11 results on '"Helle, Gerhard"'
Search Results
2. High-resolution 14C bomb peak dating and climate response analyses of subseasonal stable isotope signals in wood of the African baobab – a case study from Oman
- Author
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Slotta, Franziska, Wacker, Lukas, Riedel, Frank, Heußner, Karl-Uwe, Hartmann, Kai, and Helle, Gerhard
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500 Naturwissenschaften und Mathematik::550 Geowissenschaften, Geologie::550 Geowissenschaften ,paleoclimatology ,African baobab ,dendroclimatology - Abstract
The African baobab, Adansonia digitata L., has great paleoclimatological potential because of its wide distributional range and millennial length life span. However, dendroclimatological approaches are hampered by dating uncertainties due to its unique, parenchyma-dominated stem anatomy. Here, securely dated time series of annual wood increment growth and intra-ring stable isotopes of carbon and oxygen of cellulose for a baobab tree from Oman covering 1941 to 2005 were established and tested for relationships to hydroclimate variability. Precise dating with the atomic bomb peak (ABP) using highly resolved 14C measurements confirmed the annual character of the baobab's growth rings. F14C values of tree-ring cellulose were found up to 8.8 % lower than in the corresponding atmospheric CO2 for the period around the ABP, which in conjunction with a considerable autocorrelation of the δ13C series points to the incorporation of previous year's carbon contributing to the average age of intra-ring wood samples. F14C of terminal parenchyma bands, marking the tree-ring boundaries, were found to be considerably younger than their corresponding tree ring, indicating that parenchyma tissue is alive for many years, probably undergoing cell division and structural reorganization and contributing to secondary growth. In contrast to the δ13C time series, no significant autocorrelation was found in the δ18O series of tree-ring cellulose despite the enormous water storage potential of this stem-succulent tree species. Year-to-year variability in tree-ring width and stable isotope ratios revealed radial stem growth and the geochemistry of wood cellulose are influenced by fluctuations in the hydroclimate. In particular, δ18O was found to be a good climate proxy, followed by tree-ring width and δ13C. Tree-ring width and intra-ring δ18Omin correlated well with each other and with precipitation amount for the period from pre-monsoon May to the end of the monsoon season in September/October. Intra-annual stable isotope courses were found to be rather similar for both δ13C and δ18O. Years with particularly low monsoon rain were reflected by increased stable isotope values in the mid-section of intra-annual courses. Distinct patterns with low subseasonal isotope values seem indicative for years with heavy rainfall events from pre-monsoonal cyclones. Rain events from post-monsoonal cyclones may also be recorded; however, only 2 years of observation prevented a more conclusive evaluation., Biogeosciences, 18 (12), ISSN:1726-4170
- Published
- 2021
3. Age effects and climate response in trees: a multi-proxy tree-ring test in old-growth life stages
- Author
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Dorado Liñán, Isabel, Gutiérrez, Emilia, Heinrich, Ingo, Andreu-Hayles, Laia, Muntán, Elena, Campelo, Filipe, and Helle, Gerhard
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- 2012
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4. Interdecadal modulation of the relationship between ENSO, IPO and precipitation: insights from tree rings in Australia
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Heinrich, Ingo, Weidner, Kathrin, Helle, Gerhard, Vos, Heinz, Lindesay, Janette, and Banks, John C. G.
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- 2009
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5. UV-laser-based microscopic dissection of tree rings - a novel sampling tool for δ13C and δ18O studies.
- Author
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Schollaen, Karina, Heinrich, Ingo, and Helle, Gerhard
- Subjects
TREE-rings ,ULTRAVIOLET lasers ,DISSECTION ,ISOTOPIC analysis ,PLANT cells & tissue analysis - Abstract
UV-laser-based microscopic systems were utilized to dissect and sample organic tissue for stable isotope measurements from thin wood cross-sections., We tested UV-laser-based microscopic tissue dissection in practice for high-resolution isotopic analyses (δ
13 C/δ18 O) on thin cross-sections from different tree species. The method allows serial isolation of tissue of any shape and from millimetre down to micrometre scales. On-screen pre-defined areas of interest were automatically dissected and collected for mass spectrometric analysis., Three examples of high-resolution isotopic analyses revealed that: in comparison to δ13 C of xylem cells, woody ray parenchyma of deciduous trees have the same year-to-year variability, but reveal offsets that are opposite in sign depending on whether wholewood or cellulose is considered; high-resolution tree-ring δ18 O profiles of Indonesian teak reflect monsoonal rainfall patterns and are sensitive to rainfall extremes caused by ENSO; and seasonal moisture signals in intra-tree-ring δ18 O of white pine are weighted by nonlinear intra-annual growth dynamics., The applications demonstrate that the use of UV-laser-based microscopic dissection allows for sampling plant tissue at ultrahigh resolution and unprecedented precision. This new technique facilitates sampling for stable isotope analysis of anatomical plant traits like combined tree eco-physiological, wood anatomical and dendroclimatological studies. [ABSTRACT FROM AUTHOR]- Published
- 2014
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6. Climate signals derived from cell anatomy of Scots pine in NE Germany.
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Liang, Wei, Heinrich, Ingo, Simard, Sonia, Helle, Gerhard, Liñán, Isabel Dorado, and Heinken, Thilo
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SCOTS pine ,TREE-rings ,SPECIES distribution ,CLIMATE reconstruction (Research) ,TEMPERATE climate ,VAPOR pressure ,DENDROCLIMATOLOGY - Abstract
Tree-ring chronologies of Pinus sylvestris L. from latitudinal and altitudinal limits of the species distribution have been widely used for climate reconstructions, but there are many sites within the temperate climate zone, as is the case in northeastern Germany, at which there is little evidence of a clear climate signal in the chronologies. In this study, we developed long chronologies of several cell structure variables (e.g., average lumen area and cell wall thickness) from P. sylvestris growing in northeastern Germany and investigated the influence of climate on ring widths and cell structure variables. We found significant correlations between cell structure variables and temperature, and between tree-ring width and relative humidity and vapor pressure, respectively, enabling the development of robust reconstructions from temperate sites that have not yet been realized. Moreover, it has been shown that it may not be necessary to detrend chronologies of cell structure variables and thus low-frequency climate signals may be retrieved from longer cell structure chronologies. The relatively extensive resource of archaeological material of P. sylvestris covering approximately the last millennium may now be useful for climate reconstructions in northeastern Germany and other sites in the temperate climate zone. [ABSTRACT FROM PUBLISHER]
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- 2013
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7. A novel device for batch-wise isolation of α-cellulose from small-amount wholewood samples.
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Wieloch, Thomas, Helle, Gerhard, Heinrich, Ingo, Voigt, Michael, and Schyma, Philipp
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CELLULOSE ,STABLE isotopes ,DENDROCLIMATOLOGY ,CHEMICAL processes ,SOLUTION (Chemistry) ,EXTRACTION (Chemistry) - Abstract
Abstract: A novel device for the chemical isolation of α-cellulose from wholewood material of tree rings was designed by the Potsdam Dendro Laboratory. It allows the simultaneous treatment of up to several hundred micro samples. Key features are the batch-wise exchange of the chemical solutions, the reusability of all major parts and the easy and unambiguous labelling of each individual sample. Compared to classical methods labour intensity and running costs are significantly reduced. [Copyright &y& Elsevier]
- Published
- 2011
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8. Hydroclimatic seasonality recorded by tree ring δ18O signature across a Himalayan altitudinal transect.
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Brunello, Camilla Francesca, Andermann, Christoff, Helle, Gerhard, Comiti, Francesco, Tonon, Giustino, Tiwari, Achyut, and Hovius, Niels
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TREE-rings , *OXYGEN isotopes , *TREE growth , *ATMOSPHERIC temperature , *HUMIDITY , *STABLE isotopes - Abstract
Water stable isotope ratios of tropical precipitation predominantly reflect moisture source and precipitation intensity. Trees can incorporate the isotopic signals into annual tree-ring cellulose records, permitting reconstruction of the temporal changes of hydroclimate over decades to millennia. This is especially valuable in the Himalayas where the understanding of monsoon dynamics is limited by the lack of a dense and representative observational network. We have analyzed tree ring δ 18 O records from two distinct physiographic sites along the upper Kali Gandaki valley in the central Nepal Himalayas, representing the wet High-Himalayas and the Trans-Himalayan dryland to the north. Empirical correlations and regression analyses were compared to an in-situ calibrated oxygen isotope fractionation model, exploring the relationships between tree ring δ 18 O and seasonal-mean variability of hydroclimatic forcing at the different locations. For this purpose, gridded precipitation data from the Asian rain gauge dataset APHRODITE, as well as high resolution onsite observations (relative humidity, air temperature, δ 18 O of precipitation and radial tree growth) were used. We found that two distinct sets of meteorological values, reflecting pre-monsoon and monsoon conditions, are needed to reproduce the measured tree ring δ 18 O values from the High-Himalayan site, but that a single set of monsoonal values performs best for the Trans-Himalayan site. We conclude that Trans-Himalayan trees capture long-term changes in strength of the Indian summer monsoon. In contrast, High-Himalayan tree ring δ 18 O records a more complex hydro-climatic signal reflecting both pre-monsoon and monsoon seasons with very contrasting isotopic signatures of precipitation. This difference in the two hydroclimatic proxy records offers an opportunity to reconstruct first-order hydroclimate conditions, such as local precipitation rates, and to gain new insights into monsoon timing and seasonal water source determination across the Himalayan orographic region. • Hydroclimate seasonality is preserved in tree ring δ 18 O from the Central Himalayas. • A fractionation model confirms relationships from empirical correlation analyses. • High-Himalayan tree ring δ 18 O compounds pre- and monsoon signals • Trans-Himalayan tree ring δ 18 O only contains monsoon signal. • At different locations across the Himalayas, different climate features are recorded. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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9. Hydroclimatic variation in Far North Queensland since 1860 inferred from tree rings
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Heinrich, Ingo, Weidner, Kathrin, Helle, Gerhard, Vos, Heinz, and Banks, John C.G.
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TREES , *DENDROCLIMATOLOGY , *EASTERN redcedar , *BIOLOGICAL variation , *CLIMATE change ,AUSTRALIAN rainforests - Abstract
Abstract: In tropical Australia, palaeoclimatic proxies derived from tree rings are sought after sources for reconstructing climate variations. However, dendroclimatology has not been widely applied in tropical forests and even less so in the Australian tropics due to the extreme rarity of species producing anatomically distinct annual growth rings. Furthermore, most Australian tree species exhibit rather strong opportunistic growth with non-annual growth zones that are less suitable for dendrochronology. Recent studies on the Australian Red Cedar (Toona ciliata) in the Upper Kangaroo Valley near Sydney revealed that tree-ring based climate reconstructions are feasible with this species. This study moved 2500 km further north and concentrated on the tropical stands of T. ciliata because it is one of the few deciduous tree species in tropical Australia likely characterised by a dormant period of the cambium and thus annual tree rings. Although dendroclimatological studies indicate that some Australian tree species are suitable for reconstructing climate patterns, a well replicated tree-ring record from Far North Queensland has not been developed until now. Tree cores of T. ciliata were developed into a 140-year tree-ring widths index chronology. The analyses showed that the ring-widths indices correlate with March–June precipitation as recorded at Kairi research station. March–June precipitation was reconstructed using the tree-ring data with 35% of the variance explained. The reconstructed series contains both high- and low-frequency climate signals. This suggests that growth of T. ciliata is influenced by climate phenomena of different wave lengths which can be associated with El Niño Southern Oscillation (ENSO) and Interdecadal Pacific Oscillation (IPO). [Copyright &y& Elsevier]
- Published
- 2008
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10. Multiple tree-ring chronologies (ring width, δ13C and δ18O) reveal dry and rainy season signals of rainfall in Indonesia.
- Author
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Schollaen, Karina, Heinrich, Ingo, Neuwirth, Burkhard, Krusic, Paul J., D'Arrigo, Rosanne D., Karyanto, Oka, and Helle, Gerhard
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RAINFALL , *TREE-rings , *CHRONOLOGY , *MONSOONS , *RAIN forests - Abstract
Abstract: Climatic hazards, such as severe droughts and floods, affect extensive areas across monsoon Asia and can have profound impacts on the populations of that region. The area surrounding Indonesia, including large portions of the eastern Indian Ocean and Java Sea, plays a key role in the global climate system because of the enormous heat and moisture exchange that occurs between the ocean and atmosphere there. Here, we evaluate the influence of rainfall variability on multiple tree-ring parameters of teak (Tectona grandis) trees growing in a lowland rain forest in Central Java (Indonesia). We assess the potential of, annually resolved, tree-ring width, stable carbon (δ13C) and oxygen (δ18O) isotope records to improve our understanding of the Asian monsoon variability. Climate response analysis with regional, monthly rainfall data reveals that all three tree-ring parameters are significantly correlated to rainfall, albeit during different monsoon seasons. Precipitation in the beginning of the rainy season (Sep–Nov) is important for tree-ring width, confirming previous studies. Compared to ring width, the stable isotope records possess a higher degree of common signal, especially during portions of the peak rainy season (δ13C: Dec–May; δ18O: Nov–Feb) and are negatively correlated to rainfall. In addition, tree-ring δ18O also responds positively to peak dry season rainfall, although the δ18O rainy season signal is stronger and more time-stable. The correlations of opposite sign reflect the distinct seasonal contrast of the δ18O signatures in rainfall (18OPre) during the dry (18O-enriched rain) and rainy (18O-depleted rain) seasons. This difference in 18OPre signal reflects the combination of two signals in the annual tree-ring δ18O record. Highly resolved intra-annual δ18O isotope analyses suggest that the signals of dry and rainy season can be distinguished clearly. Thereby reconstructions can improve our understanding of variations and trends of the hydrological cycle over the Indonesian archipelago. [Copyright &y& Elsevier]
- Published
- 2013
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11. Climate signals in tree-ring width, density and δ 13C from larches in Eastern Siberia (Russia)
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Kirdyanov, Alexander V., Treydte, Kerstin S., Nikolaev, Anatolii, Helle, Gerhard, and Schleser, Gerhard H.
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FROZEN ground , *LARCHES , *PINACEAE , *TREES - Abstract
Abstract: We present the first and longest (413 years) dataset on stable carbon isotope ratios in tree-ring cellulose (δ 13C), tree-ring width (TRW), and maximum latewood density (MXD) obtained from larch trees growing on permafrost under continental climate in the Suntar Khayata mountain ridge in Eastern Siberia (Russia). With this first study we calibrate tree-ring parameters against climate quantities, and based on these results assess the potential added value of MXD and especially of δ 13C complementing TRW analysis for future climate reconstruction purposes. δ 13C chronologies were corrected for human induced changes in atmospheric CO2 since AD 1800. Two different approaches were compared i) a correction referring merely to the decline in atmospheric δ 13C (δ 13Catm) and ii) a correction additionally accounting for the increase in atmospheric partial pressure of CO2. δ 13C chronologies are characterized by strong signal strength with only 4 trees representing the population signal at the site (mean inter-series correlation=0.71 and EPS=0.90). δ 13C variation shows low similarity to TRW and MXD, while correlation between TRW and MXD is highly significant. Correlation analysis of tree-ring parameters with gridded instrumental data (Climate Research Unit, CRU TS 2.1) over the AD 1929–2000 calibration period demonstrates that TRW and MXD react as reported from other sites at cold and humid northern latitudes: precipitation plays no significant role, but strong dependencies on monthly mean, maximum and minimum temperatures, particularly of the current summer (June to August), are found (up to r =0.60, p <0.001). Combining instrumental data to a summer season mean (JJA) and TRW and MXD to a growth parameter mean (TRW+MXD), clearly shows the importance of the number of frost days and minimum temperatures during summer (r =0.67, p <0.001) to dominate tree growth and highlights the potential for climate reconstruction. Carbon isotope fixation in tree rings is obviously less controlled by temperature variables. In particular, the frost days and minimum temperature have a much smaller influence on δ 13C than on tree growth. δ 13C strongly reacts to current-year July precipitation (r =−0.44, p <0.05) and June–July maximum temperature (r =0.46, p <0.001). All significant (p <0.05) correlation coefficients are higher when using the corrected δ 13C chronology considering an additional plant physiological response on increasing atmospheric CO2 concentration, than using the chronology corrected for δ 13Catm changes alone. Spatial distribution of correlations between tree-ring data and climate variables for Eastern Siberia indicates that the summer temperature regime in the studied region is mostly influenced by Arctic air masses, but precipitation in July seems to be brought out from the Pacific region. Both the combined TRW+MXD record and the δ 13С record revealed a high reconstruction potential for summer temperature and precipitation, respectively, particularly on decadal and longer-term scales. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
- View/download PDF
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