INSIGHT INTO SOUTHERN CALIFORNIA PALEOCLIMATE SINCE MARINE ISOTOPE STAGE 5C (C. 96 KA) FROM BALDWIN LAKE, SAN BERNARDINO MOUNTAINS

Retrospective studies from lake records can provide insight into linkages between terrestrial systems and climate change. Knowledge of the past range of variability can inform predictions for an uncertain future, currently an urgent research need in water-stressed and populous Southern California. Here we present a continuous 26.5 m record from alpine Southern California, with potential to fill this spatiotemporal gap in our understanding of western U.S. paleoclimate prior to Marine Isotope Stage 2 (MIS 2, c. 29 ka). Located in Big Bear Valley of the San Bernardino Mountains, the Baldwin Lake core spans c. 95.9 – 10 ka, based on AMS radiocarbon dating and infra-red stimulated luminescence dating. Magnetic susceptibility and x-ray fluorescence data show that Baldwin Lake was a closed-basin, stratified lake for much of its history, with lowstands and bottom ventilation during transitions from glacial to interglacial periods (c. 60-57 ka, c. 15-12 ka). Slow sedimentation rates and a greater proportion of terrigenous input occurred during MIS 2, eventually transitioning to a calcium-rich massive clayey silt facies that reflect intermittent lake conditions by ~11 ka, and a playa surface during the Holocene. Bulk organic content, derived from loss-on-ignition, correlates with insolation values at 34˚N throughout the sequence. Ongoing biogenic silica analysis aims to test if paleoinsolation was the primary climatic driver in alpine Southern California from MIS 5 -1.