Abstract
It has been hypothesized that predecessors of today's bryophytes significantly increased global chemical weathering in the Late Ordovician, thus reducing atmospheric CO2 concentration and contributing to climate cooling and an interval of glaciations. Studies that try to quantify the enhancement of weathering by non-vascular vegetation, however, are usually limited to small areas and low numbers of species, which hampers extrapolating to the global scale and to past climatic conditions. Here we present a spatially explicit modelling approach to simulate global weathering by non-vascular vegetation in the Late Ordovician. We estimate a potential global weathering flux of 2.8 (km3 rock) yr−1, defined here as volume of primary minerals affected by chemical transformation. This is around three times larger than today's global chemical weathering flux. Moreover, we find that simulated weathering is highly sensitive to atmospheric CO2 concentration. This implies a strong negative feedback between weathering by non-vascular vegetation and Ordovician climate.
Highlights
It has been hypothesized that predecessors of today’s bryophytes significantly increased global chemical weathering in the Late Ordovician, reducing atmospheric CO2 concentration and contributing to climate cooling and an interval of glaciations
We present a complementary approach, which derives chemical weathering by lichens and bryophytes in the Ordovician from their net primary productivity (NPP), which is calculated by a novel, global process-based non-vascular vegetation model that simulates multiple, physiologically different, artificial species[20]
The estimates are obtained from a baseline simulation of the nonvascular vegetation model, run at eight preindustrial atmospheric level(PAL; 1 PAL 1⁄4 280 p.p.m.) of atmospheric CO2 and 14% of atmospheric O2 for 600 years to reach steady state, with an initial number of 300 species
Summary
It has been hypothesized that predecessors of today’s bryophytes significantly increased global chemical weathering in the Late Ordovician, reducing atmospheric CO2 concentration and contributing to climate cooling and an interval of glaciations. Lichens and bryophytes have been shown to significantly enhance weathering of the surface rocks on which they grow compared with abiotic conditions[1,2,3]. On the basis of field observations, it has been concluded that the emergence of large vascular plants with rooting systems in the Devonian led to a large increase in global chemical weathering rates[14]. Including this effect in a global geochemical model[14] causes a decrease in atmospheric CO2 based on the well-known silicate-weathering feedback[15]
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