A Global Model of Rock Organic Carbon Weathering and CO2 Emission

Over geological timescales, the oxidation of organic carbon in rocks (OCpetro) is a major source of carbon dioxide (CO2) to the atmosphere, thought to be similar in magnitude to the CO2 emissions from volcanism. We know that erosion is a major control on this flux: OCpetro oxidation increases with erosion, up to and greater than erosion rates of ~ 2 mm yr-1. This contrasts with silicate weathering, where rates are limited by reaction kinetics at high erosion. However, we lack knowledge of where high erosion rates impinge on OC-rich rocks, and whether the erodibility of such rock mean that these are predisposed to very high rates of CO2 release by weathering. Here we use empirical constraints on OCpetro oxidation flux with a spatially explicit global simulation model to explore the environmental controls on OCpetro oxidation. Our model considers the role of erosion and chemical weathering by using a probabilistic approach that is built on catchment-scale 10Be denudation rates, while rhenium-based estimates of oxidative weathering intensity and flux from river catchments around the world are used to constrain patterns in OCpetro oxidation. To constrain major controls on erosion and weathering we use local slopes derived from 90 m SRTM DEM data, monthly averaged MODIS evapotranspiration data, and global precipitation and temperature datasets. We also produce a map of global OCpetro stock by combining global lithological maps with the USGS Rock Geochemical Database, which includes over 167,000 samples for our analysis. We combine the denudation, rock chemistry data and weathering intensity to simulate global OCpetro weathering rates at a 1 km grid scale via a statistical probability ensemble (Monte Carlo). We will present preliminary results of our model compilation, including the effect of lithology on erosion and weathering rates. We identify regions where OCpetro could emit substantial amounts of CO2 and provide a new constraint on a major natural CO2 flux that has not been properly quantified yet.