We squeezed 20 whole-round core samples for interstitial water from Site 1101 (Table T14). Two samples were taken from each of the first six cores in Hole 1101A, except Core 178-1101A-5H, for which recovery was low. One sample was taken from each of the next six cores and from every third core thereafter. Chloride concentrations increase slightly (1.8%) in the upper 50 mbsf and decrease gradually by a similar amount at greater depths (Fig. F22) but show no obvious signs of mixing between waters of different origin; therefore, any stronger trends seen in profiles of other dissolved constituents should reflect chemical reaction processes.

The interstitial water chemistry profiles at Site 1101 (Fig. F22) closely resemble those of the upper 250 mbsf at Sites 1095 and 1096. This probably reflects the strong similarity in sedimentation rates (5-10 cm/k.y.) and organic carbon contents (<0.4 wt%) among the three rise sites (see "Sedimentation Rates" and "Organic Geochemistry,"  "Sedimentation Rates" and "Organic Geochemistry", both in the "Site 1095" chapter; and "Sedimentation Rates" and "Organic Geochemistry", both in the "Site 1096" chapter). At Site 1101, dissolved manganese increases sharply with depth to a maximum concentration (172 µM) at 12 mbsf. This gradient defines the zone of Mn oxide reduction and suboxic diagenesis. Directly below this zone, beginning at 25 mbsf, dissolved sulfate and manganese decrease steadily with depth as a result of sulfate reduction and accompanying precipitation of sulfide minerals. Sulfate decreases to zero and manganese reaches a minimum concentration (15 µM) at 130 mbsf, where measurable concentrations of methane and ethane first arise (see "Organic Geochemistry", Fig. F20).

Other indicators of organic matter decay, such as alkalinity, ammonium, and phosphate, all increase with depth in the upper sediment column (Fig. F22). Alkalinity and ammonium both reach maximum values (8.0 mM and 1.6 mM, respectively) at the bottom of the hole and probably continue to increase at greater depths, as seen at Sites 1095 and 1096. Unlike alkalinity and ammonium, dissolved phosphate increases to a maximum (>30 µM) at only 10 mbsf, then decreases sharply between 10 and 50 mbsf and remains relatively constant (2-6 µM) at greater depths. Dissolved fluoride also decreases sharply in the upper 50 mbsf and remains relatively constant (8-10 µM) at greater depths (Fig. F22). We again infer, as at Sites 1095 and 1096, that authigenic apatite begins to precipitate in the sulfate reduction zone and continues with depth until the interstitial water chemistry reaches equilibrium 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 carbonate phases, and diagenesis of clay and feldspar minerals, probably influence the chemical composition of interstitial water at Site 1101 (Fig. F22). Dissolved silica concentrations remain high (0.5 mM) throughout the hole and reach the solubility limit of opal-A (~1.0 mM; Kastner et al., 1977) at 150 mbsf, near the top of lithostratigraphic Unit III (see "Lithostratigraphy"). We infer that biogenic opal dissolves principally between 0 and 150 mbsf and the interstitial water becomes saturated with respect to silica in Unit III.

Overall, dissolved calcium increases significantly to a maximum value (15 mM) in the upper 50 mbsf, then decreases to a minimum (9 mM) at 130 mbsf, near the base of the sulfate reduction zone. Below this zone, calcium increases again toward a maximum (12 mM) at the bottom of the hole. Magnesium and potassium decrease steadily with depth by a total of 40%-50% of their initial seawater values, whereas strontium concentrations remain essentially unchanged from that of seawater (90 µM) through the upper 50 mbsf, then decrease slightly between 50 and 100 mbsf before increasing to a constant, maximum value (100 µM) below the sulfate reduction zone. The increase in dissolved calcium above 50 mbsf could result from either dissolution of carbonate minerals or diagenetic reactions among clay and silicate minerals, and the decrease in calcium at the base of the sulfate reduction zone probably reflects carbonate precipitation. Narrow intervals of carbonate-rich and carbonate-cemented sediment occur in this depth range, but not above (see "Lithostratigraphy"). The slight increase in calcium and strontium in the lower portions of the hole, below the base of lithostratigraphic Unit II (see "Lithostratigraphy"), could result from increased dissolution of carbonate or, more likely, from further diagenetic reactions among clay and silicate minerals. Uptake of magnesium and potassium also probably results from clay mineral diagenesis (cf. Gieskes and Lawrence, 1976; Perry et al., 1976).

Sixteen samples from Site 1101 were analyzed by X-ray diffraction for bulk and clay mineralogy. Twelve of these samples were taken from Core 178-1101A-10H, spanning a 415-cm interval from 77.84 to 81.99 mbsf. This interval contains one of the 19 carbonate-bearing sediment layers in Unit II (see "Lithostratigraphy"). Because of the high carbonate content of some of these 12 samples, all were treated with a buffered acetic acid-sodium acetate solution (see "Inorganic Geochemistry"  in the "Explanatory Notes" chapter). The other four samples were from Cores 178-1101A-17X and 24X in lithostratigraphic Unit III. In each of these cores, a pair of samples was taken to represent alternating sedimentary facies, one of which contained high concentrations of ice-rafted debris (Samples 178-1101A-17X-4, 60-62 cm, and 20X-6, 138-140 cm). All 16 samples were also analyzed for inorganic carbon (see "Organic Geochemistry"  in the "Explanatory Notes" chapter).

Bulk and clay mineralogy of sediments at Site 1101 was similar to that found at Sites 1095 and 1096, except that calcite was also identified in several samples. Site 1101 sediments consist primarily of quartz, feldspar, calcite, and a mixture of clay minerals, including chlorite, illite, and a mixed-layer clay, most likely mixed smectite-illite of varying proportions. Traces of amphibole were also detected in most samples, but at considerably lower abundances than those observed in most samples from Sites 1095 and 1096.

Subtle, but possibly significant, trends in bulk mineralogy occur across the carbonate-bearing layer in Core 178-1101A-10H. Calcite peak intensities show a broad maximum from 80 to 81 mbsf (Table T2), consistent with peak carbonate concentrations of 23% measured in this interval. Samples in this interval also have the highest abundances of chlorite and plagioclase relative to quartz, and distinct trends in clay mineralogy (Table T15) occur across this layer. Chlorite abundances, as illustrated by ratios of chlorite/illite and chlorite/mixed-layer clay peak intensities (Fig. F23), are lower by about a factor of two within the carbonate-bearing interval. Sediment within this interval also has the highest chlorite/quartz ratios and thus a relatively high abundance of all clay minerals, relative to other detrital phases.

The greatest variability among clay mineral assemblages in sediment samples from the rise sites (1095, 1096, and 1101) occurs between alternating sedimentary facies, rather than as a function of age or burial depth. For example, in the aforementioned carbonate-rich interglacial interval of Core 178-1101A-10H (Fig. F23) and other rise sediments of inferred interglacial origin, a clear trend exists toward lower chlorite and higher illite and mixed-layer clay abundances, as illustrated in a ternary plot of the relative abundances of these three clays among all samples analyzed (Fig. F24). Rise sediments from glacial intervals cluster strongly near the chlorite end of this diagram and most closely resemble the tills and glacial marine deposits from Site 1097, on the shelf.

Clearly, sediments from the local shelf area represent the probable source of clays deposited on the rise during glacial intervals. Clays deposited during interglacials must have a more complex origin that reflects either a different source area or some sort of physical or chemical sorting during transport. We suggest that depositional mechanisms similar to those described for Quaternary deposition on the slope in the eastern Weddell Sea (Grobe and Makensen, 1992) may play an important role here. During glacial intervals, lower sea level causes ice shelves to remain grounded almost to the continental shelf edge and enables them to deliver sediment more directly to the slope; from there, it can more easily reach the rise as turbidites or contourites. During interglacials, higher sea level moves the grounding line well shoreward of the shelf break, ice sheets deposit much of their sediment load on the shelf, and ice rafting plays an increased role in sedimentation on the continental rise.