藏南卡鲁雄峰枪勇冰川新冰期冰川发育探讨

山地冰川对气候变化响应敏感，全新世以来，冰川呈加速退缩趋势。冰川地貌是冰川变化最直接的证据。枪勇冰川发源于卡鲁雄峰，位于喜马拉雅山中段北坡雨影区，雅鲁藏布江以南，冰川末端在海拔5000 m附近，冰川面积约为6.63 km2。枪勇沟从外至内共保存有4期冰碛垄，其中以"大枪勇错"外侧的新冰期冰碛垄最为高大，终碛垄高约30 m，且形态清晰。文章基于野外观察及谷歌影像（Google Earth）上冰碛垄的分布范围，恢复并计算了新冰期时枪勇冰川面积约为10.0 km2，较现代冰川扩张了1.5倍。采用VOLTA模型计算了现代冰川的体积为0.21±0.04 km3，平均厚度约为31.7 m。基于纵剖线模型模拟了新冰期冰川表面高程，新冰期冰川平均厚度约为58.5 m，冰川体积约0.59±0.12 km3，是现代冰川体积的2.8倍，体积减小较面积退缩更为剧烈。利用积累区面积比率法（Accumulation Area Ratio Method，简称AAR），采用AAR值为0.7±0.05，基于现代冰川表面高程和模拟的新冰期冰川表面高程，计算现代冰川和新冰期冰川的物质平衡线高度（Equilibrium Line Altitude，简称ELA）分别为5780±70 m和5660±100 m，新冰期时平衡线高度降低了约120 m。而不利用模型恢复新冰期表面高程时，平衡线降低值为240 m，可能高估约120 m。新冰期时，枪勇冰川扩张受区域降温控制，冰川前进可能是对4.2 ka冷事件的响应。冰碛垄形成时代和大枪勇错孢粉数据表明，冰川可能在2.5 ka左右已经退缩，2.2 ka时退缩加剧。

Reconstruction of the Neoglacial glacier in the Qiangyong valley,Mt. Kaluxung,South Tibet

Mountain glaciers are sensitive to climate change. Glaciers have retreated significantly since the Holocene. Landforms left behind by glaciers are direct evidences of glacier changes. The Qiangyong Glacier originates from Mt. Kaluxung (28.8°N, 90.3°E; 6674 m a.s.l.) at the northern side of the central Himalayas, which is a rain shadow region on the southern side of the Yarlung Tsangpo River. The present glacier terminates around 5000 m above sea level with an area of 6.63 km2. Four moraine sets are well-preserved in the Qiangyong valley, especially the outer moraine at the end of the bigger Qiangyong Co, which has been dated to the Neoglacial by cosmogenic 10 Be dating. The Neoglacial end moraine is about 30 m above the lake, with a sharp crest. We reconstructed the extent of the Neoglacial glacier based on the field investigation and Google Earth imagery of this outer moraine. Glacier area during the Neoglacial was about 10.0 km2, about 1.5 times of modern glacier area. Based on the simulated results of the VOLTA model, the volume of the modern glacier is about 0.21±0.04 km3 and the mean ice thickness is roughly 31.7 m. We simulated ice surface elevations during the Neoglacial based on the Longitudinal Flowline Model. The ice thickness during the Neoglacial was about 58.5 m, and the ice volume was roughly 0.59±0.12 km3, which was 2.8 times of the Modern glacier volume. The glacier volume changed more severely than the glacier area. Using the Accumulation Area Ratio Method(AAR, 0.7±0.05)and the reconstructed ice surface elevations, the Equilibrium Line Altitudes(ELA)of the Modern glacier and the Neoglacial are 5780±70 m and 5660±100 m, respectively. The ELA during Neoglacial dropped about 120 m compared to Modern ELA. Without the simulation of the ice surface elevations, the ELA during Neoglacial was derived to drop about 240 m, indicating about 120 m overestimated. Glacier expansion was driven by regional cooling during the Neoglacial, especially the cooling event at 4.2 ka. The timing of moraine formation and pollen analysis in the bigger Qiangyong Co indicated the glacier may already began to retreat at about 2.5 ka, then accelerated since about 2.2 ka.