GRA bulk density, magnetic susceptibility, natural gamma-ray (NGR) emission, and P-wave velocity were measured with the MST on whole-core sections recovered from Site 1091. Color reflectance and resistivity were measured on the working half of all split APC cores using the OSU-SCAT (see "Lithostratigraphy" in the "Explanatory Notes" chapter). Color reflectance was also measured with the Minolta CM-2002 spectrophotometer on cores from Holes 1091D and 1091E. Other physical properties measurements conducted on discrete core samples included moisture, density, and P-wave velocity. Measured parameters were initial wet bulk mass (Mb), dry mass (Md), and dry volume (Vd). Velocity was measured on split-core sections using the P-wave velocity sensor 3 (PWS3). Table T15, and Figures F23 and F24, summarize the physical properties measurements performed at Site 1091.
There is good agreement between discrete-sample densities (determined using the moisture and density [MAD] method) and GRA bulk densities (Figs. F23, F25). Densities range between 1.1 and 1.4 gcm3 and show a gradual increase downhole, but the median density is low (1.2 g/cm3), reflecting the dominance of diatom-rich sediments at this site (see "Lithostratigraphy"). In the upper 270 mcd, densities >~1.3 g/cm3 are associated with carbonate oozes. Below 270 mcd, average bulk density increases as a result of lower porosities, which may, in turn, be a result of an increase in mud content and lower sedimentation rates in the lower part of the core (see "Lithostratigraphy", "Chronostratigraphy").
Reflectance generally covaries with density, resistivity, magnetic susceptibility, and NGR (Fig. F23). Notable exceptions occur when mud becomes a significant component of the sediment (e.g., below 270 mcd, and also in discrete intervals indicated on Fig. F24 at 32 and 41 mcd). In such cases, resistivity, magnetic susceptibility, and NGR increase, but reflectance shows little or no response.
P-wave velocities measured with the PWS3 velocimeter increased gradually and steadily downhole from values of 1510 m/s at the top to values of 1550 m/s at the bottom (Fig. F23), reflecting the gradual increase in bulk density. As with all previous Leg 177 sites, P-wave logger (PWL) velocities obtained from the MST were problematic in that values were considerably lower than those of the PWS3 and showed a clear bimodal distribution with mode averages of ~1450 and 1500 m/s (Fig. F23). The reason for this was a defective threshold adjustment knob, which was corrected while the first few cores were being logged at Site 1093.
The high water content of the
diatom-rich sediments results in very high porosities at Site 1091 (Fig. F23). Porosity determined gravimetrically on discrete
samples (MAD method) ranged from 74% to 90%, and resistivity showed the expected inverse
relationship with porosity (values range from 0.1 to 0.2 
m). There is an overall gradual
decrease in porosity (increase in resistivity) downhole as a result of compaction.
Deviations from this trend in the upper 270 mcd are associated with intervals of high
carbonate content, in which porosities are much lower. Below 270 mcd, porosity decreases
in response to increasing mud content in the sediments.
The downhole reflectance pattern for sediments at Site 1091 is substantially different from those observed at previous sites drilled during Leg 177. This, presumably, is a result of the intermittent but generally low carbonate content of the sediments (see "Geochemistry"). The lack of carbonate can be inferred from the generally low blue reflectance values between 0 and 80 mcd, which average ~16% and are punctuated by brief reflectance peaks (Fig. F26). These brief events, some of which exceed 30% reflectance, correspond to spikes of higher GRA density (Fig. F24). These bright, dense layers correlate with carbonate-rich intervals (see "Lithostratigraphy"), although shipboard carbonate measurements (see "Geochemistry") are too sparse to resolve these small-scale features.
Between 80 and 235 mcd, reflectance values exhibit rhythmic variability that may be related to alternation between dark diatom mats (see "Lithostratigraphy") and brighter carbonate layers. Indication of these alternations can be seen not only as simple changes in sediment brightness (Fig. F26), but also as changes in the character of the reflectance spectra (Fig. F27). Intervals rich in carbonate exhibit bright reflectance with little divergence between the blue, red, or near-infrared bands. In contrast, intervals that are rich in diatoms exhibit a greater contrast between blue and red reflectance.
Cores from Holes 1091A and 1091B were scanned for reflectance with the OSU-SCAT system, whereas cores from Holes 1091D and 1091E holes were measured using the handheld Minolta CM-2002 spectrophotometer to increase the rate of core processing. The measurements produced by these two systems were similar enough to be of assistance during shipboard hole-to-hole correlation (see "Chronostratigraphy"). There was, however, a difference in the amplitude of the signals generated by the two instruments in intervals where sediments are diatom-rich relative to the good agreement observed between the two instruments in the carbonate-rich sediments of Site 1089 (Fig. F26). The Minolta CM-2002 signal appears somewhat muted relative to that of the OSU-SCAT. This could arise from the more accurate 4-point reflectance calibration of the OSU-SCAT as opposed to the 2-point calibration used by the CM-2002. In addition, measuring cores through Glad plastic wrap with the CM-2002 contributes to slight changes in the spectral response of the instrument (Balsam et al., 1997).
A total of 150 thermal conductivity measurements were made on cores from three holes at Site 1091 (Table T16, also in ASCII format in the TABLES directory; Fig. F28). The measured values range from 0.63 to 0.76 W/(m·K), which is the lowest and narrowest range at Sites 1088-1091. The distribution of measured values is unimodal, with a mean of 0.68 W/(m·K) (Fig. F28A). The linear correlation between thermal con-ductivity and bulk density measurements is poor at this site (Fig. F28B), even though a correlation appears to exist visually (Fig. F28C). The low correlation coefficient is the result of low-resolution signals for both thermal conductivity and bulk density, as a result of the monotonous composition and water content of these diatom oozes.
