Artikkelit jotka sisältää sanan 'dating'
High resolution 14C dating of surface peat using the AMS technique.
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In an AMS (accelerator mass spectrometric) determination of 14C from moss-increment dated samples from a Sphagnum fuscum hummock, a clear peak representing the time of high 14C activity in the atmosphere due to nuclear bomb tests was found. The 14C activities in the peat profile at deeper levels, corresponding to the period down to 1600 BP, showed similar variations as the atmospheric values. The time-scale obtained from radiocarbon dating fitted well with results from moss-increment counting, pollen analysis and dendrochronological dating of a fire horizon. Using the bomb activity peak, the fraction of carbon emanating from deeper layers and refixed into growing peat was estimated. The fraction of soil carbon dioxide taken up by the contemporary Sphagnum sward was thus found to be in the order of 20%.
Keywords: Moss increment dating, peatlands, radiocarbon, Sphagnum
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Tolonen,
Dept. of Biology, Univ. Joensuu, P.O. Box III, FIN-80101 Joensuu, Finland
Sähköposti:
ei.tietoa@nn.oo
- Possnert, Sähköposti: ei.tietoa@nn.oo
- Jungner, Sähköposti: ei.tietoa@nn.oo
- Sonninen, Sähköposti: ei.tietoa@nn.oo
- Alm, Sähköposti: ei.tietoa@nn.oo
Determination of recent apparent carbon accumulation in peat using dated fire horizons.
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Two charcoal layers, originating from two forest fires, were found at between 7 and 58 cm in the peat of Lakkasuo mire. Using dendro-chronological techniques and fire scars on Scots pine {Pinus sylvestris L.) stumps, the date when these two layers was deposited could be estimated. The earlier fire swept over the mire about 1780 A.D. and the later fire, which seems to have been limited to the eastern part of Lakkasuo, occurred in 1845 A.D. Knowing the thickness of the peat layer above the dated charcoal layers, its bulk density and carbon content, the rate of carbon accumulation during the last 212-147 years could therefore be calculated for different site types in the Lakkasuo mire complex. These values ranging from 39.8 to 80.7 g C m-2 a-1. can be compared to those (28.5-42.8 g C m-2 a-1 ) 0f the peat layer down to a still older fire horizon dated using the AMS radiocarbon "wiggle matching" technique at 1040 ± 90 B.P.
Keywords: Carbon accumulation, charcoal, dating, dendrochronology, fire
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Alm,
Department of Biology, University of Joensuu, P.O. Box 111, FIN-80100 Joensuu, Finland
Sähköposti:
ei.tietoa@nn.oo
- Tolonen, Sähköposti: ei.tietoa@nn.oo
- Vasander, Sähköposti: ei.tietoa@nn.oo
Element retention and removal in ombrotrophic peat of Haadetkeidas, a boreal Finnish peat bog.
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We determined the rate elements are sequestered in hummock peat of an ombrotrophic bog. The peat below 65 cm was radiocarbon dated and the upper 65 cm was dated using the acid insoluble ash (AIA) content and Polytrichum strictum growth increments. Peat produced during the last 9 yrs contains roughly all the N, P, Ca, and Mg, and about twice the K, deposited during this period. However, these nutrients are depleted from older peat at rates that depends on mineralization and adsorption properties of the ions. Changes in inorganic chemistry occur mostly while peat is in the acrotelm. Therefore, only peat in the catotelm will show the true accumulation rate of elements. In peat below 65 cm, the annual accumulation rate, as a percent of the present annual input, is: N-38, K-2.5, P-18, Na-1.5, Ca-3, Mg-51 and S-3.5%. Dust fall increased 4-fold about 500 yrs ago and has remained at this level. Therefore, the annual accumulation of elements in peat below 65 cm, or older than 522 yrs, presumably underestimates present accumulation in the catotelm of soil-derived elements, especially Ca and P, and elements that have increased due to pollution such as N and S. This increased dust fall probably changed the floristic composition of the vegetation as well as production and decay.
Keywords: Accumulation, dating, element retention, input changes, nutrient dynamics
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Damman,
Department of Ecology and Evolutionary Biology, University of Connecticut, 75 N. Eagleville Road, Storrs, CT 06269-3042, USA
Sähköposti:
ei.tietoa@nn.oo
- Tolonen, Sähköposti: ei.tietoa@nn.oo
- Sallantaus, Sähköposti: ei.tietoa@nn.oo
Tuhka-ajoitusmenetelmän ja sammalvuosikasvainajoituksen vertailu rahkamättäissä.
English title: A comparison of ash dating and moss-increment dating in Sphagnum hummocks.
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A comparison of two methods for dating recent ombrotrophic peat hummocks was made at three mires. For depths approximately below 10 cm, acid insoluble ash dating gave greater ages than moss-increment dating; for depths above 10 cm, the methods showed more similar ages. The moss-increment dates were assumed to be generally correct since there was a good correlation between several independent dating results and moss-increment ages at one of the study sites. Despite the declining accuracy of moss-increment dating with depth, it should be the method chosen for dating recent peat in areas where the assumption of constant acid insoluble ash deposition is invalid. Increment dating is practically useful only in the moss hummocks, except for when the moss stems have been compressed into a horizontal position.
Keywords: Dating, mineral dust, peatlands, Sphagnum, surface peats
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Eustis,
Department of Ecology and Evolutionary Biology, University of Connecticut, P.O. Box U-42, Storrs, CT 06268, USA
Sähköposti:
ei.tietoa@nn.oo
- Tolonen, Sähköposti: ei.tietoa@nn.oo
Mitä suoarkistot voivat meille tulevaisuudessa kertoa?
English title: What would be the significance of peat archives in the future?
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An attempt is made to predict the progress of mire palaeoecological research in the near future. The prognosis is made in the light of recent advances in the field. Examples of some multi-faceted topics are given. They include ancient climatic changes for understanding the present changes, the greenhouse-effect, problems and new innovations in dating, organic pollutants such as PAHs and DDT, heavy metals and related air pollutants, man-made radionuclides, initiation of peatlands, peat growth, and fire history.
Keywords: Carbon balance, dating, fire, DDT, global warming, heavy metals, PAHs
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Tolonen,
Department of Biology, University of Joensuu, P.O. Box 111, SF-80101 Joensuu, Finland
Sähköposti:
ei.tietoa@nn.oo
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