9617860 Schrag Previous work by the PI has shown that vertical profiles of the oxygen isotope ratio in sediment porewaters reflect past changes in ocean bottom water and can be used to separated the effects of water composition and temperature upon isotopic signatures in marine carbonates. Preliminary results suggest that bottom waters and tropical sea surface temperatures during the last glacial period were significantly colder than at present. The project will analyze oxygen and hydrogen isotopes and C1 in sediment porewaters from a global array sites to confirm the preliminary findings and test for regional differences. Porewater diffusion models will be developed further, and some initial attempts will be made at applying the results to ocean circulation models.