- During the Miocene, ocean temperatures in the southern Benguela system (ODP 1085) detected by two organic proxies (UK37 and TEX86) decreased by about 8 and 16°C, respectively, suggesting enhanced inflow of cold Antarctic waters and intensification of wind-driven upwelling. The stronger decline in TEX86 temperatures resulted from displacement of producing organisms to sub-surface waters with increasing productivity. The Benguela upwelling system was established at 10 Ma (Rommerskirchen et al., in revision).
- Afromontane forests disappeared from SW Africa in the Late Miocene and coastal vegetation changed from tropical grassland and thicket to semi-arid succulent vegetation indicating increased summer drought in step with the development of the Benguela upwelling system. The marine-driven climate change in SW Africa triggered substantial radiation in the terrestrial flora, especially in the Aizoaceae (Dupont et al, 2011).
- Parallel to upwelling intensification, intensity of southerly and south-easterly winds increased and moisture flux onto SW Africa declined. Riverine soil organic matter contributions diminished whereas eolian transported pollen and spores increased. These changes are consistent with a northward shift and intensification of the South Atlantic high pressure system.
- C4 plant expansion, based on δ13C analyses of leaf waxes, started at 8 Ma in SW Africa (ODP 1085) paralleled by increased input from grass and desert plant pollen. Hydrogen isotope compositions of leaf wax lipids indicate cooling until 10 Ma followed by a pronounced aridification from 8 to 6 Ma. At around 6 Ma, the δD compositions depict a rapid shift to lighter values which likely reflects a change in moisture source area from predominantly Atlantic to Indian Ocean.
- Preliminary data along a N-S transect (ODP 1081: 20°S, ODP 1085: 29°S, ODP 1087: 32°S) reveals that C4 plant expansion started at 8 Ma in the northern sites (ODP 1081 and 1085) and showed the most pronounced increase at the northernmost location (ODP 1081). At the southernmost site C4 plant expansion occurred after 6 Ma. This is consistent with a higher sensitivity of C4 plant expansion under warmer climates. All records show that C4 plant expansion extended into the Pliocene.
Dupont, L.M, Linder, H.P., Rommerskirchen, F., Schefuß, E. (2011): Climate-driven rampant speciation of the Cape flora. Journal of Biogeography, online. doi:10.1111/j.1365-2699.2011.02476.x
Rommerskirchen, F., Condon, T., Mollenhauer, G., Dupont, L.M., Schefuß, E. (2011), Miocene to Pliocene development of surface and subsurface temperatures in the Benguela Current system, Paleoceanography, 26, PA3216, doi:10.1029/2010PA002074.
Rommerskirchen, F., Dupont, L.M., Mollenhauer, G., Schefuß, E. (in preparation): Climatic changes favoring C4 plant expansion in SW Africa.