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Jan Esper - One of the best experts on this subject based on the ideXlab platform.

  • Climate Signal age effects in boreal tree-rings: Lessons to be learned for paleoclimatic reconstructions
    Quaternary Science Reviews, 2016
    Co-Authors: Oliver Konter, Mauri Timonen, Ulf Büntgen, Marco Carrer, Jan Esper
    Abstract:

    Abstract Age-related alternation in the sensitivity of tree-ring width (TRW) to Climate variability has been reported for different forest species and environments. The resulting growth-Climate response patterns are, however, often inconsistent and similar assessments using maximum latewood density (MXD) are still missing. Here, we analyze Climate Signal age effects (CSAE, age-related changes in the Climate sensitivity of tree growth) in a newly aggregated network of 692 Pinus sylvestris L. TRW and MXD series from northern Fennoscandia. Although summer temperature sensitivity of TRW ( r All  = 0.48) ranges below that of MXD ( r All  = 0.76), it declines for both parameters as cambial age increases. Assessment of CSAE for individual series further reveals decreasing correlation values as a function of time. This declining Signal strength remains temporally robust and negative for MXD, while age-related trends in TRW exhibit resilient meanderings of positive and negative trends. Although CSAE are significant and temporally variable in both tree-ring parameters, MXD is more suitable for the development of Climate reconstructions. Our results indicate that sampling of young and old trees, and testing for CSAE, should become routine for TRW and MXD data prior to any paleoclimatic endeavor.

  • Climate Signal age effects evidence from young and old trees in the swiss engadin
    Forest Ecology and Management, 2008
    Co-Authors: Jan Esper, Rolf Niederer, Peter Bebi, David Frank
    Abstract:

    A potential limitation of tree-ring based Climate reconstructions is related to Climate Signal age effects (CSAE). CSAE may arise if the climatic response of young tree-rings differs from that of old tree-rings. This could mean that climatic Signals become stronger (or weaker) with tree aging, or that the seasonality of Signals or the sensitivity to a specific element (e.g., temperature, precipitation) changes over time. Such changes would affect the interpretation of dendroclimatic reconstructions, as the tree-rings included in these records are generally oldest at the end of a record (e.g., 21st century)—which is the time period generally used for calibration with instrumental data. We here addressed this concern by analyzing young and old Pinus cembra trees from three high elevation sites in the central European Alps. Core and disc samples were collected in pre-defined plots to allow for a representative analysis of tree ages with tree-ring width (TRW) measurement series categorized into age classes (i) >1880, (ii) 1880–1939, and (iii) 1940–2002. Notably we report on the Signal of the very young category (iii) not yet described in literature, and thus allow estimation of Climate response and Signal strength characteristics during the first years of the trees’ lifespans. Comparison of age classes (i)–(iii) revealed differences in TRW coherence and size, but little change in climatic Signal. CSAE are in the order of the differences recorded among high elevation sites—a conclusion that holds for inter-annual to decadal scale TRW variations at near-treeline Swiss stone pine. Such data are typically included in regional and larger-scale temperature reconstructions; thus, our results add confidence to long-term Climate estimates integrating a range of tree-ring age classes. Other findings, such as the reaction wood in juvenile tree-rings, and sensitivity of the Climate Signal to sample replication, suggest that comparisons of young and old age classes, and separate calibration of these categories against instrumental Climate data might further the estimation of long-term uncertainty changes in tree-ring based Climate reconstructions.

  • Climate Signal age effects—Evidence from young and old trees in the Swiss Engadin
    Forest Ecology and Management, 2008
    Co-Authors: Jan Esper, Rolf Niederer, Peter Bebi, David Frank
    Abstract:

    A potential limitation of tree-ring based Climate reconstructions is related to Climate Signal age effects (CSAE). CSAE may arise if the climatic response of young tree-rings differs from that of old tree-rings. This could mean that climatic Signals become stronger (or weaker) with tree aging, or that the seasonality of Signals or the sensitivity to a specific element (e.g., temperature, precipitation) changes over time. Such changes would affect the interpretation of dendroclimatic reconstructions, as the tree-rings included in these records are generally oldest at the end of a record (e.g., 21st century)—which is the time period generally used for calibration with instrumental data. We here addressed this concern by analyzing young and old Pinus cembra trees from three high elevation sites in the central European Alps. Core and disc samples were collected in pre-defined plots to allow for a representative analysis of tree ages with tree-ring width (TRW) measurement series categorized into age classes (i) >1880, (ii) 1880–1939, and (iii) 1940–2002. Notably we report on the Signal of the very young category (iii) not yet described in literature, and thus allow estimation of Climate response and Signal strength characteristics during the first years of the trees’ lifespans. Comparison of age classes (i)–(iii) revealed differences in TRW coherence and size, but little change in climatic Signal. CSAE are in the order of the differences recorded among high elevation sites—a conclusion that holds for inter-annual to decadal scale TRW variations at near-treeline Swiss stone pine. Such data are typically included in regional and larger-scale temperature reconstructions; thus, our results add confidence to long-term Climate estimates integrating a range of tree-ring age classes. Other findings, such as the reaction wood in juvenile tree-rings, and sensitivity of the Climate Signal to sample replication, suggest that comparisons of young and old age classes, and separate calibration of these categories against instrumental Climate data might further the estimation of long-term uncertainty changes in tree-ring based Climate reconstructions.

David Frank - One of the best experts on this subject based on the ideXlab platform.

  • Climate Signal age effects evidence from young and old trees in the swiss engadin
    Forest Ecology and Management, 2008
    Co-Authors: Jan Esper, Rolf Niederer, Peter Bebi, David Frank
    Abstract:

    A potential limitation of tree-ring based Climate reconstructions is related to Climate Signal age effects (CSAE). CSAE may arise if the climatic response of young tree-rings differs from that of old tree-rings. This could mean that climatic Signals become stronger (or weaker) with tree aging, or that the seasonality of Signals or the sensitivity to a specific element (e.g., temperature, precipitation) changes over time. Such changes would affect the interpretation of dendroclimatic reconstructions, as the tree-rings included in these records are generally oldest at the end of a record (e.g., 21st century)—which is the time period generally used for calibration with instrumental data. We here addressed this concern by analyzing young and old Pinus cembra trees from three high elevation sites in the central European Alps. Core and disc samples were collected in pre-defined plots to allow for a representative analysis of tree ages with tree-ring width (TRW) measurement series categorized into age classes (i) >1880, (ii) 1880–1939, and (iii) 1940–2002. Notably we report on the Signal of the very young category (iii) not yet described in literature, and thus allow estimation of Climate response and Signal strength characteristics during the first years of the trees’ lifespans. Comparison of age classes (i)–(iii) revealed differences in TRW coherence and size, but little change in climatic Signal. CSAE are in the order of the differences recorded among high elevation sites—a conclusion that holds for inter-annual to decadal scale TRW variations at near-treeline Swiss stone pine. Such data are typically included in regional and larger-scale temperature reconstructions; thus, our results add confidence to long-term Climate estimates integrating a range of tree-ring age classes. Other findings, such as the reaction wood in juvenile tree-rings, and sensitivity of the Climate Signal to sample replication, suggest that comparisons of young and old age classes, and separate calibration of these categories against instrumental Climate data might further the estimation of long-term uncertainty changes in tree-ring based Climate reconstructions.

  • Climate Signal age effects—Evidence from young and old trees in the Swiss Engadin
    Forest Ecology and Management, 2008
    Co-Authors: Jan Esper, Rolf Niederer, Peter Bebi, David Frank
    Abstract:

    A potential limitation of tree-ring based Climate reconstructions is related to Climate Signal age effects (CSAE). CSAE may arise if the climatic response of young tree-rings differs from that of old tree-rings. This could mean that climatic Signals become stronger (or weaker) with tree aging, or that the seasonality of Signals or the sensitivity to a specific element (e.g., temperature, precipitation) changes over time. Such changes would affect the interpretation of dendroclimatic reconstructions, as the tree-rings included in these records are generally oldest at the end of a record (e.g., 21st century)—which is the time period generally used for calibration with instrumental data. We here addressed this concern by analyzing young and old Pinus cembra trees from three high elevation sites in the central European Alps. Core and disc samples were collected in pre-defined plots to allow for a representative analysis of tree ages with tree-ring width (TRW) measurement series categorized into age classes (i) >1880, (ii) 1880–1939, and (iii) 1940–2002. Notably we report on the Signal of the very young category (iii) not yet described in literature, and thus allow estimation of Climate response and Signal strength characteristics during the first years of the trees’ lifespans. Comparison of age classes (i)–(iii) revealed differences in TRW coherence and size, but little change in climatic Signal. CSAE are in the order of the differences recorded among high elevation sites—a conclusion that holds for inter-annual to decadal scale TRW variations at near-treeline Swiss stone pine. Such data are typically included in regional and larger-scale temperature reconstructions; thus, our results add confidence to long-term Climate estimates integrating a range of tree-ring age classes. Other findings, such as the reaction wood in juvenile tree-rings, and sensitivity of the Climate Signal to sample replication, suggest that comparisons of young and old age classes, and separate calibration of these categories against instrumental Climate data might further the estimation of long-term uncertainty changes in tree-ring based Climate reconstructions.

Thomas Munch - One of the best experts on this subject based on the ideXlab platform.

  • what Climate Signal is contained in decadal to centennial scale isotope variations from antarctic ice cores
    Climate of The Past, 2018
    Co-Authors: Thomas Munch, Thomas Laepple
    Abstract:

    Abstract. Ice-core-based records of isotopic composition are a proxy for past temperatures and can thus provide information on polar Climate variability over a large range of timescales. However, individual isotope records are affected by a multitude of processes that may mask the true temperature variability. The relative magnitude of Climate and non-Climate contributions is expected to vary as a function of timescale, and thus it is crucial to determine those temporal scales on which the actual Signal dominates the noise. At present, there are no reliable estimates of this timescale dependence of the Signal-to-noise ratio (SNR). Here, we present a simple method that applies spectral analyses to stable-isotope data from multiple cores to estimate the SNR, and the Signal and noise variability, as a function of timescale. The method builds on separating the contributions from a common Signal and from local variations and includes a correction for the effects of diffusion and time uncertainty. We apply our approach to firn-core arrays from Dronning Maud Land (DML) in East Antarctica and from the West Antarctic Ice Sheet (WAIS). For DML and decadal to multi-centennial timescales, we find an increase in the SNR by nearly 1 order of magnitude ( ∼0.2 at decadal and ∼1.0 at multi-centennial scales). The estimated spectrum of Climate variability also shows increasing variability towards longer timescales, contrary to what is traditionally inferred from single records in this region. In contrast, the inferred variability spectrum for WAIS stays close to constant over decadal to centennial timescales, and the results even suggest a decrease in SNR over this range of timescales. We speculate that these differences between DML and WAIS are related to differences in the spatial and temporal scales of the isotope Signal, highlighting the potentially more homogeneous atmospheric conditions on the Antarctic Plateau in contrast to the marine-influenced conditions on WAIS. In general, our approach provides a methodological basis for separating local proxy variability from coherent Climate variations, which is applicable to a large set of palaeoClimate records.

  • regional Climate Signal vs local noise a two dimensional viewof water isotopes in antarctic firn at kohnen station dronning maudland
    Climate of The Past, 2016
    Co-Authors: Sepp Kipfstuhl, Johannes Freitag, Hanno Meyer, Thomas Munch, Thomas Laepple
    Abstract:

    Abstract. In low-accumulation regions, the reliability of δ18O-derived temperature Signals from ice cores within the Holocene is unclear, primarily due to the small Climate changes relative to the intrinsic noise of the isotopic Signal. In order to learn about the representativity of single ice cores and to optimise future ice-core-based Climate reconstructions, we studied the stable-water isotope composition of firn at Kohnen Station, Dronning Maud Land, Antarctica. Analysing δ18O in two 50 m long snow trenches allowed us to create an unprecedented, two-dimensional image characterising the isotopic variations from the centimetre to the 100-metre scale. Our results show seasonal layering of the isotopic composition but also high horizontal isotopic variability caused by local stratigraphic noise. Based on the horizontal and vertical structure of the isotopic variations, we derive a statistical noise model which successfully explains the trench data. The model further allows one to determine an upper bound for the reliability of Climate reconstructions conducted in our study region at seasonal to annual resolution, depending on the number and the spacing of the cores taken.

Andy Baker - One of the best experts on this subject based on the ideXlab platform.

  • paleoClimate change in ethiopia around the last interglacial derived from annually resolved stalagmite evidence
    Quaternary Science Reviews, 2018
    Co-Authors: Asfawossen Asrat, Andy Baker, Melanie J. Leng, John Hellstrom, Gregoire Mariethoz, Ian Boomer, Catherine N Jex, J M F Gunn
    Abstract:

    Abstract Oxygen and carbon (δ18Ο/δ13C) isotope, growth rate and trace element data are reported for a U-Th dated, annually-laminated stalagmite, GM1 from Goda Mea Cave, Ethiopia. The stalagmite grew intermittently around the last interglacial. The proxy records are used to develop a conceptual growth model of the stalagmite and to assess its potential for revealing a Climate Signal in this climatically sensitive northeastern African region during an important period in the evolution of Homo sapiens and dispersal of Anatomically Modern Humans out of Africa. Speleothem deposition is of short-duration occurring at ∼129 ka, ∼120 ka, in an undated growth phase, and at ∼108 ka; probably due to tectonic activity. δ18Ο composition is very stable within growth phases (1σ variability

  • Modern stalagmite δ18O: Instrumental calibration and forward modelling
    Global and Planetary Change, 2010
    Co-Authors: Andy Baker, Chris Bradley
    Abstract:

    Abstract The δ 18 O isotopic composition of stalagmite calcite frequently contains a Climate Signal, but one that is difficult to interpret in terms of either rainfall or temperature. Over glacial–interglacial time periods and decadal sampling resolution, stalagmite δ 18 O clearly contains a ‘first order’ Climate Signal where the magnitude of changes in temperature and ocean/atmospheric circulation dominate the δ 18 O signature. However, at annual–biennial resolution sampling, and within interglacial periods, the magnitude of Climate changes is smaller, and variability in δ 18 O introduced by soil, karst groundwater and cave processes can introduce considerable uncertainty into the climatic interpretation of stalagmite δ 18 O records. Here, two approaches that can quantify the Climate Signal contained with stalagmite δ 18 O are discussed. Firstly, linear regression based approaches are reviewed, which correlate stalagmite δ 18 O with instrumental Climate parameters such as temperature and rainfall. The advantages and disadvantages of complex linear regression approaches that attempt to account for groundwater mixing within the karst aquifer are discussed. Secondly, a forward modelling approach is introduced, where stalagmite δ 18 O is modelled from rainfall δ 18 O, surface Climate parameters and a simple karst hydrology model. Using a case study from Gibraltar, this latter approach demonstrates that between stalagmite variability in δ 18 O of the order of 1‰ can be explained solely by differences in karst hydrology. Forward modelling suggests that a similar variability in δ 18 O might be observed between stalagmites within a cave, or between caves within a homogenous Climate region, and highlights the difficulty in attempting to use δ 18 O as a paleo-thermometer.

  • Analysis of the Climate Signal contained within δ18O and growth rate parameters in two Ethiopian stalagmites
    Geochimica et Cosmochimica Acta, 2007
    Co-Authors: Andy Baker, Dominique Genty, Ian J. Fairchild, Asfawossen Asrat, Melanie J. Leng, Peter M. Wynn, Charlotte Bryant, Mohammed Umer
    Abstract:

    We combine surface and cave Climate monitoring with multiple stalagmite parameters to help understand and calibrate the Climate records contained within stalagmites from a region with strong rainfall seasonality. Two actively growing stalagmites from Ethiopia were analysed in order to investigate the Climate Signal contained within δ18O and growth rate parameters. The δ18O and growth rate of the two stalagmites give different responses to surface Climate due to variations in the Climate Signal transfer. Both stalagmites (Merc-1 and Asfa-3) have a Climate response that is seasonal; however this Signal is subsequently smoothed by the mixing of event and storage water within the aquifer. Merc-1 responds more to high frequency (‘event’) Climate, due to a greater ratio of event to storage water in this sample, whereas Asfa-3 responds more to low frequency (‘storage’) Climate. In addition, different parameters respond to different seasons. For example, stalagmite Asfa-3, from greater depth from the surface and with a slow drip rate, has a growth rate that responds to the amount of summer rain. In contrast, Merc-1, closer to the surface and with a faster drip rate, exhibits no clear response to surface Climate, probably due to a more complex Climate Signal transfer. δ18O response varies with stalagmite due to the interplay between rainfall forcing factors (amount, seasonality) and disequilibrium kinetics, with opposing correlations between seasonal rainfall and δ18O between the samples. Our results demonstrate that analysis of seasonal Climate forcing, and transfer functions reflecting the mixing of event and storage water, may be the most appropriate approach to develop of transfer functions appropriate for high-resolution, stalagmite Climate reconstruction.

Danny Mccarroll - One of the best experts on this subject based on the ideXlab platform.

  • stable isotope coherence in the earlywood and latewood of tree line conifers
    Chemical Geology, 2009
    Co-Authors: Anne Kress, Neil J Loader, Giles H F Young, Matthias Saurer, Rolf T W Siegwolf, Danny Mccarroll
    Abstract:

    Abstract Annually resolved and replicated tree-ring stable isotope series have the potential to reconstruct growing season environmental parameters over multi-millennial timescales. As this archive may require only minimal statistical detrending, it has the potential to preserve a large portion of low frequency Climate Signals. To date, many studies have utilised only the latewood portion of the tree ring, in an attempt to minimize carry-over effects from previous year reserves and maximise the annual nature of the Climate Signal preserved. However, the old trees from tree-line locations, necessary to build long chronologies, often display narrow ring-widths (

  • latewood width maximum density and stable carbon isotope ratios of pine as Climate indicators in a dry subalpine environment french alps
    Arctic Antarctic and Alpine Research, 2004
    Co-Authors: Mary Gagen, Danny Mccarroll, Jeanlouis Edouard
    Abstract:

    Abstract Pine latewood width, density, and stable carbon isotope ratios were measured at two sites, separated in altitude by 400 m, close to the forest limit on a south-facing slope in the western French Alps. The Signal to noise ratio in the δ13C series from each site is higher than that of either of the growth proxies. When the sites are combined, the high-frequency Climate Signal in the δ13C series is enhanced, whereas in both the ring width and density series it is weakened. Because regional Climate dominates over local site conditions, δ13C ratios from long pine chronologies will provide a better indicator of past Climate than either ring widths or densities. At dry Alpine sites, δ13C values are controlled mainly by stomatal conductance, which is linked to summer moisture stress and thus antecedent precipitation.

  • Stable carbon isotope ratios of Pinus sylvestris from northern Finland and the potential for extracting a Climate Signal from long Fennoscandian chronologies
    The Holocene, 2001
    Co-Authors: Danny Mccarroll, Frank Pawellek
    Abstract:

    Stable carbon isotope ratios were measured on the latewood cellulose of 36 Scots pine trees from four sites in northern Finland. δ13C values were corrected for changes in the δ13C of air and de-trended to remove the effect of tree age. Simple linear and multivariate correlations were used to determine the nature and strength of any Climate Signal. At three sites, the dominant controls are, in descending order, summer sunshine, temperature and antecedent precipitation. At the fourth site, the dominant controls are antecedent precipitation and air relative humidity, while summer sunshine and temperature appear unimportant. δ13C values record changes in the concentration of CO2 in the stomatal chambers, which reflects the balance between stomatal conductance and photosynthetic rate. Photosynthetic rate is controlled primarily by photon flux (sunshine) and temperature, suggesting that this dominates at three of the sites, whereas stomatal conductance is controlled by air humidity and soil moisture status (ant...