(Table 1) Comparison of diatom-bound and bulk sedimentary d15N values of ODP Holes 175-1082A and 175-1084A

The Matuyama Diatom Maximum (MDM) is a time of peak opal accumulation from 2.6 to ~2.0 Ma within the Benguela Current upwelling system that was initiated by increased influence of Southern Ocean water on the eastern South Atlantic. We measured opal, total organic carbon (TOC), and CaCO3 fluxes and C and N stable isotopes in sediments deposited from 2.4 to 1.95 Ma at Sites 1082 and 1084 to explore the biogeochemical dynamics within the Benguela region. The infusion of Southern Ocean water delivered dissolved nutrients and Southern Ocean flora and fauna, resulting in local opal accumulation increasing up to 8 g/cm**2/ky and the production of diatom mats. Some d15N measurements of diatom-bound organic matter indicate that the mats grew within the Benguela region. The bulk sediment d15N records are taken to reflect changes in the d15N of nitrate in the incoming water, where lower values at 2.4 Ma reflect less nitrate utilization in the Antarctic. A long-term increase in relative nitrate uptake in the Southern Ocean is evidenced by the gradual increase in d15N toward 1.9 Ma.

(Table 1) TOC content, BIT, TEX86 and UK'37 indices, and sea surface temperature reconstruction for the middle Miocene to Pliocene of ODP Hole 175-1085A

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 presents 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 (UK'37, SSTUK) and glycerol dialkyl glycerol tetraether (GDGT) based (TEX86, TempTEX) water temperature proxies. In concordance with global cooling during the Miocene, SSTUK 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.

Stable carbon isotope ratios of n-alkane in ODP Hole 175-1083A in the South Atlantic Ocean (Table 1)

The intensification of Northern Hemisphere Glaciation (iNHG) is one of the critical climate thresholds in the Cenozoic. This study focuses on marine sediments recovered from Marine Isotope Stages 101/100 at the Ocean Drilling Program Site 1083 to assesses the impact of the iNHG on continental southern African vegetation through n-alkane (straight-chain hydrocarbon) abundance and delta13C values. The n-alkane abundance data yield a convoluted signal due to the number of controlling factors such as the source area, transportation routes and vegetation type. The C31 n-alkane delta13C values, however, exhibit a cyclic pattern with a periodicity of c. 20 ka, and are not correlated to the abundance data. It is inferred that the signal does not represent a change in the geographical source of n-alkanes. Instead, we suggest that the variations are caused by water-stress-induced changes in either carbon isotope fractionation during C3 photosynthesis or subtle changes in the proportion of C3 and C4 plants. These changes, unlike variations in oceanographic proxies, closely track precessional forcing factors and are independent of the prevailing obliquity-forced glacial/interglacial cycles. We conclude that the varying monsoon strength, rather than pCO2 or temperature change, forced changes in southern African vegetation during this period.

Dinoflagellate cyst counts and age model from sediment samples of ODP Hole 175-1085A

Sediment samples from ODP Site 1085 were investigated in order to obtain more information on the initiation and development of the Benguela upwelling system during the middle and upper Miocene. In particular, our intent was to establish the causes of the upwelling as well as the response of the upwelling regime to the development of the Antarctic Circumpolar Current. Based on changes in the calcareous dinoflagellate cyst association, we found an initial increase of the dinoflagellate cyst productivity, probably related to the initiation of upwelling about 11.8 Ma ago. Two distinct increases in cyst productivity in conjunction with temperature decreases of the upper water masses reflect upwelling pulses off Namibia and occur at the end of the Miocene cooling events Mi5 (about 11.5 Ma) and Mi6 (about 10.5 Ma). Both cooling events are associated with an ice volume increase in Antarctica and are thought to have led to an increase in southeasterly winds, possibly causing these two upwelling pulses. We demonstrate a decrease in dinoflagellate cyst productivity and enhanced terrigenous input via the Orange River after the Mi5 event. At about 11.1 Ma, the dinoflagellate cyst productivity increases again. The polar cyst species Caracomia arctica occurs here for the first time. This implies an influence of subantarctic mode water and therefore a change in the quality of the upwelling water which allowed the Benguela upwelling to develop into modern conditions. From about 10.4 Ma, C. arctica forms a permanent part of the association, pointing to an establishment of the upwelling regime.

Compound specific stable isotopes, BIT, pollen and spores of Miocene to Pliocene sediments of ODP Hole 175-1085A

Pollen and stable carbon (d13C) and hydrogen (dD) isotope ratios of terrestrial plant wax from the South Atlantic sediment core, ODP Site 1085, is used to reconstruct Miocene to Pliocene changes of vegetation and rainfall regime of western southern Africa. Our results reveal changes in the relative amount of precipitation and indicate a shift of the main moisture source from the Atlantic to the Indian Ocean during the onset of a major aridification 8 Ma ago. We emphasise the importance of declining precipitation during the expansion of C4 and CAM (mainly succulent) vegetation in South Africa. We suggest that the C4 plant expansion resulted from an increased equator-pole temperature gradient caused by the initiation of strong Atlantic Meridional Overturning Circulation following the shoaling of the Central American Seaway during the Late Miocene.