A SPELEOTHEM RECORD OF PALEOENVIRONMENTAL CHANGE FROM RIVERBLUFF CAVE, MISSOURI, U.S.A

Three stalagmites from Riverbluff Cave in southwestern Missouri provide a record of environmental changes throughout much of the past 55,000 years. Carbon and oxygen isotopes, trace elements, mud laminae, and patterns of calcite deposition and non-deposition are the studied proxies, anchored by a series of U-Th dates. Carbon isotope changes are large and suggest major shifts in forest and grassland vegetation. Variations in trace element concentrations may be used to infer relative changes in water flux, and possibly indicating wetting or drying climate conditions. The relationship of the volume of water cycling through a cave system to the concentration of metals in speleothems is inverse for Mg and Sr and direct for Fe. Samples from Riverbluff cave show an increase in Sr and corresponding decrease in Fe, suggesting a drying trend. Mg concentrations do not exhibit a similar trend, likely due to thermal variation which changes the Mg-calcite partitioning coefficient. The patterns of calcite deposition among the three stalagmites show both similarities and differences, illustrating the importance of multiple specimens in climate reconstruction. Several periods of calcite cessation are noted, including cessation at approximately 34 ka, 12.7 ka, and 9.8 ka. A drying climate provides one possible interpretation of the breaks in calcite deposition, and is consistent with the trace element data. The date of 12.7 ka is fairly robust, and coincides with the beginning of the Younger Dryas climate episode, suggesting, perhaps, dry conditions at that time in the North American mid-continent.