The UK’37 index is based on the degree of unsaturation in organic compounds produced by haptophyte algae, which varies systematically with sea‑surface temperature. It provides highly precise temperature estimates, though calibrations differ at the warmest temperatures where the proxy approaches saturation. For MioOcean, we use established modern core‑top calibrations and treat values near UK’37 ≈ 1.0 as indicators of very warm (>29°C) surface waters.