Measurements of the CaCO3 content of the CaCO3 size index and of foraminifera weights demonstrate that a prominent dissolution event occurred in the western equatorial Atlantic at the onset of the last glacial period. The decrease in CO3= ion concentration appears to have been too large to be accounted for by the ocean acidification associated with the demise of excess interglacial biomass. Rather, it appears to have been the result of a temporary strengthening of the penetration of the glacial equivalent Antarctic Bottom Water into the Atlantic. The co-occurrence of massive Ethmodiscus rex deposition in the eastern equatorial Atlantic bears witness to a reorganization of circulation in the Atlantic. This reorganization may well reflect a temporary collapse of conveyor circulation at the onset of the last glaciation.