Tectonic control of continental weathering, atmospheric CO2, and climate over Phanerozoic times

Abstract

We explore the role of continental drift on the Phanerozoic evolution of the carbon cycle and climate with the GEOCLIM numerical model. GEOCLIM couples a 3D-climate model, a global dynamic vegetation model and a mathematical description of the chemical weathering of the continental surfaces. Twenty-one timeslices covering the whole Phanerozoic are simulated, allowing the calculation of the climate and steady-state atmospheric CO2 for each of these timeslices. We show that continental drift is a first order control parameter of the geological carbon cycle and climate. The salient features are the following: (1) the Paleozoic environment is characterized by a long term CO2 decrease; (2) the Late Permian-Late Triassic period displays very high CO2 levels; (3) atmospheric CO2 is decreasing since the Middle Cretaceous. All these features are driven by the drift of the continents and the subsequent modulation of the water cycle and weathering rates. Furthermore, continental drift imprints the long term evolution of the tropical seawater surface temperatures with periodical oscillations characterized by a frequency of about 120 Myr, in agreement with available data. Finally, we emphasize a discrepancy existing between the climate reconstructions from the most recent apatite δ18O data and the CO2 inferred from proxies. Reconstructed CO2 levels from proxies are often unrealistically low for the distant geological past.