X-ray microdensitometry on annually resolved tree-ring samples has gained an exceptional position in last-millennium paleoclimatology through the maximum latewood density (MXD) parameter, but also increasingly through other density parameters. For 50 years, X-ray based measurement techniques have been the de facto standard. However, studies report offsets in the mean levels for MXD measurements derived from different laboratories, indicating challenges of accuracy and precision. Moreover, reflected visible light-based techniques are becoming increasingly popular, and wood anatomical techniques are emerging as a potentially powerful pathway to extract density information at the highest resolution. Here we review the current understanding and merits of wood density for tree-ring research, associated microdensitometric techniques, and analytical measurement challenges. The review is further complemented with a careful comparison of new measurements derived at 17 laboratories, using several different techniques. The new experiment allowed us to corroborate and refresh "long-standing wisdom" but also provide new insights. Key outcomes include (i) a demonstration of the need for mass/volume-based recalibration to accurately estimate average ring density; (ii) a substantiation of systematic differences in MXD measurements that cautions for great care when combining density data sets for climate reconstructions; and (iii) insights into the relevance of analytical measurement resolution in signals derived from tree-ring density data. Finally, we provide recommendations expected to facilitate futureinter-comparability and interpretations for global change research.

中文翻译：

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树木年轮密度测定的科学价值和分析挑战

通过最大晚材密度 (MXD) 参数，以及通过其他密度参数，每年解析的树轮样本的 X 射线微密度测定法在上千年古气候学中获得了特殊的地位。50 年来，基于 X 射线的测量技术一直是事实上的标准。然而，研究报告了来自不同实验室的 MXD 测量的平均水平的偏移，表明准确性和精确度面临挑战。此外，基于反射可见光的技术正变得越来越流行，木材解剖技术正在成为以最高分辨率提取密度信息的潜在强大途径。在这里，我们回顾了当前对树木年轮研究的木材密度的理解和优点，相关的显微密度测量技术，和分析测量挑战。通过对 17 个实验室使用几种不同技术得出的新测量结果进行仔细比较，进一步补充了该审查。新的实验让我们证实和刷新了“长期存在的智慧”，同时也提供了新的见解。主要成果包括 (i) 证明需要进行基于质量/体积的重新校准以准确估计平均环密度；(ii) 证实 MXD 测量中的系统差异，提醒在结合密度数据集进行气候重建时要格外小心；(iii) 深入了解分析测量分辨率在来自树轮密度数据的信号中的相关性。最后，我们提供的建议有望促进未来全球变化研究的可比性和解释。