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| Titel |
Modulation of Late Cretaceous and Cenozoic climate by variable drawdown of atmospheric pCO2 from weathering of basaltic provinces on continents drifting through the equatorial humid belt |
| VerfasserIn |
D. V. Kent, G. Muttoni |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 9, no. 2 ; Nr. 9, no. 2 (2013-03-04), S.525-546 |
| Datensatznummer |
250018004
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| Publikation (Nr.) |
 copernicus.org/cp-9-525-2013.pdf |
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| Zusammenfassung |
| The small reservoir of carbon dioxide in the atmosphere (pCO2) that
modulates climate through the greenhouse effect reflects a delicate balance
between large fluxes of sources and sinks. The major long-term source of
CO2 is global outgassing from sea-floor spreading, subduction, hotspot
activity, and metamorphism; the ultimate sink is through weathering of
continental silicates and deposition of carbonates. Most carbon cycle models
are driven by changes in the source flux scaled to variable rates of ocean
floor production, but ocean floor production may not be distinguishable from
being steady since 180 Ma. We evaluate potential changes in sources and
sinks of CO2 for the past 120 Ma in a paleogeographic context. Our new
calculations show that decarbonation of pelagic sediments by Tethyan
subduction contributed only modestly to generally high pCO2 levels from
the Late Cretaceous until the early Eocene, and thus shutdown of this
CO2 source with the collision of India and Asia at the early Eocene climate
optimum at around 50 Ma was inadequate to account for the large and
prolonged decrease in pCO2 that eventually allowed the growth of
significant Antarctic ice sheets by around 34 Ma. Instead, variation in area
of continental basalt terranes in the equatorial humid belt (5° S–5° N)
seems to be a dominant factor controlling how much
CO2 is retained in the atmosphere via the silicate weathering feedback.
The arrival of the highly weatherable Deccan Traps in the equatorial humid
belt at around 50 Ma was decisive in initiating the long-term slide to lower
atmospheric pCO2, which was pushed further down by the emplacement of
the 30 Ma Ethiopian Traps near the equator and the southerly tectonic
extrusion of SE Asia, an arc terrane that presently is estimated to account
for 1/4 of CO2 consumption from all basaltic provinces that account for
~1/3 of the total CO2 consumption by continental
silicate weathering (Dessert et al., 2003). A negative
climate-feedback mechanism that (usually) inhibits the complete collapse of
atmospheric pCO2 is the accelerating formation of thick cation-deficient
soils that retard chemical weathering of the underlying bedrock.
Nevertheless, equatorial climate seems to be relatively insensitive to
pCO2 greenhouse forcing and thus with availability of some rejuvenating
relief as in arc terranes or thick basaltic provinces, silicate weathering
in this venue is not subject to a strong negative feedback, providing an
avenue for ice ages. The safety valve that prevents excessive atmospheric
pCO2 levels is the triggering of silicate weathering of continental
areas and basaltic provinces in the temperate humid belt. Excess organic
carbon burial seems to have played a negligible role in atmospheric
pCO2 over the Late Cretaceous and Cenozoic. |
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