Middle Miocene oxygen minimum zone expansion offshore West Africa: Evidence for global cooling precursor events

Abstract

Three dissolution events ca. 16 Ma, 15.5 Ma, and 14.3 Ma ago have been identified in sediments from the Congo Fan. Multiproxy benthic foraminiferal and sedimentary records suggest an expanded oxygen minimum zone consistent with enhanced upwelling at these times. Marine carbonate records from adjacent North Africa indicate coincident episodes of increased continental weathering, suggesting that an intermittently stronger polar front strengthened west African offshore winds, increasing surface water productivity, and enhanced North African weathering during these events. We propose that Columbia River Flood Basalt volcanism, estimated to have released 10⁶ Tg CO₂ and 10⁶ Tg SO₂ between 16 and 15.6 Ma ago, may have influenced these climatic changes.