This research used samples and data provided by the Ocean Drilling Program (ODP). The ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. Funding for the MGT instrument was provided by NSF under grant number OCE-9531279. The Leg 191 postcruise work was supported by U.S. Science Support Panel/Texas A&M Research Foundation contract number F001327. Prof. Jeff Schweitzer at the University of Connecticut provided advice on detector design and calibration. We are grateful for access to the calibration facilities by Richard Brown at Schlumberger Well Services in Webster, Texas, Larry Gadeken and David Smith at Halliburton Energy Services in Houston, Texas, and Prof. Liang Shen at the University of Houston, Texas. We also thank the crew and scientific staff on board the JOIDES Resolution during Leg 191 for logistical support and operational assistance.