Fourteen interstitial water samples were gathered from Hole 1083A between 3.2 and 186.6 mbsf. Whole-round samples were sampled at a frequency of one sample per core to 101.1 mbsf and every third core thereafter to total depth (Table 10). Although the total penetration at Site 1083 was less than that at Sites 1081 and 1082, there are interesting similarities and contrasts among these three neighboring sites. In general, the interstitial water chemical trends at Site 1083 are intermediate between those at Sites 1081 and 1082.
Downcore profiles of alkalinity, sulfate, and ammonium (Fig. 11) through the upper ~50 mbsf record the degradation of organic matter. Alkalinity increases to a maximum value of 37 mM at 63 mbsf, and ammonium records the greatest rate of increase through this depth range as well. The concentration of ammonium increases gradually to a broad maximum at ~100 mbsf. Sulfate is completely consumed within the upper 35 mbsf, which is midway between the depth of sulfate depletion at Sites 1081 and 1082.
Concentration profiles of Ca2+, Mg2+, and Sr2+ reflect the competing processes of carbonate dissolution and precipitation (Fig. 12). The concentration profiles of dissolved Ca2+ and Mg2+ are very similar to those observed at Sites 1081 and 1082 and largely reflect effects of carbonate precipitation including dolomitization. Dissolved Sr2+ increases to a maximum of ~500 µM at the bottom of the hole. This concentration is 2–3 times higher than that observed at Sites 1081 and 1082, reflecting the greater availability of biogenic calcite at Site 1083.
Dissolved silica is present in interstitial waters from Site 1083 at concentrations greater than representative bottom-water values (Fig. 13), indicating the dissolution of biogenic opal. Although the concentration of dissolved silica increases with depth, there is no obvious structure to the profile, other than a one-point maximum at Core 175-1083A-9H, a core that has a high abundance of diatoms (see "Biostratigraphy and Sedimentation Rates" section, this chapter). The concentration profile of dissolved silica at Site 1083 is not substantially different from profiles at Sites 1081 and 1082.
Dissolved phosphate concentrations increase with depth because of remineralization of organic matter. The increase closely follows that found at Site 1082, although the maximum value at Site 1083 is significantly less than that at Site 1082 (Fig. 13). Also, the rate of decrease in dissolved phosphate in deeper sediments at Site 1083 is greater than at Site 1082, reflecting a stronger uptake of dissolved phosphate into diagenetic phases.
The concentration of dissolved Na+ increases from seawater values to maximum values at depth (Fig. 14). This distribution of dissolved Na+ is very similar to the distributions at Sites 1081 and 1082. The concentration of dissolved K+ remains essentially unchanged throughout the sequence.
Consistent with the fact that the concentrations of many dissolved constituents at Site 1083 are intermediate to those at Sites 1081 and 1082, the salinity at Site 1083 also has intermediate values (Fig. 15). Concentrations of dissolved Cl– steadily increase to the bottom of the hole.