Study Of The Paleoceanography Evolution In The Okinawa Trough Since The Last 40000 Years

91 surface samples and two gravity piston cores(E017: 126001.38, 26034.45, water depth: 1826 m, core length: 297 cm; DOC-42: 128020.9, 30018.64, water depth: 389 m, core length: 190 cm)were used to study the paleoceanography and the paleo-Kuroshio Current evolution in the Okinawa Trough since the last 40,000 years. Micropaleontology analysis of foraminifera, Oxygen and carbon isotope measurements, AMS?C dating, grave size analysis and geochemical analysis were performed on the above materials. Based on these obtained datas, the relations between recent foraminiferal faunal, oxygen isotope of recent planktonic foraminifera and modern marine environment were discussed, further, the paleoceanography and paleo-Kuroshio Current evolution of the last 40,000 years in the Okinawa Trough were systematically studied. Oxygen isotope of recent planktonic foraminifera in the Okinawa trough clearly show close relation with modem marine environment. From (ilobigerinoides ruber to Glibogerinoides saccul~/er to Neogloboquadrina dutertrei, the 8180 of these species changes from light to heavy, indicating the average living water depth of these species gradually change from shallow to deep. In the profile across the trough the 8O show lighter values near the continent side because of the influence of fresh water, while in the east side the 8180 also change to light due to the influence of the Kuroshio Warm Current or its branch. The 8O difference between Neogloboquadrina dutertrei and Globigerinoides ruber indicate that in the northern Okinawa Trough the branch of Kuroshio Warm Currentsushima Current has more strong influence on surface water than subsurface water mass, while in the southern Okinawa Trough the Kuroshio Warm Current has more strong influence on subsurface water mass. Surface planktonic foraminifera of the southern Okinawa Trough, as a whole, belong to equatorial zone assemblage and were partly influenced by carbonate dissolution. While surface planktonic foraminifera of the northern Okinawa Trough comparatively has characteristic of temperate assemblage. The distribution of plar ktonic foraminifera in surface samples are strictly controlled by modern marine environments, both areas show the Kuroshio Warm Current is the most important factor influence the planktonic foraminifera distribution, near the main path of Kuroshio Warm Current the abundance of planktonic foraminifera is usually high. The carbonate lysocline depth(CLD) in Okinawa Trough is clearly shallower compared to the open ocean, the abundance of planktonic foraminifera and percentage of deep water agglutinated shell of benthic foraminifera both show the CLD lies at about 1700 m in the Okinawa Trough. Benthic foraminifera in surface sediments of Okinawa Trough are mainly affected by water depth and water masses. According to Q-mode factor analysis, benthic foraminifera in southern Okinawa Trough can be divided into 5 assemblages, correspond to surface and subsurface water mass of Kuroshio Current, intermediate water mass of Kuroshio Current, deep water mass of Kuroshio Current above the lysocline, bottom water masses of Kuroshio Current and severely dissolved environments in the bottom Trough respectively. Benthic foraminifera in the northern Okinawa Trough can be divided into 4 assemblages, correspond to continental shelf mixed water mass, intermediate water mass of Kuroshio Current, gyro and upwelling deposition environment and Tsushima Warm Current water mass respectively. Stratigraphy of two gravity...