The evolution of a tropical rainforest/grassland mosaic in southeastern Brazil since 28,000 @u1@u4C yr BP based on carbon isotopes and pollen records

The lack of paleoecological records from the montane Atlantic Rainforest of coastal Brazil, a hotspot of biological diversity, has been a major obstacle to our understanding of the vegetational changes since the last glacial cycle. We present carbon isotope and pollen records to assess the impact of the glaciation on the native vegetation of the Serra do Mar rainforest in Sao Paulo, Brazil. From ca. 28,000 to ~22,000 @u1@u4C yr BP, a subtropical forest with conifer trees is indicative of cool and humid conditions. In agreement carbon isotopic data on soil organic matter suggest the presence of C@d3 plants and perhaps C@d4 plants from ~28,000 to ~19,000 @u1@u4C yr BP. The significant increase in the sedimentation rate and algal spores from ~19,450 to ~19,000 @u1@u4C yr BP indicates increasing humidity, associated to an erosion process between ~19,000 and ~15,600 @u1@u4C yr BP. From ~15,600 @u1@u4C yr BP to present there is a substantial increase in arboreal elements and herbs, indicating more humid and warmer climate. From ~19,000 to ~1000 @u1@u4C yr BP, d@u1@u3C values indicated the predominance of C@d3 plants. These results are in agreement with studies in speleothems of caves, which suggest humid conditions during the last glacial maximum.