Stable water isotope record from block profiles in the ice tunnel at Chli Titlis glacier, Switzerland

Cold glaciers at the highest locations of the European Alps have been investigated by drilling ice cores to retrieve their stratigraphic climate records. Findings like the Oetztal ice man have demonstrated that small ice bodies at summit locations of comparatively lower altitudes may also contain old ice if locally frozen to the underlying bedrock. In this case, constraining the maximum age of their lowermost ice part may help to identify past periods with minimum ice extent in the Alps. However, with recent warming and consequent glacier mass loss, these sites may not preserve their unique climate information for much longer. Designed as a case study for investigating the maximum age of cold-based summit glaciers in the Alps, we utilized here an existing ice cave at Chli Titlis (3030 m), Central Switzerland. The cave offers direct access to the glacier stratigraphy without the logistical effort required in ice core drilling. In addition, a pionieering exploration had already demonstrated stagnant cold ice conditions at Chli Titlis, albeit more than 25 years ago. Our englacial temperature measurements and the analysis of the isotopic and physical properties of ice blocks sampled at three locations within the ice cave show that cold ice still exists fairly unchanged today. State-of-the-art micro-radiocarbon analysis constrains the maximum age of the ice at Chli Titlis to about 5000 years before present. By this means, the approach presented here will contribute to a future systematic investigation of cold-based summit glaciers, also in the Eastern Alps.

针对欧洲阿尔卑斯山脉最高处的寒冷冰川，科研人员通过钻取冰芯（ice core）以获取其地层气候记录。诸如厄茨塔尔冰人（Oetztal Ice Man）这类发现已证实，即便海拔相对较低的峰顶小型冰体，若与下伏基岩呈冻结状态，也可能留存古老冰层。在此背景下，明确其最底部冰层的最大形成年代，或有助于识别阿尔卑斯地区冰川规模最小的过往时期。然而，受近期气候变暖及由此引发的冰川质量亏损影响，这些点位或许无法再长久保存其独特的气候信息。本研究以探究阿尔卑斯冷基峰顶冰川（cold-based summit glacier）的最大形成年代为案例，利用了瑞士中部小铁力士山（Chli Titlis，海拔3030米）处一处现存冰洞。该冰洞可直接接触冰川地层结构，无需钻取冰芯所需的后勤保障投入。此外，早在25年前的一次开创性勘探便已证实，小铁力士山冰川存在停滞的冷基冰体。我们通过冰内温度测量，以及对冰洞内三处点位采集的冰块开展同位素与物理特性分析，结果显示当前该处冷冰状态仍基本未发生改变。借助当前最先进的微尺度放射性碳分析（micro-radiocarbon analysis）技术，我们将小铁力士山冰川冰层的最大形成年代限定在约距今5000年。通过本研究提出的研究方法，未来有望系统性开展冷基峰顶冰川的相关调查，包括东阿尔卑斯地区的此类冰川。