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| Titel |
Southeast Atlantic upwelling intensity changes influencing late Miocene C4 plant expansion? |
| VerfasserIn |
F. Rommerskirchen, T. Condon, G. Mollenhauer, E. Schefuß |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250022947
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| Zusammenfassung |
| The Late Miocene epoch (about 15 to 5 Myrs BP) is characterised by fundamental
changes in Earth’s climate system: turnovers in marine and terrestrial biota, sea-level
variability, changes in surface- und deep-water circulations, and increase in upwelling
intensities along the coasts [1,2]. During the transition period the Antarctic ice sheets
expanded and were permanently established, while additionally ice volumes began to
fluctuate [1]. Plants acting with the C4 concentrating mechanism of CO2 fixation
for photosynthesis expanded nearly simultaneous at different places in the world,
whereas the global CO2 levels exhibit no corresponding change [1,3]. However,
C4 plants are also known to have a competitive advantage in habitats of higher
temperature, light and fire intensities as well as of limited water supply, compared to the
almost ubiquitous C3 plants. This study tries to give insights to Miocene climatic
conditions in Southwest Africa and how these conditions may be linked to the C4 plant
expansion.
We focused on data from a sediment core of the Ocean Drilling Program (Leg 175, ODP
1085A), which span about 10 Myrs of the late Miocene. The core is situated in the Cape basin
at the south-western African continental margin in the upwelling zone of the Benguela
coastal current. The current brings cold, nutrient-rich waters from South Atlantic and the
Antarctic circumpolar current to the surface water along the coast of Southwest Africa.
Miocene sea surface temperatures (SST) were reconstructed by two indices, tetraether index
(TEX86) and an alkenone based index (U37K’). Both trends exhibit a shift to cooler
temperatures from around 27 to 18˚ C, but are different in rate and timing. Especially by
TEX86 reconstructed SSTs exhibit a similar trend as found for ice volume changes shown by
the δ18O curve [4]. These findings may reflect an intensification of the Benguela
upwelling current during the late Miocene, probably in association with the formation of
West Antarctic ice sheet. The increased upwelling enhances the marine primary
production shown by a small overall shift in the total organic carbon (TOC) content
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