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| Titel |
Stable carbon and nitrogen isotopes and amino acids in Holocene sediments of Lake Lonar, central India |
| VerfasserIn |
Philip Menzel, Birgit Gaye, Martin Wiesner, Nathani Basavaiah, Sushma Prasad, Martina Stebich, Ambili Anoop, Nils Riedel |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076467
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| Zusammenfassung |
| Investigations on surface sediments and a sediment core from Lake Lonar in central India
were carried out within the framework of the HIMPAC (Himalaya: Modern and Past Climate)
programme. The aim was to understand recent productivity, sedimentation, and degradation
processes and to reconstruct variations in Holocene lake conditions on the basis of
biogeochemical analysis on a 10 m long sediment core retrieved from the centre of Lake
Lonar. Located in India’s core monsoon zone, Lake Lonar offers valuable information about
the climate development of the whole region. The lake is situated at the floor of a meteorite
impact structure on the Deccan plateau basalt. The modern lake is characterised by
brackish water, high alkalinity, severe eutrophication, and bottom water anoxia. The
lake is about 6 m deep and fed by rainfall during the SW monsoon season and
three perennial streams. Since no out-flowing stream is present and no seepage
loss occurs, the lake level is highly sensitive to the balance of precipitation and
evaporation.
Here we present C/N, carbon and nitrogen isotope, and amino acid data of bulk organic
matter from modern lake and Holocene core sediments. Modern conditions are mainly related
to human activity which started to have persistent influence on the biological and chemical
lake properties at ~1200 cal a BP. The distribution of δ13C in the modern sediments is driven
by the ratio between terrestrial and aquatic organic matter, while δ15N seems to be influenced
by redox conditions at the sediment-water-interface with elevated values at shallow oxic
stations. Differences in the amino acid assemblages of oxic and anoxic surface sediment
samples were used to calculate an Ox/Anox ratio indicating the redox conditions during
organic matter degradation.
The onset of the monsoon reconstructed from the sediment core occurred at ca. 11450 cal a
BP. The early Holocene core sediments are characterised by low sedimentation
rate, low aquatic productivity, and predominantly anoxic conditions. A gradual
lowering of the lake level started at around 6350 cal a BP and culminated in the
precipitation of carbonate crystals between 4660 and 3890 cal a BP. The late Holocene
sediments indicate a low lake level and oxic conditions until anthropogenically
induced eutrophication caused high aquatic productivity and persistent bottom water
anoxia. |
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