Carbon Exchange Between the Mantle and the Crust, and its Effect Upon the Atmosphere: Today Compared to Archean Time

  1. E.T. Sundquist and
  2. W.S. Broecker
  1. David J. Des Marais

Published Online: 18 MAR 2013

DOI: 10.1029/GM032p0602

The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present

The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present

How to Cite

Des Marais, D. J. (1985) Carbon Exchange Between the Mantle and the Crust, and its Effect Upon the Atmosphere: Today Compared to Archean Time, in The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present (eds E.T. Sundquist and W.S. Broecker), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM032p0602

Author Information

  1. NASA Ames Research Center, Moffett Field, California 94035

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1985

ISBN Information

Print ISBN: 9780875900605

Online ISBN: 9781118664322

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Keywords:

  • Carbon cycle (Biogeochemistry)—Congresses;
  • Atmospheric carbon dioxide—Congresses;
  • Geological time—Congresses;
  • Paleothermometry—Congresses;
  • Geology, Stratigraphic—Congresses

Summary

Over geologic time scales of tens of millions to billions of years, atmospheric CO2 levels are influenced by the exchange of carbon between the earth's surface and the mantle. Estimates of the mid-ocean ridge mantle carbon flux can be made by estimating concentration ratios of carbon to helium in hydrothermal fluids and tholeiitic glasses and by multiplying these by the oceanic primordial 3He flux. The estimated ranges of carbon fluxes for the earth today and 3 b.y. ago are 1×1012 to 8×1012 moles yr−1 and 3×1012 to 48×1012 moles yr−1, respectively. These fluxes are comparable in magnitude to the present-day flux estimated for carbonate metamorphism, 6×1012 moles yr−1. A net carbon flux from the mantle of 10×1012 moles yr−1 would require less than 700 m.y. to generate the present-day crustal carbon inventory. Given present-day geothermal gradients, carbonate sediments can be at least partly subducted into the mantle. Perhaps between 3 and 50 percent of the sedimentary carbon presently transported by the lithospheric plates to subduction zones will eventually be injected into the upper mantle. A hotter upper mantle 3 b.y. ago would have made this injection process less efficient. During the late Archean, the earth's crustal carbon inventory very likely equaled or even exceeded the present crustal inventory. This circumstance, together with the likelihood that the land area at that time was considerably less than it is today, suggests that 3 b.y. ago the atmosphere contained at least two orders of magnitude more CO2 than it does today.