A fifty-year climatic signal in three Holocene stalagmite records from Mato Grosso, Brazil

摘要

Three stalagmites were collected in the "Perolas" cave, 150km NW of Cuiaba, Mato Grosso, Brazil, in order to reconstruct the climate history of the surrounding region. These stalagmites were similarly formed by stacking of thousands of calcitic pairs of laminae. Microphotographs of polished thin sections were used to count the laminae pairs and measure their width. A reasonable fit was found between the counting results and U/Th and ~(14)C geochronological data, proving that these pairs are annually deposited; and correlations were also found between the annual growth rate of the stalagmites and the annual water excess in the Perolas region, proving that the former parameter could be used as a climatic proxy. Three files of climatic proxy data covering 256 years were thus obtained and statistically treated to restore the historical fluctuations of the climate. Apart from well-documented periodicities, a still poorly known but very strong half-century climatic oscillation appeared in the results.