PALEOENVIRONMENTAL RECONSTRUCTION OF OWL CAVE, HIGHLAND CO., VA USING ẟ13C FROM STALAGMITE AS A PROXY

Over the past 30 years, ẟ¹³C found in calcite (CaCO₃) in stalagmites have been used as a proxy for terrestrial paleoclimate and paleoenvironmental reconstruction. Photosynthetic organisms favor the more reactive light carbon (¹²C) over its heavier counterpart (¹³C); therefore, a negative relationship exists between ẟ¹³C in vegetation and the magnitude of a plant’s photosynthetic processes. Previous research asserts that fractionation of ẟ¹³C at the surface is reflected in stalagmite ẟ¹³C. Thus, negative ẟ¹³C anomalies in stalagmites reflect a forested surface dominated by C₃ photosynthesizers, while positive anomalies reflect a grassy surface with increased C₄ vegetation.

This study seeks to explore local paleoenvironmental conditions based on ẟ¹³C from an ~18 cm stalagmite (OWL-1) extracted from Owl Cave, Highland County, VA. OWL-1 separated at a mud layer and a growth hiatus is assumed at the division between the base (OWL-1B) and top (OWL-1T). In this study, continuous growth rates for both sections of OWL-1 are hypothesized. OWL-1 subsamples were continuously sampled at 1 mm-resolution along the growth axis with a 0.4 mm-wide tungsten carbide tipped Micromill. ẟ¹³C was measured using isotope ratio mass spectrometry and standardized with NBS-18 and NBS-19. Preliminary results suggest that ẟ¹³C values for OWL-1B average 1 ‰ lighter than OWL-1T. Much of this difference is accounted for in the upper 2 cm of OWL-1T, where an observed 3 ‰ decrease in ẟ¹³C may symbol a rapid environmental shift toward C₃ forested areas. Preliminary results suggest that positive ẟ¹³C anomalies occur with 9 mm and 6 mm cyclicity in OWL-1B and OWL-1T, respectively. Previous studies in the region suggest that cyclic droughts may drive environmental changes responsible for anomalously positive ẟ¹³C. Future work includes U/Th dating for the construction of an OWL-1 age model to relate paleoenvironmental interpretations to local and global paleoclimate proxies.