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BARRETO, E. A. de S. Paleoprecipitation reconstruction in Southern Northeast Brazil during the two last glaciation cycles based on the application of oxygen isotopic records of stalagmites from Chapada Diamantina, Bahia. 2016. 127 f. Tese (doutoramento) Instituto de Geociências, Universidade de São Paulo, São Paulo. High-resolution oxygen isotopic records of CL2 and MAG stalagmites of Calixto and Marota caves, Chapada Diamantina (CD) region (12oS), Bahia State, southern Northeast Brazil (sNEB), allowed to reconstruct the past changes in precipitation between approximately 165-128 and 59-39 kyr B.P. The paleoclimatic reconstruction takes into account results from a calibration study performed in two caves in the CD region that showed a relationship between isotope signature in precipitation and cave drip water and suggested adequate environmental conditions for speleothem deposition in isotopic equilibrium with drip water. The interpretation of the speleothem O records was also based on the relationship between isotope composition of precipitation and rainfall amount from IAEA-GNIP stations in Brazil and also results from the climate model ECHAM-4. These data indicate the “amount effect” as the dominant isotope fractionation factor controlling the O variations in meteoric water forming speleothems, meaning that the decrease in the O values is associated with an increase in rainfall amount. Speleothem O records allow reconstructing the variation of paleoprecipitation on orbital and millennial time-scales during the penultimate glacial as well to correlate paleoprecipitation changes in sNEB with millennial Greenland events during the last glaciation. The CD records indicate an increase (decrease) of paleoprecipitation over Bahia related to the decrease (increase) of austral summer precipitation (ASI) at 10oS during the penultimate glacial, similar to observed in the last precession cycle. On orbital time-scale, the CD records were in antiphasing with isotopic records from southern Brazil and in phase with O speleothem values from eastern China. This pattern of precipitation is similar to observed in the last glaciation and suggest that variation in ASI affected the South American Monsoon System (SAMS) promoting changes in precipitation over sNEB in the penultimate glacial. Arid conditions in sNEB during the higher incoming of ASI are probably linked to increased eastwest upper-level subsidence into the region induced by stronger convection in the monsoon core keeping a position of South America Convergence Zone (SACZ) southward. The opposite also may occur during periods of low summer insolation in SH when the SASM was probably weaker. During the penultimate deglacial period (called Termination II) abrupt oscillations of CD records to lower values of O indicate a profound increase of precipitation coinciding with “Heinrich Stadial 11” (H11). Our interpretations are negatively correlated with precipitation changes observed in China and in western Amazon (Peru) and are positively correlated with southern Brazil. The positive anomalies of precipitation over sNEB would be associated with the displacement southward of the Intertropical Convergence Zone (ITCZ) as well with the intensification of the SASM and SACZ. Finally, abrupt isotopic oscillations to higher values observed during the marine isotope stage 3 that coincided with warm episodes in Greenland, called Dansgaard-Oeschger events (DO), were interpreted as the occurrence of drier conditions in sNEB. These precipitation changes on millennial time-scale, that is in phase with the observed in Peru, could be related to the displacement of ITCZ northward which promoting a profound desintensification of SAMS.

Reconstituição da paleoprecipitação no sul do Nordeste Brasileiro durante os dois últimos ciclos glaciais a partir da aplicação de registros isotópicos de oxigênio de estalagmites da Chapada Diamantina, Bahia.