Late quaternary environment of Central Yakutia (NE' Siberia) : signals in frozen ground and terrestrial sediments = Spätquartäre Umweltentwicklung in Zentral-Jakutien (NO-Sibirien) : Hinweise aus Permafrost und terrestrischen Sedimentarchiven

Central Yakutia represents one of earth’s most continental climate regions with severe winters and temperate summers in a periglacial setting with widespread and thick permafrost. During the late Quaternary, the landscape along the western margin of the Verkhoyansk Mountains was sculptured by repeated glaciations, fluvial activity and periglacial processes. So far, the chronology of the glaciations and environmental changes are poorly understood. In the scope of a joint Russian-German cooperation, field work was conducted on selected sites across Central Yakutia in order to collect new data on palaeoenvironmental change. The research strategy followed a multidisciplinary approach, comprising the evaluation of remote-sensing data and luminescence dating (RWTH Aachen, Germany), palaeopedological analysis (Bayreuth University, Germany), as well as sedimentological, geocryological, limnogeological studies and pollen analysis (AWI Potsdam, Germany; Melnikov Permafrost Institute and Yakutsk State University, Yakutsk, Russia). This thesis concentrates on three different aspects of environmental change: Ice-rich permafrost deposits and their isotopic composition were studied at four sites in the western Verkhoyansk foreland. The isotopic composition of ice wedges generally reflects the palaeoclimatic winter conditions. During the late Pleistocene, ice wedges formed under stable severe conditions at around 41 ka, 20 ka to 13 ka C BP. The climatic favourable early to mid-Holocene is isotopically reflected between 8.5 and 4.5 ka C BP. Towards the late Holocene and sub-recent times, a climatic deterioration is recorded, shown by lighter isotopic composition of ice wedges, which developed between 1.2 ka and 0.7 ka C BP. Provenance analysis of late Quaternary deposits were conducted on tributaries of the Aldan and Lena Rivers in Central Yakutia. Cluster analysis revealed distinct heavymineral assemblages that serve as the basis for palaeoenvironmental studies. Thus, relatively high proportions of amphibole, orthopyroxene and garnet as well as pedogenic clay minerals point to sediment provenance from the wide catchment area of the Lena and Aldan Rivers. In contrast, the three other clusters are dominated by stable heavy minerals with varying amounts of clinopyroxene, apatite and garnet as well as high percentages of illite and chlorite that are indicative of source rocks of the Verkhoyansk Mountain area. Basically, morainic deposits reveal the local mountain source signal that is overprinted by the Lena-Aldan signal in the oldest moraines by reworking processes. Alluvial sediments in the Verkhoyansk foreland show a clear Lena source signal in the middle Pleistocene, related to a stream course closer to the mountains during those times. Loess-like cover sediments are characterised by dominant Lena provenance with increasing proportions of local sediments from nearby mountain sources towards the mountain valleys. Aeolian sands in an alluvial terrace section at the mountain margin, covering the time between 30 ka and 10 ka BP, reflect temporarily dominant inputs of aeolian materials from the Lena plains. A new high-resolution lake status record of Lake Satagay from Central Yakutia reflects climate-driven hydrological changes in a typical thermokarst lake environment. The sedimentary lake record spans the last 7500 years of the midto late Holocene. The downcore variability in the composition of organic matter and the assemblages of fossil