Mantle carbon flux calculated

Abstract

A geochemist at the National Aeronautics and Space Administration (NASA) Ames Research Center (Moffett Field, Calif.) has greatly improved the accuracy of determining oceanic carbon outgassing rates by developing a new technique for extracting carbon dioxide that prevents contamination. David Des Marias burned his rock samples in pure oxygen at 450°C and then 650°C, before melting them at 1200°C to expel the gases. The samples remained in the same apparatus throughout the cleaning and melting, allowing Des Marais to clean the sample while limiting atmospheric contamination. His earlier work with lunar samples had shown that the process was effective, since only minor amounts of carbon were found in those samples after the cleaning.By analyzing samples of glassy ocean ridge tholeiites from the Mid‐Cayman Rise, the East Pacific Rise (21°N), the Mid‐Atlantic Ridge, and the Galapagos Ridge, Des Marais determined the ratio of carbon to 3He in the samples. Then, by relating that ratio to an established rate for total oceanic 3He flux, he calculated a mantle carbon flux of 20–30 million tons of carbon per year. The carbon emitted from the ocean ridges and other undersea volcanic areas represents more than 90% of the global carbon outflow from the mantle. Two other previous estimates of carbon outflow ranged from 0.1 to 10 times his result. Des Marais' finding is considered the most accurate because he was able to accurately measure carbon and 3He without depending on the assumptions made by others that all CO2 comes from volcanos and all the carbon emitted from the mantle has been preserved at the surface.