An Isotopic Investigation of a Partially Recrystallized Aragonite Stalagmite from Central New York

High-precision Uranium-Thorium dating and stable isotope (δ¹⁸O and δ¹³C) analysis of a predominantly aragonite stalagmite from Gage Caverns in Schoharie, New York have been investigated as a local paleoclimate record covering the past ~ 1.25 ka. This speleothem (Gage02) has undergone partial diagenesis from aragonite to calcite, producing observable δ¹⁸O and δ¹³C isotopic shifts between the original aragonite versus the altered calcite. U/Th samples taken from the diagenetic calcite also produce anomalous isotope results and U/Th dates when compared to the unaltered aragonite samples, providing evidence of how diagenetic processes can alter the reliability of data collected for speleological climate studies. While data from calcite regions may be suspect, unaltered aragonite regions of the speleothem provides presumably reliable data with clear trends. Aragonite δ¹⁸O and δ¹³C values range between -3.92‰ to -5.14‰ and -10.25‰ to -7.54‰, respectively, showing minor variability in the paleoclimate record of the area. Overall, Gage02 represents that of relatively cool depositional climate with small periods of warmer, wetter incongruity. When compared to regional other paleoclimate studies, Gage02 shows little correlation with many comparable proxies. However, the correspondence between Gage02 and GISP2 does resemble small commonalities over the last 1200 years B.P., indicating some regional equivalence in the record. Small cyclic changes such as peaks and toughs in these two records are potentially related to seasonal orbital forcing as well as atmospheric circulation patterns of the Northern Hemisphere. Inconsistencies between most other studies are likely attributed to the difference in unique cave systems such as varying drip rates, flow path lengths, and outgassing rates. It is commonly accepted that the late Holocene period has been climatically stable, and this study reiterates this notion. With future climate variability unknown, there exists a demand for terrestrial paleoclimate proxies. Because this study was performed using a speleothem from northeastern New York, analysis of the data was challenging, but still crucial to our understanding of climate variance in the absence of anthropogenic forcing.