A coupled geomorphic and geochemical model for testing the dominant controls on chemical weathering rates in eroding landscapes
Lead Research Organisation:
University of Edinburgh
Department Name: Sch of Geosciences
Abstract
A vigorous debate has emerged over the primary driver of chemical weathering rates. One hypothesis states that because weathering reactions are driven by pore water chemistry, climate, specifically rainfall, controls chemical weathering rates. In contrast, another hypothesis states that chemical weathering is driven by the supply of 'fresh' minerals to the weathering zone, and the dominant driver of chemical weathering is physical erosion. Studies evaluating the relative importance of these two hypotheses have had limited success. On the one hand, detailed geochemical studies that focus on pore water chemistry make no provision for geomorphic processes such as physical denudation and lateral sediment transport. Such studies cannot yield insights into the mechanisms that drive increased chemical weathering rates from eroding landscapes. This is because chemical weathering rates are spatially heterogeneous (as a century of soil science can attest) and eroding materials continuously move laterally through parts of the landscape with varying chemical weathering rates. On the other hand, studies focusing on weathering rates driven by erosion are largely based on empirical studies of basin wide weathering rates and make no provision for weathering reactions. To truly examine the relative importance of climate and physical erosion on chemical weathering rates, one must account for both weathering reactions and the generation and transport of sediment. In this study the PI proposes, for the first time, to combine a state of the art geochemical model with a detailed geomorphic model. The proposed model will be capable of predicting the coupled geochemical and geomorphic evolution of hillslope soils using both end member chemical weathering hypotheses. To test the model, and the relative importance of the two drivers of chemical weathering, a field site has been identified where the two end member hypothesis predict contrasting spatial distributions of chemical weathering. This field site has a uniquely comprehensive series of both geomorphic and geochemical measurements: at the site measurements exist to independently calibrate the model and compare model results with long term chemical weathering rates and solid state chemistry. Thus, by using a combination of state of the art numerical modelling and an exhaustive geochemical and geomorphic dataset, this project will test if climate (via rainfall and pore water chemistry) or physical erosion rates are dominant in controlling chemical weathering rates in an eroding landscape.
People |
ORCID iD |
Simon Mudd (Principal Investigator) |
Publications
Yoo K
(2011)
Evolution of hillslope soils: The geomorphic theater and the geochemical play
in Applied Geochemistry
Attal M
(2015)
Impact of change in erosion rate and landscape steepness on hillslope and fluvial sediments grain size in the Feather River basin (Sierra Nevada, California)
in Earth Surface Dynamics
Hurst M
(2012)
Using hilltop curvature to derive the spatial distribution of erosion rates
in Journal of Geophysical Research: Earth Surface
Hurst M
(2013)
Influence of lithology on hillslope morphology and response to tectonic forcing in the northern Sierra Nevada of California
in Journal of Geophysical Research: Earth Surface
Mudd S
(2010)
Reservoir theory for studying the geochemical evolution of soils
in Journal of Geophysical Research: Earth Surface
Hurst MD
(2013)
Hillslopes record the growth and decay of landscapes.
in Science (New York, N.Y.)
Description | This research combined a geomorphic with a geochemical model to examine the role played by erosion in chemical weathering of soils. Chemical weathering is a globally relevant to climate because weathering of silicate minerals, which make up much of the Earth's crust, draws down atmospheric CO2. This project examined to what degree enhanced erosion could accelerate chemical weathering, and found that increasing erosion from a slow initial erosion rate could lead to large increases in chemical weathering but at faster erosion rates there were diminishing returns such that at high erosion rates chemical weathering rates are insensitive to changes in erosion rate. In addition the research made progress in quantifying erosion rates from topographic data, and found that ridgetop curvature was an excellent indicator of erosion rate. In the past, topographic slope was frequently used but we showed that this was an imperfect indicator. This will allow better estimation of erosion rates fro topographic data in the future. |
Exploitation Route | These findings could help to establish global budgets for CO2 drawdown due to chemical weathering. |
Sectors | Environment |
Description | This research has not been used outside of academia |
Description | Constraining the topogrpahic signature of erosion rates and processes using high resolution topography |
Amount | $248,314 (USD) |
Funding ID | W911NF-13-1-0478 |
Organisation | US Army Research Lab |
Department | Army Research Office |
Sector | Public |
Country | United States |
Start | 08/2013 |
End | 09/2015 |