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| Titel |
Reconstruction of late Quaternary relative humidity changes on the southern slopes of Mt. Kilimanjaro, East Africa, using a coupled δ2H-δ18O biomarker paleohygrometer |
| VerfasserIn |
Johannes Hepp, Roland Zech, Kazimierz Różański, Mario Tuthorn, Bruno Glaser, Markus Greule, Frank Keppler, Yongsong Huang, Wolfgang Zech, Michael Zech |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133774
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| Publikation (Nr.) |
 EGU/EGU2016-14419.pdf |
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| Zusammenfassung |
| Our understanding of African paleoclimate/-hydrological history is decisively based on lake
level and lake sediment studies. It furthermore improved remarkably during the last decade
thanks to emerging stable isotope techniques such as compound-specific deuterium analysis
of sedimentary leaf wax biomarkers (δ2Hleaf wax). Here we present results from a
multi-proxy biomarker study carried out on a ~100 ka paleosol sequence developed in the
Maundi crater at ~2780 m a.s.l. on the southeastern slopes of Mt. Kilimanjaro in equatorial
East Africa. The Maundi stable isotope records established for hemicellulose-derived
sugars, lignin- and pectin-derived methoxyl groups and leaf wax-derived fatty acid
and n-alkane biomarkers (δ18Osugars, δ2Hmethoxyl groups, δ2Hfatty acids and
δ2Hn−alkanes) reveal differences but also similar patterns. Maxima characterize the
period from 70 to 60 ka, the last glacial maximum (LGM) and the Younger Dryas
(YD), whereas minima occur during the Holocene. The application of a ‘coupled
δ2Hn−alkane-δ18Osugar paleohygrometer’ allows the reconstruction of the Late Quaternary
relative humidity (RH) history of the Maundi study site. Accordingly, the reconstructed
RH changes are well in agreement with the Maundi pollen results. Apart from the
overall regional moisture availability, the intensification versus weakening of the
trade wind inversion, which affects the diurnal montane atmospheric circulation
on the slopes of Mt. Kilimanjaro, is suggested as local second important factor
controlling the RH history at Maundi. Furthermore, the Maundi results of the coupled
δ2Hn−alkane-δ18Osugar approach caution against interpreting δ2Hleaf wax (as well
as δ18Osugar) records straight forwards in terms of reflecting δ2Hprec, because
variably and primarily RH-dependent isotopic evapotranspirative enrichment of leaf
water can mask δ2Hprec changes. Concerning the biomarker-based reconstructed
Maundi δ2H/δ18Oprec record, the comparison with the reconstructed RH history
reveals an ‘anti-amount effect’. This suggests that we do not yet fully understand
the controlling factors for δ2H/δ18Oprec over East Africa and in low latitudes in
general as good as we may think and that respective further research is needed. |
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