Role of increased marine silica input on paleo‐pCO₂ levels

Changing the supply of silica to the ocean may alter p CO 2 levels. The increase in dust delivered to the ocean during glacial times increased the availability of silica for biological uptake. The increased silica levels shifted species composition: Diatom populations increased and coccolith populations decreased. Decreasing the population of coccoliths decreased the flux of calcite to the sediments, which, in turn, lowered p CO 2 levels enough to explain the glacial‐interglacial p CO 2 transition. Furthermore, the contemporary increase in dust delivered to the ocean's mixed layer may be removing significant amounts of carbon dioxide from the atmosphere at present. To set the stage, this silica hypothesis is compared with the iron fertilization and nitrogen fixation hypotheses.