Carbonate-silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100 million years
A computer model has been constructed that considers the effects on the CO/sub 2/ level of the atmosphere, and the Ca, Mg, and HCO/sub 3/ levels of the ocean, of the following processes: weathering on the continents of calcite, dolomite, and calcium-and-magnesium-containing silicates; biogenic precipitation and removal of CaCO/sub 3/ from the ocean; removal of Mg from the ocean via volcanic-seawater reaction; and the metamorphic-magmatic decarbonation of calcite and dolomite (and resulting CO/sub 2/ degassing) as a consequence of plate subduction. Assuming steady state, values for fluxes to and from the atmosphere and oceans are first derived for the modern ocean-atmosphere system. Then the consequences of perturbing steady state are examined by deriving rate expressions for all transfer reactions. These rate expressions are constructed so as to reflect changes over the past 100 my. Results indicate that the CO/sub 2/ content of the atmosphere is highly sensitive to changes in seafloor spreading rate and continental land area, and, to a much lesser extent, to changes in the relative masses of calcite and dolomite. Consideration of a number of alternative seafloor spreading rate formulations shows that in all cases a several-fold higher CO/sub 2/ level for the Cretaceous atmosphere (65-100 my BP) is obtained via the model. Assuming that CO/sub 2/ level and surface air temperature are positively correlated via an atmospheric greenhouse model, they authors predict Cretaceous paleotemperatures which are in rough general agreement with independent published data. Consequently, their results point to plate tectonics, as it affects both metamorphic-magmatic decarbonation and changes in continental land area, as a major control of world climate.
- Research Organization:
- Yale Univ., New Haven, CT
- OSTI ID:
- 6582171
- Journal Information:
- Am. J. Sci.; (United States), Vol. 283:7
- Country of Publication:
- United States
- Language:
- English
Similar Records
Quantifying melt production and degassing rate at mid-ocean ridges from global mantle convection models with plate motion history
Ocean drilling program: Recent results and future drilling plans
Related Subjects
54 ENVIRONMENTAL SCIENCES
CARBON DIOXIDE
ATMOSPHERIC CHEMISTRY
CARBONATES
MINERAL CYCLING
SILICATES
BIOGEOCHEMISTRY
CALCIUM
CLIMATES
GEOCHEMISTRY
MAGNESIUM
MASS BALANCE
MATHEMATICAL MODELS
METAMORPHIC ROCKS
OCEANOGRAPHY
PLATE TECTONICS
SEA-FLOOR SPREADING
SUBDUCTION ZONES
WEATHERING
ALKALINE EARTH METALS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMISTRY
ELEMENTS
METALS
OXIDES
OXYGEN COMPOUNDS
ROCKS
SILICON COMPOUNDS
TECTONICS
580400* - Geochemistry- (-1989)
500200 - Environment
Atmospheric- Chemicals Monitoring & Transport- (-1989)