The inorganic geochemistry program during Leg 194 was designed to provide rapid results to aid shipboard sampling and identification of key lithologic sections. The bulk of this shipboard program involved chemical analysis of interstitial waters and quantification of the chemistry and mineralogy of sediment samples.
Shipboard interstitial water analyses were performed on whole-round sections that were cut immediately after the core arrived on deck. The whole-round samples were usually taken from the lower third of every core that contained sufficient sediment for processing. After collection, the sediment was immediately extruded from the whole-round core liner and the surface was scraped to remove potentially contaminated exteriors. This sample was then placed into a titanium squeezer atop a filter previously rinsed in high-purity water to remove processing acids. Interstitial waters were retrieved by applying gradually increasing pressure to the squeezer up to a maximum pressure of 205 MPa (30,000 psi) using a hydraulic press (Manheim and Sayles, 1974). Interstitial water was collected through a 0.45-µm filter into a plastic syringe attached to the bottom of the squeezer assembly. Samples were filtered a second time through 0.45-µm polycarbonate filters and stored in plastic vials pending shipboard analyses. Aliquots for future shore-based analyses were placed in glass ampoules and were then heat sealed.
Interstitial water samples were routinely analyzed for salinity as total dissolved solids with a Goldberg optical handheld refractometer. The pH and alkalinity were determined by Gran titration with a Brinkmann pH electrode and a Metrohm autotitrator. Dissolved chloride was determined by titration with AgCl. Sodium, potassium, magnesium, calcium, and sulfate were analyzed by ion chromatography using a Dionex DX-100 ion chromatograph. Silica, phosphate, and ammonium concentrations were determined by wet chemical colorimetric methods and measured 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 a standard are
alkalinity, <1.5%; chloride, <0.2%; calcium, <0.5%; magnesium,
<0.5%; potassium, <2%; sulfate, ~1%; silica, <3%; phosphate, 4%; and
ammonium, 4%. At all sites, sodium was determined using charge balance
calculations, where
cation
charge = anion
charge.
Chemical data for interstitial waters are reported in molar units.
Fe, Mn, B, Li, and Sr concentrations were determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) following the general procedure outlined by Murray et al. (2000).
Mineralogy was determined
on solid carbonate samples using XRD analysis. Quantitative XRD analyses were
performed on bulk samples to determine the relative percentage of aragonite,
calcite, and dolomite. Samples were scanned from 15° to 35°2
at 1°/min. To overcome the limitations of using multicomponent standards,
conversion from peak areas to mineral weight percent was accomplished using the
H-factor method of Hooten and Giorgeta (1977), modified to use low-magnesium
calcite (LMC) as the common internal standard. In this method, the areas of the
peaks of interest were obtained relative to the calcite peak and calibrated
using calibration curves from a series of two-component standards. The final
weight percent of each mineral was adjusted based on the total carbonate
concentration measured on the same sample (see "Organic
Geochemistry"). In addition, the carbonate percentages were
corrected for the presence of dolomite after the method described for Leg 133
(Shipboard Scientific Party, 1991). Overall, the accuracy of the XRD analysis is
5 wt% with a standard deviation of 3 wt%.
The shipboard organic geochemistry program included four routine sets of analyses. First, headspace analysis for volatile hydrocarbons was performed as required by ODP safety regulations. Second, elemental analyses of total carbon, carbonate carbon, total nitrogen, and total sulfur content of sediment samples (and calculation of total organic carbon) was performed. Third, organic matter type, quantity, and maturity were characterized using C/N ratios and Rock-Eval pyrolysis. Lastly, biomarker scans were performed on solvent-extractable organic matter fractions. Most of the procedures and instruments used are described by Emeis and Kvenvolden (1986) and generally are the same as those used during most recent ODP legs. Brief comments on routine sampling and deviations from standard practice are noted below; more detailed notes are presented in the "Explanatory Notes" chapters of ODP Initial Reports volumes for Legs 150, 156, 164, and 181 (Shipboard Scientific Party, 1994, 1995, 1996, 1999).
Sediment-gas composition was determined on each core, primarily using the headspace sampling technique. For the headspace method, a cork borer was used to obtain a measured volume of sediment from the top of one section from each core immediately after retrieval. The sediment, with a typical volume of ~5 cm3, was placed in a 21.5-cm3 glass serum vial that was sealed with a septum and metal crimp cap. When consolidated or lithified samples were encountered, chips of material were placed in the vial and sealed. Before gas analysis, the vial was heated to 60°C for 30 min. A 5-cm3 volume of the headspace gas was extracted from each vial using a glass syringe.
A Hewlett Packard 5890 Series II gas chromotagraph (GC) system was used for gas analysis. The Series II GC determines concentration of C1 (methane), C2 (ethane), and C3 (propane) hydrocarbons with a flame ionization detector (FID). The chromatographic response was calibrated to standard gas mixtures.
Total carbon, nitrogen, and sulfur contents of sediment samples were determined with a Carlo Erba Model NA1500 CNS analyzer. Approximately 6 mg of freeze-dried, ground sediment was combusted in oxygen at 1000°C. In this process, helium acts as a carrier gas, the oxygen is removed, and the combustion gases are reduced, separated by GC, and quantified with a thermal conductivity detector (TCD). Total organic carbon (TOC) content was calculated as the difference between total carbon (TC) and the inorganic (carbonate) carbon (IC) value generated by carbonate coulometry (i.e., TOC = TC - IC). We calculated C/S ratios assuming that all of the sulfur exists as pyrite within the sediments. C/S values <2 are generally considered representative of marine environments, whereas C/S values >5 indicate freshwater environments (Berner and Raiswell, 1984).
Type and quality of organic matter in sediment were evaluated by Rock-Eval pyrolysis of hydrocarbons (Espitalié et al., 1986). In this procedure, volatile hydrocarbon content (in milligrams per gram of rock) released by heating at 300°C for 3 min is measured by the FID and labeled as an S1 peak on the Rock-Eval pyrogram. Hydrocarbon quantity (in milligrams of hydrocarbon per gram of sediment) produced by pyrolysis as the temperature is increased from 300° to 600°C at a heating rate of 25°C/min is also measured by the FID and is called the S2 peak. The nominal temperature at which the maximum rate of hydrocarbon yield is attained during S2 analysis is the Tmax value, which provides an estimate of organic matter thermal maturity, with values <435ºC indicative of immaturity relative to petroleum generation. The "oil window" is generally considered to range between Tmax values of 435° and 465°C (Espitalié et al., 1986; Peters, 1986). CO2 (in milligrams per gram), generated between 300° and 390°C, is measured using a TCD and is called the S3 peak. TOC is calculated from S1, S2, and S3, and from the oxidation of the remaining carbon in the sediment sample measured by a second TCD. The carbon-normalized hydrogen index (HI) (in milligrams of hydrocarbon per gram of carbon) and oxygen index (OI) (in milligrams of carbon dioxide per gram of carbon) are calculated from pyrolysis values by
The origin of sedimentary organic matter was further characterized using HI and organic carbon/nitrogen (C/N) values generated by the CNS analyzer. In general, high hydrogen index (>~200) and low oxygen index (<~150) values from Rock-Eval pyrolysis are indicative of marine (Type II) or lacustrine (Type I) organic matter. Furthermore, lacustrine organic matter generally shows higher HI and lower OI values than a marine counterpart (Espitalié et al., 1986; Peters, 1986). In addition, C/N ratios of ~5-8 are generally considered to be indicative of marine organic matter (Bordovskiy, 1965; Emerson and Hedges, 1988; Meyers, 1994). In contrast, terrestrially derived organic matter from higher plants (Type III) exhibits relatively low HI (<~150) and relatively high OI values, and C/N ratios of ~25-35. Oxidized Type I and II organic matter may show HI and OI values similar to those obtained from Type III, and consistently low HI and OI values are characteristic of Type IV, or highly oxidized organic matter.
An attempt to identify long-chain alkenones in the sediments to estimate paleo-sea surface temperature (SST) was made. Solvent extract (bitumen) was obtained from 1 g of freeze-dried sediment by ultrasonic extraction with dichloromethane:methanol (99:1) for 30 min. The supernatant was pipetted into a vial, and the solvent was removed under a stream of nitrogen. The total extract was dissolved in 50 µL of hexane. A 1-µL aliquot was analyzed on a Hewlett Packard 6890 GC equipped with a 50 m × 0.2 mm HP Ultra 1 (crosslinked methyl silicon gum) capillary column (0.11-µm film thickness), tied to a Hewlett Packard 5973 mass selective detector. Operating conditions for the GC were as follows:
