Composition and circulation of bottom water in the western Atlantic Ocean during the last glacial, based on pore-water analyses from the Amazon Fan

Pore waters from very rapidly deposited continental margin sediments may pr ovide a record of changes in the isotopic and chemical composition of seawa ter over time. Measurements made on pore waters extracted from sediments dr illed at five sites during Ocean Drilling Program Leg 155 on the Amazon Fan show systematic increases in delta(18)O with depth from similar to 0.1 par ts per thousand in surface sediments to similar to 0.4 parts per thousand i n glacial-age sediments from below about 40 m below sea floor. This relativ ely small glacial-interglacial difference reflects both the overall increas e in delta(18)O of seawater during the last glacial and a change in bottom- water source to the area from North Atlantic Deep Water at present to relat ively O-18 depleted Antarctic Bottom Water during the last glacial. When co mbined with delta(18)O analyses of benthic foraminifers, the pore-water dat a indicate a glacial-interglatial temperature change of about 4 degrees C.