Globobulimina affinis Mg/Ca ratios and δ¹⁸O records of IODP Site 339-U1385Data comprises IODP Site U1385 Mg/Ca, Fe/Ca and Mn/Ca ratios measured on infaunal benthic foraminifera Globobulimina affinis, along with paired (same sample) oxygen isotope ratios, determined using inductively coupled plasma-optical emission spectrophotometry (ICP-OES) and mass spectrometry in the Godwin Laboratory for Palaeoclimate Research, University of Cambridge. Paired Mg/Ca– δ¹⁸O records are used to deconvolve benthic δ18O into its deep-water temperature and δ18Oseawater components. All Mg/Ca ratios were corrected by applying a Mg/Mn ratio value of 0.32 mmol mol-1 to account for the potential presence of authigenic Mn-Fe-oxide coatings on sample foraminiferal calcite (de Lange, van Os and Poorter, 1992; Hasenfratz et al., 2017). δ¹⁸O values for Cibicidoides wuellerstorfi and Globobulimina affinis were corrected to Uvigerina by the respective offsets of +0.64 and -0.3 ‰ after Shackleton et al. (2000). Data are referenced to the LR04 stack (Lisiecki and Raymo, 2005) on the age model of Hodell et al. (2023).