CONTROLS ON FLUVIAL PALEODISCHARGE AND SEDIMENT INFLUX: CURRENT PARADIGMS AND POTENTIAL FUTURE SCENARIOS FROM PASSIVE (GULF OF GUINEA) AND ACTIVE (CENTRAL AMERICA) MARGINS

The paradigm of fluvial paleodischarge and sediment influx in the tropics provides valuable information on the controls/drivers on climate evolution, eutrophication and sedimentary organic matter preservation. The seasonal migration of Intertropical Convergence Zone (ITCZ) and variability in monsoonal strength determined by precessional forcing are the main controls on precipitation and fluvial discharge. This study is comparing data from selected cores from the nearshore (40 m) and continental shelves (2,000-4,000 m) of the Gulf of Guinea (Congo, Niger Delta, Ghana/Ivory Coast margin) and Central America (Costa Rica, Panama Gulf) to test these controls during the latest Pliocene to Quaternary.

Integrated terrestrial and marine palynological records from the T89-16 Core (Congo) and GCs 1-3 (Niger Delta) in the Gulf of Guinea (GoG) record these drivers at the millennial-centennial time-scale. Paleoenvironmental inferences suggest that “flood pulse events” have influenced sedimentation rates on the Congo Fan and the Niger Delta. The data highlight a sequence of abrupt changes in the two locations registered by influxes of post-depositional pollen and non-pollen data to the GoG (Cyperaceae, Poaceae, Podocarpus, charred grass cuticles, Pediastrum, Ti/Zi ratios, sedimentation rates). These sporadic influxes provide evidence for enhanced fluvial discharge and river-induced upwelling during which fresh water plume nutrient rich, sedimentary organic matter, and sedimentation rates stimulated primary production, and phytoplankton blooms and preservation (e.g., dinoflagellate cyst productivity and demise). We suggest that this fluvial paleodischarge event from the Last Glacial Maximum (20 ka yr.) and subsequent deglaciation (18 to 9 ka yr.) likely resulted from latitudinal migration of the mean ITCZ across the GoG from its more southerly Last Glacial Maximum, suggesting the extension of monsoonal influences and mild arid conditions over the region.

Future investigations of cores from Costa Rica, Panama, and the Ghana/Ivory Coast margin will further test the effect of ITCZ and monsoonal forcing, and compare current paradigm shifts for regional and global coherence of the detailed causative controls within the passive Atlantic and active Pacific margins.