The future of the past: A robust framework for the upgrade and development of the international radiocarbon calibration/comparison curves

考古学和地球科学的许多研究人员通过放射性碳测年法从他们所处理的保存下来的沉积物中获取植物或动物遗骸的时间尺度。然而，放射性碳日期与日历日期不同，必须根据植物或动物生活时大气中放射性碳含量的变化进行校正。这种从放射性碳年代到日历年龄的转换，即所谓的校准，并不是一种直接的修正。放射性碳测年的校准只能通过与合适的校准曲线进行比较来完成。这样的曲线是基于已知日历年龄的样本中的放射性碳的测量，例如树木年轮，或者在不那么严格的意义上，基于可以使用独立测年方法的其他类型的样本。对于在海洋中生长的样品，如贝壳和珊瑚，需要一条单独的校准曲线来考虑海洋水循环的变化，这种变化可能会从海洋深处带来“老”水(水库效应)。已定期改进校准曲线，以提供更好的日历年龄估计。2004年，IntCal工作组利用对水库效应的估计校正，根据距今12,400年前的放射性碳年轮和距今26,000年的独立测年海洋样品，构建了新的校准曲线。这些曲线不是简单地平均数据，而是使用统计工具(模型)构建的，这些工具考虑到所用样品的日历年龄以及放射性碳日期的不确定性。当时，26,000年以前的数据并不一致，因此没有提供曲线，但给出了数据集与潜在真实曲线相差多大的估计。在过去的几年里，许多研究都在从各种记录中产生放射性碳数据集。这些数据集中的许多现在都有相当好的一致性，因此应该可以提供曲线来估计距今55,000年前的日历年龄。此外，新的树木年轮记录正在出现，这将提高校准曲线的精度。统计方法也在迅速发展，因此我们在2004年对模型所作的一些简化假设将不再是必要的。该项目与IntCal工作组合作，将开发一个易于维护的校准质量放射性碳数据数据库，用于定期更新校准曲线。统计学上的进步将使我们能够改进以前的模型，以进一步完善校准曲线。对精心挑选的珊瑚的测量将有助于确定校准曲线中使用的海洋样本需要进行哪些校正。通过改进放射性碳校准，该项目将在考古学和重建过去环境的众多研究中增进对事件顺序和时间的了解。

Many researchers in archaeology and the geosciences obtain timescales for their projects by radiocarbon dating plant or animal remains from the preserved deposits with which they work. Radiocarbon dates are not the same as calendar dates, however, and have to be corrected for variations in the radiocarbon content of the atmosphere at the time that the plant or animal lived. This conversion of radiocarbon dates to calendar ages, known as calibration, is not a straightforward correction. Calibration of radiocarbon dates can only be done by comparison to a suitable calibration curve. Such curves are based on measurements of radiocarbon in samples of known calendar age such as tree-rings, or in a less strict sense, on other types of samples where an independent method of dating can be used. For samples which grew in the ocean, such as shells and corals, a separate calibration curve is needed to account for changes in ocean water circulation which may bring up 'old' water from the ocean depths (the reservoir effect). The calibration curves have been refined periodically to provide better estimates of the calendar ages. In 2004, the IntCal Working Group constructed new calibration curves from radiocarbon dated tree-rings back to 12,400 years before present and from independently dated ocean samples, using an estimated correction for the reservoir effect, back to 26,000 years before present. Rather than simply averaging the data, these curves were constructed with statistical tools (models) that allowed for the uncertainty in the calendar ages of the samples used as well as the radiocarbon dates. At that time data beyond 26,000 years before present did not agree so no curve was provided but an estimate of how far the data sets differed from the underlying true curve was given. In the last few years a lot of research has gone into producing radiocarbon datasets from a variety of records. Many of these datasets are now in fairly good agreement so it should be possible to provide curves for estimating calendar ages back to 55,000 years before present. In addition new tree-ring records are becoming available which will improve the precision of the calibration curve. Statistical methods have also been rapidly advancing and so some of the simplifying assumptions that we made about the models in 2004 will no longer be necessary. Working in collaboration with the IntCal Working Group, this project will develop an easily maintainable database of calibration quality radiocarbon data to be used to produce updates to the calibration curves on a regular basis. Advances in statistics will allow us to improve on the previous models to further refine the calibration curves. Measurements of carefully selected coral will help determine what corrections are needed for ocean samples to be used in calibration curves. By improving radiocarbon calibration this project will improve the understanding of the sequence and timing of events in numerous studies in archaeology and in the reconstruction of past environments.