Reconstrução paleoclimática da Baía de Guanabara através da análise isotópica de amostras de sambaquis

Abstract

The 14C activity measuring method through benzene synthesis was validated and optimized at the Institute of Radiation Protection and Dosimetry to attend the growing demand of 14C applications at environmental area. Its validation was done through the International Atomic Energy Agency’s reference standards processing, AMS dating technique (Heidelberg - Germany) results comparison and through detection boundaries setup. In this work, were dated 52 samples (National Museum / UFRJ) of coal and shells of mollusk and oysters from Guanabara Bay northeast region archaeological sites, Rio de Janeiro, and were calculated the region’s marine reservoir effect values: ΔR = -34 ± 56 years 14C and ΔR = -132 ± 42 years 14C for the 4320 ± 80 years period 14C and 2600 ± 40 years 14C, respectively. Mg/Ca, Sr/Ca and Ba/Ca elemental ratios were determined, as well as δ 13C and δ 18O values for the Guanabara Bay region paleoenvironmental reconstruction. Based on the δ 18O values, it was possible to consider that Guanabara Bay system presented more marine characteristics than estuarine during Northgrippian age to Meghalayan. It was deducted that Guanabara Bay average seawater surface temperature increased about 4°C during 6380 - 4790 years BP to 2870 - 2388 years BP period, with seawater δ 18O value increase from -1.3 ‰ to -0.7 ‰. It is important to emphasize the study relevance due to the lack of paleoclimatic data for the Guanabara Bay region.