Tropical rain forest and climate dynamics of the Atlantic lowland, Southern Brazil, during the late Quaternary

Palynological analysis of a core from the Atlantic rain forest region in Br azil provides unprecedented insight into late Quaternary vegetational and c limate dynamics within this southern tropical lowland. The 576-cm-long sedi ment core is from a former beach-ridge "valley," located 3 kin inland from the Atlantic Ocean. Radiocarbon dates suggest that sediment deposition bega n prior to 35,000 C-14 yr B.P. Between ca. 37,500 and ca. 27,500 C-14 yr B. P. and during the last glacial maximum (LGM; ca. 27,500 to ca. 14,500 14C y r B.P.), the coastal rain forest was replaced by grassland and patches of c old-adapted forest. Tropical trees, such as Alchornea, Moraceae/Urticaceae, and Arecaceae, were almost completely absent during the LGM. Furthermore, their distributions were shifted at least 750 km further north, suggesting a cooling between 3 degreesC and 7 degreesC and a strengthening of Antarcti c cold fronts during full-glacial times. A depauperate tropical rain forest developed as part of a successional sequence after ca. 12,300 C-14 yr B.P. There is no evidence that Araucaria trees occurred in the Atlantic lowland during glacial times. The rain forest was disturbed by marine incursions d uring the early Holocene period until ca. 6100 C-14 yr B.P., as indicated b y the presence of microforaminifera. A closed Atlantic rain forest then dev eloped at the study site. (C) 2001 University of Washington.