@article{AichnerHerzschuhWilkesetal.2012, author = {Aichner, Bernhard and Herzschuh, Ulrike and Wilkes, Heinz and Schulz, Hans-Martin and Wang, Yongbo and Plessen, Birgit and Mischke, Steffen and Diekmann, Bernhard and Zhang, Chengjun}, title = {Ecological development of Lake Donggi Cona, north-eastern Tibetan Plateau, since the late glacial on basis of organic geochemical proxies and non-pollen palynomorphs}, series = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, volume = {313}, journal = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, number = {2}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0031-0182}, doi = {10.1016/j.palaeo.2011.10.015}, pages = {140 -- 149}, year = {2012}, abstract = {Organic geochemical proxy data from surface sediment samples and a sediment core from Lake Donggi Cona were used to infer environmental changes on the northeastern Tibetan Plateau spanning the last 18.4 kyr. Long-chain n-alkanes dominate the aliphatic hydrocarbon fraction of the sediment extract from most surface sediment samples and the sediment core. Unsaturated mid-chain n-alkanes (nC(23:1) and nC(25:1)) have high abundances in some samples, especially in core samples from the late glacial and early Holocene. TOC contents, organic biomarker and non-pollen-palynomorph concentrations and results from organic petrologic analysis on selected samples suggest three major episodes in the history of Lake Donggi Cona. Before ca. 12.6 cal ka BP samples contain low amounts of organic matter due to cold and arid conditions during the late glacial. After 12.6 cal ka BP, relatively high contents of TOC and concentrations of Botryococcus fossils, as well as enhanced concentrations of mid-chain n-alkanes and n-alkenes suggest a higher primary and macrophyte productivity than at present This is supported by high contents of palynomorphs derived from higher plants and algae and was possibly triggered by a decrease of salinity and amelioration of climate during the early Holocene. Since 6.8 cal ka BP Lake Donggi Cona has been an oligotrophic freshwater lake. Proxy data suggest that variations in insolation drive ecological changes in the lake, with increased aquatic productivity during the early Holocene summer insolation maximum. Short-term drops of TOC contents or biomarker concentrations (at 9.9 cal ka BP, after 8.0 and between 3.5 and 1.7 cal ka BP) can possibly be related to relatively cool and dry episodes reported from other sites on the north-eastern Tibetan Plateau, which are hypothesized to occur in phase with Northern Hemisphere cooling events.}, language = {en} } @article{AnoopPrasadBasavaiahetal.2012, author = {Anoop, A. and Prasad, S. and Basavaiah, Nathani and Brauer, Achim and Shahzad, F. and Deenadayalan, K.}, title = {Tectonic versus climate influence on landscape evolution: A case study from the upper Spiti valley, NW Himalaya}, series = {Geomorphology : an international journal on pure and applied geomorphology}, volume = {145}, journal = {Geomorphology : an international journal on pure and applied geomorphology}, number = {4}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0169-555X}, doi = {10.1016/j.geomorph.2011.10.028}, pages = {32 -- 44}, year = {2012}, abstract = {We have undertaken structural, geomorphological, and morphometric analyses to investigate the role of tectonism and climate in the landscape evolution in the upper Spiti valley, NW Himalayas. Geomorphometric analyses coupled with field investigations reveal active tectonic deformation in the Spiti region. The calculated geomorphic indices (steepness, concavity and Hack) demonstrate uplift/subsidence along the Kaurik-Chango fault, whereas transverse topographic index (T-index) reveals basin tilting associated with active faulting near Hansa and Lingti valley. Investigation of well-dated Mane palaeolake sediments also provides evidence of regional tectonic instability. Four episodes (ca. 7.8, 7.4, 6.5 and 6.1 cal ka) of neotectonic activity have been identified during the period of the lake's existence. We have also compiled data on the regional climate variability and compared it with the age of the Mane palaeo-landslide. Our results indicate that the landslide occurred towards the end of the early Holocene intensified monsoon phase and is located near an active fault. Our data on regional tectonic instability and the coincidences of modern and palaeo-landslides with zones of active deformation suggest that tectonism is an important factor governing landscape stability in the Spiti region.}, language = {en} } @misc{BattarbeeLambBennettetal.2015, author = {Battarbee, Richard W. and Lamb, Henry F. and Bennett, Keith and Edwards, Mary and Bjune, Anne E. and Kaland, Peter E. and Berglund, Bj{\"o}rn E. and Lotter, Andr{\´e} F. and Sepp{\"a}, Heikki and Willis, Kathy J. and Herzschuh, Ulrike and Birks, Hilary H.}, title = {John Birks}, series = {The Holocene}, journal = {The Holocene}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-404544}, pages = {14}, year = {2015}, abstract = {We describe the career of John Birks as a pioneering scientist who has, over a career spanning five decades, transformed palaeoecology from a largely descriptive to a rigorous quantitative science relevant to contemporary questions in ecology and environmental change. We review his influence on students and colleagues not only at Cambridge and Bergen Universities, his places of primary employment, but also on individuals and research groups in Europe and North America. We also introduce the collection of papers that we have assembled in his honour. The papers are written by his former students and close colleagues and span many of the areas of palaeoecology to which John himself has made major contributions. These include the relationship between ecology and palaeoecology, late-glacial and Holocene palaeoecology, ecological succession, climate change and vegetation history, the role of palaeoecological techniques in reconstructing and understanding the impact of human activity on terrestrial and freshwater ecosystems and numerical analysis of multivariate palaeoecological data.}, language = {en} } @phdthesis{Bittermann2015, author = {Bittermann, Klaus}, title = {Semi-empirical sea-level modelling}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-93881}, school = {Universit{\"a}t Potsdam}, pages = {v, 88}, year = {2015}, abstract = {Semi-empirical sea-level models (SEMs) exploit physically motivated empirical relationships between global sea level and certain drivers, in the following global mean temperature. This model class evolved as a supplement to process-based models (Rahmstorf (2007)) which were unable to fully represent all relevant processes. They thus failed to capture past sea-level change (Rahmstorf et al. (2012)) and were thought likely to underestimate future sea-level rise. Semi-empirical models were found to be a fast and useful tool for exploring the uncertainties in future sea-level rise, consistently giving significantly higher projections than process-based models. In the following different aspects of semi-empirical sea-level modelling have been studied. Models were first validated using various data sets of global sea level and temperature. SEMs were then used on the glacier contribution to sea level, and to infer past global temperature from sea-level data via inverse modelling. Periods studied encompass the instrumental period, covered by tide gauges (starting 1700 CE (Common Era) in Amsterdam) and satellites (first launched in 1992 CE), the era from 1000 BCE (before CE) to present, and the full length of the Holocene (using proxy data). Accordingly different data, model formulations and implementations have been used. It could be shown in Bittermann et al. (2013) that SEMs correctly predict 20th century sea-level when calibrated with data until 1900 CE. SEMs also turned out to give better predictions than the Intergovernmental Panel on Climate Change (IPCC) 4th assessment report (AR4, IPCC (2007)) models, for the period from 1961-2003 CE. With the first multi-proxy reconstruction of global sea-level as input, estimate of the human-induced component of modern sea-level change and projections of future sea-level rise were calculated (Kopp et al. (2016)). It turned out with 90\% confidence that more than 40 \% of the observed 20th century sea-level rise is indeed anthropogenic. With the new semi-empirical and IPCC (2013) 5th assessment report (AR5) projections the gap between SEM and process-based model projections closes, giving higher credibility to both. Combining all scenarios, from strong mitigation to business as usual, a global sea-level rise of 28-131 cm relative to 2000 CE, is projected with 90\% confidence. The decision for a low carbon pathway could halve the expected global sea-level rise by 2100 CE. Present day temperature and thus sea level are driven by the globally acting greenhouse-gas forcing. Unlike that, the Milankovich forcing, acting on Holocene timescales, results mainly in a northern-hemisphere temperature change. Therefore a semi-empirical model can be driven with northernhemisphere temperatures, which makes it possible to model the main subcomponent of sea-level change over this period. It showed that an additional positive constant rate of the order of the estimated Antarctic sea-level contribution is then required to explain the sea-level evolution over the Holocene. Thus the global sea level, following the climatic optimum, can be interpreted as the sum of a temperature induced sea-level drop and a positive long-term contribution, likely an ongoing response to deglaciation coming from Antarctica.}, language = {en} } @misc{CaoHerzschuhNietal.2014, author = {Cao, Xianyong and Herzschuh, Ulrike and Ni, Jian and Zhao, Yan and B{\"o}hmer, Thomas}, title = {Spatial and temporal distributions of major tree taxa in eastern continental Asia during the last 22,000 years}, series = {The Holocene}, volume = {25}, journal = {The Holocene}, number = {1}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-404176}, pages = {13}, year = {2014}, abstract = {This study investigates the spatial and temporal distributions of 14 key arboreal taxa and their driving forces during the last 22,000 calendar years before ad 1950 (kyr BP) using a taxonomically harmonized and temporally standardized fossil pollen dataset with a 500-year resolution from the eastern part of continental Asia. Logistic regression was used to estimate pollen abundance thresholds for vegetation occurrence (presence or dominance), based on modern pollen data and present ranges of 14 taxa in China. Our investigation reveals marked changes in spatial and temporal distributions of the major arboreal taxa. The thermophilous (Castanea, Castanopsis, Cyclobalanopsis, Fagus, Pterocarya) and eurythermal (Juglans, Quercus, Tilia, Ulmus) broadleaved tree taxa were restricted to the current tropical or subtropical areas of China during the Last Glacial Maximum (LGM) and spread northward since c. 14.5 kyr BP. Betula and conifer taxa (Abies, Picea, Pinus), in contrast, retained a wider distribution during the LGM and showed no distinct expansion direction during the Late Glacial. Since the late mid-Holocene, the abundance but not the spatial extent of most trees decreased. The changes in spatial and temporal distributions for the 14 taxa are a reflection of climate changes, in particular monsoonal moisture, and, in the late Holocene, human impact. The post-LGM expansion patterns in eastern continental China seem to be different from those reported for Europe and North America, for example, the westward spread for eurythermal broadleaved taxa.}, language = {en} } @article{CaoHerzschuhNietal.2015, author = {Cao, Xianyong and Herzschuh, Ulrike and Ni, Jian and Zhao, Yan and B{\"o}hmer, Thomas}, title = {Spatial and temporal distributions of major tree taxa in eastern continental Asia during the last 22,000 years}, series = {The Holocene : an interdisciplinary journal focusing on recent environmental change}, volume = {25}, journal = {The Holocene : an interdisciplinary journal focusing on recent environmental change}, number = {1}, publisher = {Sage Publ.}, address = {London}, issn = {0959-6836}, doi = {10.1177/0959683614556385}, pages = {79 -- 91}, year = {2015}, abstract = {This study investigates the spatial and temporal distributions of 14 key arboreal taxa and their driving forces during the last 22,000 calendar years before ad 1950 (kyr BP) using a taxonomically harmonized and temporally standardized fossil pollen dataset with a 500-year resolution from the eastern part of continental Asia. Logistic regression was used to estimate pollen abundance thresholds for vegetation occurrence (presence or dominance), based on modern pollen data and present ranges of 14 taxa in China. Our investigation reveals marked changes in spatial and temporal distributions of the major arboreal taxa. The thermophilous (Castanea, Castanopsis, Cyclobalanopsis, Fagus, Pterocarya) and eurythermal (Juglans, Quercus, Tilia, Ulmus) broadleaved tree taxa were restricted to the current tropical or subtropical areas of China during the Last Glacial Maximum (LGM) and spread northward since c. 14.5kyr BP. Betula and conifer taxa (Abies, Picea, Pinus), in contrast, retained a wider distribution during the LGM and showed no distinct expansion direction during the Late Glacial. Since the late mid-Holocene, the abundance but not the spatial extent of most trees decreased. The changes in spatial and temporal distributions for the 14 taxa are a reflection of climate changes, in particular monsoonal moisture, and, in the late Holocene, human impact. The post-LGM expansion patterns in eastern continental China seem to be different from those reported for Europe and North America, for example, the westward spread for eurythermal broadleaved taxa.}, language = {en} } @article{CaoTianDallmeyeretal.2019, author = {Cao, Xianyong and Tian, Fang and Dallmeyer, Anne and Herzschuh, Ulrike}, title = {Northern Hemisphere biome changes (> 30 degrees N) since 40 cal ka BP and their driving factors inferred from model-data comparisons}, series = {Quaternary science reviews : the international multidisciplinary research and review journal}, volume = {220}, journal = {Quaternary science reviews : the international multidisciplinary research and review journal}, publisher = {Elsevier}, address = {Oxford}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2019.07.034}, pages = {291 -- 309}, year = {2019}, abstract = {Ongoing and past biome transitions are generally assigned to climate and atmospheric changes (e.g. temperature, precipitation, CO2), but the major regional factors or factor combinations that drive vegetation change often remain unknown. Modelling studies applying ensemble runs can help to partition the effects of the different drivers. Such studies require careful validation with observational data. In this study, fossil pollen records from 741 sites in Europe, 728 sites in North America, and 418 sites in Asia (extracted from terrestrial archives including lake sediments) are used to reconstruct biomes at selected time slices between 40 cal ka BP (calibrated thousand years before present) and today. These results are used to validate Northern Hemisphere biome distributions (>30 degrees N) simulated by the biome model BIOME4 that has been forced with climate data simulated by a General Circulation model. Quantitative comparisons between pollen- and model-based results show a generally good fit at a broad spatial scale. Mismatches occur in central-arid Asia with a broader extent of grassland throughout the last 40 ka (likely due to the over-representation of Artemisia and Chenopodiaceae pollen) and in Europe with over-estimation of tundra at 0 cal ka BP (likely due to human impacts to some extent). Sensitivity analysis reveals that broad-scale biome changes follow the global signal of major postglacial temperature change, although the climatic variables vary in their regional and temporal importance. Temperature is the dominant variable in Europe and other rather maritime areas for biome changes between 21 and 14 ka, while precipitation is highly important in the arid inland regions of Asia and North America. The ecophysiological effect of changes in the atmospheric CO2-concentration has the highest impact during this transition than in other intervals. With respect to modern vegetation in the course of global warming, our findings imply that vegetation change in the Northern Hemisphere may be strongly limited by effective moisture changes, i.e. the combined effect of temperature and precipitation, particularly in inland areas. (C) 2019 Elsevier Ltd. All rights reserved.}, language = {en} } @article{CaoTianTelfordetal.2017, author = {Cao, Xianyong and Tian, Fang and Telford, Richard J. and Ni, Jian and Xu, Qinghai and Chen, Fahu and Liu, Xingqi and Stebich, Martina and Zhao, Yan and Herzschuh, Ulrike}, title = {Impacts of the spatial extent of pollen-climate calibration-set on the absolute values, range and trends of reconstructed Holocene precipitation}, series = {Quaternary science reviews : the international multidisciplinary research and review journal}, volume = {178}, journal = {Quaternary science reviews : the international multidisciplinary research and review journal}, publisher = {Elsevier}, address = {Oxford}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2017.10.030}, pages = {37 -- 53}, year = {2017}, abstract = {Pollen-based quantitative reconstructions of past climate variables is a standard palaeoclimatic approach. Despite knowing that the spatial extent of the calibration-set affects the reconstruction result, guidance is lacking as to how to determine a suitable spatial extent of the pollen-climate calibration-set. In this study, past mean annual precipitation (P-ann) during the Holocene (since 11.5 cal ka BP) is reconstructed repeatedly for pollen records from Qinghai Lake (36.7 degrees N, 100.5 degrees E; north-east Tibetan Plateau), Gonghai Lake (38.9 degrees N, 112.2 degrees E; north China) and Sihailongwan Lake (42.3 degrees N, 126.6 degrees E; north-east China) using calibration-sets of varying spatial extents extracted from the modern pollen dataset of China and Mongolia (2559 sampling sites and 168 pollen taxa in total). Results indicate that the spatial extent of the calibration-set has a strong impact on model performance, analogue quality and reconstruction diagnostics (absolute value, range, trend, optimum). Generally, these effects are stronger with the modern analogue technique (MAT) than with weighted averaging partial least squares (WA-PLS). With respect to fossil spectra from northern China, the spatial extent of calibration-sets should be restricted to radii between ca. 1000 and 1500 km because small-scale calibration-sets (<800 km radius) will likely fail to include enough spatial variation in the modern pollen assemblages to reflect the temporal range shifts during the Holocene, while too broad a scale calibration-set (>1500 km radius) will include taxa with very different pollen-climate relationships. (C) 2017 Elsevier Ltd. All rights reserved.}, language = {en} } @article{CourtinAndreevRaschkeetal.2021, author = {Courtin, J{\´e}r{\´e}my and Andreev, Andrei and Raschke, Elena and Bala, Sarah and Biskaborn, Boris and Liu, Sisi and Zimmermann, Heike and Diekmann, Bernhard and Stoof-Leichsenring, Kathleen R. and Pestryakova, Luidmila Agafyevna and Herzschuh, Ulrike}, title = {Vegetation changes in Southeastern Siberia during the late pleistocene and the holocene}, series = {Frontiers in Ecology and Evolution}, volume = {9}, journal = {Frontiers in Ecology and Evolution}, publisher = {Frontiers Media}, address = {Lausanne}, issn = {2296-701X}, doi = {10.3389/fevo.2021.625096}, pages = {18}, year = {2021}, abstract = {Relationships between climate, species composition, and species richness are of particular importance for understanding how boreal ecosystems will respond to ongoing climate change. This study aims to reconstruct changes in terrestrial vegetation composition and taxa richness during the glacial Late Pleistocene and the interglacial Holocene in the sparsely studied southeastern Yakutia (Siberia) by using pollen and sedimentary ancient DNA (sedaDNA) records. Pollen and sedaDNA metabarcoding data using the trnL g and h markers were obtained from a sediment core from Lake Bolshoe Toko. Both proxies were used to reconstruct the vegetation composition, while metabarcoding data were also used to investigate changes in plant taxa richness. The combination of pollen and sedaDNA approaches allows a robust estimation of regional and local past terrestrial vegetation composition around Bolshoe Toko during the last similar to 35,000 years. Both proxies suggest that during the Late Pleistocene, southeastern Siberia was covered by open steppe-tundra dominated by graminoids and forbs with patches of shrubs, confirming that steppe-tundra extended far south in Siberia. Both proxies show disturbance at the transition between the Late Pleistocene and the Holocene suggesting a period with scarce vegetation, changes in the hydrochemical conditions in the lake, and in sedimentation rates. Both proxies document drastic changes in vegetation composition in the early Holocene with an increased number of trees and shrubs and the appearance of new tree taxa in the lake's vicinity. The sedaDNA method suggests that the Late Pleistocene steppe-tundra vegetation supported a higher number of terrestrial plant taxa than the forested Holocene. This could be explained, for example, by the "keystone herbivore" hypothesis, which suggests that Late Pleistocene megaherbivores were able to maintain a high plant diversity. This is discussed in the light of the data with the broadly accepted species-area hypothesis as steppe-tundra covered such an extensive area during the Late Pleistocene.}, language = {en} } @article{DallmeyerClaussenWangetal.2013, author = {Dallmeyer, A. and Claussen, Martin and Wang, Y. and Herzschuh, Ulrike}, title = {Spatial variability of Holocene changes in the annual precipitation pattern a model-data synthesis for the Asian monsoon region}, series = {Climate dynamics : observational, theoretical and computational research on the climate system}, volume = {40}, journal = {Climate dynamics : observational, theoretical and computational research on the climate system}, number = {11-12}, publisher = {Springer}, address = {New York}, issn = {0930-7575}, doi = {10.1007/s00382-012-1550-6}, pages = {2919 -- 2936}, year = {2013}, abstract = {This study provides a detailed analysis of the mid-Holocene to present-day precipitation change in the Asian monsoon region. We compare for the first time results of high resolution climate model simulations with a standardised set of mid-Holocene moisture reconstructions. Changes in the simulated summer monsoon characteristics (onset, withdrawal, length and associated rainfall) and the mechanisms causing the Holocene precipitation changes are investigated. According to the model, most parts of the Indian subcontinent received more precipitation (up to 5 mm/day) at mid-Holocene than at present-day. This is related to a stronger Indian summer monsoon accompanied by an intensified vertically integrated moisture flux convergence. The East Asian monsoon region exhibits local inhomogeneities in the simulated annual precipitation signal. The sign of this signal depends on the balance of decreased pre-monsoon and increased monsoon precipitation at mid-Holocene compared to present-day. Hence, rainfall changes in the East Asian monsoon domain are not solely associated with modifications in the summer monsoon circulation but also depend on changes in the mid-latitudinal westerly wind system that dominates the circulation during the pre-monsoon season. The proxy-based climate reconstructions confirm the regional dissimilarities in the annual precipitation signal and agree well with the model results. Our results highlight the importance of including the pre-monsoon season in climate studies of the Asian monsoon system and point out the complex response of this system to the Holocene insolation forcing. The comparison with a coarse climate model simulation reveals that this complex response can only be resolved in high resolution simulations.}, language = {en} } @phdthesis{Draeger2016, author = {Dr{\"a}ger, Nadine}, title = {Holocene climate and environmental variability in NE Germany inferred from annually laminated lake sediments}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-103037}, school = {Universit{\"a}t Potsdam}, pages = {xv, 144 Seiten}, year = {2016}, abstract = {Understanding the role of natural climate variability under the pressure of human induced changes of climate and landscapes, is crucial to improve future projections and adaption strategies. This doctoral thesis aims to reconstruct Holocene climate and environmental changes in NE Germany based on annually laminated lake sediments. The work contributes to the ICLEA project (Integrated CLimate and Landscape Evolution Analyses). ICLEA intends to compare multiple high-resolution proxy records with independent chronologies from the N central European lowlands, in order to disentangle the impact of climate change and human land use on landscape development during the Lateglacial and Holocene. In this respect, two study sites in NE Germany are investigated in this doctoral project, Lake Tiefer See and palaeolake Wukenfurche. While both sediment records are studied with a combination of high-resolution sediment microfacies and geochemical analyses (e.g. µ-XRF, carbon geochemistry and stable isotopes), detailed proxy understanding mainly focused on the continuous 7.7 m long sediment core from Lake Tiefer See covering the last ~6000 years. Three main objectives are pursued at Lake Tiefer See: (1) to perform a reliable and independent chronology, (2) to establish microfacies and geochemical proxies as indicators for climate and environmental changes, and (3) to trace the effects of climate variability and human activity on sediment deposition. Addressing the first aim, a reliable chronology of Lake Tiefer See is compiled by using a multiple-dating concept. Varve counting and tephra findings form the chronological framework for the last ~6000 years. The good agreement with independent radiocarbon dates of terrestrial plant remains verifies the robustness of the age model. The resulting reliable and independent chronology of Lake Tiefer See and, additionally, the identification of nine tephras provide a valuable base for detailed comparison and synchronization of the Lake Tiefer See data set with other climate records. The sediment profile of Lake Tiefer See exhibits striking alternations between well-varved and non-varved sediment intervals. The combination of microfacies, geochemical and microfossil (i.e. Cladocera and diatom) analyses indicates that these changes of varve preservation are caused by variations of lake circulation in Lake Tiefer See. An exception is the well-varved sediment deposited since AD 1924, which is mainly influenced by human-induced lake eutrophication. Well-varved intervals before the 20th century are considered to reflect phases of reduced lake circulation and, consequently, stronger anoxic conditions. Instead, non-varved intervals indicate increased lake circulation in Lake Tiefer See, leading to more oxygenated conditions at the lake ground. Furthermore, lake circulation is not only influencing sediment deposition, but also geochemical processes in the lake. As, for example, the proxy meaning of δ13COM varies in time in response to changes of the oxygen regime in the lake hypolinion. During reduced lake circulation and stronger anoxic conditions δ13COM is influenced by microbial carbon cycling. In contrast, organic matter degradation controls δ13COM during phases of intensified lake circulation and more oxygenated conditions. The varve preservation indicates an increasing trend of lake circulation at Lake Tiefer See after ~4000 cal a BP. This trend is superimposed by decadal to centennial scale variability of lake circulation intensity. Comparison to other records in Central Europe suggests that the long-term trend is probably related to gradual changes in Northern Hemisphere orbital forcing, which induced colder and windier conditions in Central Europe and, therefore, reinforced lake circulation. Decadal to centennial scale periods of increased lake circulation coincide with settlement phases at Lake Tiefer See, as inferred from pollen data of the same sediment record. Deforestation reduced the wind shelter of the lake, which probably increased the sensitivity of lake circulation to wind stress. However, results of this thesis also suggest that several of these phases of increased lake circulation are additionally reinforced by climate changes. A first indication is provided by the comparison to the Baltic Sea record, which shows striking correspondence between major non-varved intervals at Lake Tiefer See and bioturbated sediments in the Baltic Sea. Furthermore, a preliminary comparison to the ICLEA study site Lake Czechowskie (N central Poland) shows a coincidence of at least three phases of increased lake circulation in both lakes, which concur with periods of known climate changes (2.8 ka event, 'Migration Period' and 'Little Ice Age'). These results suggest an additional over-regional climate forcing also on short term increased of lake circulation in Lake Tiefer See. In summary, the results of this thesis suggest that lake circulation at Lake Tiefer See is driven by a combination of long-term and short-term climate changes as well as of anthropogenic deforestation phases. Furthermore, the lake circulation drives geochemical cycles in the lake affecting the meaning of proxy data. Therefore, the work presented here expands the knowledge of climate and environmental variability in NE Germany. Furthermore, the integration of the Lake Tiefer See multi-proxy record in a regional comparison with another ICLEA side, Lake Czechowskie, enabled to better decipher climate changes and human impact on the lake system. These first results suggest a huge potential for further detailed regional comparisons to better understand palaeoclimate dynamics in N central Europe.}, language = {en} } @article{GarcinMelnickStreckeretal.2012, author = {Garcin, Yannick and Melnick, Daniel and Strecker, Manfred and Olago, Daniel and Tiercelin, Jean-Jacques}, title = {East African mid-Holocene wet-dry transition recorded in palaeo-shorelines of Lake Turkana, northern Kenya Rift}, series = {Earth \& planetary science letters}, volume = {331}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2012.03.016}, pages = {322 -- 334}, year = {2012}, abstract = {The 'wet' early to mid-Holocene of tropical Africa, with its enhanced monsoon, ended with an abrupt shift toward drier conditions and was ultimately replaced by a drier climate that has persisted until the present day. The forcing mechanisms, the timing, and the spatial extent of this major climatic transition are not well understood and remain the subject of ongoing research. We have used a detailed palaeo-shoreline record from Lake Turkana (Kenya) to decipher and characterise this marked climatic transition in East Africa. We present a high-precision survey of well-preserved palaeo-shorelines, new radiocarbon ages from shoreline deposits, and oxygen-isotope measurements on freshwater mollusk shells to elucidate the Holocene moisture history from former lake water-levels in this climatically sensitive region. In combination with previously published data our study shows that during the early Holocene the water-level in Lake Turkana was high and the lake overflowed temporarily into the White Nile drainage system. During the mid-Holocene (similar to 5270 +/- 300 cal. yr BP), however, the lake water-level fell by similar to 50 m, coeval with major episodes of aridity on the African continent. A comparison between palaeo-hydrological and archaeological data from the Turkana Basin suggests that the mid-Holocene climatic transition was associated with fundamental changes in prehistoric cultures, highlighting the significance of natural climate variability and associated periods of protracted drought as major environmental stress factors affecting human occupation in the East African Rift System. (}, language = {en} } @misc{GoswamiBoersRheinwaltetal.2018, author = {Goswami, Bedartha and Boers, Niklas and Rheinwalt, Aljoscha and Marwan, Norbert and Heitzig, Jobst and Breitenbach, Sebastian Franz Martin and Kurths, J{\"u}rgen}, title = {Abrupt transitions in time series with uncertainties}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {576}, issn = {1866-8372}, doi = {10.25932/publishup-42311}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-423111}, pages = {10}, year = {2018}, abstract = {Identifying abrupt transitions is a key question in various disciplines. Existing transition detection methods, however, do not rigorously account for time series uncertainties, often neglecting them altogether or assuming them to be independent and qualitatively similar. Here, we introduce a novel approach suited to handle uncertainties by representing the time series as a time-ordered sequence of probability density functions. We show how to detect abrupt transitions in such a sequence using the community structure of networks representing probabilities of recurrence. Using our approach, we detect transitions in global stock indices related to well-known periods of politico-economic volatility. We further uncover transitions in the El Nino-Southern Oscillation which coincide with periods of phase locking with the Pacific Decadal Oscillation. Finally, we provide for the first time an 'uncertainty-aware' framework which validates the hypothesis that ice-rafting events in the North Atlantic during the Holocene were synchronous with a weakened Asian summer monsoon.}, language = {en} } @article{Herzschuh2019, author = {Herzschuh, Ulrike}, title = {Legacy of the Last Glacial on the present-day distribution of deciduous versus evergreen boreal forests}, series = {Global ecology and biogeography : a journal of macroecology}, volume = {29}, journal = {Global ecology and biogeography : a journal of macroecology}, number = {2}, publisher = {John Wiley \& Sons, Inc.}, address = {Hoboken}, issn = {1466-822X}, doi = {10.1111/geb.13018}, pages = {198 -- 206}, year = {2019}, abstract = {Issue Despite their rather similar climatic conditions, eastern Eurasia and northern North America are largely covered by different plant functional types (deciduous or evergreen boreal forest) composed of larch or pine, spruce and fir, respectively. I propose that these deciduous and evergreen boreal forests represent alternative quasi-stable states, triggered by their different northern tree refugia that reflect the different environmental conditions experienced during the Last Glacial. Evidence This view is supported by palaeoecological and environmental evidence. Once established, Asian larch forests are likely to have stabilized through a complex vegetation-fire-permafrost soil-climate feedback system. Conclusion With respect to future forest developments, this implies that Asian larch forests are likely to be governed by long-term trajectories and are therefore largely resistant to natural climate variability on time-scales shorter than millennia. The effects of regional human impact and anthropogenic global warming might, however, cause certain stability thresholds to be crossed, meaning that irreversible transitions occur and resulting in marked consequences for ecosystem services on these human-relevant time-scales.}, language = {en} } @misc{Herzschuh2020, author = {Herzschuh, Ulrike}, title = {Legacy of the Last Glacial on the present-day distribution of deciduous versus evergreen boreal forests}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {2}, issn = {1866-8372}, doi = {10.25932/publishup-52405}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-524057}, pages = {11}, year = {2020}, abstract = {Issue Despite their rather similar climatic conditions, eastern Eurasia and northern North America are largely covered by different plant functional types (deciduous or evergreen boreal forest) composed of larch or pine, spruce and fir, respectively. I propose that these deciduous and evergreen boreal forests represent alternative quasi-stable states, triggered by their different northern tree refugia that reflect the different environmental conditions experienced during the Last Glacial. Evidence This view is supported by palaeoecological and environmental evidence. Once established, Asian larch forests are likely to have stabilized through a complex vegetation-fire-permafrost soil-climate feedback system. Conclusion With respect to future forest developments, this implies that Asian larch forests are likely to be governed by long-term trajectories and are therefore largely resistant to natural climate variability on time-scales shorter than millennia. The effects of regional human impact and anthropogenic global warming might, however, cause certain stability thresholds to be crossed, meaning that irreversible transitions occur and resulting in marked consequences for ecosystem services on these human-relevant time-scales.}, language = {en} } @article{HerzschuhBorkowskiScheweetal.2014, author = {Herzschuh, Ulrike and Borkowski, Janett and Schewe, Jacob and Mischke, Steffen and Tian, Fang}, title = {Moisture-advection feedback supports strong early-to-mid Holocene monsoon climate on the eastern Tibetan Plateau as inferred from a pollen-based reconstruction}, series = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, volume = {402}, journal = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0031-0182}, doi = {10.1016/j.palaeo.2014.02.022}, pages = {44 -- 54}, year = {2014}, abstract = {(Paleo-)climatologists are challenged to identify mechanisms that cause the observed abrupt Holocene monsoon events despite the fact that monsoonal circulation is assumed to be driven by gradual insolation changes. Here we provide proxy and model evidence to show that moisture-advection feedback can lead to a non-linear relationship between sea-surface and continental temperatures and monsoonal precipitation. A pollen record from Lake Ximencuo (Nianbaoyeze Mountains) indicates that vegetation from the eastern margin of the Tibetan Plateau was characterized by alpine deserts and glacial flora after the Last Glacial Maximum (LGM) (21-15.5 cal kyr BP), by alpine meadows during the Late Glacial (15.5-10.4 cal kyr BP) and second half of the Holocene (5.0 cal kyr BP to present) and by mixed forests during the first half of the Holocene (10.4-5.0 cal kyr BP). The application of pollen-based transfer functions yields an abrupt temperature increase at 10.4 cal kyr BP and a decrease at 5.0 cal kyr BP of about 3 degrees C. By applying endmember modeling to grain-size data from the same sediment core we infer that frequent fluvial events (probably originating from high-magnitude precipitation events) were more common in the early and mid Holocene. We assign the inferred exceptional strong monsoonal circulation to the initiation of moisture-advection feedback, a result supported by a simple model that reproduces this feedback pattern over the same time period. (C) 2014 Published by Elsevier B.V.}, language = {en} } @article{HerzschuhNiBirksetal.2011, author = {Herzschuh, Ulrike and Ni, Jian and Birks, H. John B. and B{\"o}hner, J{\"u}rgen}, title = {Driving forces of mid-Holocene vegetation shifts on the upper Tibetan Plateau, with emphasis on changes in atmospheric CO2 concentrations}, series = {Quaternary science reviews : the international multidisciplinary research and review journal}, volume = {30}, journal = {Quaternary science reviews : the international multidisciplinary research and review journal}, number = {15-16}, publisher = {Elsevier}, address = {Oxford}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2011.03.007}, pages = {1907 -- 1917}, year = {2011}, abstract = {Numerous pollen records across the upper Tibetan Plateau indicate that in the early part of the mid-Holocene, Kobresia-rich high-alpine meadows invaded areas formerly dominated by alpine steppe vegetation rich in Artemisia. We examine climate, land-use, and CO2 concentration changes as potential drivers for this marked vegetation change. The climatic implications of these vegetational shifts are explored by applying a newly developed pollen-based moisture-balance transfer-function to fossil pollen spectra from Koucha Lake on the north-eastern Tibetan Plateau (34.0 degrees N; 97.2 degrees E; 4540 m a.s.l.) and Xuguo Lake on the central Tibetan Plateau (31.97 degrees N; 90.3 degrees E; 4595 m a.s.l.), both located in the meadow-steppe transition zone. Reconstructed moisture-balances were markedly reduced (by similar to 150-180 mm) during the early mid-Holocene compared to the late-Holocene. These findings contradict most other records from the Indian monsoonal realm and also most non-pollen records from the Tibetan Plateau that indicate a rather wet early- and mid-Holocene. The extent and timing of anthropogenic land-use involving grazing by large herbivores on the upper Tibetan Plateau and its possible impacts on high-alpine vegetation are still mostly unknown due to the lack of relevant archaeological evidence. Arguments against a mainly anthropogenic origin of Kobresia high-alpine meadows are the discovery of the widespread expansion of obviously 'natural' Kobresia meadows on the south-eastern Tibetan Plateau during the Lateglacial period indicating the natural origin of this vegetation type and the lack of any concurrence between modern human-driven vegetation shifts and the mid-Holocene compositional changes. Vegetation types are known to respond to atmospheric CO2 concentration changes, at least on glacial-interglacial scales. This assumption is confirmed by our sensitivity study where we model Tibetan vegetation at different CO2 concentrations of 375 (present-day), 260 (early Holocene), and 650 ppm (future scenario) using the BIOME4 global vegetation model. Previous experimental studies confirm that vegetation growing on dry and high sites is particularly sensitive to CO2 changes. Here we propose that the replacement of drought-resistant alpine steppes (that are well adapted to low CO2 concentrations) by mesic Kobresia meadows can, at least, be partly interpreted as a response to the increase of CO2 concentration since 7000 years ago due to fertilization and water-saving effects. Our hypothesis is corroborated by former CO2 fertilization experiments performed on various dry grasslands and by the strong recent expansion of high-alpine meadows documented by remote sensing studies in response to recent CO2 increases.}, language = {en} } @article{HuangOberhaenslivonSuchodoletzetal.2014, author = {Huang, Xiangtong and Oberhaensli, Hedi and von Suchodoletz, Hans and Prasad, Sushma and Sorrel, Philippe and Plessen, Birgit and Mathis, Marie and Usubaliev, Raskul}, title = {Hydrological changes in western Central Asia (Kyrgyzstan) during the Holocene as inferred from a palaeolimnological study in lake Son Kul}, series = {Quaternary science reviews : the international multidisciplinary research and review journal}, volume = {103}, journal = {Quaternary science reviews : the international multidisciplinary research and review journal}, publisher = {Elsevier}, address = {Oxford}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2014.09.012}, pages = {134 -- 152}, year = {2014}, abstract = {The hydrology of western Central Asia is highly sensitive to climatic perturbations. In order to understand its long-term variability and to infer linkages between precipitation and atmospheric and oceanic systems, we conducted a thorough sedimentary and geochemical study on a composite core retrieved in lake Son Kul (central Kyrgyzstan). A multi-proxy approach was conducted on lake sediments based on grain size analyses, magnetic susceptibility, total organic carbon (TOC), total nitrogen (TN) and carbon and oxygen isotope analyses on bulk and biogenic materials (ostracoda and molluscs shells) at a resolution equivalent to ca 40 years, aiming to characterise the sequence of palaeolimnological changes in Son Kul. As indicated by delta O-18 record of bulk carbonates, mainly consisting of aragonite, the Holocene hydrological balance was negative during most of time, suggesting an excess of evaporation (E) over precipitation (P). Limnological conditions fluctuated rapidly before 5000 cal yr BP indicating significant changes in regional hydrology and climate. In particular, the long-term negative hydrological balance was impeded by several short stages with marked increase of precipitation, lasting several decades to a few centuries (e.g., 8300-8200, 6900-6700, 6300-6100, 5500-5400, 5300-5200 and 3100 -3000 cal yr BP). Precipitation changes as inferred from 8180 data are also documented by increased minerogenic detritus and higher TOC. We propose that the seasonal pattern of precipitation varied transiently in western Central Asia during the Holocene, although evaporation changes may also account for the rapid changes observed in delta O-18 data. When the annual water balance was less critical (P <= E), the excess of water might be ascribed to increased precipitation during cold seasons mainly because winter precipitation has more negative delta O-18 than its summer equivalent. Conversely, when the annual water balance is negative (P E), the moisture was mainly delivered during the warm season, as between 5000 and 2000 cal yr BP. Our results thus imply that moisture sources could have changed as well during the Holocene. Moisture was delivered as today mainly during summer from the extended Caspian-Aral Basin and eastern Mediterranean, although Arctic and even North Atlantic seas might be important moisture sources when seasonal precipitation was dominated by winter precipitation. We hypothesise that warming Arctic and North Atlantic seas were important for the North Hemisphere circulation during the cold season. (C) 2014 Elsevier Ltd. All rights reserved.}, language = {en} } @article{JambrinaEnriquezSachseValeroGarces2016, author = {Jambrina-Enriquez, Margarita and Sachse, Dirk and Valero-Garces, Blas L.}, title = {A deglaciation and Holocene biomarker-based reconstruction of climate and environmental variability in NW Iberian Peninsula: the Sanabria Lake sequence}, series = {Journal of paleolimnolog}, volume = {56}, journal = {Journal of paleolimnolog}, publisher = {Springer}, address = {Dordrecht}, issn = {0921-2728}, doi = {10.1007/s10933-016-9890-6}, pages = {49 -- 66}, year = {2016}, abstract = {The molecular biomarker composition of two sediment cores from Sanabria Lake (NW Iberian Peninsula) and a survey of modern plants in the watershed provide a reconstruction of past vegetation and landscape dynamics since deglaciation. During a proglacial stage in Lake Sanabria (prior to 14.7 cal ka BP), very low biomarker concentration and carbon preference index (CPI) values similar to 1 suggest that the n-alkanes could have derived from eroded ancient sediment sources or older organic matter with high degree of maturity. During the Late glacial (14.7-11.7 cal ka BP) and the Holocene (last 11.7 cal ka BP) intervals with higher biomarker and triterpenoid concentrations (high \%nC(29) , nC(31) alkanes), higher CPI and average carbon length (ACL), and lower P-aq (proportion of aquatic plants) are indicative of major contribution of vascular land plants from a more forested watershed (e.g. Mid Holocene period 7.0-4.0 cal ka BP). Lower biomarker concentrations (high \%nC(27) alkanes), CPI and ACL values responded to short phases with decreased allochthonous contribution into the lake that correspond to centennial-scale periods of regional forest decline (e.g. 4-3 ka BP, Roman deforestation after 2.0 ka, and some phases of the LIA, seventeenth-nineteenth centuries). Human activities in the watershed were significant during early medieval times (1.3-1.0 cal ka BP) and since 1960 CE, in both cases associated with relatively higher productivity stages in the lake (lower biomarker and triterpenoid concentrations, high \%nC(23) and \%nC(31) respectively, lower ACL and CPI values and higher P-aq). The lipid composition of Sanabria Lake sediments indicates a major allochthonous (watershed-derived) contribution to the organic matter budget since deglaciation, and a dominant oligotrophic status during the lake history. The study constrains the climate and anthropogenic forcings and watershed versus lake sources in organic matter accumulation processes and helps to design conservation and management policies in mountain, oligotrophic lakes.}, language = {en} } @phdthesis{Lauterbach2011, author = {Lauterbach, Stefan}, title = {Lateglacial to Holocene climatic and environmental changes in Europe : multi-proxy studies on lake sediments along a transect from northern Italy to northeastern Poland}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-58157}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Sediment records of three European lakes were investigated in order to reconstruct the regional climate development during the Lateglacial and Holocene, to investigate the response of local ecosystems to climatic fluctuations and human impact and to relate regional peculiarities of past climate development to climatic changes on a larger spatial scale. The Lake Hańcza (NE Poland) sediment record was studied with a focus on reconstructing the early Holocene climate development and identifying possible differences to Western Europe. Following the initial Holocene climatic improvement, a further climatic improvement occurred between 10 000 and 9000 cal. a BP. Apparently, relatively cold and dry climate conditions persisted in NE Poland during the first ca. 1500 years of the Holocene, most likely due to a specific regional atmospheric circulation pattern. Prevailing anticyclonic circulation linked to a high-pressure cell above the remaining Scandinavian Ice Sheet (SIS) might have blocked the eastward propagation of warm and moist Westerlies and thus attenuated the early Holocene climatic amelioration in this region until the final decay of the SIS, a pattern different from climate development in Western Europe. The Lateglacial sediment record of Lake Mondsee (Upper Austria) was investigated in order to study the regional climate development and the environmental response to rapid climatic fluctuations. While the temperature rise and environmental response at the onset of the Holocene took place quasi-synchronously, major leads and lags in proxy responses characterize the onset of the Lateglacial Interstadial. In particular, the spread of coniferous woodlands and the reduction of detrital flux lagged the initial Lateglacial warming by ca. 500-750 years. Major cooling at the onset of the Younger Dryas took place synchronously with a change in vegetation, while the increase of detrital matter flux was delayed by about 150-300 years. Complex proxy responses are also detected for short-term Lateglacial climatic fluctuations. In summary, periods of abrupt climatic changes are characterized by complex and temporally variable proxy responses, mainly controlled by ecosystem inertia and the environmental preconditions. A second study on the Lake Mondsee sediment record focused on two small-scale climate deteriorations around 8200 and 9100 cal. a BP, which have been triggered by freshwater discharges to the North Atlantic, causing a shutdown of the Atlantic meridional overturning circulation (MOC). Combining microscopic varve counting and AMS 14C dating yielded a precise duration estimate (ca. 150 years) and absolute dating of the 8.2 ka cold event, both being in good agreement with results from other palaeoclimate records. Moreover, a sudden temperature overshoot after the 8.2 ka cold event was identified, also seen in other proxy records around the North Atlantic. This was most likely caused by enhanced resumption of the MOC, which also initiated substantial shifts of oceanic and atmospheric front systems. Although there is also evidence from other proxy records for pronounced recovery of the MOC and atmospheric circulation changes after the 9.1 ka cold event, no temperature overshoot is seen in the Lake Mondsee record, indicating the complex behaviour of the global climate system. The Holocene sediment record of Lake Iseo (northern Italy) was studied to shed light on regional earthquake activity and the influence of climate variability and anthropogenic impact on catchment erosion and detrital flux into the lake. Frequent small-scale detrital layers within the sediments reflect allochthonous sediment supply by extreme surface runoff events. During the early to mid-Holocene, increased detrital flux coincides with periods of cold and wet climate conditions, thus apparently being mainly controlled by climate variability. In contrast, intervals of high detrital flux during the late Holocene partly also correlate with phases of increased human impact, reflecting the complex influences on catchment erosion processes. Five large-scale event layers within the sediments, which are composed of mass-wasting deposits and turbidites, are supposed to have been triggered by strong local earthquakes. While the uppermost of these event layers is assigned to a documented adjacent earthquake in AD 1222, the four other layers are supposed to be related to previously undocumented prehistorical earthquakes.}, language = {en} }