Global Warming May Be Delayed By Increase In Ocean Silica

CHESTNUT HILL, MA (6-19-00) -- Increasing amounts of silica in the ocean may be removing large amounts of carbon dioxide from the atmosphere, slowing its overall build-up and delaying the onset of global warming. According to Boston College Geologist Kevin G. Harrison, writing in the June 2000 issue of Paleoceanography, an increase in ocean silica levels also could explain why atmospheric carbon dioxide levels decreased by 30 percent during glacial times, a significant change that has perplexed scientists for decades.

According to Harrison, human activity has doubled the amount of dust delivered to the oceans today. Until now, scientists have been unable to propose an elegant mechanism to link this increase in dust with decreasing atmospheric carbon dioxide. In Paleoceanography, Harrison proposes just such a mechanism: The Silica Hypothesis.

This hypothesis suggests that changing the supply of silica to the ocean may alter pCO2 levels. Some of the silica present in the dust dissolves and becomes available for biological uptake. In glacial times, the increased silica levels shifted species composition, changing the distribution of plankton species. Diatom populations increased and coccolith populations decreased. This shift increased the ability of the ocean to remove carbon dioxide from the atmosphere: decreasing the population of coccoliths decreased the flux of calcite to the sediments, which in turn lowered pCO2 levels.

Harrison's model estimates that a seven-fold increase in dustiness would have lowered carbon dioxide levels from 280 ppm to 200 ppm--enough to explain the observed glacial-interglacial pCO2 transition.

Organic biomarkers in the sedimentary record support Harrison's hypothesis.

Harrison notes that present-day increases in dust level suggest that the same diatom-based mechanism may be at work today, removing significant amounts of carbon dioxide from the atmosphere and slowing the rate of global warming.

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For the full text of this article, entitled "Role of increased marine silica input on paleo-pCO 2 levels," see the June 2000 issue of Paleoceanography, (Vol. 15, No. 3, pp. 292-298).