EFFECT OF DEEP-SEA SEDIMENTARY CALCITE PRESERVATION ON ATMOSPHERIC CO2 CONCENTRATION

DURING the last glaciation, the atmospheric carbon dioxide concentrati on was about 30% less than the Holocene pre-industrial value1. Althoug h this change is thought to originate in oceanic processes2, the mecha nism is still unclear. On timescales of thousands of years, the pH of the ocean (and hence the atmospheric CO2 concentration) is determined by a steady-state balance between the supply rate of calcium carbonate to the ocean from terrestrial weathering, and the alteration and remo val of carbonate by burial in sediments2-4 . Degradation of organic ca rbon in sediments promotes the dissolution of calcium carbonate in sed imentary pore water5,6, so that a change in the relative rates at whic h organic carbon and calcium carbonate are deposited on the sea floor should drive a compensating change in ocean pH. Here we use a model th at combines ocean circulation, carbon cycling and other sedimentary pr ocesses to explore the relationship between deep-sea-sediment chemistr y and atmospheric CO2 concentration. When we include organic-carbon-dr iven dissolution in our model, a 40% decrease in the calcite depositio n rate is enough to decrease the atmospheric CO2 Concentration to the glacial value.