|Erosion of Deccan Traps determined by river geochemistry: impact on the global climate and the 87Sr/86Sr ratio of seawater|Dessert, C.; Dupre, B.; François, L.M.; Schott, J.; Gaillardet, J.; Chakrapani, G.; Bajpai, S. (2001). Erosion of Deccan Traps determined by river geochemistry: impact on the global climate and the 87Sr/86Sr ratio of seawater. Earth Planet. Sci. Lett. 188(3-4): 459-474. dx.doi.org/10.1016/S0012-821X(01)00317-X
In: Earth and Planetary Science Letters. Elsevier: Amsterdam. ISSN 0012-821X; e-ISSN 1385-013X, meer
erosion; rivers; geochemistry; Sr-87; Sr-86; Deccan Traps; global change;
|Auteurs|| || Top |
- Dessert, C.
- Dupre, B.
- François, L.M.
- Schott, J.
- Gaillardet, J.
- Chakrapani, G.
- Bajpai, S.
The impact of the Deccan Traps on chemical weathering and atmospheric CO2 consumption on Earth is evaluated based on the study of major elements, strontium and 87Sr/86Sr isotopic ratios of the main rivers flowing through the traps, using a numerical model which describes the coupled evolution of the chemical cycles of carbon. alkalinity and strontium and allows one to compute the variations in atmospheric pCO2, mean global temperature and the 87Sr/86Sr isotopic ratio of seawater, in response to Deccan trap emplacement. The results suggest that the rate of chemical weathering of Deccan Traps (21-63 t/km2/yr) and associated atmospheric CO consumption (0.58-2.54 x 106 mol C/km2/yr) are relatively high compared to those linked to other basaltic regions. Our results on the Deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of CO2 consumption during weathering of basalts, according to the relationship:
f = R-f x C(0)exp[-Ea/R(1/T-1/298)]
where f is the specific CO2 consumption rate (mol/km2/yr), R-f is runoff (mm/yr), C-0 is a constant (= 1764 mu mol/l), Ea represents an apparent activation energy for basalt weathering (with a value of 42.3 kJ/mol determined in the present study), R is the gas constant and T is the absolute temperature (K-o). Modelling results show that emplacement and weathering of Deccan Traps basalts played an important role in the geochemical cycles of carbon and strontium. In particular, the traps led to a change in weathering rate of both carbonates and silicates, in carbonate deposition on seafloor, in Sr isotopic composition of the riverine flux and hence a change in marine Sr isotopic composition. As a result, Deccan Traps emplacement was responsible for a strong increase of atmospheric pCO2 by 1050 ppmv followed by a new steady-state pCO2 lower than that in pre-Deccan times by 57 ppmv, implying that pre-industrial atmospheric pCO2 would have been 20% higher in the absence of Deccan basalts. pCO2 evolution was accompanied by a rapid warming of 4°C, followed after 1 Myr by a global cooling of 0.55°C. During the warming phase, continental silicate weathering is increased globally. Since weathering of continental silicate rocks provides radiogenic Sr to the ocean, the model predicts a peak in the 87Sr/86Sr ratio of seawater following the Deccan Traps emplacement. The amplitude and duration of this spike in the Sr isotopic signal are comparable to those observed at the Cretaceous-Tertiary boundary. The results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on Earth.