INITIAL RESULTS FROM ZACA DRY LAKE REVEAL EVIDENCE FOR HOLOCENE CLIMATE CHANGE, SANTA BARBRA COUNTY, CALIFORNIA

A 4.64 meter sediment piston core was extracted from Zaca Dry Lake, a natural spill-over basin down-drainage from perennial Zaca Lake, in July 2009. Zaca Dry Lake is a probable landslide formed depression; it is located in the Monterey Shale unit in the San Rafael Mountains of Santa Barbara County, California. Zaca Dry Lake is ideally located for paleoclimatic research for two reasons: 1) it fills in a geographic gap in coastal California where very little is known about past climate; and, 2) it is proximal to the Pacific Ocean therefore making it an excellent location for comparing land-sea paleoclimate records and responses. In addition to physical description, five basic analyses were used to interpret the lake’s history: mass magnetic susceptibility, total organic matter, total carbonate, micro-fossil counts, and thin section petrography. Our initial results indicate that Zaca Dry Lake is at least 7,500 calendar years old. Sedimentologically, there is no evidence that Zaca Dry Lake was ever a deep perennial lake – for example, like its neighbor Zaca Lake - but instead fluctuated between a wetland or a shallow lake over the past 7,500 years. The occurrence of a strange carbonate layer 0.5 meters thick consisting of concentrically layered, sub-mm scale carbonate nodules may be the evidence of a mid-Holocene “highstand”/perennial shallow lake. An increase in the abundance of oogonia and gastropods above the carbonate layer is inferred to represent a possible long-term drying or transition to a wetland before 2,500 calendar years. Sediments younger than 2,500 years are missing due to human activity in the drainage basin.