ANALYSIS OF SPELEOTHEM TRACE ELEMENT SIGNATURES AS A HOLOCENE PALEOCLIMATE PROXY AT GAGE CAVERN, NEW YORK

Trace element variations in the calcite of ancient speleothems can be used as proxies for paleo-rainfall and other hydrologic conditions in karst terrain. A ~30 cm stalagmite collected from the Gage Caverns in Schoharie County, New York was U/Th dated to have formed initially 4235 ± 14 years B.P. We analyzed the speleothem for the trace element ratios Mg/Ca, Sr/Ca, and Ba/Ca using laser ablation mass-spectrometry. Peaks in Mg/Ca ratios were observed approximately at 500, 650, 1450, 1621, and 1686 yr B.P., indicating periods of increased water residence time within the limestone bedrock overlying Gage Cavern, and thus more ‘prior calcite precipitation’. Prior calcite precipitation occurs during dry periods when the CO₂ of the dripwater degasses upstream of speleothem formation causing CaCO₃ to precipitate, thus removing calcium from the drip water and causing speleothem Ba/Ca, Sr/Ca, and Mg/Ca ratios to increase. Mg/Ca exhibit a gradual decrease in ratios that reach minimum values near 1150 yr B.P., consistent with the onset of the Medieval Warm Period (MWP) during which temperatures and rainfall increased at the mid-high latitudes. The 1400 yr BP Bond Event in which the tropical latitudes experienced increased aridity and polar latitudes underwent extensive cooling can also be detected locally in trace element ratio increases ~1450 yr B.P., a possible result of rapidly lower temperatures caused by shifting the North Atlantic polar front and North American Jet Stream southward. With the continued analysis of the Gage Cavern speleothem, we expect similar increases in trace element concentrations to be recorded at ~2800 and ~4200 yr B.P., consistent with North Atlantic ice rafting events where a shifting polar front decreased temperature and rainfall volume throughout North America. In addition to global trends in climate change, the Gage Cavern speleothem is expected to yield localized, possibly seasonal fluctuations in climate that occurred in the northeastern United States.