Abstract The study of anatomical irregularities in tree rings has recently gained momentum as a complement to traditional tree-ring measurements as they may provide information on extreme climatic events. Two anomalies, blue rings (BR) and frost rings (FR), were analyzed in bristlecone pine (Pinus longaeva D.K. Bailey) trees located along an elevation gradient in northeastern Nevada. These two subannual ring anomalies were systematically compiled for two periods; one centered on 536 CE (well-known for a volcanically-induced period of climatic cooling) and the other on 1965 CE (useful due to the availability of instrumental climate data). During the period 523–545 CE (n ≥ 10 trees), both BR and latewood FR (LWFR) were recorded abundantly in 532 and 536, as well as a BR cluster from 539 to 542 CE. Years when trees solely recorded a BR (without an accompanying LWFR) were more frequent in the earlier period than in the modern period (1954–2006 CE; n ≥ 10 trees) when both anomalies tended to co-occur. These results suggest a shorter growing season in the 536 period than in the 20th century. Modern BR/LWFR were most abundant in 1965 and 1978 CE. Both anomalies were mainly observed in the highest elevation trees and both were produced in years characterized by cooler than average temperatures throughout the growing season. Anatomically, BR and LWFR did not differ significantly in tracheid dimensions except that LWFR clearly showed damages associated with sub-freezing temperatures. The main feature distinguishing BR and LWFR from “normal” tree rings was a significant reduction in latewood secondary wall thickness. In P. longaeva, BR like pale latewood (light) rings, result from short and cool growing seasons which leads to reduced (or interrupted) lignification of tracheids. In species producing extremely narrow latewood like P. longaeva it may be difficult to macroscopically identify pale latewood years, thus rendering microscopic investigation of BR as a climate proxy useful in paleoclimatic research.

中文翻译：

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高海拔狐尾松（Pinus longaeva DK Bailey）蓝环和霜环的形成、结构和气候意义

摘要 作为对传统年轮测量的补充，对树木年轮解剖结构不规则的研究获得了动力，因为它们可以提供有关极端气候事件的信息。在内华达州东北部沿海拔梯度分布的狐尾松 (Pinus longaeva DK Bailey) 树中分析了两个异常现象，蓝环 (BR) 和霜环 (FR)。这两个亚年环距是系统地编制了两个时期；一个集中在公元 536 年（以火山引起的气候冷却时期而闻名），另一个集中在公元 1965 年（由于仪器气候数据的可用性，因此很有用）。在公元 523-545 年期间（n ≥ 10 棵树），在公元 532 年和 536 年记录了大量的 BR 和晚材 FR（LWFR），以及从公元 539 年到 542 年的 BR 簇。在早期，树木仅记录 BR（没有伴随的 LWFR）的年份比现代时期（公元 1954-2006 年；n ≥ 10 棵树）更频繁，因为这两种异常往往同时发生。这些结果表明 536 年的生长季节比 20 世纪短。现代 BR/LWFR 在公元 1965 年和 1978 年最为丰富。这两种异常现象主要在海拔最高的树木中观察到，并且都发生在整个生长季节温度低于平均温度的年份。从解剖学上讲，BR 和 LWFR 在管胞尺寸上没有显着差异，只是 LWFR 清楚地显示出与低于冰点温度相关的损坏。将 BR 和 LWFR 与“正常”年轮区别开来的主要特征是晚材次生壁厚的显着减少。在 P. longaeva 中，BR 像浅色晚材（浅色）环，是由于生长季节短而凉爽，导致管胞减少（或中断）木质化。在像 P. longaeva 这样生产极窄晚材的物种中，可能难以从宏观上识别浅晚材年份，因此将 BR 作为气候代理的微观研究在古气候研究中非常有用。