Shipboard interstitial water (IW) analyses for Leg 189 were conducted on 5- to 15-cm-long whole-round sediment sections cut and capped immediately after the core arrived on deck. The general sampling frequency utilized the following scheme: three samples per core in the upper ~60-70 mbsf, followed by one per core from 60 to 100 mbsf, then one every third core to total depth. Before squeezing, the outer rind of each whole-round sediment section was carefully scraped with a stainless steel spatula to remove potential contamination.
Interstitial waters were extracted by placing the whole-round samples in a titanium and stainless steel squeezing device that is a modified version of the standard stainless steel squeezer of Manheim and Sayles (1974). Squeezing was performed at ambient temperature by applying as much as 40,000 lb of pressure (~4150 psi) with a Carver laboratory hydraulic press (Model 2702). Interstitial water was extruded first through a prewashed Whatman No. 1 filter and then through a 0.45-µm Gelman polysulfone disposable filter into a precleaned plastic syringe. After collecting up to 30 mL of interstitial water, the syringe was removed to dispense aliquots for shipboard and shore-based analyses.
Interstitial water analyses followed the procedures outlined by Gieskes et al. (1991). Salinity as total dissolved solids was routinely measured with a Goldberg optical handheld Reichart refractometer. Alkalinity was measured immediately after squeezing by Gran titration with a Brinkmann pH electrode and a Metrohm autotitrator; pH was determined on the National Bureau of Standards scale as part of the alkalinity titration. Dissolved chloride (Cl-) was determined by titration with AgNO3. Dissolved silica (H4SiO40) and ammonium (NH4+) concentrations were measured using a Milton Roy Spectronic 301 spectrophotometer. Standard seawater from the International Association for the Physical Sciences of the Ocean was used for calibrating most techniques.
Calcium, magnesium, potassium, and sulfate were determined on 1/200 diluted aliquots in nanopure water using a Dionex DX-120 ion chromatograph. Lithium and strontium concentrations were quantified by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) with a Jobin Yvon JY2000. Tenfold dilutions of the interstitial water were used for all ICP elemental studies. Standards for all ICP-AES techniques were initially matrix matched as closely as possible to samples using filtered surface seawater spiked with the appropriate concentrations of specific elements and serially diluted according to the method outlined by Murray et al. (2000). However, we noticed that the Ba2+ spike to the standard solutions resulted in precipitation of barite (BaSO4), leading to poor Ba reproducibility. In addition, during subsequent tests with SO42--free synthetic seawater solutions, we also noticed that we could not reproduce Sr2+ concentrations measured during initial runs using surface seawater. We inferred that Sr2+ was being coprecipitated with the barite in the standards, resulting in anomalously high Sr2+ concentrations in unknowns. Therefore, we began reanalysis of samples for Sr2+ concentrations using the standards matrix matched with synthetic seawater, which resulted in similar trends but with reduced and more realistic absolute values. Only Sr2+ data obtained with the synthetic seawater standards are reported. Because we could not further test possible SO42--free solution matrix effects, the Sr2+ data should be viewed with caution, although trends are probably real. No effect on Li+ values was observed between surface seawater and synthetic seawater standards, which are considered robust. The precision of the methods based on replicate analyses are reported in Table T7.