Krachler Michael, Mohl Carola, Emons Hendrik, Shotyk William
Institute of Environmental Geochemistry, University of Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany.
Environ Sci Technol. 2003 Jun 15;37(12):2658-67. doi: 10.1021/es0263083.
Vanadium, Cr, and Ni accumulating in a Swiss peat bog since 12 370 14C yr B.P. have been measured using inductively coupled plasma-mass spectrometry (ICP-MS) after acid dissolution in a microwave autoclave. Strict quality control schemes were applied to guarantee the accuracy of the applied analytical methodology. The concentration gradients in the peat column and comparison with Pb indicate that V, Cr, and Ni are effectively immobile in the ombrotrophic section of the peat profile but that Ni is added to the minerotrophic peat layers by chemical weathering of the underlying sediments. The lowest metal concentrations were found during the Holocene climate optimum (5320-8230 14C yr B.P.) when "natural background" values averaged 0.55 +/- 0.13 microg g(-1) V, 0.76 +/- 0.17 microg g(-1) Cr, and 0.46 +/- 0.09 microg g(-1) Ni (n = 18); given the average bulk density (0.05 g/cm3) and accumulation rate (0.05 cm/ yr) of peat in this zone, the corresponding atmospheric fluxes are approximately 14, 19, and 12 microg m(-2) yr(-1) for V, Cr, and Ni, respectively. The highest concentrations of V, Cr, and Ni were found during the Younger Dryas cold climate event (centered at 10 590 14C yr B.P.) when background values were exceeded by about 40 times. Elevated concentrations and accumulation rates were also found at 8230 and 5320 14C yr B.P., which are consistent with the elevated dust fluxes recorded by Greenland ice cores. By far the greatest contribution of the three elements to the peat inventory is atmospheric soil dust, and the metal fluxes vary not only with climate change but also land-use history (especially the beginning of forest clearing for agriculture ca. 6 millennia ago). The V/Sc, Cr/Sc, and Ni/ Sc ratios were remarkably similar to their corresponding ratios in the earth's crust until the onset of the Industrial Revolution (240 14C yr B.P.), which largely validates the use of crustal concentrations for calculating enrichment factors (EF) for these elements. In modern samples, the EFs of V, Cr, and Ni reach maximum values between 2.4 and 4.1, relative to background; anthropogenic emissions are a more likely explanation of the elevated EFs than either plant uptake or chemical diagenesis. This study demonstrates the usefulness of peat bogs as archives of atmospheric metal deposition and underpins the potential of peat cores to help distinguish between lithogenic and anthropogenic metal sources.
自公元前12370年14C以来，瑞士泥炭沼泽中积累的钒、铬和镍，在微波高压釜中酸溶解后，使用电感耦合等离子体质谱法（ICP-MS）进行了测量。采用了严格的质量控制方案，以确保所应用分析方法的准确性。泥炭柱中的浓度梯度以及与铅的比较表明，钒、铬和镍在泥炭剖面的雨养区实际上是不迁移的，但镍通过下层沉积物的化学风化作用被添加到矿质营养泥炭层中。在全新世气候适宜期（公元前5320 - 8230年14C）发现了最低的金属浓度，当时“自然背景”值平均为0.55±0.13微克/克钒、0.76±0.17微克/克铬和0.46±0.09微克/克镍（n = 18）；考虑到该区域泥炭的平均堆积密度（0.05克/立方厘米）和堆积速率（0.05厘米/年），钒、铬和镍相应的大气通量分别约为14、19和12微克/平方米·年。在新仙女木寒冷气候事件期间（以公元前10590年14C为中心）发现了钒、铬和镍的最高浓度，当时背景值超过了约40倍。在公元前8230年和5320年14C也发现了浓度和堆积速率升高的情况，这与格陵兰冰芯记录的尘埃通量增加一致。到目前为止，这三种元素对泥炭存量的最大贡献是大气土壤尘埃，并且金属通量不仅随气候变化而变化，还随土地利用历史（特别是约6千年前开始的农业森林砍伐）而变化。直到工业革命开始（公元前240年14C），钒/钪、铬/钪和镍/钪的比值与地壳中相应的比值非常相似，这在很大程度上验证了用地壳浓度来计算这些元素的富集因子（EF）。在现代样品中，相对于背景，钒、铬和镍的富集因子达到2.4至4.1之间的最大值；人为排放比植物吸收或化学成岩作用更有可能解释富集因子升高的原因。这项研究证明了泥炭沼泽作为大气金属沉积档案的有用性，并支持了泥炭芯有助于区分成岩和人为金属来源的潜力。
