Abstract:
Pliocene Age sediments from ODP Leg 175, Site 1085-A and B in the Cape Basin were analyzed to investigate the impact of the onset of Northern Hemisphere glaciation (ONHG) on the South Atlantic Benguela Current system from 4 -2 Ma. Proxies for productivity (concentrations and mass accumulation rates of total organic carbon (Corg), carbon to nitrogen ratios (C:N), weight percent sand, calcium carbonate and percent biogenic silica (opal)) peak at 3.2, 3.0, 2.4, and 2.25 Ma. Increased terrigenous sedimentation coeval with increased productivity indicators suggests that strengthened winds led to upwelling and enhanced productivity. However, at least some of the productivity signal may be due to enhanced preservation. Rapid burial by either eolian or fluvial transport links these intervals with continental climate changes resulting from 1) increased winds and/or dust availability due to higher aridity in the Namibia/northern South Africa region; 2) lowered sea-level related to increased ice volume; or 3) some combination. A switch from a hydrographic regime dominated by corrosive southerly component water masses (e.g., Antarctic Intermediate Water) to a northerly component water mass more hospitable to biogenic sediments (e.g., NADW) might also enhance preservation. That the peaks in productivity/ preservation are coincident with periods of increased preservation at Caribbean Site 999 (Haug and Tiedemann, 1998) indicates an inter-hemispheric oceanographic link. Future studies will allow us to focus on the specific relationships between oceanographic and terrestrial climate change, in addition to identification of leads and lags between the Northern and Southern Hemisphere systems, but this study documents that the Cape Basin record of marine sedimentation reflects global climate changes associated with the onset of Northern Hemisphere glaciation.