[1] Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY 10964 USA
[2] Aix Marseille Univ, CNRS IRD Coll France, UM 34, CEREGE, Aix En Provence, France
[3] Univ Bern, Inst Geol Sci, CH-3012 Bern, Switzerland
[4] Univ Maine, Dept Earth Sci, Orono, ME 04469 USA
[5] Univ Maine, Climate Change Inst, Orono, ME 04469 USA
[6] ETH, Inst Teilchenphys, Zurich, Switzerland
[7] Lawrence Livermore Natl Lab, Ctr Accelerator Mass Spectrometry, Livermore, CA 94550 USA
[8] Univ Calif Berkeley, Dept Earth & Planetary Sci, Berkeley, CA 94720 USA