Oxygen isotope ratios (δ¹⁸O) of tree-ring cellulose are a novel proxy for summer hydroclimate in monsoonal Asia. In central Japan, we collected 67 conifer wood samples, mainly Chamaecyparis obtusa, with ages encompassing the past 2600 years. The samples were taken from living trees, archeological wood, architectural wood, and buried logs. We analyzed stable isotope ratios of oxygen (δ¹⁸O) and hydrogen (δ²H) in tree-ring cellulose in these samples (more than 15 000 rings in total) without using a pooling method and constructed a statistically reliable tree-ring cellulose δ¹⁸O time series for the past 2500 years. However, there were distinct age trends and level offsets in the δ¹⁸O record, and cellulose δ¹⁸O values showed a gradual decrease as an individual tree matures. This suggested it is difficult to establish a cellulose δ¹⁸O chronology for low-frequency signals by simple averaging of all the δ¹⁸O time series data. In addition, there were opposite age trends in the cellulose δ²H, and δ²H gradually increased with tree age. There were clear positive correlations in the short-periodicity variations between δ¹⁸O and δ²H, probably indicating a common climate signal. A comparison of the δ¹⁸O and δ²H time series in individual trees with tree-ring width suggested that the opposite age trends of δ¹⁸O and δ²H are caused by temporal changes in the degree of post-photosynthetic isotope exchange with xylem water (physiological effect), accompanied by changes in stem growth rate that are influenced by human activity in the forests of central Japan. Based on the assumptions that cellulose δ¹⁸O and δ²H vary positively and negatively with constant proportional coefficients due to climatological and physiological effects, respectively, we solved simultaneous equations for the climatological and physiological components of variations in tree-ring cellulose δ¹⁸O and δ²H in order to remove the age trend. This enabled us to evaluate the climatic record from cellulose δ¹⁸O variations. The extracted climatological component in the cellulose δ¹⁸O for the past 2600 years in central Japan was well correlated with numerous instrumental, historical, and paleoclimatological records of past summer climate at various spatial and temporal scales. This indicates that integration of tree-ring cellulose δ¹⁸O and δ²H data is a promising method to reconstruct past summer climate variations on annual to millennial timescales, irrespective of the growth environment. However, analytical and statistical methods need to be improved for further development of this climate proxy.

中文翻译：

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通过整合树木年轮中稳定的氧和氢同位素，在日本中部进行了2600年的夏季气候重建

氧同位素比率（δ ¹⁸ O）树轮纤维素的是用于季风亚夏季hydroclimate一种新颖的代理。在日本中部，我们收集了67个针叶木材样本，主要是Chamaecyparis obtusa，其年龄涵盖了过去2600年。样品取自活树，考古木，建筑木和埋木。我们分析了氧的稳定同位素比率（δ ¹⁸ O）和氢（δ ² H）在树轮纤维素这些样品（超过15个000环总共）在不使用池的方法和构建的统计学上可靠的树轮纤维素δ ¹⁸过去2500年的时间序列。然而，有明显的年龄趋势和水平偏移的δ ¹⁸ Ø记录和纤维素δ ^18个O值呈逐渐下降作为一个单独的树的成熟。这表明它是难以建立一个纤维素δ ¹⁸由所有的简单平均直径：年表为低频信号δ ¹⁸ O时间序列数据。此外，有在纤维素对面年龄趋势δ ² H和δ ² H带树龄逐渐增加。有在之间的短周期性变化清晰正相关δ ¹⁸ O和δ² H，可能表示一个共同的气候信号。所述的比较δ ¹⁸ O和δ ²与年轮个别树木ħ时间序列宽度建议的相对年龄趋势δ ¹⁸ O和δ ² H的通过与后光合同位素交换的程度随时间的变化引起的木质部水（生理效应），伴随茎生长速率的变化，该变化受人类在日本中部森林中活动的影响。基于以下假设：纤维素δ ¹⁸ O和δ ²ħ变化正和负恒定比例系数由于气候和生理作用，分别，我们解决了联立方程对树轮纤维素变化的气候和生理部件δ ¹⁸ O和δ ²以除去年龄趋势小时。这使我们能够评估从纤维素气候记录δ ^18种Ø变化。在纤维素提取的气候分量δ ¹⁸在日本中部，过去2600年的O与各种时空尺度的过去夏季气候的许多仪器，历史和古气候记录有着很好的相关性。这表明，整合树轮纤维素的δ ¹⁸ O和δ ² H数据是重建上年度到千年时间尺度过去夏季气候变化，而不管生长环境的一个有前途的方法。但是，需要进一步改进分析和统计方法以进一步开发这种气候替代指标。