A sink- or a source-driven carbon cycle at the geological time scale? Relative importance of palaeogeography versus solid earth degassing rate in the Phanerozoic climatic evolution
A sink- or a source-driven carbon cycle at the geological time scale? Relative importance of palaeogeography versus solid earth degassing rate in the Phanerozoic climatic evolution (in Advances in paleogeography, G. Meinhold (prefacer))
Geological Magazine (February 2019) 156 (2): 355-365
The Phanerozoic evolution of the atmospheric CO (sub 2) level is controlled by the fluxes entering or leaving the exospheric system. In this contribution, we focus on the role played by the palaeogeographic configuration on the efficiency of the CO (sub 2) sink by continental silicate weathering, and on the impact of the magmatic degassing of CO (sub 2) . We use the spatially resolved numerical model GEOCLIM to compute the response of the silicate weathering and atmospheric CO (sub 2) to continental drift for 22 time slices of the Phanerozoic. Regarding the CO (sub 2) released by the magmatic activity, we reconstruct several Phanerozoic histories of this flux, based on published indices. Again using the GEOCLIM model, we calculate the CO (sub 2) evolution for each degassing scenario. We show that the palaeogeographic setting is a main driver of the climate from 540 Ma to about the beginning of the Jurassic, with the noticeable exception of the Late Palaeozoic ice age. Regarding the role of the magmatic degassing, the various reconstructions do not converge towards a single signal, and thus introduce large uncertainties in the calculated CO (sub 2) level over time. Nevertheless, the continental dispersion, which prevails since the Jurassic, promotes CO (sub 2) consumption by weathering and forces atmospheric CO (sub 2) to stay low. Warm climates of the "middle" Cretaceous and early Cenozoic require enhanced CO (sub 2) degassing by magmatic activity.