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

Abstract

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.

A potential barrier to deep Antarctic circumpolar flow until the late Miocene?

“…This developed as a tear in the South American plate, on which the Northeast Georgia Rise is located, as the South Sandwich subduction zone retreated eastward (Barker, 1995;Smalley et al, 2007;Govers and Wortel, 2005). Interestingly, polar calcareous dinofl agellate cyst species fi rst appear in the sedimentary record off southwestern Africa at 11.1 Ma (Heinrich et al, 2011), also supporting a late Miocene ACC onset.…”

From the Namib around the world: biogeography of the Inuleae–Plucheinae (Asteraceae)

“…14 Ma. Alternatively, the mode and tempo of aridification (van Zinderen Bakker, ; Heinrich et al ., ) could imply that the ancestor of the subtribe was pre‐adapted to arid environments. As the number of large‐scale biogeographical studies of Namib Desert plants is few, it remains unknown if this is a unique/rare example or part of a more common pattern.…”

Scrippsiella trochoidea cysts in recent sediments from Amur Bay, Sea of Japan: distribution and phylogeny

“…Zonneveld et al (1997) reported that the total abundance of cysts in oxidised sediments was only about 10% of that observed in unoxidised sediments, a difference explained by a selective preservation of cyst species due to different oxygen conditions, rather than to the differential settling of grains. Moreover, the solubility of calcium carbonate increases with decreasing temperature (Vink et al 1999, Heinrich et al 2011, contributing to partial to complete dissolution of the calcareous components of the cyst wall.…”