A new Dating Method for Glacier ice Using Radiocarbon Analysis of Carbonaceous Particles

In the deepest parts, ice cores from high elevation glaciers are difficult or even impossible to date with conventional dating techniques due to strong layer thinning. Traditional radiocarbon applications by means of plant or insect fragments are of limited use since such material is rarely found in glacier ice. We are therefore developing a new method for radiocarbon dating, using the organic carbon fraction (OC) of carbonaceous particles contained in ice. Carbonaceous particles are produced by incomplete combustion of carbon containing material and are long-range transported even to very remote locations. For the time period before the industrial use of fossil fuels, OC is believed to originate from biogenic sources only and therefore radiocarbon dating with its 14C/12C ratio should be possible. Today, Accelerator Mass Spectrometry measurements of this ratio are possible with as little as 0.02 - 0.1 mg carbon (corresponding to 500 - 1000 g of ice) with expected uncertainties for future dating of 200 years. Additionally, the 14C/12C ratio of carbonaceous particles from younger layers gives a unique and absolute measure of the contemporary to fossil carbon source ratio. This can be used for source apportionment of biogenic and anthropogenic emissions during the industrial time period (from around 1870 to the present), and can give evidence for reconstruction of biomass burning events in the past. First analysis of ice from an Alpine glacier has been performed, indicating that the oldest ice is about 1500 years old, which is younger than predicted by 3D glacier flow modelling.