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Developing millennial tree-ring chronology for Turku (Åbo) and comparing palaeoclimatic signals inferred from archaeological, subfossil and living Pinus sylvestris data in Southwest Finland

Helama Samuli, Ratilainen Tanja, Ruohonen Juha, Taavitsainen Jussi-Pekka

Studia Quaternaria

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2024

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Vol. 41, Nr 1

1--11

EN

Archaeological and living tree data were used to construct tree-ring chronologies over the medieval (AD 1183–1430) and recent (AD 1812–2020) periods in Turku, which is historically an important population centre in Southwest Finland and the country. Comparisons between the two tree-ring assemblages, and between the previously built chronologies from the Åland (historical timber) and Tavastia (lacustrine subfossils and living trees) sites, provided ways of understanding the growth patterns and their linkages to climatic, environmental, and edaphic factors. Tree growth in and around Turku was affected by warm-season precipitation and winter temperature. Similar relationships were previously evident also in the Åland tree rings, whereas the data from a wetter Tavastia site did not exhibit similar precipitation signal. The site conditions influence also the correlations which are higher between Turku and Åland than between Turku and Tavastia chronologies. Construction of long continuous chronology is impaired by human-related activities, the Great Fire of Turku in 1827 and logging, which have diminished the availability of dead and living-tree materials, respectively. These conditions lead to hardships of filling the gap between the medieval and recent periods and updating the archaeological datasets with compatible living-tree data, which are both demonstrated by our results.

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An 854-year tree-ring chronology of scots pine for south-west Finland

Helama S., Holopainen J., Timonen M, Mielikainen K

Studia Quaternaria

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2014

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Vol. 31, Nr 1

61--68

EN

A near-millennial tree-ring chronology (AD 1147-2000) is presented for south-west Finland and analyzed using dendroclimatic methods. This is a composite chronology comprising samples both from standing pine trees (Pinus sylvestris L.) and subfossil trunks as recovered from the lake sediments, with a total sample size of 189 tree-ring sample series. The series were dendrochronologically cross-dated to exact calendar years to portray variability in tree-ring widths on inter-annual and longer scales. Although the studied chronology correlates statistically significantly with other long tree-ring width chronologies from Finland over their common period (AD 1520-1993), the south-west chronology did not exhibit similarly strong mid-summer temperature or spring/early-summer precipitation signals in comparison to published chronologies. On the other hand, the south-west chronology showed highest correlations to the North Atlantic Oscillation indices in winter/spring months, this association following a dendroclimatic feature common to pine chronologies over the region and adjacent areas. Paleoclimatic comparison showed that tree-rings had varied similarly to central European spring temperatures. It is postulated that the collected and dated tree-ring material could be studied for wood surface reflectance (blue channel light intensity) and stable isotopes, which both have recently shown to correlate notably well with summer temperatures.

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Stable carbon isotope analysis of subfossil wood from Austrian Alps

Kłusek M., Pawełczyk S.

Geochronometria

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2014

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Vol. 41, no. 4

400--408

EN

The presented studies were carried out in order to check the usefulness of subfossil wood for stable isotope analysis. The aim of research was also to define the optimal method of subfossil samples preparation. Subfossil samples used during the presented studies are a part of the multicentury dendrochronological scale. This chronology originates in an area situated around a small mountain lake — Schwarzersee, in Austria. The obtained results of stable carbon isotope measurements confirmed that the method of α-cellulose extraction by the application of acidic sodium chlorite and sodium hydroxide solutions removes resins and other mobile compounds from wood. Therefore, in the case of the analysed samples, the additional chemical process of extractives removing was found to be unnecessary. Studied wood samples contained an adequate proportion of α-cellulose similar to the values characteristic for the contemporary trees. This proved an adequate wood preservation which is essential for the conduction of isotopic research.

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Dendrochronological and radiocarbon dating of subfossil wood from the Morava River basin

Kolář T., Rybníček M.

Geochronometria

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2011

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Vol. 38, no. 2

155-161

EN

The paper deals with dendrochronological and radiocarbon dating of subfossil trunks found in the basin of the Morava River. The research into subfossil trunks had been conducted in the Czech Republic in the past but the research stopped in 2001. 160 records of measurements of subfossil, predominantly oak trunk samples, are preserved from that time. Three years ago the research was reo-pened and again the most trunks were found in the basin of the Morava River. 92 samples of oak trunks and 7 samples of other tree species (poplar, elm, maple, beech) were taken from selected sites. The samples were processed in compliance with the standard dendrochronological methodology. To date the samples, Czech, Austrian, Polish and German standard chronologies were used. In cases when the dendrochronological dating was unsuccessful, the samples were sent for radiocarbon dating. In total, 35 samples were dated, mainly by the radiocarbon method. Subfossil trunks from gravel pit Tovačov were dated and classified into 4 different periods, the oldest being from 2780-2190 BC. In Osek nad Bečvou, the samples were taken from two sites. Whereas from the 4 trunks taken in the riv-er channel each was from a different period, the trunks from the gravel pit come from 981-1015 AD. The trunks found in the Morava River basin near Strážnice were dated to the 10th-15th century. In the future, we expect to extend the amount of the acquired samples with the aim to create a link to the existing standard chronology or to create a long floating average tree-ring curve.