16. Quantitative time-series reconstructions of holsteinian and Eemian temperatures using botanical data

Abstract

Botanical fossils have successfully been used for quantitative climate reconstructions. Recent developments emphasize the need for statistical approaches which are robust to methodological problems such as the lack of modern analogues and which can quantify uncertainties. Therefore, a method based on probability density functions (pdf method) was chosen to reconstruct January and July mean temperatures throughout the Holsteinian interglacial stage at two Central European sites. The reconstructions were compared with those of the Eemian interglacial stage for two sites located very close to the Holsteinian sites. The reconstructions quantify similarities and differences between the Eemian and the Holsteinian temperature development. Both interglacials start with a relatively fast warming and end with a distinct cooling. During their course, they show uninterrupted interglacial conditions. However, the Holsteinian seems to be less stable than the Eemian with some intra-interglacial coolings. The magnitude of the main cooling in the mid-Holsteinian is reconstructed as approximately 5°C for January temperature. No great change is reconstructed for July temperature during this episode. The temperature course within the two interglacial stages differs. Reconstructed Holsteinian January and July temperatures were higher in the later part of the interglacial with highest reconstructed most probable values of 2°C and almost 20°C, respectively. The lowest reconstructed temperatures were2°C for January and 17.5°C for July. In contrast, the Eemian had its temperature optimum during its early phase. For the Eemian, the trend is more pronounced in January than July temperature with a continuous decrease of 3°C before the beginning of the early Weichselian. For the Holsteinian, a decrease of 10–15°C in average January and 3°C in July temperature is reconstructed at the very end of the interglacial, which resembles in magnitude to the temperature decrease at the end of the Eemian.