Most of our current understanding of paleohydrologic patterns of the southwestern United States stems from terrestrial records of low resolution (>100 yr). However, the timing and spatial extent of paleoclimatic changes have remained unclear for the late Holocene in the area west of the southern Sierra Nevada, where recovered terrestrial records are rare. To assess the western extent of regional changes in the moisture during the late Holocene, a core from Soda Lake on the Carrizo Plain of southern California spanning the last 4500 yrs was studied at decadal resolution (25-30 yr). Decadal changes in the biogeochemistry of Soda Lake and the surrounding Carrizo Plain are reflected in the total organic carbon, total sulfur, salt content, detrital grain-size distribution, and carbon-isotopic composition of organic matter in the sediments. These parameters are used to infer changes in lake level and periods of intensified aridity, providing a local paleoclimate reconstruction for comparison with existing records from eastern Sierra Nevada and Great Basin.
The Soda Lake core reveals that several significant paleoclimatic shifts occurred west of the Sierra Nevada during the late Holocene. Long-term lake expansion of Soda Lake occurred prior to ~3400 cal yr BP (calibrated using CALIB 4.0), followed by two high lake-level periods: one ~2900-2600 cal yr BP and the second at ~2250 cal yr BP. A significant desiccation event occurred shortly after the second high stand. Lake level was low 2000-1500 cal yr BP, then rose slightly at ~1350 cal yr BP before returning to low lake levels which persisted 1200-800 cal yr BP. Thus, similarities between climate records east and west of the Sierra Nevada suggest regionally significant late Holocene climatic variations.