Late Pleistocene paleoclimate in the Black Hills of South Dakota from isotope records in speleothems

Two coeval speleothems from the Black Hills are used to investigate δ18O and δ13C variations within Reed’s Cave and reconstruct climate during the Wisconsin glacial period from 82 000 to 24 000 years ago. Variation in growth rates between the two speleothems reveals a strong control of hydrology and surface vegetation on isotopic variability and response of δ18O to climate. High-resolution δ18O and δ13C data show that local environmental conditions can produce an offset of δ18O values of up to 4‰ in coeval speleothems but still reveal important climate events. The transition from warmer to cooler periods results in an increase in δ18O of calcite (δ18Oct) in sample RC2 while in sample RC20, another equilibrium deposit coeval to part of the RC2 record, δ18Oct is offset from RC2 by between 0 and −3.5‰, and shows much higher frequency isotopic variation. Speleothem RC2 records interglacial/glacial transitions and interstadial events that are also present in speleothems from North America and Europe. Spectral analysis of the δ18Oct records for both speleothems reveals periodicity at 1000 to 2000 years, similar to millennial scale variability seen in the North Atlantic sediments and the Greenland ice cores.