冲绳海槽黑潮流域近4万年以来的古海洋环境演化

IOCAS-IR > 海洋环流与波动重点实验室

	冲绳海槽黑潮流域近4万年以来的古海洋环境演化
	向荣
学位类型	博士
	2001
学位授予单位	中国科学院海洋研究所
学位授予地点	中国科学院海洋研究所
学位专业	海洋地质学
关键词	冲绳海槽古黑潮演化温跃层底层水团演化溶解作用氧同位素有孔虫分布
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、AMS~(14)C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δ~(18)O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δ~(18)O在近陆端因受冲淡小影响较强而变轻，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显的影响，冲绳海槽北部区浮游有孔虫组合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1700 m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连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AMS~(14)C测年和生物地层学对柱状岩芯进行了地层划分和对比，E107孔记录了冰消期以来大约15,000 a来的古环境演化记录，具有较高的沉积速率，DOC－42孔保存在主要是末冰期中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。浮游有孔虫有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增强。冲绳海槽南部E107孔的底栖有孔虫组合把映了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期早期义部水体则较高氧含量为主。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13100 a BP有一个明显的变化，在这之前产温跃层深度较浅，平均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的温跃层深度的两次明显的降低，分别对应于新仙女木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40000a 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末次冰期还要低，反映了区域海洋环境的重大变化。冲绳海槽南部E107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，笔者对未次冰盛期古黑潮流径提出了新的推测。
其他摘要	91 surface samples and two gravity piston cores(E017:126°01.38'E, 26°34.45'N, water depth: 1826 m, 190 cm) were used to study the paleoceanography and the paleo-Kuroshio Current evolution in the Okinawa Trough since the last 40000 years. Micropaleontology analysis of foraminifera, Oxygen and carbon isotope measurements, AMS~(14)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 40000 years in the Okinawa Trough were systematically studied. Oxygen isotope of recent planktonic foraminifera in the Okinawa trough clearly show close relation with modern marine environment. From Globigerinoides ruber to Glibogerinoides sacculifer to Neogloboquadrina dutertrei, the δ~(18)O 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 δ~(18)O show lighter values near the continent side because of the influence of fresh water, while in the east side the δ~(18)O also change to light due to the influence of the Kuroshio Warm Current or its branch. The δ~(18)O difference between Neogloboquadrina dutertrei and Globigerinoides ruber indicate that in the northern Okinawa Trough the branch of Kuroshio Warm Current-Tsushima 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 planktonic 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 this 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 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 piston cores were divided based on the results of oxygen isotope combined with AMS~(14)C dating and biostratigraphy. Core E107 has a paleoenvironmental record of the last 15,000 years since the last deglaciation and has a comparatively high sediment rate. Core DOC-42 has a low-resolution record of marine paleoenvironment between 40-10 ka BP during the last glacial periods. Indexes of fragmental ratios of palnktonic foraminifera and deep water agglutinated shell of benthic foraminifera indicate a gradually strengthen carbonate dissolution in the southern Okinawa Trough since the last deglaciation and the present shallow carbonate lysocline was at last formed at about 2000 a B.P.. foraminiferal assemblage of core E017 show two different nutritional conditions of bottom water in the Okinawa Trough since the last 15,000 years: High organic flux and high nutrition before 6500 a BP and low organic flux from 6500 a BP to present. Bottom water evolution recorded by core DOC-42 was affected by both organic flux and oxygen concentration, benthic foraminiferal assemblages show high organic flux with rapid fluctuation of oxygen concentration during oxygen isotope stage 3, a comparatively lower organic flux and medium oxygen concentration during oxygen isotope stage 2 and high oxygen concentration low organic flux during early oxygen isotope stage 1. Use the themocline depth transfer function of Anderson and Ravelo(1997) the change of DOT(depth of thermocline) was quantitatively reconstructed in the southern Okinawa Trough, a clear change of DOT happened at about 13100 a BP with a shallow DOT average of 89 m before this tie and then deepen after with an average depth of 166 m. Three are two obvious shallow of DOT correspond to Younger Dryas and the great change of Kuroshio Warm Current around 6500 a BP respectively, indicate the upper ocean structure experienced a rapid change during these events. Two low temperature and low salinity stage during the last glacial were found form the northern Okinawa Trough according to the paleo-temperature of transfer function and characteristic species of planktonic foraminifera, the one during the early oxygen isotope stage 3 at about 40,000 a BP was even colder than the one in the oxygen isotope stage 2, showing special regional marine paleoenvironment in the northern Okinawa Trough during the last glacial periods. The grave size variation, geochemical characteristic, indicator species of Kuroshio Current, sea surface temperature and bottom water property recorded by core E017 all show that great change happened around 6500 a BP in the southern Okinawa Trough, this great change were also recorded by other cores in the southern Okinawa Trough, indicating the paleo-Kuroshio Current in the southern Okinawa Trough had a great change around 6500 a BP.The paleoenvironment of the northern Okinawa Trough of the last 20,000 years, however, has much difference compared with that of the southern Okinawa Trough. A new speculation of the paleo-path of Kuroshio Current in the Okinawa Trough during the LGM was suggested on the basis of the former studies of paleo-Kuroshio Current evolution.
页数	203
语种	中文
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/833
专题	海洋环流与波动重点实验室
推荐引用方式 GB/T 7714	向荣. 冲绳海槽黑潮流域近4万年以来的古海洋环境演化[D]. 中国科学院海洋研究所. 中国科学院海洋研究所,2001.

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