This study presents a comprehensive morphometric analysis of Reticulofenestra coccoliths from Late Miocene to Pleistocene sediments from International Ocean Discovery Program (IODP) Site U1541, drilled in the Pacific sector of the Southern Ocean during Expedition 383 (in 2019). Twenty samples were taken during the sampling party in College Station, Texas (USA) in 2020 ranging from the Late Miocene to Pleistocene, prepared and examined (in 2024) under a LEICA EZ4 W petrographic microscope at 1000x magnification. Coccolith width and length were measured in light microscope on 2000 moderately- to well-preserved Reticulofenestra specimens, which were divided into four different size groups: R. minuta (7 µm). Age model is based on benthic foraminifera δ18O data according to Middleton et al. (2024, doi:10.5194/gchron-6-125-2024) for the uppermost 85 m core composite depth below seafloor (CCSF) of the shipboard splice, and to Winckler et al. (2021, doi:10.14379/iodp.proc.383.105.2021) for the rest (below 85 m CCSF).