Pore waters from very rapidly deposited continental margin sediments may provide a record of changes in the isotopic and chemical composition of seawater over time. Measurements made on pore waters extracted from sediments drilled at five sites during Ocean Drilling Program Leg 155 on the Amazon Fan show systematic increases in δ18O with depth from ∼0.1‰ in surface sediments to ∼0.4‰ in glacial-age sediments from below about 40 m below sea floor. This relatively small glacial-interglacial difference reflects both the overall increase in δ18O of seawater during the last glacial and a change in bottom-water source to the area from North Atlantic Deep Water at present to relatively 18O depleted Antarctic Bottom Water during the last glacial. When combined with δ18O analyses of benthic foraminifers, the pore-water data indicate a glacial-interglacial temperature change of about 4 °C.

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