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GLIN==> SEMINAR - May 11 (Ann Arbor)


Tuesday, May 11, 2004

10:30 a.m.

""Lacustrine organic matter bulk and isotopic markers of environmental processes and paleoenvironmental changes: Examples from Lagoa do Caço (Maranhão State, Brazil).""

Dr. Abdel Sifeddine
IRD: Institut de Recherche pour le Développement. France

GLERL Main Conference Room
2205 Commonwealth Blvd.
Ann Arbor, MI 48105
For directions:


Organic matter is important to the reconstruction of paleoenvironmental changes from lacustrine sediments. Organic matter and its allochtonous and autochtonous fractions provide information about the evolution of ecosystems in the lake catchment and in the sedimentation basin and about physical and chemical water column conditions. Most studies that use organic matter as a marker of paleoenvironmental changes have been limited in their interpretations to descriptions of relative evolution. We present results of our study of recent sedimentation of lacustrine organic proxies and the application of these results to improved reconstruction of past environmental changes in Lagoa do Caço, Brazil. We measured organic C/N ratios, δ13C‰ and δ15N‰ values of surficial sediments collected along four transverse transects and one longitudinal transect in this lake. Each transverse profile starts from a margin characterized by emergent macrophytes, crosses the central part of the lake and finishes in the other margin of the lake. The bulk and isotopic results characterise the different depth zones of the Caço lake and identify the processes that control variations of bulk and isotopic parameters of organic matter in Lagoa do Caço. Generally, along each transect, these parameters show in the marginal zone a gradient between 0 to 4 meters decreasing for C/N and δ13C‰ values and increasing for δ15N‰ values. These parameters remain stable between 4 and 10 meters. Based on these results, we have reconstructed the history of lake level changes from sediment cores and also the changes in lake production linked to development of these ecosystems as consequences of lake level changes over the past 20,000 years.

For more information, contact:
Dr. Thomas Johengen
University of Michigan/CILER
Phone: 734-741-2203
Email:  johengen@umich.edu

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