Photographs, 18O/16O isotopic ratios, XRF-derived elemental and N, C concentration data are provided for sediment cores from Deep Sea Drilling Project Site 225, central Red Sea. This site was originally drilled in April 1972 by rotatary drilling to recover cores through parts of the Plio-Pleistocene sediments for studies of past Red Sea water properties and regional climate. The rotary drilling disturbed the sediments by varied amounts, though left some 1.5-m sections of core almost intact. The X-ray fluorescence (XRF) data comprise elemental proportions for the core archive sections selected where they showed the least drilling disturbance. These and the core photographs were obtained at Kochi University, Japan, using an ITRAX core scanner during 2023 and 2024. Given the age of the cores, the archive sections are not perfectly flat, hence the ITRAX-derived elemental data may be distorted by varied distance between the sensor and the core, as well as by cracks within the core. The user needs to judge these data against the core photographs. As the lighter 16O isotope is evaporated preferentially over 18O and tends to get locked up in ice sheets during glacial periods, measurements of the ratio 18O/16O in carbonate sediments are often useful for recording evidence of global climatic cycles. In the Red Sea, the ratio is further affected by local evaporation, as the basin has been variably isolated from the Indian Ocean, partly as a result of sea-level variations affecting the exchange of water between the basins. Samples of ~20 cm3 were selected with two sets of intervals. Coarse-interval sampling was chosen spanning the Plio-Pleistocene for reconnaissance, while denser sampling was carried out across particular intervals of scientific interest. Within these intervals, the shells of foraminifera were separated into different species. Shells of Cibicidoides mundulus were primarily selected for measurements of 18O/16O. Analyses were carried out in 2024 at the University of Southampton (UK) using a Kiel carbonate device coupled to a Mat253 IRMS. XRF core scanning and sampling were carried out by technical staff of the Marine Core Research Institute, Kochi University under supervision of the IODP Core Curator Yusuke Kubo. Diederik Liebrand disaggregated the samples, separated the foraminifera shells and carried out the oxygen isotopic measurements. Selected samples were also analysed for nitrogen and carbon contents (weight percent of bulk sample in columns B and C) at the University of Liverpool by Steve Crowley.
