Micro radiocarbon dating of the particulate organic carbon fraction in Alpine glacier ice: method refinement, critical evaluation and dating applications
Micro radiocarbon dating of the particulate organic carbon fraction in Alpine glacier ice: method refinement, critical evaluation and dating applications
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DOI：
10.11588/heidok.00020712
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发表时间：
2016
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影响因子：
--
通讯作者：
H. Hoffmann
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文献类型：
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作者：
H. Hoffmann
这项工作主要是对阿尔卑斯冰川冰的颗粒有机碳分数(POC)进行放射性碳测年。之所以选择这个有机碳部分，是因为最初首选的溶解有机碳部分(DOC)被发现由于在阿尔卑斯山较高的位置加入原位生成的14C而产生偏差。高阿尔卑斯山冰中的POC浓度通常很低，平均在每公斤冰10至50微克之间。因此，对阿尔卑斯山冰芯进行POC 14C测年成为一个巨大的挑战，因为在阿尔卑斯山冰芯中，可供测年的质量不超过几百克冰。在这项工作中，部署了一种独特的样品制备系统(REFILOX)，该系统具有可重复使用的过程空白，总碳质量为(1.5+/-1.0)微克，甚至低于340°C下燃烧的检测下限。该系统还设置了气体离子源，用于直接测量二氧化碳AMS(加速器质谱仪)14C。总而言之，这些新颖的样品制备系统可以对低至2微米的样品进行可靠的测年，对于长达15 000年BP的年龄，相对误差不超过10%。为了全面的年龄解释，研究了POC年龄偏差效应，如输入古老的撒哈拉沙尘或沉积物物质。撒哈拉尘埃的年龄范围一直是2200-2800年BP，而沉积物样品显示的年龄范围长达20 000多年BP。POC燃烧温度调查表明，通过在不高于340°C的温度下燃烧可以最好地避免包含老化材料的此类偏差。首次将该方法应用于来自铁力斯冰川(瑞士阿尔卑斯山，3020 ma.s.l)的冰块样品。产生了一个一致的基本冰期，几乎是公元前5000年。此外，从高阿尔卑斯山冰架Colle Gnifetti(瑞士阿尔卑斯山，4500米)钻取的冰芯中采集了16个样本。已经进行了POC微型放射性碳年代测定，并揭示了到目前为止还没有完全解释的系统性年龄偏移，其年龄比基于年度地层计数的工作年表所建议的更年轻。
This work focuses on radiocarbon dating of the Particulate Organic Carbon fraction (POC) of Alpine glacier ice. This organic carbon fraction was chosen, because the initially preferred Dissolved Organic Carbon fraction (DOC) was found to be biased by incorporation of in situ produced 14C at high Alpine sites. Concentrations of POC in high Alpine ice are generally very low, ranging on average between 10 and 50 µgC per kg ice. Thus, POC 14C dating of Alpine ice cores, where available masses for dating are not exceeding a few hundred grams of ice, becomes a large challenge. Within this work, a unique sample preparation system (REFILOX), with a process blank reproducibly at a total carbon mass of (1.5 +/- 1.0) µgC or even below detection limit for combustion at 340 °C, has been deployed. This system was complemented by the setup of a gas ion source for direct CO2 AMS (Accelerator Mass Spectrometry) 14C measurements. Together, these novel sample preparation systems allow reliable dating of samples down to 2 µgC with a relative error not exceeding 10% for ages up to 15 000 years BP. For comprehensive age interpretation,POC age biasing effects such as input of old Saharan dust or sediment material have been investigated. The Saharan dust consistently featured an age range of 2200-2800 years BP and the sediment samples showed ages up to more than 20 000 years BP. POC combustion temperature investigations revealed that such biases by incorporated aged material can be avoided best by combustion at a temperature not higher than 340 °C. A first application of the method to ice block samples from Titlis glacier (Swiss Alps, 3020 m a.s.l.) yielded a consistent basal ice age of almost 5000 years BP. Additionally, 16 samples from an ice core drilled at the high Alpine glacier saddle Colle Gnifetti (Swiss Alps, 4500 m a.s.l.) have been POC micro-radiocarbon dated and revealed a so far not fully explained systematic age offset to younger ages than proposed by the annual layer counting based working chronology.