Was there an abrupt cold climatic event in the middle Eemian? Pollen record from a palaeolake at the Hieronimowo site, NE Poland

Seventy samples of lacustrine sediments from a palaeolake at the Hieronimowo site, NE Poland were investigated by pollen analysis method. The obtained results indicate that the examined sequence spans the whole Eemian Interglacial (MIS 5e), the beginning of the Early Vistulian (Weichselian; MIS 5d) and some undefined period of the Plenivistulian (Middle Weichselian; MIS 2-4). The specific feature of the studied profile is the great thickness of deposits representing the hornbeam phase of the Eemian Interglacial (E5 R PAZ), which was the younger part of the climatic optimum of this interglacial, and the very well developed pollen record of this phase, that is absent in other profiles in NE Poland. Due to this, our study allowed, for the first time in NE Poland, the detailed reconstruction of changes in the vegetation and in the mean January and July temperature during the middle part of the Eemian Interglacial. This reconstruction unequivocally rules out the existence of an abrupt short-lasting cold event at that time. Only a gradual slight increase in temperature was apparent during the older part of the hornbeam phase (to >21 °C for July, and to >0 °C for January) and gradual decrease during its younger part (to >17 °C for July, and to > -5 °C and <-2 °C for January). So during the warmest part of the hornbeam phase, reconstructed temperatures for July were similar as in older part of the Eemian optimum (hazel phase, E4 R PAZ), however they were approximately 2 °C higher for January.