SAMPLES AND METHODS

Samples of obvious carbonate nodules or layers in cores were collected at the sampling table on the JOIDES Resolution during Leg 188. After the cruise, the nodules were sectioned perpendicular to bedding and about one-fourth of each nodule was powdered for X-ray diffraction and carbon and oxygen isotope analysis. Semiquantitative determination of mineralogy by X-ray diffraction analysis was performed at the U.S. Geological Survey in Lakewood, Colorado. Samples were analyzed for stable carbon and oxygen isotopic compositions at Mountain Mass Spectrometry in Evergreen, Colorado. The samples were reacted with phosphoric acid containing excess P₂O₅ at 90°C in an automated preparation system, and the resulting was CO₂ gas was analyzed on a VG Isogas Sira Series II mass spectrometer.

Interstitial water was extracted from sediments by squeezing and was analyzed for the usual pore water ionic constituents by standard procedures aboard the JOIDES Resolution (Geiskes et al., 1991; O'Brien, Cooper, Richter, et al., 2001). Methane in cores was measured by the headspace method (Pimmel and Claypool, 2001) and converted to an estimated dissolved methane concentration (O'Brien, Cooper, Richter, et al., 2001). After Leg 188, pore water samples were analyzed for ³⁴S of dissolved sulfate at the U.S. Geological Survey, Lakewood, Colorado. Barium sulfate was precipitated from acidified pore water with excess barium chloride and then was decomposed to sulfur dioxide for measurement of ³⁴S in an online sample preparation-stable isotope ratio mass spectrometer. Pore water samples were also analyzed in shore-based laboratories for various properties, including carbon isotopic composition of dissolved inorganic carbon, at Boston and Harvard Universities.