A New Lake Sediment Record from North Yolla Bolly Lake (40° N) Reveals Multi-Scale Holocene Hydrologic Variability in Northwest California

This study seeks to create a reconstruction of Holocene hydrologic variability of the Northern Coast Range of California using sediment cores collected from North Yolla Bolly Lake (Tehama County California). North Yolla Bolly (NYBL)Lake is a glacially formed-lake in the Northern Coast Range of California. At 40.2° N latitude, the lake is located at the average latitude of the California (CA) precipitation dipole, which is the leading mode of winter precipitation spatial variability in California (Wise 2010). As a result NYBL is well-situated for examining changes in the average position and strength of the CA precipitation dipole over the Holocene. In order to develop a record of Holocene Hydrologic variability, a multi indicator methodology was followed. The methods include: cm-scale magnetic susceptibility, organic and carbonate content via loss-on-ignition, grain size determination, C(org):N(total) ratios, and sub-cm scale XRF. Age control is based on AMS dates (n=15) taken from macroscopic organic material such as conifer needles, seeds, or charcoal. For this part of the project we focus on the interval between 10-2 kcal BP. Based on these data the Holocene is characterized by a wet (i.e. deep lake) early-to-mid Holocene (11.7-4.2 kcal BP) with a shift to drier (i.e. shallow eutrophic lake) during the late-Holocene (4.2-2 kcal BP). Superimposed on this millennial scale changes are variations in precipitation-related runoff as inferred from sand content, with intervals of major precipitation events (i.e., above average sand content) recorded at between 10-9.1, 8.3-8.28, 6.9-6.7, 5.3-5.2, 4.8-4.78, 4.3-4.0, 3.49-3.46, and 2.46-2.23 kcal BP. Conversely, there are several intervals of notable below-average runoff between 10.08-10.04, 9-8.5, 8.26-6.97, 6.5-5.5, 5.03-4.9, 4.73-4.33, 3.99-3.6, 3.42-2.49, and 2.2-2.03 kcal BP. Our interpretations will be compared to other hydrologic reconstructions from CA both to the north and south, such as Lake Elsinore (33.6° N), Lower Bear Lake (34.2° N), Silver Lake (35.3° N), Tulare Lake (36.0° N), Barley Lake (39.5° N), and Sanger Lake (41.9° N). Potential climatic forcings driving the inferred hydrologic changes are also examined, such as Milankovitch forcings, Pacific Ocean SSTs, and North Atlantic Meridional Overturning Circulation.