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Remobilization of crustal carbon may dominate volcanic arc emissions

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Science  21 Jul 2017:
Vol. 357, Issue 6348, pp. 290-294
DOI: 10.1126/science.aan5049

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Volcanoes find a new carbon platform

The geological carbon cycle assumes that carbon is emitted by volcanic eruptions and removed through various forms of burial. Mason et al. found that not all volcanic eruptions have the same source for carbon in their volcanic gas. Arc volcanic activity appears to harvest carbon from old carbonate platforms, which results in a massive difference in the isotopic signature of the carbon emitted during eruption. This discovery requires revision of the global carbon cycle, decreasing the amount of organic carbon believed to be being buried.

Science, this issue p. 290

Abstract

The flux of carbon into and out of Earth’s surface environment has implications for Earth’s climate and habitability. We compiled a global data set for carbon and helium isotopes from volcanic arcs and demonstrated that the carbon isotope composition of mean global volcanic gas is considerably heavier, at –3.8 to –4.6 per mil (‰), than the canonical mid-ocean ridge basalt value of –6.0‰. The largest volcanic emitters outgas carbon with higher δ13C and are located in mature continental arcs that have accreted carbonate platforms, indicating that reworking of crustal limestone is an important source of volcanic carbon. The fractional burial of organic carbon is lower than traditionally determined from a global carbon isotope mass balance and may have varied over geological time, modulated by supercontinent formation and breakup.

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