SAMPLING AND METHODS

We asked the Shipboard Scientific Party of ODP Leg 184 to take 35 interstitial water samples and 29 headspace gas samples from Site 1146 for our shore-based laboratory. More than 400 sediment samples were also collected from Site 1146.

We analyzed 24 interstitial water samples from Hole 1146A, with a frequency of one per 10 m between 0 and 75 mbsf and one per 29 m between 75 and 506 mbsf. We also measured 11 samples from Hole 1146C, with a frequency of one per 19 m between 406 and 598 mbsf. Interstitial water was extracted with a titanium squeezer from whole-round sections 5-10 cm long, which were cut immediately after core retrieval on deck. Water samples were placed into plastic syringes and filtered through 0.45-µm Gelman polysulfone disposable filters and then stored in heat-sealed acid-washed glass vials for shore-based analyses (Wang et al., 2000). The concentrations of sodium (Na⁺), calcium (Ca²⁺), lithium (Li⁺), chloride (Cl^-), and sulfate (SO₄^2-) were measured postcruise for all interstitial water samples, and isotopic compositions of oxygen and hydrogen were measured on 18 samples. The concentrations of Na⁺ and Ca²⁺ were measured by inductively coupled plasma-atomic emission spectrometry, with an analytical precision of 3%, and Li⁺ concentrations were measured by inductively coupled plasma-mass spectrometry, with an analytical precision of 3%. The Cl^- concentration was measured by volumetric methods, and SO₄^2- concentration was measured by turbidimetry. Isotopic compositions of hydrogen and oxygen were determined by the standard CO₂ equilibrium method, using a Finnegan MAT-251 mass spectrometer with an analytical precision of 2 for hydrogen and 0.2 for oxygen.We also analyzed 13 headspace samples collected from Hole 1146A, with a frequency of one per 19 m between 342.6 and 592.1 mbsf and 16 samples collected from Hole 1146C, with a frequency of one per 19 m between 406.5 and 482.8 mbsf and one per 9.6 m between 482.8 and 598.3 mbsf. As soon as cores arrived on deck, a sediment sample of 5 cm³ was collected using a borer tool, the sample was placed in a 21.5-cm³ glass serum vial, and the vial was sealed on deck (Wang et al., 2000). After the samples arrived in the shore-based laboratory, the headspace gas was extracted following the standard headspace sampling method. The compositions of methane (C₁), ethane (C₂), propane (C₃), isobutene (i-C₄), n-butane (n-C₄), isopentane (i-C₅), and n-pentane (n-C₅) were analyzed for all samples using a SQ-203 gas chromatograph, and the carbon isotopic composition of methane was measured for nine samples with a Finnegan MAT-251 mass spectrometer. The mineralogical compositions of two authigenic carbonate concretions from sediments were identified by X-ray diffraction (XRD). The oxygen and carbon isotopic compositions of siderite were measured using a MAT-251-EM mass spectrometer. Samples were treated at 50°C with 100% phosphoric acid for 4 days. The isotopic compositions are expressed in the conventional notation relative to the Peedee belemnite (PDB) reference. The analytical precision is 0.2 for both ¹⁸O and ¹³C values.