Abstract
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.
Highlights
High-altitude glaciers and ice caps from midlatitudes and tropical regions contain valuable signals of past climate and atmospheric variability at regional and local scales and are located in areas with large biological diversity and inhabited by the majority of the world’s population
The results for the Mt Ortles ice core were not included because larch leaf and water-insoluble organic carbon (WIOC) samples were extracted from depths with significantly different ages
Since the introduction about 10 years ago of the 14C dating technique for glacier ice, in which the WIOC fraction of carbonaceous aerosol particles embedded in the ice matrix was used, major improvements in separating the Organic carbon (OC) from the Elemental carbon (EC) fraction and in accelerator mass spectrometry (AMS) technology have been achieved
Summary
High-altitude glaciers and ice caps from midlatitudes and tropical regions contain valuable signals of past climate and atmospheric variability at regional and local scales and are located in areas with large biological diversity and inhabited by the majority of the world’s population. Uglietti et al.: Radiocarbon dating of glacier ice: overview, optimisation, validation and potential pogenic pollution sources, thereby preserving the signature of human activities This information can generally be retrieved from glacier ice cores, but needs to be placed in a precise chronological context to allow meaningful interpretation with respect to environmental and climatic changes. Determined by the 210Pb half-life of 22.3 years and its atmospheric concentration, the time period accessible for dating is in the order of a century (Gäggeler et al, 1983; Eichler et al, 2000; Herren et al, 2013) All these dating techniques fail in the older and deeper parts of glaciers, where plastic deformation of the ice under the weight of the overlying mass results in horizontal ice flow, stretching annual layers continuously with increasing depth. ALC, RH, 3H, 14C, 2p model ALC, RH, 3H, 210Pb, 14C, 2p model 14C of organic-rich layers and WIOC ALC, RH, 3H, 210Pb, 14C, 2p model ALC, RH, 3H, 210Pb, 14C, MC ALC, 14C
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
