Role of increased marine silica input on paleo-pCO(2) levels

Changing the supply of silica to the ocean may alter pCO(2) levels. The inc rease in dust delivered to the ocean during glacial times increased the ava ilability of silica for biological uptake. The increased silica levels shif ted species composition: Diatom populations increased and coccolith populat ions decreased. Decreasing the population of coccoliths decreased the flux of calcite to the sediments, which, in turn, lowered pCO(2) levels enough t o explain the glacial-interglacial pCO(2) transition. Furthermore, the cont emporary increase in dust delivered to the ocean's mixed layer may be remov ing significant amounts of carbon dioxide from the atmosphere at present. T o set the stage, this silica hypothesis is compared with the iron fertiliza tion and nitrogen fixation hypotheses.