This research used samples and/or data 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. The authors wish to express their thanks to the ODP Leg 202 Shipboard Scientific Party. Two anonymous referees are also acknowledged for their valuable comments and suggestions. Research grants REN 2003-08642-CO2/CLI (MEC) and Junta de Castilla y León (SA088/04) supported this study. W. Wei acknowledges receipt of samples from ODP and research funds from the U.S. Science Support Program (USSSP).