Shipboard interstitial water analyses were performed on 5- to 10-cm-long whole-round sections cut immediately after core retrieval on deck. At each site, samples were gathered at a frequency of one per core for the upper 100 mbsf and from every third core thereafter to the bottom of the hole. Additionally, samples were gathered at three sites (1075, 1080, and 1082) for high-resolution studies at a frequency of one per section of core for the uppermost ~60 mbsf. Please refer to the individual site chapters (this volume) for details of the respective sampling plans.
Interstitial waters were collected using the trace metal noncontaminating titanium squeezer, which is modified from the standard ODP stainless-steel squeezer of Manheim and Sayles (1974). When whole-round samples were gathered more quickly than they could be squeezed, the samples were capped at each end, taped, and stored in a refrigerator for several hours. After extrusion from the core liner in the chemistry laboratory, the surface of each whole-round sample was carefully scraped with a spatula to remove potential contamination from drilling and coring processes. After loading the squeezer, pore waters were extruded by applying as much as 40,000 lbs (~4150 psi) of pressure using a hydraulic press. Interstitial water samples were collected into plastic syringes and filtered through 0.45-µm Gelman polysulfone disposable filters and stored in plastic vials before analysis. Aliquots for postcruise shore-based analyses by the shipboard scientists and others were retained in heat-sealed, acid-washed plastic tubes and glass vials.
Interstitial water samples were routinely analyzed for salinity as total dissolved solids with a Goldberg optical hand-held refractometer (Reichart); pH and alkalinity by Gran titration with a Brinkmann pH electrode and a Metrohm autotitrator; and dissolved silicate, phosphate, and ammonium by spectrophotometric methods with a Milton Roy Spectronic 301 spectrophotometer (Gieskes et al., 1991). The International Association of Physical Sciences Organizations' standard seawater was used for calibrating most techniques and for determining 1σ standard deviations. These standard deviations have been previously determined to be alkalinity, <1.5%; Cl-, 0.4%; Ca2+, <1%; Mg2+, 0.5%; and H4SiO4 and NH4+, ~5% (Gieskes et al., 1991). In addition, K+, Mg2+, Ca2+, and SO42- were analyzed by ion chromatography using a Dionex DX-100 instrument. The 1σ standard deviations have been determined to be K+, <3%; Mg2+ and Ca2+, <3%; SO42-, <4%; and Na+, <5% (Gieskes et al., 1991).
The presence of elevated levels of hydrogen sulfide (H2S) in some samples would interfere with the spectrophotometric analysis of PO43- and dissolved H4SiO4 because of the use of reducing agents during the analytical protocols. To account for this interference, several modifications of the standard Gieskes et al.'s (1991) analytical methodology were tested. At Site 1075, to oxidize the H2S, a 1.5-mL aliquot of those samples with H2S detectable by nose (all samples from Cores 175-1075A-3H through 6H) was treated with 80 µL of concentrated H2O2 (30%) and heated for 20 min at 50°C to drive off any unreacted H2O2. Judging from the improved smoothness of the chemical profiles, this procedure was acceptable. However, commencing with Site 1079, an aliquot of all samples (including those without H2S detectable by nose) was routinely acidified with HCl before the H4SiO4 and PO43- analyses, with 1 mL of the sample being acidified with 0.1 mL of 1N HCl and allowed to sit for up to 12 hr. Standards were treated the same as the samples. The acidified sample was used directly in the H4SiO4 analysis protocol outlined by Gieskes et al. (1991). For the PO43- analysis, 0.2 mL of the acidified sample was diluted with 1.8 mL of Nanopure water and 2 mL of the mixed reagent of Gieskes et al. (1991) for the spectrophotometric analysis.
Strontium concentrations were quantified using flame atomic absorption (AA) spectrometry (Varian SpectrAA-20). Strontium was analyzed on 1/10 diluted samples using a nitrous oxide acetylene flame. Standards for all flame AA techniques were matched in matrix composition to the samples. A more detailed description of all methods and standards used can be found in ODP Technical Note 15 (Gieskes et al., 1991).