In his "silica hypothesis," Asst. Prof. Kevin G. Harrison (Geology and Geophysics) has proposed that increases in the level of dust may slow the accumulation of carbon dioxide, and slow the rate of global warming.
Asst. Prof. Kevin G. Harrison (Geology and Geophysics) has identified a mechanism that can drastically alter atmospheric carbon dioxide levels. Presented in a recent issue of the journal Paleoceanography, his "silica hypothesis" suggests that the contemporary increase in dustiness caused by human activity may slow the accumulation of carbon dioxide, and in turn, slow the rate of global warming.
Harrison's hypothesis proposes that variations in the supply of silica to the ocean alters the species composition of phytoplankton. Such shifts, he says, have a large effect on levels of carbon dioxide in the atmosphere.
"Dust," he explained, "contains silica, some of which dissolves and becomes available for biological uptake. Diatoms, for example, use silica to make shells. Increasing the supply of dust - and therefore silica - to the ocean increases diatom populations, which in turn increases the ability of the ocean to remove carbon dioxide from the atmosphere."
Researchers have observed enhanced uptake of atmospheric carbon dioxide in oceanic regions where the dust delivery is greatest, Harrison said.
While fossil fuel combustion and deforestation have increased carbon dioxide levels in the atmosphere by 30 percent in the past 150 years, Harrison said, the rate of this increase has been slower than expected. He believes that the doubling in the amount of dust delivered to the ocean because of human activity may have changed the balance of phytoplankton species in the ocean enough to explain the slower-than-expected increase in atmospheric CO2 levels.
Harrison's silica hypothesis may also explain another mystery that has perplexed scientists for decades. During glacial times, atmospheric carbon dioxide levels were 30 percent lower than during non-glacial times. Harrison thinks that the seven-fold increase in dust observed during glacial times caused this decrease, and notes that organic biomarkers in the marine sediments provide support for this theory.
A review of Harrison's hypothesis in the journal Nature concluded that his research provides a "fresh illustration of how central marine biogeochemistry is in understanding the long-term variation of atmospheric CO2 and of Earth's climate."
Harrison believes that solving the atmospheric puzzle of glacial times is important to the study of global warming today. "The scientific community has little credibility in forecasting future carbon dioxide levels if we are unable to explain this huge carbon dioxide change in the recent geological past," he said.
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