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Twenty-one 14C accelerator mass spectrometric analyses were obtained for three Holocene stalagmites from the Uamh-an-Tartair cave (Sutherland, Scotland) in order to estimate the past dead carbon proportion (dep). Results show that the dep increases from 22 to 38% from 3780 years ago to the present. Because δ13C variation is small within each sample, it is concluded that this dep increase is the product of the ageing of soil organic matter related to peat bog development above the cave that produced older soil CO2 and not from a more intense dissolution of the surrounding carbonates, which would have led to a δ13C increase. Comparison with samples from other sites in Europe shows no intersite correlation between dep and δ13C, but a relatively good intersite correlation is observed between dep and average site temperature. Thus, temperature may be a major factor controlling the production of old soil organic matter CO2 and, therefore, the dead carbon content of seepage water. In contrast to the Scotland stalagmites, two other Holocene samples from sites in southern France and Belgium exhibit a good correlation between δ13C and dep, which can be explained in terms of variations in the intensity of limestone dissolution. Consequently, δ13C variations observed in stalagmites are not always due to changes in the vegetation type (C3/C4) as has been commonly assumed; 13C/12C variations in speleothem calcite may also be controlled by the soil organic matter age and, in some cases, by the intensity of the limestone dissolution. Conversely, a largely constant speleothem δ13C signal, as observed for the Scotland stalagmites, does not necessarily imply that surface climate and vegetation conditions were stable since the dcp variations, in this case, are clearly related to the peat bog development during stalagmite growth. Copyright © 2001 Elsevier Sciene Ltd.
Author(s): Genty D, Baker A, Massault M, Proctor C, Gilmour M, Pons-Branchu E, Hamelin B
Publication type: Article
Publication status: Published
Journal: Geochimica et Cosmochimica Acta
Year: 2001
Volume: 65
Issue: 20
Pages: 3443-3457
ISSN (print): 0016-7037
ISSN (electronic): 1872-9533
Publisher: Pergamon
URL: http://dx.doi.org/10.1016/S0016-7037(01)00697-4
DOI: 10.1016/S0016-7037(01)00697-4
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