1. Paleoecological Environmental Assessment and Research Laboratory (PEARL); Department of Biology; Queen's University; Biosciences Complex Kingston ON K7L 3N6 Canada
2. Center for Accelerator Mass Spectrometry; Lawrence Livermore National Lab; Livermore CA 94551 USA
3. Geological Survey of Canada (Atlantic); Natural Resources Canada; Bedford Institute of Oceanography; Dartmouth NS B2Y 4A2 Canada
4. Department of Earth and Atmospheric Sciences; University of Nebraska-Lincoln; Lincoln NE 68588 USA