Stable climatic conditions in central Germany during the last interglacial

JOURNAL OF QUATERNARY SCIENCE (2000) 15 (5) 469–473Copyright 2000 John Wiley & Sons, Ltd.

Rapid communicationStable climatic conditions in central Germanyduring the last interglacialTATJANA BOETTGER1*, FRANK W. JUNGE2 and THOMAS LITT3

1UFZ-Centre for Environmental Research Leipzig-Halle, Department of Hydrogeology, Research Group forPalaeoclimatology, Halle/Saale, Germany2Leipzig University, Institute of Geophysics and Geology, Research Group for Palaeoclimatology, Leipzig, Germany3Bonn University, Institute for Palaeontology, Bonn, Germany

Boettger, T., Junge, F. W. and Litt, T. 2000. Stable climatic conditions in central Germany during the last interglacial. J. Quaternary Sci., Vol. 15, pp. 469–473. ISSN 0267-8179.

Received 16 October 1999; Revised 14 February 2000; Accepted 23 February 2000

ABSTRACT: Stable isotopic data from the high-resolution limnic sequence in the opencast mineat Grobern (central Germany) confirm the relatively stable climate of the last interglacial deducedfrom pollen analyses. After significant warming during the transition from the Saalian to theEemian, stable warm climatic conditions set in once the climatic optimum was reached in thecourse of biozones E4 to E5. From the middle of biozone E6b, a gradual temperature decreasecan be observed, reaching a minimum at the start of biozone E7. The division of the earlyWeichselian glacial in central Germany into two stadials (Herning, Rederstall) and two interstadi-als (Brorup, Odderade) is also documented by the findings. Copyright 2000 John Wiley &Sons, Ltd.

KEYWORDS: lake sediments; stable isotopes; palaeoclimate; last interglacial; central Germany.

Different climatic archives in the literature contain conflictinginformation about the course of the climate during the lastinterglacial in the Northern Hemisphere. The carefully exam-ined ice-core record from Greenland (Greenland Ice-coreProject (GRIP) Members, 1993; Johnsen et al., 1997) as wellas findings from individual marine (Sejrup et al., 1995) andcontinental European records (Field et al., 1994; Thouvenyet al., 1994; Cheddadi et al., 1998) provide indications thatthe climate of the last interglacial, the Eemian, was inter-spersed with a number of very cold spells. These eventsshow that short-term climatic fluctuations in the Eemianinterglacial may also have influenced the European conti-nent. Numerous pollen diagrams from the Eemian inter-glacial, however, do not provide any indication of suddensharp cold spells in western or central Europe, but documentinstead a stable climatic course throughout the Eemian(Zagwijn, 1996).

As a relative-stratigraphical method, pollen analysis (which

* Correspondence to: Tatjana Boettger, UFZ-Centre for EnvironmentalResearch Leipzig-Halle, Department of Hydrogeology, Theodor-Lieser-Strasse4, D-06120 Halle/Saale, Germany.Email: boettgerKhdg.ufz.de

Contract grant sponsor: Climatic variability and Signal Analysis Program,German BMBFContract grant number: FK2: 07KV01/1

assesses vegetation history) provides a basis for the palaeocli-matic and palaeoecological interpretation of isotopic datain the continental area. The d18O value of autochthonousfreshwater carbonates is determined by the d18O value andtemperature of the lake water at the time of its formation.The d18O values of the lake water reflect mainly the changesin the isotopic composition of the atmospheric precipitationof the catchment area, which is a function of climaticparameters, and the hydrological regime in the lake (degreeof evaporation), with the highest d18O values correspondingto warm and low values to cold climatic conditions. Thed13C values of both the carbonate and the organic sedimentfractions enable a better understanding of the behaviour ofthe d18O curve by reacting indirectly to climatic changes.For example, d13C of bulk organic carbon could dependon climatically linked changes in aqueous productivity, onfluctuations in the relative proportions of land-derived versuslake-derived organic carbon input, or changes in the isotopiccomposition of terrestrial components. During productivity,organic matter mainly incorporates the lighter carbon isotope(12C) from the limited reservoir of dissolved carbon dioxide.Values of d13Corg and d13Ccarb increase in response todecreasing concentrations of dissolved CO2 owing to highercarbon demand during photosynthesis (Hollander et al.,1988; Hollander and McKenzie, 1991). Depending on differ-ences in carbon isotope fractionation during photosynthesis,plants may be classified as C3 (higher plants with a rangeof d13C values of ca. −23 to −34‰ versus V-PDB), C4

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(grasses with a range of d13C values of ca. −7 to −23‰)and CAM plants (succulents mostly growing in a water-restricted environment). Hence d13Corg variables can causea climatically related C3–C4 vegetation shift if land-derivedorganic matter makes up a significant part of the bulksediment organic carbon (Bowen, 1991).

We present the findings of isotope–geochemical studiesof a complete high-resolution Eemian to early Weichselianlimnic sequence at Grobern, central Germany (Fig. 1). Asthe results of pollen analysis and the initial stable isotopefindings of this sequence (Litt et al., 1996) had a relativelycoarse profile resolution (sample interval 10 cm), it couldnot be ruled out that we might have overlooked the suddencold spells described for the Eemian. We therefore reducedthe sample interval to 1–2 cm in the Eemian stage forisotope–geochemical studies. The total of 170 samples exam-ined both for bulk carbonate and for total organic substanceenabled the high-resolution study of the entire sedimentsequence.

The accumulation of lake sediments starts on the top ofthe Saalian glaciation till with the late Saalian clay. Aboveit follow the limnic sequence of the Eemian (up to 4 mthick), which can be subdivided into seven biozones charac-terised by the close alternating stratification of lime andcoarse or fine detrital muds. This is followed by early Weich-

Figure 1 Map of central Europe showing the study area of the Eemian to early Weichselian sequence from the opencast mine Grobernwithin central Germany.

Copyright 2000 John Wiley & Sons, Ltd. J. Quaternary Sci., Vol. 15(5) 469–473 (2000)

selian sediments: coarse clay muds within the stadials andorganogenic sediments (calcareous muds, coarse and finedetrital muds, and peat) in the interstadials.

In both the Eemian (E) and the early Weichselian (WE)stages, close correlation was observed between the curvesrecording the carbonate level, its isotopic values (d13C, d18O),and the content and d13C value of total organic carbon inthe sediment (Fig. 2). The carbonate content of the sedimentwas determined in the warm stages by autochthonous car-bonate; in the cool stages carbonate formation was by con-trast very low or completely absent. The instability of thevalues in the carbonate contents in the profile is probablydue to the rapidly changing lithological conditions (closealternating stratification of lime and fine detrital muds).

The contact between the penultimate glacial (the Saalian)and the subsequent interglacial (Eemian) is recorded in allisotopic curves as a clear transition to more positive values.The range of the climatic optimum within the Eemian (E4b–5) is characterised by the heaviest carbonate isotopic valueswithin the sequence examined. As the profile continues intothe second half of biozone E6b, carbonate precipitation andd18O values remain more or less constant. From this stageonwards we observe a gradual, continuous trend among theisotopic indicators to lighter values. This trend comes to anend in the last part of E6b, at which point the carbonate

471CLIMATIC STABILITY DURING LAST INTERGLACIAL

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Figure 3 Pollen diagram of the Eemian–early Weichselian sequence from Grobern (adapted from Litt et al., 1996).

content also drops. In E7 we observe a renewed rise in thecarbonate level and the isotopic values, culminating in adistinct peak in all isotopic indicators.

The Corg level of the sediment, overwhelmingly representedby the remains of aquatic plants, continuously rises during thecourse of the Eemian interglacial and reaches even higherlevels in the Brorup (biozones WEIIa–d) interstadial. This docu-ments very high bioproduction in the lake during these warmstages. By contrast, the cooler stadials are characterised by lowCorg levels in the sediment. The proportion of terrestrial organicmatter (both C3 and C4 plants) in this sequence is very small


compared to lake-derived organic matter and can be neglected(Litt, personal information; see also Litt, 1994). Therefore inthis case the equilibrium between the productivity and theavailability of dissolved CO2 in the lake seems to be the keyfactor for the d13C values of the carbonate and the organicmatter (as also indicated by the significant correlationbetween them). The isotopic values of the organic carboncan be used as indirect climatic indicators via temperature-controlled bioproduction. No signs of drastic slumps in biop-roduction during the Corg content and d13C curves withinthe Eemian were observed (Fig. 2).

473CLIMATIC STABILITY DURING LAST INTERGLACIAL

In the transition to the early Weichselian, both carbonateand Corg levels as well as all isotopic values finally drop toa certain level, corresponding to glacial conditions of theearly Weichselian stadials (biozones WEI and III). The indi-vidual climatic zones during the early Weichselian stage aredistinguishable by pronounced d18O changes of 2–3‰. Thed13C values of the carbonate and the Corg react similarly.The first early Weichselian interstadial is characterised byintensive carbonate formation and a constant, clearly positivetrend in all isotopic indicators. A clear division of the Brorupinto two phases is documented by a minimum during WEIIcin all curves.

According to the d18O isotopic values, the entire Eemianinterglacial in the Grobern profile is climatically stable. Thisconfirms the previous palynological findings (Fig. 3). Aftersignificant warming during the transition from the Saalian tothe Eemian, stable warm climatic conditions set in once theclimatic optimum was reached during the course of biozonesE4 to E5. From the middle of biozone E6b, a gradualtemperature decrease without pronounced fluctuations isobserved, reaching a minimum at the start of biozone E7.Short-term cold fluctuations within the Eemian describedfrom other climatic archives cannot be confirmed by thefindings obtained here (stable isotopes, pollen). These com-bined stable isotopic and palaeobotanical results contrastsharply with the several published findings of central Euro-pean Eemian pollen profiles and with the GRIP ice-core. Itmust be stressed that by containing both biostratigraphicaland isotope signals, high-resolution continental records havean advantage over ice-core records.

Within biozone E7, a further short-term phase of warmingis substantiated by all the indicators in several samples.However, its amplitude is not on the scale of the Eemianclimatic optimum, but is instead comparable with the con-ditions found in the first early Weichselian interstadial. Thisclimatic oscillation is not discernible in the pollen stratigra-phy. This may be due to the slower or insufficient reactionof the vegetation to short-term warming phases—contrastingwith immediate reaction to changes in temperature by iso-topic variations in the course of carbonate precipitation, apurely chemical process.

The isotopic data of the high-resolution limnic sequenceat Grobern confirm the relatively stable climatic conditionknown in central Germany during the Eemian. The divisionof the early Weichselian glacial in central Germany intotwo stadials and two interstadials is also documented bythe findings (Litt et al., 1996; Walking and Coope, 1996).Moreover, the division of the Brorup interstadial is expressedin the isotopic values.

Acknowledgements This work is a contribution to the ‘ClimaticVariability and Signal Analysis’ program supported by the German


BMBF (Project FKZ:07KV01/1). We thank L. Eiβmann (Leipzig) andJ. Piotrowski (Aarhus) for valuable discussions and comments onthe manuscript.

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Stable climatic conditions in central Germany during the last interglacial