『Abstract
A model sensitivity study is performed in order to explore the
impact of the development of thick weathering profiles in the
equatorial area on the geological evolution of climate. Long term
climatic evolution is driven by the balance existing between solid
Earth degassing and continental silicate weathering. The CO2 consumption through continental silicate weathering
is here calculated as a function of climate, based on the correlation
existing with mean annual continental runoff for large drainage
basins. These correlations appear to be dependent on the climatic
regime: under mid-latitude temperate climate, the silicate weathering
is 5 times more sensitive to continental runoff than in the warm
humid equatorial belt. These correlations emphasize the role of
the thick weathering profiles existing in equatorial area, shielding
the bedrock from further weathering. We use this set of relationships
between runoff and silicate weathering as a function of the geoclimatic
zone, to explore the impact of this shield effect on the Mesozoic
evolution of climate, using the GEOCLIM model. Compared to previous
work, we suggest that atmospheric CO2 was
generally underestimated in the past, evidencing a complex interplay
between the paleogeographic setting, and the shield effect. Particularly,
calculated atmospheric CO2 during the Early-Middle
Jurassic rises up to 1600 ppmv, while it was limited to 700 ppmv
when shield effect was neglected, corresponding to a global warming
of more than 4℃. This study emphasizes the need for the building
up of numerical models describing the growth of the weathering
profiles that can be coupled to vegetation and climate models
to investigate biogeochemical cycle and climate evolution, even
at the geological timescale.
Keywords: Modelling; CO2; Weathering; Mesozoic』
1. Introduction
2. Weathering laws as a function of climate zones
3. Exploring the geological past: the GEOCLIM numerical model
4. Results
4.1. The Early-Middle Jurassic
4.2. The Carnian and Cenomanian
5. Implications and limitations
6. Conclusions
Acknowledgements
References