The impact of hydroclimate and dam construction on terrigenous detrital sediment composition in a 250-year Santa Barbara Basin record off southern California

The recurrence and magnitude of southern California hydroclimate extremes are poorly resolved due to the relatively short duration (<140 years) of modern instrumental precipitation and stream gauge records. Terrigenous detrital sediments are often used to reconstruct long-term hydroclimate changes as precipitation increases river runoff and sediment transport into nearby basins. Here we assess the potential of elemental and mineralogical sediment composition from Santa Barbara Basin (SBB, California) box core SPR0901-04BC, a ∼250 year record, as a proxy for precipitation and/or river runoff. Additionally we explore the impact of anthropogenic modification of rivers on sediment composition. Potassium and Ti concentrations and kaolinite + chlorite abundances are significantly correlated with regional precipitation. Transfer function modeling demonstrates that precipitation alone predicts Ti concentration variability well, but not clay mineral abundances. However, when dam construction within catchments draining into SBB is included, kaolinite + chlorite abundances can be modeled. We propose kaolinite + chlorite and illite sources in the upper reaches of catchments are trapped behind dams, while smectite sources in lower catchment areas are unimpeded and continue to be deposited in the basin. Linear correlations and model results suggest detrital elemental concentrations are more suitable for precipitation and river runoff reconstruction than clay mineral composition. Correlations observed between sediment composition and precipitation demonstrate the potential for marine sediment proxies to extend weather and climate records beyond the instrumental record, however anthropogenic land use modification, specifically damming, must be considered.