No abstract

High-precision uranium-thorium mass spectrometric chronology and (18)O-(13)C isotopic analysis of speleothem calcite from Cold Water Cave in northeast Iowa have been used to chart mid-Holocene climate change. Significant shifts in dagger(18)O and dagger(13)C isotopic values coincide with well-documented Holocene vegetation changes. Temperature estimates based on (18)O/(16)O 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 dagger(13)C 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.

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Measurement of protactinium-231 (231Pa) in carbonates by thermal ionization mass spectroscopy yields 231Pa ages that are more than 10 times more precise than those determined by decay counting. Carbonates between 10 and 250,000 years old can now be dated with 231Pa methods. Barbados corals that have identical 231Pa and thorium-230 (230Th) ages indicate that the timing of sea level change over parts of the last glacial cycle is consistent with the predictions of the Astronomical Theory. Two Devils Hole calcite subsamples record identical 231Pa and 230Th ages, suggesting that the chronology of this climate record is accurate.