Unraveling Santa Barbara Basin Lithogenic Sediment Composition and Application to Southern California Quaternary Hydroclimate

Abstract

The demand for fresh water outpaces the supply in southern California. Fresh water resources will become increasingly limited as anthropogenic-forced air temperatures rise, and populations grow. Water management is challenging, as the hydroclimate of southern California is highly erratic, with intervals of drought punctuated by intense rainfall. This rainfall variability is influenced by the strength and position of the North Pacific high pressure system, atmospheric rivers, and the El Niño-Southern Oscillation (ENSO). Understanding the natural hydroclimate variability beyond the instrumental record is critical to meeting water resource management requirements. On the coast of southern California Santa Barbara Basin (SBB) sediments preserve a record of flood deposits and annual rainfall, enabling hydroclimate reconstruction over millennia. In this dissertation, I analyze the natural and anthropogenic influences on SBB detrital sediment. In Chapter 2, I identify the provenance of Holocene flood deposits and Last Glacial Maximum (LGM) sediment in SBB through mineralogical and geochemical comparison to stream-bed sediments collected from adjacent river catchments. The southern slopes of the Santa Ynez and Topatopa Mountains are the primary source of Holocene flood deposits. Detrital sediment deposited during the LGM indicates increased sediment flux from the eastern Santa Ynez Mountain (Southern Slopes) and the Channel Islands, compensating the loss of Santa Clara River input at this time. In Chapter 3, I discern the impact of hydroclimate events and dam construction on SBB sediment composition since ~ A.D. 1760. Modeling results predict kaolinite and Ti content using precipitation, and indicate that Ti can be used as a paleoprecipitation proxy beyond the instrumental record. However, damming impounds sediment and impacts clay mineralogy disproportionately, indicating an anthropogenic impact on SBB sediments. In Chapter 4, I investigate southern California’s natural hydroclimate variability during glacial Termination V (TV, ~430-420 ka) using the siliciclastic elemental paleoprecipitation proxy developed for the annually laminated SBB sediments. Flooding, prolonged droughts, and ENSO variability are captured in the TV paleoprecipitation record, similar to the present. Prolonged droughts are attributed to poleward expansion of the subtropical dry zone during deglaciation. Thus the precipitation patterns characterizing southern California hydroclimate are remarkably persistent through time.