Norbert Kühl

A model‐data comparison of European temperatures in the Eemian interglacial

Compared to the wide range of different models used for the analysis of the climate system, GCMs have the most complex representation of the atmospheric physical processes. We have chosen the ECHO-G model as a state-ofthe-art OA-GCM to simulate the climatic conditions at 125 kyr BP by adapting the orbital parameters and greenhouse gas concentrations. [4] For terrestrial palaeoclimate reconstructions, the use of botanical fossils is well-established, because vegetation is in close relation to climate. Mainly pollen can be found in large numbers in suitable sediments, and macro remains add valuable information for important climate indicator species. For the reconstructions, recently developed botanical � � � � � � � � � � � � � � � � � � � � � ��

The European Modern Pollen Database (EMPD) project

Modern pollen samples provide an invaluable research tool for helping to interpret the quaternary fossil pollen record, allowing investigation of the relationship between pollen as the proxy and the environmental parameters such as vegetation, land-use, and climate that the pollen proxy represents. The European Modern Pollen Database (EMPD) is a new initiative within the European Pollen Database (EPD) to establish a publicly accessible repository of modern (surface sample) pollen data. This new database will complement the EPD, which at present holds only fossil sedimentary pollen data. The EMPD is freely available online to the scientific community and currently has information on almost 5,000 pollen samples from throughout the Euro-Siberian and Mediterranean regions, contributed by over 40 individuals and research groups. Here we describe how the EMPD was constructed, the various tables and their fields, problems and errors, quality controls, and continuing efforts to improve the available data.

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

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.

Late-glacial and Holocene European pollen data

ABSTRACT The European Pollen Database (EPD) is a community effort to archive and make available pollen sequences from across the European continent. Pollen sequences provide records that may be used to infer past vegetation and vegetation change. We present here maps based on 828 sites from the EPD giving an overview of changes in postglacial pollen assemblages in Europe over the past 15,000 years. The maps show the distribution and abundance of 54 different pollen taxa at 500 year intervals, supported by new age-depth models and associated chronological uncertainty analysis. Results show the individualistic patterns of spread of different pollen taxa, and provide a standardized dataset for further analysis, defining a spatial context for the study of past plant and vegetation changes and other aspects of environmental history in Europe.

Trees tracking a warmer climate: The Holocene range shift of hazel (Corylus avellana) in northern Europe

Palaeoecological records provide a rich source of information to explore how plant distribution ranges respond to climate changes, but their use is complicated by the fact that, especially when based on pollen data, they are often spatially too inaccurate to reliably determine past range limits. To solve this problem, we focus on hazel (Corylus avellana), a tree species with large and heavy fruits (nuts), which provide firm evidence of the local occurrence of species in the past. We combine the fossil nut records of hazel from Fennoscandia, map its maximum distribution range during the Holocene thermal maximum (HTM) and compare the fossil record with the Holocene hazel range shift as simulated by the LPJ-GUESS dynamic vegetation model. The results show that the current northern range limit of hazel in central and eastern Fennoscandia is constrained by too short growing seasons and too long and cold winters and demonstrate that the species responded to the HTM warming of about 2.5°C (relative to the present) by shifting its range limit up to 63–64°N, reached a rough equilibrium with the HTM climatic conditions and retreated from there to about 60°N during the last 4000 years in response to the late-Holocene cooling. Thus, the projected future warming of about 2.5°C would reverse the long-term southward retraction of species’ northern range limit in Europe and is likely to lead to hazel being a common, regeneratively reproductive species up to 63–64°N. In addition to the accuracy of the projected warming, the likelihood of this scenario will depend on inter-specific competition with other tree taxa and the potential of hazel to migrate and its population to grow in balance with the warming. In general, the range dynamics from the HTM to the present suggest a tight climatic control over hazel’s range limit in Fennoscandia.

A combined pollen and δ18OSphagnum record of mid-Holocene climate variability from Dürres Maar (Eifel, Germany)

In this study we investigate pollen and oxygen isotopes of moss cellulose from the peat bog ‘Dürres Maar’ in the Eifel low mountain range, Germany (450 m a.s.l.) to quantitatively infer mid-Holocene climate change for the period between ~7000 and 3800 cal. BP. Pollen was analysed on the same samples from which Sphagnum leaves were isolated to extract cellulose for the determination of its oxygen isotope composition (δ18O Sphagnum ). To quantitatively estimate January and July temperature and annual precipitation from the pollen data, we applied a probabilistic indicator taxa method (‘pdf-method’). The pollen-based reconstructions indicate July temperatures ~1°C higher around 6000 cal. BP than after ~5500 cal. BP, which is consistent with a ~1‰ decrease in δ18O Sphagnum during the same period. While the pollen-based climate reconstructions indicate little variability in summer temperature after ~5500 cal. BP, winter temperature shows several pronounced cold excursions of ~2–4°C in this period, which was likely accompanied by changes in precipitation patterns. Test reconstructions leaving out specific taxa indicate that not only larger climate trends, but also relatively small-scale climate variability can robustly be reconstructed with the pdf-method. This is of particular importance for reliable reconstructions of climate variability not only during the Holocene, but also in former interglacials, for which archives are rare and pollen is often the only suitable proxy in terrestrial records. The stable isotope values agree with the reconstructions based on pollen for the time between ~4500 and 3500 cal. BP, but not for the period before 4500 cal. BP. We explain this difference by atmospheric circulation patterns being different in the mid and late Holocene, respectively.

Transfer Functions for Paleoclimate Reconstructions — Applications

The aim of this study was to describe the applicability and the use of transfer functions in paleoclimate and paleoenvironmental research. In this chapter, different proxies (i.e. pollen, diatoms, carbon isotopes) were used in order to reconstruct the regional climate and environmental history throughout the Holocene. Case studies based on WA and WA-PLS transfer functions using diatoms showed the capability of siliceous algae to record environmental and climatic changes. However, the paleotemperature reconstruction from diatoms and their comparison with a pollen-based temperature reconstruction at Lake Lama, Siberia only revealed similar trends indicating different processes affecting the diatoms and pollen. The WA-based TP reconstructions from diatoms at Lake Woserin and Lake Holzmaar, Germany showed the response of the organisms to increased anthropogenic activities additionally to climate. Temperature reconstructions using carbon isotopes from tree-rings at high elevation sites of the Tibetan Plateau indicated that tree growth is temperature limited, although anthropogenic effects of changing atmospheric δ13CO2 and pCO2 may influence the calibration with measured meteorological data. Beside these reconstructions, we presented the methodology of a probability-based approach for a paleoclimate reconstruction using pollen distributions from sediments of the Dead Sea which is currently carried out.

Erratum to: The European Modern Pollen Database (EMPD) project

Unfortunately, the list of authors contains a number of duplications, omissions and other errors in the original publication of the article. The correct list appears in this erratum.

Multi-Scale Processes and the Reconstruction of Palaeoclimate

In this section, we focus on multi-scale problems encountered when reconstructing palaeoclimate on the basis of terrestrial botanical proxy data (pollen and macro remains). Climate and the taxonomical composition of the vegetation are affected and linked by complex geoprocesses acting on various spatial and temporal scales. We describe how the resolution of these data — both in space and time — limits the scale of features which can be reconstructed. We then present a Bayesian statistical transfer function relating vegetation and climate which is based on a Boolean approach (“taxon existent”-“taxon nonexistent”). This transfer function allows for an effective avoidance of “no modern analogue”-situations and intents to reduce the influence of sub-scale processes (e. g. local effects) and of non-climatic factors on the reconstruction.