『Abstract
Weathering rates of minerals may be limited by the reaction kinetics
of the constitutive minerals or the supply of fresh minerals delivered
to the near surface by denudation. We use a model of denudation
and reaction kinetics to analyze the relative importance of each
in moderating silicate-weathering fluxes in different erosional
environments for different, commonly occurring silicate minerals.
We find that minerals that reside in the near-surface weathering
zone for far longer than the reaction takes to complete, as is
the case with slow denudation, produce weathering fluxes that
respond most strongly to changes in denudation rate. Conversely,
when transit through the weathering zone is rapid relative to
a given mineral's weathering timescale, the weathering responds
most vigorously to changes in the reaction kinetics. Based on
field- and laboratory-measured values of silicate-weathering kinetic
constants, observed weathering zone thicknesses in relation to
denudation rates, and denudation rates inferred from topography,
it appears that fresh mineral supply may play a sub-equal or dominant
role in moderating silicate-weathering fluxes for four mineral
phases considered. If correct, this suggests that the concentration
of atmospheric CO2, which is regulated by
silicate weathering over geologic timescales, may depend on those
factors that control long-term erosion rates across Earth's surface.
Keywords: chemical weathering; landscape evolution; silicate mineral
weathering; geologic carbon cycle』
1. Introduction
2. The model
3. Results
3.1. General model behavior
3.2. Erosion rates versus reaction kinetics
4. Discussion
5. Conclusions
Appendix A. Model parameters used in text
References