A 4000-YEAR SPELEOTHEM STABLE ISOTOPIC RECORD FROM DEVILS ICE BOX CAVE, CENTRAL MISSOURI

Carbon and oxygen stable isotopic profiles spanning the last ~4000 years have been constructed from two stalagmites from Devils Ice Box cave, located near Columbia, Missouri on the northern edge of the Ozark Plateau. Despite significant temporal overlap, the mineralogical and isotopic signatures of each stalagmite are quite distinct. Both samples DI-01-01 and DI-01-03 preserve average d ¹⁸O values of ~-5‰ (PDB), although the variability in the latter sample is significantly larger. The carbon isotopic ratios of both samples are offset by approximately 7‰, with d ¹³C values in DI-01-01 and DI-01-03 averaging -3‰ and -10‰, respectively. The oxygen and carbon isotopic ratios of DI-01-01 are consistent with other regional speleothem records, suggesting a transition from a prairie/grassland ecosystem to a more forested regime at approximately 1500 yr BP. Carbon isotopic signatures from DI-01-03 correlate neither with DI-01-01 nor with regional, coeval stalagmite sequences. The samples also differ in appearance, with DI-01-01 composed of dense, optically clear calcite while DI-0103 contains abundant clays, is slightly porous, and is composed of milky white calcite. The origin of these optical and isotopic differences is unclear. Chronologies are anchored using two U-Th TIMS dates per stalagmite, none of which involved very low U or very high ²³²Th, and dates fell in correct stratigraphic order, suggesting that the chronology is sound. The oxygen isotopic composition of coeval stalagmites has been demonstrated to vary due to pre-infiltration evaporative enrichment of ¹⁸O, but despite oxygen isotopic variability, the carbon isotopic ratios in these samples were consistent. If the differences between the two stalagmites are not resolved, reliable climatic inferences cannot be extracted from this data set. Instead we will have to determine what controls in the cave environment caused the carbon isotopes to vary among coeval stalagmites from the same cave