Abstract. A novel technique making use of laser ablation coupled online to accelerator mass spectrometry (LA-AMS) allows analyzing the radiocarbon (¹⁴C) concentration in carbonate samples continuously at high spatial resolution within very short analysis times. This new technique can provide radiocarbon data similar to the spatial resolution of stable carbon (C) isotope measurements by isotope-ratio mass spectrometry (IRMS) and, thus, can help to interpret δ¹³C signatures, which otherwise are difficult to understand due to numerous processes contributing to changes in C-isotope changes ratios. In this work we analyzed δ¹³C and ¹⁴C on the Holocene stalagmite SPA 127 from the high-alpine Spannagel Cave (Austria). Combined stable carbon and radiocarbon profiles allow to identify three growth periods characterized by different δ¹³C signatures: (i) the period > 8 ka BP is characterized by relatively low δ¹³C values with small variability combined with a comparably high radiocarbon reservoir effect (expressed as dead carbon fraction, dcf) of around 60 %. This points towards C contributions of host rock dissolution and/or from an old organic matter (OM) reservoir in the karst potentially mobilized due to the warm climatic conditions of the early Holocene. (ii) Between 3.8–8 ka BP a strong variability in δ¹³C reaching values from −8 to +1 ‰ with a generally lower dcf was observed. The δ¹³C variability is most likely caused by changes in gas exchange processes in the cave, which are induced by reduced drip rates as derived from reduced stalagmite growth rates. Additionally, the lower dcf indicates that the OM reservoir is contributing less to stalagmite growth in this period possibly as a result of reduced precipitation or because it is exhausted. (iii) In the youngest section between 2.4–3.8 ka BP, comparably stable and low δ¹³C values combined with an increasing dcf reaching up to 50 % are again hinting towards a contribution of an aged OM reservoir in the karst.

中文翻译：

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由高碳洞穴中的放射性碳和稳定碳同位素推断出的全新世气候变化

摘要。利用在线耦合到加速器质谱（LA-AMS）的激光烧蚀的新技术可以在很短的分析时间内以高空间分辨率连续分析碳酸盐样品中的放射性碳（¹⁴ C）浓度。这种新技术可以提供类似于稳定的碳的空间分辨率（C）同位素测量由同位素比率质谱仪（IRMS），并因此可以帮助解释δ放射性碳数据^13个Ç签名，否则是困难的，由于理解导致C同位素变化比率变化的众多过程。在这项工作中，我们分析δ ¹³ C和¹⁴C来自高高山Spannagel洞穴（奥地利）的全新世石笋SPA 127。组合稳定的碳和放射性碳型材允许识别特征在于不同的δ三个增长周期¹³ Ç签名：（i）所述周期> 8 KA BP的特征在于相对低的δ ¹³ C值的小的变化与比较高的放射性碳贮存效果的组合（表示为约60％的死碳分数（dcf）。这表明由于早期全新世的温暖气候条件，潜在地动员了岩溶中的宿主岩溶解和/或来自旧有机质（OM）储层的C贡献。（ⅱ）之间KA 3.8-8 BP强烈变异δ ¹³ Ç达到-8〜1‰值具有通常较低的DCF进行了观察。δ¹³ C的变化很可能是由洞穴中气体交换过程的变化引起的，这是由于石笋生长速率降低而导致的滴落速率降低所致。此外，较低的dcf表示在此期间OM储层对石笋生长的贡献较小，这可能是由于降水减少或耗尽了。（ⅲ）在2.4-3.8 KA BP之间最小的部分，相当稳定的低δ ¹³ C值与DCF达到高达50％的增加的组合再次暗示朝向喀斯特老化OM储存器的贡献。