Change in water availability is of great concern in the coastal southwest United States (CSWUS). Reconstructing the history of water pre-1800 AD requires the use of proxy data. Lakes provide long-lived, high-resolution terrestrial archives of past hydrologic change, and their sediments contain a variety of proxies. This study presents geochemical and sedimentological data from Zaca Lake, CA (Santa Barbara County) used to reconstruct a 3000 year history of winter season moisture source (δDwax) and catchment run-off (125-2000μm sand) at decadal resolution. Here we show that winter season moisture source and run-off are highly variable over the past 3000 years; superimposed are regime shifts between wetter or drier conditions that persist on average over multiple centuries. Moisture source and run-off do not consistently covary indicating multiple atmospheric circulation modes where wetter/drier conditions prevail. Grain-size analysis reveals two intervals of multi-century drought with less run-off that pre-date the "epic droughts" as identified by Cook etal. (2004). A well-defined wet period with more run-off is identified during the Little Ice Age. Notably, the grain size data show strong coherence with western North American percent drought area indices for the past 1000 years. As a result, our data extend the history of drought and pluvials back to 3000 calendar years BP in the CSWUS. Comparison to tropical Pacific proxies confirms the long-term relationship between El Niño and enhanced run-off in the CSWUS. Our results demonstrate the long-term importance of the tropical Pacific to the CSWUS winter season hydroclimate.
Bibliographical noteFunding Information:
Funding for this project includes support from: NSF EAR-1002649 to SJF, MEK and NSF EAR-0318511 to MEK. Funding for the radiocarbon dates was provided by LLNL grant LDRD-09-ERI-003 to SRZ; this is LLNL-JRNL-653836 . Thanks to Alex Simms (UCSB) for help with the seismic reflection survey, Zaca Lake Retreat for access to the lake and their hospitality, and Dr. Ken Adams and an anonymous reviewer for insightful and helpful reviews.
Copyright 2014 Elsevier B.V., All rights reserved.
- Hydrogen isotope
- Leaf wax
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