我国西北夏季风边界千年尺度变化的证据--来自盐池和猪野泽盐类矿物分析结果

我国夏季风西北缘是响应长尺度气候变化最为敏感的区域之一, 但夏季风边界变化与千年尺度气候变化之间的关系尚不明确, 相关研究仍缺乏足够证据。夏季风西北缘湖泊沉积物中盐类矿物种类与含量的时空变化, 有助于推测气候变化特征。盐池和猪野泽分别位于祁连山北麓的河西走廊中段和东段, 是研究长时间尺度亚洲夏季风影响区西北边界变化的关键区域。研究全新世千年尺度下, 夏季风西北边界的变化对夏季风西北缘气候变化过程的影响, 对明确季风边缘区千年尺度季风变化机制, 预测未来长尺度气候变化有重要意义。因此, 本文选择盐池古湖泊盐池剖面(YC), 猪野泽青土湖01、02剖面(QTH01、QTH02)等三个剖面, 开展全新世千年尺度下, 亚洲季风西北边界地区湖泊沉积物盐类矿物时空变化对比研究。结果显示:QTH01、QTH02剖面盐类矿物以碳酸盐为主, 硫酸盐类矿物仅零星出现, 而YC剖面硫酸盐类矿物含量相对较高, 同时出现了氯化物型矿物, 全新世气候特征整体较猪野泽更为干旱。末次冰期和早全新世, 三个剖面受季风输送水汽影响明显, 碳酸盐类矿物能较好沉积, 季风边界在这一时期向北扩张, 推进到祁连山中段地区;中全新世QTH01、QTH02剖面受夏季风影响减弱, 湖泊退缩, 碳酸盐类矿物含量达到峰值, YC剖面则表现出极端干旱的气候特征, 硫酸盐类矿物因“盐效应”含量下降, 此时夏季风西北部水汽输送边界位于石羊河流域和盐池流域之间;晚全新世盐池和猪野泽均以风成沉积为主, 气候干旱, 碳酸盐类矿物难以保存, 硫酸盐和氯化物矿物含量出现高值, 说明夏季风西北边界进一步向南迁移。综上所述, 盐类矿物含量变化能良好反应夏季风西北缘全新世气候变化特征, 同时证明, 在全新世千年尺度上, 夏季风西北边界在盐池流域和石羊河流域之间存在变化。

An Evidence of Millennial-Scale Summer Monsoon Boundary Change in the Northwest China——Analysis Results From Saline Minerals in Lake Sediments of Yanchi Lake and Zhuye Lake

The northwest margin of summer monsoon in China is one of the most sensitive areas to response long-time scale climate change, but the related researches between summer monsoon boundary changes and millennial-scale climate change driving mechanism are still lack of sufficient evidence. The temporal and spatial variation of types and content of saline minerals in lake sediments could speculate the characteristics of climate change in the northwest margin of summer monsoon. Yanchi Lake is located in the northern Qilian Mountains and the central Hexi Corridor, while Zhuye Lake is located in the eastern Hexi Corridor, which is a key research area for the long-term northern boundary changes of the Asian summer monsoon. It has important significance for clarifing monsoon change mechanism under millennial-scale and predict long-time scale climate change to study how the motion of the northwest border of summer monsoon impact climate change process in the northwest margin of summer monsoon. In this paper, we chose YC section in Yanchi Lake and QTH01 and QTH02 sections in Zhuye Lake, which located at different positions of Hexi Corridor, to conduct a millennial-scale comparative study of temporal and spatial variation of types and content of saline minerals. The results revealed that saline minerals in QTH01 and QTH02 sections are mainly carbonate minerals like calcite and aragonite, and there are only sporadic sulfate minerals, while sulfate minerals content in YC section is relatively high, and there also exist chloride type minerals which indicated the more arid environment in Yanchi Lake than in Zhuye Lake. During the late glacial and early Holocene, all of the three sections were influenced by monsoon conveying water vapor, carbonate minerals well sedimentated, and monsoon boundary expanded to the middle region of Qilian mountains in this period. The summer monsoon effect weakened in middle Holocene, Zhuye Lake retreated with carbonate mineral contents reached peak values, and Yanchi Lake showed extreme drought climate characteristics and the content of sulfate minerals decreased because of the “salt effect”. The northwestern border of summer monsoon should be between the Shiyang river drainage basin and the Yanchi drainage basin in middle Holocene. Yanchi Lake and Zhuye Lake were given priority to eolian deposition in late Holocene, carbonate minerals were difficult to conserve in such arid climate, sulfate and chloride mineral contents had high value, and the northwestern border of summer monsoon further retreated to south. In conclusion, the variations of salt mineral contents are well respond to Holocene climate change characteristics, and the northwestern border of summer monsoon swung between the Shiyang river drainage basin and the Yanchi drainage basin under millennial-scale during Holocene.