-cles and AMSC dating. Some paleoclimatic informationcontained in sediments of these cores was extracted to dis-cuss the paleoclimatic change rules and the short-time scaleevents presented in interglacial period. Analysis on thevariation of oxygen isotope values in stage two shows that themiddle part of the Okinawa Trough may have been affectedby fresh water from the Yellow River and the Yangtze Riverduring the Last Glacial Maximum (LGM). The oxygen iso-tope value oscillating ranges of the cores have verified thatthe marginal sea has an amplifying effect on climate changes.The δC of benthic foraminifera Uvigerina was lighter inthe glacial period than that in the interglacial period, whichindicates that the Paleo-Kuroshio’s main stream movedeastward and its influence area decreased. According to thetemperature difference during the "YD" period existing inCore 180 and other data, we can reach the conclusion thatthe (?)iimatie changes in the middle Okinawa Trough areawere controlled by global climatic changes, but some re-gional factors had also considerable influence on the climatechanges. Some results in this paper support Fairbanks’spoint that the "YD" event was a brief stagnation of sea levelrising during the global warming up procession. Moreover,the falling of sea level in the glacial period weakened theexchange between the bottom water of the Okinawa Troughand the deep water of the northwestern Pacific Ocean andresulted in low oxygen state of bottom water in this area.These procedures are the reasons for carbonate cycle in theOkinawa Trough area being consistent with the "Atlantictype " carbonate cycle.