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• W2616397370 abstract "Changing environmental conditions associated with a predicted change in global temperaturesis believed to affect water availability on the Tibetan Plateau, which provides freshwater toapproximately 20% of the global population. The reconstruction of past environmentalconditions may provide past climatic analogues to modern warming scenarios and help toelucidate the environmental response to climate forcing. One of the most abundant archives ofLate Quaternary environmental conditions on the Tibetan Plateau are lacustrine sedimentsassociated with lake systems. However, lake systems are known to reveal complexity in theirresponse to climate forcing resulting in individualized sedimentary patterns for different lakesystems. This individuality delimits the potential to infer supra-regional patterns ofenvironmental change. This thesis presents a reconstruction of environmental conditions duringthe last ~12 ka around Lake Heihai, situated on the northern fringe of the Tibetan Plateau.Special focus is given on analyzing the climatic sensitivity of inorganic sediment fluxes, i.e.fluxes of allogenic minerals originating from the terrestrial surroundings of the lake as well asfluxes of endogenic minerals precipitated in the water column of the lake.A cluster analysis on the mineralogical composition of terrestrial reference samples revealedfour major source areas, distributed evenly on two bordering mountain ranges: the KunlunMountains in the south and the Burhan Buda Mountains in the north of the lake. Especiallysediment source areas on the Kunlun range differ in their main mode of activation, which ispredominantly precipitation generated and glacial runoff. An end-member analysis of grain sizedistributions of the siliciclastic detrital fraction revealed that sediment supply from the BurhanBuda range is a consequence of eolian dynamics. The findings suggests a blockage effect of theKunlun range on southerly air masses, leading to an extended rain shadow north of the Kunlunrange. Endogenic mineral formation in Lake Heihai is dominated by carbonate precipitation.The geochemical analysis of carbonate mineral phases apparent within lacustrine sedimentsrevealed, that the main control on the predominant endogenic carbonate mineral phase is theratio between solute magnesium and calcium (Mg/Ca) in lake waters. The solute lake waterMg/Ca is controlled by solute composition of inflowing waters as well as lake internal Mgenrichment relative to Ca by the removal of Ca due to carbonate precipitation. The solutecomposition of inflowing waters, in turn, is mainly influenced by weathering intensities oflimestone outcrops in the drainage basin of the lake.Changes in the inorganic mineral assemblage of a sediment core from the deepest part of thelake revealed major variations in sediment fluxes during the past ~12 ka induced by varyingenvironmental conditions. After a prolonged dry and cold phase during the Late Glacial,allogenic sediment supply to Lake Heihai is characterized by a sudden intensification ofprecipitation generated sediment supply around ~10.7 cal. ka BP and a gradual decrease from~7.9 cal. ka BP to present. This Holocene trend is in phase with known variations in atmosphericcirculation systems over monsoonal Asia. The gradual long-term trend to more arid conditionsis accompanied by several changes in the predominant endogenic carbonate phase, one of whichevidences the onset of permafrost formation at ~3.9 cal. ka BP and hence a completedisappearance of the lake body. The disappearance is synchronous to a phase of weakenedmonsoonal precipitation as recorded in several continental and terrestrial archives throughoutthe Asian continent. For the central Kunlun Fault system, this climate event is the driest andcoldest of the past 12 ka. However, while allogenic sediment supply is directly affected byclimatic variations in the study area, endogenic mineral precipitation is additionally controlledby lake-internal feedbacks not directly influenced by climatic variations, like e.g.geomorphologically controlled changes in the hydrological condition.The observed local paleoenvironmental evolution in the region of Lake Heihai was comparedto two well-studied lake systems: Lake Donggi Cona situated on the north eastern TibetanPlateau and Lake Nam Co on the southern Tibetan Plateau. The supra-regional comparison wasbased on the allogenic sediment input because of the climatic sensitivity of the allogenicsediment supply system. Variations in allogenic sediment supply were characterized by factoranalysis of elemental concentration in core sediments measured by X-Ray fluorescence scans.To account for a potential individual response of lake systems to climate forcing, a phase spacereconstruction was carried out on the previously calculated elemental factors. Phase spacereconstruction revealed that despite the individuality in the environmental setting of each lake,a similar sedimentary system consisting of three (yet unidentified) essential variables controlsthe allogenic sediment supply in each drainage basin. The Holocene dynamics in the allogenicsediment flux suggests the presence of a universal attracting state for lakes situated on theTibetan Plateau. The attracting state is mainly characterized by short-term variationsynchronous to solar output variations. Forcing mechanisms not originating from solarvariations destabilize the systems dynamics and lead to unpredictable responses in sedimentarypatterns of the lake systems. The last major destabilization phase was evident in the EarlyHolocene under increased monsoonal rainfall intensities caused by orbital variations. Theresults have great implications for temporal and spatial variations in atmospheric circulationpatterns over monsoonal Asia and will help to facilitate the prediction of future monsoonalprecipitation patterns under varying climatic conditions." @default.
• W2616397370 created "2017-05-26" @default.
• W2616397370 creator A5043472996 @default.
• W2616397370 date "2015-01-01" @default.
• W2616397370 modified "2023-09-23" @default.
• W2616397370 title "Lake system development on the northern Tibetan Plateau during the last ~12 ka" @default.
• W2616397370 hasPublicationYear "2015" @default.
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