Mg/Ca in multiple species of planktonic foraminifera from five time slices since the Middle Miocene to present (target ages 15, 12.5, 10, 7.5, 4.5, 2.5 and 0 Ma). These samples are from a range of globally and latitudinally distributed DSDP (Deep Sea Drilling Program), ODP (Ocean Drilling Program), IODP (International Ocean Discovery Program) open ocean sites. From low to high latitudes these are: Site U1338, U1489 (Eastern and Western Equatorial Pacific), Sites 871, 872, and Site U1490, (Western Tropical Pacific), Site 242 (Mozambique Channel, Indian Ocean), U1482 (Australian Continental Margin), Site 516 (Western Atlantic Ocean), Site 1138 (Kerguelen Plateau, Southern Ocean). The Mg/Ca ratios were measured using Inductively coupled mass spectrometry (ICP-MS) at Cardiff University between December 2018 and June 2019. The data were collected to explore Mg/Ca values for modern and extinct species at different intervals of time (which were different climatically) and at different geographical locations. This data was collected by E.Mawbey as part of a project funded by NERC (Q10 project) to investigate changes in foraminiferal depth habitat in response to different climate conditions.