Pollen-based temperature and precipitation reconstructions were carried out using the probability density function "pdf" method (Kühl et al., 2002, doi:10.1006/qres.2002.2380). The “pdf method” has been previously applied to other Middle Pleistocene pollen archives, i.e., Hetendorf, Munster-Breloh and Gröbern-Schmerz (Kühl and Litt, 2007, doi:10.1016/S1571-0866(07)80041-8) and Bilshausen (Kühl and Gobet, 2010, doi:10.1016/j.quascirev.2010.08.006), which are located in a close distance to Dethlingen. The method estimates taxon-climate relations by probability density functions. Because it uses climate dependencies of many taxa and combines individually estimated plant climate relationships rather than relating complete pollen assemblages to climate, the method is relatively robust to scenarios when a taxon has shifted its climatic requirements with time (see Kühl et al., 2002, for a detailed description). The temperature reconstructions (Fig. S2) clearly show the continuous warming trend and the late climatic optimum that is characteristic for the Holsteinian interglacial (Kühl and Litt, 2007). In particular, a gradual increase in mean January temperatures, and to a lesser extent also in mean July temperatures, is observed during pollen zone (PZ) IX. Maximum temperatures are reached during the upper PZ XII and PZ XIII. During the OHO, the mean January temperatures decline by ~5 °C, whereas summer temperatures remain rather stable.