Whole-round cores for interstitial water analysis were taken from Hole 1128B at a rate of two samples per section from the upper four cores, one per core down to Core 182-1128B-6H and every other core thereafter, recovery permitting. No samples were taken from Hole 1128C. Samples from Hole 1128D were taken at a rate of one sample every other core, recovery permitting. Samples were analyzed according to the procedures outlined in the "Inorganic Geochemistry" in the "Explanatory Notes" chapter. These data are presented in Table T9 and Figures F21, F22, F23, F24, and F25.
Salinity shows an increase from 34 to 35 at a depth of 11.7 mbsf in Hole 1128B. Below 11.7 mbsf the salinity remains constant to a depth of 236.8 mbsf. Between Cores 182-1128B-26X and 28X, near the base of Hole 1128B, there was a marked drop in salinity from 35 to 32. This decrease is also evident in Hole 1128D, and a salinity of ~32 is maintained to a depth of 434.8 mbsf in Core 182-1128D-22R (Fig. F21). The concentration of Cl- increases from 563 to 571 mM by Core 182-1128B-6H and remains relatively constant (561 and 565 mM) to a depth of 236.8 mbsf. The increase in Cl- and salinity in the upper portion of Hole 1128B is probably related to the increase in seawater salinity that occurred during the last sea-level lowstand (McDuff, 1978), with high-salinity waters characteristic of the last glacial period diffusing downward into older sediments. Between Cores 182-1128B-26X and 28X, the Cl- concentration falls abruptly to 534 mM. Changes in chlorinity are not directly related to variations in salinity in the lower portion of Site 1128 (Fig. F22), implicating controls other than evaporation on the pore-water salinity (see "Discussion").
The concentrations of Mg2+ and K+ decrease with increasing depth, whereas concentrations of Ca2+, Li+, H4SiO40, and Sr2+ increase (Figs. F23, F24; Table T9). The concentration of Mg2+ decreases from a value of 52.1 mM in Core 182-1128B-1H to 42.9 mM in Core 182-1128B-26X at a depth of 236.8 mbsf. Below this depth an abrupt decrease in concentration occurs at the bottom of Hole 1128B and continues in Hole 1128D. This abrupt change between Cores 182-1128B-26X and 28X is also manifested as a decrease in the concentration of K+ and an increase in the concentrations of Ca2+ and Li+ (Fig. F24). The concentration of Sr2+ shows an increase to 117 µM by a depth of 30.7 mbsf and subsequently a gradual increase throughout the remainder of Holes 1128B and 1128D. The concentration of Sr2+ does not appear to change significantly between Cores 182-1128B-26X and 28X. The concentration of H4SiO40 shows a steady rise from the normal bottom-water concentrations to a maximum of 1126 µM at 198.3 mbsf. Exceptions to this increase are three samples in Cores 182-1128B-4H and 5H that all have H4SiO40 concentrations similar to those measured in Core 182-1128B-1H. The most probable explanation for the low H4SiO40 in these samples is that they reflect penetration of bottom water into the formation. However, although slight anomalies were noted in other parameters at this depth (Table T9), none of the other chemical parameters measured are particularly diagnostic of bottom seawater and therefore the origin of the H4SiO40 concentrations in these samples remains enigmatic.
The concentration of SO42- gradually decreases to a value of 21.6 mM in Core 182-1128B-26X. Consistent with the change in several of the other elements, SO42- shows a large decrease in concentration between 236.8 and 253.3 mbsf. The concentration of SO42- decreases to 2.9 mM by the base of Hole 1128D. Although the decrease in SO42- in the lower portion of Hole 1128D is associated with a slight increase in alkalinity, there is no noticeable smell of H2S that might suggest the reduction of SO42- by bacteria. However, the decrease in SO42- is associated with an increase in the concentration of NH4+ (Table T9), indicating that the decrease in the concentration of SO42- was originally linked to the oxidation of organic material. The apparent absence of H2S at the present time could reflect the removal of H2S by diffusion or through the formation of solid iron sulfide phases.
Alkalinity increases to a value of 4.52 mM by a depth of 21.2 mbsf, approximately coincident with the initial increase in Sr2+. Below this depth there is a reduced rate of increase to 236.8 mbsf in Core 182-1128B-26X. At this depth there is an abrupt increase in alkalinity, which is coincident with the changes in other geochemical parameters noted previously. The pH, measured using the punch-in electrode method, showed a consistent decline with depth until 86.1 mbsf in Core 182-1128B-10H, where hardness of the core precluded further use of this technique (Fig. F25). In contrast, pH measured using the normal ODP method (see "Inorganic Geochemistry" in the "Explanatory Notes" chapter) showed a great deal of variability.
Because Sr2+ is added to pore fluids by the recrystallization of biogenic forms of aragonite and calcite (Baker et al., 1982), the low increase in the concentration of Sr2+ with increasing depth at Site 1128 indicates a relatively low rate of carbonate recrystallization. The steepest gradient in Sr2+ occurs in the upper 20-30 mbsf, accompanied by an increase in the concentration of alkalinity and a decrease in the concentration of SO42-. This interval appears to be the most active region of carbonate recrystallization, with reduced carbonate saturation probably being linked to the diagenesis of organic material. Changes in the concentrations of Ca2+, Mg2+, and K+ deeper in Holes 1128B and 1128D are probably a result of clay mineral alteration, rather than the result of diagenetic reactions involving carbonates. Clay mineral diagenesis consumes Mg2+ and K+ and produces Ca2+ (Gieskes, 1973). Perhaps the most significant aspect of the pore-water geochemistry at Site 1128 is the abrupt change in most of the pore-water parameters (except Sr2+) between Cores 182-1128B-26X and 28X. This change is observed near the transition between lithostratigraphic Units II and IV (see "Lithostratigraphy"). Differences in pore-water parameters probably result from the presence of relatively impermeable barriers to vertical diffusion and the existence of a separate hydrological unit in the older sediments. Although no such barriers were recovered during coring, the downhole logs (see "Downhole Measurements") revealed a section between 250 and 280 mbsf that contained numerous relatively impermeable layers, with the potential to act as impediments to vertical movement of ions. The pore fluids in the lower unit, therefore, are being altered by local diagenetic reactions. The products of these reactions are impeded from exchanging with the overlying units. As mentioned above, the salinity and chlorinity are decoupled in this unit (Fig. F22). This arises as a result of the loss of cations and anions through precipitation and adsorption reactions. This hypothesis can be tested by summing the mass of cations and anions and comparing the total with measured salinity. This comparison shows that salinity determined by the two methods agrees within the error of the analytical methods used (see "Inorganic Geochemistry" in the "Explanatory Notes" chapter). The low chlorinity of this unit, however, is probably not a result of diagenesis and may reflect the chlorinity of some continentally derived fluid or the dewatering of clays under compaction.
The sediments at Site 1128 are composed of low-Mg calcite (LMC), quartz, and clay minerals (Fig. F26; Table T10, also in ASCII format). No samples were analyzed above Core 182-1128B-4H. Lithostratigraphic Unit I is composed predominantly of LMC, with the exception of the slumped unit in Cores 182-1128B-7H and 8H that contains high concentrations of clay minerals and quartz (see "Lithostratigraphy"). In contrast, Unit II is composed predominantly of noncarbonate minerals, the main component of which is clay. In Unit IV the main component is quartz.