Index properties (gravimetric wet bulk density, porosity, and moisture content) were generally determined on one or two samples (volume = ~10 cm3) per working-half section on all cores from Hole 1082A using Method C (see "Explanatory Notes" chapter, this volume).
Other shipboard physical properties measurements included determination of compressional (P-wave) ultrasonic velocity, density, magnetic susceptibility, and natural gamma radiation with the MST system on whole-round sections of cores from each hole (see "Explanatory Notes" chapter, this volume).
Compressional (P-wave) velocity and undrained vane shear strength measurements were conducted on the working half of every section from Hole 1082A. Sampling resolution was one or two sample points per section. For the discrete P-wave measurements, the modified Hamilton Frame was used to determine ultrasonic velocities. Thermal conductivity was measured on every second section in every core from Hole 1082A.
P-wave velocities (Fig. 29), GRAPE density (Fig. 30), and magnetic susceptibility (Figs. 31A) were determined every 2 cm for the first nine cores (0–90 mbsf); natural gamma radiation was measured with a sampling period of 30 s at 30-cm resolution during that depth interval (Figs. 31B). MST data are included on CD-ROM (back pocket, this volume). Below 90 mbsf, the resolution was reduced to 32 cm for the latter, whereas the other sensors were run at 4-cm resolution. Compressional velocities were recorded at a threshold of 100 incremental units to exclude weaker signals from the profile. No signals were recorded with the MST P-wave logger below 30 mbsf because of numerous cracks and voids within the cored sediments (Fig. 29). MST P-wave values appear to be systematically lower than discrete velocity values, but they reveal some correlation.
Magnetic susceptibility (Figs. 31A) and natural gamma radiation (Figs. 31B) correlate well over the entire depth range of 600 m, although on a smaller depth scale, differences between the two profiles are apparent. GRAPE density and index properties wet bulk density fit very well together (Fig. 30), although the index properties values are generally higher. This difference can be attributed to gas expansion affecting most parts of each core and reducing the total sediment volume measured with the GRAPE. All physical properties data sets reveal clear and pronounced cyclicities, opening opportunities for future high-resolution studies. However, thorough editing will be required to correct for sediment deformation caused by gas expansion, to combine parallel holes, and to prepare data for time-series analysis methods.
Discrete velocities range from 1520 to 1605 m/s between 0 and 48 mbsf. The P-wave logger of the MST generated lower values down to 30 mbsf, where signal attenuation becomes too high to determine first arrivals (Fig. 29). The discrete velocity profile correlates well with the undrained vane shear strength values, which may give an indication of the sediment deformation during core retrieval caused by gas expansion (Figs. 29).
Results of discrete measurements of wet bulk density, porosity, and moisture content are presented in Fig. 32A, Fig. 32B, and Fig. 32C, respectively (also see Table 15 on CD-ROM, back pocket, this volume). The density values vary between 1250 and 1800 kg/m3. The overall trend of the wet bulk density profile shows increasing values because of compaction. However, a smooth long-term variability exists in the advanced APC section. A decrease in wet bulk density can be identified (e.g., from 40 to 80 mbsf), indicating a major compositional change.
In general, porosity and moisture profiles show the expected inverse correlation with the density curve. Porosities decrease from 82% in the top section to 50% at 530 mbsf (Fig. 32B), and moisture content varies between 65% at the top of Hole 1082A and 30% to 530 mbsf (Fig. 32C).
The thermal conductivity profile (Figs. 31C) at Hole 1082A was measured in every second core section (see "Explanatory Notes" chapter, this volume). The profile shows a better degree of similarity with the magnetic susceptibility (Figs. 31A) than with the natural gamma radiation profile (Figs. 31B).
Undrained vane-shear measurements were performed in the bottom part of each core section. The profile between 0 and 200 mbsf shows a gradual increase in vane shear from the top of Hole 1082A to 100 mbsf, followed by a decrease in shear strength. The low shear-strength values below 118 mbsf are probably related to the change from APC to XCB drilling. XCB cores are generally biscuited and contain a surplus of pore fluid as an effect of the drilling process. Figure 31A–D shows a comparison of shear strength with magnetic susceptibility, natural gamma radiation, and thermal conductivity. Local maxima in shear strength are usually found in the middle of each section. Lower values coincide with the top and the bottom of each section where gas expansion may have changed the sediment structure most.