(Table 1) Pore water isotopes from DSDP Hole 74-525B, with respect to the Vienna-SMOW standard

During the coring of Hole 525B with the hydraulic piston corer, a number of sediment samples were squeezed and the pore waters retained for stable isotope study. Both 18O/16O and D/H ratios were determined on the same samples. Within the limits of experimental error the measurements are consistent with the variations resulting from evaporation-precipitation processes; there is no evidence that diagenetic processes in the sediment affected the isotopic composition of the waters, which therefore reflect changes in the isotopic composition of the ocean during the Cenozoic. The data are consistent with the hypothesis that a change of about 0.9 per mil (18O/16O) occurred during the middle Miocene, reflecting the growth of the Antarctic ice sheet at that time.