Abstract
ABSTRACTAlpine glaciers are valuable archives for the reconstruction of human impact on the environment. Besides dating purposes, measurement of radiocarbon (14C) content provides a powerful tool for long-term source apportionment studies on the carbonaceous aerosols incorporated in ice cores. In this work, we present an extraction system for14C analyses of dissolved organic carbon (DOC) in ice cores. The setup can process ice samples of up to 350 g mass and offers ultra-clean working conditions for all extraction steps. A photo-oxidation method is applied by means of external UV irradiation of the sample. For an irradiation time of 30 min with catalyzation by addition of Fe2+and H2O2, we achieve an efficiency of 96 ± 6% on average. Inert gas working conditions and stringent decontamination procedures enable a low overall blank of 1.9 ± 1.6 μg C with a F14C value of 0.68 ± 0.13. This makes it possible to analyze the DOC in ice samples with a carbon content of as low as 25 μg C kg−1ice. For a first validation, the new method was applied to ice core samples from the Swiss Alps. The average DOC concentration and F14C values for the Fiescherhorn ice core samples show good agreement with previously reported data for the investigated period of 1925–1936 AD.
Highlights
For meaningful interpretation of the recorded signals in ice cores from glacier archives, accurate dating is essential
We present an extraction system for 14C analyses of dissolved organic carbon (DOC) in ice cores
For ice cores from high-alpine glaciers 14C-dating is valuable for the ice in the bottom part, where strong thinning of annual layers prevents the use of annual layer counting or the assignment of reference horizons for dating (Thompson et al 1998; Schwikowski et al 1999a)
Summary
For meaningful interpretation of the recorded signals in ice cores from glacier archives, accurate dating is essential. The DOC extraction setup is decontaminated by running a procedure to remove potential sources of carbon contamination: After flushing the vacuum line with helium and zeroing the nondispersive infrared CO2 detector (NDIR, LI-820A, LI-COR, USA, modified to allow in-line operation by improved connection seals), the glass setup is pressurized with helium slightly above atmospheric pressure (1.04 bar) to create the inert gas atmosphere. For determination of the oxidation efficiency, multiple standard solutions covering a range of concentrations were prepared from different organic substances using UPW for dissolution which had previously been cleaned from DOC and IC in our photo-reactor as described earlier. Based on these values and assuming constant contamination, mCOX and F14COX can be estimated by applying isotopic mass balance calculations (Hwang and Druffel 2005). Our method still performs excellently in terms of low carbon background if compared to other setups, with our values being at the low end (Table 1)
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