Climate projections for the coastal southwestern United States predict a change in the frequency and magnitude of precipitation, perhaps with an overall drying. Despite the uncertainty in model projections, it is clear that any change to the region?s winter dominated, ?feast or famine? hydroclimatology will have consequences for the highly-populous, water-stressed region. This proposal develops a decadal to subcentennial scale, continuous sedimentary archive from Lake Elsinore, California using physical (grain size), biological (pollen), chemical (C:N), and isotopic (leaf wax hydrogen isotopes) analyses. Characterized by exceptional resolution and archive continuity, this unique terrestrial site in the coastal southwest offers an unparalleled opportunity to evaluate hydrologic and ecologic change across abrupt climatic transitions during the late Glacial period (9-33ka). The cores will be characterized using a diverse, multi-proxy approach to capture large magnitude, late Glacial transitions, including leaf wax D/H shifts of >100?, grain size evidence for variable run-off, and palynological evidence for changes in catchment vegetation. Lake Elsinore?s exceptional archive is characterized by continuous deposition, high sedimentation rates, and the capacity for very high resolution radiocarbon age control using discrete organic material. Beyond representing a high quality archive of past terrestrial environmental change, Lake Elsinore sediments will enable proposed correlations with published marine reconstructions including local and distal marine records of Pacific sea surface temperatures (SSTs), as well as Atlantic SSTs and evidence for Meridional Overturning Circulation in order to assess the driving causes of the region?s hydrologic and ecologic change. The team will focus on global abrupt climatic transitions including Heinrich events 1-3, and the transitions into and out of the Bolling-Allerod and the Younger Dryas. Although these transitions differ from the projected anthropogenic climate change, they offer large magnitude, abrupt transitions capable of providing maximum insights into forcing-response relationships. The working hypothesis is that hydrologic changes and ecologic shifts are closely in step and responding to local and global abrupt climatic transitions in the late Glacial to early Holocene. The questions are how much and how fast are these local responses demonstrated, and what might be the implications for the future. The lead investigator?s institution, Cal State Fullerton, reaches a large number of minority, and especially Hispanic students. The proposal engages two female co-investigators, one of whom is an early career Assistant professor. The proposed study will provide training and research opportunities for graduate and undergraduate research at three institutions, with a focus on building the analytical and interpretative skill sets. This research will also provide the first terrestrially-based, decadal to subcentennial scale record of how the vegetation of the coastal southwest responds to abrupt climatic transitions. The development of a baseline understanding of the causes, responses, and recovery of past hydrologic and ecologic change is of interest beyond the paleoclimate field with implications for ecologists, conservationists, and policy decisions pertaining to the California Floristic Biodiversity Hotspot.
Intellectual Merit: The Intellectual Merit criterion encompasses the potential to advance knowledge Lake Elsinore is located in the arid, highly populated coastal southwest United States. The region is also part of the California Floristic Biodiversity Hotspot where ecological change is eliminating and/or stressing the region’s native species. Compounding this ecological crisis is the region’s sensitivity to drought. Furthermore, as the region’s population continues to grow and water demands rise, susceptibility to changes in water availability will become increasingly severe. In this study, we used sediments from Lake Elsinore to explore the history of water, its atmospheric source, and vegetation in the coastal southwest United States. Lake Elsinore is the largest natural lake in the region, and it contains a thick sequence of mud recording thousands of years of climate change. Our team consists of scientists from Cal-State Fullerton, the University of Southern California, and Columbia University. Each investigator provides special skills aimed at the reconstruction of past water availability (CSUF), its atmospheric source (USC), and past vegetation dynamics (CU). Project outcomes for the vegetation and water source components are provided separately from this report. Here, I focus on the core sedimentology as related to past water availability. Combining radiocarbon dates and a variety of sedimentological analyses (such as the amount of sand in the sediment), we developed the first sub-decadal record of water history for the region spanning 9,000 to 33,000 years. Changes in percent sand are used to infer past run-off in association with winter precipitation. Wetter winters generate more run-off and thus more sand in the sediment record. Our sand results indicate large scale, and often abrupt, changes in run-off over the past 33,000 years. Of particular interest is evidence for changes that are unmatched in the historical record in both magnitude and duration. Our results suggest that the state of winter climate (wet or dry) can change abruptly and sustain that change for decades to centuries. Our results are relevant to modern climate studies because they provide a baseline understanding of past changes in water availability and thus provide context for future scenarios caused by global climate change. Finally, our research will continue to examine this new record of past water availability with a focus on explaining how and why past changes in winter climate happen. Broader Impacts: The Broader Impacts criterion encompasses the potential to benefit society and contribute to the achievement of specific, desired societal outcomes. Our research benefits society in several ways. First, we have reconstructed a pre-20th century climate record of changes in water availability. This record provides a baseline understanding of how and why winter climate changes in the drought sensitive, highly populated coastal southwest United States. Like investigating in a stock before investing your money, our research provides a perspective on past water changes that can inform present and future water management practices (investments) for the region. Of particular concern is our evidence for abrupt and sustained changes in the average state of winter climate. Water managers and policy makers need to consider, and prepare for, future abrupt and sustained changes in water availability that may exceed in magnitude anything witnessed in the historical record. Second, our research involved the education of four students at California State University, Fullerton. Three of these students are woman and two represent the first in their families to attend college. The latter two have since moved on to their MS degrees based on the research experiences afforded through this NSF funded project. Women are significantly underrepresented in the geological sciences; therefore, it is important to provide research opportunities to underrepresented populations, such as this project. Third, our research has been presented in various media (newspaper, websites, radio) thus educating non-scientists about important water-related issues. Fundamentally, these media type outreach campaigns are critical to educating the next generation of citizen scientists. For example, Kirby created a Lab Facebook Page dedicated to his (and related) paleo and modern climate research. This Facebook Page reaches 1000s of viewers over time, tapping into social media and thus the next generation of citizen scientists.
