SAMPLES AND METHODS

We received a total of ~260 pore water samples of 5–10 mL each sealed in glass containers from all sites drilled during Leg 204. Pore water was extracted from whole-round cores of 10–25 cm length, usually sampled soon after core recovery. These sediment cores were skinned off to remove potential seawater contamination during drilling and were squeezed with Manheim-type squeezers following the ODP sampling protocol for the extaction of pore water (Tréhu, Bohrmann, Rack, Torres, et al., 2003). Dissolved chloride concentration was measured by triplicate titration with silver nitrate (AgNO₃) on board ship with precisions better than 0.4%; the values were corrected for the presence of the other halogens assuming seawater ratios (Torres et al., 2004). Total iodine and bromine concentrations were measured by inductively coupled plasma–mass spectrometry, using the Thermal X7 instrument at the University of Rochester (New York, USA). We followed established methods (Muramatsu and Wedepohl, 1998), except for replacing nitric acid with a tertiary amine solution (Spectrasol CFA-C), which was added to the solution matrix to prevent precipitation in the tubing. A washout time of 2 min was found to be sufficient to allow the signal to return to background levels. Accuracies for concentration values of iodine and bromine are better than 1% and are not reported individually.

A major goal of this investigation is the determination of ¹²⁹I/I ratios in the pore water samples. So far, ¹²⁹I/I ratios have been measured on a subset of 41 samples selected from all 9 sites. Iodine was extracted and precipitated as AgI at the Rochester Cosmogenic Isotope Laboratory (New York, USA), using methods outlined in Fehn et al. (1992). The relatively high iodine concentrations in the samples allowed preparation of AMS targets from individual pore water samples. The actual AMS determinations were carried out at PrimeLab, Purdue University (Indiana, USA), again following established routines (Sharma et al., 2000). Individual accuracies of the AMS determinations (1) are listed together with the ratios. The actual accuracy of a determination reflects the stability of the AMS system as well as the amount of sample material provided. About 1 mg of AgI is sought for an actual AMS determination, but ratios have been determined with amounts as low as 0.1 mg of AgI, although with diminished accuracy.