Novel Dating of Alpine Glaciers by 39Ar-ATTA (ArTTA-ICE)

阿尔卑斯山顶峰冰川保存了有关过去气候条件的宝贵信息，因为它们的内层结构可以表明它们对气候波动的反应，如冰川增长、间歇或质量损失时期。这些信息尚未恢复，但由于当地极端气候的持续变暖，冰川档案面临着直接的压力。特别是，目前还不清楚过去1000年来的气候波动，如所谓的“小冰期”，对冰盖的山顶地区造成了多大程度的影响。了解冰川内部的年龄分布是破译冰川过去堆积史的关键。因为在这些地点不可能进行年度地层计数，年龄信息必须来自放射性测年。在100-1000年的年龄范围内，只有惰性气体放射性同位素39Ar的半衰期为269年，可以作为水和冰的放射性测年工具。然而，~(39)Ar的丰度极低，1公斤现代冰中仅含有约10.000个~(39)Ar原子。最近在原子捕获痕量分析(ArTTA)测量~(39)Ar方面的重大技术进步，通过将所需的样本量从吨减少到几公斤，为实现冰川冰的~(39)Ar测年铺平了道路。该项目旨在开发、验证并最终应用ArTTA测年方法来恢复未开发的气候记录。奥地利科学院和海德堡大学正在进行的研究活动为拟议的研究创造了一个独特的机会。启动合作先导研究已经成功地证明了39Ar冰川测年的可行性。拟议的活动包括全面的方法开发，即不仅仅是论证可行性，而是对潜力和局限性进行系统分析。~(39)Ar测年的验证利用了已有年龄信息的冰川遗址和额外的放射性测年，例如14C。然后，应用~(39)Ar测年方法恢复了阿尔卑斯山顶峰冰川内部年龄结构所包含的独特气候记录。从今天冰川的质量和能量平衡中转移，可以推断出与过去积累变化相对应的气候波动。基础设施和现有的知识密度使欧洲阿尔卑斯山的顶峰冰川成为这一目的的独特目标。最终，该项目将在古气候研究中引入39Ar的冰川测年，从而有望通过将14C应用于冰川冰而取得类似的进展。因此，该项目还将有助于揭示过去气候变化对高山冰川的影响，这有助于证实对未来冰川消退的预测，并与社会对气候变化的反应直接相关。

Alpine summit glaciers preserve valuable information on past climate conditions, because their internal layer architecture can indicate their response to climate fluctuations as periods of glacier growth, hiatus or mass loss. This information has not yet been recovered, but the glacier archive is under immediate pressure by ongoing warming conditions with local climate extremes. In particular, at present it is not clear to what extent climate fluctuations over the last 1000 years, such as the so-called "Little Ice Age", have affected ice-covered summit regions. Knowledge of the internal age distribution is key to decipher the past accumulation history of the glacier. Because annual layer counting is not possible at these sites, age information has to come from radiometric dating. In the age range of 100-1000 years, only the noble gas radioisotope 39Ar has a suitable half-life of 269 years to serve as a radiometric dating tool for water and ice. However, the abundance of 39Ar is extremely low, with only about 10.000 39Ar atoms contained in 1 kg of modern ice. Recent major technical advances in measuring 39Ar by Atom Trap Trace Analysis (ArTTA) have paved the way to make 39Ar dating of glacier ice feasible by reducing the required sample size from tons to a few kilograms. This project aims at developing, validating and ultimately applying the ArTTA dating method to retrieve untapped climate records. A unique opportunity for the proposed research is generated by ongoing research activities at the Austrian Academy of Sciences and Heidelberg University. Starting a collaborative pilot study has already successfully demonstrated the feasibility of 39Ar glacier ice dating. The proposed activities comprise full method development, i.e. to go beyond mere demonstration of the feasibility to a systematic analysis of the potential and limitations. The validation of the 39Ar dating makes use of glacier sites with already existing age information and additional radiometric dating, e.g. 14C. Then, the 39Ar dating is applied exemplarily to recover the unique climate record comprised in the internal age architecture of Alpine summit glaciers. The transfer from today's mass and energy balance of the glaciers allows to infer climate fluctuations corresponding to the past accumulation change. The infrastructure and the already existing density of knowledge make summit glaciers in the European Alps a unique target for this purpose. Ultimately, the project will introduce glacier ice dating by 39Ar in paleo-climate research, thereby promising similar advances as through the application of 14C to glacier ice. Accordingly, this project will also help to reveal the impact of past climate changes on alpine glaciers, which is useful to substantiate projections of future glacier retreat and immediately relevant for the societal response to climate change.