Diatom responses to limnological and climatic changes at Ribains Maar (French Massif Central) during the Eemian and Early Würm |
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| Institution: | 1. Earth and Environmental Sciences, University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland;2. Departamento de Biodiversidad y Biología Experimental, FCEyN-UBA, Buenos Aires, Argentina;3. Geomorphology and Polar Research (GEOPOLAR), Institute of Geography, University of Bremen, Celsiusstr. FVG-M, D-28359 Bremen, Germany;1. Paleoecological Environmental Assessment and Research Laboratory, Queen''s University, Department of Biology, 116 Barrie Street, Kingston, ON K7L 3N6, Canada;2. Dorset Environmental Science Centre, Ontario Ministry of the Environment, Conservation and Parks, P.O. Box 39, 1026 Bellwood Acres Road, Dorset, ON P0A 1E0, Canada;3. Hutchinson Environmental Sciences Limited, 4482 97 Street NW, Edmonton, AB T6E 5R9, Canada;4. Hutchinson Environmental Sciences Limited, Suite 202, 501 Krug Street, Kitchener, ON N2B 1L3, Canada;1. Dipartimento di Scienze della Terra, dell''Ambiente e delle Risorse, Università degli Studi di Napoli, Federico II Largo S. Marcellino 10, 80138, Napoli, Italy;2. Istituto per l''Ambiente Marino Costiero (IAMC)–CNR, Calata Porta di Massa, Interno Porto di Napoli 80, 80133, Napoli, Italy;3. Department of Geoscience, University of Wisconsin, Madison, WI, USA;4. Istituto per l''Ambiente Marino Costiero (IAMC)–CNR, Via del Mare 3, 91021 Campobello di Mazara, TP, Italy;1. Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK;2. Research Laboratory for Archaeology and the History of Art, University of Oxford, Oxford OX1 3QY, UK;3. Department of Geology, Trinity College Dublin, College Green, Dublin 2, Ireland;4. GFZ German Research Centre for Geosciences, Section 5.2 – Climate Dynamics and Landscape Evolution, Telegrafenberg, 14473 Potsdam, Germany;5. Intituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, sezione Catania, Piazza Roma, 2 – 95123 Catania, Italy;6. Institute of Geosciences, Mineralogy – Geochemistry, Albert-Ludwigs-University Freiburg, Albertstrasse 23b, 79104 Freiburg, Germany;1. Chair of Geomorphology & BayCEER, University of Bayreuth, 95440 Bayreuth, Germany;2. Department of Human Evolution, Max-Planck-Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany;3. Institute of Ecology, Subject Area Landscape Change, Leuphana University, Scharnhorststr. 1, C13.115, 21335 Lüneburg, Germany;4. Freiberg Instruments GmbH, Delfterstr. 6, 09599 Freiberg, Germany;5. GEOMAR Helmholtz-Zentrum, Centre for Ocean Research Kiel, Wischhofstrasse 1-3, 24148 Kiel, Germany |
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| Abstract: | High-resolution diatom analysis was carried out to assess the limnological and climatic changes that took place at Ribains maar (French Massif Central) during the Late Pleistocene (～131–～105 ka BP), with a focus on the Eemian interglacial in particular. Numerical analyses were used to show that most of the variability in the fossil diatom assemblages was due to climate independently from the changes in the lake catchment vegetation (as represented by pollen data). Diatom-based quantitative reconstructions of the past limnological conditions, as well as a comprehensive literature review on the auto-ecological requirements for the principal diatom taxa, were used to interpret the record. An absolute time-scale for the sequence was derived by matching the major pollen shifts with the radiometrically dated changes in oxygen isotopes observed in Italian stalagmites. This study shows that at Ribains maar, the transition from the Riss (=Saalian) Glacial to the Eemian interglacial was marked by a gradual increase in the contribution of spring-blooming diatom species, indicating a longer growing season and milder winter/spring conditions at that time. A short cooling event interrupts this trend and may correspond to a stadial. At the start of the Eemian a peak in benthic taxa and the suppression of spring-blooming flora probably reflects the effects of deglaciation on the catchment. During the Eemian interglacial itself three main phases were distinguished within the diatom record. The first phase (～8000 years in duration) was dominated by Stephanodiscus minutulus, which suggests that intense mixing in the water-column took place during spring. The pollen record was simultaneously dominated by Quercus and Corylus that typify this phase as the climatic optimum of the Eemian. The second phase, almost equal in duration to the first phase (～7000 years), is generally dominated by Cyclotella taxa and suggests a less productive lake and much reduced period of spring mixing compared with the first phase. In the pollen diagram this corresponds to an interval dominated by Carpinus–Picea–Abies that indicates a cooler and wetter climate. The third and last phase of the Eemian, ～2000 year long, saw the return to Stephanodiscus-dominated assemblages, indicating a warming that may correspond to the Dansgaard–Oeschger event 25 identified in the Greenland ice-core record. In the early stage of the Würm Glacial (=Weichselian), assemblages in the Melisey I stadial (～3000 year long) were dominated by either Aulacoseira subarctica or Asterionella formosa, which suggest colder spring conditions than during the late Eemian, but not as cold as the ones indicated by the pollen record. Stephanodiscus spp. again dominate during the Saint-Germain Ia interstadial (～5000 year long) suggesting a return to the conditions that prevailed before the Melisey stadial, in agreement with the pollen record. The record ends with the Montaigu cold event, which is characterised by a Pinus peak in the pollen record, and corresponds to a large abundance of A. subarctica in the diatom sequence. Throughout the Eemian the abundance of Stephanodiscus spp., which is thought to be driven by winter conditions, show cyclic fluctuations that most likely match the cooling events identified in a pollen record from Germany. Variation in insolation throughout the Eemian may have been the driving factor behind the species succession observed in the diatom sequence. While this study demonstrates that diatom analysis of lake sediment can provide very detailed information on long-term climate change, a review of the few other diatom investigations published on European Eemian deposits shows that this technique has been so far seldom used to its full potential in this context in central and southern Europe. |
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