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Abstract

DURING the last glaciation, the atmospheric carbon dioxide concentration was about 30 less than the Holocene pre-industrial value1. Although this change is thought to originate in oceanic processes2, the mechanism is still unclear. On timescales of thousands of years, the pH of the ocean (and hence the atmospheric COconcentration) is determined by a steady-state balance between the supply rate of calcium carbonate to the ocean from terrestrial weathering, and the alteration and removal of carbonate by burial in sediments2-4. Degradation of organic carbon in sediments promotes the dissolution of calcium carbonate in sedimentary pore water 5,6, so that a change in the relative rates at which organic carbon and calcium carbonate are deposited on the sea floor should drive a compensating change in ocean pH. Here we use a model that combines ocean circulation, carbon cycling and other sedimentary processes to explore the relationship between deep-sea-sediment chemistry and atmospheric COconcentration. When we include organic-carbon-driven dissolution in our model, a 40 decrease in the calcite deposition rate is enough to decrease the atmospheric COconcentration to the glacial value. © 1994 Nature Publishing Group.