【作者】 郑旭峰；

【导师】 李安春；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 海洋地质学， 2014， 博士

【摘要】 本文通过对冲绳海槽西坡海底峡谷区沉积特征及其环境响应的沉积学研究，旨在重建冲绳海槽海底峡谷区50ka以来的古环境演化历史，进而探讨区域季风、洋流以及海平面变化所存在的科学问题。东海广阔流场分布以及海底峡谷区天然的地理和地形优势，为我们获得高分辨率的、具有代表性的沉积学记录提供有利的条件。在本研究中，我们分别选取海底峡谷轴部、峡谷扇以及槽底的四个沉积物柱状样A27、Oki02、A7和Oki01。利用强有力的粒度分析方法，包括粒度旋转主成分分析(V-PCA)、端元分析方法(EMMA)，分别从Oki02和A7孔的沉积物粒度中分离出独立的黑潮端元F3和EM1和冬季风端元GSI和EM2，以讨论沉积物输运机制。结合粘土矿物分析和地球化学分析，以区分沉积物源。同时，还应用XRF岩芯扫描所获得的常量元素比值log(Ti/Ca)和log(Fe/Ca)，以表征陆源沉积物输入量的变化，进而重建东亚冬季风、黑潮和浊流沉积作用历史。进一步对比热带辐合带上其他季风、降雨指标以及厄尔尼诺指标，探讨黑潮和冬季风变化的潜在控制机制。研究结果表明：响应于构造和洋流的变化，冲绳海槽南部海底峡谷区A27孔经历了沉积-剥蚀-沉积的过程。50.0-48.0ka，黑潮尚未进入冲绳海槽，沉积基本以源于黄河和长江的稳定的半深海沉积物为主。48.0-35.0ka是冲绳海槽构造活动非常强烈的时期。强烈的火山、地震作用，不仅使海底峡谷区A27孔基本处于剥蚀和沉积缺失状态，而且逐渐使得冲绳海槽南部的陆桥打开。35.0-34.0ka冲绳海槽构造活动逐渐减弱，浊流沉积开始在峡谷保存。34.0-12.0ka，冲绳海槽南部的陆桥彻底坍塌，黑潮进入冲绳海槽，这一方面带来了台湾东部的沉积物，另一方面阻挡长江和黄河的沉积物向冲绳海槽南部搬运。全新世伊始，响应于岁差所驱动的东亚夏季风增强以及热带“ENSOPOWER”的减弱，黑潮经历了大幅度的增强；黑潮的增强及其所产生的“水障作用“，一方面阻挡了大多数夏季源于中国东部的沉积物，另一方面使得大部分黄河物质无法到达冲绳海槽, A7、Oki02和Oki01孔中粘土矿物物源由以长江和黄河为主转变为以陆架、长江以及少量台湾物质为主，log(Ti/Ca)和log(Fe/Ca)比值也有较大减小。相反，在强烈东北季风以及黑潮的水障减弱的冬季，季风Ekman效应所产生的下降流以及强烈的水体混合，仍然能将丰富的中国东部的陆源沉积物以底部雾状层的形式沿着海底峡谷和陆坡向海槽搬运。这时黑潮逐渐达到稳定，海平面对东海的环流的影响已经很小，东海的“夏贮冬输”模式基本形成。底部雾状层粒度端元GSI、EM2以及陆源物质指示的log(Ti/Ca)基本记录冬季风的信号。另外，GSI、EM2和log(Ti/Ca)之间以及它们与苏禄海的初级生产力，青海多洼黄土平均粒径和湖光岩玛珥湖沉积物的磁化率在全新世的一致性变化，进一步说明GSI、EM2和log(Ti/Ca)作为冬季风指标的可靠性。对比同纬度上东葛洞石笋的东亚夏季风指标δ18O，发现东亚冬季风与夏季风具有非常一致的反向变化，这种反向变化关系反映全新世热带辐合带的南移。更进一步对比热带辐合带上的季风、降雨指标，包括安曼石笋δ18O，委内瑞拉卡里亚科湖泊的Ti含量，北半球夏季日照量变化以及南半球秘鲁石笋δ18O，发现它们之间具有非常一致的变化，这进一步支持热带辐合带对全球季风、降雨的调控作用，从而支持高纬和低纬过程在不同尺度对季风的驱动。为了更定量描述季风体系的相互关系，从而分离出太阳外部的驱动以及地球内部ENSO的调控，在研究中我们还分别应用交叉互相关分析、小波分析以及全局谱分析，对于东亚冬季风与夏季风指标进行了分析。交叉互相关分析结果显示东亚冬季风与夏季风在12.0-5.5ka具有非常强的反向相关性(-0.8),这种反相关说明季风体系直接响应于太阳辐射所驱动的热带辐合带的纬向迁移,即外部调控；从5.5-2.5ka，东亚冬季风与夏季风的耦合性减弱(-0.5)，这种减弱与这个时期厄尔尼诺-南方涛动的加强有关。2.5-0ka，东亚冬夏季风的关系进一步脱偶，从反向相关变成正相关甚至没有相关性，这种东亚冬季风与夏季风之间关系的脱偶现象与2.5ka后厄尔尼诺-南方涛动进一步加强以及人类对于气候以及环境的干扰有关。全局谱分析和小波分析的结果表明东亚冬夏季风具有相似的1500,500以及260年的周期。粒度V-PCA和EMMA分析得到黑潮端元F3、EM1具有非常一致的变化，而且它们与其他黑潮指标，包括A7和MD0124-04孔的普林虫含量、ODP1202孔中分选性粉砂含量以及日本海沿岸的MD01-2421孔黑潮指标具有非常好的一致性。进一步对比其他热带ENSO指标以及季风指标，结合现代观测结果，表明黑潮在12.0ka急剧增强是响应于岁差变化所驱动的“ENSOPOWER“的减弱以及东亚夏季风的增强。而5.0ka以来黑潮的高频变化和减弱，可能与叠加于轨道尺度的更高频次的ENSO活动有关。进一步对黑潮指标F3、EM1进行全局谱分析、小波分析，还发现黑潮2600、1500以及260年周期。这些黑潮周期更一步说明热带ENSO以及季风与中纬度黑潮的复杂的、非线性的关系。更多还原

【Abstract】 This study focuses on the paleoenvironmental evolution and characteristic ofsubmarine canyon system in the west slope of the Okinawa Trough since50ka, aimingto resolve various scientific problems with regard to current and monsoon system; Thebrode current system of East China Sea and the unique geographic and geomorphicfeatures of submarine canyon systems in the west slope of the Okinawa Trough providehigh resolution, representive records for paleoenviromental reconstruction.We chose four sediment cores A27,Oki02,A7,Oki01from axis of south submarinecanyon, deep-sea fan and basin respectively. We have first time unravelled independentKuroshio Current (F3and EM1) and East Asian winter monsoon (GSI and EM2)proxies by using V-PCA and EMMA on grain size matrix of detrital components ofsediments in the Okinawa Trough, so as to discuss the transport mechanisms. Combinedwith clay mineral and geochemistry analysis, we have further differentiated theprovenance of research area. Based on clear discurssions on provenance and transportmechanisms, we have described the terrigenous sediment influx using XRF scannnerelemental ratios log(Ti/Ca) and log(Fe/Ca), and thus reconstruct the history of KuroshioCurrent and monsoon system. Further comparison with other monsoon and rainfallproxies located on the zone of ITCZ and ENSO proxies have been conducted for betterelucidate the potential forcing and thus resolve various scientific problems.Our results indicates that core A27in the south Okinawa Trough has experiencedaccumulation-erosion-accumulation processes in response to the evolution of regionaltectonic activity, current system. From50.0-48.0ka, the sediments in submarine canyonare mainly composed of hemipelagic silty mud with accumulation rate of65cm/ka,when the Kuroshio Current was outside the Okinawa Trough and clay mineral derviedmainly from Yellow and Yangtze River. The intensified tectonic activity and thesubsequent volcano and earthquake activity not only cause the erosion and sedimentmissing in submarine canyon but also open the bridge bwtween Taiwan and Ryukyuislands gradually. From35.0-34.0ka, tectonic activity has weakened gradually and thetriggered-turbidity sediment has began accumulating on the submarine canyon system, which thus has enhanced the sedimentation rate of core A27also；From34.0-12.0ka，the bridge between Taiwan and Ryukyu islands has collapsed completely and theKuroshio Current has entered the Okinawa Trough, which not only has broughtsediments of Taiwan Island to core A27, but also has resisted much sediments fromYangtze and Yellow River. The clay minerals of core A27have shifted from Yellow andYangtze River to Taiwan island and East China Sea continental shelf, when theaccumulation rate has descended correspondingly. Since the Holocene, the KuroshioCurrent has intensified greatly in response to precession-induced enhancement of EastAsian summer monsoon and decrease of “ENSO power”. The intensified KuroshioCurrent and the subsequent formation of Kuroshio-induced “water barrier” not onlymasks the fluvial signal driven by summer monsoon but also blocks the clay mineralssourced from Yellow River, one of the major contributors prior to12ka BP. This isevident by the shift of clay mineral provenance from Yellow and Yangtze River tomixture of East China Sea continental shelf and Yangtze River and the decrease oflog(Ti/Ca) and log(Fe/Ca). On the contrary, the strong East Asian winter monsoon andweak Kuroshio “water barrier” may favor the export of abundant terrigenous materialfrom East China to the Okinawa Trough via monsoon forcing Ekman transport andstrong mixing. Meanwhile, the relatively steady sea level and Kuroshio Current in theHolocene minimizes the sea level effect on the circulation patter, when the “storage insummer and export in winter” model has been constructed. The newly proposed indexGSI, EM2and log(Ti/Ca), which well represents winter monsoon, are consistent withother winter monsoon proxies. The consistency further validate the credibility of ourmonsoon proxies. The newly proposed index GSI, EM2and log(Ti/Ca) exhibits anegative correlation with the18O record in Dongge Cave in China. Such anti-correlation suggests the southward migration of the Intertropical Convergence Zone(ITCZ) in Holocene. The consistency among our records and rainfall records in Peru,monsoon records in Oman and averaged summer insolation pattern at30°Nfurthersupport the global-wide impact of ITCZ on monsoon systems.For quantitative description of the relationship of monsoon system and unravelingthe internal ENSO forcing and external insolation forcing from monsoon proxy, we also have conducted cross-correlation analysis, wavelet analysis and global spectra analysisto access the East Asain monsoon proxies. Cross-Correlation Analyses for GSI andlog(Ti/Ca) against18O record in Dongge Cave further unravel a decoupling betweenthe East Asian winter and summer monsoon during5500-2500cal yr BP, and a greatercomplexity in recent2500yr. Such decoupling is attributable to exacerbated ENSOmode alternation activity and even human interference that superimposed on insolationand ITCZ forcing. Global spectra and wavelet analysis indicate that the East Asianwinter and summer monsoon show similar1500,500and260year cycle and the cyclevary with the change of time.The newly proposed grain size index F3and EM2, indicators of Kuroshio Current,show consitent variation with other Kuroshio Current proxies includingP.obliquiloculata in Core A7and MD0124-04, sortable silt(10-63μm) of CoreODP1202and δT of two cores near the coastal area of Japan Sea. The comparisonbetween Kuroshio proxies and ENSO, monsoon indicators, coupling with modernobservation results, indicate that the enhancement of Kuroshio Current since theHolocene is a response of precession forcing decrease of “ENSO power” andintensification of East Asian summer monsoon. The centennial scale variation since5.0ka is ascribed to higher ENSO variation superimposed on orbital scale variation.Global spectra analysis, wavelet analysis on Kuroshio Current proxies indicate that theKuroshio Current shows2600,1500and260year cycle, which further illustrate thecomplex and norlinear relationship between middle latitude Kuroshio Current and lowlatitude ENSO and monsoon.更多还原