TY - JOUR A1 - Herzschuh, Ulrike A1 - Kürschner, Harald A1 - Mischke, Steffen T1 - Temperature variability and vertical vegetation belt shifts during the last similar to 50,000 yr in the Qilian Mountains (NE margin of the Tibetan Plateau, China) N2 - A 13.94-m-long sediment core, collected from a medium-sized lake in the Qilian Mountains (NE Tibetan Plateau, China), was analysed palynologically at 81 horizons. The interpretation of indicator taxa yielded various vertical shifts of the vegetation belts. These palaeovegetation results have been checked with lake surface pollen spectra from 8 takes representing different altitudinal vegetation belts. Our main findings are the following: A short period of the late Marine Isotope Stage 3 (around similar to 46,000 yr ago) was characterized by interglacial temperature conditions with a tree line above its present-day altitude. During the LGM, the vicinity of the lake was not covered by ice but by sparse alpine vegetation and alpine deserts, indicating that the climate was colder by similar to 4-7 degrees C than today Markedly higher temperatures were inferred from higher arboreal pollen frequencies between similar to 13,000 and similar to 7000 yr ago with a Holocene temperature optimum and a maximal Picea-Betula mixed-forest expansion between similar to 9000 and similar to 7000 yr ago, when temperatures exceeded the present-day conditions by at least 1-2 degrees C. Alpine steppes and meadows and sub-alpine shrub vegetation dominated around the lake since the middle Holocene, suggesting that vegetation and climate conditions were exceptionally stable in comparison to previous periods. Y1 - 2006 UR - http://www.sciencedirect.com/science/journal/00335894 U6 - https://doi.org/10.1016/j.yqres.2006.03.001 SN - 0033-5894 ER - TY - JOUR A1 - Herzschuh, Ulrike A1 - Kramer, Annette A1 - Mischke, Steffen A1 - Zhang, Chengjun T1 - Quantitative climate and vegetation trends since the late glacial on the northeastern Tibetan Plateau deduced from Koucha Lake pollen spectra N2 - Quantitative information on vegetation and climate history from the late glacial-Holocene on the Tibetan Plateau is extremely rare. Here, we present palynological results of a 4.30-m-long sediment record collected from Koucha Lake in the Bayan Har Mountains, northeastern Tibetan Plateau. Vegetation change has been traced by biomisation, ordination of pollen data, and calculation of pollen ratios. The application of a pollen-climate calibration set from the eastern Tibetan Plateau to Koucha Lake pollen spectra yielded quantitative climate information. The area was covered by alpine desert/steppe, characteristic of a cold and dry climate (with 50% less precipitation than today) between 16,700 and 14,600 cal yr BP. Steppe vegetation, warm (similar to 1 degrees C higher than today) and wet conditions prevailed between 14,600 and 6600 cal yr BR These findings contradict evidence from other monsoon-influenced areas of Asia, where the early Holocene is thought to have been moist. Low effective moisture on the northeastern Tibetan Plateau was likely due to high temperature and evaporation, even though precipitation levels may have been similar to present- day values. The vegetation changed to tundra around 6600 cal yr BP, indicating that wet and cool climate conditions occurred on the northeastern Tibetan Plateau during the second half of the Holocene. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/00335894 U6 - https://doi.org/10.1016/j.yqres.2008.09.003 SN - 0033-5894 ER - TY - JOUR A1 - Herzschuh, Ulrike A1 - Mischke, Steffen A1 - Meyer, Hanno A1 - Plessen, Birgit A1 - Zhang, Chengjun T1 - Lake nutrient variability inferred from elemental (C, N, S) and isotopic (delta C-13, delta N-15) analyses of aquatic plant macrofossils N2 - This paper aims to highlight the potential of using elemental and stable isotope analyses of aquatic macrophytes in palaeolimnological studies. Potamogeton pectinatus material was collected from modem plants (n=68) and from late glacial and Holocene-aged sediments from Koucha Lake (northeastern Tibetan Plateau; 34.0 degrees N; 97.2 degrees E; 4540 m a.s.l.). It was analyzed for delta C-13(Potamogeton) (modern: -23 to 0 parts per thousand, fossil: -19 to -4 parts per thousand) and delta N-15(Potamogeton) (modern: -11.0 to +13.8 parts per thousand, fossil: -9.5 to +6.7 parts per thousand) in addition to elemental carbon and nitrogen (modem C/N-Potamogeton: 7 to 29; fossil: 13 to 68) and sulfur (fossil: 188-899 mu mol/g dry weight). Fossil data were interpreted in terms of palaeo-nutrient availability and palaeo-productivity based on the modem relationships between various proxies and certain environmental data. Productivity of Potamogeton pectinatus mats at Koucha Lake as indicated by palaeo-epsilon(Potamogeton-TIC) (i.e. the enrichment of delta C-13(Potamogeton) relative to the delta(CTIC)-C-13) was reduced during periods of high conductivity, especially between 10.3 and 7.4 cal kyr BP. Potamogeton pectinatus material from these periods was also characterized by high S-Potamogeton indicating high sulfide concentrations and anoxic conditions within the sediments. However, C/N- Potamogeton ratios and delta N-15(Potamogeton) from the lower core section were found to have been altered by decompositional processes. A pronounced shift in the aquatic productivity of Lake Koucha occurred at similar to 7.4 cal kyr BP when the hydrological conditions shifted towards an open lake system and water depth increased. At this time a strong increase in productivity led to a strong decrease in the water HCO3- concentration as inferred from the application of a epsilon-(Potamogeton-TIC)-InHCO3- transfer function. A comparison of reconstructed productivity changes from Koucha Lake with further environmental proxies suggests that primary productivity changes are probably a function of internal lake dynamics and were only indirectly triggered by climate change. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/02773791 U6 - https://doi.org/10.1016/j.quascirev.2010.05.011 SN - 0277-3791 ER - TY - JOUR A1 - Herzschuh, Ulrike A1 - Birks, H. John B. A1 - Mischke, Steffen A1 - Zhang, Chengjun A1 - Böhner, Jürgen T1 - A modern pollen-climate calibration set based on lake sediments from the Tibetan Plateau and its application to a Late Quaternary pollen record from the Qilian Mountains N2 - Aim: Fossil pollen spectra from lake sediments on the Tibetan Plateau have been used for qualitative climate reconstruction, but no modern pollen-climate calibration set based on lake sediments is available to infer past climate quantitatively. This study aims to develop such a dataset and apply it to fossil data. Location: The Tibetan Plateau, between 30 and 40 degrees N and 87 and 103 degrees E. Methods: We collected surface sediments from 112 lakes and analysed them palynologically. The lakes span a wide range of mean annual precipitation (P-ann; 31-1022 mm), mean annual temperature (T-ann; -6.5 to 1 degrees C), and mean July temperature (T-July; 2.6-19.7 degrees C). Redundancy analysis showed that the modern pollen spectra are characteristic of their respective vegetation types and local climate. Transfer functions for P-ann, T-ann and T-July were developed with weighted averaging partial least squares. Model performance was assessed by leave-one-out cross-validation. Results: The root mean square errors of prediction (RMSEP) were 104 mm (P-ann), 1.18 degrees C (T-ann) and 1.17 degrees C (T-July). The RMSEPs, when expressed as percentages of the gradient sampled, were 10.6% (P-ann), 15.7% (T-ann) and 11.9% (T-July). These low values indicate the good performance of our models. An application of the models to fossil pollen spectra covering the last c. 50 kyr yielded realistic results for Luanhaizi Lake in the Qilian Mountains on the north-eastern Tibetan Plateau (modern P-ann 480 mm; T-ann-1 degrees C). T-ann and P-ann values similar to present ones were reconstructed for late Marine Isotope Stage 3, with minimum values for the Last Glacial Maximum (c. 300 mm and 2 degrees C below present), and maximum values for the early Holocene (c. 70 mm and 0.5 degrees C greater than present). Main conclusions: The modern pollen-climate calibration set will potentially be useful for quantitative climate reconstructions from lake-sediment pollen spectra from the Tibetan Plateau, an area of considerable climatic and biogeographical importance. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=0305-0270 U6 - https://doi.org/10.1111/j.1365-2699.2009.02245.x SN - 0305-0270 ER - TY - JOUR A1 - Herzschuh, Ulrike A1 - Mischke, Steffen A1 - Meyer, Hanno A1 - Plessen, Birgit A1 - Zhang, Chengjun T1 - Using variations in the stable carbon isotope composition of macrophyte remains to quantify nutrient dynamics in lakes N2 - The apparent isotope enrichment factor epsilon(macrophyte) of submerged plants (epsilon(macrophyte-DIC) = delta C-13(macrophyte) - delta C-13(DIC)) is indicative of dissolved inorganic carbon (DIC) supply in neutral to alkaline waters and is related to variations in aquatic productivity (Papadimitriou et al. in Limnol Oceanogr 50:1084-1095, 2005). This paper aims to evaluate the usage of epsilon(macrophyte) inferred from isotopic analyses of submerged plant fossils in addition to analyses of lake carbonate as a palaeolimnological proxy for former HCO3 (-) concentrations. Stable carbon isotopic analysis of modern Potamogeton pectinatus leaves and its host water DIC from the Tibetan Plateau and Central Yakutia (Russia) yielded values between -23.3 and +0.4aEuro degrees and between +14.0 and +6.5aEuro degrees, respectively. Values of epsilon (Potamogeton-DIC) (range -15.4 to +1.1aEuro degrees) from these lakes are significantly correlated with host water HCO3 (-) concentration (range 78-2,200 mg/l) (r = -0.86; P < 0.001), thus allowing for the development of a transfer function. Palaeo-epsilon (Potamogeton-ostracods) values from Luanhaizi Lake on the NE Tibetan Plateau, as inferred from the stable carbon isotope measurement of fossil Potamogeton pectinatus seeds (range -24 to +2.8aEuro degrees) and ostracods (range -7.8 to +7.5%) range between -14.8 and 1.6aEuro degrees. Phases of assumed disequilibrium between delta C-13(DIC) and delta C-13(ostracods) known to occur in charophyte swards (as indicated by the deposition of charophyte fossils) were excluded from the analysis of palaeo-epsilon. The application of the epsilon (Potamogeton-DIC)-HCO3 (-) transfer function yielded a median palaeo-HCO3 (-) -concentration of 290 mg/l. Variations in the dissolved organic carbon supply compare well with aquatic plant productivity changes and lake level variability as inferred from a multiproxy study of the same record including analyses of plant macrofossils, ostracods, carbonate and organic content. Y1 - 2010 UR - http://www.springerlink.com/content/100294 U6 - https://doi.org/10.1007/s10933-009-9365-0 SN - 0921-2728 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 - JOUR A1 - Wischnewski, Juliane A1 - Mackay, Anson W. A1 - Appleby, Peter G. A1 - Mischke, Steffen A1 - Herzschuh, Ulrike T1 - Modest diatom responses to regional warming on the southeast Tibetan Plateau during the last two centuries JF - Journal of paleolimnolog N2 - A general mean annual temperature increase accompanied with substantial glacial retreat has been noted on the Tibetan Plateau during the last two centuries but most significantly since the mid 1950s. These climate trends are particularly apparent on the southeastern Tibetan Plateau. However, the Tibetan Plateau (due to its heterogeneous mountain landscape) has very complex and spatially differing temperature and precipitations patterns. As a result, intensive palaeolimnological investigations are necessary to decipher these climatic patterns and to understand ecological responses to recent environmental change. Here we present palaeolimnological results from a (210)Pb/(137)Cs-dated sediment core spanning approximately the last 200 years from a remote high-mountain lake (LC6 Lake, working name) on the southeastern Tibetan Plateau. Sediment profiles of diatoms, organic variables (TOC, C:N) and grain size were investigated. The (210)Pb record suggests a period of rapid sedimentation, which might be linked to major tectonic events in the region ca. 1950. Furthermore, unusually high (210)Pb supply rates over the last 50 years suggest that the lake has possibly been subjected to increasing precipitation rates, sediment focussing and/or increased spring thaw. The majority of diatom taxa encountered in the core are typical of slightly acidic to circumneutral, oligotrophic, electrolyte-poor lakes. Diatom species assemblages were rich, and dominated by Cyclotella sp., Achnanthes sp., Aulacoseira sp. and fragilarioid taxa. Diatom compositional change was minimal over the 200-year period (DCCA = 0.85 SD, p = 0.59); only a slightly more diverse but unstable diatom assemblage was recorded during the past 50 years. The results indicate that large-scale environmental changes recorded in the twentieth century (i.e. increased precipitation and temperatures) are likely having an affect on the LC6 Lake, but so far these impacts are more apparent on the lake geochemistry than on the diatom flora. Local and/or regional peculiarities, such as increasing precipitation and cloud cover, or localized climatic phenomena, such as negative climate feedbacks, might have offset the effects of increasing mean surface temperatures. KW - Diatoms KW - Tibetan Plateau KW - Mountain lake KW - Climate change KW - Lake sediments KW - Palaeolimnology Y1 - 2011 U6 - https://doi.org/10.1007/s10933-011-9533-x SN - 0921-2728 VL - 46 IS - 2 SP - 215 EP - 227 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Wischnewski, Juliane A1 - Mischke, Steffen A1 - Wang, Yongbo A1 - Herzschuh, Ulrike T1 - Reconstructing climate variability on the northeastern Tibetan Plateau since the last Lateglacial - a multi-proxy, dual-site approach comparing terrestrial and aquatic signals JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - A sediment core from a closed basin lake (Lake Kuhai) from the semi-arid northeastern Tibetan Plateau was analysed for its pollen record to infer Lateglacial and post glacial vegetation and climatic change. At Lake Kuhai five major vegetation and climate shifts could be identified: (1) a change from cold and dry to relatively warmer and more moist conditions at 14.8 cal ka BP: (2) a shift to conditions of higher effective moisture and a stepwise warmer climate at 13.6 cal ka BP; (3) a further shift with increased moisture but colder conditions at 7.0 cal ka BP; (4) a return to a significantly colder and drier phase at 6.3 cal ka BP; (5) and a change back to relatively moist conditions at 2.2 cal ka BP. To investigate the response of lake ecosystems to climatic changes, statistical comparisons were made between the lake Kuhai pollen record and a formerly published ostracod and sedimentary record from the same sediment core. Furthermore, the pollen and lacustrine proxies from lake Kuhai were compared to a previously published pollen and lacustrine record from the nearby Lake Koucha. Statistical comparisons were done using non-metric multidimensional scaling and Procrustes rotation. Differences between lacustrine and pollen responses within one site could be identified, suggesting that lacustrine proxies are partly influenced by in-lake or local catchment processes, whereas the terrestrial (pollen) proxy shows a regional climate signal. Furthermore, we found regional differences in proxy response between lake Kuhai and Lake Koucha. Both pollen records reacted in similar ways to major environmental changes, with minor differences in the timing and magnitude of these changes. The lacustrine records were very similar in their timing and magnitude of response to environmental changes; however, the nature of change was at times very distinct. To place the current study in the context of Holocene moisture evolution across the Tibetan Plateau, we applied a five-scale moisture index and average link clustering to all available continuous palaeo-climate records from the Tibetan Plateau to possibly find general patterns of moisture evolution on the Plateau. However, no common regional pattern of moisture evolution during the Holocene could be detected. We assign this to complex responses of different proxies to environmental and atmospheric changes in an already very heterogeneous mountain landscape where minor differences in elevation can cause strong variation in microenvironments. Y1 - 2011 U6 - https://doi.org/10.1016/j.quascirev.2010.10.001 SN - 0277-3791 VL - 30 IS - 1-2 SP - 82 EP - 97 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Wischnewski, Juliane A1 - Kramer, Annette A1 - Kong, Zhaochen A1 - Mackay, Anson W. A1 - Simpson, Gavin L. A1 - Mischke, Steffen A1 - Herzschuh, Ulrike T1 - Terrestrial and aquatic responses to climate change and human impact on the southeastern Tibetan Plateau during the past two centuries JF - Global change biology N2 - Rapid population growth and economic development have led to increased anthropogenic pressures on the Tibetan Plateau, causing significant land cover changes with potentially severe ecological consequences. To assess whether or not these pressures are also affecting the remote montane-boreal lakes on the SE Tibetan Plateau, fossil pollen and diatom data from two lakes were synthesized. The interplay of aquatic and terrestrial ecosystem response was explored in respect to climate variability and human activity over the past 200 years. Nonmetric multidimensional scaling and Procrustes rotation analysis were undertaken to determine whether pollen and diatom responses in each lake were similar and synchronous. Detrended canonical correspondence analysis was used to develop quantitative estimates of compositional species turnover. Despite instrumental evidence of significant climatic warming on the southeastern Plateau, the pollen and diatom records indicate very stable species composition throughout their profiles and show only very subtle responses to environmental changes over the past 200 years. The compositional species turnover (0.36-0.94 SD) is relatively low in comparison to the species reorganizations known from the periods during the mid-and early-Holocene (0.64-1.61 SD) on the SE Plateau, and also in comparison to turnover rates of sediment records from climate-sensitive regions in the circum arctic. Our results indicate that climatically induced ecological thresholds are not yet crossed, but that human activity has an increasing influence, particularly on the terrestrial ecosystem in our study area. Synergistic processes of post-Little Ice Age warming, 20th century climate warming and extensive reforestations since the 19th century have initiated a change from natural oak-pine forests to seminatural, likely less resilient pine-oak forests. Further warming and anthropogenic disturbances would possibly exceed the ecological threshold of these ecosystems and lead to severe ecological consequences. KW - climate change KW - compositional species turnover KW - diatoms KW - human impact KW - pollen KW - Procrustes rotation KW - Tibetan Plateau Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2486.2011.02474.x SN - 1354-1013 VL - 17 IS - 11 SP - 3376 EP - 3391 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Mischke, Steffen A1 - Ginat, Hanan A1 - Al-Saqarat, Bety A1 - Almogi-Labin, Ahuva T1 - Ostracods from water bodies in hyperarid Israel and Jordan as habitat and water chemistry indicators JF - Ecological indicators : integrating monitoring, assessment and management N2 - The hyperarid region of Israel and Jordan covers a large area where numerous sites of Pleistocene lake sediments suggest that climate conditions were significantly wetter during the Pleistocene. This region experienced a significant increase in aridity in recent decades and the number of existing surface waters is diminishing rapidly. We studied ostracod shells from 49 pond and stream sites to determine the species distribution and to infer ecological preferences especially with respect to general differences in water movement, conductivity and ion composition. Twenty-two ostracod species were identified in total of which 12 taxa occur at three or more sites. Among the rarer species. Cyprinotus scholiosus was identified for the first time after two records from Plio- and Pleistocene sites in Yemen and Saudi Arabia. Further, Paracypretta amati was recorded and its ecological preferences discussed for the first time following the description of the species from its type locality in Sudan. Cypridopsis elongata is the only typical inhabitant of lotic habitats, strictly preferring freshwater conditions and waters with an alkalinity/Ca ratio around 1 and cations dominated by Ca(2+) and anions by HCO(3)(-). In contrast, Cyprideis torosa, Limnocythere inopinata and Heterocypris incongruens apparently prefer waters dominated by Na(+) associated with cations and Cl(-) associated with anions. Heterocypris salina and C. torosa occur over a wide conductivity (or salinity) range and in waters with alkalinity/Ca ratios around 1 and with significant alkalinity depletion. Humphcypris subterranea, Ilyocypris spp. and H. sauna are the only taxa which do not show any preference with respect to both the cation and anion dominance of the waters. The ecological preferences of the ostracod species from water bodies in the study area are discussed in detail and can be used for a qualitative assessment of the hydrodynamical and hydrochemical conditions of former water bodies in the presently hyperarid environment based on ostracod species composition analysis of Pleistocene aquatic sediments. KW - Ostracoda KW - Non-marine KW - Water chemistry KW - Ecology KW - Near East Y1 - 2012 U6 - https://doi.org/10.1016/j.ecolind.2011.07.017 SN - 1470-160X VL - 14 IS - 1 SP - 87 EP - 99 PB - Elsevier CY - Amsterdam ER -