Atmospheric CO 2 consumption by chemical weathering in North America

Abstract

CO 2 consumption by chemical weathering is an integral part of the boundless carbon cycle, whose spatial patterns and controlling factors on continental scale are still not fully understood. A dataset of 338 river catchments throughout North America was used to empirically identify predictors of bicarbonate fluxes by chemical weathering and interpret the underlying controlling factors. Detailed analysis of major ion ratios enables distinction of the contributions of silicate and carbonate weathering and thus quantifying CO 2 consumption. Extrapolation of the identified empirical model equations to North America allows the analysis of the spatial patterns of the CO 2 consumption by chemical weathering. Runoff, lithology and land cover were identified as the major predictors of the riverine bicarbonate fluxes and the associated CO 2 consumption. Other influence factors, e.g. temperature, could not be established in the models. Of the distinguished land cover classes, artificial surfaces, dominated by urban areas, increase bicarbonate fluxes most, followed by shrubs, grasslands, managed lands, and forests. The extrapolation results in an average specific bicarbonate flux of 0.3 Mmol km −2 a −1 by chemical weathering in North America, of which 64% originates from atmospheric CO 2, and 36% from carbonate mineral dissolution. Chemical weathering in North America thus consumes 50 Mt atmospheric CO 2-C per year. About half of that originates from 10% of the area of North America. The estimated strength of individual predictors differs from previous studies. This highlights the need for a globally representative set of regionally calibrated models of CO 2 consumption by chemical weathering, which apply very detailed spatial data to resolve the heterogeneity of earth surface processes.