SEASONAL VARIATIONS IN MODERN SPELEOTHEM CALCITE GROWTH
Eight drip sites were studied over three years, during which growth rates ranged from less than 1 to 75 mg/day on a substrate of approximately 100 cm2. Mean growth rate at different drip sites correlates directly to mean drip rate. Within an individual cave, different drip sites exhibit similar temporal cycles in growth rates, including sites with large differences in their mean growth rate. These cycles correspond to seasonal changes above the cave, with the lowest growth rates occurring during hot, dry summers, and peak growth rates occurring in fall and winter. Drip sites from caves 140 km apart exhibit similar cycles in growth rates, indicating a controlling mechanism on at least this regional scale. This seasonal correspondence of growth rates likely reflects the control of temperature and effective precipitation on soil carbon dioxide productivity and attendant output to vadose waters. These results indicate that growth rate variations in ancient speleothems may serve as a proxy with seasonal resolution. Using the approach outlined here, speleothem growth rate proxies and, moreover, geochemical proxies may be evaluated and calibrated for individual and regional cave systems.