m can be measured at spatial resolutions along the core of ~2-4 cm. In cores from Leg 205, measurements were taken every 4 cm.
Physical properties were measured on unsplit cores and on the undisturbed parts of split cores. The MST was used for nondestructive measurements of wet bulk density, electrical resistivity, magnetic susceptibility, and natural gamma radiation in unsplit cores. Thermal conductivity measurements were also conducted on unsplit and split sediment cores and split rock cores. Compressional wave velocities were measured on both soft and lithified sediment and rock cores. Portions of split cores that were undisturbed by drilling and sampling, gas expansion, bioturbation, cracking, and large voids were used to obtain specimens for moisture and density measurements and calculations (wet bulk density, grain density, dry bulk density, water content, void ratio, and porosity).
Physical property measurements were conducted after the cores had at least 2-4 hr to equilibrate to near-ambient room temperature (i.e., 21°-24°C), except where noted. Many of the measurements can vary with core temperature and should be obtained in a stable temperature environment for best results. A summary of each of the physical property measurement procedures for Leg 205 is outlined below and described in more detail by Blum (1997).
Cores were first run through the MST, which combines five sensors on an automated track to measure magnetic susceptibility, bulk density, electrical resistivity, and natural gamma ray emission on whole-core sections. The respective sensors are the magnetic susceptibility meter, the gamma ray attenuation (GRA) densiometer, the noncontact electrical resistivity (NCR) sensor, and the natural gamma ray (NGR) detector. MST measurement of P-wave velocities was not conducted because measured MST P-wave velocities on XCB and RCB cores are usually of poor quality as a result of the small core diameter and loss of coupling between the liner and the core. MST data were sampled at discrete intervals, with the sampling rate chosen to optimize the resolution and quality of the data.
Magnetic susceptibility was measured with a Bartington meter MS2 using an 80-mm internal diameter sensor loop (88-mm coil diameter) operating at a frequency of 565 Hz and an alternating field of 80 A/m (0.1 mT). The sensitivity range was set to the low sensitivity setting (1.0 Hz). The sample period and interval were set to 2 s and 4 cm, respectively. The raw mean value of the measurements was calculated and stored automatically. The quality of these results degrades in XCB and RCB sections, where the core may be undersized and/or disturbed. Nevertheless, the general downhole trends can be useful for stratigraphic correlations, and peaks may help to identify discrete ash layers. The MS2 meter measures relative susceptibilities, which have not been corrected for the differences between core and coil diameters.
Bulk density was measured for unsplit core sections as they passed through the GRA densiometer, using a sampling period of 2 s every 4 cm on the MST. The gamma ray source was 137Cs. For each site, the GRA bulk densities and the bulk densities measured on discrete samples were compared.
The relatively new Geotek NCR system was installed for trial purposes during Leg 204 (Shipboard Scientific Party, 2003). The NCR technique operates by inducing a high-frequency magnetic field in the core from a transmitter coil, which in turn induces electrical currents in the core that are inversely proportional to the resistivity. A receiver coil measures very small magnetic fields that are regenerated by the electrical current. To measure these very small magnetic fields accurately, a difference technique has been developed that compares the readings generated from the measuring coils to the readings from an identical set of coils operating in air. This technique provides the requisite accuracy and stability. Resistivities between 0.1 and 10 m can be measured at spatial resolutions along the core of ~2-4 cm. In cores from Leg 205, measurements were taken every 4 cm.
Calibration was achieved by filling short lengths of core liner (~25 cm each) with water of known concentrations of NaCl (Shipboard Scientific Party, 2003). This provides a series of calibration samples with known resistivities that are then placed on the MST and logged. Averaged measurements for the samples were then plotted against the known resistivity to define a power law calibration equation.
NGR emissions are a function of the random and discrete decay of radioactive atoms and are measured through scintillation detectors as outlined by Hoppie et al. (1994). During Leg 205, NGR emissions were measured for 20 s per each 10 cm length of core, except where noted. NGR calibration was performed at the beginning of the leg, and sample standards were measured at the end of every site.
Thermal conductivity was measured using the TK04 system described by Blum (1997). This system employs a single-needle probe (Von Herzen and Maxwell, 1959) heated continuously in full-space configuration for soft sediments and in half-space configuration for lithified sediments and igneous rock cores. Under conditions of moderate to full recovery, thermal conductivity measurements were conducted at a frequency of at least two per core.
Thermal conductivity was measured for full-core unconsolidated sediment sections using a full-space single-probe TeKa (Berlin) TK04 unit. A hole was drilled in the outer core liner, and the 2-mm temperature probe was inserted into the working half of the core section. For igneous rock samples, a smooth surface was prepared on a ~5-cm split-core specimen that had been placed in a water bath for a minimum of 15 min. The half-space needle probe was secured onto the flat surface of the half core. At the beginning of each half-space and full-space measurement, temperatures in the samples were monitored automatically, without applying a heater current, until the background thermal drift was determined to be <0.04°C/min. The heating was then started, and the temperature increase in the probe was recorded.
The reported thermal conductivity measurement for each sample was the average of three repeated measurements for the full-space method and four measurements for the half-space method. Data are reported in watts per meter Kelvin with a stated error of ~5%. Assessment of thermal stability is automatic with the TK04 meter, which does not require shipboard calibration.
Moisture and density (MAD) measurements were determined by measuring wet mass, dry mass, and dry volume of specimens from the split cores. Samples for MAD measurements were collected at a frequency of two per complete section in sediment and one per section in igneous rock. Where whole-round samples were taken from a section, one of the two MAD samples was taken adjacent to it. Care was taken to sample undisturbed parts of the core and to avoid drilling slurry.
Immediately after the samples were collected, wet sediment mass (Mwet) was measured. Dry sediment mass (Mdry) and dry sediment volume (Vdry) were determined after the samples had dried in a convection oven for 24 hr at a temperature of 105 ± 5°C. Wet and dry masses were determined using electronic balances that compensate for the ship's motion, and dry volume was measured using a gas pycnometer.
Moisture content, grain density, bulk density, and porosity were calculated from the measured wet mass, dry mass, and dry volume as described by Blum (1997). Corrections were made for the mass and volume of evaporated seawater using a seawater density of 1.024 g/cm3 and a salt density of 2.20 g/cm3.
The method for measurement of compressional wave velocity (VP) was dependent on the degree of sediment consolidation. The velocity meter was calibrated by measuring VP in water.
For the hard rock and semilithified or lithified sediments sampled during Leg 205, only the PWS3 contact probe system, described by Boyce (1976), could be employed. The PWS3 system calculates velocity using measured traveltime and sample thickness measured with a digital micrometer. If core recovery permitted, one set of velocity measurements was conducted per section, with additional measurements taken in sections characterized by varying lithology.
