Timing and trigger mechanisms of abrupt cold events during the Holsteinian interglacial based on analyses of annually laminated sediments

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The Holsteinian interglacial has been correlated with marine Isotope substage 11 c, which is centred at around 400,000 yr BP (Beaulieu et al. 2001, Tzedakis et al. 2003). During that time the climate forcing, i.e. the orbitally driven Insolation and concentration of greenhouse gases, was most similar to the present Situation (Berger & Loutre 2002, ERICA members 2004). Therefore, marine isotope substage 11 c and its terrestriai equivalent, the Holsteinian, are considered äs the best paleoclimatic analogues for the Holocene (McManus et al. 2003, Kukla 2003). In this context, two cold events manifested by the abrupt decline of several thermophile tree species within the Holsteinian interglacial at several sites across NW-Europe (e.g. Turner 1970, H. Müller 1974, Binka & Nitychoruk 1995), gain new relevance. What was the origin and timing of these abrupt cold events which occurred during an interglacial that represents the best analogue to our present Holocene? Here it is proposed to investigate the exact timing and trigger mechanisms of these events based on analyses of annually laminated lake Sediments from Dethlingen (N-Germany). Due to own preliminary work, the core material is already available and low-resolution pollen analyses have been performed to ensure the core indeed comprises the Holsteinian. Now it is proposed to perform varve counting and high-resolution (decadal to centennial scale) pollen analyses for the entire record. In particular, it is proposed to perform ultra-high-resolution (annual resolution) analyses of pollen, geochemical, and geophysicai parameters on the critical inten/als of the two cold events. The ultra-high-resolution analyses of the annually laminated sediment will provide information about the exact timing and thus information about the mechanisms that triggered the abrupt coolings within interglacial boundary conditions.