Establishment and exploration of a gas ion source for micro-scale radiocarbon dating of glaciers and groundwater

加速器质谱仪（AMS） 14C分析中CO2气体离子源操作的最新进展为年代研究开辟了广泛的新应用，例如环境和考古应用。该提案旨在在曼海姆Curt-Engelhorn-Zentrum f<s:2> r Archäometrie （CEZA）的Klaus-Tschira实验室的AMS系统MICADAS上实现气体离子源，并将这种新能力用于环境研究的前沿应用，即冰川冰中含有的少量有机碳和地下水中特定有机化合物的年代测定。寒冷的冰川保存着关于过去气候和大气成分的独特记录。此外，中纬度冰芯可以重建最近的冰化学变化，但不能用地层方法确定年代。对于这样的冰体，目前只有基于冰基质中有机质的14C分析的放射性测年法才能提供全新世晚期及以后的合理测年潜力。这种方法的挑战在于这种物质的可用性非常有限，但是通过气体离子源分析冰中有机碳的微克样本的能力现在应该能够可靠地确定冰的14C年代。地下水是世界范围内的重要水资源，特别是在半干旱地区，此外还构成了有用的气候档案。用溶解无机碳（DIC）中的14C测定地下水的年代是标准的，但由于碳酸盐地球化学的复杂，存在问题。基于溶解有机碳（DOC）的地下水测年尝试取得了不同程度的成功，但现在新的分析发展使得对各种DOC成分进行化合物特定的14C分析成为可能，从而有机会确定适合测年的化合物。该项目基于合作科学家在14C分析和应用以及冰川冰和地下水作为档案的使用方面的丰富经验，包括这些系统的14C测年方法的开发和应用。它将在CEZA的MICADAS AMS上通过常规基地的气体离子源建立14c测量，以分析5至40微克C范围内的二氧化碳样品，精度低至0.5%。通过改进现有的冰川冰样样品制备技术，可以获得小冰样（约100 g）中颗粒和溶解有机组分的可靠的14C值。这种能力将应用于确定冷的、沉积的冰川以及小尺度的、冷的高山凝结冰体的年龄。该项目将进一步开发和测试所需的工具，通过地下水的有机成分对地下水进行微尺度、特定化合物的放射性碳测年。为此目的，将对上莱茵地堑地区的地下水样本进行分析，那里有广泛的同位素数据，包括DIC - 14C值，可供比较。

Recent progress in the operation of CO2 gas ion sources for accelerator mass spectrometer (AMS) 14C analysis on microgram-size samples opens a wide range of new applications in dating studies, e.g. for environmental and archeological applications. This proposal aims at implementing a gas ion source at the AMS system MICADAS at the Klaus-Tschira Laboratory of the Curt-Engelhorn-Zentrum für Archäometrie (CEZA) in Mannheim and to use this new capability for cutting-edge applications in environmental studies, namely the dating of small amounts of organic carbon contained in glacier ice and of specific organic compounds in ground water. Cold glaciers hold unique records on past climate and atmospheric composition. Mid-latitude ice cores furthermore enable reconstructions of recent ice chemistry changes, but cannot be dated by stratigraphic methods. For such ice bodies, only radiometric dating based on 14C analysis of organic matter contained in the ice matrix presently offers a reasonable dating potential in the late Holocene and beyond. The challenge of this approach lies in the very restricted availability of this matter, but the ability to analyse microgram samples of organic carbon from ice via a gas ion source should now enable reliable 14C dating of ice. Ground water constitutes an important water resource worldwide, especially in semi-arid regions, and in addition constitutes a useful climate archive. Dating of ground water by 14C in the dissolved inorganic carbon (DIC) is standard but problematic due to the complex carbonate geochemistry. Dating of ground water based on dissolved organic carbon (DOC) has been attempted with mixed success, but now the new analytical developments enable compound-specific 14C analyses of the various DOC components, offering the chance to identify compounds suitable for dating. This project is based on the extensive experience of the collaborating scientists in 14C analytics and applications as well as in the use of glacier ice and ground water as archives, including the development and application of 14C dating methods for these systems. It will establish 14C-measurements at the MICADAS AMS of the CEZA via a gas ion source on a routine base to analyse CO2-samples in the range of 5 to 40 microgram C at a precision down to 0,5 %. By improving existing sample preparation techniques for glacier ice samples, reliable 14C values of the particulate and dissolved organic fractions from small (some 100 g) ice samples shall be obtained. This capability will be applied to constrain ages of cold, sedimentary glaciers as well as of small scale, cold Alpine congelation ice bodies. The project will further develop and test the tools required for micro-scale, compound-specific radiocarbon dating of ground water via its organic fraction. For this purpose, ground water samples from the Upper Rhine Graben area will be analysed, where extensive isotopic data, including DIC 14C values, are available for comparison.