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doi:10.2204/iodp.proc.314315316.220.2012

Analytical methods

A 20–50 cm long whole-round core was sectioned soon after core recovery and scraped in a nitrogen-filled glove bag to avoid surface sediments that could have been contaminated with seawater, drilling fluid, oxidation, and/or smearing in the borehole. The core section was then squeezed with a shipboard hydraulic press to extract interstitial fluid through 0.45 µm filters. A sample aliquot was diluted with 5% tetramethyl ammonium hydroxide (TMAH) solution for the determination of total dissolved iodine concentration and measured by inductively coupled plasma–mass spectrometer (ICP-MS), HP4500 (Hewlett Packard/Agilent), at the University of Tokyo, with a standard deviation better than 2.7%. All concentrations are listed in Table T1 together with depth.

For the measurement of ¹²⁹I/I ratio, silver iodide (AgI) was precipitated from the interstitial fluid samples by extracting iodine reduced from iodate with sodium bisulfite into chloroform (Fehn et al., 1992; Lu et al., 2010). Because >0.1 mg of AgI is required for reliable ¹²⁹I/I analyses (Lu et al., 2007), we combined 3–7 neighboring samples from Sites C0001 and C0002. These targets were analyzed for ¹²⁹I/I ratios at PRIME Lab, Purdue University (Sharma et al., 2000). The weighted average depth and iodine concentration of ¹²⁹I/I samples are calculated from iodine concentrations and volume of sample aliquots combined for AgI precipitation (Table T2). Error margins for depth in the ¹²⁹I/I profile therefore reflect the interval between the shallowest and deepest aliquots.

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