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 1092. Color reflectance and resistivity were measured on the working half of all split APC cores using the Oregon State University Split Core Analysis Track (OSU-SCAT) (see "Explanatory Notes" chapter). 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 T14 and Figure F16 summarize the physical properties measurements performed at Site 1092.
All physical properties measured at Site 1092 generally covary. As with previous Leg 177 sites, downhole variations in physical properties are controlled largely by changes in the proportion of carbonate vs. siliceous sedimentary components. GRA bulk densities and discrete-sample bulk densities generally agree very well (Fig. F17). Porosity determined gravimetrically on discrete samples (moisture and density [MAD] method) and sediment resistivity show the expected inverse relationship. Low porosities (high resistivities) are associated with intervals of high carbonate content. As was observed at Site 1091, carbonate-rich intervals exhibit bright reflectance with little divergence between the blue, red, or near-infrared bands. In contrast, diatom-rich intervals exhibit a greater contrast between blue and red reflectance. In Figure F16 reflectance in the blue band (450-550 nm) is shown for all holes at Site 1092. In Hole 1092A, between 65 and 105 mcd, reflectance values were approximately 5% lower on average than in Holes 1092B-1092D. The reason for this has been attributed to an insufficient number of calibration points in this interval. Correction of these data may be possible.
In the upper 35 mcd of Site 1092, physical properties exhibit rhythmic variability related to alternation between diatom-rich and carbonate-rich layers. In the upper 20 mcd, there is cyclicity with a period of ~2 m. Between 20 and 35 mcd, the period of cyclicity increases to ~4 m (Fig. F18), probably as a result of increased sedimentation rates in this interval (see "Chronostratigraphy"). Increased sedimentation rates are consistent with the trends in bulk density and magnetic susceptibility, both of which increase below 35 mcd.
At 35 mcd, the large amplitude alternations between siliceous and carbonate dominance end, followed by a transition zone between 35 and 50 mcd where a carbonate-dominated lithology begins (see "Lithostratigraphy"). This transition is clearly visible in the suite of physical properties measurements shown in Figure F18, especially in the red/blue values where, after an initial sudden decrease, values gradually approach 1.0 (high carbonate content) by 50 mcd.
Magnetic susceptibility increases in the interval between 49 and 59 mcd. This would suggest an increase in terrigenous content that may have resulted from decreased sedimentation rates and/or increased terrigenous influx. Mud content determined by smear-slide analysis is low (see "Lithostratigraphy") and can, therefore, not be linked to the magnetic susceptibility. In fact, alternations between finer grained foraminifer/nannofossil layers and coarse foraminifer-rich layers (see "Lithostratigraphy"), in conjunction with the low mud content, may suggest some winnowing in this interval. The cores contain numerous large dropstones in this interval (see "Lithostratigraphy"), which are most likely the cause of the increased magnetic susceptibility.
Between 60 and 110 mcd, there is progressively less downhole variation in the suite of measured physical properties. Below ~110 mcd, density is ~1.8 g/cm3. Reflectance and resistivity also increase (porosity decreases), corresponding to the increase in carbonate content in the same depth interval (see "Geochemistry"; "Lithostratigraphy"). Below 110 mcd, downhole variations in physical properties are of much lower amplitude than above this depth. This is especially true of bulk density values, which are very uniform between 110 and 190 mcd.
Near the base of the section, around 188 mcd, there is a gap in the record resulting from incomplete recovery. The last two cores (177-1092A-19H and 20H) show a clear change in physical properties (Figs. F16, F19), and biostratigraphic evidence suggests a hiatus around 190 mcd (see "Chronostratigraphy"). GRA bulk density drops to ~1.7 g/cm3, porosity increases, and magnetic susceptibility increases notably. Smear-slide analysis (see "Lithostratigraphy") indicates higher foraminifer content relative to nannofossils, which can explain the decrease in density and lower porosity. The increase in magnetic susceptibility requires either an increase in terrigenous material or a change in its mineralogical composition, which may be indicated by the higher clay mineral to quartz plus feldspar content of the lithogenic fraction (see "Lithostratigraphy"). The red/blue reflectance values increase in Cores 177-1092-19H and 20H (Fig. F19), indicating that a noncarbonate component becomes significant. The rarity of diatoms, however, cannot be the cause. Instead, the redder color may be related to iron oxides, and this is consistent with the greater magnetic susceptibility.
Figure F20 shows P-wave velocities measured with the PWS3 velocimeter and P-wave logger (PWL). PWS3 velocities generally reflect the trends in bulk density described above. Higher velocities were observed in the upper 65 mcd of Site 1092 than at any previous Leg 177 site. This is presumably a result of the higher concentration of ice-rafted terrigenous grains. Below 65 mcd, where IRD is much less common (see "Lithostratigraphy"), velocities are more similar to those of other carbonate-rich sediments from other Leg 177 sites. The 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 (Fig. F20). The reason for this was a defective threshold adjustment knob, resulting in the inaccurate auto-picking of P-wave traveltimes by the PWL. The problem was corrected during the first few cores logged at Site 1093.
A total of 91 thermal conductivity measurements were taken from Holes 1092A-1092C (Table T15, also in ASCII format in the TABLES directory). The values range between 0.69 and 1.23 W/(m·K), the widest range measured among Sites 1088-1092. The distinct bimodal distribution of values (Fig. F21) reflects a sudden decrease of porosity from ~80% to ~60%, as well as a change in lithology, in the depth interval between 40 and 60 mcd. The lower values, with an average between 0.7and 0.8 W/(m·K), represent the diatom ooze intervals within Subunit IA (see "Lithostratigraphy"). The higher values, clustering between 1.1 and 1.2 W/(m·K), characterize the calcareous ooze of Subunit IB.