Laboratory Methods

Chemistry

Lab Documentation

The chemical laboratory aboard the JOIDES Resolution is a modern, state of-the-art shipboard facility providing an impressive capability for both organic and inorganic geochemical analyses. A primary responsibility of shipboard organic geochemists is to provide data on petroleum hydrocarbons for safety and environmental concerns. In addition, instrumentation is available for determination of source, amount, and maturity of organic matter; carbonate content; and total carbon, nitrogen and sulfur. Inorganic geochemists have a wide array of analytical instruments at their disposal for determination of a large range of interstitial water constituents that typically includes pH, alkalinity, chloride, calcium, magnesium, sulfate, potassium, strontium, sodium, manganese, phosphate, silica, and ammonium and others as desired. Two marine lab specialists provide dedicated, 24-hour technical support to the chemistry laboratory on most cruises.

Organic Geochemistry

Safety Monitoring
Organic geochemists perform a vital function to the ship and to the ODP by providing routine monitoring for hydrocarbon gases and accumulations (Pimmel and Claypool, 2001; ODP Technical Note 30). Typically, an approximately 5 cm³ sediment head-space sample is collected at a frequency of 1/core, heated, and the evolved gases are analyzed on one of two Hewlett Packard 6890 Gas Chromatographs (GC) that are dedicated for gas monitoring (Fig. 1). Alternatively, when gas pockets are detected in the core liner, a vacutainer-type sample can be used to take a direct sample of the gas. One GC is equipped with a 2.4 m x 0.32 cm stainless steel column, packed with HaySep S (80-100 mesh) and a FID for rapid determination of methane, ethane, ethylene, propane, and propylene. The other GC is configured as a multi-valve, multi-column Natural Gas Analyzer (NGA). A 60 m x 0.32 mm capillary column and a FID separates and measures hydrocarbons from methane to hexane. In addition, non-hydrocarbon gases (hydrogen sulfide, oxygen, nitrogen, carbon dioxide, carbon monoxide, carbon disulfide) can be analyzed with the NGA GC at the same time as hydrocarbon gases via a packed column and a TCD. Data are collected and analyzed on a Pentium PC using HP Chemstation.

High-Molecular-Weight Hydrocarbons and Organic Matter Type
A third HP 6890 GC, coupled to a HP 5973 Mass Selective Detector, is available for analysis of solvent-soluble organic material. It is equipped with a 30 m x 250 µm capillary column and an autosampler (Fig. 2).

The Delsi-Nermag Rock-Eval II (Fig. 3) uses a whole-rock pyrolysis technique to identify the type and maturity of organic matter and to detect petroleum potential of the sediments by determining volatile hydrocarbons, hydrocarbons released by thermal cracking of kerogen, and carbon dioxide released by thermal degradation of organic matter. Total organic carbon and Tmax (degrees C), which is a parameter that can access the maturity of organic matter, are also determined.

Elemental Analysis
Sediment samples can also be analyzed by the organic geochemist for total carbon, nitrogen, and sulfur, and carbonate carbon. Total organic carbon of sediment can be determined by calculating the difference between total carbon and carbonate carbon. Carbonate carbon is measured by coulometric titration using a Coulometrics 5011 carbonate carbon analyzer (Fig. 4).

A Carlo-Erba NA 1500 CNS Analyzer is used to determine total carbon, nitrogen, and sulfur (Fig. 5). With sufficient warning, the CNS analyzer can be plumbed to determine C and N only at the beginning of a cruise.

Inorganic Geochemistry

Shipboard interstitial water analyses are typical performed on waters extracted from 5- to 10-cm³ whole-round sections. For details on methods used for interstitial water analyses on board the JOIDES Resolution, consult Gieskes et al (1991; ODP Technical Note 15).The routine shipboard sampling program for interstitial waters calls for one whole-round sample to be taken every core for the first six cores, and then one sample every third core thereafter. Waters are extracted from the sediment using titanium squeezers (Fig. 3) and applying pressure up to 40,000 lb (about 4150 psi) with an hydraulic press (Fig. 6).

Immediately after extraction and filtration, aliquots are analyzed for salinity by a hand-held Goldberg optical refractometer and for pH and alkalinity by Gran titration with a Brinkman pH electrode and a Metrohm autotitrator (Fig. 7). Other constituents typically analyzed by titration include chloride, calcium, and magnesium. A variety of nutrients and other pore-water constituents (e.g., ammonium, silica, phosphate, bromide, and manganese) can be determined via colorimetric methods using a Milton Roy Spectronic 301 spectrophotometer. Numerous cation and anions can be analyzed by ion chromatography using a recently acquired Dionex DX-120 (Fig. 8), typically sulfate, calcium, and magnesium, but also including potassium and sodium.

A variety of other elements can be determined inductively coupled plasma emission spectrometry on a Jobin-Yvon JY2000 ICP-ES (Fig. 9). A typical suite of elements determined for interstitial waters include Sr, Li, Fe, Mn, and Ba. Technical Note 29 describes recommended preparation, analysis, and data reduction techniques and instructions for interstitial water, sediment, and hard rock chemical analyses by ICP.

Resources

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