青藏高原东缘极高山地(贡嘎山和四姑娘山)第四纪冰川年代学与冰期环境重建研究

Gongga Mountains and Siguniang Mountains cover a portion of the eastern margin of the Tibetan Plateau, and are climatically located in a transitional region between the East Asia monsoon and the Indian monsoon. The glacier type in the two regions is the typical monsoonal temperate glacier, which is sensitive to the changing climate. These glaciers experienced large advances and retreats during the glacial-interglacial cycles of the Quaternary, and the glacial landforms, especially the deposited landforms from multiple glaciations, are well-preserved in the valley. In this project, we will study the glacial landform in this area, by undertaking geomorphological and sedimentological analysis combined with the numerical dating (e.g. OSL, 10Be and ESR). Having identify the timing of the multiple glaciations, we will compare the timing and the style of glaciations between different regions, then enables us to reconstruct the paleo-ELAs by various methods and intergraded the results. Based on the works above, we will estimate palaeoclimatic conditions of the former extent of glaciations using glacier-climate models, by inference, a better understanding of the relationship between glacier fluctuations and the climate forcing. Given the two regions having experienced the intensive new tectonic uplift, this study associate with the records of Quaternary glaciation, sedimentary stratum, terrace and fault on its bordering mountains, will potentially infer the development model and initiation timing of alpine glaciers, as well as their relationship with the history of uplift on the eastern margin of the Tibet Plateau.

青藏高原东缘的极高山地—贡嘎山和四姑娘山处于两大亚洲季风系统的交汇区，发育有对气候变化响应十分敏感的季风海洋型冰川，且保存有诸多轮廓层次清楚、序列齐全的冰川遗迹。本项目拟在详细地貌地层学和冰川沉积学工作的基础上，建立起其全面可靠的第四纪冰川演化的相对时空序列；运用OSL、10Be并辅以ESR对其进行系统的年代学研究，获知其进入冰冻圈的时代及可能对某些特殊气候时段的响应；再基于各次冰川作用的范围，综合运用多种方法计算出古ELA，并据此重建区域的古气候特征，为探讨两种季风系统交汇区古冰川发育与气候间关系提供更多的重要依据，也为区域古气候变化(尤其是高海拔地区)研究提供一个新的也更为可靠的代用指标。此外，该区新构造抬升强烈，结合周边山地的第四纪冰川、沉积地层、阶地与断层等的研究，还对解读高原东缘极高山地第四纪冰川的发育模式、启动时间及其与第四纪新构造隆升间的关系具有十分重要的理论意义。

青藏高原不仅受西风和季风两大气候系统的双重影响，还是中、低纬度最大的山地冰川作用区，因而其第四纪以来古冰川演化规律及其气候驱动一直备受关注。目前，高原上众多山地冰期–间冰期尺度上第四纪冰川演化序列的数值年表已被建立起来，而随着亚轨道尺度上古气候变化取得了更系统和深入的认识，使该尺度下高原古冰川如何响应气候变化成为当下第四纪冰川领域的研究热点。在此背景下，本项目以青藏高原东缘两座极高山地（贡嘎山和四姑娘山）的第四纪冰川沉积序列为研究对象，构建起了其演化的精准年代学框架，并基于古冰川作用的时代和范围利用冰川能量–流动模型模拟了冰川作用区的古气候状况，探讨了其冰川演化的气候驱动机制。首先确认高原东缘极高山地第四纪以来至少经历了MIS6、MIS3中期、Heinrich(H)3、H2、H1、全新世早期、新冰期以及小冰期等8次较大规模的冰进。截止目前，该成果是高原东部山地古冰川演化最为完善的绝对年代序列，可直至小冰期，因而可成为高原东部季风区山地冰川演化的标尺；此外，这一序列也表明高原东缘的古冰川不仅记录到了冰期–间冰期尺度的气候变化信息，也能灵敏地响应亚轨道尺度气候波动的影响。针对末次冰期以来数次冰进的模拟结果，则显示全球末次冰盛期(LGMG)、H1、新冰期和小冰期冰进主要受控于气温的降低，MIS3中期与全新世早期冰进则为较丰富降水和低温共同驱动；该结果也进一步表明高原东缘古冰川演化无论在冰期–间冰期尺度上，还是亚轨道尺度上都主要受气温控制，而亚轨道尺度上南亚季风波动引起的降水变化在一定程度上也可能会影响到冰川演化。该成果是从机理上解读和理解亚轨道尺度上冰川变化的气候驱动因素，对后续相关研究具有重要的借鉴意义，也为区域古气候变化研究(尤其高海拔区)提供了一种新的也更为可靠的代用指标。