A stalagmite record of changes in atmospheric circulation and soil processes in the Brazilian subtropics during the Late Pleistocene

We present a high-resolution, 116,000-year carbon stable isotope record from a stalagmite from southern Brazil, which has been precisely dated using the U-series method. Evaluation of carbon and oxygen isotope ratios together with the speleothem growth history suggest that the carbon isotopic composition of the speleothem is primarily controlled by biogenic CO2 supply from the soil, which is in turn affected by temperature and secondarily rainfall amount. Thus, the speleothem provides evidence of paleoenvironmental change in southern Brazil during the last glacial period. Predominantly high δ13C values and low stalagmite growth rates reflect persistent cool conditions during most of the glacial period in subtropical Brazil. This cooling is probably related to an intensified extratropical circulation with more frequent and intense cold surges, reaching a maximum at approximately 19 ky B.P. This cooling tendency is interrupted during periods of high obliquity values within the full glacial period at 93–85 and 47–40 ky B.P, and after 19 ky B.P, when a dramatic decrease in δ13C marks the deglaciation time in the continent. Unlike δ18O, the δ13C record does not exhibit a strong response to precessional forcing; instead it shows a strong 40 ky obliquity signal. Here we propose that local temperature and thus the biological processes in the soil are primarily steered by the gradients of temperature between low and mid-high latitudes, which influence the meridional heat transport. These gradient changes in turn are paced by obliquity.