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| Titel |
Coupling 2H and 18O biomarker results provides new insight into palaeohumidity changes in East Africa during the last glacial |
| VerfasserIn |
Johannes Hepp, Roland Zech, Mario Tuthorn, Bruno Glaser, Kazimierz Różański, Wolfgang Zech, Michael Zech |
| 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 |
250101753
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| Publikation (Nr.) |
 EGU/EGU2015-952.pdf |
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| Zusammenfassung |
| We couple compound-specific δ2H results of leaf wax-derived n-alkanes with
compound-specific δ18O results of hemicellulose-derived sugars extracted from
the loess-paleosol-sequence Maundi (3Ë 10’27.5”S, 37Ë 31’05.8”E) located on
the south-eastern slopes of Mt. Kilimanjaro at ~ 2780 m above sea level. This
coupled biomarker approach allows inter alia establishing a ca. 100 ka record of
the isotopic composition of leaf water. Accordingly, the deuterium-excess of leaf
water may serve as a proxy for palaeohumidity. Furthermore, the coupled biomarker
approach allows reconstructing the isotopic composition of palaeoprecipitation
(by using the slope the local evaporation line derived from a simple Craig-Gordon
model).
Our results suggest that sedimentary δ2Hleaf-wax records should not be interpreted
directly in terms of reflecting δ2Hprec because variable leaf water evaporative enrichment can
strongly overprint the δ2Hprec signal. The Maundi δ2Hn-alkane record can be
compared with δ2Hwax records from Lake Challa, Lake Tanganyika and Lake Malawi.
Accordingly, the Maundi δ2Hn-alkane record is generally in good agreement with the
Lake Challa and the Lake Tanganyika δ2Hwax records. However, a clear altitude
effect can be seen in the δ2H records (Maundi: 2780 m a.s.l.; Lake Challa: 880 m
a.s.l.; Lake Tanganyika: 773 m a.s.l.; Lake Malawi: 474 m a.s.l.). Moreover, the
Maundi δ2Hn-alkane record reveals a clear smaller range compared to the other
δ2Hwax records. Finally, especially the Lake Malawi δ2Hwax record reveals also
clearly different features than the other available δ2Hwax records. These differences
resulted in different interpretations of the δ2Hwax records (amount effect vs. source
effect).
Our coupled δ18Osugar and δ2Hn-alkane approach sheds new light into this
discussion. In brief, reconstructed low deuterium-excessleaf-water values during the
African Humid Period (AHP) indicate humid climatic conditions. By contrast, higher
deuterium-excessleaf-water values indicate that arid climatic conditions prevailed during the
Younger Dryas (YD), the Last Glacial Maximum (LGM) and during a mega drought period
(MD) having occurred ~ 70-60 ka BP.
Including the Maundi precipitation record in a circum pacific comparison may help to
identify the drivers of past isotopic composition on east equatorial African precipitation. |
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