No one cause can be found for the observation that glacial pCO₂ was 80-90 μatm lower than in interglacial periods. Some ideas that have been presented include:

• Ocean circulation models are more diffusive than the modern ocean, underestimating the pCO2 sensitivity to the biological pump
• The Redfield N/P number was different in glacial time.
• Double the inventory of H4SiO4 in the ocean, raising the pH of the deep ocean.
• Cooling in the Southern Ocean at the same time as CO2 is falling is considered as a cause, but is nowhere strong enough to cause the observed drop.
• Increased dust flux in the glacials caused more nitrogen fixation, which allowed a greater CO2 drawdown in surface waters.
• Long residence time of NO3 in ocean explains how CO2 can continue to increase after the dust flux ix zero, and means productivity changes can be global.
• The Glacial Burial Hypothesis
• Glacial bottom waters were possibly much more saline, May have an unsuspected large density
• The glacial deep ocean was more stably stratified than it is today. Geothermal heat would have slowly warmed it from below, destabilizing it, like a discharging capacitor. This injects salt into the upper North Atlantic, kick-starting thermohaline circulation. Reinvigorated circulation warms up Greenland and the North Atlantic.
• Overturnings occur in nature through a positive feedback that involves mid-latitude westerly winds.
• species change in phytoplankton produced only 20-25% Carbonate plus Opal during ice ages vs 90% now.
• Carbon Storage on exposed continental shelves during the glacial-interglacial transition
• The climate instability of glacial times probably resulted from abrupt switches in ocean circulation.