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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.

The time-averaged shear-wave velocity of the upper 30 m of the crust (Vs30) is the primary parameter used to predict local ground-motion amplification. When measurement-based methods for determining Vs30 are not available, proxy-based prediction methods are employed instead. The principally used proxy for Vs30 prediction is based on topographic slope, although there have been developments in hybrid slope-geology proxies in recent years. While slope exerts a first-order control on Vs30, there are still considerable deviations between measured Vs30 and predicted Vs30 from the slope proxy, especially in rock sites. In this study, we compiled 218 sites of measured Vs30 in southern California to examine whether the use of high-resolution DEMs or combined topographic metrics of slope, curvature, relief, and distance to the San Andreas Fault can produce better predictions of Vs30. We find that positive residuals, or faster-than-predicted Vs30 from the slope proxy, tend to lie in valley landforms for rock sites. Our results indicate that Vs30 is best predicted with the single metric of slope calculated from a 30 m resolution DEM smoothed over a radius of 900 m. However, Vs30 is also well-estimated using a multivariable model combining slope calculated from a 30 arc-second DEM with curvature calculated smoothed over radii of 700 m and 900 m from a 30 m DEM. The influence of curvature on Vs30 may be a result of bedrock weathering processes, which predict thicker weathered zones beneath ridgetops and thinner weathered zones beneath valleys. Therefore, ridgetops are expected to correspond with thicker slow-velocity zones, while valleys are expected to correspond with thinner slow-velocity zones.