MULTI-DECADAL CLIMATE VARIABILITY IN SOUTHERN CALIFORNIA OVER 2 MILLENNIA

There is a keen interest in understanding the frequency and severity of droughts and floods in southern California, although annually resolved millennial high resolution records are rare. We have recently recovered two 9m sediment core from Zaca Lake, CA. This site, located within 50 km of the Santa Barbara Basin, is ideal for terrestrial-marine paleoclimate comparisons. The sediments span the past 2 millennia with a sedimentation rate of c. 0.3 cm/yr. The age model is based upon 9 radiocarbon dates, an historical event in 1938, and the ¹³⁷Cs peak in 1963; further age control from first appearances of non-native pollen in the nineteenth and twentieth century will be added. Euxinic bottom waters and mm-scale color laminations imply minimal bioturbation. Elemental abundance analyzed at up to 2 mm resolution by scanning XRF yields quasi-annual resolution. Ti, Rb and Zn covary extremely closely, and together with grain size analysis is indicative of detrital input, associated with unusually wet conditions. Ti is diagenetically immobile, unlike other elements (eg Fe, Mn) and not scavenged by minerals produced in the water column (eg Ca, Sr). Detrital inputs were unusually high around 100, 200, 400, 1130, 1200, 1400 and 1600 AD. We identify major regional floods that extend to the Santa Barbara basin as well as numerous additional climate events, providing a new archive of wet-dry cycles in heavily populated southern California.