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During Integrated Ocean Drilling Program (IODP) Expeditions 320 and 321, a series of sites associated with the paleoequator was cored in order to reconstruct Eocene to Holocene paleoceanographic conditions. Two sites of particular interest to this study are Sites U1334 (7°59.998′N, 131°58.408′W; 4799 m water depth) and U1338 (2°30.469′N, 117°58.178′W; 4200 m water depth). Sediments from Site U1334 represent the Eocene–Oligocene transition and provide insight into the response of the equatorial Pacific region associated with the greenhouse–icehouse transition. Sediments from Site U1338 represent early–middle Miocene to recent paleoceanographic conditions in the equatorial Pacific region, in particular the significant increase in sedimentation during the early middle Miocene.

Diatoms were examined from both sites, the Eocene–Oligocene sequence of Site U1334 and the Neogene–recent sequence of Site U1338. The purpose of the study was to document the overall variability in total diatom, silicoflagellate, and radiolarian abundance, as well as the variation in diatom species throughout the examined intervals. The emphasis of this study concerns variations in the diatom flora.