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| Titel |
Southeast African paleo-hydrological evolution for the last 35 kyr |
| VerfasserIn |
Yiming Wang, Thomas Larsen, Nils Andersen, Thomas Blanz, Ralph Schneider |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041676
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| Zusammenfassung |
| The modern precipitation in Southeast Africa is modulated by multitude of factors,
particularly the sea surface temperature (SST). However, the degree of coupling between SST
and hydrological cycles during the past in Southeast Africa is still poorly understood. In
this study, we use the δD and δ13C of sedimentary with odd numbered long-chain
n-alkanes (n-C27,29,31,33), in concert with other marine proxies (i.e. SST based
on alkenones, Mg/Ca, δ18O of foraminifera, XRF core scanning) from a marine
sediment core 16160-3 near the Zambezi river mouth (18º14.47’S, 37º52.27’W,
1334 m water depth) to reconstruct past hydrological changes and infer climate
controlling mechanisms for Southeast Africa. The preliminary results show that
δD from the very abundant long-chain alkane n-C29, which mostly derives from
terrestrial trees, anti-correlates strongly with the SST record, but the correlation is
less pronounced for the other abundant n-C31alkane. The δD signal of n-alkane is
assumed to reflect changes in humidity, as lower/higher values indicate wetter/drier
conditions. When δD values of n-alkanes increased (drier conditions) during the last
glacial-interglacial cycle (35-15kyr in our record), the SST was also getting cooler. The
observed coolest SST period was between 20 and 15kyr, which was also the driest on the
continent. The high fluctuations of n-alkane δD (both n-C31 and n-C29) are observed
from 15 to 10kyr, which may indicate that the δD records from Southeast Africa
are highly sensitive to rapid climate changes during Bølling/Allerød and Younger
Dryas. n-Alkane concentrations throughout the core show covariance with the
XRF records of Ti /Ca ratio and Fe/Ca ratio, both proxies for continental runoff.
Together, the XRF data and n-alkane concentrations suggest much greater runoff
during the glacial period (35 to 14kyr) compared to the Holocene. The n-alkane
concentrations do not follow the δD humidity signal completely; suggesting the
terrestrial weathering and run off are partly independent from precipitation changes. |
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