Palynological analyses in the laminated sediment of Lake Holzmaar (Eifel, Germany): duration of Lateglacial and Preboreal biozones SUZANNE ALICE G. LEROY, BERND ZOLITSCHKA, JO ¨ RG F. W. NEGENDANK AND GUY SERET Leroy, S. A. G., Zolitschka, B., Negendank, J. F. W. & Seret, G. 2000 (March): Palynological analyses in the laminated sediment of Lake Holzmaar (Eifel, Germany): duration of Lateglacial and Preboreal biozones. Boreas, Vol. 29, pp. 52–71. Oslo. ISSN 0300-9483. The laminated sediment of Lake Holzmaar (Germany) has provided a continuous varve chronology for the last 3500 varve years (vy) and beyond that a floating varve chronology back to more than 22 500 vy BP. This chronology in calendar years, in combination with palynology, enables us to determine the timing and the magnitude of Lateglacial and Early Holocene environmental changes on land (from 13 838 to 10 930 vy BP). The palynological diagram has a mean time resolution of 27 vy between samples. This paper establishes for the first time the biozonation for Lake Holzmaar below the Laacher See Tephra. Fifteen pollen subzones grouped in four biozones are defined by cluster analysis. After a period disturbed by microturbidites, only a part of the Bølling is present. Three cold periods have been evidenced by pollen analyses: the Older Dryas (96-vy-long), the Younger Dryas (654-vy-long) and the Rammelbeek phase (237-vy-long). The Allerød (883- vy-long) is bipartite with a first Betula-dominated period followed by a Pinus-dominated one. The Younger Dryas is also bipartite, with first a decrease of winter temperatures along with a change to a more continental climate. It is followed by a drier phase with a second decrease in temperatures, probably this time also affect- ing summer temperatures. The Preboreal is 702-yr-long. The duration of most phases corresponds to published records, except for that of the Younger Dryas. Cluster and rate-of-change analyses indicate a sharp change in the terrestrial vegetation assemblages that may be caused by a sedimentary hiatus of erosive origin during this cold and dry period. As a result, the chronology of Holzmaar has to be revised most likely below the middle of the Younger Dryas. Comparison with the varve record of Meerfelder Maar, a neighbour maar lake, suggests adding 320 vy below 12 025 vy. Suzanne Leroy, Centre of Palaeoecology, School of Archaeology and Palaeoecology, Queen’s University of Belfast, Belfast, BT7 1NN N. Ireland. (Present address: Department of Geography and Earth Sciences, Brunel University, Uxbridge, Middlesex UB8 3PH, UK. E-mail: suzanne.leroy@brunel.ac.uk); Bernd Zolitschka and Jo ¨ rg Negendank, GeoForschungsZentrum Potsdam, PB 3.3 – Sedimente und Beckenbildung, Telegrafenberg, D-14473 Potsdam, Germany; Guy Seret, Laboratoire de Pale ´ontologie et Pale ´oge ´ographie, Institut ge ´ologi- que, Universite ´ Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium; received 15th July 1998, accepted 21st September 1999 The North Atlantic Seaboard Programme (NASP, a working group of IGCP-253) produced the most reliable synthesis of climatic changes during the last Glacial– Interglacial transition (Lowe et al. 1995), where limitations of radiocarbon dating and an update of palaeoclimatic reconstruction are given. It seems accepted that the best estimation of mean annual temperature is possible with fossil coleopteran data and not with terrestrial vegetation, owing to ecological factors such as migration rates and soil development (Iversen 1958). After the last glacial period, at 13.2 radiocarbon ka BP, a steep increase of annual tempera- ture from 8 to 9°C occurred in Britain. After this maximum, a gentle decrease takes place over 2200 radiocarbon years until 8°C is reached again in the Younger Dryas which is characterized by an earlier cold and moist period followed by a later colder and drier episode in mainland Britain, Belgium, The Netherlands and Massif Central (Lowe et al. 1995). Following the Younger Dryas, a second steep rise occurs until 9°C is reached again at the beginning of the Holocene (11 600– 11 500 calibrated years before present, Gulliksen et al. 1998). This history is punctuated by widespread climatic events, such as the Aegelsee Oscillation or the Older Dryas oscillation around 12 ka BP and the Gerzensee oscillation around or shortly after 11 ka BP (Lowe et al. 1995). In addition, in NW Europe a cold fluctuation has been recognized in the Preboreal. A temperature estimate based on ice accu- mulation data from Greenland shows the same trend (Kapsner et al. 1995). Owing to problems of radiocarbon plateaus in the Lateglacial and Early Holocene, especially at the most interesting periods of rapid environmental changes, the duration of these climatic events is difficult to deter- mine, if possible at all, using radiometric dating methods (Wohlfarth 1996; Bjørck et al. 1996; Hajdas et al. 1995c). A good solution to this chronological problem is to provide ages obtained by counting annually laminated sediments and ice core records. The seasonally laminated sedimentary sequence of Lake Holzmaar (West Eifel Volcanic Field, Germany, Fig. 1) has provided one of the few quasi-continuous varve chronologies with an absolute chronology back to 3500 vy and a floating chronology back to more than 22 500 vy BP (Brauer et al. 1994; Hajdas et al. 1995a, c;