We squeezed 22 whole-round core samples for interstitial water at Site 1095 (Table T31). Two samples were taken from each of the first two cores in Hole 1095A, targeting alternating gray barren and brown biogenic lithologies, interpreted respectively as glacial and interglacial sedimentary units. Otherwise, single samples were taken from every third core in Holes 1095A and 1095B, as recovery permitted and regardless of lithology. Interstitial water chemistry did not exhibit any systematic differences in composition between inferred glacial and interglacial intervals, which suggests that diffusion and slow sedimentation suffice to smooth out any possible effects resulting from meter-scale lithologic variability. Chloride concentrations decrease slightly (2.6%) with depth (Fig. F29) but show no obvious signs of mixing between different water masses; therefore, any stronger trends seen in profiles of other dissolved constituents should reflect chemical reaction processes.

The interstitial water chemistry at Site 1095 (Fig. F29) shows clear evidence for active diagenesis of buried organic matter, although the predominantly terrigenous sediment contains only low amounts of organic carbon (<0.4 wt%; see "Organic Geochemistry"). Dissolved manganese increases sharply with depth to a maximum concentration (120 µM) at 25 mbsf, reflecting dissolution of Mn oxides under suboxic conditions. Directly below this zone, dissolved sulfate and manganese decrease steadily with depth as a result of sulfate reduction and accompanying precipitation of sulfide minerals. Manganese reaches a minimum concentration (10 µM) near 160 mbsf, at the base of the sulfate reduction zone, where sulfate decreases to zero and significant concentrations of methane and ethane first arise (see "Organic Geochemistry"; Fig. F30). In addition, other dissolved by-products of organic matter decay, such as alkalinity, ammonium, and phosphate, all increase steadily with depth in the upper sediment column. Alkalinity reaches maximum concentrations (7.0 mM) between 80 and 170 mbsf, then decreases steadily with depth to a minimum concentration (1.2 mM) at the bottom of Hole 1095B, whereas ammonium reaches maximum concentrations (>1250 µM) in a broad zone between 220 and 420 mbsf, then decreases by one-third at greater depths. Unlike alkalinity and ammonium, phosphate reaches maximum concentrations (7.0 µM) between 5 and 25 mbsf, decreases somewhat erratically with depth through the sulfate reduction zone, and maintains a constant concentration (3.0 µM) below. Note that dissolved fluoride decreases sharply between the surface and 100 mbsf and also maintains a constant concentration (8-10 µM) at greater depths. The coincident uptake of phosphate and fluoride by the sediment could reflect precipitation of authigenic apatite, although in disseminated amounts too small to detect, and the constant phosphate and fluoride concentrations at depth could correspond to equilibrium values with respect to this mineral phase (Jahnke et al., 1983; Schuffert et al., 1994).

Other inorganic processes such as dissolution of biogenic silica and carbonate, reprecipitation of authigenic silica and carbonate phases, diagenesis of clay and feldspar minerals, and possibly even reactions with underlying basaltic crust probably influence the chemical composition of interstitial water at Site 1095. Dissolved silica increases exponentially with depth and achieves maximum concentrations of nearly 1.1 mM, or approximately the solubility limit of opal-A (Kastner et al., 1977), in two separate zones from 100 to 200 mbsf and 300 to 400 mbsf (Fig. F29). These zones coincide roughly with sedimentary intervals where siliceous microfossils occur in greatest abundance (see "Biostratigraphy"; Fig. F14). Slightly lower dissolved silica concentrations characterize the interval from 200 to 300 mbsf, and silica decreases again at depths below 400 mbsf. We infer that biogenic opal dissolves principally between 0 and 100 mbsf, with substantial dissolution occurring even in the uppermost meter of sediment because the first interstitial water sample has a relatively high silica concentration (nearly 400 µM) compared to typical deep-ocean values (<200 µM). We also infer that authigenic silica precipitates somewhere below 400 mbsf, and we cannot exclude the possibility that certain silica phases may recrystallize between 100 and 400 mbsf.

In general, dissolved calcium concentrations increase, and dissolved magnesium concentrations decrease downhole throughout all depth intervals at Site 1095 (Fig. F29). Noticeable inflections in the gradients of calcium and magnesium occur at depths of ~160 and 400 mbsf. These inflections suggest the possible existence of specific reaction horizons at these depths and the involvement of multiple processes in controlling the behavior of calcium and magnesium. Possible mechanisms invoked previously to explain similar observations at many other ocean drilling sites include replacement of calcite by dolomite, formation of authigenic smectite and other clay minerals, and alteration of basaltic basement rocks (cf. Lawrence et al., 1975; Gieskes and Lawrence, 1976; Perry et al., 1976). The first potential reaction horizon coincides with the base of the sulfate reduction zone and thus could reflect ongoing dolomite formation because dissolved sulfate can inhibit this process (Baker and Kastner, 1981). Initial smear-slide and X-ray diffraction (XRD) analyses, however, have not revealed any dolomite occurrences at Site 1095. Moreover, the sediments generally contain low amounts (<0.1 wt%) of inorganic carbon (see "Organic Geochemistry," Table T30), such that only small amounts of replacement dolomite could possibly form. Considering the predominantly fine-grained, carbonate-poor, terrigenous nature of the sediment recovered at Site 1095, clay mineral reactions probably exert the strongest influence on the observed calcium and magnesium profiles. The steady decrease of dissolved potassium with depth to near-zero concentration at the bottom of Hole 1095B supports this assessment. Strontium concentrations remain constant at ~90 µM (seawater levels) from 0 to 54 mbsf, then increase steadily to 145 µM by 296 mbsf. This increase suggests that minor dissolution of trace carbonates may occur in this interval. Magnesium concentrations below 400 mbsf would extrapolate to near zero at the inferred basement depth of ~1240 m (see "Seismic Stratigraphy") and thus may represent a diffusion gradient resulting from basalt alteration. Similar extrapolation of the much steeper calcium gradient, however, gives an unlikely concentration of >300 mM at basement. As such, the observed increase in calcium below 400 mbsf must have another cause.

A total of 22 samples were analyzed by XRD for both bulk and clay mineralogy at Site 1095. In five cores, two samples were taken where alternating colors were interpreted as possible barren glacial and biogenic interglacial intervals. Most unpaired samples were taken from presumed glacial intervals. All samples were found to consist primarily of quartz, feldspar, and a mixture of clay minerals. The clays consist of chlorite, illite, and a poorly defined phase with a broad and variable diffraction peak between 6º and 9º 2 that shifted after glycolation (Fig. F31). This phase is tentatively identified as a mixed-layer clay, most likely mixed smectite-illite in varying proportions. Traces of amphibole were also detected in all samples.

The relative abundances of quartz and feldspar, as measured by the ratio of their principal diffraction peaks, remain nearly constant among all samples, but clay mineral abundances vary significantly. In bulk-sediment samples, the 3.19-Å plagioclase diffraction peak ranges consistently between 30% and 45% of the height of the 3.34-Å quartz peak (Table T32). Considerable variability among the clays, however, is demonstrated by the widely varying intensity of the 7-Å chlorite peak. This appears to be a real feature of the mineral abundances, not an artifact of sample preparation, because bulk samples with low chlorite/quartz intensity ratios also have low relative intensities of chlorite in their clay-sized fractions (Table T33). Relative abundances of the three clay minerals are illustrated in Figure F32. Chlorite/illite values vary by a factor of four, with the highest values generally occurring below 128 mbsf. Mixed-layer/illite ratios also vary by a factor of four but show no obvious trend with depth. Chlorite/mixed-layer clay ratios show the greatest degree of variability, with the lowest values generally obtained for biogenic-rich samples from presumed interglacial intervals (see "Lithostratigraphy"). Thus, the greatest variability among clays may occur between alternating sedimentary facies instead of as a function of age or burial depth.

Trace-element concentrations were measured by X-ray fluorescence on splits of the 22 bulk-sediment samples analyzed by X-ray diffraction (Table T34). Most of the measured elements exhibit peak concentrations in the uppermost 50 mbsf, typically between 40 and 100 mbsf, and then concentrations decrease by 20% to 30% with depth. For example, Rb concentrations exceed 100 ppm in the uppermost 50 mbsf but average about 85 ppm from 90 to 500 mbsf. The generally similar patterns observed for Nb, Zr, Y, Zn, Rb, Ni, Cr, and Ce could reflect greater dilution with depth by quartz or biogenic opal, but available data suggest otherwise. Bulk-sediment XRD analyses show a tendency toward lower quartz concentrations with depth (Table T32), and sedimentological analyses (see "Lithostratigraphy") show a distinct decrease in preservation of biogenic opal with depth.

Barium exhibits a similar decrease in concentration with depth, except for three samples with distinctly high concentrations from the interglacial intervals at 5, 18, and 28 mbsf (1400, 970, and 880 ppm Ba, respectively). These interglacial intervals contain 60% to 100% more barium than corresponding glacial intervals from the same cores. Sediments can concentrate barium from seawater during decomposition of organic matter (Dymond et al., 1992), and elevated barium in interglacial intervals probably reflects increased biogenic productivity in the surface water at Site 1095. Note, however, that no barium peak occurs with the interglacial interval at 128 mbsf because barite dissolves readily in anoxic sediments, and a diagenetic barium front should occur at the base of the sulfate reduction zone (Brumsack and Gieskes, 1983; von Breymann et al., 1990). More-detailed analyses of barium in these sediments could prove useful in characterizing productivity cycles of the Pleistocene.