岗日嘎布玉东曲末次冰消期冰川演化及其^(10)Be暴露测年研究

Cosmogenic ^(10)Be constraints on the last deglacial glacier behaviors in the Yudongqu Valley,Gangrigabu Range,southeast Tibetan Plateau

末次冰盛期(Last Glacial Maximum,LGM)结束后,全球经历末次冰消期进入全新世,这代表了过去十万年以来最为显著的气候转型事件。末次冰消期的开始在全球范围内近乎同步,但其背后的气候驱动机制仍不明确。中低纬度,如青藏高原及其周边地区的山地冰川对气候变化响应敏感,准确限定LGM结束前后冰川地貌的时代可为上述问题的解决提供可靠的古冰川信息。然而,目前青藏高原仍缺乏足够有针对性的研究。本文选取位于青藏高原东南部的岗日嘎布作为研究区,对该区格泥峰东侧的玉东曲谷口分布的冰碛垄序列进行了详细的地貌调查和宇宙成因核素^(10)Be暴露测年研究。采自玉东曲谷口附近6道冰碛垄中地貌相对年代较老的4道冰碛垄的14个冰川漂砾^(10)Be暴露年龄介于(13.3±1.0)~(19.3±1.4)ka。利用累积概率密度和简化卡方等统计分析方法排除异常值后,将这4道冰碛垄中地貌相对年代较年轻两道的形成时代限定为(17.0±0.5)ka和(18.4±1.0)ka,分别对应末次冰消期和LGM后期。与气候记录进行对比后,我们认为这两次冰川波动响应可能受控于印度洋-太平洋暖池海表温度的夏季气温变化。

The Last Glacial Termination marks the transition from the global Last Glacial Maximum(LGM)to the interglacial Holocene.This transition is the most striking climate reorganization on Earth,over the past 100 ka.The global LGM termination has been widely regarded as nearly synchronous around the world,yet,proposed mechanisms behind this synchroneity remain contentious.Mountain glaciers in the mid-latitude regions,such as those in the Tibetan Plateau(TP),are highly sensitive to climate change,and hence can provide invaluable information for clarifying this conundrum.However,glacial chronologies as regards the LGM termination remain extremely limited in the TP and its surrounding mountains.This impedes a full understanding of potential climatic mechanisms forcing glacial fluctuations in the vast TP.In this study,we examined the lateral moraine remnants formed near the valley-mouth of the Yudongqu valley,Gangrigabu Range,southeast TP,using^(10)Be surface exposure dating.Apparent^(10)Be exposure-ages(n=14)obtained from four out of six lateral moraine relics there range from(13.3±1.0)ka to(19.3±1.4)ka.On the basis of statistical test,we identified six potential outliers with the aid of probability density function plots.We then examined whether the clustering of remaining^(10)Be exposure-ages were merely caused by measurements or not using the reduced chi-square test and P value.After excluding the potential outliers,the two geomorphologically younger moraines were robustly dated to(17.0±0.5)ka and(18.4±1.0)ka,representing two glacial culminations that correspond well to the LGM termination.We then compared the^(10)Be-based moraine chronologies with climatic proxies,such as Northern Hemisphere summer solar insolation,ice-volume equivalent sea level,stalagmiteδ^(18)O record,chironomidinferred mean July temperature record,sea surface temperature(SST),and atmospheric CO_(2) concentrations.We conclude that the two glacial events identified in the Yudongqu Valley were in response to changes in summer air temperature connected with SSTs in the Indo-Pacific Warm Pool(IPWP)