Eemian Lake Development, Hydrology and Climate: A Multi-Stratigraphic Study of the Hollerup Site in Denmark

A classic northwest European open section with lacustrine Eemian sediments, Hollerup, has been studied with respect to sedimentology, geochemistry, stable isotopes, diatoms and mineral magnetic analyses, and correlated by geochemistry and diatoms to a previously pollen analysed section by Andersen (1965). This correlation has enabled the section to be related to Muller\u27s (1974) tentative Eemian absolute chronology, and shows that the Hollerup Eemian sediments appear to cover c. 11,000 yr. Our studies show that the onset of the Eemian was characterized by a major lake level rise followed by an almost 3000 yr long period of high, but oscillating lake levels. It is argued that the latter part of this period of highly maritime climate can be defined as the Eemian climatic optimum. This period was interrupted by a few hundred years long phase of low lake level, coinciding with the immigration of spruce, followed by medium-high lake levels. The next c. 3500 yr, coinciding with the Carpinus pollen zone, seem to have been characterized by fairly humid and mild conditions, although slightly more arid than during the preceding optimum. The Carpinus period ended with a more than 1000 yr long gradual lake level fall, and this period of lake level change, concurring with the transition into the Pinus pollen dominated period, terminated with an extreme low lake level event. This 300-500 yr long arid phase coincides with a distinct peak in pine pollen, and was followed by higher but slightly oscillating lake levels in a cooler climate. The end of the Eemian seems to have been characterised by a gradual cooling, until almost pure clastic sedimentation and a marked expansion of herb pollen grains mark the onset of the Weichselian. Based on regional correlations to other European terrestrial and North Atlantic marine proxy records, we argue that the distinct hydrologic and climatic events displayed in the Hollerup record were possibly caused by a combination of sea level changes, changes in the hydrologic cycle and changing oceanic circulation patterns. The latter two may have been triggered by the opening and closure of the Baltic Sea-White Sea connection, the initial build-up of continental ice sheets, and the first major impacts of meltwater induced freshwater in key areas for thermohaline circulation. (C) 2000 Elsevier Science Ltd