Placing the 'Fault' on C[O.sub.2].

AuthorCarr, Steve
PositionTHE ENVIRONMENT

In an effort to understand carbon emissions from the Earth's interior and how they affect the atmosphere, scientists at the University of New Mexico and colleagues conducted research to study carbon emissions through fault systems in the East African Rift (EAR).

Carbon dioxide from Earth's interior is thought to be released into the atmosphere mostly via degassing from active volcanoes. C[O.sub.2] also can escape along faults away from active volcanic centers. However, such tectonic degassing is poorly constrained and largely has been unmeasured.

Led by geochemistry Ph.D. student Hyunwoo Lee, the scientists set out to measure diffuse C[O.sub.2] flux from the Magadi-Natron basin in the EAR between Kenya and Tanzania.

"C[O.sub.2] is the main source of the greenhouse effect," says Lee. "Natural carbon emissions come from volcanoes and are derived from magma. Mostly, people have thought the major sources of magmatic emissions have come through active volcanic events. Our research is [an] attempt to quantify magmatic C[O.sub.2] gases from nonvolcanic and continental rift regions."

EAR is the world's largest active continental rift and is comprised through distinct western and eastern sectors. Several active volcanoes emit large volumes of C[O.sub.2], including Nyiragongo in the Congo and Oldoinyo Lengai in Tanzania. Additionally, significant amounts of C[O.sub.2] are stored in large anoxic lakes in this region.

"Widespread continental rifting and super-continent breakup could produce massive, long-term C[O.sub.2] emissions and contribute to prolonged greenhouse conditions like those of the Cretaceous," notes Lee. 'To measure diffuse [CO.sub.2] flux, we used an EGM-4 C[O.sub.2] gas analyzer with a cylindrical accumulation chamber. The gas samples were then diverted from the chamber into pre-evacuated glass vials in order to carry out gas chemistry and carbon isotope analyses in our laboratories."

Additional gas samples collected along fault zones in the Magadi-Natron basin showed an elevated C[O.sub.2] flux and provided further evidence that faults act as permeable pathways facilitating the ascent of deeply-derived C[O.sub.2]. This particular study area represented a conservative 10% of the entire Natron-Magadi region.

The data from all samples then were compared to gas data from the active volcano Oldoinyo Lengai and found to have carbon isotope compositions that indicate a strong magmatic contribution to the observed C[O.sub.2].

James Muirhead...

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