Bomb 14C Recorded in Laminated Speleothems: Calculation of Dead Carbon Proportion
Bomb 14C Recorded in Laminated Speleothems: Calculation of Dead Carbon Proportion
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层压洞穴中记录的炸弹 14C：死碳比例的计算
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
M. Massault
中科院分区：
文献类型：
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作者：
D. Genty;M. Massault
为了计算死碳比例（dcp），我们用加速器质谱（AMS）对法国西南部和比利时四个不同洞穴的6个石笋、3个钟乳石和7个渗漏沃茨进行了放射性碳测量。研究的所有洞穴都是现代的，每年都有层压，这提供了一个准确的年表的优势，分辨率超过一年。再加上AMS测量所需的方解石非常少（方解石存款在1.5年和7年之间），我们得到的死碳值在± 1.5%的不确定性范围内。结果表明，方解石沉积物的死碳比例为9.2%~ 21.9%，水的死碳比例为3.6%~ 21.9%。在每个采样点，dcp是均匀的。尽管中心间dcp变化> 11%，但其平均值15.5% ± 4.4仍在可接受值15% ± 5（稀释因子0.85 ± 0.5）的不确定度范围内。我们将每个地点的平均dcp与当地的地质、植被和气候进行比较。在相似的地质和温度条件下，森林覆盖下的dcp值最高，差异达9%。然而，比利时的网站，这也是一个森林下显示的DCP非常接近的DCP下发现的草原网站法国西南部，这证明了其他未知因素可能在溶解过程中发挥重要作用。次生方解石沉积和再溶解在土壤区或更有可能在裂缝系统到达洞穴本身之前，也可以解释网站之间的差异。原子能机构的同位素模型（皮尔逊模型适用于开放系统）是在良好的协议与测量活动。
We performed radiocarbon measurements using accelerator mass spectrometry (AMS) on 6 stalagmites 3 stalactites and 7 seepage waters from four different caves in Southwest France and Belgium in order to calculate the dead carbon proportion (dcp). All the speleothems studied are modern and annually laminated, which offers the advantage of an accurate chronology, with better than one-year resolution. Coupled with the fact that very little calcite is necessary for an AMS measurement (between 1.5 and 7 yr of calcite deposit), we obtained dead carbon values within an uncertainty limit of ± 1.5%. Results show that the dead carbon proportion varies from 9.2% to 21.9% for calcite deposits and from 3.6% to 21.9% for water. In each sampling site, the dcp is homogeneous. Although the inter-site dcp varies by >11%, its average value of 15.5% ± 4.4 still lies within the uncertainty range of the accepted value of 15% ± 5 (dilution factor of 0.85 ± 0.5). We compare the average dcp of each site with the local geology, vegetation and climate. Given similar geology and temperature the highest dcp values are found under forest cover; dcp difference is up to 9%. However, the Belgian site, which is also under a forest shows a dcp very close to the dcp found under grassland sites of Southwest France, which proves that other unknown factors may play an important role in dissolution processes. Secondary calcite deposition and redissolution in the soil zone or more likely in the fracture system before reaching the cave itself could also explain the inter-site differences. The IAEA isotopic model (Pearson model adapted for open systems) is in good agreement with the measured activities.