Dendrochronologische Befunde zur jüngeren Flußgeschichte von Main, Fulda, Lahn und Oker

Mit Hilfe einer Häufigkeitsverteilung der Keim- und Absterbedaten von 166 sub fossilen Eichenstämmen werden für das Obermaintal jeweils zwei Phasen der Auwaldbildung und -zerstörung im Subatlantikum nachgewiesen. Ein Zusammenhang der Auwaldzerstörung (von 25 BC bis 375 AD und von 600 AD bis 800 AD) mit Rodungsperioden in der römischen Kaiserzeit und im Frühmittelalter und einer dadurch verursachten Steigerung der Flußaktivität ist wahrscheinlich. Die Daten weiterer 74 Eichen aus Aufschlüssen an Fulda, Lahn und Oker zeigen für diese Flußgebiete neben Parallelen zur Entwicklung am Main auch deutliche Unterschiede auf.researc

Über die Anwendung der Dendrochronologie in der Moorforschung am Beispiel subfossiler Eichenstämme aus niedersächsischen Mooren

Die jahrringchronologische Auswertung subfossiler Eichenstämme aus drei niedersächsischen Mooren führt zum Nachweis eines im wesentlichen zwischen 350 und 150 v. Chr. an den verschiedenen Fundstellen gleichzeitig erfolgten Absterbens von Eichenbeständen. Es ergeben sich Hinweise auf eine Klimaschwankung in dieser Zeit. Die Bildungsgeschichte des Hochmoores bei Sieden läßt sich durch die Aufnahme von Baumfunden in situ in Verbindung mit den zugehörigen Moorprofilen rekonstruieren. Das norddeutsche Jahrringmaterial kann mit der Eisenzeitlichen Auwaldeichenchronologie synchronisiert werden und verlängert diese um gut 200 Jahre zum Älteren.researc

Tree-rings reveal two strong solar proton events in 7176 and 5259 BCE

The Sun sporadically produces eruptive events leading to intense fluxes of solar energetic particles (SEPs) that dramatically disrupt the near-Earth radiation environment. Such events have been directly studied for the last decades but little is known about the occurrence and magnitude of rare, extreme SEP events. Presently, a few events that produced measurable signals in cosmogenic radionuclides such as 14C, 10Be and 36Cl have been found. Analyzing annual 14C concentrations in tree-rings from Switzerland, Germany, Ireland, Russia, and the USA we discovered two spikes in atmospheric 14C occurring in 7176 and 5259 BCE. The ~2% increases of atmospheric 14C recorded for both events exceed all previously known 14C peaks but after correction for the geomagnetic field, they are comparable to the largest event of this type discovered so far at 775 CE. These strong events serve as accurate time markers for the synchronization with floating tree-ring and ice core records and provide critical information on the previous occurrence of extreme solar events which may threaten modern infrastructure

Diverging climate trends in Mongolian taiga forests influence growth and regeneration of Larix sibirica

Central and semiarid north-eastern Asia was subject to twentieth century warming far above the global average. Since forests of this region occur at their drought limit, they are particularly vulnerable to climate change. We studied the regional variations of temperature and precipitation trends and their effects on tree growth and forest regeneration in Mongolia. Tree-ring series from more than 2,300 trees of Siberian larch (Larix sibirica) collected in four regions of Mongolia’s forest zone were analyzed and related to available weather data. Climate trends underlie a remarkable regional variation leading to contrasting responses of tree growth in taiga forests even within the same mountain system. Within a distance of a few hundred kilometers (140–490 km), areas with recently reduced growth and regeneration of larch alternated with regions where these parameters remained constant or even increased. Reduced productivity could be correlated with increasing summer temperatures and decreasing precipitation; improved growth conditions were found at increasing precipitation, but constant summer temperatures. An effect of increasing winter temperatures on tree-ring width or forest regeneration was not detectable. Since declines of productivity and regeneration are more widespread in the Mongolian taiga than the opposite trend, a net loss of forests is likely to occur in the future, as strong increases in temperature and regionally differing changes in precipitation are predicted for the twenty-first century

Dendrochronological investigations of timber from wooden track ways in northwestern Germany - supplement, revision, re-evaluation

Dendrochronological investigations of wooden track ways enable high-resolution chronologies regarding their construction and utilisation. Therefore, timber from wooden track ways taken from excavations in northwest German peatlands has been dendro-dated already in the 1970s and 1980s. Some of these results show discrepancies or have not been published yet. The missing results are presented and contradictions between published data and data generated by our investigations are discussed and partially revised. The data originate from 17 track ways (1874 samples) of the period 1360 BC to 334 AD

Results and potential of dendroecological investigations on subfossil bog-pines from Northwest Germany

Subfossile Kiefern werden in vielen Mooren Nordwestdeutschlands gefunden. Durch die Transgression der Moore wurden Kiefern an der Basis der Torfe eingebettet und befinden sich oft am Übergang von Niedermoor- zu Hochmoortorfen. Stubbenhorizonte innerhalb der Torfkörper dokumentieren Bewaldungsphasen der Moore. Durch dendrochronologische Untersuchungen wurden subfossile Kiefern von 40 Fundorten datiert und erstmalig eine Kiefernchronologie für Nordwestdeutschland aufgebaut. Die untersuchten Kiefernhölzer belegen zu bestimmten Zeitabschnitten gehäufte Absterbe- oder Keimungsphasen sowie signifikante Änderungen der Jahrringbreiten der Hölzer aus verschiedenen Mooren. Teilweise zeichnen sich auch bei den früher bearbeiteten subfossilen Eichen zeitparallel entsprechende Phasen ab, so dass diese Signale, klimatisch verursacht, als Abbild von Vernässungsphasen angesehen werden.researc

The climatic interpretation of pan-European signature years in oak ring-width series

Large-scale signature years, in which oak growth across much of northern Europe varies consistently, are identified. Postulating that the likely cause of such widespread departures in growth is climatic, it is shown that these years were characterized by pan-European anomalies in soil-moisture availability, rainfall and temperature, with enhanced growth associated with an extended period of increased soil-moisture availability and reduced growth associated with lower temperatures and reduced soil moisture. These climatic anomalies are, in turn, associated with a large-scale and persistent perturbation in the atmospheric circulation that involves the circumpolar vortex and appears related to the Arctic Oscillation. The 2000-year record of signature-year occurrence shows variations in frequency at the decadal and century levels. It is necessary to interpret this record with caution. Nevertheless, these results do confirm earlier suggestions that large-scale climatic information is contained in regional composite archaeological chronologies. With supporting evidence from other sources, it should be possible to extract useful proxy climate data, even though the precise provenance of the timbers from which the records were derived might not be known

South Swedish bog pines as indicators of Mid-Holocene climate variability

Dendroclimatic investigations of subfossil Scots pine (Pinus sylvestris) from two raised bogs in southern Sweden yielded a continuous floating 1492-year long tree-ring record. By cross-dating with bog-pine chronologies from Lower Saxony, Germany, the South Swedish record was assigned an absolute age of 5219-3728 BC. The cross-match between ring-width chronologies from these two regions, separated by 500-700 km, is remarkably strong and the correlation positive, which indicates that large-scale climate dynamics had a significant impact on the growth of bog pines during the Holocene Thermal Maximum (HTM) when bog-pine distribution reached a maximum in both regions. However, local population dynamics were also influenced by peatland ontogeny and competition, as shown by differences in replication and mean tree age between the Swedish and German records. Comparisons with chronologies developed from modern bog pines in southern Sweden indicate that more coherent climate was controlling pine growth on natural peatlands during warm periods in the past. This study demonstrates the usefulness of Swedish subfossil bog-pine material as a climate proxy, with particular potential for decadal- to centennial-scale reconstructions of humidity fluctuations. (C) 2011 Istituto Italiano di Dendrocronologia. Published by Elsevier GmbH. All rights reserved