Expedition 388 Scientific Prospectus: Equatorial Atlantic Gateway

International Ocean Discovery Program (IODP) Expedition 388 seeks to answer first-order questions about the tectonic, climatic, and biotic evolution of the Equatorial Atlantic Gateway (EAG). The scheduled drilling operations will target sequences of Late Cretaceous and Cenozoic sediments offshore northeast Brazil, just south of the theorized final opening point of the EAG. These sequences are accessible to conventional riserless drilling in the vicinity of the Pernambuco Plateau, part of the northeastern Brazilian continental shelf. This region was chosen to satisfy two key constraints: first, that some of the oldest oceanic crust of the equatorial Atlantic and overlying early postrift sediments are present at depths shallow enough to be recovered by riserless drilling, and second, Late Cretaceous and Paleogene sediments preserved on the Pernambuco Plateau are close enough to the continental margin and at shallow enough paleowater depths (<2000 m) to provide well-preserved organic biomarkers and calcareous microfossils for multiproxy studies of greenhouse climate states. New records in this region will allow us to address major questions in four key objectives: the early rift history of the equatorial Atlantic, the biogeochemistry of the restricted equatorial Atlantic, the long-term paleoceanography of the EAG, and the limits of tropical climates and ecosystems under conditions of extreme warmth. Tackling these major questions with new drilling in the EAG region will advance our understanding of the long-term interactions between tectonics, oceanography, ocean biogeochemistry, and climate and the functioning of tropical ecosystems and climate during intervals of extreme warmth.