Amazon cone isotopic stratigraphy: evidence for the source of the tropical freshwater spike
Abstract The isotopic stratigraphy of piston cores from the upper fan of the Amazon Cone reveals a negative planktic foraminiferal δ18O deviation from the global oxygen isotope signal that extends back into the last deglacial period. The benthic foraminiferal δ18O signal agrees with the global oxygen isotope signal and supports the lithological interpretation that the glacial/interglacial boundary occurs at the iron-rich crust on the Amazon Cone. The negative planktic foraminifera δ18O deviation from the global δ18O signal is interpreted as evidence of increased deglacial Amazon freshwater discharge to the equatorial Atlantic Ocean. 14C dates suggest that the Amazon tropical freshwater discharge initiated at 13.5 ky B.P., peaked at 9.6 ky B.P., and terminated at approximately 6 ky B.P. The timing of the tropical meltwater spike (Showers and Margolis, 1985) which peaked in the southern Venezuelan Basin at 9.6 ky B.P. can be linked to the flooding of the Amazon shelf and the reinitiation of the Brazilian Coastal Current. This change in equatorial circulation and advection of Amazon River freshwater to the North Atlantic via the Caribbean Surface Current, the Gulf of Mexico-Loop Current, the western Atlantic-Gulf Stream and the North Atlantic Drift may be the cause for the rapid termination of the Younger Dryas cool period.