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| Titel |
Holocene climate variability and oceanographic changes off western South Africa |
| VerfasserIn |
Xueqin Zhao, Lydie Dupont, Michael E. Meadows, Enno Schefuß, Ilham Bouimetarhan, Gerold Wefer  |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250138634
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| Publikation (Nr.) |
 EGU/EGU2017-1713.pdf |
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| Zusammenfassung |
| South Africa is located at a critical transition zone between subtropical and warm-temperate
climate zones influenced by the Indian and Atlantic oceans. Presently, the seasonal changes
of atmospheric and oceanic systems induce a pronounced rainfall seasonality comprised of
two different rainfall zones over South Africa. How did this seasonality develop during the
Holocene?
To obtain a better understanding of how South African climates have evolved during the
Holocene, we conduct a comprehensive spatial-temporal approach including pollen
and dinoflagellate cyst records from marine sediment samples retrieved from the
Namaqualand mudbelt, a Holocene terrigenous mud deposit on the shelf of western South
Africa. The representation of different vegetation communities in western South
Africa is assessed through pollen analysis of surface sediments. This approach
allows for climate reconstructions of the summer rainfall zone (SRZ) using Group 1
(Poaceae, Cyperaceae, Phragmites-type and Typha) and winter rainfall zone (WRZ)
using Group 2 (Restionaceae, Ericaceae, Anthospermum, Stoebe/Elytropappus-type,
Cliffortia, Passerina, Artemisia-type and Pentzia-type) from a single marine archive.
The fossil pollen data from gravity core GeoB8331-4 indicate contrasting climate
patterns in the SRZ and WRZ especially during the early and middle Holocene. The
rainfall amount in the SRZ is dominated by insolation forcing, while in the WRZ it is
mainly attributed to the latitudinal position of the southern westerlies. Dinoflagellate
cyst data show significantly different oceanographic conditions associated with
climate changes on land. High percentages of autotrophic taxa like Operculodinium
centrocarpum and Spiniferites spp. indicate warm and stratified conditions during the
early Holocene, suggesting reduced upwelling. In contrast, the middle Holocene is
characterized by a strong increase in heterotrophic taxa in particular Lejeunecysta
paratenella and Echinidinium spp., indicating cool and nutrient-rich waters with active
upwelling. Thus, sea surface temperatures are dominated by upwelling dynamics
influenced by the latitudinal position of the southern westerlies rather than warm
waters via the Agulhas leakage. The paleo-productivity changes during the late
Holocene are controlled by the freshwater influx of the Orange River indicated
by abundant fluvial-related taxa such as Brigantedinium spp., Protoperidinium
americanum and Lejeunecysta oliva. This corroborates the increase of Poaceae/Asteraceae
ratio suggesting increased summer rainfall in the SRZ. Therefore, the terrestrial
(pollen) and marine (dinoflagellate cyst) records generated from the same sediment
sequence enable a clear understanding of the mechanisms driving variability in the
Holocene of South Africa and provide significant insight into the land-ocean linkages. |
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