The upper sediment of Site U1540 (115 m) was recovered from the Subantarctic Zone, located in the central-eastern Pacific Southern Ocean, during IODP Expedition 383. The record spans 1.73 Ma, with temporal coverage focused on the Mid-Pleistocene Transition (~1.25–0.7 Ma). The sediments were analyzed for diatom abundances at a spacing of ~30 cm, processed using standard diatom preparation techniques, and analyzed by light microscopy (400–500 valves per sample) with taxonomic identification to species level.