SEDIMENTOLOGICAL EVIDENCE FOR A GLACIAL RESPONSE TO THE 8.2 KA EVENT FROM DRY LAKE, SAN GORGONIO WILDERNESS: SOUTHERN CALIFORNIA

Magnetic susceptibility, total organic matter, grain size, microfossil analysis and 27 AMS 14C dates on an 8 m core collected from Dry Lake, located in the San Gorgonio Wilderness, Southern California, provide the first high-resolution terrestrial record of the 8.2 ka “cool” event in coastal southwestern North America. Situated at 2630 m, Dry Lake is in the headwater catchment of the Santa Ana River in the San Bernardino Mountains of the Transverse Ranges. The site’s proximity to the Pacific Ocean and latitudinal position near the southern most extent of the polar front jet stream place Dry Lake in an ideal setting to respond to, and record perturbations in, Pacific ocean/atmosphere circulation over a range of time scales. Here, we present lithologic and proxy data indicating an extra-tropical climate response to the proposed 8,200 cal yr. B.P. North Atlantic-derived event. The event is characterized by an abrupt spike in magnetic susceptibility and a lithologic change from lake clay to sand. We interpret these observations to represent a period of enhanced precipitation (i.e. erosion) and possible glacial activity due to southerly displacement of the polar front jet stream in response to altered North Atlantic thermohaline circulation. These results provide indirect evidence of teleconnections between North Atlantic Deep Water formation and Pacific ocean/atmosphere circulation as well as temporal constraints for glacial chronologies as proposed by Owen et al (2003). Therefore, in accordance with other research, our observations indicate the 8.2 ka event may be more global in nature than previously concluded, affecting both the North Atlantic and Pacific ocean/atmosphere systems. Furthermore, should models predicting a reduced thermohaline circulation in the North Atlantic in response to Arctic sea ice melting be correct, the 8.2 ka event, as recorded in Dry Lake, may provide an analog of future climate change for the coastal southwest.