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Abstract: Middle Pleistocene warm periods are particularly useful for comparison with our present warm period. One of them, Marine Isotope Stage (MIS) 11, has been considered a potential analogue for the Holocene, whereas older interglacials, e.g. MIS 13, are distinctly different. However, terrestrial Middle Pleistocene sites, other than the Holsteinian, and quantitative climate reconstructions for this period are very rare in Europe. A unique terrestrial site in North Central Europe is known from Bilshausen, Germany. The sediments are varved and indicate that this interglacial lasted ∼25,000 years, more than twice as long as the Holocene so far. The warm period probably correlates to MIS 11, or possibly to MIS 13. A new palynological investigation with large pollen counts is presented which forms the basis for quantitative temperature reconstructions based on the probabilistic indicator taxa approach (the so-called pdf-method). The range of tree species that formed the vegetation during the Bilshausen warm period is reminiscent of the Holocene, but the vegetational as well as the reconstructed climatic development shows distinct differences. No pronounced initial successional phase is recorded in the pollen stratigraphy from Bilshausen. In addition, a mesocratic or optimum phase of forest development as in the Holocene is unclear in the Bilshausen sequence. Reconstructed temperature values are several °C lower than Holocene temperatures for most of the Bilshausen interglacial. Only for several millennia in the late phase of the Bilshausen interglacial were July temperatures higher than the Holocene July temperatures. Seasonality was much stronger during the Bilshausen interglacial and the temperature trends differ between the two interglacials. Likely reasons for the pronounced differences are, on one hand, global temperature, insolation changes and atmospheric circulation. On the other hand, more regional factors such as the configuration of the North Sea basin may also be responsible for the colder winter temperatures and stronger seasonality during the Bilshausen interglacial compared to the Holocene. Reliable absolute dating of the Bilshausen interglacial is needed, which would allow a more detailed evaluation of the forcing factors that determined the climate during the Bilshausen interglacial. [Copyright &y& Elsevier]

Abstract: Dramatic changes in European vegetation occurred during the transition from the Eemian interglacial to Weichselian glacial climates, correlative with major changes in global ice core and marine records. Quantitative knowledge of climate change is important for understanding of the climate system and for climate modelling, for which reconstructions of this transitional period are of special interest. However, it has been difficult to quantify the climatic changes involved in the Eemian to Early Weichselian transition from terrestrial archives due to the lack of modern vegetation analogues. To circumvent this problem, we applied a suitable multivariate probabilistic approach to pollen and plant macrofossil assemblages to reconstruct temperature and precipitation for this transition in central Europe. Our reconstructions span the interval from the beginning of the Eemian (Marine Isotope Stage (MIS) 5e) to the Odderade interstadial (MIS 5a). They indicate a relatively stable Eemian, with increasing precipitation reducing the continentality of the climate with time. During the transition from the Eemian to the Herning stadial, mean July and January temperatures decreased by ∼4°C and by as much as ∼20°C, respectively. Temperatures remained high enough to support forests during the stadials, and we infer that the reconstructed decrease of precipitation below 500mm per year caused the extirpation of forests during these periods. Thus, we conclude that precipitation, although difficult to reconstruct, is of vital importance for explaining vegetation change during the Eemian and Eemian/Early Weichselian transition. [Copyright &y& Elsevier]

Vegetation and climate during the last ice age and the Last Glacial Maximum (LGM, ∼23,000–19,000 cal BP) were considerably different than during the current interglacial (Holocene). Cold climatic conditions and growing ice-sheets during the last glaciation radically reduced forest extent in Europe to a restricted number of so-called “refugia”, mostly located in the southern part of the continent. On the basis of paleobotanical analyses the Euganian Hills (Colli Euganei) in northeastern Italy have previously been proposed as one of the northernmost refugia of temperate trees (e.g. deciduous Quercus, Tilia, Ulmus, Fraxinus excelsior, Acer, Abies alba, Fagus sylvatica, Carpinus and Castanea ) in Europe. In this study we provide the first quantitative, vegetation independent summer air temperature reconstruction for Northern Italy spanning the time ∼31,000–17,000 cal yr BP, which covers the coldest periods of the last glacial, including the LGM and Heinrich stadials 1 to 3. Chironomids preserved in a lake sediment core from Lago della Costa (7m a.s.l.), a small lake at the south-eastern edge of the Euganean Hills, allowed quantitative reconstruction of Full and Late Glacial summer air temperatures using a combined Swiss-Norwegian temperature inference model based on chironomid assemblages from 274 lakes. Chironomid and pollen evidence from Lago della Costa derives from finely stratified autochthonous organic gyttja sediments, which excludes major sediment mixing or reworking. After reconstructing paleo-temperatures, we address the question whether climate conditions were warm enough to permit the local survival of temperate tree species during the LGM and whether local expansions and pollen-inferred contractions of temperate tree taxa coincided with chironomid-inferred climatic changes. Our results suggest that chironomids at Lago della Costa have responded to major climatic fluctuations such as temperature decreases during the LGM and Heinrich stadials. The vegetation of the Euganean Hills shows responses to these climatic oscillations although the effects of temperature changes were probably also strongly influenced by changes in humidity. Reconstructed July air temperatures at Lago della Costa never fell below 10–13 °C (error range of reconstruction ∼ ±1.5–1.6 °C), which is considerably above the limit considered necessary for forest growth (8–10 °C). Instead rather mild climatic conditions prevailed ∼31,000–17,000 cal yr BP with average summer temperatures between ∼12 and 16 °C, which most likely allowed survival of temperate tree taxa in the warmest (and moistest) microhabitats of the Euganean Hills during the LGM. Only assuming local survival is it possible to explain the repeated expansions and collapses of temperate trees at Lago della Costa which faithfully accompanied the climatic oscillations. [ABSTRACT FROM AUTHOR]

We reconstruct mean July temperature (Tjul) from three sites on the island of Andøya, northern Norway for the period 15 000–9000 cal yr BP using three biotic proxies. A probabilistic indicator species approach (pdf method) was used for plant macrofossil data from all sites (M-Tjul). Reconstructions based on pollen (P-Tjul) (2 sites) and chironomids C-Tjul) (1 site) were done using weighted averaging and weighted-averaging partial least-squares, respectively. A sediment proxy for catchment glacier development was measured at the main site, Lusvatnet. The July temperature reconstructions from all the sites show a similar development through the deglaciation. An initial July temperature of 4 °C increased to a maximum of 7–8 °C during the Allerød at c.13 200 cal yr BP. There was no marked cooling at the start of the Younger Dryas (YD) chronozone, at Lusvatnet, C-Tjul decreased after 12 700 cal yr BP to a low of 6 °C at about 12 550 cal yr BP before increasing markedly around 12 400 cal yr BP. Conversely, P-Tjul rose slowly through the early YD. Both proxies exceeded the Allerød temperatures for around 300 years before decreasing towards a minimum of 6 °C at c. 12 000 cal yr BP. M-Tjul maintained a mean of c. 8 °C throughout the YD. Different sensitivities of proxies are discussed. Their different responses during the YD at the three sites, along with the glacial evidence, highlight the role of aridity. At c. 11 500 cal yr BP, July temperatures increased rapidly over Andøya to about 10 °C, and then rose gradually to maximum values of 12 °C at c. 9700 cal yr BP. The temperature reconstructions are consistent with the flow of Atlantic water into the Nordic Seas except during the YD, when variability in sea ice may have been more important. During the early Holocene there are some differences between sites, resulting from local site factors such as altitude and exposure, soil development, and catchment instability. [ABSTRACT FROM AUTHOR]