A 21,000 YEAR RECORD OF HYDROCLIMATIC VARIABILITY FROM BIG LAKE, CALIFORNIA (NORTHERN CALIFORNIA COAST RANGE)

Our study focuses on Big Lake, located in the Northern Coast Range of California. Big Lake represents a key site for understanding California’s water history due to its position along the north-south California precipitation dipole. BigLRC 19-01, BigLRC19-04, and BigLRC 19-05 were taken along a transect from the lake’s depocenter to nearshore. Discrete organic material was sampled from the cores for radiocarbon dating to create an age model. Core BigLRC19-1 spans 21,000 calendar years before present – an exceptionally long record for a small lake. The following sedimentological analyses were performed at 1 cm contiguous intervals on all three sediment cores: magnetic susceptibility (MagS), grain size (10 size classes), and percent total organic matter (%TOM, loss-on-ignition at 550℃). We used principal component analysis (PCA) on the longest and oldest core – core BigLRC19-1 – to isolate the dominant sedimentary interrelationships. PC 1 explains 50.2 % of the data variability. Positive PC 1 values are associated with MagS, % clay, % very fine, fine silt, and very coarse sand which we infer to represent low energy, deep water conditions with greater runoff from the drainage basin. PC 1 negative values are associated with % TOM, medium and coarse silt, and very fine, fine, medium, and coarse sand. We interpret negative PC 1 values as high energy, shallow water conditions. The late Glacial is characterized as a wetter climate with deeper water conditions. Lake level drops at the end of the Younger Dryas and highly variable until about 8.5 kcal years BP. A comparison of all 3 cores suggests a severe and sustained lowstand between 8.5 and 5.0 kcal years BP. Conditions rebound to a wetter climate after 5.0 kcal years BP, punctuated by a dry Medieval Climatic Anomaly and a wet Little Ice Age, although the timing for the MCA and LIA requires additional age control.