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The Cryosphere An interactive open-access journal of the European Geosciences Union
The Cryosphere, 10, 3091-3105, 2016
https://doi.org/10.5194/tc-10-3091-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Review article
21 Dec 2016
Radiocarbon dating of glacier ice: overview, optimisation, validation and potential
Chiara Uglietti1,2,3, Alexander Zapf1,2,3,†, Theo Manuel Jenk1,3, Michael Sigl1,3, Sönke Szidat2,3, Gary Salazar2,3, and Margit Schwikowski1,2,3 1Laboratory of Environmental Chemistry, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
2Department of Chemistry and Biochemistry, University of Bern, 3012 Bern, Switzerland
3Oeschger Centre for Climate Change Research, University of Bern, 3012 Bern, Switzerland
deceased
Abstract. High-altitude glaciers and ice caps from midlatitudes and tropical regions contain valuable signals of past climatic and environmental conditions as well as human activities, but for a meaningful interpretation this information needs to be placed in a precise chronological context. For dating the upper part of ice cores from such sites, several relatively precise methods exist, but they fail in the older and deeper parts, where plastic deformation of the ice results in strong annual layer thinning and a non-linear age–depth relationship. If sufficient organic matter such as plant, wood or insect fragments were found, radiocarbon (14C) analysis would have thus been the only option for a direct and absolute dating of deeper ice core sections. However such fragments are rarely found and, even then, they would not be very likely to occur at the desired depth and resolution. About 10 years ago, a new, complementary dating tool was therefore introduced by our group. It is based on extracting the µg-amounts of the water-insoluble organic carbon (WIOC) fraction of carbonaceous aerosols embedded in the ice matrix for subsequent 14C dating. Since then this new approach has been improved considerably by reducing the measurement time and improving the overall precision. Samples with ∼ 10 µg WIOC mass can now be dated with reasonable uncertainty of around 10–20 % (variable depending on sample age). This requires about 300 to 800 g of ice for WIOC concentrations typically found in midlatitude and low-latitude glacier ice. Dating polar ice with satisfactory age precision is still not possible since WIOC concentrations are around 1 order of magnitude lower. The accuracy of the WIOC 14C method was validated by applying it to independently dated ice. With this method, the deepest parts of the ice cores from Colle Gnifetti and the Mt Ortles glacier in the European Alps, Illimani glacier in the Bolivian Andes, Tsambagarav ice cap in the Mongolian Altai, and Belukha glacier in the Siberian Altai have been dated. In all cases a strong annual layer thinning towards the bedrock was observed and the oldest ages obtained were in the range of 10 000 years. WIOC 14C dating was not only crucial for interpretation of the embedded environmental and climatic histories, but additionally gave a better insight into glacier flow dynamics close to the bedrock and past glacier coverage. For this the availability of multiple dating points in the deepest parts was essential, which is the strength of the presented WIOC 14C dating method, allowing determination of absolute ages from principally every piece of ice.

Citation: Uglietti, C., Zapf, A., Jenk, T. M., Sigl, M., Szidat, S., Salazar, G., and Schwikowski, M.: Radiocarbon dating of glacier ice: overview, optimisation, validation and potential, The Cryosphere, 10, 3091-3105, https://doi.org/10.5194/tc-10-3091-2016, 2016.
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Short summary
A meaningful interpretation of the climatic history contained in ice cores requires a precise chronology. For dating the older and deeper part of the glaciers, radiocarbon analysis can be used when organic matter such as plant or insect fragments are found in the ice. Since this happens rarely, a complementary dating tool, based on radiocarbon dating of the insoluble fraction of carbonaceous aerosols entrapped in the ice, allows for ice dating between 200 and more than 10 000 years.
A meaningful interpretation of the climatic history contained in ice cores requires a precise...
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