Is has long been known that the end of an ice age brings about an increase in atmospheric carbon dioxide, but the process by which this happens hasn’t been so clear.
Scientists theorized that meltwater from the northern ice cap may have capped the northern oceans with freshwater, preventing deep saltwater from rising in the north. Instead, the wind patterns and oceans currents changed, bringing deep ocean water to the surface in the south, releasing carbon dioxide into the atmosphere. This is the widely accepted theory that seems to explain how the ocean currents changed to release carbon dioxide sequestered in the deep sea.
What it doesn’t explain, however, is why there are opal formations in the northern seabed that coincide with these same events. The current theory means there would be no opal deposits at all. Researchers from ETH Zurich’s Geological Institute found opal deposits, in a core spanning roughly 550,000 years of geological history, roughly every 100,000 years. The timing of these opal deposits is around the same time as the end of each ice age, exactly when carbon dioxide was being released into the atmosphere. The combination of deep sea silicates and carbon dioxide would have resulted in massive blooms of diatoms.
After the diatoms died off, their microscopic skeletons dissolved as they sank into the ocean, eventually forming deposits of opal. The new theory, coinciding with the finding of these northern opal deposits, suggests that ocean currents simply stopped. Deep sea silicates and carbon dioxide would diffuse vertically and lead to the same diatomic blooms. Still, it is just theory, but it could still explain how carbon dioxide sequestered in the deep sea during the ice age eventually came to be released into the atmosphere.