Stefan Klotz

Continental European Eemian and early Würmian climate evolution: comparing signals using different quantitative reconstruction approaches based on pollen

Analyses of Eemian climate dynamics based on different reconstruction methods were conducted for several pollen sequences in the northern alpine foreland. The modern analogue and mutual climate sphere techniques used, which are briefly presented, complement one another with respect to comparable results. The reconstructions reveal the occurrence of at least two similar thermal periods, representing temperate oceanic conditions warmer and with a higher humidity than today. Intense changes of climate processes become obvious with a shift of winter temperatures of about 15 °C from the late Rissian to the first thermal optimum of the Eemian. The transition shows a pattern of summer temperatures and precipitation increasing more rapidly than winter temperatures. With the first optimum during the Pinus–Quercetum mixtum–Corylus phase (PQC) at an early stage of the Eemian and a second optimum period at a later stage, which is characterised by widespread Carpinus, climate gradients across the study area were less intense than today. Average winter temperatures vary between −1.9 and 0.4 °C (present-day −3.6 to 1.4 °C), summer temperatures between 17.8 and 19.6 °C (present-day 14 to 18.9 °C). The timberline expanded about 350 m when compared to the present-day limit represented by Pinus mugo. Whereas the maximum of temperature parameters is related to the first optimum, precipitation above 1100 mm is higher during the second warm period concomitant to somewhat reduced temperatures. Intermediate, smaller climate oscillations and a cooling becomes obvious, which admittedly represent moderate deterioration but not extreme chills. During the boreal semicontinental Eemian Pinus–Picea–Abies phase, another less distinct fluctuation occurs, initiating the oscillating shift from temperate to cold conditions.

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

Abstract A new approach is proposed to obtain quantitative temperature reconstructions from Early and Middle Pleistocene pollen and megafloral records. Utilizing the indicator species concept pioneered by Iversen (1944, Geologiska Foreningen 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 on 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 from European pollen records was established. To increase the temperature resolution of the method, procedures were developed to assess the most likely intervals for the actual temperatures within the calculated common thermospheres and the routine evaluation of the mean temperatures of the warmest and coldest months (MTW and MTC). After calibrating the approach on modern assemblages, it was applied to Tiglian and Holsteinian pollen sequences from Lieth (northern Germany) and Lac du Bourget (northern French Alps). For both records the method yields detailed temperature reconstructions of temperate and cold episodes. During the coldest episode of the Lieth section, the MTC may have been as low as −16°C. Corresponding MTW values range from 14.5 to 21°C, thus testifying to a strong continentality at that time. During the warmest period reconstructed for the Lieth section, the MTC was similar to the value as measured in the area today (1.5°C), whereas the MTW was probably higher than at present (20.1°C). For the coldest interval from the Lac du Bourget pollen sequence, the reconstructed MTC values reach a minimum of −15°C. Corresponding MTW values range from 15 to 22°C, again implying a strong continentality. For the warmest period our approach yields MTC values between −2 and 2°C and MTW values between 16.5 and 22°C. For both records, the resolution for the MTW and MTC reaches 1.5 and 2.5°C, respectively.

Cyclic climate fluctuations during the last interglacial in central Europe

Differentiating natural climate change from anthropogenic forcing is a major challenge in the prediction of future climates. In this context, the investigation of interglacials provides valuable information on natural climate variability during periods that resemble the present. This paper shows that natural cyclic changes in winter climates affected central European environments during the last interglacial, i.e., the Eemian, 126–110 ka. As a result of the extraordinarily high counting sums performed at Eemian pollen samples, it was possible to reveal a robust presence–absence pattern of the insect-pollinated, and therefore in the pollen rain underrepresented, taxon Hedera . This plant is known to require the influence of oceanic winter climates, i.e., moist and mild, in northwest and central Europe. By analogy with recent findings from the North Atlantics Holocene interglacial, the trigger of the Eemian climate variability may have been changes in solar activity, possibly amplified by changes in North Atlantic ocean currents and/or in the North Atlantic Oscillation. Our findings suggest natural cyclic changes to be a persistent feature of interglacial climates.

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

Abstract 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.

Elevation-induced variations of pollen assemblages in the North-western Alps: An analysis of their value as temperature indicators

Seventy-seven modern pollen samples from various elevations (350-2680 m a.s.l.) in two different areas of the north-western Alps (the Aosta Valley, Italy and the Taillefer Massif, France) were statistically analyzed to derive correlations between pollen assemblages, elevation and temperature at the sampled points. Numerical classifications were performed on pollen data to judge similarities between the two areas. The results show that a strong relationship exists between altitude and variations in pollen taxa percentages despite some floristic differences between the two areas. As a test, transfer functions from pollen percentages to elevation and temperature were calculated from pollen data. The reconstruction appears to be reliable, with a higher reliability at sites located over 1000m. This analysis aims to serve as a basis for further quantitative reconstruction of temperature changes during the Holocene based on fossil pollen data from sensitive regions that encompass a significant altitudinal gradient.