Paper No. 7
Presentation Time: 3:25 PM
EVIDENCE FOR MULTI-SCALE ENVIRONMENTAL CHANGE DURING THE HOLOCENE IN SOUTHERN CALIFORNIA (LAKE ELSINORE)
Recently acquired drill cores from Lake Elsinore's depocenter provide one of the first, continuous, multi-scale records of Holocene environmental change in coastal southwestern North America (CSWNA). 21 AMS 14C dates spanning 9,800 calendar years BP provide excellent age control. 150 tie points over 9.5 meters between two depocenter cores using multiple sedimentological data indicate spatial sediment integrity. As a result, we present our results at this point using a single core that contains the most compete suite of sedimentological and geochemical analyses. The Holocene is characterized by a long-term drying trend attributed to insolation forcing and its modulation of storm tracks. This interpretation of Holocene climate evolution in CSWNA is largely congruent with other climate records from western North America. Unlike the central to northern CA records, early Holocene climate in CSWNA is also characterized by more frequent large storms as recorded by discrete storms facies. The early Holocene stormy interval is attributed to an expanded North American monsoon and more frequent tropical cyclones, both of which are modulated by higher, early Holocene summer insolation. An apparent shift in the amplitude of climate change occurs mid-Holocene, possibly related to the onset of modern ENSO conditions. It is less clear how the CSWNA mid-Holocene climate shift is related to other records from western North America. Historical calibration indicates that delta18O(calcite) is a reliable proxy for lake-level (i.e., hydrologic balance) in Lake Elsinore. The late-Holocene, from which we have delta18O(calcite) data, is characterized by eight multi-decadal to centennial scale, wet-dry oscillations superimposed on millennial-scale wet-dry trends. An independently dated sediment core from Lake Elsinore's littoral zone shows similar, less-resolved delta18O(calcite) trends. Most intriguing is a comparison between independently dated Pyramid Lake and Lake Elsinore delta18O(calcite) data over the past 4,000 calendar years, which indicates remarkable spatial and temporal similarities. Based on modern climatological patterns, the late-Holocene phasing of CA climate may represent sustained intervals of positive or negative PDO at multi-decadal to centennial timescales.