Paleoclimate of the last two millenia in Northeast Brasil revealed by lake Boqueirão sedimentation.

The climate of Northeast Brazil is strongly related to ITCZ position upon Tropical Atlantic ocean during South Hemisphere summer and autumn. This position is related to SST gradients and Northeast Brazil is thus a key region for past ITCZ reconstructions. It is generally considered, in paleoclimate studies, that during phases of ITCZ southern shift, the climate in northern South America is drier while it is wetter in Amazonia and Northeast Brazil. Two cores have been collected and studied in the frame of ANR project ESCARSEL in lake Boqueirao (5°25'S, 35°55'W). The proxies of lake level variations at this site are sand content, bulk sedimentary organic matter characteristics (TOC, C/N, Hyfrogen Index, Oxygen Index, δ 13 C, δ 15 N) and organic markers as PTMES and des-A-triterpens. The lake level, which was very variable until 200 BC, presented low levels at 350, 800 and 1300 AD. The lowest level of the last 2000 years has occurred between 1450 and 1960 AD when the lake completely dried. Comparison with other South America data does not show a good agreement between observations and ITCZ shift hypothesis, particularly during the LIA which is cold in the Northern Hemisphere and dry in both northern and southern tropical Atlantic. During the medieval period, analysis of a Coupled Global Circulation Model (MILL5 simulation from CERFACS) at 1250 AD suggests an influence of volcanic eruptions on the dry phase observed in Northeast Brazil region at that time.