The calcite isyocline as a constraint on glacial/interglacial low-latitude production changes

We investigate the response of the calcite lysocline to changes in the export production of the low-latitude surface ocean (the combined equatorial, tropical, and subtroical regions). We employ different CaCO₃ throughput schemes in a time-dependent ocean carbon cycle model to separate the CaCO₃ production/iysocline balance from the other components of the model response and to estimate the effect of dissolution driven by organic matter decomposition in surface sediments. With this model, we carry out three experiments based on a previous hypotheses for the cause of glacial/interglacial atmospheric CO₂ variations: (1) a simple increase in low-latitude production, (2) a decrease in its CaCO₂/organic carbon rain ratio, and (3) an increase in the depth of organic carbon regeneration. None of these changes, when taken alone, can lower atmospheric CO₂ to glacial levels without violating observations of the glacial iysocline depth. If a low-latitude production increase were accompanied by a decrease in the CaCO₃/organic carbon ratio ratio, then these simultaneous changes could lower atmospheric CO₂ to observed glacial levels without causing a significant change in the ocean-average depth of the iysocline. However, even with these simultaneous changes, the required increase in production is 50% or more of the modern rate of production.