SPATIAL MODELING SUGGESTS ACCRETED ARC SEDIMENTS ARE A MAJOR SOURCE OF JUVENILE STRONTIUM TO THE OCEAN

The weathering of rocks is a critical process driving global carbon cycling and long-term climate stabilization. The trace element Strontium (Sr) is a powerful tracer of such processes. Dendritic network models have proven valuable in predicting variation in [Sr] concentrations and isotope ratios (87Sr/86Sr) across large river systems. These models also support inference about sources and processes controlling Sr fluxes from such systems, although this capacity has not been exploited in previous work. Here, we apply these methods to model strontium [Sr] and ⁸⁷Sr/⁸⁶Sr values of a large river draining accreted volcanic arc terranes of the northern Cordillera of North America. The [Sr] and ⁸⁷Sr/⁸⁶Sr river models have excellent fit to observations with RMSE=0.05: R²=0.67 and RMSE=0.0003: R²=0.87, respectively. The results reveal that mixed siliciclastic sedimentary units dominate the Sr weathering flux within these systems. Extrapolation using global arc sediment distributions suggests such units could source ~15% of the modern riverine Sr flux, constituting a major source of juvenile Sr to the ocean. Because the weathering of arc sediments lags arc growth and may persist over 100s of millions of years, we suggest that the preservation and accretion of mixed siliciclastic units formed in these settings should be considered when scaling arc weathering contributions through geologic time. Contributions from such sediments could amplify and/or smooth the arc-derived rock weathering and 87Sr/86Sr flux over long timescales, altering interpretations of biogeochemical cycles and the silicate weathering feedback.