O paleoclima do Holoceno na região de influência do Sistema de Monções da América do Sul e o potencial uso dos isótopos de Sr em conchas de sambaquis como indicador climático

Abstract

The seasonal variability of the South American Monsoon System (SAMS) is not fully understood. One of the ways to fill the gaps in research on this mechanism is through paleoclimatic reconstructions. The aim of this work is to search for a connection, from the use of climatic proxies for the Holocene, between the paleoclimatic profiles of the South and Southeast region with the Amazon Basin and also to evaluate the potential of the diversity of shells in sambaquis as a climatic indicator. To this end, a database was created containing occurrences and paleoclimate proxies from the literature review, in order to base future discussions involving new climate proxies related to SMAS. The data were classified according to the Köppen-Geiger Climate Classification System. 48 locations were obtained with paleoclimatic data for the South and Southeast of Brazil, which were analyzed and combined with Amazonian data and indices and satellite data of spatial coverage from the SACZ (South Atlantic Convergence Zone). For the proposal for paleoclimatic reconstruction were sampled ten sambaquis the state of Rio de Janeiro and Santa Catarina.Mollusks samples were colleted and taxonomically identified. In the sambaquis 35 taxa of mollusks were identified and seven shells of Phacoides pectinatus from the Forte and Beirada sites were selected for sclerochronology that showed few growth lines. In the geochemical analysis stage tests were carried out with recent shells of that same taxon for analysis of the 87Sr / 86Sr ratio through laser ablation mass spectrometry. In general, paleoclimatic data from the South and Southeast of Brazil are not regionally integrated and mostly use palynology as an analytical method. The most fpund climate type in these regions is and the region that has more studies is the Southeast. The most studied temporal range is Megalayano. Two SACZ behaviors (type I and II) were identified. The paleoclimate of these two regions was not stable under the Holocene.Between 10 and 5,000 years B.P. the climate was less stable and arid and from 5,000 years B.P. to the present day the climate has been more stable and with more moisture. The variation of SACZ was small and was gradually increased over the Holoceno. It is possible to combine the Holocenic paleoclimatic data from these two regions with data from the Amazon, apply paleoclimatic indices and list inferences about the climate connections involved, suggest new behaviors of the SACZ and consider the effects on climate on the evolution of human migration along the brazilian territory. The isotopic data obtained attest to the viability of the method and suggest that there is a relationship between the strontium ratio studied and environmental variables such as Sea Surface Temperature. The data also allow us to infer that sambaquis bivalves may be proxies to help in understanding the SAMS in the Holocene from the combination of sclerochronology and strontium isotope geochemistry techniques. However, further studies are needed to amplify the understanding of the variability of this system from this proxy