摘要:哈尔滨黄土位于松嫩平原东北部，处于欧亚大陆中纬度干旱—半干旱地带的东部边缘，是季风和非季风区的过渡地带，对季风气候的变化非常敏感。然而，由于沉积档案露头的缺乏，使得该地区的气候变化研究极为薄弱。为此，我们对哈尔滨黄土进行了磁化率、总有机碳（TOC）和地球化学测试，并结合小波分析，对松嫩平原中更新世以来的夏季风演变及其控制机制进行研究。结果表明，中更新世以来松嫩平原的夏季风演化分为两个阶段：1） 460～180 ka时期，哈尔滨黄土较低的化学风化程度和TOC值指示了弱的夏季风强度；另外，在此时期还存在3个次一级的夏季风的微弱增强，叠加在夏季风强度偏弱这一大趋势之上。2） 180 ka～至今，哈尔滨黄土—古土壤序列的磁化率、化学风化程度和TOC值呈现出逐渐增大的趋势，表明东亚夏季风强度逐渐增强。通过哈尔滨黄土与邻区赤峰黄土和黄土高原洛川黄土的磁化率和粒度综合对比分析，表明松嫩平原首先响应间冰期夏季风主导的温度升高及降水增加带来的气候变化，但这种响应的持续时间偏短；哈尔滨黄土记录了360～340 ka和280～250 ka两次显著的夏季风减弱的气候现象，这是全球气候和区域环境变化综合作用的结果。小波分析结果表明，哈尔滨黄土—古土壤序列磁化率小波变换的主导周期为98 ka（100 ka），结合海平面温度、全球CO2浓度、60°N太阳辐射量、深海氧同位素综合对比分析，表明松嫩平原夏季风演化主要受全球冰量驱动；36 ka和44 ka（40 ka）倾角周期以及最低振荡29 ka周期的出现，表明倾角驱动的低纬太阳辐射变化对松嫩平原夏季风起到微弱调控作用，而岁差驱动的低纬太阳辐射变化对松嫩平原影响较小。
关键词: 东亚夏季风/
哈尔滨黄土/
松嫩平原/
地球化学组成/
磁化率
Abstract:Harbin loess is located in the northeast of Songnen Plain, on the eastern edge of arid and semi-arid zone in the middle latitude of Eurasia. It is a transition zone between monsoon and non-monsoon regions and is very sensitive to the change of monsoon climate. However, due to the lack of outcrops of sedimentary archives, the study of climate change in this area is weak. Therefore, we measured the magnetic susceptibility, total organic carbon (TOC) and geochemistry element of the Harbin loess, and combined with wavelet analysis, studied the evolution and control mechanism of summer monsoon in the Songnen Plain since Middle Pleistocene. The results show that the evolution of summer monsoon in the Songnen Plain can be divided into two stages since the Middle Pleistocene:1) From 460 ka to 180 ka, the lower chemical weathering degree and TOC values of the Harbin loess indicate the weak intensity of summer monsoon. In addition, there were three sub-orders of the summer monsoon during this period, superimposed on the general trend of weak summer monsoon. 2) From 180 ka to now, the magnetic susceptibility, chemical weathering degree and TOC values of the Harbin loess-paleosol sequence show a gradually increasing trend, indicating that the intensity of East Asian summer monsoon is gradually enhanced. Through the comprehensive comparative analysis of the magnetic susceptibility and grain size of the Harbin loess, the Chifeng loess and Luochuan loess in the Chinese Loess Plateau, it shows that the Songnen Plain first responds to the climate change caused by the temperature rise and precipitation increase dominated by the interglacial summer monsoon, but the duration of this response is relatively short; The loess of Harbin recorded two significant climatic phenomena of summer monsoon weakening from 360 ka to 340 ka and 280 ka to 250 ka, which were the result of the comprehensive action of global climate and regional environmental change. The results of wavelet analysis show that the dominant period of wavelet transform of susceptibility of the Harbin loess-paleosol sequence is 98 ka (100 ka). Combined with the comprehensive comparative analysis of sea-level temperature, global CO2 concentration, 60°N solar radiation and marine isotope stages, it shows that the evolution of summer monsoon in the Songnen Plain is mainly driven by global ice volume. The occurrence of dip periods of 36 ka and 44 ka(40 ka) and the occurrence of the lowest oscillation period of 29 ka indicate that the dip driven variation of low latitude solar radiation has a weak regulation effect on the summer monsoon in Songnen Plain, while the precession driven variation of low latitude solar radiation has little effect on the summer monsoon in Songnen Plain.
Key words:East Asian summer monsoon/
Harbin loess/
Songnen Plain/
Geochemical composition/
Magnetic susceptibility
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