The Benguela upwelling related to the Miocene cooling events and the development of the Antarctic Circumpolar Current: evidence from calcareous dinoflagellate cysts

Sediment samples from ODP Site 1085 were investigated in order to obtain moreinformation on the initiation and development of the Benguela upwelling system duringthe middle and upper Miocene. In particular, our intent was to establish the causes of theupwelling as well as the response of the upwelling regime to the development of theAntarctic Circumpolar Current. Based on changes in the calcareous dinoflagellatecyst 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 increasesin cyst productivity in conjunction with temperature decreases of the upper water massesreflect upwelling pulses off Namibia and occur at the end of the Miocene coolingevents Mi5 (about 11.5 Ma) and Mi6 (about 10.5 Ma). Both cooling events are associatedwith an ice volume increase in Antarctica and are thought to have led to an increasein southeasterly winds, possibly causing these two upwelling pulses. We demonstratea decrease in dinoflagellate cyst productivity and enhanced terrigenous input via theOrange River after the Mi5 event. At about 11.1 Ma, the dinoflagellate cyst productivityincreases again. The polar cyst speciesCaracomia arcticaoccurs here for the firsttime. This implies an influence of subantarctic mode water and therefore a change in thequality of the upwelling water which allowed the Benguela upwelling to develop intomodern conditions. From about 10.4 Ma,C. arcticaforms a permanent part of theassociation, pointing to an establishment of the upwelling regime