Radiocarbon Determination of Particulate Organic Carbon in Non-Temperated, Alpine Glacier Ice

Abstract

ABSTRACT. Dating ice samples from glaciers via radiocarbon is a challenge that requires systematic investigations. This work describes an approach for extraction and accelerator mass spectrometry (AMS) 14 C analysis of the particulate organic carbon (POC) fraction in glacier ice samples. Measurements were performed at VERA (Vienna Environmental Research Accelerator) on ice samples obtained mainly from the non-temperated ablation zone of the Grenzgletscher (Grenz Glacier) system (Monte Rosa Massif, Swiss Alps). The samples were obtained from 2 sampling sites situated roughly on a common flow line. The sample masses used were between 0.3 and 1.4 kg of ice, yielding between 18 and 307 µg of carbon as POC. The carbon contamination introduced during sample processing varied between 5.4 and 33 µg C and originated mainly from the quartz filters and the rinsing liquids used in processing. Minimum sample sizes for successful graphitization of CO 2 in our laboratory could be reduced to <10 µg carbon, with a background in the graphitization process of ~0.5 µg of 40-pMC carbon. Evaluation of the whole procedure via 11 Grenzgletscher samples revealed a surprisingly large scatter of pMC values. We obtain a mean calibrated age of 2100 BC to AD 900 (95.4% confidence level), which is not significantly different for the 2 sampling sites. Discussions of these results suggest that single 14 C dates of glacial POC are presently of limited significance. Future improvements with respect to analytical precision and sample characterization are proposed in order to fully explore the POC dating potential.

Towards radiocarbon dating of ice cores

“…Contamination with either modern or fossil carbon, in principle possible at each step of sample processing, will influence the final results, especially considering the low carbon concentrations expected in ice-core samples (Slater and others, 2002;Steier and others, 2006). Therefore, a low and reproducible procedural blank is required to minimize uncertainties of the obtained radiocarbon ages (Jenk and others, 2007).…”

“…The latter can be quantified, and a blank estimation for correction is presented here. Finally, 14 C/ 12 C ratios from the separated EC fractions are compared with those of OC, to evaluate the potential to use total carbon (TC = OC + EC) for dating as proposed by Steier and others (2006). The aim of this paper is to give a critical evaluation of the potential of this new dating method.…”

A Gas Ion Source for Radiocarbon Measurements at 200 kV

“…The graphitization is time consuming and samples <50 µg require great efforts for preparation and measurement. Losses during the graphitization and increased blank values are described (Weissenbök et al 2000;Steier et al 2006;Jenk et al 2007), so that for small samples, direct CO 2 measurements seem to be an alternative solution. At the beginning, indeed, the results were very encouraging Hedges 1987, 1990;Middleton et al 1989).…”

“…for biomedical applications, which often make it necessary to perform many 14 C analyses of small chromatographic fractions, prone to fail in routine graphitization procedures (Hughey et al 2000). Furthermore, the apportionment of fossil and non-fossil carbon of airborne aerosols using 14 C is becoming increasingly important in atmospheric sciences Steier et al 2006;Szidat et al 2006). For this application, typically <50 µg carbon is available per sample and graphitization yields are frequently reduced by interfering reaction gases.…”

Radiocarbon dating of glacier ice: overview, optimisation, validation and potential

“…Therefore, and because of the reasons summarised next, WIOC was selected from the different carbonaceous particle fractions as the most promising target for 14 C dating. First, WIOC is mainly of biogenic origin in pre-industrial times (Jenk et al, 2006) and, therefore, supposed to contain a contemporary 14 C signal representative of the age of the ice (Jenk et al, 2006;Steier et al, 2006). Second, the average WIOC concentration in ice is higher than the respective EC concentration, allowing for smaller ice samples and a potentially higher time resolution, which consequently provides a better signal-to-noise ratio (mainly determined by the overall blank) and smaller uncertainty of the dating results.…”