The role of CaCO 3 compensation in the glacial to interglacial atmospheric CO 2 change

The only viable explanations put forth to date for the glacial to interglacial change in atmospheric CO 2 content suggested from measurements of the CO 2 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 CO 2 pressure suggested by the ice core results also creates significant change in the deep ocean's CO 3 = content. Evidence from deep sea sediments suggests that these CO 3 = changes are compensated on the time scale of a few thousand years by reductions or increases in amount of CaCO 3 accumulating in deep sea sediments. This compensation process has two important consequences. First, it significantly increases the magnitude of the CO 2 change per unit of nutrient forcing. Second, it causes a delay in the response of the atmospheric CO 2 change. While the first of these consequences is a boon to those seeking to explain the CO 2 change, the second may prove to be a curse. The ice core CO 2 record shows no evidence of a significant lag between the CO 2 response and the polar warming. In any case it is important that we improve our knowledge of the magnitude and timing of the CaCO 3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes.