1. Department of Environmental Systems Science; ETH Zürich; Universitätstrasse 2 8092 Zürich Switzerland
2. Department of Environmental Sciences - Botany; University of Basel; Schönbeinstrasse 6 4056 Basel Switzerland
3. Department of Geological Sciences; Indiana University; Bloomington IN 47405-1405 USA
4. Stable Isotope Biogeochemistry Laboratory; Science Laboratories; Durham University; South Road Durham DH1 3LE UK
5. Climate and Environmental Physics; Physics Institute and Oeschger Centre for Climate Change Research; University of Bern; Sidlerstrasse 5 3012 Bern Switzerland
6. Department of Medical Biochemistry and Biophysics; Umeå University; 901 87 Umeå Sweden