13. OXYGEN ISOTOPIC COMPOSITION OF INTERSTITIAL WATERS FROM LEG 154: DETERMINATION OF THE TEMPERATURE AND ISOTOPIC COMPOSITION OF THE GLACIAL OCEAN1

Daniel P. Schrag,2 Gretchen Hampt,3 and David W. Murray4

ABSTRACT

Oxygen isotope measurements of interstitial waters from Ocean Drilling Program Leg 154, sampled at high resolution from Sites 925 and 929, are used to reconstruct the oxygen isotopic composition of deep water during the last glacial maximum (LGM). The data from both sites show an increase with depth, predicted by modeling the diffusion of water through the sediment, although only data from Hole 925E are appropriate for calculating the composition of seawater during the LGM. Using a numerical model to simulate diffusion of water in the sediments, we obtained a glacial-interglacial change in the of seawater at Site 925 of 0.8 0.1‰. This implies that the bottom water at Site 925 cooled by approximately 4C during the LGM. Although these data from a single site do not represent a global average, we suggest that the substantial cooling of deep water at Site 925 is consistent with a global average change in the of seawater of 1.0‰. This value is within the limits imposed by the freezing point of seawater and is more consistent with estimates of the of continental ice during the glacial maximum. In addition, a lower contribution from ice volume to the change in of planktonic foraminifers allows for 1-2 additional cooling in the tropics during the LGM, partially reconciling the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from Barbados corals and terrestrial climate proxies.

1Shackleton, N.J., Curry, W.B., Richter, C., and Bralower, T.J. (Eds.), 1997. Proc. ODP, Sci. Results, 154: College Station, TX (Ocean Drilling Program).
2Department of Geological and Geophysical Sciences, Princeton University, Princeton, NJ 08544-1003, U.S.A. schrag@geo.princeton.edu
3Institute of Marine Sciences, University of California at Santa Cruz, Santa Cruz, CA 95064, U.S.A.
4Department of Geological Sciences, Brown University, Providence, RI 02912, U.S.A.