[1] Univ Miami, Rosenstiel Sch Marine & Atmospher Sci, Miami, FL 33149 USA
[2] Univ Colorado, NOAA, Paleoclimatol Program, Boulder, CO 80309 USA
[3] Univ Colorado, Inst Arctic & Alpine Res, Boulder, CO 80309 USA
[4] Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY 10964 USA
[5] Univ Calif Lawrence Livermore Natl Lab, Ctr Accelerator Mass Spectrometry, Livermore, CA 94551 USA