25. GEOCHEMISTRY OF INTERSTITIAL WATERS¹

Joris M. Gieskes,² Dan Schrag,³ Lui-Heung Chan,⁴ Libo Zhang,⁴ and Rick W. Murray⁵

ABSTRACT

This study investigates the distribution of the inorganic constituents in the interstitial waters obtained in drill sites of the Ocean Drilling Program (ODP) Leg 152 in the Irminger Sea and off the east coast of Greenland. These studies are accompanied by detailed analyses of the distribution of the oxygen isotopes of the interstitial waters as well as by the strontium isotope ⁸⁷Sr/⁸⁶Sr ratio of the dissolved strontium in Sites 918 and 919. In the shelf Sites 914–916 and in the basin Site 918 there is evidence for the input of meteoric waters in the deeper parts of the drill holes, probably originating from reservoirs in the underlying basement rocks, which were subaerially deposited in Paleocene time. Strontium isotopic studies indicate several depth horizons where reaction between pore waters and volcanic material alter contemporaneous seawater signatures. All sites show evidence for a substantial input of volcanic material, typically showing considerably enhanced ratios of titanium over aluminum in the sediment. Lithium isotopes, for the first time determined in detail in ODP sites, indicate a complex pattern, suggesting reactions and exchange with the solid phases. The complex pattern will be of interest to future studies of the distribution of this isotopic ratio. Oxygen isotopic studies, in addition to showing evidence for meteoric water inputs at depth, show two other important features: (1) In the upper sediment column higher than present delta¹⁸O(H₂O) values indicate the presence of a predicted glacial maximum in the isotopic composition in seawater; a chloride maximum also typically occurs, but at a depth somewhat different from that of delta¹⁸O(H₂O), mostly because of different diffusive boundary conditions. (2) A minimum in delta¹⁸O(H₂O) occurs at about 250 meters below seafloor (mbsf) in Site 918, a phenomenon not expected from the distribution of the inorganic constituents. Instead of a minimum at about 550 mbsf, where concentration extrema in calcium, magnesium, and chloride imply the involvement of alteration of volcanic ash, no distinct extremum in delta¹⁸O(H₂O) is detected.

¹Saunders, A.D., Larsen, H.C., and Wise, S.W., Jr. (Eds.), 1998. Proc. ODP, Sci. Results,152: College Station, TX (Ocean Drilling Program).
²Scripps Institution of Oceanography, University of California, La Jolla, CA 92093-0215, U.S.A. jgieskes@ucsd.edu
³Department of Geological Sciences, Princeton University, Princeton, NJ 08544, U.S.A.
⁴Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803-4101, U.S.A.
⁵Department of Earth Sciences, Boston University, Boston, MA 02215, U.S.A.