西南季风演化与南半球气候的联系

薛滨++金章东++强小科++张恩楼

摘 要：印度（西南）季风降水对我国西南地区有着重要的影响，但是与东亚季风相比较，总的来说对印度季风的研究十分薄弱，并且其认识主要来自于海洋沉积物。那么西南季风演化的规律究竟是什么？西南季风与东亚季风、西风环流在时空上的演化关系是什么？它们之间的演化存在着怎样的动力学联系？西南季风气候变迁与南北半球气候所驱动的海陆气相互作用的动力学机制究竟是什么？这些都是值得关注的科学问题。通过云南鹤庆深钻湖泊沉积物的深入分析，结合不同盆地周边的地层、火山岩及地貌特征，建立区域构造-沉积旋回演化的年代框架，分析其记录的季风气候演化历史及其与青藏高原、南半球气候变化的联系。同时拟在南部的云南腾冲青海钻取沉积物岩心，建立MIS3以来沉积序列高分辨率年代框架，分析各环境代用指标，结合现代湖泊环境定量转换函数研究，加强湖泊生物指标定量研究，获取冰期/间冰期旋回尺度上的西南季风演化过程。在构造尺度上，揭示西南季风强度、变率及季节性变迁的动力学机制，及其与高原阶段性隆升的内在联系、对区域剥蚀-风化过程的制约；在冰期/间冰期尺度上，研究植物种群和湖泊生物多样性的演替阶段与过程，开展海洋和陆地生物地球化学指标（碳氧同位素、微量元素）对比研究，从机理上探讨南北半球气候与西南季风周期、季节性的内在联系。云南鹤庆盆地获得的666 m高质量湖泊岩心，提供了更新世以来高分辨率的印度夏季风陆地记录，揭示了更新世过去260万年印度季风变迁的历史，通过印度夏季风指标序列在冰期-间冰期旋回内的精细结构，揭示了南北半球间跨赤道气压梯度的变化及印度季风变化影响的动力学机制。在间冰期内，印度夏季风的变化主要受控于印度低压的强度，间冰期气温增高所引起的北半球热力牵引也是导致印度季风增强的重要因素；而在盛冰期中，印度季风极小值发生在南极温度几乎达到最低值时，印度夏季风强度却往往提前于全球冰量最大值约1.4至3.5万年出现，此后开始增强，这是南半球气温变化通过马斯克林高压而产生的气压推动的结果。云南腾冲青海沉积记录了末次冰盛期的古气候特征，总体主要受控于印度季风强弱的变化。该记录与亚洲季风区石笋、阿拉伯海等记录的季风气候变化趋势非常一致，表明18Ka以来印度夏季风受北半球太阳和ITCZ平均位置移动的影响。该记录同时与格陵兰冰芯δ18O记录高度相关，证实印度季风与高纬气候之间具有密切联系。

关键词：湖泊沉积物 西南季风 古气候动力学机制 南半球

The Southwest Monsoon： Evolution and Its Link with the Southern Hemisphere

Xue Bin1 Jin Zhangdong2 Qiang Xiaoke2 Zhang Enlou1

（1.Nanjing Institute of Geography and Limnology， Chinese Academy of Sciences； 2.Institute of Earth Environment， Chinese Academy of Sciences）

Abstract：India monsoon （southwest monsoon） plays a very important role on the southwestern China， however， few researches were concentrated on this area compared with the east Asian monsoon. What is the evolution of southwest monsoon， and how did it link with the southeast monsoon as well as the westlie circulation， and furthermore， what is the mechanism behind among the monsoon systems and inter-hemisphere linkage. All these needed to be concerned scientifically. This project aims to reconstruct the tectonic-sedimental cycles and palaeoclimate changes in terms of the monsoon evolution and Tibetan plateau uplifting as well as south hemisphere impact， in the long time scale， based on the further analysis on the sediments from the Heqing Basin of Yunnan province， China. Meanwhile in the short timescale， the palaeoclimate changes sine MIS 3 would be researched based on the sediments from the Qinghai lake， a small volcanic-origin from southwest part of Yunnan. The Heqing palaeolake sediments present a high-resolution continental record from southwestern China that demonstrates the importance of interhemispheric forcing in driving India summer monsoon （ISM） variability at the glacial-interglacial time scale as well. Interglacial ISM maxima are dominated by an enhanced Indian low associated with global ice volume minima. In contrast， the glacial ISM reaches a minimum， and actually begins to increase， before global ice volume reaches a maximum. We attribute this early strengthening to an increased cross-equatorial pressure gradient derived from Southern Hemisphere high-latitude cooling. This mechanism explains much of the nonorbital scale variance in the Pleistocene ISM record. The Qinghai lake sediments record the palaeoclimate changes since LGM， which is controlled by the India monsoon system. The consistent changes with the record from Arab sea and the cave stalagmite suggest that the India summer monsoon was controlled by the north hemisphere insolation and the ITCZ migration， and the close linkage with the record from the Greenland ice core δ18O also suggest the dynamic mechanism between the India monsoon and the high latitude climate to some extent.

Key Words：Lake sediments； Southwest monsoon； Palaeoclimate dynamics； Southern hemisphere

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