Journal ArticleDOI
The carbonate-silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100 million years
TLDR
In this article, 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 3/from the ocean; removal of Mg from the ocean via volcanic-seawater reaction; and the metamorphic-magmatic decarbonAbstract:
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 mymore » 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.« lessread more
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Journal ArticleDOI
Global silicate weathering and CO2 consumption rates deduced from the chemistry of large rivers
TL;DR: In this article, newly compiled data on the 60 largest rivers of the world are used to calculate the contribution of main lithologies, rain and atmosphere to river dissolved loads, and the relationship between the chemical weathering rates of silicates and the possible controlling parameters are explored.
Journal ArticleDOI
87Sr/86Sr, δ13C and δ18O evolution of Phanerozoic seawater
Ján Veizer,Ján Veizer,Davin Ala,Karem Azmy,Peter Bruckschen,Dieter Buhl,Frank Bruhn,Frank Bruhn,Giles A.F. Carden,Giles A.F. Carden,Andreas Diener,Stefan Ebneth,Yves Goddéris,Yves Goddéris,Torsten Jasper,Christoph Korte,Frank Pawellek,Olaf G. Podlaha,Olaf G. Podlaha,Harald Strauss +19 more
TL;DR: In this article, a total of 2128 calcitic and phosphatic shells, mainly brachiopods with some conodonts and belemnites, were measured for their δ 18 O, δ 13 C and 87 Sr / 86 S values.
Journal ArticleDOI
Tectonic forcing of late Cenozoic climate
TL;DR: In particular, tectonically driven increases in chemical weathering may have resulted in a decrease of atmospheric C02 concentration over the past 40 Myr as discussed by the authors. But this was not shown to be the case for the uplift of the Tibetan plateau and positive feedbacks initiated by this event.
Journal ArticleDOI
Atmospheric carbon dioxide concentrations over the past 60 million years
TL;DR: The boron-isotope ratios of ancient planktonic foraminifer shells are used to estimate the pH of surface-layer sea water throughout the past 60 million years, which can be used to reconstruct atmospheric CO2 concentrations.
Journal ArticleDOI
Large igneous provinces: crustal structure, dimensions, and external consequences
Millard F. Coffin,Olav Eldholm +1 more
TL;DR: In this article, the authors compile all known in situ LIPs younger than 250 Ma and analyze dimensions, crustal structures, ages, and emplacement rates of representatives of the three major LIP categories: Ontong Java and Kerguelen-Broken Ridge oceanic plateaus, North Atlantic volcanic passive margins, and Deccan and Columbia River continental flood basalts Crustal thickness ranges from 20 to 40 km, and the lower crust is characterized by high (70-76 km s?1) compressional wave velocities.