While most agree that the glacial to interglacial CO2 changes in atmospheric CO2 content have been driven by alterations in the ocean's biogeochemical cycling, the exact mechanism by which this was accomplished remains unclear. Candidate scenarios can be divided into two groups i.e., those which involve only the upper ocean (Martin's iron hypothesis, my nutrient hypothesis, the Harvardton Bear polar nutrient hypothesis) and those which involve the entire ocean (Berger's coral reef hypothesis, Archer's respiration CO2 hypothesis, Boyle's nutrient deepening hypothesis). A distinction between these two groups could be made were it possible to reconstruct the CO3= ion concentration in the deep glacial ocean. This paper will summarize the progress in our quest to make such a reconstruction.