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Title: Critically evaluating the role of the deep subsurface in the 'chemical weathering thermostat'
Author: Hayes, Nick R.
ISNI:       0000 0004 8500 2805
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2019
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The drawdown of atmospheric CO2 by the chemical weathering of silicate rocks represents one of the primary controls on the long-term climate of the Earth (Walker et al., 1981; Berner et al., 1983). Chemical weathering rates are themselves modulated by climate conditions and atmospheric CO2 concentrations, with this feedback cycle termed the "Chemical Weathering Thermostat". However, the depth at which weathering occurs, and to what extent different parameters affect weathering, is poorly constrained and hinders our ability to investigate the impact of weathering on climate in palaeo settings. This thesis investigated weathering-climate interactions at a range of spatial and temporal scales. Initially, the impact of climate on weathering profile morphology and chemical weathering rates were examined at the profile-scale using geochemical data from granitic field sites in the literature, as well as new analyses from a temperate granitic critical zone. Secondly, Reactive Transport Modelling was used to simulate the response of simple granitic weathering profiles to differing climate regimes and subsurface architecture conditions. Finally, insights from field site investigations and Reactive Transport Modelling were applied to the global scale using a coupled geochemical and climate model, GEOCLIM, to investigate the impact of changing palaeogeography on potential weathering fluxes through the Cretaceous-Eocene period. This thesis identifies a strong hydrological control on chemical weathering rates, supporting the findings of previous studies (Maher, 2010; Godd´eris et al., 2014; Ibarra et al., 2016) and further challenging the concept of global temperatures as a strong control on chemical weathering rates. Furthermore, climate conditions determine the morphology of a weathering profile. Under humid conditions, weathering fronts become sharper and the impact of temperature is amplified. Finally, palaeogeographical configurations have a substantial impact on long-term CO2 concentrations by affecting the distribution of precipitation/runoff and thus chemical weathering rates.
Supervisor: Buss, Heather ; Lunt, Dan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available