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Isotopic fingerprints on lacustrine organic matter from Laguna Potrok Aike (southern Patagonia, Argentina) reflect environmental changes during the last 16,000 years |
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| Authors: | Christoph Mayr Andreas Lücke Nora I Maidana Michael Wille Torsten Haberzettl Hugo Corbella Christian Ohlendorf Frank Schäbitz Michael Fey Stephanie Janssen Bernd Zolitschka |
| Institution: | 1. GeoBio-Center LMU and Department of Earth and Environmental Sciences, University of Munich, Richard Wagner-Str. 10, 80333, Munich, Germany 2. Institute of Chemistry and Dynamics of the Geosphere, ICG V: Sedimentary Systems, Research Center Jülich, 52425, Jülich, Germany 3. Department for Biodiversity and Experimental Biology, University of Buenos Aires—CONICET, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina 4. University of Cologne, Gronewaldstr. 2, 50931, Cologne, Germany 5. Sedimentology and Environmental Geology, Geoscience Center, University of G?ttingen, Goldschmidtstr. 3, 37077, G?ttingen, Germany 6. Argentine Museum of Natural History, Av. Angel Gallardo 470, Buenos Aires, Argentina 7. Geomorphology and Polar Research (GEOPOLAR), Institute of Geography, University of Bremen, Celsiusstr. FVG-M, 28359, Bremen, Germany |
| Abstract: | A combination of carbon-to-nitrogen ratios (TOC/TN), Rock Eval-analyses, and stable isotope values of bulk nitrogen (δ15N) and organic carbon (δ13Corg) was used to characterize bulk organic matter (OM) of a piston core from the Patagonian maar lake Laguna Potrok Aike (Argentina) for the purpose of palaeoenvironmental reconstruction. Sedimentary data were compared with geochemical signatures of potential OM sources from Laguna Potrok Aike and its catchment area to identify the sources of sedimentary OM. Correlation patterns between isotopic data and TOC/TN ratios allowed differentiation of five distinct phases with different OM composition. Before 8470 calibrated 14C years before present (cal. yrs BP) and after 7400 cal. yrs BP, isotopic and organo-geochemical fingerprints indicate that the sediments of Laguna Potrok Aike consist predominantly of soil and diatom OM with varying admixtures of cyanobacterial and aquatic macrophyte OM. For a short phase of the early Holocene (ca. 8470–7400 cal. yrs BP), however, extremely high input of soil OM is implied by isotopic fingerprints. Previous seismic and geochronological results indicate a severe lake-level drop of 33 m below present-day shortly before 6590 cal. yrs BP. It is suggested that this lake level drop was accompanied by increased erosion of shore banks and channel incision enhancing soil OM deposition in the lake basin. Thus, isotopic data can be linked to hydrological variations at Laguna Potrok Aike and allow a more precise dating of this extremely low lake level. An isotopic mixing model was used including four different sources (soil, cyanobacteria, diatom and aquatic macrophyte OM) to model OM variations and the model results were compared with quantitative microfossil data. |
| Keywords: | Stable isotopes Rock Eval analyses Organic matter Soil erosion Isotope mixing model South America Late Quaternary Lake sediments |
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