西藏东南部末次冰期早阶段冰川作用及其古气候意义

西藏东南部的“古乡冰期”和“白玉冰期”是划分中国第四纪冰期的蓝本。其中，白玉冰期即末次冰期，分为早阶段和晚阶段，相对应的冰川沉积广泛分布于本区的波堆藏布谷地。已有的冰川数值年代结果显示，末次冰期晚阶段的冰川作用发生于海洋氧同位素阶段（MIS）2。然而，关于早阶段的冰进记录，目前却未有确切的年代学证据，此次冰川作用究竟发生于MIS 4还是MIS 3，是一个悬而未决的问题。在前人研究及野外地貌调查的基础上，运用光释光测年手段对波堆藏布谷地疑似形成于末次冰期早阶段的冰碛垄进行测年，年代结果介于（56.4±4.2）~（65.9±3.9） ka之间，相当于MIS 4。藏东南地区MIS 4冰期冰川作用年代与青藏高原及其周边山地具有可比性，表明该阶段冰川作用发生的普遍性。通过对比北半球低纬度地区夏季太阳辐射及亚洲季风区古气温与古降水指标记录，认为藏东南地区MIS 4冰期冰川作用可能是对北半球低纬度地区夏季太阳辐射减弱及气温下降的响应，与季风降水无关。

Glacial activity during early stage of Last Glaciation in southeastern Tibet and its paleoclimate implication

The “Guxiang Glaciation” and “Baiyu Glaciation”， originated from Bodui Zangbo Valley， southern slope of eastern Nyainqêntanglha Range in southeastern Tibet， are the representative periods of Quaternary glaciations in Tibetan Plateau. Among them， Baiyu Glaciation （Last Glaciation） can be divided into early and late stages， and their corresponding glacial sediments are widely distributed in Bodui Zangbo Valley. Numerical dating of glacial deposits has suggested that the glacier advance during the late stage occurred in marine oxygen isotope stage 2 （MIS 2）. However， the earlier glacial event has been lacking of effective chronology. Furthermore， whether this glaciation happened during MIS 4 or MIS 3 remains an open question. Based on previous researches and detailed field investigation， this study used optically stimulated luminescence （OSL） technique to date the moraines which have been suspected to construct during the early stage of Last Glaciation. The OSL ages range from （56.4±4.2） to （65.9±3.9） ka， corresponding to MIS 4. The ages could compare to other dated glacial advances in Tibetan Plateau and its surrounding mountains， suggesting this glacial event ever commonly occurred. Compared with summer insolation at 30° N and paleo-temperature and precipitation proxy records from regions dominated by India summer monsoon， it is likely that the reduced summer insolation at 30° N and decreased temperature caused the glacier expansion during MIS 4 in southeastern Tibet， not related to the summer monsoon and moisture.