LATE PLEISTOCENE PALEOCLIMATE IN THE BLACK HILLS OF SOUTH DAKOTA FROM ISOTOPE RECORDS IN SPELEOTHEMS

We report TIMS and ICP/MS U-series dated records of d¹⁸O_ct for speleothems which grew in Reed's Cave, SD (central N. America) during the Wisconsin glacial period. Coeval speleothems exhibit offsets in d¹⁸O_ctshowing that different drip sites in a cave respond differently to climate change. The opposite sign of d(d¹⁸O_ct)/dT for samples 99902 and 20000 reflect a complex hydrological system in Reed's Cave that shows varying seasonal bias at multiple drip sites. Similar shifts in climate from interglacial to glacial conditions in the mid-continent are displayed in speleothems from Reed's Cave and Crevice Cave but local conditions have significant influence on the small-scale variations in d¹⁸O_ct . U-series ages for the d¹⁸O_ct record at Reed's Cave provide an independent chronology for Heinrich events and Dansgaard-Oeschger oscillations that are present in these records. Spectral analysis reveals millennial-scale variations also seen in Greenland ice cores. Data from Reed's Cave speleothems suggest that there is very little lag between climate responses in North Atlantic and central North America. Rapid changes in the size and extent of the ice sheets may be seen more promptly in the speleothem records.