PALEOCLIMATIC RECONSTRUCTION OF EARLY HOLOCENE COASTAL CALIFORNIA USING SPELEOTHEM ARCHIVES

Paleoclimate records from the Sierra Nevada indicate that the climate in California underwent profound changes during the Holocene. However, less is known about how terrestrial climate varied along the California coast at this time. Speleothem records from coastal California have the potential to shed valuable light on changes in temperature and precipitation during the Holocene and should highlight the similarities and differences between coastal and inland climates in this region. Here we present preliminary data from a speleothem collected from a cave near Santa Cruz, CA that precipitated from 8.6 to 7.0 ka. Stalagmite growth rate was 100 µm/yr on average during this period, indicating the potential to develop a high-resolution (sub-annual-scale) record of early Holocene climate for central coastal California. Initial measurements of stable isotopes (δ¹⁸O and δ¹³C) and trace elements (Mg, Sr, Ba, P, S) were conducted at sub-centennial resolution. Variations in stalagmite δ¹⁸O likely reflect changes in moisture source to the region. Stalagmite Sr/Ca and Ba/Ca are highly positively correlated (r_s= 0.76, p= 0), indicating that these proxies primarily reflect prior carbonate precipitation in the epikarst. Stalagmite Mg/Ca is negatively correlated with Sr/Ca and Ba/Ca (r_s= -0.56, p=0.0006; r_s= -0.37, p=0.034 respectively), suggesting that Mg/Ca may be controlled by the extent of water-rock interaction along the seepage water flow path that is related to water-supply. Stalagmite δ¹³C displays a stronger correlation with Mg/Ca than any other proxy, suggesting a relationship between δ¹³C and water supply to the cave. This stalagmite record indicates that the climate of coastal California was significantly influenced by the 8.2 kyr cold event, displaying colder conditions and increased influence of North Pacific sourced storms coincident with changes in the Greenland ice core and Chinese speleothem records. Further research into δ¹⁸O variability in this stalagmite has the potential to reveal relationships between moisture source and atmospheric rivers along the California coast and climate oscillations such as the El Niño Southern Oscillation and the Pacific Decadal Oscillation.