12,500 YEARS OF HYDROLOGIC VARIABILITY RECORDED IN SEDIMENTS FROM TULE LAKE, CA

Tule Lake is a small landslide-formed lake (1340 m AMSL) located in Potter Valley – 67 km east of Fort Bragg, CA. As of summer 2018, Tule Lake did not contain standing water and was covered with various marsh grasses and tules. However, there is evidence for standing water in the past via Google Earth historical images and stranded logs at the lake’s outlet (presently 2-3 m above the lake surface). A 3.69 m Russian core was extracted (TLRC18-1) from the central basin of Tule Lake in summer 2018. The core was opened, described, and photographed in the field and transported back to Cal State Fullerton for analysis. The sediment is characterized by a brown, homogenous organic mud from the surface to 2.67 m. From 2.67 – 3.69 m, the sediment is characterized by brown to light brown, organic-rich mud with occasional laminations. Distinct grey layers occur at 2.82, 3.08-3.10, and 3.51-3.66 m. The core was sub-sampled at 1 cm contiguous intervals for a variety of analyses, including: water content, bulk density, magnetic susceptibility, LOI 550° C (percent total organic matter), LOI 950° C (percent total carbonate), and grain size. Age control is based on 7 x AMS ¹⁴C dates determined on discrete organic materials. ²¹⁰Pb and ¹³⁷Cs constrain the past 200 years. Data analyses are in progress. However, the project’s objective is to reconstruct hydrologic variability in the region and determine the drivers of its hydrologic variability. We are interested specifically in examining the behavior of the California precipitation dipole (Wise, 2010) over the Holocene through comparisons with existing hydrologic reconstructions north and south of Tule Lake.