Until now, scientists have been unable to measure how much of the heat-trapping greenhouse gas carbon dioxide (CO2) escapes from the Earth’s interior through lava — an important piece of information for determining how much atmospheric CO2 comes from man-made sources instead of natural ones.
Using a new technique that is able to measure the concentration of different elements in incredibly tiny samples of rock, researchers determined for the first time how much CO2 the molten material contains.
“Among other things,” says study researcher Erik Hauri of the Carnegie Institution of Washington’s Department of Terrestrial Magnetism, “it’s now possible to estimate precisely the sources of carbon in the volcanic part of the planet’s carbon cycle.”
Hauri and colleagues published their results in the October 3 Nature.
The researchers analyzed bits of magma entrapped in crystals called olivine from samples collected from the mid-ocean Siqueiros transform fault, which is offset from the East Pacific Rise off of the coast of Mexico.
Some 85% of the world’s volcanoes are located on such mid-ocean rises. Typically CO2 and other volatiles bubble away into the atmosphere as they reach the surface during eruptions and thus elude measurement. The trapped particles of magma that the scientists collected, however, contained the original amount of volatiles because the surrounding crystal prevented volatile loss.
Using a device called an ion microprobe, the researchers determined the abundance of different isotopes, or atomic species, and measured the volatiles present.
They found that other non-volatile elements, notably potassium and niobium, were correlated with the CO2, providing added evidence that the CO2 concentrations are original.
“It’s always eye opening,” says Hauri, “to find quantitative connections between the deep interior of the Earth and the chemistry of the oceans and atmosphere.
I believe that this new technique, applied to other volcanic areas, will help scientists better define how much volcanoes are contributing to the greenhouse effect.”
In addition to helping scientists learn more about the planet’s carbon cycle, the study is also important for advancing our understanding of the convection process of the Earth’s deep mantle, its chemical composition, and the behavior of the overlying crust.
Researchers for this study include Alberto Saal and Charles Langmuir of the Lamont-Doherty Earth Observatory at Columbia University; Michael Perfit of the University of Florida’s Department of Geological Sciences; and Erik Hauri of the Department of Terrestrial Magnetism, Carnegie Institution of Washington.
