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Present and past nonanthropogenic CO2 degassing from the solid earth

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Bibliographic Details
Journal Title: Reviews of Geophysics
Authors and Corporations: Kerrick, Derrill M.
In: Reviews of Geophysics, 39, 2001, 4, p. 565-585
Type of Resource: E-Article
Language: English
published:
American Geophysical Union (AGU)
Description
Summary: <jats:p>Global carbon cycle models suggest that CO<jats:sub>2</jats:sub> degassing from the solid Earth has been a primary control of paleoatmospheric CO<jats:sub>2</jats:sub> contents and through the greenhouse effect, of global paleotemperatures. Because such models utilize simplified and indirect assumptions about CO<jats:sub>2</jats:sub> degassing, improved quantification is warranted. Present‐day CO<jats:sub>2</jats:sub> degassing provides a baseline for modeling the global carbon cycle and provides insight into the geologic regimes of paleodegassing. Mid‐ocean ridges (MORs) discharge 1–3 × 10<jats:sup>12</jats:sup> mol/yr of CO<jats:sub>2</jats:sub> and consume ∼3.5 × 10<jats:sup>12</jats:sup> mol/yr of CO<jats:sub>2</jats:sub> by carbonate formation in MOR hydrothermal systems. Excluding MORs as a net source of CO<jats:sub>2</jats:sub> to the atmosphere, the total CO<jats:sub>2</jats:sub> discharge from subaerial volcanism is estimated at ∼2.0–2.5 × 10<jats:sup>12</jats:sup> mol/yr. Because this flux is lower than estimates of the global consumption of atmospheric CO<jats:sub>2</jats:sub> by subaerial silicate weathering, other CO<jats:sub>2</jats:sub> sources are required to balance the global carbon cycle. Nonvolcanic CO<jats:sub>2</jats:sub> degassing (i.e., emission not from the craters or flanks of volcanos), which is prevalent in high heat flow regimes that are primarily located at plate boundaries, could contribute the additional CO<jats:sub>2</jats:sub> that is apparently necessary to balance the global carbon cycle. Oxidation of methane emitted from serpentinization of ultramafics and from thermocatalysis of organic matter provides an additional, albeit unquantified, source of CO<jats:sub>2</jats:sub> to the atmosphere. Magmatic CO<jats:sub>2</jats:sub> degassing was probably a major contributor to global warming during the Cretaceous. Metamorphic CO<jats:sub>2</jats:sub> degassing from regimes of shallow, pluton‐related low‐pressure regional metamorphism may have significantly contributed to global warming during the Cretaceous and Paleocene/Eocene. CO<jats:sub>2</jats:sub> degassing associated with continental rifting of Pangaea may have contributed to the global warming that was initiated in the Jurassic. During the Cretaceous, global warming initiated by CO<jats:sub>2</jats:sub> degassing of flood basalts, and consequent rapid release of large quantities of CH<jats:sub>4</jats:sub> by decomposition of gas hydrates (clathrates), could have caused widespread extinctions of organisms.</jats:p>
Physical Description: 565-585
ISSN: 8755-1209
1944-9208
DOI: 10.1029/2001rg000105