Establishment and exploration of a gas ion source for micro-scale radiocarbon dating of glaciers and groundwater
Final Report Abstract
Alpine mountain glaciers as well as groundwater aquifers are valuable climate archives, but their reliable dating is challenging. In glacier ice older than a few hundred years, radiocarbon analyses of the particulate organic carbon (POC) fraction are the only option, but the POC concentrations in ice are exceedingly small. Similarly, the promising dissolved organic carbon (DOC) fraction in groundwater is small and a desirable further selection of specific compounds would reduce the available amount of carbon even more. The main objective of this project was therefore to establish a gas ion source system at the MICADAS AMS in Mannheim, to facilitate reliable and reproducible 14C measurements of sample sizes down to 5 µgC or even less. In addition, methods for the contamination-free preparation of such small amounts of carbon needed to be developed. In the course of this project, the gas ion source was successfully implemented and characterized. Moreover, a completely new system (REFILOX) for the preparation of small amounts of POC from ice samples was developed, tested, and applied. The system achieved a reduction of the process blank (contamination) by a factor of ten compared to previously used methods. These analytical innovations enabled systematic investigations of the POC fraction in alpine ice for the purpose of 14C dating, including an assessment of disturbing effects such as Sahara dust present in the samples. It was found that low combustion temperatures of about 340 °C during the sample preparation in the REFILOX system gave the best results with respect to the separation of the actual POC sample from reservoir effects. Successful applications of the new methods for ice dating were carried out on samples from the Titlis glacier, yielding basal ages of about 5000 years BP, as well as for an ice core from the Colle Gnifetti. The age profile from this core reveals a gradual increase of age followed by a sudden jump at about 80 % of the total depth, to approach a basal age of about 4000 years. These results are of fundamental importance for further glaciological and palaeoclimatic interpretations. First applications of the gas ion source in combination with a DOC extraction line for DOC-14C groundwater dating were successfully performed. With these innovations, the bulk DOC fraction in groundwater is now easily accessible for 14C dating even from small water samples. The DOC was found to be less affected by reservoir effects than the usually analysed DIC fraction, but further investigation of specific compounds is needed to obtain unbiased groundwater ages.
Publications
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(2018) A New Sample Preparation System for Micro- 14 C Dating of Glacier Ice with a First Application to a High Alpine Ice Core from Colle Gnifetti (Switzerland). Radiocarbon 60 (2) 517–533
Hoffmann, H., Preunkert, S., Legrand, M., Leinfelder, D., Bohleber, P., Friedrich, R. and
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(2018) Temperature and mineral dust variability recorded in two low-accumulation Alpine ice cores over the last millennium. Clim. Past (Climate of the Past) 14 (1) 21–37
Bohleber, P., Erhardt, T., Spaulding, N., Hoffmann, H., Fischer, H. and Mayewski, P.,
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2014. Micro radiocarbon dating applications in Alpine glaciology. 18th Alpine Glaciology Meeting, Innsbruck, Austria
Hoffmann, H.
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2014. Setup and first applications of a gas ion source for micro radiocarbon dating at the MICADAS-AMS system in Mannheim, Germany. AMS 13, Aix-en-provence, France. PRE 20
Hoffmann, H., Kromer, B., Wagenbach, D. and Fahrni, S.
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2015. Micro Radiocarbon Dating - Applications and challenges in Alpine glaciology. EGU General Assembly, Vienna, Austria. EGU2015-9119
Hoffmann, H., Bohleber, P. and Wagenbach, D.
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2016. Micro radiocarbon dating of the particulate organic carbon fraction of Alpine glacier ice: method refinement, critical evaluation and dating applications. Dissertation, Heidelberg University, 184 pp
Hoffmann, H. M.
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2016. Micro Radiocarbon dating – Applications and challenges in Alpine glaciology. International Partnerships in Ice Core Sciences (IPICS), Hobart, Australia. T10-42
Hoffmann, H., Bohleber, P. and Wagenbach, D.
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2017. Nextgeneration ice core technology reveals true minimum natural levels of lead (Pb) in the atmosphere: Insights from the Black Death. GeoHealth 1, 211–219
More, A. F., Spaulding, N. E, Bohleber, P., Handley, M., J., Hoffmann, H., Korotkikh, E. V., Kurbatov, A., V., Loveluck, C., P., Sneed, S., B., McCormick, M. and Majewski, P.
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2017. Status report: Implementation of gas measurements at the MAMS 14C AMS facility in Mannheim, Germany. Nuclear Instruments and Methods in Physics B 410, 184-187
Hoffmann, H., Friedrich, R., Kromer, B. and Fahrni, S.
