A HIGH-RESOLUTION RECORD OF HOLOCENE CLIMATE CHANGE IN SPELEOTHEM CALCITE FROM COLD WATER CAVE, NORTHEAST IOWA

High-precision uranium-thorium mass spectrometric chronology and O-18-C-13 isotopic analysis of speleothem calcite from Cold Water Cave in northeast lowa have been used to chart mid-Holocene climate change. Significant shifts in deltaO-18 and deltaC-13 isotopic values coincide with well-documented Holocene vegetation changes. Temperature estimates based on O-18/O-16 ratios suggest that the climate warmed rapidly by about 3-degrees-C at 5900 years before present and then cooled by 4-degrees-C at 3600 years before present. Initiation of a gradual increase in deltaC-13 at 5900 years before present suggests that turnover of the forest soil biomass was slow and that equilibrium with prairie vegetation was not attained by 3600 years before present.