A multiproxy record from Baldwin Lake, San Bernardino Mountains, allowed us to examine variation and relationships between erosion, wildfire, vegetation, and climate in subalpine Southern California from 120 to 15 ka. Bulk organics, biogenic silica, and molar C:N data were generally antiphased with magnetic and trace element data and displayed long-term (105 year) shifts between autochthonous and allocthonous deposition. This was most pronounced during Marine Isotope Stage (MIS) 5, and we hypothesize that local summer insolation was the primary driver for Baldwin Lake's productive and unproductive lake state alternations. Wildfire history was inferred from charcoal concentrations and vegetation change from pollen. Relationships between these ecological processes, basin deposition, and summer insolation were often nonlinear. Sagebrush expansion, wildfire, and weak basin weathering characterized MIS 4, while during MIS 2, the basin was highly erosive, rarely burned, and the forest was impacted by shifts in Southern Californian hydroclimate. Despite coniferous forest cover throughout MIS 3, submillennial oscillations in charcoal, pollen, and bulk organic content occurred, consistent with pollen records from Eurasia's Mediterranean biome that span multiple glacial-interglacial cycles. Highly resolved global CO2 records and sea surface temperatures in key regions of the Pacific show no apparent relationship to these landscape conditions, and we suggest submillennial hydroclimatic variability as a potential driver. Highly resolved long pollen records from Southern California are an urgent research need to better understand the finer-scale (≤103 year) interactions between past vegetation, wildfire, and erosion, given the current natural disaster risks that 21st century climate change poses to both human and ecological communities.
Bibliographical noteFunding Information:
Grants and fellowships from the Society of Woman Geographers, UCLA Graduate Division Dissertation Year Fellowship, and UCLA La Kretz Center for California Conservation Science to K. C. G. supported the analyses conducted in this work. Additional funding came from the UCLA Department of Geography John Muir Memorial Endowment. The authors declare no conflicts of interest. Baldwin Lake sedimentary, geochemical, and charcoal data are archived in the NOAA National Centers for Environmental Information (https://www.ncdc.noaa.gov/paleo/study/28750). Full pollen counts are also available at the Neotoma Paleoecology Database (apps.neotomadb.org/Explorer/?datasetid=46603), and we are grateful to Eric Grimm for his advice on taxonomic interpretation and archiving these data. We thank Larry Winslow and Scott Eliason for their insight and assistance during fieldwork. We also thank several students for assistance in the lab including Lauren Brown, Elaine Chang, Tamryn Kong, Alec Lautanen, Victor Leung, Scott Lydon, Setareh Nejat, Alex Pakalniskis, and Marcus Thomson. K. C. G. thanks the Past Global Changes (PAGES) working group for support to present an earlier version of this research at the ?Fire Prediction Across Scales? workshop and feedback from the research community. Reviews and comments from Andrew Cohen, James Russell, and an anonymous reviewer greatly improved the manuscript.
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- Mediterranean biome
- Southern California
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