Holocene history of a lake filling and vegetation dynamics of the Serra Sul dos Carajás, southeast Amazonia

Abstract

Down-core changes in sedimentary facies, elemental geochemistry, pollen, spore, δ 13 C, δ 15 N and radiocarbon records from a filled lake, named R4, of the Serra Sul dos Carajás were used to study the relationship between the paleomorphological and paleoecological processes and their significance for Holocene paleoclimatology of the southeast Amazonia. The sediment deposition of the R4 lake started around 9500 cal yr BP. Increase of detrital components from 9500 to 7000 cal yr BP suggests high weathering of surrounding catchment rocks and soils, and deposition into the lake basin under mudflows. At that time, montane savanna and forest formation were already established suggesting predominance of wet climate. However, from 7000 to 3000 cal yr BP, a decline of detrital input occurred. Also, forest formation and pteridophytes were declined, while palms and macrophytes were remained relatively stable, indicating that water levels of the lake is likely dropped allowing the development of plants adapted to subaerial condition under drier climate conditions. After 3000 cal yr BP, eutrophication and low accommodation space lead to high lake productivity and the final stage of the lake filling respectively, and forest formation may has acquired its current structure, which suggests return of wetter climate conditions.

Upland Lakes of the Carajás Region: Origin and Development through Time

“…The Interpretation of speleothem data from Paraíso cave in eastern Amazonia indicate wetter climate conditions than present at around 6 ka cal BP (Wang et al, 2017). This contradicts a long set of paleoclimate studies in the Carajás region, that indicates dominance of montane savanna and SDF during the mid-Holocene under drier climate conditions (Absy et al, 1991;Sifeddine et al, 2001;Cordeiro et al, 2008;Hermanowski et al, 2014;Guimarães et al, 2016, Reis et al, 2018Guimarães et al, 2018b). Assumptions about the Holocene pollen assemblage of Carajás only reflect canga vegetation with small signals from HETF, then reflecting local changes on the plateau itself and making difficult any regional scale vegetation changes (Smith and Mayle, 2017), must be viewed with caution.…”

“…Generalized profile of the geochemical (Al/K with black line, Ti/K with blue-dashed line), isotopic (δ 13 C with black line, δ 15 N with blue dashed line), and pollen (canga vegetation with red line, forest with green line and cooladapted taxa with blue line) data of active (3 Irmãs, Violão and Serra Leste) and filled (R1, R2, R4, R5, ST02, LB3, LB4 and LTM) lakes. Light blue and red vertical bars represent wet and dry lacustrine phases in the ULs of Carajás according to Sifeddine et al (2001), Guimarães et al (2016Guimarães et al ( , 2018b, . Divided in 2 parts.…”

“…Drier mid-Holocene on Carajás region was proposed by Sifeddine et al (2001), Cordeiro et al (2008), Guimarães et al (2016), Reis et al 2018, Guimarães et al (2018b) mainly based on multi-elemental and organic isotope geochemistry with strong indications of hydric deficit, low weathering and sedimentation rates. In addition, LB3 and R2 lakes (~ 40 km distant from each other) were sub aerially exposed during this period with full formation of iron oxides and mud cracks ( Figure A.2).…”

“…It contradicts palynological and geochemical data from Serra dos Carajás. Such studies proposed extensive dries up of the upland lakes and dominance of montane savanna (canga vegetation) and dry-adapted semideciduous tropical dry forests (SDF), in detriment of humid evergreen tropical forest (HETF) (Absy et al, 1991;Sifeddine et al, 2001;Hermanowski et al, 2014;Guimarães et al, 2016Guimarães et al, , 2018b.…”

“…Palynological and geochemical studies were conducted on upland swamps in this region (Absy et al, 1991;Sifeddine et al, 2001;Cordeiro et al, 2008;Hermanowski et al, 2014;Guimarães et al, 2016Guimarães et al, , 2018b, so most of these records may reflect hydrarch succession and basin-filling rather than a paleoclimate signal. ULs may become more similar to terrestrial habitats during negative water balance produced by prolonged hydric stress, which may affect ecological attributes of water-dependent biota (Lopes et al, 2011;Mormul et al, 2015).…”