Dados sobre as mudanças do clima e da vegetação da Amazônia durante o Quaternário

Absy, Maria Lúcia

doi:10.1590/1809-43921980104929

Cited by 13 publications

(8 citation statements)

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“…Therefore, the vegetation change from arboreal to grassy savanna probably occurred between 4572 and 11 420 BP. The two major dry periods reported to have occurred in tropical and sub-tropical regions of South America were from 4000 to 5000 BP, and from 10 400 to 10 500 BP (Absy & van der Hammen 1976;Absy 1980;Absy et ai 1991;Servant el ai 1993), which agree with the range found in the Pantanal soil.…”

Section: Discussionsupporting

confidence: 71%

“…Obviously, a change caused by a climatic fluctuation would equally affect both areas, as they are adjacent to each other. Eor regions where the climate has become drier for a period, as in the Amazon, it is expected that the establishment of a C4-rich vegetation is facilitated (van der Hammen 1974;Absy & van der Hammen 1976;Absy 1980;Markgraf 1989;Bush ct al. 1990;Absy et al 1991).…”

Section: Discussionmentioning

confidence: 99%

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Past vegetation changes in the Brazilian Pantanal arboreal–grassy savanna ecotone by using carbon isotopes in the soil organic matter

Victória¹,

Fernandes

Martinelli³

et al. 1995

Global Change Biology

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Measurements of the organic carbon inventory, its stable isotopic composition and radiocarbon content were used to deduce vegetation history from two soil profiles in arboreal and grassy savanna ecotones in the Brazilian Pantanal. The Pantanal is a large floodplain area with grass-dominated lowlands subject to seasonal flooding, and arboreal savanna uplands which are only rarely flooded. Organic carbon inventories were lower in the grassy savanna site than in the upland arboreal savanna site, with carbon decreasing exponentially with depth from the surface in both profiles. Changes in ^^C of soil organic matter (SOM) with depth differed markedly between the two sites. Differences in surface SOM "C values reflect the change from C3 to C4 plants between the sites, as confirmed by measurements of '^C of vegetation and the soil surface along a transect between the upland closed-canopy forest and lowland grassy savanna. Changes of ^^C in SOM with depth at both sites are larger than the 3-4 per mil increases expected from fractionation associated with organic matter decomposition. We interpret these as recording past changes in the relative abundance of C3 and C4 plants at these sites. Mass balances with ^'*C and "C suggest that past vegetational changes from C3 to C4 plants in the grassy savanna, and in the deeper part of the arboreal savanna, occurred between 4600 and 11 400 BP, when major climatic changes were also observed in several places of the South American Continent. The change from C4 to C3, observed only in the upper part of the arboreal savanna, was much more recent (1400 BP), and was probably caused by a local change in the flooding regime.

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Section: Discussionsupporting

confidence: 71%

Section: Discussionmentioning

confidence: 99%

Past vegetation changes in the Brazilian Pantanal arboreal–grassy savanna ecotone by using carbon isotopes in the soil organic matter

Victória¹,

Fernandes

Martinelli³

et al. 1995

Global Change Biology

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“…The maximum in the proportion of grass pollen was found in the middle Holocene from ca. 6,000 to 4,000 years before present (BP) for several placed in South America (Absy 1980;Servant et al 1989;Markgraf 1989;Absy et al 1991;Ledru 1992Ledru , 1993Servant et al 1993), from 10.500 to 10,400 years BP for central Brazil (Servant et al 1989(Servant et al , 1993Ledru 1993), and ca. 13.000 years BP for eastern Amazonia (Absy et al 1991).…”

Section: Introductionmentioning

confidence: 99%

Carbon-13 variation with depth in soils of Brazil and climate change during the Quaternary

et al. 1996

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Paleoecological and geomorphological studies indicate that, during the middle Holocene, there was a predominance of drier conditions with grassy savannahs replacing forests across the South American continent. Modern savannahs are composed mainly of C4 plants and soils developed under this type of vegetation show enrichment in 13C compared to soils under C3 vegetation cover. If soils contain stabilized organic mauer formed in the middle Holocene, we hypothesize that former C4 vegetation would be evidenced by a large enrichment of nc in soil organic matter (SOM). We investigate this possibility examining the depth variation of carbon isotopic composition in 21 soil profiles collected by different researchers at 14 different sites in Brazi I. Of these, profiles from only three sites showed a marked increase of nc with depth (9-10%0 enrichment in one difference between the surface soil and deepest depth); two sites showed intermediate enrichment (4-5%0), and nine sites showed a small enrichment of approximatelly 2.5%0. The majority of sites showing all-C3 derived SOM were in the Amazon region. Possible causes for the absence of a large I 3C enrichment with depth are: ( I) dominance of C3 rather than C4 grasses in mid-Holocene savannahas, (2) soil profiles did not preserve organic matter derived from mid-Holocene plants, (3) the retreat of forest areas did not occur on a regional scale, but was a much more localized phenomenon.

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“…A associação de solos corresponde ao Cambissolo Háplico nas posições bem drenadas da paisagem e ao Gleissolo nas depressões de acordo com a classifi cação Embrapa (2006). A cobertura vegetal corresponde ao contato fl oresta-savana, testemunho das variações paleoclimáticas quaternárias ocorridas no Brasil (Ab'Saber, 1977;Absy, 1980;Pessenda et al, 2001;Sanaiotti et al, 2002).…”

Section: Introductionunclassified

Pedogênese-Morfogênese Em Uma Topossequência Representativa Da Paisagem Sw Da Amazônia Brasileira

Rosolen

2012

Rev. Bras. Geomorfol.

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ResumoO intemperismo e a perda geoquímica dos elementos que compõem as rochas e solos são mecanismos importantes de evolução das paisagens tropicais. Na região sudoeste da Amazônia brasileira, a presença de depressões topográfi cas nas superfícies dos platôs suavizados e rebaixados determina a associação de solo Cambissolo, relativamente bem drenado, de constituição laterítica e presente nas partes topografi camente elevadas dos platôs, com solo Gleissolo mal drenado, sazonalmente saturado, desferruginizado e rico em matéria orgânica, presente nas depressões topográfi cas. Nesta unidade de paisagem, o estudo de uma topossequência representativa do sistema pedológico mostrou que o Cambissolo evolui verticalmente por pedoplasmação a partir de horizontes plínticos e o Gleissolo evolui lateralmente, transformando as características originais do Cambissolo, devido ao caráter semi-aberto da depressão e ao fl uxo hídrico subsuperfi cial lateral que esvazia, nos meses de baixa precipitação, a depressão saturada de água. Determinações dos teores dos óxidos totais por espectrometria de raios-X e da natureza dos argilominerais por difratometria de raios-X evidenciaram evolução lateral remontante do Gleissolo a partir do centro da depressão. Condições redutoras e conexão da depressão com o eixo de drenagem resultaram em acentuada perda de argila e aumento relativo da fração arenosa e da macroporosidade na matriz do solo, acompanhado por decréscimo dos teores de Fe 2 O 3 , Al 2 O 3 e outros elementos químicos. O empobrecimento químico e de argilas resultam em mudanças mineralógicas com presença marcante de caulinita, vermiculita-Al e gibbsita, acompanhada por diminuição da illita. A relação pedogênese-morfogênese é determinada pelo regime hídrico, que acentua a erosão geoquímica, o aprofundamento e alargamento das depressões e o consequente aumento da dissecação e lento rebaixamento da superfície topográfi ca. Palavras-chave:Depressão Topográfi ca; hidromorfi a; evolução da paisagem; bacia Amazônica. AbstractThe geochemical weathering and the losses of elements that composed rocks and soils are important mechanisms of tropical landscape evolution. Topographic depressions developed on lower and fl at plateaus of the southwest part of Brazilian Amazon River determine the occurrence of the Cambissolo-Gleissolo soil association. The well drained Cambissolo which has lateritic composition is located at high topographic position of the plateaus while seasonal waterlogged Gleissolo that has depletion of iron and accumulation of organic matter is located at topographic depression. In this landscape unit, the study of soil association of a representative toposequence has showed that the Inceptisol develops vertically by pedoplasmation from plinthic horizons, and the Entisol develops laterally, transforming the original characteristics of Cambissolo that due to the semi-open

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Dados sobre as mudanças do clima e da vegetação da Amazônia durante o Quaternário

Cited by 13 publications

References 0 publications

Past vegetation changes in the Brazilian Pantanal arboreal–grassy savanna ecotone by using carbon isotopes in the soil organic matter

Past vegetation changes in the Brazilian Pantanal arboreal–grassy savanna ecotone by using carbon isotopes in the soil organic matter

Carbon-13 variation with depth in soils of Brazil and climate change during the Quaternary

Pedogênese-Morfogênese Em Uma Topossequência Representativa Da Paisagem Sw Da Amazônia Brasileira

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