Shipboard interstitial water analyses for Leg 188 were performed on 5- to 20-cm whole-round sediment sections, which were cut and capped immediately after the core arrived on deck. Before squeezing, the outside surface of each whole-round section was carefully removed with a spatula to minimize potential contamination. Whole rounds were placed into a titanium and stainless steel squeezing device and squeezed at ambient temperature by applying pressure up to 40,000 lb (~4150 psi) with a hydraulic press (Manheim and Sayles, 1974). Interstitial water was extruded through a prewashed Whatman no. 1 filter fitted above a titanium screen. All interstitial water samples were filtered through 0.45-mm Gelman polysulfone disposable filters and collected into clean plastic syringes. After collection of up to 30 mL of interstitial water, the syringe was removed, a fresh 0.45-mm Gelman filter was attached, and aliquots were dispensed into plastic vials for shipboard analyses and into acid-washed plastic vials and 5-mL glass ampoules (heat sealed) for future shore-based work.
Interstitial water analyses followed the procedures outlined by Gieskes et al. (1991). Interstitial water samples were routinely analyzed for salinity with a Goldberg optical hand-held refractometer (Reichart), yielding a unitless approximate value for the concentration of dissolved solids. Alkalinity was measured by Gran titration with a Brinkmann pH electrode and a Metrohm autotitrator, and pH was measured on the National Institute of Standards scale as part of the alkalinity titration. It should be noted that pH measurements obtained in this fashion are not always reliable, given that the algorithm employed for pH measurement before the start of the alkalinity titration is adversely influenced by degassing. Dissolved chloride (Cl-) was determined by titration with AgNO3. Dissolved silica (H4SiO4), ammonium (NH4+), and phosphate (PO43-) concentrations were determined by spectrophotometric methods with a Milton Roy Spectronic 301 spectrophotometer (Gieskes et al., 1991). International Association for the Physical Sciences of the Ocean standard seawater was used for calibrating most techniques. The reproducibility of these analyses, determined by repeated measurements of standards, are alkalinity, <1.5%; Cl-, <0.3%; H4SiO4, <3%; PO43- and NH4+, ~3%. Calcium (Ca2+), magnesium (Mg2+), potassium (K+), and sulfate (SO42-) were measured to within 3%-5% on 1/200 diluted aliquots in nanopure water using a Dionex DX-120 ion chromatograph.
Lithium (Li+), manganese (Mn2+), and strontium (Sr2+) were quantified by inductively coupled plasma-atomic emission spectrometry (ICP-AES) with a Jobin-Yvon JY2000. Tenfold dilutions of the interstitial water sample were used for all of the elemental analyses by ICP-AES. Standards for all ICP-AES techniques were matrix matched as closely as possible to samples using filtered surface seawater that had been spiked with the appropriate concentrations of specific elements and serially diluted according to the method outlined by Murray et al. (in press). Both accuracy and precision are generally better than 1%-2% for these elements. All of the chemical data are reported in molar concentration units.