| Radiocarbon analyses along the Berkner core in Antarctica
R.S.W. van de Wal1, R. Mulvaney2, H.A.J. Meijer3, M. de Rooij3, C. van der Veen1
1:Institute for Marine and Atmospheric research Utrecht, Utrecht University, The Netherlands
2:British Antarctic Survey, Madingley Road, CB3 0Et, UK.
3:Center for Isotope Research, University of Groningen, The Netherlands
Samples, 21 in total from the Berkner core spanning 35 kyrs, are analyzed for 14CO and 14CO2 with a dry extraction technique in combination with accelerator mass spectrometry. In situ produced 14CO is 19±9 at/g, which is within the uncertainties equal to measurements for the EDML and Dome C cores and slightly above background levels. Despite these low levels of 14CO a significant in situ 14CO2 concentration is deduced from a comparison of the measured 14C ages with glaciological estimates of the air age of the core. Calculating the in situ 14CO2/14CO ratio shows values ranging from -1 to 2 prohibiting a simple correction for in situ production. In addition we noted that a previously developed model for in situ correction of 14CO2, based on degassing of 14CO2 from the matrix, as developed for the EDML core does not provide correct ages for the Berkner core. Without a correction for in situ production 14C ages are in agreement with glaciological estimates for the first 15 Kyr BP for older samples the 14C measurements underestimate the ages for unknown reasons, which are probably not related to in situ production during the formation of the ice. |