Shipboard interstitial water analyses were performed on 10- to 40-cm-long whole-round sections that were cut and capped immediately after the core arrived on deck. The whole-round samples were usually taken from the bottom of sections of every core that had sufficient recovery, at greater frequency in the top five cores, and across horizons of special interest. Interstitial waters were retrieved by applying the minimum pressure necessary to the sediment and gradually increasing up to an internal maximum pressure of the squeezer, calculated from the pressure of the press and the ratio of the piston areas of the press and squeezer, of 68 Mpa (10,000 psi) (Manheim and Sayles, 1974). Before squeezing, the sediment was immediately extruded from the whole-round core liner, the surface was carefully scraped to remove potentially contaminated exteriors, and the cleaned sediment was placed into a titanium squeezer on top of a filter that had been previously rinsed in high-purity water. Interstitial water was collected through the filter into a plastic syringe attached to the bottom of the squeezer assembly then filtered through a 0.45-µm polycarbonate filter. Samples were stored in plastic vials pending shipboard analyses. Aliquots for future shore-based analyses were placed in acid-washed plastic tubes and heat-sealed glass ampules.
Interstitial water samples
were routinely analyzed for salinity as total dissolved solutes with a Goldberg
optical handheld refractometer (Reichart); for pH and alkalinity by Gran
titration with a Brinkmann pH electrode and a Metrohm autotitrator; for
dissolved chloride, calcium, and magnesium concentrations by titration; and for
silica, phosphate, and ammonium by spectrophotometric methods with a Milton Roy
Spectronic 301 spectrophotometer, following the analytical techniques described
by Gieskes, et al. (1991). International Association of Physical Sciences
Organizations (IAPSO) standard seawater was used for calibrating most
techniques. The reproducibility of these analyses, expressed as 1-
standard deviations of means of multiple determinations of IAPSO standard
seawater or of a standard, are alkalinity, <1.5%; chloride, <0.2%;
calcium, <0.5%; magnesium, <0.5%; silica, <3%; and phosphate and
ammonium, 4%. At all sites, sodium was determined using charge balance
calculations where 
(cation
charge) = (anion
charge).
Potassium and sulfate were
analyzed by ion chromatography (IC) using the Dionex DX-100. The reproducibility
of these analyses expressed as 1-
standard deviations of means of multiple determinations of IAPSO standard
seawater are potassium, <2%, and sulfate, ~1%. Calcium and magnesium were
also routinely determined using IC, but for most analyses the titration data are
reported except where specifically noted; the titration method for calcium and
magnesium provided more accurate and precise results. For calcium, a precision
of ~2% (1-
standard deviation of repeat IAPSO determinations/published IAPSO concentration)
of IAPSO standards was obtained by IC as opposed to <0.5% by titration. For
magnesium, the precision was low (~5% by IC) and also compared unfavorably with
<0.5% relative error by titration. Although the IC method is not optimized
for the high concentrations of sodium and chloride found in marine interstitial
waters relative to the concentrations of the other constituents, they were
routinely analyzed with the other cations and anions, respectively. Even for
sodium and chloride the precision by IC is ~1% for Cl and <2% for Na;
however, the accuracy is very low. These IC results, however, provided a useful
check on the general trends of the depth profiles.
Chemical data for interstitial waters are reported in molar units.
Hydrogen concentrations of interstitial waters were determined on ~5-cm3 bulk-sediment samples that were collected immediately after the core arrived on deck. Whole-round sediment samples were first transferred into an anaerobic glove box and then subsamples were transferred into 20-mL headspace vials. Care was taken to avoid sediment that had been contaminated during drilling or handling. In soft sediments, this involved sampling interior material with a cut off syringe, whereas in harder materials, the outer disrupted parts of the core were pared off. Following the placement of the sediment sample in the headspace vial and removal of the vial from the glove bag, the headspace was flushed with oxygen-free and hydrogen-free nitrogen. The vials were then incubated at in situ temperatures and analyzed for hydrogen over a period of a few days. Individual subsamples were prepared in replicate. Replicate samples were autoclaved prior to incubation in order to quantify abiogenic hydrogen. A trace analytical reduction gas analyzer was used to determine headspace hydrogen concentrations.
The water sampling temperature probe tool (WSTP) (Barnes, 1988) was used for sampling bottom seawater at Sites 1173 and 1175 and for in situ extraction of interstitial water. The tool is lowered on the coring wire to the end of the drill string, where it hooks onto an assembly just above the bit with the probe tip extruding below the bit. The bit was lowered either into bottom water, ~50 m above mudline without pumping to avoid mixing surface water (drill water) with bottom seawater, or into the bottom with the filter assembly projecting ~1.1 m past the bit. A time-operated valve opens and interstitial water is drawn under negative pressure through the filter and into the sampler. The filter assembly is 22 cm long and its surface area is 200 cm2.
Prior to deployment, the fluid path is backfilled with distilled water that has been previously degassed by nitrogen bubbling. The overflow cylinder is flushed with nitrogen and evacuated. A timer is set for a fixed time after which the valve opens, exposing the sampling line and chamber to ambient pressure. The timer also closes the valve after a prearranged time interval of 5-15 min.
Fluid from the titanium and stainless steel coils was filtered (through a 0.45-µm filter) and analyzed following the procedures described for the interstitial water squeezed from whole-round samples.
Inorganic carbon was determined using a Coulometrics 5011 carbon dioxide coulometer equipped with a System 140 carbonate carbon analyzer. A known mass (40-50 mg) of freeze-dried (dedicated carbonate samples) or oven-dried (physical properties samples) ground sediment was reacted in a 2-N HCl solution. The liberated CO2 was titrated in a monoethanolamine solution with a colorimetric indicator, and the change in light transmittance was monitored with a photodetection cell. The percentage of carbonate was calculated from the inorganic carbon content assuming that all carbonate is present as calcium carbonate:
The precision of these
analyses, expressed as 1-
standard deviations of means of multiple determinations of a pure carbonate
standard is <1%.
Total nitrogen, carbon, and sulfur of sediment samples were determined using a Carlo Erba Model NA 1500 NCS analyzer. Mixtures of vanadium pentoxide and crushed, freeze-dried samples (~5 mg) were combusted in an oxygen atmosphere at 1000°C, converting total (organic and inorganic) carbon to CO2, sulfur to SO2, and nitrogen to NO2. The NO2 was then reduced to N2 using copper. The gases were separated by gas chromatography and measured with a thermal conductivity detector. The precision of these analyses, expressed as 1 standard deviation, is 2%-3%. Total organic carbon (TOC) was determined by calculating the difference between total carbon (TC) from the NCS analyzer and inorganic carbon from the coulometer:
