1. Norwegian University of Life Sciences; Department of Plant and Environmental Sciences; P.O. Box 5003; NO-1432; Ås; Norway
2. Oregon State University; Department of Geosciences; Corvallis; OR; 97330; USA
3. Seattle University; College of Science and Engineering; Seattle; WA; 98122; USA
4. Department of Earth Science; University of Bergen; NO-5007; Bergen; Norway
5. Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse (CSNSM); F-91405; Campus Orsay; France
6. University of Oslo; Department of Geosciences; NO-0316; Oslo; Norway