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| Titel |
Biomarker Record of Lake Van: Signals for Holocene Climate and Ecosystem Changes in Eastern Anatolia |
| VerfasserIn |
Ozlem Bulkan, Heinz Wilkes, M. Namik Çağatay |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097680
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| Publikation (Nr.) |
 EGU/EGU2014-13285.pdf |
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| Zusammenfassung |
| The ecosystem of Lake Van deserves special attention as the largest soda lake on
Earth (area: 3522 km2; maximum water depth: 451 m; water volume: 576 km3; and
alkalinity of 152 meq L-1; Kempe et al., 1991; Thiel et al., 1997). We present
new organic geochemical data on four Lake Van cores recovered from different
parts, extending back to 10500 (uncalibrated) years before present. A total of 65
samples were analyzed using basic organic geochemical (LECO and Rock-Eval) and
the 27 samples by detailed molecular organic geochemical methods (GC-MS and
GC-IRMS).
Bulk/molecular organic geochemical properties of the sediments from cores P01, P04 and
P05 (eastern part of the lake) indicate that the uppermost 2.5 m intervals of the cores exhibit
different characteristics than the lower parts. TOC content varies between 0.7% and 6% and
HI values between 175 and 535 mgHC/gTOC, with an average value of 325 mgHC/gTOC.
The results indicate that the organic matter is of mixed to algal origin. This conclusion is
supported by the n-alkane distribution, having its maximum at nC17, and strongly suggesting
predominantly aquatic producers. Lower intervals are lithologically characterized
by relatively thicker varves, laminae and bands. TOC content varies in a narrow
range between 0.9% and 1.5%. Low HI values (105-282 mgHC/gTOC) indicate
organic matter input of terrestrial plant origin, which is supported by the n-alkane
composition having the predominance of the C29 and C31 n-alkanes. However, core P07
(southwestern part of the lake) exhibits some differences in terms of sedimentary and
bulk/organic geochemical properties. The whole core is characterized by a very
distinct varved structure showing strong seasonality and the lack of bioturbation.
Sediments contain relatively low TOC (0,9 to 2.8%) with the organic matter consisting
predominantly of terrestrial to mixed type, as indicated by HI values of 78-330
mgHC/gTOC and C/N values of 8-10. The upper 2.3 m interval shows a dominance of
long chain n-alkanes, whereas the lower parts contain a higher contribution of C17,
C21 and C33 n-alkanes, indicating higher organic matter contribution from algal
sources.
δD values of n-alkanes vary over a wide range between -121oand -254ofor the nC17,
nC27, nC29 and nC31 alkanes in the sediments collected from the eastern part of the lake.
The lightest and heaviest values were measured for nC27. Relatively heavier values were
observed for the sediments of the southwestern core, where δD values ranged from -110oto
-202ofor the nC17, nC27, nC29 and nC31 alkanes. In general, nC17 exhibits the lightest δD
values in Lake Van sediments. Such light isotopic values of this compound probably reflect
isotopically light δD values of the lake water. Relatively heavy δD values of long-chain odd
carbon numbered n-alkanes may be enriched in relation to evaporation processes (Sachse et
al., 2006).
We propose that significant ecological changes have occurred in the lake ecosystem since
the early Holocene in terms of terrestrial organic matter flux and/or primary production
processes which is related to climate shifts. Volcanic events appear to be also an important
factor for the lake Van ecosystem. Probably, after the accumulation of the T-3 tephra layer
(dated 2.8 cal ka BP by Landman et al., 1996, and Litt et al., 2009) the ecosystem
has significantly changed and primary organic matter productivity has obviously
increased.
References:
Kempe S., Kazmirczak J., Landmann G., Konuk T., Reimer A., and Lipp A.,
1991. Largest known microbialites discovered in Lake Van, Turkey. Nature, 349,
605-608.
Landmann G, Reimer, A., Lemcke G, Kempe, S., 1996, Dating Late Glacial abrupt
climate changes in the 14,570 yr long continuous varve record of Lake Van, Turkey,
Palaeogeography, Palaeoclimatology, Palaeoecology 122 (1996) 107-118.
Litt, T., Krastel, S., Sturm, M., Kipfer, R., Orcen, S., Heumann, G., Franz, S.O., Ulgen, U
and Niessen, F., 2009, ‘PALEOVAN’, International Continental Scientific Drilling
Program (ICDP): site survey results and perspectives, Quaternary Science Reviews, 28;
1555–1567.
Sachse, D., Radke, J., Gleixner, G., 2006. δD values of individual n-alkanes from
terrestrial plants along a climatic gradient – implications for the sedimentary biomarker
record. Organic Geochemistry 37, 469–483.
Thiel, V., Jenisch, A., Landman, G., Reimer, A., Michaelis, W., 1997, Unusual
distributions of long-chain alkenones and tetrahymanol from the highly alkaline Lake Van,
Turkey. Geochimica et Cosmochimica Acta, 61, 10, 2053-2064. |
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