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Little Ice Age flood events recorded in sag pond sediments in the Carrizo Plains National Monument, CA.

Matthew E. Kirby, Samuel K. Hippard, Lisa N. Martinez, Dahlia Serrato, Joseph Carlin, Nicole Bonuso, Christian Novich, & Sinan O. Akciz

In Preparation September 18, 2023, SCEC Contribution #13320

In California (CA), severe precipitation events (SPEs) are often associated with winter season atmospheric rivers. These SPEs can generate hurricane-scale precipitation, creating a variety of natural hazards such as floods and landslides. For California, the most complete SPE-flood record yet generated is a 9,000-year paleoflood reconstruction from the Santa Barbara Basin (Du et al., 2018). Finding terrestrial counterparts to compare to the Santa Barbara Basin is a challenge in Southern California where lake basins are rare and the terrestrial spatiotemporal signature of SPE floods remains largely unconstrained. Here, we present five, 1-2 m sediment cores from a sag pond along the San Andreas Fault in the southern Carrizo Plain. A master core (CLPC21-4) was selected for a variety of chronological, sedimentological, and biological analyses. Principal Component Analysis on these data reveals two end member sediment unit types: event versus ambient sedimentation. We identify two sediment units likely generated by SPEs. These two units are especially distinct within CLPC21-4, characterized by erosive bases, above average sand, normal grading, low magnetic susceptibility, and low total organic matter. Moreover, they are visually apparent across all five cores within the sag pond and thin from source to sink. Age control for the two units is constrained by AMS C-14 dates on discrete organic materials and supported by the identification of Erodium’s first appearance ca. 1750-1765 CE in the Santa Barbara region (Mensing and Byrne, 1998). Using these age constraints, we infer the maximum limiting age range for Event 1 from 1470-1640 CE and Event 2 from 1740-1800 CE. Within the limits of dating, site-specific proxy sensitivities, and inherent meteorological heterogeneity, we propose a probable correlation to Santa Barbara Basin flood events at 1525 CE and 1760 CE. Our results suggest that sag ponds may represent a viable and untapped paleoflood archive for California. Future work will focus on a latitudinal series of sag ponds to determine the spatiotemporal sequence and correlativity of SPEs in the sediment record.

Kirby, M. E., Hippard, S. K., Martinez, L. N., Serrato, D., Carlin, J., Bonuso, N., Novich, C., & Akciz, S. O. (2023). Little Ice Age flood events recorded in sag pond sediments in the Carrizo Plains National Monument, CA.. Journal of Paleolimnology, (in preparation).