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| Titel |
The origin of branched GDGTs in lake environments: Tracing allochthonous and autochthonous sources using compound-specific carbon isotope analysis |
| VerfasserIn |
Yuki Weber, Cindy De Jonge, Ellen C. Hopmans, Jaap S. Sinninghe Damsté, Adrian Gilli, Moritz F. Lehmann, Helge Niemann |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250104292
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| Publikation (Nr.) |
 EGU/EGU2015-3711.pdf |
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| Zusammenfassung |
| Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial membrane lipids that
are ubiquitous in soils and peat, as well as in sediments and suspended particulate matter
(SPM) of lakes, rivers and coastal marine environments. It has been found that the relative
distribution of brGDGTs changes systematically with ambient temperature and pH, making
them promising proxy indicators for paleoclimatic reconstructions in sedimentary archives. In
lacustrine deposits, it was initially assumed that brGDGTs mainly originate from
allochthonous soil organic matter, thus reflecting the integrated mean annual air
temperature (MAAT) within the watershed. Most recent research, however, strongly
suggest that the brGDGTs used for paleo-thermometry can also be produced in situ
within the lake system, offsetting the temperature-brGDGT relationships commonly
known from soils. Until now, disentangling the relative contribution of allochthonous
versus autochthonous brGDGT sources in lacustrine sediments was impossible,
complicating the use of brGDGTs for quantitative paleotemperature reconstructions. We
recently discovered a novel brGDGT isomer with a strongly 13C-depleted carbon
isotope composition of about 46.6‰ in sediments of a small eutrophic Alpine lake
(Lake Hinterburg, Switzerland), which was not present in soils collected from the
catchment. Furthermore, all other major brGDGTs in the sediment uniformly displayed
δ13C values of about 43Âo strongly contrasting the C-isotopic composition of
brGDGTs from catchment soils (ca. 27Â). These findings raise two prime questions: (1)
Are lake-derived brGDGTs generally more depleted in 13C with respect to their
allochthonous counterparts? (2) Does the δ13C of sedimentary brGDGTs serve as a
reliable indicator for lacustrine in situ production of brGDGTs? To address these
questions, we determined the 13C content of brGDGTs in surface sediments from
various lakes across the Swiss Alps by CG-IRMS analysis of their alkyl chains after
chemical degradation. Our data set provides valuable and unique insight into the stable
carbon isotope composition of brGDGTs in lake environments, and will aid in our
efforts to test and establish brGDGT-based proxies in aquatic sedimentary archives. |
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