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Titel |
Distribution and stable isotope composition of leaf wax n-alkanes as tracers for organic matter transport along hydrological transects in the NW Argentine Andes |
VerfasserIn |
Stefanie Tofelde, Dirk Sachse, Taylor Schildgen, Manfred R. Strecker |
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 |
250106991
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Publikation (Nr.) |
EGU/EGU2015-6677.pdf |
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Zusammenfassung |
The burial of organic matter in marine sediments represents the main long-term sink for
reduced carbon in the global carbon cycle, with the fluvial system being the predominant
transport mechanism. Organic matter deposited in marine and continental sediments contains
valuable information on ecological and climatic conditions, and organic proxy data is thus
often used in paleoclimate research.
To use sedimentary records to investigate past environmental conditions in the terrestrial
realm, processes dictating the transport of organic matter, including spatial and temporal
resolution as well as the influence of climatic and tectonic processes, have to be
understood. In this study, we test if a lipid biomarker based approach can be used
to trace present-day organic matter sources in a fluvial watershed draining two
intermontane basins in the southern-central Andes of NW Argentina, a tectonically
active region with pronounced topographic, rainfall, and vegetation gradients. We
investigated the distribution of long-chain leaf-wax n-alkanes, a terrestrial plant biomarker
(and as such representative of terrestrially sourced carbon), in river sediments and
coarse particulate organic matter (CPOM) along two altitudinal and hydrological
gradients. We used n-alkane abundances and their stable carbon and hydrogen isotopic
values as three independent parameters for source discrimination. Additionally, we
analyzed the control of environmental parameters on the isotopic signatures in leaf-wax
n-alkanes.
The general pattern of n-alkane distribution in river sediments and CPOM samples in our
study area suggest that vascular plants are the major source of riverine organic matter. The
stable carbon isotopic composition of nC29 alkanes suggests a nearly exclusive input of C3
vegetation. Although C4 plants are present in the lower catchment areas, the total percentage
is too low to have a detectable influence on the carbon isotopic composition in river sediment
and CPOM samples.
Considering environmental parameters, nC29 alkane δ13C values are significantly
correlated with mean annual rainfall in the respective catchment area, with less negative δ13C
values in drier areas (r = – 0.63, p < 0.01). The variability in stable hydrogen isotopic
composition (δD) of nC29 alkanes is determined mostly by the δD value of the source water
and aridity. We find that the apparent fractionation (?app), defined as the difference in
hydrogen isotopic composition of plant source waters and synthesized leaf-wax n-alkanes, is
significantly correlated with aridity (r = -0.65, p < 0.005), with a smaller apparent
fractionation in drier areas, as well as with mean annual rainfall (r = -0.59, p < 0.01),
relative humidity (r = -0.56, p < 0.02), and actual evapotranspiration (r = -0.53, p <
0.05).
Our data indicate that vascular plants are the major source of riverine organic matter, with
their stable carbon and hydrogen isotopic compositions influenced by climatic parameters.
Thus, on spatial scales covering large gradients in environmental parameters, the analysis of
leaf-wax n-alkanes can be used for organic matter source assessment in orogenic settings. |
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