TY - JOUR A1 - Herzschuh, Ulrike A1 - Ni, Jian A1 - Birks, H. John B. A1 - Böhner, Jürgen T1 - Driving forces of mid-Holocene vegetation shifts on the upper Tibetan Plateau, with emphasis on changes in atmospheric CO2 concentrations JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - 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. KW - Tibetan Plateau KW - Pollen KW - Holocene KW - Transfer function KW - Kobresia meadow KW - Atmospheric CO2 concentration Y1 - 2011 U6 - https://doi.org/10.1016/j.quascirev.2011.03.007 SN - 0277-3791 VL - 30 IS - 15-16 SP - 1907 EP - 1917 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Huang, Xiangtong A1 - Oberhaensli, Hedi A1 - von Suchodoletz, Hans A1 - Prasad, Sushma A1 - Sorrel, Philippe A1 - Plessen, Birgit A1 - Mathis, Marie A1 - Usubaliev, Raskul T1 - Hydrological changes in western Central Asia (Kyrgyzstan) during the Holocene as inferred from a palaeolimnological study in lake Son Kul JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - 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. KW - Holocene KW - Tien Shan (western Central Asia) KW - Oxygen and carbon isotopes KW - Hydrological balance Y1 - 2014 U6 - https://doi.org/10.1016/j.quascirev.2014.09.012 SN - 0277-3791 VL - 103 SP - 134 EP - 152 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Jambrina-Enriquez, Margarita A1 - Sachse, Dirk A1 - Valero-Garces, Blas L. T1 - A deglaciation and Holocene biomarker-based reconstruction of climate and environmental variability in NW Iberian Peninsula: the Sanabria Lake sequence JF - Journal of paleolimnolog N2 - 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. KW - Plant n-alkanes KW - Lipid biomarker KW - Sanabria Lake KW - n-Alkanes KW - Holocene KW - Lateglacial KW - Iberian Peninsula Y1 - 2016 U6 - https://doi.org/10.1007/s10933-016-9890-6 SN - 0921-2728 SN - 1573-0417 VL - 56 SP - 49 EP - 66 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Lauterbach, Stefan A1 - Witt, Roman A1 - Plessen, Birgit A1 - Dulski, Peter A1 - Prasad, Sushma A1 - Mingram, Jens A1 - Gleixner, Gerd A1 - Hettler-Riedel, Sabine A1 - Stebich, Martina A1 - Schnetger, Bernhard A1 - Schwalb, Antje A1 - Schwarz, Anja T1 - Climatic imprint of the mid-latitude Westerlies in the Central Tian Shan of Kyrgyzstan and teleconnections to North Atlantic climate variability during the last 6000 years JF - The Holocene : an interdisciplinary journal focusing on recent environmental change N2 - In general, a moderate drying trend is observed in mid-latitude arid Central Asia since the Mid-Holocene, attributed to the progressively weakening influence of the mid-latitude Westerlies on regional climate. However, as the spatio-temporal pattern of this development and the underlying climatic mechanisms are yet not fully understood, new high-resolution paleoclimate records from this region are needed. Within this study, a sediment core from Lake Son Kol (Central Kyrgyzstan) was investigated using sedimentological, (bio) geochemical, isotopic, and palynological analyses, aiming at reconstructing regional climate development during the last 6000 years. Biogeochemical data, mainly reflecting summer moisture conditions, indicate predominantly wet conditions until 4950 cal. yr BP, succeeded by a pronounced dry interval between 4950 and 3900 cal. yr BP. In the following, a return to wet conditions and a subsequent moderate drying trend until present times are observed. This is consistent with other regional paleoclimate records and likely reflects the gradual Late Holocene diminishment of the amount of summer moisture provided by the mid-latitude Westerlies. However, climate impact of the Westerlies was apparently not only restricted to the summer season but also significant during winter as indicated by recurrent episodes of enhanced allochthonous input through snowmelt, occurring before 6000 cal. yr BP and at 5100-4350, 3450-2850, and 1900-1500 cal. yr BP. The distinct similar to 1500year periodicity of these episodes of increased winter precipitation in Central Kyrgyzstan resembles similar cyclicities observed in paleoclimate records around the North Atlantic, likely indicating a hemispheric-scale climatic teleconnection and an impact of North Atlantic Oscillation (NAO) variability in Central Asia. KW - Central Asia KW - climate KW - Holocene KW - lake sediments KW - mid-latitude Westerlies KW - NAO Y1 - 2014 U6 - https://doi.org/10.1177/0959683614534741 SN - 0959-6836 SN - 1477-0911 VL - 24 IS - 8 SP - 970 EP - 984 PB - Sage Publ. CY - London ER - TY - JOUR A1 - Marquer, Laurent A1 - Gaillard, Marie-Jose A1 - Sugita, Shinya A1 - Poska, Anneli A1 - Trondman, Anna-Kari A1 - Mazier, Florence A1 - Nielsen, Anne Birgitte A1 - Fyfe, Ralph M. A1 - Jonsson, Anna Maria A1 - Smith, Benjamin A1 - Kaplan, Jed O. A1 - Alenius, Teija A1 - Birks, H. John B. A1 - Bjune, Anne E. A1 - Christiansen, Jorg A1 - Dodson, John A1 - Edwards, Kevin J. A1 - Giesecke, Thomas A1 - Herzschuh, Ulrike A1 - Kangur, Mihkel A1 - Koff, Tiiu A1 - Latalowa, Maligorzata A1 - Lechterbeck, Jutta A1 - Olofsson, Jorgen A1 - Seppa, Heikki T1 - Quantifying the effects of land use and climate on Holocene vegetation in Europe JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - Early agriculture can be detected in palaeovegetation records, but quantification of the relative importance of climate and land use in influencing regional vegetation composition since the onset of agriculture is a topic that is rarely addressed. We present a novel approach that combines pollen-based REVEALS estimates of plant cover with climate, anthropogenic land-cover and dynamic vegetation modelling results. This is used to quantify the relative impacts of land use and climate on Holocene vegetation at a sub-continental scale, i.e. northern and western Europe north of the Alps. We use redundancy analysis and variation partitioning to quantify the percentage of variation in vegetation composition explained by the climate and land-use variables, and Monte Carlo permutation tests to assess the statistical significance of each variable. We further use a similarity index to combine pollen based REVEALS estimates with climate-driven dynamic vegetation modelling results. The overall results indicate that climate is the major driver of vegetation when the Holocene is considered as a whole and at the sub-continental scale, although land use is important regionally. Four critical phases of land-use effects on vegetation are identified. The first phase (from 7000 to 6500 BP) corresponds to the early impacts on vegetation of farming and Neolithic forest clearance and to the dominance of climate as a driver of vegetation change. During the second phase (from 4500 to 4000 BP), land use becomes a major control of vegetation. Climate is still the principal driver, although its influence decreases gradually. The third phase (from 2000 to 1500 BP) is characterised by the continued role of climate on vegetation as a consequence of late-Holocene climate shifts and specific climate events that influence vegetation as well as land use. The last phase (from 500 to 350 BP) shows an acceleration of vegetation changes, in particular during the last century, caused by new farming practices and forestry in response to population growth and industrialization. This is a unique signature of anthropogenic impact within the Holocene but European vegetation remains climatically sensitive and thus may continue to respond to ongoing climate change. (C) 2017 Elsevier Ltd. All rights reserved. KW - Climate KW - Holocene KW - Human impact KW - Land use KW - LPJ-GUESS KW - Europe KW - Pollen KW - REVEALS KW - Vegetation composition Y1 - 2017 U6 - https://doi.org/10.1016/j.quascirev.2017.07.001 SN - 0277-3791 VL - 171 SP - 20 EP - 37 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Marquer, Laurent A1 - Gaillard, Marie-Jose A1 - Sugita, Shinya A1 - Trondman, Anna-Kari A1 - Mazier, Florence A1 - Nielsen, Anne Birgitte A1 - Fyfe, Ralph M. A1 - Odgaard, Bent Vad A1 - Alenius, Teija A1 - Birks, H. John B. A1 - Bjune, Anne E. A1 - Christiansen, Jörg A1 - Dodson, John A1 - Edwards, Kevin J. A1 - Giesecke, Thomas A1 - Herzschuh, Ulrike A1 - Kangur, Mihkel A1 - Lorenz, Sebastian A1 - Poska, Anneli A1 - Schult, Manuela A1 - Seppa, Heikki T1 - Holocene changes in vegetation composition in northern Europe: why quantitative pollen-based vegetation reconstructions matter JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - We present pollen-based reconstructions of the spatio-temporal dynamics of northern European regional vegetation abundance through the Holocene. We apply the Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) model using fossil pollen records from eighteen sites within five modern biomes in the region. The eighteen sites are classified into four time-trajectory types on the basis of principal components analysis of both the REVEALS-based vegetation estimates (RVs) and the pollen percentage (PPs). The four trajectory types are more clearly separated for RVs than PPs. Further, the timing of major Holocene shifts, rates of compositional change, and diversity indices (turnover and evenness) differ between RVs and PPs. The differences are due to the reduction by REVEALS of biases in fossil pollen assemblages caused by different basin size, and inter-taxonomic differences in pollen productivity and dispersal properties. For example, in comparison to the PPs, the RVs show an earlier increase in Corylus and Ulmus in the early-Holocene and a more pronounced increase in grassland and deforested areas since the mid-Holocene. The results suggest that the influence of deforestation and agricultural activities on plant composition and abundance from Neolithic times was stronger than previously inferred from PPs. Relative to PPs, RVs show a more rapid compositional change, a largest decrease in turnover, and less variable evenness in most of northern Europe since 5200 cal yr BP. All these changes are primarily related to the strong impact of human activities on the vegetation. This study demonstrates that RV-based estimates of diversity indices, timing of shifts, and rates of change in reconstructed vegetation provide new insights into the timing and magnitude of major human distribution on Holocene regional, vegetation, feature that are critical in the assessment of human impact on vegetation, land-cover, biodiversity, and climate in the past. KW - Holocene KW - Human impact KW - Northern Europe KW - Pollen KW - Quantitative regional plant abundance KW - Rate of compositional change KW - REVEALS (Regional Estimates of VEgetation KW - Abundance from Large Sites) model KW - Vegetation diversity indices Y1 - 2014 U6 - https://doi.org/10.1016/j.quascirev.2014.02.013 SN - 0277-3791 VL - 90 SP - 199 EP - 216 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Menzel, Philip A1 - Gaye, Birgit A1 - Mishra, Praveen Kumar A1 - Anoop, Ambili A1 - Basavaiah, Nathani A1 - Marwan, Norbert A1 - Plessen, Birgit A1 - Prasad, Sushma A1 - Riedel, Nils A1 - Stebich, Martina A1 - Wiesner, Martin G. T1 - Linking Holocene drying trends from Lonar Lake in monsoonal central India to North Atlantic cooling events JF - Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences N2 - We present the results of biogeochemical and mineralogical analyses on a sediment core that covers the Holocene sedimentation history of the climatically sensitive, closed, saline, and alkaline Lonar Lake in the core monsoon zone in central India. We compare our results of C/N ratios, stable carbon and nitrogen isotopes, grain-size, as well as amino acid derived degradation proxies with climatically sensitive proxies of other records from South Asia and the North Atlantic region. The comparison reveals some more or less contemporaneous climate shifts. At Lonar Lake, a general long term climate transition from wet conditions during the early Holocene to drier conditions during the late Holocene, delineating the insolation curve, can be reconstructed. In addition to the previously identified periods of prolonged drought during 4.6-3.9 and 2.0-0.6 cal ka that have been attributed to temperature changes in the Indo Pacific Warm Pool, several additional phases of shorter term climate alteration superimposed upon the general climate trend can be identified. These correlate with cold phases in the North Atlantic region. The most pronounced climate deteriorations indicated by our data occurred during 62-5.2,4.6-3.9, and 2.0-0.6 cal ka BP. The strong dry phase between 4.6 and 3.9 cal ka BP at Lonar Lake corroborates the hypothesis that severe climate deterioration contributed to the decline of the Indus Civilisation about 3.9 ka BP. (C) 2014 Elsevier B.V. All rights reserved. KW - Lake sediment KW - Indian monsoon KW - Holocene KW - Climate reconstruction KW - Stable carbon isotope KW - Amino acid Y1 - 2014 U6 - https://doi.org/10.1016/j.palaeo.2014.05.044 SN - 0031-0182 SN - 1872-616X VL - 410 SP - 164 EP - 178 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Mischke, Steffen A1 - Lai, Zhongping A1 - Aichner, Bernhard A1 - Heinecke, Liv A1 - Mahmoudov, Zafar A1 - Kuessner, Marie A1 - Herzschuh, Ulrike T1 - Radiocarbon and optically stimulated luminescence dating of sediments from Lake Karakul, Tajikistan JF - Quaternary geochronology : the international research and review journal on advances in quaternary dating techniques N2 - Lake Karakul in the eastern Pamirs is a large and closed-basin lake in a partly glaciated catchment. Two parallel sediment cores were collected from 12 m water depth. The cores were correlated using XRF analysis and dated using radiocarbon and OSL techniques. The age results of the two dating methods are generally in agreement. The correlated composite core of 12.26 m length represents continuous accumulation of sediments in the lake basin since 31 ka. The lake reservoir effect (LRE) remained relatively constant over this period. High sediment accumulation rates (SedARs) were recorded before 23 ka and after 6.5 ka. The relatively close position of the coring location near the eastern shore of the lake implies that high SedARs resulted from low lake levels. Thus, high SedARs and lower lake levels before 23 ka probably reflect cold and dry climate conditions that inhibited the arrival of moist air at high elevation in the eastern Pamirs. Low lake levels after 6.5 ka were probably caused by declining temperatures after the warmer early Holocene, which had caused a reduction in water resources stored as snow, ice and frozen ground in the catchment. Low SedARs during 23-6.5 ka suggest increased lake levels in Lake Karakul. A short-lived increase of SedARs at 15 ka probably corresponds to the rapid melting of glaciers in the Karakul catchment during the Greenland Interstadial le, shortly after glaciers in the catchment had reached their maximum extents. The sediment cores from Lake Karakul represent an important climate archive with robust chronology for the last glacial interglacial cycle from Central Asia. (C) 2017 Elsevier B.V. All rights reserved. KW - Radiocarbon and OSL dating KW - Lake sediments KW - Pamir mountains KW - Late pleistocene KW - Holocene Y1 - 2017 U6 - https://doi.org/10.1016/j.quageo.2017.05.008 SN - 1871-1014 SN - 1878-0350 VL - 41 SP - 51 EP - 61 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Mischke, Steffen A1 - Zhang, Chengjun T1 - Ostracod distribution in Ulungur Lake (Xinjiang, China) and a reassessed Holocene record JF - Ecological research N2 - Ostracod shells in surface sediments from Ulungur Lake (Xinjiang, China) belong mainly to Limnocythere inopinata as the dominant species, and Candona neglecta and Darwinula stevensoni as accompanying, less abundant taxa. Shells of an additional nine species were recorded only sporadically. The three most abundant ostracods have wide tolerance ranges in terms of salinity, substrate and water depth. The similarly recorded bivalve Pisidium subtruncatum, and the gastropods Gyraulus chinensis and Radix auricularia belong to the most tolerant representatives of the genera. The bivalve and gastropods, in addition to the ostracod assemblage, reflect the fact that Ulungur Lake has experienced strong lake level and salinity variations due to water withdrawal in the catchment and the counteracting diversion of river waters to the lake in recent decades. The substrate in Ulungur Lake is typically fine-grained, apart from the delta region of the Ulungur River channel, which is marked by relatively coarse-grained detrital sediments barren of ostracod shells. This channel was created 40 years ago to divert water to Ulungur Lake and support its local fisheries and recreational facilities. A reassessed Holocene ostracod record from the lake shows that a significantly higher salinity and lower lake level existed in the early Holocene before 6.0 ka in response to the regional climate. In contrast, a higher lake level and lowest salinity is inferred for the late Holocene period between ca. 3.6 and 1.3 ka before present. Afterwards, the lake level declined and salinity increased in response to regional moisture reduction, although conditions similar to the early Holocene lake status were not re-established. Our surface-sediment-derived data provide a baseline for analysis of future environmental variations due to global climate change and regional water management. KW - Ostracoda KW - Water depth KW - Substrate KW - Holocene KW - Central Asia Y1 - 2011 U6 - https://doi.org/10.1007/s11284-010-0768-1 SN - 0912-3814 VL - 26 IS - 1 SP - 133 EP - 145 PB - Springer CY - Tokyo ER - TY - GEN A1 - Mischke, Steffen A1 - Zhang, Chengjun A1 - Fan, Rong T1 - Early to mid-Holocene lake high-stand sediments at Lake Donggi Cona, northeastern Tibetan Plateau, China - T2 - Quaternary research : an interdisciplinary journal KW - Microfossils KW - Ostracoda KW - Lake level KW - Wetlands KW - Depositional setting KW - Tibetan Plateau KW - Holocene Y1 - 2015 U6 - https://doi.org/10.1016/j.yqres.2014.06.005 SN - 0033-5894 SN - 1096-0287 VL - 83 IS - 1 SP - 256 EP - 258 PB - Elsevier CY - San Diego ER -