Diatom census counts were used to quantitatively estimate summer sea-surface temperatures (SST) over the last 40,000 years in core MD12-3396CQ, collected in 2012 on board the R.V. Marion Dusfresne northeast of Kerguelen Island, Southern Ocean. The transfer function used to reconstruct summer (Janunary to March) SST is the Modern Analog Technique that here uses 249 surface sediment samples (modern analogs), the relative abundances of 32 diatom species and the chord distance to select the five most similar modern analogs (Crosta et al., 2020). This method yields a root mean square error of prediction of ~1 °C. The core chronology is detailed in Gottschalk et al. (2020).