Miocene

Climate-driven rampant speciation of the Cape flora
Dupont, L.M., Linder, H.P., Rommerskirchen, F., Schefuß, E.
Journal of Biogeography 38 (2011) 1059-1068

Abstract
The Cape Flora is exceptional in terms of endemism and species richness, which is the result of strong speciation in certain groups of plants. This radiation of the Cape Flora has been dated for the Late Miocene and is associated with the start of the Benguela Upwelling System. To test whether the radiation of the Cape Flora is correlated with marine-driven climate change, we studied the palynology of the thoroughly dated Middle to Late Miocene sediments of ODP Site 1085 retrieved from the Atlantic Ocean off the mouth of the Oranje
River. Both marine upwelling and terrestrial contributions are recorded at this site, which allows a direct correlation between the changes in the terrestrial flora and the marine Benguela Upwelling System in the south-east Atlantic. Pollen types from plants of tropical affinity disappeared, and those from the Cape flora gradually increased between 10 and 6 Ma. Inferred vegetation changes for the Late Miocene south-western African coast are the disappearance of Podocarpus-dominated Afromontane forests, and a change in the vegetation of the coastal plain from tropical grassland and thicket to semi-arid succulent vegetation. These changes are indicative of increased summer drought, and are in step with the development of the southern Benguela Upwelling System. They pre-date the Pliocene uplift of the East African escarpment, suggesting that it did not play a role in stimulating vegetation change. Some Fynbos elements were present throughout the recorded period (from 11 Ma), suggesting that at least some elements of this vegetation were already in place during the onset of the Benguela Upwelling System. This is consistent with a marine-driven climate change in south-western Africa triggering substantial speciation in the terrestrial flora, especially in the Aizoaceae.

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Miocene to Pliocene development of surface and subsurface temperatures in the Benguela Current system
Rommerskirchen, F., Condon, T., Mollenhauer, G., Dupont, L., Schefuß, E.
Paleoceography 26 (2011) PA3216

Abstract
The initiation of the Benguela upwelling has been dated to the late Miocene, but estimates of its sea surface temperature evolution are not available. This study represents data from Ocean Drilling Program (ODP) Site 1085 recovered from the southern Cape Basin. Samples of the middle Miocene to Pliocene were analyzed for alkenone based sea surface temperature (SST) and glycerol dialkyl glycerol tetraether (GDGT) based water temperature (TempTEX) proxies. In concordance with global cooling during the Miocene, SST
and TempTEX exhibit a decline of about 8°C and 16°C, respectively. The temperature
trends suggest an inflow of cold Antarctic waters triggered by Antarctic ice sheet
expansion and intensification of Southern Hemisphere southeasterly winds. A temperature
offset between both proxies developed with the onset of upwelling, which can be
explained by differences in habitat: alkenone-producing phytoplankton live in the euphotic zone and record sea surface temperatures, while GDGT-producing Thaumarchaeota are displaced to colder subsurface waters in upwelling-influenced areas and record subsurface water temperatures. We suggest that variations in subsurface water temperatures were
driven by advection of cold Antarctic waters and thermocline adjustments that were due to
changes in North Atlantic deep water formation. A decline in surface temperatures, an
increased offset between temperature proxies, and an increase in primary productivity
suggest the establishment of the Benguela upwelling at 10 Ma. During the Messinian
Salinity Crisis, between 7 and 5 Ma, surface and subsurface temperature estimates became
similar, likely because of a strong reduction in Atlantic overturning circulation, while high
total organic carbon contents suggest a “biogenic bloom.” In the Pliocene the offset
between the temperature estimates and the cooling trend was reestablished.

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