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 - Birks, H. John B. T1 - Evaluating the indicator value of Tibetan pollen taxa for modern vegetation and climate N2 - Pollen taxa of known indicator value are of great potential in the qualitative interpretation of pollen diagrams. Here we apply several numerical approaches to a lake-sediment based pollen data-set from the eastern and central Tibetan Plateau (112 samples) to assess the indicator value of Tibetan pollen taxa for modem vegetation types and for modern climate. Results from Multi-Response Permutation Procedures indicate that the differences between groups of pollen spectra originating from the same vegetation type (temperate desert, temperate steppe, alpine desert, alpine steppe, high-alpine meadow, subalpine shrub, and patchy forest) are statistically significant. Indicator Species Analyses identify several indicator taxa for most vegetation types. Multivariate regression tree analysis indicates that about 390 mm of annual precipitation is the most critical threshold for the modern pollen spectra. This roughly separates desert and steppe vegetation from high-alpine meadow, subalpine shrub, and patchy forest vegetation. A strong pollen-climate relationship on the Tibetan Plateau is confirmed by the large number of statistically significant pollen taxa-climate (annual precipitation or/and annual temperature) relationships as evaluated by statistical response- modelling, involving generalised linear models. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/00346667 U6 - https://doi.org/10.1016/j.revpalbo.2010.02.016 SN - 0034-6667 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 - Liu, Xingqi A1 - Kubatzki, Claudia A1 - Lohmann, Gerrit T1 - Retracted: What caused the mid-Holocene forest decline on the eastern Tibet-Qinghai Plateau? N2 - Aim: Atmospheric CO2 concentrations depend, in part, on the amount of biomass locked up in terrestrial vegetation. Information on the causes of a broad-scale vegetation transition and associated loss of biomass is thus of critical interest for understanding global palaeoclimatic changes. Pollen records from the north-eastern Tibet-Qinghai Plateau reveal a dramatic and extensive forest decline beginning c. 6000 cal. yr bp. The aim of this study is to elucidate the causes of this regional-scale change from high-biomass forest to low-biomass steppe on the Tibet-Qinghai Plateau during the second half of the Holocene. Location: Our study focuses on the north-eastern Tibet-Qinghai Plateau. Stratigraphical data used are from Qinghai Lake (3200 m a.s.l., 36 degrees 32'-37 degrees 15' N, 99 degrees 36'-100 degrees 47' E). Methods: We apply a modern pollen-precipitation transfer function from the eastern and north-eastern Tibet-Qinghai Plateau to fossil pollen spectra from Qinghai Lake to reconstruct annual precipitation changes during the Holocene. The reconstructions are compared to a stable oxygen-isotope record from the same sediment core and to results from two transient climate model simulations. Results: The pollen-based precipitation reconstruction covering the Holocene parallels moisture changes inferred from the stable oxygen-isotope record. Furthermore, these results are in close agreement with simulated model-based past annual precipitation changes. Main conclusions: In the light of these data and the model results, we conclude that it is not necessary to attribute the broad-scale forest decline to human activity. Climate change as a result of changes in the intensity of the East Asian Summer Monsoon in the mid-Holocene is the most parsimonious explanation for the widespread forest decline on the Tibet-Qinghai Plateau. Moreover, climate feedback from a reduced forest cover accentuates increasingly drier conditions in the area, indicating complex vegetation-climate interactions during this major ecological change. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=1466-822X U6 - https://doi.org/10.1111/j.1466-8238.2009.00501.x SN - 1466-822X 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 -