【作者】 向荣；

【导师】 阎军；

【作者基本信息】 中国科学院海洋研究所 ， 海洋地质学， 2001， 博士

【摘要】 本文采用取自冲绳海槽的91个站位的表层样品和2个柱状岩芯，通过微体古生物有孔虫分析、氧碳同位素测试、AMS¹⁴C测年、沉积物粒度和地球化学分析，探讨了现代生物群落、表层沉积物氧同位素与现代海洋环境之间的关系，进而对冲绳海槽区域近4万年来的古海洋环境和古黑潮演化进行了详细的研究。 表层沉积物中的浮游有孔虫氧同位素与现代海洋环境之间的关系密切，浮游有孔虫从G.ruber到G.sacculifer到N.dutertrei其δ¹⁸O值由轻变重，表明三种有孔虫其生活水层依次由浅到深。在横穿海槽的剖面上浮游有孔虫δ¹⁸O在近陆端因受冲淡水影响较强而变轻，而在东侧站位，受黑潮暖流或其支流的影响氧同位素同样有变轻的趋势。N.dutertrei和G.ruber的氧同位素差值表明了冲绳海槽北部区域黑潮支流对表层水体的影响要大于次表层水体，而在冲绳海槽南部区域，黑潮暖流对次表层水体有相对较强的影响。 冲绳海槽南部表层沉积物中的浮游有孔虫整体上属于赤道区组合，溶解作用对该区的浮游有孔虫群落有明显的影响，冲绳海槽北部区浮游有孔虫组合相对具有温带群落的特征。浮游有孔虫分布与海洋环境密切相关，南北区的浮游有孔虫分布都明显受暖流的影响，在暖流的主流轴处浮游有孔虫丰度通常较高。 冲绳海槽具有相对较浅的碳酸盐溶跃面，浮游有孔虫丰度和底栖有孔虫深水胶结壳的含量都进一步表明了该区碳酸钙溶跃面大约在1700m水深左右，比开放大洋明显要浅得多。 表层沉积物中的底栖有孔虫主要受水深和水团等因素的制约。水深制约着有孔虫属种的分带，也影响底栖有孔虫的组合。根据Q型因子分析，冲绳海槽南部表层沉积物中的底栖有孔虫从陆架边缘到海槽底部可以划分为5个特定的组合，分别对应黑潮表层水和次表层水影响环境、黑潮中层水影响环境、溶跃面以上的黑潮深层水影响环境、黑潮底层水团影响环境和溶解作用较强的槽底环境；北部区的底栖有孔虫群落反映了四个组合，分别代表了陆架混合水团影响环境、黑潮暖流中层水影响环境、冷涡沉积和上升流沉积区影响环境以及对马暖流水团影响下的环境。 以氧同位素曲线为基础，结合AMS¹⁴C测年和生物地层学对柱状岩芯进行了地层划分和对比，E017孔记录了冰消期以来大约15,000a来的古环境演化记录，具有较高的沉积速率，DOC-42孔保存的主要是末次冰期中40-10ka BP期间的古环境沉积记录，沉积物记录的分辨率相对较低。 浮游有孔虫的碎壳比和底栖有孔虫深海胶结壳含量表明了现代冲绳海槽的浅溶跃 面是大约最近2000 a BP才开始突然变浅形成的，碳酸盐的溶解作用从冰消期到现在 逐渐增强。冲绳海槽南部 EOI7孔的底栖有孔虫组合反映了 15，000 a来的底层水团具 有两种完全不同的营养状况，约 6500 a BP以前有机质通量较高，6500 a BP以后有机 质通量则明显降低。DOC－42孔的底栖有孔虫组合反映该区约4万年以来的底部水团 演化主要受有机质通量和氧含量的共同制约，氧同位素3期主要为高有机质通量的沉 积环境，伴随有氧含量水平的较大波动：氧同位素2期有机质通量有所降低，氧含量 整体为中等水平；氧同位素1期早期底部水体则以较高氧含量为主。 浮游有孔虫温跃层转换函数反映了冲绳海槽中部的温跃层在约门 100 a BP有一个 明显的变化，在这之前的温跃层深度较浅，平均为 89 m，而在该时间以后，温跃层平 均深度变为 166 m。此外在 160 cm处和 100 cm的温跃层深度有两次明显的降低，分 别对应于新仙女术事件和黑潮暖流的重新入侵，表明这两个事件导致了海洋上层水体 结构的突然变化。 冲绳海槽北部浮游有孔虫转换函数古温度和浮游有孔虫的低温、低盐特征种反映 了在氧同位素3期早期约40000 a BP和氧同位素2期间存在两个明显的低温、低盐阶 段，可能与沿岸水在该期间加强有关。其中氧同位素3期早期的表层海水古水温比本 次冰期还要低，反映了区域海洋环境的重大变化。 冲绳海槽南部 EOI7孔的沉积物粒度、地球化学特征、黑潮特征指示种、表层古 水温以及底层水团的性质均在6500 a BP左右发生了重大的改变，与冲绳海槽南部的 其他岩芯反映的古环境变化基本一致，表明了南部海槽在6500 a BP前后古黑潮流径 发生了重大变化。而冲绳海槽北部区域2万年以来的古环境则与南部有明显差异，总 结前人对冲绳海槽古黑潮流径的研究，笔者对末次冰盛期古黑潮流径提出了新的推 测。更多还原

【Abstract】 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更多还原