Meteoric beryllium-10 fluxes from soil inventory measurements in the East River watershed, Colorado, USA

Meteoric beryllium-10 ( 10 Be met ) has a wide range of applications as a geochronometer and tracer of geological processes. 10 Be met is produced in the atmosphere by cosmic rays and delivered to Earth's surface primarily via precipitation. 10 Be met is particularly suitable for quantifying surface process rates where use of in situ-produced 10 Be is challenging, such as landscapes with quartz-poor bedrock. However, using 10 Be met for dating and quantifying surface process rates requires constraining depositional fluxes across space and time. Although empirical and physical models for predicting fluxes exist, the predictions can deviate substantially from measured values. Here we quantify 10 Be met flux in the East River watershed in Colorado, USA where precipitation is dominated by snowfall. We measured the 10 Be met inventory in soils on five glacial moraines 13–18 ka in age that span 700 m of elevation and calculated 10 Be met fluxes by dividing each inventory by moraine age. Inheritance-corrected fluxes range from 4.31×10 5 –1.80×10 6 atoms cm −2 yr −1 and fluxes corrected using modeled erosional and desorption losses differ by a factor of 0.3 to 2.1. The predicted fluxes are well correlated with elevation, mean annual precipitation, mean snow depth, and snow water equivalent ( R 2 =0.71 to 0.99). Regression models applied to gridded elevation, precipitation, snow depth, and snow water equivalent data predict watershed-averaged fluxes of 1.1×10 6 –3.8×10 6 atoms cm −2 yr −1 . Predicted fluxes from a published empirical model that estimates fluxes as a function of precipitation were 1.8–3.8 times higher than inheritance-corrected site fluxes, and 1.0 to 6.0 times higher than erosion- and desorption-corrected fluxes calculated using a profile-average desorption model. Fluxes predicted by general circulation models generally fall within the range of our empirically estimated watershed-averaged fluxes, although the degree of agreement depends on the predictor variable and whether inheritance-corrected or erosion- and desorption-corrected fluxes are used. Our results highlight both the importance of factors that drive variability in 10 Be met delivery to soils and how local calibration can improve estimates of 10 Be met flux in mountain watersheds.