Landscape and Climate Changes in Southeastern Amazonia from Quaternary Records of Upland Lakes

Abstract

The upland lakes (ULs) in Carajás, southeastern Amazonia, have been extensively studied with respect to their high-resolution structural geology, geomorphology, stratigraphy, multielement and isotope geochemistry, palynology and limnology. These studies have generated large multiproxy datasets, which were integrated in this review to explain the formation and evolution of the ULs. These ULs evolved during the Pliocene–Pleistocene periods through several episodes of a subsidence of the lateritic crust (canga) promoted by fault reactivation. The resulting ULs were filled under wet/dry and warm/cool paleoclimatic conditions during the Pleistocene period. The multielement geochemical signature indicates that the detrital sediments of these ULs were predominantly derived from weathered canga and ferruginous soils, while the sedimentary organic matter came from autochthonous (siliceous sponge spicules, algae, macrophytes) and allochthonous (C3/C4 canga and forest plants and freshwater dissolved organic carbon) sources. Modern pollen rain suggests that even small ULs can record both the influence of canga vegetation and forest signals; thus, they can serve as reliable sites to provide a record of vegetation history. The integrated data from the sedimentary cores indicate that the active ULs have never dried up during the last 50 ka cal BP. However, subaerial exposure occurred in filled ULs, such as the Tarzan mountain range during the Last Glacial Maximum (LGM) and the Bocaína and S11 mountain ranges in the mid-Holocene period, due to the drier conditions. Considering the organic proxies, the expansion of C4 plants has been observed in the S11 and Tarzan ULs during dry events. Extensive precipitation of siderite in UL deposits during the LGM indicated drier paleoenvironmental conditions, interrupting the predominantly wet conditions. However, there is no evidence of widespread forest replacement by savanna in the Carajás plateau of southeastern Amazonia during the late Pleistocene and Holocene.

Late Quaternary hydroclimate and vegetation changes in an upland lake in southeastern Amazonia

“…Zone 2 (8.500-13.500 cal yr BP) showed decreased values of Hedyosmum (0-1%; 0-19 Meyers 1997, Troxler & Richards 2009, Sahoo et al 2015, Guimarães et al 2023a).…”

“…In addition, the decrease in the flow of the Amazon River has been associated with drier periods (Guimarães et al 2012). In the Carajás region, the rainfall levels dropped from the Late to the Middle Holocene (Absy et al 1991, Cordeiro et al 2008, Hermanowski et al 2012, Turcq et al 1998, Reis et al 2017, Guimarães et al 2021, 2023a.…”

“…However, these studies assumed that glacial-interglacial climate variations caused different responses in the forest composition. Some of them stated that in drier conditions, areas of open vegetation, such as savannas, advanced over forested areas (Absy et al 1991, Sifeddine et al 2001, Turcq et al 2002, Cordeiro et al 2008, Hermanowski et al 2012, D'Apolito et al 2017, in opposition to the hypothesis of forest stability (Colinvaux et al 1996, Bush 2002, Guimarães et al 2016, 2023a, Reis et al 2017. However, Amazonian tree cover can be quite resilient to reduced precipitation (Kukla et al 2021), questioning the widespread opening of forests during glacial times (Reis et al 2022), or strengthening the occurrence of isolated dry corridors of precipitation (Bush 2017), or wider networks of gallery or riparian forests connecting different biomes (De Oliveira et al 1999, Werneck et al 2012.…”

“…Together with palynological analyses, C and N isotopes were very important to elucidate factors related to floristic composition, history of plant communities and sources of organic matter in Carajás lakes (Guimarães et al 2023a). A detailed characterization of the organic matter components is a challenge, since it presents multiple sources, representing dynamic components of the sediments (Pereira et al 2022).…”

Urban Heat Island Assessment in the Northeastern State Capitals in Brazil Using Sentinel-3 SLSTR Satellite Data

“…Several factors can contribute to UHI formation, such as a city's impermeability, dark building components, geometrically unfavorable buildings for proper air circulation, man-made heat and pollution sources, and low wind speeds [7][8][9].…”