HOLIVAR2006 Abstracts
Increased precipitation in SE Brazil during the Holocene recorded in sediments of Lago Aleixo.
Dirk Enters1, Hermann Behling2, Lydie Dupont3 and Bernd Zolitschka1
1GEOPOLAR, Institute of Geography, University of Bremen, D-28359 Bremen, Germany
2Palynology and Climate Dynamics, University of Göttingen, D-37073 Göttingen, Germany
3Geosciences, P.O. Box 330440, University of Bremen, D-28334 Bremen, Germany
Contact: Dirk Enters (enters@uni-bremen.de)
Lago Aleixo is located in the transition zone between tropical Atlantic rainforest and savannah vegetation (cerrado) in SE Brazil. Climatic changes, especially changes in precipitation rates, affect the distribution of these vegetation types. In this region, precipitation is influenced by the annual movement of the Intertropical Convergence Zone (ITCZ), the South Atlantic Anticyclone, Antarctic cold fronts, and El Nino-Events. The fossil pollen assemblages and geochemical proxies from laminated sediments of Lago Aleixo, SE Brazil, indicate that this sediment archive represents a sensitive record of environmental change in tropical South America.
Our analyses reveal that open savannah vegetation (campo cerrado) existed until approx. 6800 cal. yr BP. Then, increased precipitation and a shorter annual dry period allowed gallery forests and semi-deciduous forests to expand, leading to a more closed cerrado vegetation type. Higher rainfall caused increased minerogenic input into Lago Aleixo as evidenced by the fluctuating Ti and K contents in this part of the record. Elevated Ca/Al ratios starting around 6000 cal. yr BP can be explained by intensified chemical weathering of feldspars under more humid climate. Around 800 cal. yr BP a closed semi-deciduous forest developed under present-day climatic conditions and relatively low Ti and K signals in the sediment indicate a stable environment. The recent strong anthropogenic impact is displayed by a drastic rise of herbs accompanied by a decrease of forest species. Increased soil erosion after deforestation is documented by high K and Ti values.
Dirk Enters is a member of GEOPOLAR, Institute of Geography, University of Bremen. For his PhD, he reconstructed land use changes and soil erosion based on lacustrine sediments from central Germany. His research interests are paleoenvironmental reconstructions from (preferably laminated) lake sediments.