Palaeotemperature calculations from the Praetiglian/Tiglian (Plio–Pleistocene) pollen record of Lieth, northern Germany: implications for the climatic evolution of NW Europe

The temperature evolution during the Praetiglian and Tiglian (Plio–Pleistocene) of northern Germany and the southern North Sea area is reconstructed based on the pollen record from Lieth, northern Germany. The examined record covers the time span from approximately 2.6 to 1.7 Ma. Calculations of the temperatures of the warmest (MTW) and coldest (MTC) months are presented utilizing the mutual climatic range principle. The thermal resolution of the reconstruction is increased through the calculation of most likely intervals for actual temperature ranges. For the analyzed pollen record, the MTW and MTC resolution reaches up to 1.5 °C using 100% most likely intervals and up to 1 °C using 70% most likely intervals. A seasonality index is calculated as a further tool for evaluating the climate development. The results indicate that cold and temperate stages during the Praetiglian and Tiglian were characterized by strong variations in winter temperatures in combination with relatively constant summer temperatures. Seasonality was highest during cold stages and lowest during the thermal optima of temperate stages. These seasonality variations are attributed to sea level changes as expressed in the North Sea Basin. Low seasonalities, which tend to co-occur with periods of high sea level, are interpreted to represent increased maritime influence. The seasonality variations may also be related to changes in Atlantic Ocean circulation and a southward shift of the polar front. The comparison of temperature calculations from Lieth with pollen-based temperature estimates for corresponding time intervals from the Netherlands reveals similarities and differences. For cold periods, the quantitatively obtained temperatures from Lieth are generally more extreme than the estimates from the Netherlands. These contrasts are too high to result solely from differences in the evaluation methods as can be shown through the application of our quantitative approach to pollen spectra from the Netherlands. Hence, the observed temperature contrasts between northern Germany and the Netherlands also reflect a temporary climate differentiation between these regions during cooler periods of the Praetiglian and Tiglian. The differentiation may be due to the respective vicinities of these regions to the North Sea.