Radiolarian and Sedimentologic Paleoproductivity Proxy Record From the Benguela Upwelling System, DSDP Site 532, 0-6 Ma

The Neogene history of the Benguela upwelling system is fundamental to better understand both regional climate change and how the global ocean cycles nutrients, including carbon. We examined the 0-6 my record of the system at ca. 400 kyr spacing from Walvis Ridge DSDP Leg 75 Site 532. More than 70 radiolarian taxa were counted and two indices computed: a water depth ratio index reflecting mid water export productivity, and the URI index of species that are biogeographically restricted to tropical upwelling regions. Both proxies have been applied so far only to the late Pleistocene. Other proxies measured on the samples include BFAR, TOC, % and MAR carbonate, bulk opal and radiolarian presevation (semiquantitative), foraminiferal dissolution indices, and stable isotopes of oxygen and carbon. The radiolarian water depth index, and to a lesser degree the URI, show gradually increasing productivity in the early Pliocene and high productivity through the late Pleistocene. This general productivity pattern for the region has been established by numerous prior studies. The radiolarian water depth index is strongly correlated to TOC, and importantly is not affected by low opal concentration and poor radiolarian preservation in the basal Pliocene and late Pleistocene. Carbonate, and carbonate microfossil based indices such as BFAR by contrast show largely inverse trends to radiolarians and TOC, but are interpreted as being predominantly dissolution controlled, as indicated by the carbonate dissolution proxies. Our results show that radiolarian faunas yield useful productivity proxies in these upwelling sediments as far back as the latest Miocene. Further, radiolarian based productivity proxies are relatively robust to preservation or the supply of silica to surface waters, which is thought to affect bulk opal based measures of productivity in the region.