UCLA

Chemical weathering of bedrock plays a central role in regulating Earth’s biogeochemical cycles and atmospheric CO2. However, how dust weathering rates contribute to the total weathering budget remains poorly known. Here, we address this question by testing a hypothesis that continental weathering of dust could possibly account for a substantial proportion of the total silicate weathering budget estimated from dissolved chemical loads in rivers. To accomplish this, we calculated a mass balance of atmospheric general-circulation-model estimates of dust deposition (elemental inputs to the land surface) and measurements of riverine dissolved load (elemental outputs) for 44 rivers from around the globe. We first estimated an upper bound of dust contribution to total weathering. Then, we used a steady-state weathering model of shallow weathering to estimate the proportions of dust and rock weathering. Our results show that the magnitude and spatial distribution of dust deposition can account for a substantial amount of silicate-derived measured dissolved chemical flux in rivers. The predicted fractions of Si and silicate-derived Ca + Mg flux that are produced by dust weathering are both independently 41%, which represent substantial components of total Si and silicate-derived Ca + Mg weathering fluxes. According to these weathering proportions, rock and dust contributions could be similar during both modern and Last Glacial Maximum periods. While our results do not rule out the long-held view that rock weathering in soil dominates continental weathering fluxes, they also do not rule out a scenario in which dust accounts for a substantial fraction of observed global dissolved loads. Our results also highlight the need to better understand the dynamics of dust deposition and subsequent weathering when assessing regional and global weathering impacts on biogeochemical cycling and long-term climate change.