THE HOLOCENE CALIFORNIA PRECIPITATION DIPOLE TRACKED USING LAKE SEDIMENTS

The position and strength of the California precipitation dipole dictates the amount and distribution of winter precipitation in the western United States. At present, our knowledge of the dipole is limited to a 500-year tree ring reconstruction (Wise, 2016). However, a longer perspective is required to capture the full breath of dipole behavior. The objective of this project is to use a north-south latitudinal transect of existing and new lake sediment records over the Holocene in California to characterize a longer timescale history of the dipole’s position and strength. Since summer 2017, we have collected sediment cores (n = 20) from six lakes in the northern coast range of California. All of the sites are characterized as high elevation, small drainage basins, and a closed basin hydrology. Together, these criteria provide archives that should respond rapidly to changes in precipitation amount and intensity. Using a variety of physical (e.g., grain size), chemical (e.g., C:N ratios), and biological analyses (e.g., pollen and diatoms), we will reconstruct changes in relative lake level, precipitation intensity (via runoff indicators), and vegetation. Each site extends to at least 9,000 years (12,900 max.) based on 121 total AMS C-14 dates obtained on discrete organic materials – additional dates are pending. Our high-density age control is aimed at resolving decadal to multi-decadal hydrologic variability. We will use novel statistical methods to evaluate the similarities and/or differences in the timing of regional hydrologic variability along a north-south CA lake latitudinal transect. Finally, we will assess the drivers (e.g., insolation, Pacific SSTs, AMOC) of past dipole variability as inferred from our lake records.