The role of CaCO3 compensation in the glacial to interglacial atmospheric CO2 change

Abstract

The only viable explanations put forth to date for the glacial to interglacial change in atmospheric CO2 content suggested from measurements of the CO2 content of gas extracted from ice cores involve changes in the ocean's nutrient cycles. Any nutrient change capable of creating the 80 µatm changes in atmosphere CO2 pressure suggested by the ice core results also creates significant change in the deep ocean's CO3= content. Evidence from deep sea sediments suggests that these CO3= changes are compensated on the time scale of a few thousand years by reductions or increases in amount of CaCO3 accumulating in deep sea sediments. This compensation process has two important consequences. First, it significantly increases the magnitude of the CO2 change per unit of nutrient forcing. Second, it causes a delay in the response of the atmospheric CO2 change. While the first of these consequences is a boon to those seeking to explain the CO2 change, the second may prove to be a curse. The ice core CO2 record shows no evidence of a significant lag between the CO2 response and the polar warming. In any case it is important that we improve our knowledge of the magnitude and timing of the CaCO3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes.