Universität zu Köln

The modern surface sediments of Lake El'gygytgyn as well as downcore samples of the uppermost 30 m of the sediment sequence were investigated for their grain-­size distribution and inorganic geochemistry. A set of 55 surface sediment samples were recovered during the summer campaign in 2003. In 2009, an ICDP expedition was carried out in order to acquire a continuous record of lake sediments down to the sediment base, and further into the underlying bedrock. The analyzed sequence covers the time interval of MIS 9 to MIS 18. The objective of this thesis is to investigate the interdependency of grain-size and inorganic geochemistry of Lake El´gygytgyn sediments. The grain-size was measured with a laser particle analyzer, and the inorganic geochemistry was analyzed using ICP-OES (surface samples) and the ITRAX XRF core scanner (downcore samples), respectively. Prior to the grain-size analyses, a multi-­step pre-­treatment procedure was developed in order to remove organic material, vivianite and biogenic silica. The procedure was validated by TOC, BSi, XRD, SEM and binocular microscope investigations to ensure that  these autochthonous deposits were completely removed from the samples, and that the pre-treatment does not alter the grain-size distribution. To quantify the interdependency of grain-­size and geochemistry, different multivariate statistic methods, i.e. the Principal Component Analysis (PCA) and the Redundancy Analysis (RDA), were applied. For the surface sediments, the statistical methods yielded three different clusters of grain-­size parameters and inorganic geochemistry data. This strongly suggests a considerable correlation between grain-size and inorganic geochemistry, with Si, Ca, Na, K predominantly enriched in very coarse silt to fine sand. The spatial distribution of these elements and grain-­size classes confirms the existence of a wind induced current pattern in Lake El'gygytgyn already suspected by former investigations. Furthermore, the strong clustering of the silt fraction and mafic related elements (e.g. Fe, Ti, Ni) implies a major source-rock effect with silt predominantly delivered by the largest inlet whose catchment mainly consists of mafic volcanic rocks. Within the investigated core sequence the grain-­size distribution is clearly super-­imposed by climate variations on a glacial/interglacial timescale. The results of the multivariate statistics (PCA and RDA) indicate a strong positive correlation of Fe, Ti and to a certain amount Al, with the fine fraction (< medium silt) typically enriched during glacial periods. In contrast most of the other elements plot with coarser grain-­sizes (coarse silt to fine sand) having their highest contents during interglacial times. The dominant triggering of the grain-­size and geochemistry data by global climate variations is confirmed by the good fit to the global marine benthic ?18O record.