The African baobab, Adansonia digitata L., has great paleoclimatological potential because of its wide distributional range and millennial length life span. However, dendroclimatological approaches are hampered by dating uncertainties due to its unique, parenchyma-dominated stem anatomy. Here, securely dated time series of annual wood increment growth and intra-ring stable isotopes of carbon and oxygen of cellulose for a baobab tree from Oman covering 1941 to 2005 were established and tested for relationships to hydroclimate variability. Precise dating with the atomic bomb peak (ABP) using highly resolved ¹⁴C measurements confirmed the annual character of the baobab's growth rings. F¹⁴C values of tree-ring cellulose were found up to 8.8 % lower than in the corresponding atmospheric CO₂ for the period around the ABP, which in conjunction with a considerable autocorrelation of the δ¹³C series points to the incorporation of previous year's carbon contributing to the average age of intra-ring wood samples. F¹⁴C of terminal parenchyma bands, marking the tree-ring boundaries, were found to be considerably younger than their corresponding tree ring, indicating that parenchyma tissue is alive for many years, probably undergoing cell division and structural reorganization and contributing to secondary growth. In contrast to the δ¹³C time series, no significant autocorrelation was found in the δ¹⁸O series of tree-ring cellulose despite the enormous water storage potential of this stem-succulent tree species. Year-to-year variability in tree-ring width and stable isotope ratios revealed radial stem growth and the geochemistry of wood cellulose are influenced by fluctuations in the hydroclimate. In particular, δ¹⁸O was found to be a good climate proxy, followed by tree-ring width and δ¹³C. Tree-ring width and intra-ring δ¹⁸O_min correlated well with each other and with precipitation amount for the period from pre-monsoon May to the end of the monsoon season in September/October. Intra-annual stable isotope courses were found to be rather similar for both δ¹³C and δ¹⁸O. Years with particularly low monsoon rain were reflected by increased stable isotope values in the mid-section of intra-annual courses. Distinct patterns with low subseasonal isotope values seem indicative for years with heavy rainfall events from pre-monsoonal cyclones. Rain events from post-monsoonal cyclones may also be recorded; however, only 2 years of observation prevented a more conclusive evaluation.

中文翻译：

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非洲猴面包树木材中亚季节稳定同位素信号的高分辨率¹⁴ C 炸弹峰值测年和气候响应分析——来自阿曼的案例研究

非洲猴面包树，Adansonia digitata L.，由于其广泛的分布范围和千年的寿命，具有巨大的古气候学潜力。然而，树木气候学方法因其独特的、以薄壁组织为主的茎解剖结构而受到年代不确定性的阻碍。在这里，建立了涵盖 1941 年至 2005 年的阿曼猴面包树的年度木材增量生长和环内纤维素碳氧稳定同位素的安全日期时间序列，并测试了与水文气候变化的关系。使用高分辨率¹⁴ C 测量对原子弹峰 (ABP) 进行精确测年证实了猴面包树年轮的年度特征。˚F ¹⁴发现树木年轮纤维素的 C 值比 ABP 周围时期相应的大气 CO ₂中的C 值低 8.8 % ，这与δ ¹³ C 系列的相当大的自相关性一起表明加入了前一年的碳贡献到环内木材样品的平均年龄。发现标志着树木年轮边界的末端薄壁组织带的F ¹⁴ C 比其相应的树木年轮年轻得多，表明薄壁组织组织存活多年，可能正在经历细胞分裂和结构重组并促进次生生长。与δ ¹³ C 时间序列相比，在尽管这种茎肉质树种具有巨大的储水潜力，但δ ¹⁸ O 系列的树轮纤维素。树木年轮宽度和稳定同位素比率的逐年变化表明径向茎生长和木质纤维素的地球化学受水文气候波动的影响。特别是，发现δ ¹⁸ O 是一个很好的气候代理，其次是年轮宽度和δ ¹³ C。年轮宽度和年轮内 δ ¹⁸ O _min彼此相关并且与该时期的降水量相关从 5 月季风前到 9/10 月季风季节结束。发现两者的年内稳定同位素过程相当相似δ ¹³ C 和δ ¹⁸ O。季风降雨特别少的年份反映在年内过程中段稳定同位素值的增加。具有低亚季节同位素值的不同模式似乎预示着季风前气旋产生强降雨事件的年份。季风后气旋的降雨事件也可能被记录；然而，仅仅 2 年的观察阻止了更结论性的评估。