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Peak activities of radiocaesium (137Cs) in lake sediments have frequently been used to infer the ages of sediments deposited in the 1960s (137Cs derived from nuclear bomb testing) or in 1986 (Chernobyl derived 137Cs). Records of the vertical distribution of 137Cs in sediments can thus be used to provide accurate dates for a critical period in which palaeoecological reconstructions often overlap contemporary monitoring data. However, knowledge regarding how the distribution of 137Cs in sediments is affected by post‐depositional processes is limited to interpretations based on the 137Cs distribution in sediments sampled at a single given date. This study assesses the extent to which the 137Cs record in annually laminated (varved) lake sediments is affected by post‐depositional diffusion, using 11 archived sediment cores sampled between 1986 and 2007. The sediment record reveals how Chernobyl 137Cs incorporated into the 1986 varve diffused downwards in the core at a decreasing rate over time, whereas the surface sediments continued to receive inputs of 137Cs mobilized from the catchment soils or lake margin. In spite of these processes, all cores post‐dating the Chernobyl accident had a clear and well‐resolved peak in the 1986 varve, justifying the use of this feature as a fixed chronostratigraphic feature. Because of the very high levels of Chernobyl fallout at this site, downwards migration of Chernobyl 137Cs has, however, completely masked the nuclear weapons 137Cs fallout peak that had been clearly preserved in the 1964 varve of a pre‐Chernobyl core sampled just three weeks before the Chernobyl accident. In consequence, the weapons fallout marker is likely to be of little use for determining 137Cs dates in areas strongly affected by high levels of Chernobyl fallout. 相似文献
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Improved methods for sampling, photographing and varve-counting of varved lake sediments 总被引：14，自引：0，他引：14
INGEMAR RENBERG 《Boreas: An International Journal of Quaternary Research》1981,10(3):255-258
An improved crust-freeze sampler for taking undisturbed cores of the surface sediments from ice-covered lakes is described together with a technique for subsampling the frozen sediment. Hints are given on how photography and varve-counting in frozen and in fresh cores of varved lake sediments can be made easier, and on how to make thin sections of sediments for examination under the light microscope 相似文献
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INGEMAR CATO 《Boreas: An International Journal of Quaternary Research》1985,14(2):117-122
In the Ångermanälven river valley in northern Sweden the Swedish geochronological time scale has been connected with the present (1978) by means of varved clayey-silty sediments. A 75-year-old problem has thereby been solved. Ragnar Lidén's previously calculated gap of 980 years between his youngest varve 7,522, found at Prästmon, and the historical year 1900 A.D. should be extended by 365 years. This implies that the zero year in Döviken (Indalsälven river valley), reviewed by Borell and Offerberg and commonly used in the Swedish time scale to mark the boundary between the finiglacial and postglacial epochs is Sweden, should be dated to 7,288 B.C. (9,238 B.P.) instead of the old date 6,923 B.C. given by Nilsson in 1960. 相似文献
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BARBARA WOHLFARTH SVANTE BJÖRCK INGEMAR CATO GÖRAN POSSNERT 《Boreas: An International Journal of Quaternary Research》1997,26(4):347-353
A new varve diagram from the river Ångermanälven could be correlated to the postglacial varve chronology to between 4903 and 4415 varve years BP. An AMS 14 C measurement on terrestrial macrofossils obtained between 4715 and 4706 varve years BP gave a calibrated age of between 5730 and 5040 calendar years BP. The discrepancy between varve and calender-year age indicates that an error or part of an error in the Swedish varve chronology may be situated between 2000 and 5000 varve years BP. 相似文献
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