METHODS

High-resolution sampling at Sites 1109 and 1115 successfully recovered IW from whole rounds taken from nearly every recovered sedimentary core in each hole. At Site 1118 where the first 200 mbsf was drilled without coring, a lower-resolution sampling program was undertaken with whole rounds collected every second or third core beginning near 250 mbsf. The suite of 26 IW samples obtained at Site 1118 complements the more than 130 IW samples collected from Sites 1109 and 1115.

Methods for recovery of IW and details of the sample handling and shipboard analyses are described in Taylor, Huchon, Klaus, et al. (1999) and are only briefly described here. IW was recovered by mechanical squeezing of 5- to 15-cm whole-round cores in a titanium squeezer, modified after the standard ODP stainless steel squeezer of Manheim and Sayles (1974), to provide contamination-free IW samples. Samples were initially collected from the squeezer through 0.45-µm Gelman polysulfone disposable filters into scrupulously cleaned 50-mL plastic syringes. IW to be used for trace element analysis was filtered through acid-washed 0.2-µm Gelman polysulfone disposable filters, transferred to acid-washed high-density polyethylene bottles, acidified with 50 µL of ultra-high purity HNO₃, and stored chilled until analysis. Samples for isotopic analyses were transferred from the syringe to glass vials without additional filtering and immediately sealed.

Dissolved Ba was determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) using a Leeman Labs model PS1 echelle grating spectrometer (e.g., De Carlo, 1992) or by mass spectrometry (ICP-MS) using a VG Plasma Quad II-S instrument. The ICP-OES was calibrated using a series of standards prepared by addition of single-element standards (Ba²⁺) to a NaCl matrix, as described by De Carlo and Kramer (2000). The ICP-MS was calibrated using a series of aqueous standards diluted from a NIST-traceable stock multielement standard. Instrument drift was monitored at masses 115, 147, and 209 using In, Sm, and Bi as internal standards.

Dissolved Rb⁺ was determined by atomic emission spectrometry (AES) using the method of standard addition on a Perkin Elmer Model 603 double-beam spectrometer. The atomic emission of Rb was measured at 780 nm using a 0.2-nm slit width. Because IW can show wide variations in matrix composition (e.g., salt concentrations), a background correction technique developed in our laboratory for analysis of geothermal and hydrothermal fluids was used (Fraley and De Carlo, unpubl. data). This method compensates for the large background absorption signals often encountered in high-salinity fluids (e.g., De Carlo and Kramer, 2000). A subgroup of IW samples was analyzed for Rb by AES and by ICP-MS to evaluate the comparability of results obtained by the two methods. The methods generally yielded comparable results, although the ICP-MS data seem biased toward lower values than the results obtained by AES.

The oxygen isotopic composition of the pore water samples was determined in the Isotope Biogeochemical Laboratory at the University of Hawaii using a microscale adaptation of Epstein and Mayeda's (1953) CO₂-H₂O equilibration method, described by Tüchsen et al. (1987). Aliquots of water (120 mg, measured gravimetrically) were equilibrated with 22 µmol of CO₂ (measured using a calibrated Baratron gauge) at 22°C for at least 48 hr. The oxygen isotopic composition of purified CO₂ was measured using a Finnigan MAT 252 isotope-ratio mass spectrometer. Oxygen isotopic data are expressed in per mil () deviation from the VSMOW (Vienna standard mean ocean water) standard:

¹⁸O = {[(¹⁸O/¹⁶O)_smpl/(¹⁸O/¹⁶O)_VSMOW] - 1} x 100.

The ¹⁸O values are normalized such that the ¹⁸O value of standard light Antarctic precipitation is -55.5. The 2- precision for replicate ¹⁸O analyses of samples and the VSMOW standard is ±0.2.

The isotopic composition of dissolved strontium in the pore water samples was determined at the University of Hawaii Radiogenic Isotope Laboratory. The method used for analyzing strontium isotopic samples in this laboratory was described by Mahoney et al. (1991). The following modifications were applied in the current study: aliquots of pore water samples (350 µL) were mixed with equal volumes of 2-N HCl and loaded onto a 0.6 cm x 20 cm column of AG50WX8 cation-exchange resin, strontium was eluted with 2-N HCl, each Sr sample (150 ng) was then loaded onto a tungsten filament with a Ta₂O₅ substrate, and strontium samples were analyzed in dynamic multicollector mode on a VG sector thermal-ionization mass spectrometer. During the course of analyzing the ODP Leg 180 Sr isotope samples, National Bureau of Standards Standard Reference Material (SRM) 987 was analyzed 11 times, with an average ⁸⁷Sr/⁸⁶Sr = 0.710253 and a total range of ±0.000022.

A subset of squeeze cakes from Site 1109 was selected for chemical and mineralogical analyses on the basis of the presence of volcanic matter in the sediments (Taylor, Huchon, Klaus, et al., 1999). The clay fraction was separated from the selected squeeze cakes by a combination of wet sieving and gravimetric methods as follows: samples were weighed after freeze drying and divided into a fine (<63 µm) and a coarse (>63 µm) fraction by wet sieving. Subsequent grain-size separation into a silt (2-63 µm) and a clay (<2 µm) fraction was performed by settling of particles in standing cylinders according to Stokes' law (Moore and Reynolds, 1989).

The clay mineralogy was determined by X-ray diffractometry (XRD), using a Philips model PW 1710 X-ray diffractometer equipped with monochromatic CuK radiation. Oriented samples were produced by vacuum filtration through a 0.15-µm filter. Measurements were carried out on air-dried and glycol-saturated samples. Randomly oriented powder preparations were produced (measurement made over 60-75°2) to identify di- or trioctahedral clay minerals from hkl = 060 reflections.

The clays were dissolved using a CEM model MDS100 microwave digestion system. Approximately 100 mg of each sample was placed in a Teflon reaction vessel, to which were added 500 µL of 18 W-cm distilled deionized water, 6 mL of concentrated HF, and 4 mL of a 3:1 mixture of concentrated HNO₃:HCl. Samples were sealed, placed in the microwave oven, and digested until no visible residue remained. The vessels were allowed to cool, vented, and the solution evaporated to near dryness. The final paste was redissolved in 0.3-M HNO₃, diluted to ~100 g, and weighed to the nearest milligram. Quality control samples included approximately one blank and one SRM (NRC-Canada marine estuarine sediment: MESS-1) for every 10 samples and were carried through all procedures. Trace element concentrations in the digested clay samples were determined by ICP-MS after calibration with a series of multielement standards prepared from serial dilution of a NIST-traceable stock standard. Accuracy of our analyses was verified by comparison of our results for digestions of MESS-1 with other published values (e.g., Garbe-Schönberg, 1993).