西南季風演化與南半球氣候的聯系

薛濱++金章東++強小科++張恩樓

摘 要：印度（西南）季風降水對我國西南地區有著重要的影響，但是與東亞季風相比較，總的來說對印度季風的研究十分薄弱，并且其認識主要來自于海洋沉積物。那么西南季風演化的規律究竟是什么？西南季風與東亞季風、西風環流在時空上的演化關系是什么？它們之間的演化存在著怎樣的動力學聯系？西南季風氣候變遷與南北半球氣候所驅動的海陸氣相互作用的動力學機制究竟是什么？這些都是值得關注的科學問題。通過云南鶴慶深鉆湖泊沉積物的深入分析，結合不同盆地周邊的地層、火山巖及地貌特征，建立區域構造-沉積旋回演化的年代框架，分析其記錄的季風氣候演化歷史及其與青藏高原、南半球氣候變化的聯系。同時擬在南部的云南騰沖青海鉆取沉積物巖心，建立MIS3以來沉積序列高分辨率年代框架，分析各環境代用指標，結合現代湖泊環境定量轉換函數研究，加強湖泊生物指標定量研究，獲取冰期/間冰期旋回尺度上的西南季風演化過程。在構造尺度上，揭示西南季風強度、變率及季節性變遷的動力學機制，及其與高原階段性隆升的內在聯系、對區域剝蝕-風化過程的制約；在冰期/間冰期尺度上，研究植物種群和湖泊生物多樣性的演替階段與過程，開展海洋和陸地生物地球化學指標（碳氧同位素、微量元素）對比研究，從機理上探討南北半球氣候與西南季風周期、季節性的內在聯系。云南鶴慶盆地獲得的666 m高質量湖泊巖心，提供了更新世以來高分辨率的印度夏季風陸地記錄，揭示了更新世過去260萬年印度季風變遷的歷史，通過印度夏季風指標序列在冰期-間冰期旋回內的精細結構，揭示了南北半球間跨赤道氣壓梯度的變化及印度季風變化影響的動力學機制。在間冰期內，印度夏季風的變化主要受控于印度低壓的強度，間冰期氣溫增高所引起的北半球熱力牽引也是導致印度季風增強的重要因素；而在盛冰期中，印度季風極小值發生在南極溫度幾乎達到最低值時，印度夏季風強度卻往往提前于全球冰量最大值約1.4至3.5萬年出現，此后開始增強，這是南半球氣溫變化通過馬斯克林高壓而產生的氣壓推動的結果。云南騰沖青海沉積記錄了末次冰盛期的古氣候特征，總體主要受控于印度季風強弱的變化。該記錄與亞洲季風區石筍、阿拉伯海等記錄的季風氣候變化趨勢非常一致，表明18Ka以來印度夏季風受北半球太陽和ITCZ平均位置移動的影響。該記錄同時與格陵蘭冰芯δ18O記錄高度相關，證實印度季風與高緯氣候之間具有密切聯系。

關鍵詞：湖泊沉積物 西南季風 古氣候動力學機制 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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