The uncertainty of measurements of carbon and oxygen stable-isotope ratios of carbonate materials is commonly assumed to be the analytical uncertainty determined from replicate analyses of single samples, but this ignores the possibility that heterogeneity of the material studied is greater than the analytical uncertainty. To test this question, we took eight samples from each of 13 layers or specimens of various non-marine (“continental”) carbonates and found ranges of δ13C and δ18O of 0.3 to 5.1‰, all exceeding the range of the typical lab-reported analytical uncertainty, ± 0.1‰, placed around single samples. These results are similar to previous replicate sampling of marine limestone layers, which revealed ranges of 0.2 to 2.8‰. Both sets of results, and other published data, demonstrate that analytical uncertainty derived from replicate analysis of a single sample is not a valid estimate of the uncertainty of δ13C or δ18O values characterizing a layer or specimen, and they remind us that we should not place great credence in anomalies or events defined by single samples of layers or specimens, regardless of the replication of analysis of that single sample. Our results indicate that the required layer-level or specimen-level uncertainty can be derived only from replicate sampling at different locations in layers or specimens, and that the layer-level or specimen-level uncertainty is inevitably greater than typical lab-reported analytical uncertainty. Credibility of anomalies or events in time series would be increased by replicate sampling of a random or dispersed subset of layers to estimate the variability of all layers and/or by replicate sampling of layers at and around a potential but unconfirmed event. The significance of the variability discussed above is evident in use of δ18O data to estimate paleotemperatures, where a difference of 1‰ in δ18O implies a difference of 4°C in temperature. Use of a single sample resulting in mischaracterization of the δ18O of an ancient material by 1.5‰ relative to the true mean for that material (which our results suggest is quite possible) would lead to a corresponding misestimation of temperature of 6°C, a significant difference in paleoenvironmental studies.

中文翻译：

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天然碳酸盐材料单层或标本中碳和氧稳定同位素组成的实质异质性：大陆碳酸盐重复取样的新证据肯定了海洋石灰石的先前证据

通常假定碳酸盐材料的碳氧稳定同位素比率的测量不确定度是通过单个样品的重复分析确定的分析不确定度，但这忽略了所研究材料的异质性大于分析不确定度的可能性。为了测试该问题，我们从13层碳酸盐样品或各种非海洋（“大陆”）碳酸盐样品中各取了8个样品，发现δ13C和δ18O的范围为0.3至5.1‰，均超出了实验室报告的典型范围单个样品周围的分析不确定度为±0.1‰。这些结果与先前对海洋石灰岩层的重复采样相似，揭示范围为0.2至2.8‰。两组结果以及其他已发布的数据，证明了从单个样品的重复分析中得出的分析不确定性不是对表征层或样品的δ13C或δ18O值的不确定性的有效估计，并且它们提醒我们，我们不应在单个样品定义的异常或事件中拥有很高的可信度层或样本的数量，而不管该单个样本的分析重复进行。我们的结果表明所需的层级或样品级不确定度只能从层或样品中不同位置的重复采样中得出，并且层级或样品级不确定度不可避免地要大于实验室报告的典型分析不确定度。通过对随机或分散的子集层进行重复采样以估计所有层的可变性和/或通过对潜在但未确认事件及其周围的层进行重复采样，可以提高时间序列中异常或事件的可信度。上面讨论的可变性的重要性在使用δ18O数据估算古温度时很明显，其中δ18O的1‰的差异意味着温度相差4°C。使用单个样品会导致古老材料的δ18O相对于该材料的真实均值错误表征1.5‰（我们的结果表明这是完全可能的）将导致相应地错误估计6°C的温度，这是很明显的。古环境研究的差异。上面讨论的可变性的重要性在使用δ18O数据估算古温度时很明显，其中δ18O的1‰的差异意味着温度相差4°C。使用单个样品会导致古老材料的δ18O相对于该材料的真实均值错误表征1.5‰（我们的结果表明这是完全可能的）将导致相应地错误估计6°C的温度，这是很明显的。古环境研究的差异。上面讨论的可变性的重要性在使用δ18O数据估算古温度时很明显，其中δ18O的1‰的差异意味着温度相差4°C。使用单个样品会导致古老材料的δ18O相对于该材料的真实均值错误表征1.5‰（我们的结果表明这是完全可能的）将导致相应地错误估计6°C的温度，这是很明显的。古环境研究的差异。