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Integrated Ocean Drilling Program Expedition 320/321, "Pacific Equatorial Age Transect" (Sites U1331–U1338), was designed to recover a continuous Cenozoic record of the equatorial Pacific by coring above the paleoposition of the equator at successive crustal ages on the Pacific plate. These sediments record the evolution of the equatorial climate system throughout the Cenozoic. As we have gained more information about the past movement of plates and when in Earth's history "critical" climate events took place, it became possible to drill an age-transect ("flow-line") along the position of the paleoequator in the Pacific, targeting important time intervals to reconstruct how the equatorial Pacific was involved in the climate change. The Pacific Equatorial Age Transect (PEAT) program cored eight sites from the sediment surface to basement, with basalt aged between 53 and 18 Ma, covering the time period following maximum Cenozoic warmth, through initial major glaciations, to today. The PEAT program allows the reconstruction of extreme changes of the calcium carbonate compensation depth (CCD) across major geological boundaries during the last 53 m.y. A very shallow CCD during most of the Paleogene makes it difficult to obtain well-preserved carbonate sediments during these stratigraphic intervals, but we recovered a unique sedimentary biogenic sediment archive for time periods just after the Paleocene/Eocene boundary event, the Eocene cooling, the Eocene–Oligocene transition, the "one cold pole" Oligocene, the Oligocene–Miocene transition, and the middle Miocene cooling. Together with older Deep Sea Drilling Project and Ocean Drilling Program drilling in the equatorial Pacific, we can also delineate the position of the paleoequator and variations in sediment thickness from ~150°W to 110°W longitude. Expedition 321, the second part of the PEAT program, focused on the time period roughly from 25 Ma forward. During Expedition 321 two major Neogene equatorial Pacific sediment sections were recovered at Sites U1337 and U1338.