A Revised Model of Global Silicate Weathering Considering the Influence of Vegetation Cover on Erosion Rate
Abstract. Silicate weathering, which is of great importance regulating global carbon cycle, has been found to be affected by complicate factors including climate, tectonics, vegetation, and etc. However, the exact transfer function between these factors and silicate weathering rate is still unclear, leading to large model-data discrepancies of the CO2 consumption associated with silicate weathering. Here we propose a simple parameterization for the influence of vegetation cover on erosion rate to improve the model-data comparison based on a state-of-the-art silicate weathering model. We found out that the current weathering model tends to overestimate the silicate weathering fluxes in the tropical region, which can hardly be explained by either the uncertainties in climate and geomorphological conditions or the optimization of model parameters. We show that such an overestimation of tropic weathering rate can be rectified significantly by considering the shielding effect of vegetation cover on the erosion rate of the leached soils considering that the geographic distribution of such soils is coincident with regions with the highest leaf area index (LAI). We propose that the heavy vegetation in the tropical region likely slows down the erosion rate, much more so than thought before, through reducing extreme stream flow in response to precipitation. The silicate weathering model thus revised gives a smaller global weathering flux which is arguably more consistent with the observed value and the recently reconstructed global outgassing, both of which are subject to uncertainties. The model is also easily applicable to the deep-time Earth to investigate the influence of land plant on global biogeochemical cycle.
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