Climate and environmental changes on the southwest of Amazon Basin over the last 1800 years documented by isotopic records in speleothems

Abstract

The South America Monsson System (SAMS) and Intertropical Convergence Zone (ITCZ) are the main responsible by convection over tropical and extratropical regions of South America. Despite several studies have shown that both systems are sensitive to solar variability (Novello et al., 2016; Bird et al., 2011) the interrelationship between SAMS and ITCZ was not well documented for the last millennium over the Amazon Basin. Reconstructing tropical hydroclimate history has been difficult, particularly in the Amazon Basin, one of Earth's major centers of deep atmospheric convection, largely because most study sites are located on the periphery of the basin (most in the Peruvian Andes) and interpretations can be complicated by sediment preservation, uncertainties in chronology, and topographical setting. Meehl et al. (2009) reported that peaks in solar forcing increase the energy input to the surface ocean at subtropical latitudes, thereby enhancing evaporation and near-surface moisture, which is carried by the trade winds to the convergence zones. Through this mechanism convective activity in the regions influenced by the upward branches of Hadley cell can be intensified, resulting in strengthened regional tropical precipitation regimes due to enhanced solar forcing (van Loon et al., 2004). This change in Hadley cell cold modulate the positions of the ITCZ, as well, modulate the intensity of SAMS. To verify the relationship between these convective systems with radiative forcing new paleoclimate records from non-explored study sites is required. The understanding of SAMS variability during the last millennia has been improved by studies involving d18O and trace elements on speleothems. For the current project, we propose the study of speleothems collected in caves of Rondonia State (Brazil) where still have a gap of high-resolution records for the last millennium. The stalagmites for this study were already collected, and its d18O and d13C records will be integrated with previously published records from several sites in South America, such as the Peruvian Andes (Bird et al., 2011), Cariaco Basin in Venezuela (Haug et al, 2001) and Paraiso Cave in Pará (Wang et al, 2017), in order to understand the evolution of SAMS over the Amazon Basin. Therefore, the current research plan has as a goal the study of the paleoclimatic changes during late Holocene (~3 thousand years) over Southwest Amazon Basin, based on high resolution isotopic variations of oxygen and carbon in speleothems precisely dated by the U/Th method, as well as the analysis of trace elements.