It's a Cool, Cool Miocene World - Part II

Well folks, I hope the suspense of learning about Middle to Late Miocene climate and tectonics in Africa hasn’t kept anyone up at night. With final exams, conferences and a new puppy (fun!) the blog had to take a back seat for a bit. But now, with the lazy (ha!) days of summer upon us, let’s continue with the…

TOP FIVE Incredibly Fascinating Facts (Theories? Speculations?) about Middle to Late Miocene Climate Change in Africa (and Worldwide too!)

#4. Evolution of ocean currents along the margin of Southwest Africa

Several deep-sea drilling sites have been investigated in the South Atlantic in an effort to characterize evolving ocean current circulation and latitudinal temperature gradients. For example, the following figure is from Robert et al. (2005) and shows the location of DSDP sites off the coast of SW Africa.



As Mel commented after the last post, there are some interesting links between ocean currents in this region and climate and sedimentation along the coast. The present-day Benguela current dominates ocean circulation and consists of a wide, cold layer approximately 80m thick that flows northward along the southwest African coastline. A counter-current flows southward at approximately 200-600m water depth and transports oxygen-depleted tropical waters. Beneath these currents the Antarctic Intermediate Water spreads nutrient-rich waters through the Cape Basin. To read more about the interaction of these currents, check out Robert et al. (2005) and Westerhold et al. (2005).

Deep marine climate proxy data from DSDP sites provide information about the evolution of these currents through time. For example, Antarctic nannofossils have been recovered from Early Oligocene sediments along the Walvis Ridge indicating northward ocean current intensification during this period. Upwelling along the southwest African coast likely began in the Late Miocene during formation of Antarctic ice sheets and caused increasing aridity along the Namib coastline. This is a really neat example of the interaction between deep ocean processes and climate/sedimentation on the adjacent continent!