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Buntgen U.,Swiss Federal Institute of forest | Buntgen U.,Oeschger Center for Climate Change Research | Brazdil R.,Masaryk University | Brazdil R.,Academy of Sciences of the Czech Republic | And 7 more authors.
Quaternary Science Reviews | Year: 2011

A predicted rise in anthropogenic greenhouse gas emissions and associated effects on the Earth's climate system likely imply more frequent and severe weather extremes with alternations in hydroclimatic parameters expected to be most critical for ecosystem functioning, agricultural yield, and human health. Evaluating the return period and amplitude of modern climatic extremes in light of pre-industrial natural changes is, however, limited by generally too short instrumental meteorological observations. Here we introduce and analyze 11,873 annually resolved and absolutely dated ring width measurement series from living and historical fir (Abies alba Mill.) trees sampled across France, Switzerland, Germany, and the Czech Republic, which continuously span the AD 962-2007 period. Even though a dominant climatic driver of European fir growth was not found, ring width extremes were evidently triggered by anomalous variations in Central European April-June precipitation. Wet conditions were associated with dynamic low-pressure cells, whereas continental-scale droughts coincided with persistent high-pressure between 35 and 55°N. Documentary evidence independently confirms many of the dendro signals over the past millennium, and further provides insight on causes and consequences of ambient weather conditions related to the reconstructed extremes. A fairly uniform distribution of hydroclimatic extremes throughout the Medieval Climate Anomaly, Little Ice Age and Recent Global Warming may question the common believe that frequency and severity of such events closely relates to climate mean stages. This joint dendro-documentary approach not only allows extreme climate conditions of the industrial era to be placed against the backdrop of natural variations, but also probably helps to constrain climate model simulations over exceptional long timescales. © 2011 Elsevier Ltd. Source


Buntgen U.,Swiss Federal Institute of forest | Buntgen U.,Oeschger Center for Climate Change Research | Tegel W.,Albert Ludwigs University of Freiburg | Heussner K.-U.,German Archaeological Institute DAI | And 4 more authors.
Climate Research | Year: 2012

Uncertainty related to the rate and magnitude of predicted anthropogenic climate change highlights the need to enhance our understanding of past natural fluctuations in the Earth's climate system. This task emphasizes the importance of high-resolution palaeoclimatic records that cover industrial and pre-industrial times. Annually resolved and absolutely dated tree-ring measurements are a key input for cross-disciplinary research. Ambiguity due to paucity of data, however, characterizes many tree-ring data analyses. By utilizing nearly 12 000 living and historical ring width series from European fir Abies alba Mill., we demonstrate how massive sample replication can generate robust estimates of past growth rates, which may help reduce methodological and statistical constraints associated with many traditional tree-ring studies. © Inter-Research 2012. Source


Wild E.M.,University of Vienna | Steier P.,University of Vienna | Fischer P.,Gothenburg University | Hoflmayer F.,German Archaeological Institute DAI
Radiocarbon | Year: 2013

Radiocarbon dating of plant remains is often difficult due to the complete dissolution of the samples in the alkaline step of the ABA pretreatment. At the VERA laboratory, this problem was encountered frequently when numerous Bronze and Early Iron Age samples from the eastern Mediterranean were dated in the course of the special research program SCIEM2000 and in other collaborations with archaeologists focused on that area and time period. For these samples, only a 14C age determination of the humic acid fraction was possible. Humic acids from archaeological samples are always assessed as a second-choice material for 14C dating. It is assumed that the 14C ages may be affected by the presence of humic acids originating from other (younger) organic material, e.g. from soil horizons located above a sample. Therefore, when humic acids are dated a verification of the dates is crucial. To address this basic requirement, we started some time ago to date both fractions of charred seeds, wood, and charcoal samples whenever available, i.e. the residue after the ABA treatment and the humic acids extracted from the samples in the alkaline step. The results of this comparison showed that for the investigated eastern Mediterranean archaeological sites, 50 (out of 52) humic acid dates were in agreement with the 14C dates of the respective ABA-treated samples. Statistical analysis of the age differences leads to the conclusion that the extracted humic acids originated from the samples themselves or from contemporaneous material and were not appreciably contaminated by extraneous material of different age. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona. Source


Kaiser K.,German Research Center for Geosciences | Heinrich I.,German Research Center for Geosciences | Heine I.,German Research Center for Geosciences | Natkhin M.,Thunen Institute of Forest Ecosystems | And 8 more authors.
Journal of Hydrology | Year: 2015

In the glacially formed landscape of north-eastern Germany pronounced hydrological changes have been detected in recent decades, leading to the general question how lake levels and related groundwater levels perform in a long-term perspective, i.e. during the last c. 100. years. But long-term lake-level records are rare; most observations do not start before the late 20th century. Therefore, the potential of historic hydrological data, comprising drowned trees (as a geo-/bioarchive) and aerial as well as map imagery (as a document archive) was tested in order to derive discrete-time lake-level stands. These data are contrasted with lake-level simulations, obtaining a continuous-time series.Two small glacial lakes without connection to the stream network (i.e. closed lakes) were investigated in the Schorfheide area, c. 70. km north of Berlin. Both are dominantly fed by groundwater and precipitation but differ in their hydrogeological and catchment characteristics. For one lake a c. 40. year-long gauging record is available, showing high lake levels in the 1980s followed by a lowering of c. 3. m till the mid-2000s. In both lakes submerged in situ tree remains were discovered and dated by dendrochronology, revealing low lake levels during the first half of the 20th century. One lake was almost completely dry until c. 1960. Aerial photos provided data on lake levels since the 1930s which are corroborated by evidence of topographic mapping. Combining the empiric data with retrograde lake-level modelling, a well-proven lake-level record can be established for one lake that covers the last c. 90. years. The same general lake-level dynamics could be reconstructed by means of proxy data for the other lake. In both cases climate has been the dominant driver of lake-level dynamics. Comparisons with other multi-decadal lake-level records from the region show that these differ, depending on the hydrological lake type which modifies water feeding and water level. The results clearly showed that lake levels exhibited substantial long-term changes that should be taken into account in future hydroclimatic and hydrological studies. © 2015 Elsevier B.V. Source


Seeliger M.,University of Cologne | Bartz M.,University of Cologne | Erkul E.,University of Kiel | Feuser S.,University of Rostock | And 5 more authors.
Quaternary International | Year: 2013

During Hellenistic times, when the Pergamenian kingdom was prospering, Pergamum was operating an important harbour, used by merchants and military at the city of Elaia. This paper focuses on the development, utilisation and decay of the closed harbour of Elaia, which is discussed in the context of the landscape evolution of the environs of the ancient settlement. Based on geoarchaeological, archaeological and literary evidence, the construction of two harbour moles in order to provide shelter against wave action and enemies can be attributed to the early Hellenistic period. Geoelectric measurements revealed the construction profile of the moles. Coring evidence indicated that together with mole construction, a greater area of the formerly shallow marine and sublittoral terrain was consolidated, most probably to create space for harbour installations. The closed harbour basin was used intensely during Hellenistic and Roman times. Later, continued siltation hindered further usage. In combination with the decline of the city of Elaia in Late Antiquity, this was the reason why the harbour was abandoned. Scenarios for the time of the maximum transgression of the sea around 2500 BC, the early Hellenistic times around 300 BC, and Late Antiquity AD 500, are presented. © 2013 Elsevier Ltd and INQUA. Source

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