Climatic Influences on ẟ18O in California Rainwater and Cave Dripwaters

Abstract:

Stalagmites have the potential to record paleoclimate temperature and precipitation variability across a region through interpretation of d¹⁸O of stalagmite calcite (d¹⁸O_cc). Interpreting d¹⁸O_cc in highly seasonal climates, such as California, is confounded as d¹⁸O_cc responds to precipitation amount, precipitation source, air temperature variability, and in-cave dynamics. To deconvolve the possible drivers for d¹⁸O_cc in California we measure the rainwater d¹⁸O and d²H in three locations, Cloverdale (CVD; 102 m elevation), Davis (DVS; 16 m elevation), and Santa Rosa (SR; 50 m elevation), and we measure the d¹⁸O and d²H of dripwater two cave sites, California Caverns (CC; 500 m elevation) and Lilburn Cave (LL; 1600 m elevation). The d¹⁸O of rainwater and dripwater vary seasonally. Rainwater d¹⁸O is significantly driven by amount (unit) of precipitation and dripwater d¹⁸O is driven primarily by air temperature variability. The difference between average d¹⁸O (-16.23 and -3.71‰) values of the three precipitation sites – SR and CVD, which are more proximal to the coast, and inland DVS – captures fractionation related to increasing distance from the Pacific. The difference in average dripwater d¹⁸O (-12.07 and -8.38‰) for the two cave sites – lower elevation CC and higher elevation LL – potentially reflects a lapse rate between the lower elevation site and the higher site. The results from this study demonstrates that precipitation, rather than air temperature, variability strongly influences California rainwater d¹⁸O signals. This study will aide future interpretations of d¹⁸O_cc from California caves.