INORGANIC GEOCHEMISTRY

The interstitial water (IW) sampling program at Sites 1110, 1111, 1112, and 1113 was limited because of extremely difficult coring conditions and concomitant poor core recovery. A total of eight IW samples was obtained from these sites. We collected four samples at Site 1110 from the first two sections of Core 180-1110B-1H, three from Site 1111, a single sample from the mudline core at Site 1112, and none from Site 1113.

Results and Discussion

The IW was analyzed for salinity, pH, alkalinity, major cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) and anions (Cl^-, SO₄^2-), SiO₂, NH₄⁺, Sr²⁺, and Li⁺. Results of shipboard inorganic chemical analyses are presented in Table T11. No trend is evident in the IW constituents from Hole 1110B, except possibly for a depletion in Li⁺ from seawater concentrations (27 µM) to a range of ~14.7-20.1 µM, with the lowest value observed at 2.95 mbsf. Variations of other parameters are within analytical error.

The IW samples were recovered from deeper sediments (69-127 mbsf) at Site 1111, and significant deviations from seawater concentrations are observed. These include elevated alkalinities, slightly elevated Na⁺ and Cl^- concentrations, an increasingly substantial SO₄^2- and Ca²⁺ depletion with depth, and variable but depleted Li⁺ concentrations.

Insufficient data are available to permit a reliable interpretation of the results at Sites 1110 and 1112. Although only very limited data exist for IW from sediments at Site 1111, the increase in alkalinity and decrease in dissolved SO₄^2- with depth are consistent with bacterial decomposition of organic matter. The depleted Li⁺, Ca²⁺, and Mg²⁺ concentrations also suggest diagenetic reactions, possibly involving biogenic silica and carbonates and alteration of volcanic minerals.