【作者】 南青云；

【导师】 李铁刚；

【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， 2008， 博士

【摘要】 本文利用黑潮流域主流轴上的两个柱状沉积物岩芯MD05-2908以及PC-1为研究材料,在AMS¹⁴C测年的基础上,利用高分辨率的有机地球化学分析记录结合浮游有孔虫氧、碳同位素,恢复并重建了过去25,000 cal a BP以来黑潮流域古海洋环境演化的历史。以及表层海水生产力以及物质输送状况的演化历史。通过利用U₃₇^k’古海水温度以及盐度指标恢复重建了过去25,000 cal a BP以来海洋表层海水温度、盐度;通过机碳、氮含量以及同位素变化、长链正构烷烃以及正构烷醇等指标重建了过去7000a B.P.以来的陆源物质输入历史;通过长链不饱和烯酮含量以及有机碳同位素指标恢复了过去7000a B.P.以来海水表层生产力的历史。此外,通过基于以上各种指标的环境信息与区域以及全球其它气候记录进行对比研究以及不同环境指标的时间系列分析,探讨了该区表层环流系统以及生产力的演化对于全球气候变化的响应,揭示了不同尺度的短周期高频率全球变化事件在黑潮流域的具体作用过程和响应机制。通过这些研究取得了以下的主要认识:基于有机地球化学指标的古气候环境记录与黑潮流域已有的研究成果有很好的对应关系,从我们高分辨率的有机地球化学记录中可以识别出全新世黑潮强弱变化的几次明显的事件;25000a B.P.以来黑潮流域的环境变化与全球环境变化有着很好的对应性,黑潮强弱演化总体趋势与全球气候背景演化相一致,黑潮对高频气候变化事件的记录与全球记录具有同步性,这种同步性尤其体现在末次冰消期以来的气候快速高频振荡以及全新世以来的气候突变事件上。全球性的高频气候事件对黑潮主体本身及黑潮流域的相邻区域的大气和海洋环流都具有重要的控制作用,这种控制作用主要通过副高、ITCZ以及季风三种气候要素之间相互关联、彼此影响造成的。具体表现为:太阳辐射量的减少导致热力差异减小,这种相对减小弱化了热带西太平洋的对流活动,造成了西太平洋副热带高压长期偏南、偏东,ITCZ平均北界位置偏南,降雨带长时间集中在南部地区,增强的降雨量提高了风化剥蚀以及沉积物向海洋搬运的能力,陆源物质供应量增加;同时,辐射量以及热力差的减小又与加强的东亚冬季风相联系,增强的冬季风导致了近底层“雾状层”物质的向海传输,物质传输效率增高。这种物源供应以及搬运量的双重增加导致了冲绳海槽流域物质通量的增加。基于有机地球化学指标的海洋表层生产力的变化与陆源物质供应量以及黑潮流的强弱变化存在着对应关系,通常情况增加的海洋表层生产力对应着高的陆源物质输入以及相对较弱的黑潮。这种变化与东亚夏季风的以及冬季风的强弱都有很好的一致性。陆源物质的输入增加了表层营养物质的含量,导致生产力的勃发;陆源物质的输入增加又对应着减少的太阳辐射量,偏南的ITCZ北界位置以及副热带高压,这些对应于减弱的东亚夏季风（增强的东亚冬季风）。黑潮流域的高沉积速率事件对应于减弱的黑潮强度和增加的ENSO频度,这些事件与上述的副热带高压、ITCZ位移和强弱的变化相一致。黑潮流域过去25000a B.P.以来南北温度的差异有冰期加大而全新世减小的趋势,但这种冰期与全新世的差异很小,我们认为末次盛冰期的时候黑潮主流轴没有移出冲绳黑潮,只是由于强度的减弱受陆架水体的影响有所加大。黑潮流域很好的记录到了包括数千年尺度的D/O旋回周期到大气——海洋系统内部振荡所致的PDO、NAO等数十年尺度的高频振荡,说明黑潮流域对过去全球及区域环境变化事件有很好的响应。黑潮流域各古海洋指标所记录周期上的一致性说明这些环境因子控制机理上具有的一致性,即大背景上受太阳活动所引起的辐射量变化控制,局部的高频快速气候波动又受到局域性的气候因素如海气相互作用的放大影响。更多还原

【Abstract】 Two gravity cores MD05-2908 and PC-1, which are under the main axis of Kuroshio Current （KC）, are adopted in this thesis. Based on detailed AMS¹⁴C dates, by using high-resolution organic geochemistry records （such as the content and isotopic composition of carbon and nitrogen, the content of long-chain n-alkane, n-alkanol and unsaturated alkenone） we reconstructed the history of sea surface environmental evolution of the Kuroshio Current main flow for the past 25,000a B.P.. In this study, sea surface temperature （SST） and salnity （SSS） of the past 25,000a B.P. were calculated by using the U₃₇^k’-derived paleo-thermometer index and the foraminifer oxygen isotopic composition. The evolution of history of terrigenous material input during the last 7,000a B.P. was reconstructed via the content and composition of carbon and nitrogen and biomarkers. And the history of sea-surface paleoproductivity for the last 7,000a B.P. was reconstructed by using long-chain unsaturated alkenone and organic carbon isotopic composition. By correlation with records from north hemisphere ice-raft events, GRIP2 ice core and records from Okinawa trough, we analyzed the response mechanisms of sea surface circulation on the past global climate changes. By correlation with those global high frequency climate events we discussed the responses of Kuroshio Current evolution to the global high-frequency climate events. In assistant with spectrum and wavetest methods, we discussed the controlling mechanisms of high-frequency climatic events recorded in the Okinawa Trough. By all these methods and approaches we got the following viewpoints and conclusions. There are good correlations between our organic geochemical based paleoenvironmental records and those reported records in the Kuroshio Current flow. Those former reported Kuroshio variation events （especially during the middle to late Holocene） can be recognized from our high-frequency geochemistry records. There are good correspondings between the Kuroshio variations and global climate changes for the past 25,000 a B.P.. The variation trend of Kuroshio strength is similar to that of global climate changes, and the records of high-frequency climate events identified from our organic geochemistry records are synchronous with those records reported elsewhere in the world. This synchronization reveals the fact that the climate changes in the Kuroshio Current is influenced by global climate changes and there is no obvious time lag or leading.Global high-frequency events show prominent controls on both the main flow of the Kuroshio Current and the atmospheric and oceanic circulation in the nearby areas. This controlling pattern is carried on by the three climatic controlling factors in this area, namely the western Pacific subtropic high （WPSH）, the intertropical convergence zone （ITCZ） and the East Asian monsoon （EAM）. These three factors correlate and restrict each other, and they are dominated by the solar radiant intensity . Concretely, the decrease of the solar radiant intensity induces a reduced heat-difference between the tropical western pacific ocean and the high latitude land area, which weakens the convection activities in the tropical western pacific, as a result, the WPSH is restricted to the south and east part of China, heavy and concentrated rainfall maintains at the east and south part of China. The intensified rainfall enhances the weathering velocity and the river discharges, which together results a increased mass supply into the East China Sea. Furthermore, the East Asian winter monsoon （EAWM） is influenced by the solar radiant intensity. An intensified EAWM always corresponds to a reduced solar radiant intensity, which results in an increasing of“nepheloid layer”transportation. In the South Okinawa Trough （SOT）, this kind of“nepheloid layer”transportation is the primary contribution to the mass accumulated in SOT. Thus, intensified EAWM leads the increasing of material supply in the past 7000a B.P.. The organic geochemistry-induced sea-surface paleo-productivity records show similar variations to that of land-material input for the past 7000a B.P.. The increase in land material greatly enriches the nutrient supplement in the sea surface, which stimulates the primary productivity. For the past 7000 a B.P., the increase of primary productivity always correlates to increased land materials input and decreased Kuroshio current. Indicates the increased influences of land nutrient supplement together with diluted land water.The high-sedimentation rate events correspond to the decreased Kuroshio intensity and the increased ENSO frequency. There are closely relationships with ENSO and the WPSH, the EAM and the migrations of ITCZ.The Kuroshio current shows a decreased SST difference between the middle and the north part of Okinawa Trough from the past 25000a B.P. to present, the maximum difference occurred in the LGM, indicates a decreased Kuroshio Current influences over that time. However, the SST differences between the middle and north part of the Okinawa trough show very little variations between LGM and the Holocene, suggests the Kuroshio Current had always been in the Okinawa Trough both in the Holocene and in the LGM.Periodicity analysis shows the Kuroshio Current give a good records of global high-frequency cycles including the millennial scale D/O cycle and the atmosphere—ocean inter-oscillation induced multi-decadal cycles such as the PDO and NAO, reveals quite sensitive corresponds to the global and regional high-frequency climate events. Periods records picked-up from different proxies show similar periods, which reveals these paleo-environmental proxies have the same controlling factors. The periodicities show that the solar activity has the basic influences on the Kuroshio current and the adjacent areas while those regional climate factors superimposed their influences on the backgroud climate variations and enlarged those high-frequency climate changes.更多还原