1. Department of Earth Sciences, University of Aarhus, DK-8000 Aarhus, C.F. Moellers Allé 1120, Denmark.
2. Heidelberger Akademie der Wissenschaften, Institut fur Umweltphysik, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany.
3. Institute of Botany, Hohenheim University, D-70593 Stuttgart, Germany.
4. Accelerator Mass Spectrometry 14C Dating Centre, Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark.