The atmospheric CO₂ of the Last Glacial Maximum (LGM) was approximately 30% less than the preanthopogenic value of 280 ppmv. Numerous hypotheses have been proposed to explain this shift in atmospheric CO₂ levels. Most scientists working in this field would agree that this change has its origins in the marine realm, though the mechanism is hotly debated. It is also agreed that the mechanism that causes the reduction in atmospheric CO₂ content has something to do with lower accumulation rates of CaCO₃ in the shallow and the deep sea. Two of the favoured mechanisms are the Coral Reef Hypothesis which points to reduced amounts of "reefal" carbonate during the glacials compared with interglacials and simply changing the ratio of organic carbon to carbonate carbon burial in pelagic regions. The Coral Reef Hypothesis has the advantage that it is potentially fast, with a possible sea level response, but mass balance constraints indicate this can not be the whole story. The other mechanism, we will call the "Archer Hypothesis" is feasible but has no obvious mechanism to "turn on" and "turn off" productivity. Areas such as the Southern Ocean were obvious candidates to such variation but total productivity appears to have shifted but not changed dramatically on this time scale.

On the Scott Plateau we have found very clear evidence of decreasing oceanic productivity from the LGM through the climate transition to Stage 1. We would like to present a new model which links these changes in productivity with the onset and strength of the South East Asian Monsoon. There is mounting evidence that the fresh water flux into the South China Sea and the Indonesian region in general was comparatively low during the LGM resulting in higher salinities in the whole Australasian region through the equatorial eastern Indian Ocean. Today a freshwater "cap" acts to reduce any potential for vertical mixing and hence diminishing the chances of higher productivity in the area . We are proposing that this "cap" is directly related to the strength of the South East Asian monsoon and as the SEA monsoon gained strength during the deglacial, productivity in the Indonesian Archipelago and eastern Indian Ocean declined to its present state. AMS C14 dates from the South China Sea and the Scott Plateau show the establishment of the full monsoon and the final reduction in productivity correlate perfectly. Given the strength of the SEA monsoon has an obvious link with the warming of the Asian continent (presumably Milankovitch driven warming), this model would provide a strong link between the climate of the largest continent, oceanic productivity over a wide area of the planet, and hence the mysterious synchronicity of atmospheric pCO₂ change and Milankovitch cyclicity.