Variations in Calcite Dissolution Fluxes in the Equatorial Atlantic and Pacific and Evaluation of Carbonate Dissolution Due to Oxidation of Corg

To explain the glacial drop of atmospheric CO 2 it is necessary to understand the conditions for CaCO3 dissolution in the oceans. We measured high resolution profiles of 23~ normalized carbonate in pairs of cores from the Ceara Rise in the Western equatorial Atlantic and from the Ontong Java Plateau in the Western equatorial Pacific. In each case one core (GeoB 1523-1 in the Atlantic and RNDB 74P in the Pacific) is located at a depth above the lysocline and the other core (EW9209 1JPC in the Atlantic and ERDC 127P in the Pacific) at a depth below the lysocline. We then reconstructed (i) the dissolution of CaCO3 due to variations of the depth of the lysocline and (ii) the depth of the sedimentary lysocline during the last 250 kyrs. In the Atlantic we deduced an increase of the lysocline-induced carbonate dissolution during the glacials and even during some of the cooler interglacial substages. The correlation to the Southern Ocean deep water carbonate preservation index (SOPI) (Howard and Prell, 1994) suggests that during the glacials and during the glacial substages of isotope marine isotope stage five (MIS 5) a reduction in the production of NADW and/or an enhanced northern penetration of AABW occurred. On the Ontong Java Plateau we found a dissolution peak at the onset of MIS 6, as well as enhanced lysoclineinduced dissolution in MIS 5 and at the end of the MIS 4. 'Excess' carbonate dissolution takes place at all times on the seafloor even at depths lying above the calcite saturation horizon (Emerson and Bender, 1981). Dissolution has at least two causes. The first one arises from the geochemical environment (e.g. the CO 2concentration in the water column) bathing the sediments. The other one is due to the oxidation of organic matter in the sediments, as proposed by Archer and Maier-Reimer (1994). We evaluated total excess carbonate dissolution in the same way as done by Broecker and Sanyal (1997). In the Atlantic total excess CaCO3 dissolu-