Fossiliferous deposits infilling a channel at Whittlesey, eastern England, are dated by amino acid racemization to the Last Interglacial, and pollen analysis indicates deposition in Ipswichian biozones Ip Ib and Ip IIb. Multidisciplinary palaeoenvironmental analyses of these deposits provide a rare insight into Ip Ib subzone conditions. Specifically, the Ip Ib deposits contain exotic thermophiles Naias minor, Belgrandia marginata, Bembidion elongatum, Pelochares versicolor, Caccobius schreberi, Onthophagus massai and Emys orbicularis, usually associated with Ip IIb. Combined palaeotemperature reconstructions based on beetle, ostracod and vertebrate assemblages of the Ip Ib deposits indicate that summers (mean July range +19 to +22°C) were at least 2°C warmer than at present, whereas winters (mean January air temperature range 0 to +7°C) were probably similar to those of today. These palaeotemperature ranges encompass those for Ip IIb deposits at Trafalgar Square (+20 to +21°C and +1.5 to +3°C), previously considered the only Ipswichian site to record temperatures significantly warmer than Holocene temperatures. Of particular significance is that thermal optimal conditions commenced in Ip Ib, rather than being confined to Ip IIb. This demonstrates rapid warming and biological response to early Ipswichian climate amelioration, which accords with the deep-sea Last Interglacial and European Eemian records.

Supplementary material: Supplementary Tables S1-S7 are available at

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