中低纬度MIS 3b(54～44 ka BP)冷期与冰川前进

MIS 3b (54～44 ka BP) Cold Period and Glacial Advance in Middle and Low Latitudes

MIS 3b冷期在古里雅冰芯记录表现为 5 4～ 44kaBP比现代温度低 5℃的冷期 ,与MIS 3c (早期 )和MIS 3a (晚期 )温度高出现代 3℃和 4℃情况迥然相反 ,而和以 2 3ka的岁差周期 (precessionalcycle)所导致的日射变化一致 ,在 6 5°N～ 6 0°S间有重大作用 .初步检阅现代有测年资料的末次冰期冰川前进文献 ,发现MIS 3b冷期导致的山地冰川前进分布在亚洲、欧洲、北美洲、南美洲、大洋洲 12个地区 2 3个地点 .当时降水较多与冷期降温抑制消融相结合 ,使冰川伸展范围都超过气候严寒而干燥的MIS 2期内通常所说 2 5～ 15kaBP末次冰盛期 (LGM)的冰川规模 .若干种新的测年方法包括改进的光释光 (OSL)法、红外释光 (IRSC)法、宇宙成因3 He、10 Be、2 6Al和3 6Cl测年、U系法、连同原应用的14 C法、热释光 (TL)法、ESR法和径迹法 (fissiontrackmethod)有助于末次冰期多次冰川前进时间的确定 ,但某些数据也存在不确定性 .虽然古里雅冰芯记录明确了MIS 3b冷期的重要性 ,但我国西部山区对该期冰川前进的定年研究还很少 ,亟应加强工作 。

The records of Guliya ice core showed that there was a MIS 3b cold period between 54～44 ka BP, when temperature was 5 ℃ below present average. In contrast to this, temperatures in the warm periods at MIS 3c (early) and MIS 3a (late) were 3 ℃ and 4 ℃ above present average, respectively. This has been proved to be consistent with the insolation changes caused by a precessional cycle of 23 ka and a significant global impact appeared between 65 N～60 S. From preliminary analysis of the literatures concerning well-dated glacier advances during the Last Glaciation, it has been found that MIS 3b cold period resulted in glacial advances at 23 sites of 12 regions in Asia, Europe, North America, South America and Ocean. In this paper the authors give a brief review to these sites. The plentiful precipitation during MIS 3b coupling with the suppressive effect of low temperature on ice ablation, glaciers advanced beyond the extent of the cold-dry MIS 2 between 25～15 ka BP (LGM). Several new dating methods, such as modified optically stimulated luminescence (OSL) method, infrared stimulated luminescence (IRSC) method, cosmogenic {} 3He, {} 10Be, {} 26Al and {} 36Cl dating method, Uranium series dating method, together with {} 14C method, TL method, ESR method and fission track method, effectively improve the dating of several glacial advances during the Last Glaciation. Despite the importance of the records of Guliya ice core in defining the MIS 3b cold period, few data was held on glacial advance during that time in West China, further study is essential.