Paleoclimate reconstruction based on high-resolution multiproxy geochemistry of speleothems from Paraná and São Paulo states, Brazil

• Ano de defesa: 2020
• Autor(a) principal: Rodrigues, Julio Cauhy
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Cave floods; Climate reconstruction; Espeleotemas; Extreme precipitation events; Extremos de precipitação; Inundação em caverna; Paleoclimate; Paleoflood; Paleoinundação; Speleothems
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/44/44142/tde-19102021-085528/

One of the greatest limitations on evaluating climate changes impact and the occurrence of the extremes events resides in the limitation of historical data. In this context, speleothems records from cave galleries subjected to recurrent flood events are used to assess past frequency of extreme events. Detrital layers within speleothems deposited during flood recession are used here to reconstruct the occurrence of cave flood events for the last seven thousand years, allowing the study of these events beyond the pre-industrial period. Speleothems from Lage Branca and Malfazido caves are used here to reconstruct the frequency of cave paleo floods for the Mid-Late Holocene and for the last millennium, respectively. Well-resolved chronology for the speleothems were obtained by U/Th age method. Visual methods associated with PIXEs analysis were used to identify detrital layers associated with floods within the speleothems. Stable isotopes analyses were performed to access atmospheric-circulation conditions. Trace elements analysis (LA-ICP-MS) were performed for Malfazido speleothem and a previous record of trace element from Cristal cave are used. Correlation between the trace element ratios suggest that PCP and PAP are the main control in trace elements concentrations. Therefore, a novel high-resolution record is presented using principal component analysis for each speleothem that can account for most of the variance observed in the multivariate dataset. These PCs are used here as proxies for assess hydrological conditions in the cave sites by its relations with PCP and PAP. Statistical analysis of 18O with paleoclimate indices showed a possible link between the study area and SSTs anomalies from Atlantic and Pacific Ocean. Comparisons with paleoclimatic indices suggest that periods of high cave flood frequency in Malfazido cave may be related to SSTs anomalies associated with enhancement in SAMS activity over SESA or to El Niño-conditions and a possible link between extreme precipitation events and volcanic forcing is commented. Also, the paleoclimate reconstructions indicates that the transition between Middle and Late Holocene is marked by changing in the atmospheric circulation for conditions with higher South America Monsoon System (SAMS) activity and enhancement of summer rainfall as indicated by 18O and trace elements of speleothems from PETAR site. These changes are related to an abrupt increase in the paleoflood cave frequency after 4200 B.P., with a trend in 18O and trace elements indicating higher SAMS activity and wetter conditions. After 2000 B.P., Lage Branca cave may have been more susceptible to flood events due to increased summer precipitation, as showed by a hiatus in both speleothems characterized by a thick detrital layer. In summary, novel high resolution records of Malfazido and Cristal cave contribute in an unprecedented manner to understand the frequency of extreme precipitation events related to cave floods, and in which atmospheric-circulation and hydrological conditions that these changes in frequency; and the novel Lage Branca speleothems paleoflood record contribute to understand how low frequency cave flood can be affected by changes in the atmospheric circulation in response to change in the mean climate state associated with the modulations by insolation on the SAMS.