Reconstruction of regional atmospheric circulation features during the late Pleistocene in subtropical Brazil from oxygen isotope composition of speleothems

Two high-resolution oxygen isotope records of speleothems from caves located in subtropical Brazil provide a broad view of regional climate variations and related forcing during the late Pleistocene and Holocene. Here, we present a new record precisely dated by U-series extending back to 131 kyr BP from a speleothem collected in Santana Cave. Comparison with the 116 kyr BP record from Botuvera Cave confirms that the seasonal change in regional rainfall distribution is primarily controlled by variations in summer insolation on Milankovitch timescales. However, significant negative anomalies of delta O-18 from 60 kyr BP to 10 kyr BP in the records suggest that the Northern Hemisphere glacial boundary conditions, in particular Heinrich events, impacted the mean location and/or convective activity of the South American summer monsoon (SASM), resulting in enhanced transport of depleted moisture from the Amazon Basin into the region. In addition, comparison of the two records indicates a steep north-south gradient in delta O-18 of rainfall throughout, which is interpreted as reflecting different relative contribution of extratropical and monsoonal precipitation to the two locations. For some time periods, more pronounced negative delta O-18 anomalies occur in the northern part and more positive anomalies in the southern part of the region, which appear to be associated with more abundant monsoonal and extratropical rainfall, respectively. The last interglacial period is characterized by the highest delta O-18 values in the entire St8 record, indicating a dominance of extratropical winter rainfall and thus, the most northward position of the summer SASM for the last 131 kyr BP. (c) 2006 Elsevier B.V. All rights reserved.