Carbon and oxygen stable isotopes are used as indicators of paleovegetation and climate, respectively. Profiles of each isotope have been constructed from three late Holocene stalagmites (DI-01-01, DI-01-02, and DI-01-03) from Devils Ice Box cave, on the northern edge of the Ozark Plateau, near Columbia, Missouri. Radiogenic isotope dating techniques were used to anchor the chronologies of the three stalagmites. Two U-Th TIMS dates were obtained from both DI-01-01 and DI-01-02, and one TIMS date from DI-01-03. The oxygen isotopic profiles for each are similar (approx. -5 per mil), although DI-01-03 varied significantly (-4.95 +/- 0.58 per mil). This stability indicates a steady climate/temperature in the region. In contrast, the carbon isotopic signatures of each stalagmite are quite distinct. Sample DI-01-01 contains a carbon isotopic trend which is consistent with other regional speleothem records, suggesting a transition from a prairie/grassland ecosystem to forest at approximately 1,500 years ago. DI-01-02 is characterized by consistently high (-2 per mil) d13C values, suggesting continuous prairie over the cave throughout the late Holocene. DI-01-03 contains consistently low (-10 per mil) d13C values throughout the same interval, suggesting continuous forest. The samples also differ in appearance; DI-01-01 is composed of dense, optically clear calcite, while DI-01-02 is similar, but more porous, and DI-01-03 is composed of porous, milky white calcite with abundant clays. The origin of these optical and isotopic differences is unclear, however, the porous nature of DI-01-02 and DI-01-03 makes their isotopic records suspect. Therefore, DI-01-01 is most likely to contain an accurate record of vegetation in the area during the late Holocene, suggesting that the region underwent a change from prairie to forest about 1,500 years ago.
Michelle DuPree, ’03 Valley Park, MO
Sponsor: Rhawn Denniston