Miocene changes in the vertical structure of the Southeast Atlantic near-surface water column: Influence on the paleoproductivity

Stable isotopes of benthic and planktonic foraminifers and faunal analyses of planktonic foraminifers from two cores in the South Atlantic reveal paleoceanographic changes during the Mid-Miocene cooling interval (~14-7Ma). At ODP site 1092 (46.4°S, 7.1°E) the benthic d18O increase (~14.1-13.2 Ma) generates extraordinary heavy values, compared to other oceanic regions. This evolution suggests the subantarctic Atlantic to be a prime site of deep water formation. Surface water cooling is indicated by the gradual advance of relatively cooler foraminiferal faunas from ~13.6Ma to 10.3Ma. Since then both faunas and surface to deep d18O gradients indicate a hydrography similar to the modern Polar Frontal Zone.ODP site 1085 (29.4°S, 14.0°E), situated in the modern Southwest African upwelling area, exhibits a shift from (sub-)tropical faunas to cool, eutrophic faunas at ~11.3Ma, while increasing surface to deep planktonic d13C gradients imply enhanced surface productivity. Since ~10.5Ma, planktonic d18O records imply cooling and reduced thermal stratification of the upper ocean, most likely reflecting an invigoration of coastal upwelling.