Browsing by Author "Reis, Luiza Santos"

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    Hydroclimate and vegetation changes in southeastern Amazonia over the past ?25,000 years
    (Elsevier Ltd, 2022-04-07T00:00:00) Reis, Luiza Santos; Bouloubassi, Ioanna; Mendez-Millan, Mercedes; Guimar�es, Jos� Tasso Felix; de Ara�jo Romeiro, Luiza; Sahoo, Prafulla Kumar; Pessenda, Luiz Carlos Ruiz
    Stable isotope analysis of plant waxes (?13Cwax and ?Dwax) along with detailed pollen data provide a new perspective on vegetation and precipitation variability in Serra Sul de Caraj�s, southeastern (SE) Amazonia, over the past ?25 cal kyr BP. The ?Dwax record indicates drier conditions during the Last Glacial Maximum (LGM) and a transition to wetter conditions into the Holocene, while the ?13Cwax data reveal that vegetation did not experienced C3/C4 shifts and remained dominated by C3-plant communities. Under glacial conditions C3-savanna was prominent on the Serra Sul plateau with tropical forest areas limited to the lower slopes. Tropical forests expanded upslope and forest patches developed on the plateau as a response to more humid and warmer conditions during the Holocene. Pollen data indicate a shift towards more open landscape of savanna, woodlands, and open forests during the mid-Holocene. The ?Dwax record exhibits a distinct moisture variability during the Holocene, not always coherent with the vegetation data (pollen), especially during the mid-Holocene interval. Our study confirms the complexity and the overall lack of coherence among Holocene moisture proxy records throughout the monsoon domain in South America and suggest that Holocene local moisture conditions might not follow the regional monsoonal variability. Our data further stress the need for more multi-proxy reconstructions of hydroclimate patterns in SE Amazonia. � 2022 Elsevier Ltd
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    Landscape and Climate Changes in Southeastern Amazonia from Quaternary Records of Upland Lakes
    (MDPI, 2023-03-27T00:00:00) Guimar�es, Jos� Tasso Felix; Sahoo, Prafulla Kumar; e Souza-Filho, Pedro Walfir Martins; da Silva, Marcio Sousa; Rodrigues, Tarc�sio Magevski; da Silva, Edilson Freitas; Reis, Luiza Santos; de Figueiredo, Mariana Maha Jana Costa; Lopes, Karen da Silva; Moraes, Aline Mamede; Leite, Alessandro Sab�; da Silva J�nior, Renato Oliveira; Salom�o, Gabriel Negreiros; Dall�Agnol, Roberto
    The upland lakes (ULs) in Caraj�s, 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 Boca�na 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 Caraj�s plateau of southeastern Amazonia during the late Pleistocene and Holocene. � 2023 by the authors.