The purpose of physical properties measurements conducted during Leg 177 was to provide (1) near-continuous records for hole-to-hole correlation, the construction of complete stratigraphic sequences, and core-to-downhole log ties; and (2) estimates of properties related to composition of the sediments, which can then be used as high-resolution proxy records related to paleoenvironmental changes.
The first measurement station was the MST, which combines four sensors on an automated track to measure bulk density, magnetic susceptibility, natural gamma-ray emission, and P-wave velocity on whole-core sections. Next, thermal conductivity was measured on whole-core sections in intervals where downhole temperature measurements were taken. Then, the cores were split and the working half was used for further physical properties measurements. These included diffuse spectral reflectance and resistivity measured with the OSU-SCAT, P-wave velocity, water content, and grain density measurements to calculate bulk density, porosity, and related properties. Most of the methods are described in detail in the Physical Properties Handbook (Blum, 1997) and are summarized here.
Estimates of bulk density were obtained from MST GRA measurements of whole-round core sections at intervals of 2 cm and 4 s sampling time. The calibration was based on aluminum standards of different thickness mounted in a water-filled core liner (Blum, 1997). This calibration takes into account (1) the higher Compton attentuation coefficient in water compared to common minerals, (2) count rate effects (Weber et al., 1997), and (3) a correction for the core liner. For each site, we calculated the correlation between the GRA bulk densities and the bulk densities determined on core specimens using the moisture-density method (see below). GRA densities were ~5% higher than bulk densities measured on discrete samples. This discrepancy will be investigated postcruise by grain-density measurements on dry samples.
Natural gamma-ray measurements were taken for periods of 4 s every 2, 4, or 8 cm, depending on time constraints determined by core flow through the laboratory. Calibration was performed at the beginning of the leg and at Site 1093. Background radiation was determined with a water core to be about 14 cps. No subtraction of background radiation was done on the data presented in the plots. The total counts were useful for definition of some lithologic trends.
Although measuring time was 4 s, the MST program needed 6 additional seconds to upload the measured counts at each 2-cm step. During the upload time, the measurement systems were idle, slowing down the core flow. However, combined MST measurements made at 2-cm resolution and 4-s measuring time, still took no more than 21 min per core section in total. This did not exceed the standard run time (21 min/section) that it takes for a core to move through the cryogenic magnetometer. As a result of an electronic malfunction, data collected from Cores 177-1092B-14H through 177-1093C-5H showed a great degree of scattering. This was also seen in the control measurements after each section (Fig. F10).
Magnetic susceptibility was measured with the Bartington meter MS2 using an 8-cm loop and the low sensitivity setting of 1.0 Hz. Sample periods were 4 s and sampling intervals 2 cm. The mean value of the four measurements was stored. Volume-normalized SI units (×10-5) for the magnetic susceptibility were calculated from the sensor signals by multiplication with a factor of 0.63 (coil-to-core diameter ratio, Bartington manual; Shipboard Scientific Party, 1994). Magnetic susceptibility was one of the most useful records for core-to-core correlation and composite depth construction.
Thermal conductivity measurements are required for geothermal heat flow determinations. Thermal conductivity was measured after the cores had equilibrated to ambient temperature, about 3-4 hr after recovery, using a single-needle probe, in full-space configuration (von Herzen and Maxwell, 1959; Blum, 1997). Data are reported in W/(m·K) with an estimated error of ~5%.
Reference measurements of a red rubber standard, conducted while occupying Sites 1088, 1092, 1093, and 1094, gave a value of 0.870 ± 0.014 W/(m·K) (1.7% error; Table T6, also in ASCII format in the TABLES directory). This standard was particularly useful because the value is close to those obtained from the cores drilled during Leg 177. The empirical value for the red rubber standard, obtained during early ODP operation and used during recent legs, is 0.96 ± 0.05 W/(m·K). We suggest that the Leg 177 value obtained with the new TK04 unit (see Blum [1997] for description and references) is more accurate and precise.
Moisture and density (MAD) measurements, as defined for ODP shipboard procedures, include gravimetric determinations of water content, bulk density, grain (solid) density, and related properties such as porosity, void ratio, and dry density. Initial wet bulk mass (Mb), dry mass (Md), and volume (Vd) were measured after drying the samples in a convection oven for 24 hr at temperatures of 105ºC. Tests conducted at the beginning of Leg 177 with samples dried at 60º and 105ºC, and freeze-drying with and without frozen samples showed that freeze-drying for 24 hr would give comparable results (Fig. F11). Freeze-dried samples could still be used for further sedimentological investigations (clay mineralogy, grain size, etc.), whereas oven drying may alter the clay mineralogy and causes problems for the disaggregation of the samples.
Samples collected for MAD measurements were taken at an average frequency of one per core section. However, where frequent lithologic changes occurred, denser sampling was undertaken to ensure measurements were available from all significant lithologies throughout the core. In cores of particularly homogeneous lithology, the sampling interval was reduced to two samples per core. The MAD samples were taken at the same position as measurements of P-wave velocity (see below). This ensures that the different parameters represent the same sediment type, and can be correlated without interpolation. In XCB cores, which frequently showed "biscuiting" type of disturbance, particular care was taken to sample undisturbed parts of the core sections and to avoid the drilling slurry.
P-wave velocity was measured orthogonal to the core axis in steps of 2-4 cm on whole-round core sections with the P-wave logger (PWL) mounted on the MST. At Sites 1088 through 1092, PWL data were compromised because of a malfunctioning calibration screw for setting threshold detection. This was finally repaired in Section 177-1093A-5H-1, and the detection delay was changed from 2 to 3 µs because the first excursion of the received signal was negative (Blum, 1997). Data collected before the repair can be salvaged after filtering and correction using the P-wave velocity sensor 3 (PWS3) measurements (see below).
In addition, P-wave velocity was measured on split-core sections using the PWS3 contact probe system (a modified Hamilton frame), which measures orthogonal to the core axis across the split-core section and core liner through transducer contact with the sediment on top and the core liner on bottom, respectively. Two types of P-wave transducer pairs (PWS1 and PWS2), inserted along and orthogonal to the core axis into soft sediment, were used in only a few intervals to minimize core disturbance. If a signal was retrieved, the P-wave velocity was comparable to the corresponding velocity obtained from the PWS3 probe.
The PWS1 split-core velocimeter calculates velocity based on a fixed distance and measured traveltime. In addition to traveltime, the PWS3 system measures variable sample thickness with a digital micrometer that is zeroed periodically. The calibration procedures for both the PWL and PWS3 were done after Blum (1997).
Quantitative estimates of sediment diffuse spectral reflectance and resistivity were generated by the shipboard sedimentologists using the OSU-SCAT. The handheld, Minolta CM-2002 spectrophotometer was also used to measure sediment color reflectance on selected intervals. The OSU-SCAT spectrophotometer system (Mix et al., 1992) consists of a computer-controlled motorized-track assembly that advances a core section into sampling position under a commercially available light integration sphere. The integration sphere is brought into contact with the sediment via a computer-controlled vertical stepping motor. Temperature, conductivity, and strain sensors detect contact with the sediment surface and provide measurements of sediment resistivity (see "Resistivity"). During operation, light with known spectral characteristics passes through fiber optics and is steered using a directional mirror toward two reference ports and a measurement port. The light that is diffusely reflected off the sediments is integrated within the sphere, split into constituent wavelengths by a diffraction grating, and collected with a multichannel detector.
An earlier version of this instrument was employed during Leg 138 (Mix et al., 1992). The current version was used for postcruise analysis of cores collected during Leg 154, and for shipboard analysis of cores during Legs 162 and 167. The new design has incorporated four improvements: (1) the addition of the integration sphere; (2) the use of a motorized mirror for source-beam direction, rather than a source-beam splitter; (3) determination of internal "white" reference on each sample and "black" background estimations for all standards and alternating samples; and (4) the spectral range of the instrument was extended beyond the visible to include both UV and nIR wavelengths. These improvements have increased the signal-to-noise ratio considerably over the earlier version of the instrument.
Reflected light was measured in 1024 bands of 0.682-nm width ranging from 250 to 950 nm at Site 1088, but in the visible and nIR range only (~400-950 nm) at Sites 1089-1094 because of a failure of the UV light source. It would have been desirable to measure all core sections from all multiple holes at 2-cm intervals, comparable to MST measurements. However, time constraints and the relatively slow vertical motion of the integration sphere limited the measurement program to 4- to 6-cm intervals on all APC and some XCB cores from one designated hole at each site (usually the A hole), and on chosen intervals from the other holes at each site. As a result of this, the spliced composite section defined mainly by MST measurements is not entirely covered by OSU-SCAT measurements. However, a SCAT-composite section could be constructed for the majority of the multiple-hole intervals. For shipboard analysis, the raw data were converted to percent reflectance and averaged into four 100-nm-wide bands defined as UV (250-350 nm), blue (450-550 nm), red (650-750 nm), and nIR (850-950 nm). These bands are 50 nm wider than those used on previous ODP legs to allow integration of a greater fraction of the spectral signal. As an aid to defining lithostratigraphic units we employed the red band, which is near the instrument's maximum response. This band was also used as an aid in constructing composite sections (see "Composite Depths"). The blue band was used for comparison to shipboard measurements of the carbonate content of sediment (carbonate has a somewhat higher reflectance at this wavelength than at longer wavelengths; see Mix et al., 1992).
During shipboard analysis, it was noted that the reflectance values from the Minolta CM-2002 were consistently offset and of lower amplitude than reflectance measurements generated with the OSU-SCAT system. Possible explanations for the offset were differences in the calibrations of the two instruments and the use of Glad plastic wrap over cores when working with the CM-2002 to protect its integrating sphere and glass lens. The CM-2002 employs a two-point calibration using a white ceramic transfer standard and a black-light trap to set the full range of the instrument. In contrast, the OSU-SCAT system measures internal white and black-trap standards with each sample and corrects for reflectance caused by imperfections in the integrating sphere using four external Spectralon standards with nominal reflectance of 2%, 40%, 75% and 100%. To intercalibrate the two instruments, we repeatedly measured the OSU-SCAT's external standards using the CM-2002 (n = 20 for each standard). The results demonstrate that the Minolta CM-2002 in SCE mode generates reflectance values that are consistently lower (by ~7%-8%) than those obtained from the OSU-SCAT (Fig. F12). The effect of using Glad wrap was to increase the reflectivity of the 2% standard to ~4% (effectively acting as a mirror) and to decrease the reflectance of the brighter standards. The Glad-wrap effect was smaller than the calibration offset between the two instruments. The data from the Minolta instrument are presented in uncorrected form in this volume. Postcruise work will focus on determining spectrally resolved correction factors to enable direct comparison of the Minolta and OSU-SCAT instruments in the visible wavelength range.
Measurements of sediment resistivity were generated by the OSU-SCAT every 4-6 cm in split core sections. (see "Reflectance"). The resistivity meter consists of two Wenner-type arrays (channels A and B) located on opposite sides of the landing board of the OSU-SCAT's integration sphere (Fig. F13) Each array is aligned in the direction of the core's long axis, and consists of four electrodes that penetrate the sediment to a depth of ~0.5 cm. A ± 0.3-V, 980-Hz sine wave is applied to the outer electrodes, and the current through the sediment is measured. The inner electrodes are used to measure the drop in potential. A measure of resistivity (R0) is then obtained through the relationship:
R0 = V/I × C, (3)
where V is the voltage, I
is the current, and C is an empirically derived "cell constant" that is a
function of the cross-sectional area and length of sample through which the current
passes. Calibration of the OSU-SCAT resistivity meter in synthetic water samples yielded a
cell constant of C = 0.9. The resistivity is then expressed in units of 
m. Since resistivity is
dependent on temperature (as temperature increases resistivity decreases), the temperature
of the sediment must be recorded at the same time as resistivity measurements are made.
The OSU-SCAT landing board has two temperature probes (Fig. F13), thereby allowing correction to 20ºC using the following empirical
relationship:
R0 = Rt·[1 + 0.025·(T - 20)]. (4)
If the resistivity of the mineral particles is very large compared with the interstitial water, then the proportion of the current carried by the minerals can be ignored. The conductivity of ocean water is approximately 10 orders of magnitude larger than that of silicate minerals. Because water has such a large effect, it is assumed that measurements are made under saturated conditions; therefore, precautions need to be taken to minimize core drying after splitting, such as covering exposed sections with plastic wrap. The resistivity measured at any given depth will depend on the volume fractions of the sedimentary constituents, their individual conductivities, and the sedimentary microstructure. Empirical relationships can account for these variations using a variation of Archie's Law (Archie, 1942; Boyce, 1968):
F = a
-m, (5)
F = R0/Rw, (6)
where F is the formation
factor, is the
porosity fraction, a is a proportionality constant, and m is a constant that is a function
of the particular lithology. The formation factor for a particular lithology represents
the reduction in brine conductivity, caused by the presence of an insulating phase
(sediment), and is related to the porosity and the tortuosity, which represents the fluid
path around the solid grains and the interconnectivity of the pore spaces. The formation
factor is expressed as the ratio of the temperature-corrected resistivity of the saturated
sediment (R0) to that of the interstitial water (Rw).
The interstitial water is assumed to be standard seawater with a salinity of 35 parts per
million at 20ºC, and has a resistivity of 0.209 m (i.e., Rw = [2.803 + 0.0996·T]-1).
If resistivity and porosity data are both available from the same sediment sample (e.g., the discrete-sample porosities measured by the MAD method), then an exponential fit to a plot of the formation factor (from Eq. 6) vs. porosity can be used to estimate the a and m constants in Equation 5.
Resistivity can also be used to estimate diffusion coefficients for ionic species. In principle, the manner in which saturated sediments transmit electrical current is analogous to their ability to permit molecular diffusion. The diffusivity of dissolved species within sediments is a function of the species themselves, the temperature, the porosity, and the tortuosity (geometry) of the free channels in the sediment. Therefore, the diffusion coefficient (d) of a given molecule or ionic species within the sediment is given by
d = do/F, (7)
where do is the diffusion coefficient for the given species in free solution at a given temperature and ionic strength, and F is the formation factor. If the sediments contain a high concentration of clay minerals, however, then the clay can conduct a significant part of the current and will result in artificially high diffusion coefficients. The low clay mineral concentrations in most Leg 177 cores suggest that resistivity may provide a means of approximating diffusion coefficients in siliceous and carbonate oozes.
The high-resolution resistivity data
collected during Leg 177 generally have a high signal-to-noise ratio, although periodic
technical problems with the lander assembly did result in data from one or more of the
channels being compromised temporarily until the problem was rectified. There was also a
consistent offset between the A and B channels of ~0.2 m, and channel A sometimes showed an inverse
correlation with channel B, even during calibration runs in seawater. This may be an
electronic problem with amplification of the A channel signal. As a consequence, only data
from the B channel are shown in this volume. Data from the B channel show an excellent
correlation with the GRA bulk density and an anti-correlation with discrete sample (MAD
method) porosities (see "Physical Properties" sections in the site chapters).
Postcruise analysis of the resistivity data will first involve further evaluation of their quality and a diagnosis of the problem with the A channel. This will hopefully allow correction of the A channel data and an improved signal-to-noise ratio. Resistivity measurements will then be used in conjunction with spectral reflectance and whole-core logging data from the MST, to investigate sediment mineralogy and fabric.
