On the hidden significance of differing micro-sites on tree-ring based climate reconstructions

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Long-term summer temperature variations in the Pyrenees from detrended stable carbon isotopes

Substantial effort has recently been put into the development of climate reconstructions from tree-ring stable carbon isotopes, though the interpretation of long-term trends retained in such timeseries remains challenging. Here we use detrended δ13C measurements in Pinus uncinata tree-rings, from the Spanish Pyrenees, to reconstruct decadal variations in summer temperature back to the 13th century. The June-August temperature signal of this reconstruction is attributed using decadally as well as annually resolved, 20th century δ13C data. Results indicate that late 20th century warming has not been unique within the context of the past 750 years. Our reconstruction contains greater am-plitude than previous reconstructions derived from traditional tree-ring density data, and describes particularly cool conditions during the late 19th century. Some of these differences, including early warm periods in the 14th and 17th centuries, have been retained via δ13C timeseries detrending - a novel approach in tree-ring stable isotope chronology development. The overall reduced variance in earlier studies points to an underestimation of pre-instrumental summer temperature variability de-rived from traditional tree-ring parameters

Tree-Ring Amplification of the Early Nineteenth-Century Summer Cooling in Central Europe

Les prokinéticines sont des facteurs angiogènic potentiels qui se liant aux récepteurs couplés aux protéines G (PKR1 et PKR2) pour initier leurs effets biologiques. Nous avons montré que le transfert transitoire du gène PKR1 après ligation de l’artère coronaire réduit la mortalité et préserve la fonction du ventricule gauche en favorisant la néovascularisation et protegé des cardiomyocytes. Nous avons montré que des souris transgéniques (TG) surexprimant PKR1 dans le coeur aucune anomalie spontanée dans les cardiomyocytes, mais on observe une augmentation de néovascularization. Cependant des souris TG surexprimant PKR2 dans le coeur ont montré de l'hypertrophie excentrique et la perméabilité vasculaire. Pour la première fois nous avons montré que la balance entre l'activation de la voie de signalisation de PKR1 et de PKR2 pouvait être très importante pour protéger les cardiomyocytes des lésions causées par l'ischémie et/ou d’induire la neovascularisation dans le coeur.Cardiovascular disease is first cause of mortality worldwide. Prokineticins are potent angiogenic factors that bind to two G protein-coupled receptors (PKR1 and PKR2) to initiate their biological effects. We showed that transient PKR1 gene transfer after coronary ligation reduces mortality and preserves left ventricular function by promoting neovascularization and protecting cardiomyocytes. Next we showed that transgenic (TG) mice overexpressing PKR1 in heart exhibit neovascularization without inducing any spontaneous pathology in cardiomyocytes. However TG mice overexpressing PKR2 in heart exhibit eccentric hypertrophy in cardiomyocyte and vascular leakage. As a conclusion, for the first time we have shown that the balance between the activation of PKR1 and PKR2 signaling could be very important to prevent cardiomyocytes from ischemic insult and/or to induce neovascularization in heart

Trends and signals in tree-ring parameters

Tree-rings are frequently used to develop annually resolved paleoclimate reconstructions of periods in time when meteorological instrumental measurements are not available. Commonly used proxy records derived from tree-rings are ring width, maximum latewood density, and stable carbon and oxygen isotopes. Calibrating the different tree-ring proxies against available meteorological data is a prerequisite for reconstruction approaches, as results provide the essential statistical relationships to convert proxy data into the targeted climate data. Additionally, the evaluation of potential non-climatic biases is crucial for accurate calibration results. In this dissertation, methods for identifying proxy-specific biases are developed and evaluated for associated impact on various calibration setups. Focus is placed on age-related climate sensitivity trends in growth and density data, insect-induced disturbances in interannual growth patterns, and effects of elevated atmospheric CO2 concentrations on stable isotopic compositions. Age-related alternation in the climate sensitivity of tree-ring width data has been previously reported and is here revisited by analyzing a large dataset of 692 Pinus sylvestris L. series from northern Fennoscandia. Additionally and for the first time, maximum latewood density measurements of the same trees are included. Results indicate significant decreasing climate sensitivity with increasing age in both tree-ring parameters, while density data are less affected, thus, more suitable for the development of climate reconstructions. Temperature reconstructions for this region can dismiss age-related biases, by using density data from evenly distributed cambial ages, i.e. including young and old trees, as a function of time. The larch budmoth (Zeiraphera diniana Gn.) is characterized by regular population oscillations and cyclic mass outbreaks (8-10 years), causing interannual disturbances in tree-ring width chronologies from host trees and reduced climate signal strength. In contrast to reported historical evidence over 1200 years from the European Alps, cyclic mass outbreaks in the Slovakian High Tatra Mountains are, in this dissertation, found to be absent during the last 300 years. Low stand densities in the spatially limited larch forests in this habitat prevent larch budmoth populations from peaking at mass outbreaks levels. The significantly synchronized Larix decidua Mill. (host) and Pinus cembra L. (non-host) chronologies, both free of insect-induced pulsed disturbances, exhibit distinct early-summer temperature signals ideal for East-European temperature reconstructions. Stable isotope data from tree-rings provide extensive information on interactions between tree-physiological processes and external climatic forcing. Annually and decadally resolved stable carbon (δ13C) and oxygen (δ18O) isotope time series from Pinus uncinata Ramond ex DC tree-rings from the Spanish Pyrenees exhibit climate sensitivity - δ18O values are controlled by spring precipitation and other more complex factors, and δ13C data embeds a significant summer temperature signal. However, different correction methods addressing effects of elevated atmospheric CO2 on the carbon isotopic composition add low-frequency information to the data, and alter the magnitude of the climate signal strength and its temporal robustness. Selecting the most appropriate correction method remains challenging, as the habitat-specific natural adaptation of tree-intrinsic physiological processes to elevated atmospheric CO2 could not be clarified, and objective criteria for best-fit corrections are still missing. Using the correction method resembling summer temperature characteristics, a newly developed 750-year decadal summer temperature reconstruction comprises greater amplitude compared to previously reported reconstructions derived from ring width and density data. Additionally, the novel approach in tree-ring stable isotope chronology development of detrending-techniques are applied to the δ13C isotopic data, providing the background of this temperature reconstruction. The detection and evaluation methods for potential biases in calibration setups presented in this dissertation can be utilized as conceptual basis to evaluate existing and to advance future reconstruction, thereby, improving our understanding of long-term climate variations.Die Jahrringe verschiedener Baumarten werden häufig für dendroklimatische Forschung genutzt, vor allem für Rekonstruktionen vergangener Klimaschwankungen. Dabei können unterschiedliche Datengrundlagen gewonnen werden, wie z. B. die Jahrringbreite, die maximale Spätholzdichte und die Zusammensetzung der stabilen Kohlenstoff- und Sauerstoffisotope. Eine Analyse der Klimasignale in Jahrringzeitreihen bildet die Basis für Klimarekonstruktionen, denn die ermittelten statistischen Klimawachstumsbeziehungen ermöglichen die Übertragung der Ergebnisse aus der Kalibrationsperiode auf Jahrringdaten der Rekonstruktionsperiode in vorindustrieller Zeit, für die in der Regel meteorologische instrumentelle Messdaten fehlen. Zusätzlich ist eine Bewertung der potenziell verfälschenden Einflussgrößen in der Kalibrationsanalyse obligatorisch. Diese Dissertation legt den Schwerpunkt auf die Evaluation unterschiedlicher Kalibrationseinstellungen, entwickelt Methoden zur Identifizierung parameterspezifischen Verzerrungen und bestimmt das Ausmaß ihrer Auswirkungen. Im Speziellen sind altersbedingte Trends in der Klimasensitivität, Störungen im jährlichen Wachstumsmuster durch Insektenbefall und die Auswirkungen der erhöhten atmosphärischen CO2-Konzentrationen von Interesse. Ziel dieser Arbeit ist es, in unterschiedlichen Kalibrationsanalysen „nicht-klimatische“ Einflussgrößen zu identifizieren, sowie Lösungsstrategien für deren Vermeidung zu entwickeln. Die altersbedingten Veränderungen der Klimasensitivität in Ringbreitendaten sind Gegenstand der Untersuchung in mehreren publizierten Studien. In dieser Arbeit wird dieses Thema durch die Analyse von Pinus sylvestris L. Jahrringbreiteserien aus dem nördlichen Fennoskandien aufgegriffen und durch die erstmalige Hinzunahme von Dichtedaten der gleichen Bäume erweitert. Die Ergebnisse zeigen eine signifikante altersbedingte Abnahme der Temperatursensitivität mit zunehmendem Alter. Die Dichtedaten erweisen sich hiervon weniger beeinflusst und sind folglich besser geeignet für Klimarekonstruktionen. Temperaturrekonstruktionen dieser Region zeigen keine altersbedingten Verzerrungen, wenn die zugrundeliegenden Daten unter der Prämisse von gleich verteilten Altersgruppen, also von jungen als auch alten Bäume, erhoben wurden. Der Lärchenwickler (Zeiraphera diniana Gn.) wird mit regelmäßigen Populationsschwankungen und zyklischen Massenvermehrungen (alle 8-10 Jahre) in Verbindung gebracht, was zu Veränderungen in der Jahrringbreite und reduzierter Klimasensitivität von Wirtsbäumen führt. Im Gegensatz zu den bekannten 1200-jährigen historischen Belegen aus den Alpen, lehnen die Ergebnisse dieser Arbeit die Annahme einer zyklischen Massenvermehrung des Lärchenwicklers für die letzten 300 Jahre in der slowakischen Hohen Tatra ab. Niedrige Bestandsdichten in räumlich begrenzten Lärchenwäldern verhindern die massenhafte Vermehrung des Lärchenwicklers. Signifikant gleichläufige Larix decidua Mill. (Wirt) und Pinus cembra L. Jahrringserien, bestehend aus 323 Proben, zeigen zudem deutliche Klimasignale frühsommerlicher Temperaturschwankungen und liefern somit ideale Voraussetzungen für osteuropäische Temperaturrekonstruktionen. Die Analyse von stabilen Isotopendaten aus Jahrringen bietet umfangreiche Informationen über Auswirkungen von externen klimatischen Einflussfaktoren auf physiologische Prozesse der Bäume. Kohlenstoff- (δ13C) und Sauerstoff- (δ18O) Isotopendaten von Pinus uncinata Jahrringen aus den spanischen Pyrenäen weisen signifikante Klimasensitivität auf. Während die δ18O Zeitreihen durch Frühjahrsniederschläge und andere komplexere Faktoren gesteuert werden, zeigen die δ13C Zeitreihen ein eindeutiges Sommertemperatursignal. Aufgrund der erhöhten atmosphärischen CO2 Konzentration werden in dieser Dissertation unterschiedliche Korrekturverfahren für δ13C Daten verwendet, welche jedoch die niederfrequenten Trends verändern, was Auswirkungen auf die Klimasignalstärke nach sich zieht. Welches Korrekturverfahren als letzte Instanz ausgewählt werden soll bleibt eine Herausforderung, da die natürliche Anpassung der baumphysiologischen Prozesse an diesem Standort nicht quantifiziert werden konnten und objektive Kriterien für eine optimale CO2-Korrektur weiterhin fehlen. Mit einem neuartigen Ansatz trendbereinigter δ13C Daten im juvenilen Baumalter konnte eine 750-jährige Rekonstruktion dekadischer Sommertemperaturen entwickelt werden. Diese Rekonstruktion zeigt im historischen Verlauf größere Temperaturamplituden im Vergleich zu bereits publizierten Rekonstruktionen, welche auf traditionellen Jahrringparametern beruhen. Vorhandene als auch zukünftige Rekonstruktionen können durch Anwendung der vorgestellten Nachweismethoden auf mögliche Verzerrungen überprüft werden. Die Ergebnisse dieser Dissertation liefern somit einen Beitrag zur Debatte über zuverlässige Schätzungen vergangener Klimaschwankungen und deren Bedeutung als Grundlage für die Vorhersage zukünftiger Trends

Pre‐instrumental summer precipitation variability in northwestern Greece from a high‐elevation Pinus heldreichii network

The spatiotemporal variability of precipitation is of vital importance to Mediterranean ecology and economy, but pre‐instrumental changes are not well understood. Here, we present a millennial‐length June–July precipitation reconstruction derived from a network of 22 Pinus heldreichii high‐elevation sites in the Pindus Mountains of northwestern Greece. Tree‐ring width chronologies from these sites cohere exceptionally well over the past several hundred years (r1467–2015 = 0.64) revealing coherence at inter‐annual to centennial timescales across the network. The network mean calibrates significantly against instrumental June–July precipitation over the past 40 years (r1976–2015 = 0.71), even though no high‐elevation observational record is available representing the moist conditions at the treeline above 1,900 m a.s.l. For the final reconstruction, the instrumental target data are adjusted to provide realistic estimates of high‐elevation summer rainfall back to 729 CE. The reconstruction contains substantially more low‐frequency variability than other high‐resolution hydroclimate records from the eastern Mediterranean including extended dry periods from 1,350 to 1,379 CE (39 ± 4.5 mm) and 913 to 942 (40 ± 8.4 mm), and moist periods from 862 to 891 (86 ± 11 mm) and 1,522 to 1,551 (80 ± 3.5 mm), relative to the long‐term mean of 61 mm. The most recent 30‐year period from 1986 to 2015 is characterized by above average June–July precipitation (73 ± 2 mm). Low‐frequency changes in summer precipitation are likely related to variations in the position and persistence of storm tracks steering local depressions and causing extensive rainfall (or lack thereof) in high‐elevation environments of the Pindus Mountains.Associated with a strengthening of circum‐global sub‐tropical high‐pressure belts, climate models unequivocally predict a decrease of Mediterranean precipitation, accompanied by an increase of extreme events in the upcoming decades. Long‐term desiccation will amplify evaporative demand challenging plant metabolism and foster an even greater need to irrigate Mediterranean crops. We place these recent hydroclimate dynamics into a long‐term context and explore the feasibility of reconstructing low‐frequency precipitation variability by employing a large network of high‐elevation Pinus heldreichii sites from northwestern Greece.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165

Climate signal age effects in boreal tree-rings: Lessons to be learned for paleoclimatic reconstructions

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A 1200+year reconstruction of temperature extremes for the northeastern Mediterranean region

Proxy evidence is necessary to place current temperature and hydroclimatic changes in a long-term context and to assess the full range of natural and anthropogenic climate forcings. Here, we present the first millennium-length reconstruction of late summer (August-September) temperature variability for the Mediterranean region. We compiled 132 maximum latewood density (MXD) tree-ring series of living and relict Pinus heldreichii trees from a network of four high-elevation sites in the Pindus Mountains of Greece. Forty series reach back into the first millennium and the oldest sample dates to 575 CE. At annual to decadal scales, the record correlates significantly with August-September temperatures over the Balkan Peninsula and northeastern Mediterranean (r1950-2014 = 0.71, p < 0.001). We produce two reconstructions emphasizing interannual and decadal scale variance over the past millennium. Analysis of temperature extremes reveals the coldest summers occurred in 1035, 1117, 1217, 1884 and 1959 and the coldest decades were 1061-1070 and 1811-1820. The warmest summers occurred in 1240 and 1474, and the warmest decades were 1141-1150 and 1481-1490. Comparison of this new reconstruction with MXD-based summer temperature reconstructions across Europe reveals synchronized occurrences of extreme cool summers in the northeastern Mediterranean, and an antiphase-relationship with warm summer temperatures over the British Isles and Scandinavia. This temperature dipole is related to anomalies in the latitudinal position of the North Atlantic Jet. Despite the representation of common atmospheric forcing patterns, the occurrence of warm extremes is limited to few events, suggesting potential weaknesses of MXD to record warm temperature anomalies. In addition, we acknowledge problems in the observational data to capture local temperature variability due to small scale topographic differences in this high-elevation landscape. At a broader geographical scale, the occurrence of common cold summer extremes is restricted to years with volcanically induced changes in radiative forcing.Deutsche Forschungsgemeinschaft [ES 161/9-1Inst 247/665-1 FUGG]; National Science Foundation [AGS-1349942]12 month embargo; published online: 29 November 2018This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]