Ten cores contain successions of planktonic foraminiferal assemblages and sedimentary components that record late Quaternary climatic changes in the western equatorial Atlantic Ocean. The climatic cooling that began at the end of the last interglaciation (X zone) and continued throughout the last glaciation (Y zone) led to the sequential disappearance of tropical Globorotalia menardii flexuosa, Globoquadrina hexagona, and Pulleniatina obliquiloculata and the incursion of cool-water Globoquadrina dutertrei, Globorotalia truncatulinoides, G. inflata, and Globigerina bulloides. Despite a twofold increase in cool equatorial species, a tropical climate prevailed throughout the last glaciation. Paleotemperature estimates derived by factor analysis and regression techniques indicate only a small (0.1° to 3.6°C) difference between glacial and postglacial winter temperatures. The coldest sea-surface temperatures occurred at about 73,000 B.P. Concurrently, calcareous remains underwent extensive dissolution, which is reflected in the cores by CaCO3 and coarse-fraction minimums, excessive fragmentation of planktonic foraminiferal shells, absence of pteropods, and an increase in the ratio of benthic to planktonic foraminifera. Faster water-mass circulation during the early part of the last glaciation as compared to the Holocene Epoch is postulated to account for the increased dissolution. Sea-level lowering (approximately 100 m) during the last glaciation and most of the last interglaciation allowed South American rivers to discharge large quantities of terrigenous sediment, which was continuously transported to the continental rise and abyssal plains by gravity-controlled sediment flows. Sea-level rise during the Holocene Epoch shut off the terrigenous-sediment supply to the deep sea, and the continental rise and abyssal plains became a regime of pelagic sedimentation. Prior to the Holocene Epoch, the supply of terrigenous sediment was shut off only for a brief period at the beginning of the last interglaciation. This indicates that a warm (interglacial) period similar to the Holocene Epoch occurred at the beginning of the last glacial-interglacial cycle. Comparison of the timing of calcium-carbonate fluctuations of the cores with the timing of stadial-interstadial periods inferred from the continental stratigraphy of the eastern Great Lakes region reveals an excellent correlation. Interstadial (warm) periods correlate with carbonate maximums, whereas stadial (cold) periods correlate with carbonate minimums.