We thank Tracy Frank, Cheryl Kelley, and Woody Wise for comments on the manuscript and Jim Ogg, Paul Sikora, and Paul Wilson for helpful discussions. Samples were provided by the Ocean Drilling Program (ODP). ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. Funding for this study was provided by the U.S. Science Support Program.