Reconstructing palaeotemperatures for the Early and Middle Pleistocene using the mutual climatic range method based on plant fossils

A new approach is proposed to obtain quantitative temperature reconstructio ns from Early and Middle Pleistocene pollen and megafloral records. Utilizi ng the indicator species concept pioneered by Iversen (1944, Geologiska For eningen Forhandlingar Stockholm 66, 463-483), the new methodology overcomes the problem of non-analogue plant communities by only taking into account the presence/absence of taxa rather than their relative abundances. Based o n the present day thermal tolerances of the taxa from a fossil assemblage, the temperature interval in which all taxa from this assemblage can coexist is determined. A databank containing the climate tolerances of 85 taxa fro m European pollen records was established. To increase the temperature reso lution of the method, procedures were developed to assess the most likely i ntervals for the actual temperatures within the calculated common thermosph eres and the routine evaluation of the mean temperatures of the warmest and coldest months (MTW and MTC). After calibrating the approach on modern ass emblages, it was applied to Tiglian and Holsteinian pollen sequences from L ieth (northern Germany) and Lac du Bourget (northern French Alps). For both records the method yields detailed temperature reconstructions of temperat e and cold episodes. During the coldest episode of the Lieth section, the M TC may have been as low as - 16 degreesC. Corresponding MTW values range fr om 14.5 to 21 degreesC, thus testifying to a strong continentality at that time. During the warmest period reconstructed for the Lieth section, the MT C was similar to the value as measured in the area today (1.5 degreesC), wh ereas the MTW was probably higher than at present (20.1 degreesC). For the coldest interval from the Lac du Bourget pollen sequence, the reconstructed MTC values reach a minimum of - 15 degreesC. Corresponding MTW values rang e from 15 to 22 degreesC, again implying a strong continentality. For the w armest period our approach yields MTC values between - 2 and 2 degreesC and MTW values between 16.5 and 22 degreesC. For both records, the resolution for the MTW and MTC reaches 1.5 and 2.5 degreesC, respectively. (C) 2000 El sevier Science Ltd. All rights reserved.