Chemical weathering of volcanic rocks in the tropics

: Using small scale studies to determine the mechanisms, rates and impacts of perturbations

Abstract

Identifying and quantifying deep critical zone (CZ) weathering mechanisms is crucial to understanding the landscape evolution of the Earth’s surface and the
development/regulation of the CZ as a whole (Buss et al., 2008; 2013; Dosseto et al., 2012; Moore et al., 2014; 2015; 2017). Weathering along deep CZ rock fractures likely controls the solute weathering flux to the hydrosphere (Chapela Lara et al., 2017; Kurtz et al., 2011; Schopka and Derry, 2012; White et al., 1998) and the flux of nutrients to the subsurface biosphere (Buss et al., 2005; 2010) in humid tropical catchments with very high weathering rates. Chemical weathering is one of the primary rate-limiting steps of the global geochemical cycle as a whole (Barth, 1961). In this regard, chemical weathering also exerts a major control on the global carbon cycle, regulating atmospheric CO2 over geologic timescales (Berner et al., 1983; Walker et al., 1981); therefore, controls on deep chemical weathering processes may be critical in terms of
understanding and modelling global climate. However, the relative importance of
chemical weathering in the deep CZ versus that in soils, and the processes that control deep weathering rates are still poorly understood (Anderson and Dietrich, 2001; Buss et al., 2005; 2008; 2010; Tipper et al., 2006).

This research examined the weathering of volcanic rocks in the tropics and determined that oxidative weathering is the key mechanism driving weathering deep in the subsurface CZ. By conducting weathering studies on a grain-scale and using U-series isotope data as a time constraint, mineral specific weathering rates were calculated, which converge with those determined experimentally. Comparison with weathering rates calculated on different timescales, spatial scales and lithologies provided useful insights into the key weathering mechanisms that drive chemical weathering in the tropics.

Date of Award	14 Nov 2017
Original language	English
Awarding Institution	The University of Bristol
Sponsors	Natural Environment Research Council
Supervisor	David Sherman (Supervisor) & Heather L Buss (Supervisor)