Late Quaternary vegetational and climate dynamics in northeastern Brazil, inferences from marine core GeoB 3104-1

Late Quaternary paleoenvironments from northeastern (NE) Brazil have been s tudied by pollen analysis of marine sediment. The studied core GeoB 3104-1 (3 degrees 40' S, 37 degrees 43' W, 767 m b.s.l.) from the upper continenta l slope off NE Brazil is 517 cm long and > 42,000 C-14 yr BP old. Chronolog ical control was obtained by 12 radiocarbon (AMS) dates from individuals of the foraminiferal species Globigerinoides sacculifer. Modern pollen analog s were received from 15 river, lake and forest soil surface samples from NE Brazil. Marine pollen dates indicate the predominance of semi-arid caating a vegetation in NE Brazil during the recorded period between > 42,000 and 8 500 C-14 yr BP. The increased fluvial input of terrigenous material, with h igh concentrations of pollen and specially fern spores, into the marine dep osits, about 40,000, 33,000 and 24,000 C-14 yr BP and between 15,500 and 11 ,800 C-14 yr BP, indicate short-term periods of strong rainfall on the NE B razilian continent. The expansion of mountain, floodplain and gallery fores ts characterize the interval between 15,500 and 11,800 C-14 yr BP as the we ttest recorded period in NE Brazil, which allowed floristic exchanges betwe en Atlantic rain forest and Amazonian rain forest, and vice versa. The pale odata from core GeoB 3104-1 confirm the, in general, dry pre-last Glacial M aximum (LGM) and LGM conditions and the change to wet Lateglacial environme nts in tropical South America. The annual movement of the intertropical con vergence zone over NE Brazil, the strong influence of the Antarctic cold fr onts and changes of the high-pressure cell over the southern Atlantic, may explain the very wet Lateglacial period in NE Brazil. The documented NE Bra zilian short-term signals correlate with the documented Dansgaard-Oeschger cycles and Heinrich events from the northern Hemisphere and suggest strong teleconnections. (C) 2000 Elsevier Science Ltd. All rights reserved.