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Interstitial water samples were taken on board the JOIDES Resolution following procedures given in the "Methods" chapter. Samples were treated immediately after collection by adding 100 μL of a saturated cadmium acetate solution per 5 mL of sample to precipitate all H2S and inhibit further activity of sulfate-reducing microorganisms. The precipitated CdS was separated using a centrifuge, and the supernatant was filtered through a 0.45 μm membrane filter and acidified with HCl. The sulfate was precipitated as BaSO4 by adding BaCl2 within 1 h of acidification. Samples were centrifuged, washed with hot water, and dried overnight at 60°C.
For 34S measurements, the sulfate samples were weighed in Sn cups together with vanadium pentoxide as catalyst and measured on a Thermo Finnigan Mat 253 stable isotope mass spectrometer in continuous flow mode using the Conflo III open split interface and an Eurovector 3000 elemental analyzer. SO2 reference gas was injected through the dual inlet system. The system was calibrated by using International Atomic Energy Agency (IAEA)-SO-5 (0.49‰ Vienna Canyon Diablo Triolite [VCDT]) and National Bureau of Standards (NBS)-127 (21.1‰ VCDT) international standards. Analytical reproducibility as determined by a BaSO4 in-house standard (8.2‰ VCDT) is ±0.17‰. Analytical reproducibility as determined by IAEA-SO-5 is ±0.08‰. Data are reported in conventional delta notation with respect to VCDT.
For 18OSO4 measurements, ~135 μg BaSO4 was added to Ag cups and pyrolyzed at 1350°C on a Hekatech HT-EA using He as a carrier gas. The produced CO gas was routed through an Ascarite trap, separated on a Molsieve 5A column, and subsequently measured on a Thermo Finnigan Mat 253 mass spectrometer in continuous flow mode using the Conflo III open split interface. The CO reference gas was injected via the Conflo III interface. The system was calibrated by using U.S. Geological Survey (USGS) 32 (25.7‰ Vienna standard mean ocean water [VSMOW]), NBS-127 (8.6‰ VSMOW), and IAEA-SO-6 (–11.34‰ VSMOW) international standards. Analytical reproducibility of the measurements was determined by running several replicates of NBS-127. We report the 1 value as ±0.12‰. The data are reported in conventional delta notation with respect to VSMOW.