The stable oxygen isotope ratios of whole tree-ring α-cellulose (δO) have been interpreted as an indicator of early summer hydroclimate in the Meiyu region of East Asia. However, the underlying physical mechanism often remains unclear. Here we provide a mechanistic understanding through intra-annual tree-ring oxygen isotope analysis and process-based δO modelling over the period 1979–2006. The selected tree species for analysis is , whose δO exhibit the strongest linear relationship with relative humidity (RH) in June. The results indicated that the June RH signal is predominantly contained in tree-ring earlywood rather than latewood. The strong response of δO to June RH is not due to the legacy effect. Using the proxy system model (PSM) of δO, we obtained a modeled δO time series that is significantly positively correlated with the measured δO time series. The modeled and measured δO series show similar relationships with monthly RH. Sensitivity experiments with PSM revealed that the June RH signal is originated from the oxygen isotopes of source water and leaf water. Rapid cellulose formation in June plays a role in enhancing the June RH signal. Our study demonstrates how δO record early summer hydroclimate signals from a process perspective, and that the PSM is effective in modelling the interannual δO variability in the Meiyu region.

中文翻译：

---

使用东亚梅雨地区的代理系统模型破译水文气候信号到树轮δ18O的传递


整个树轮α-纤维素（δ18O）的稳定氧同位素比率被解释为东亚梅雨地区初夏水气候的指标。然而，潜在的物理机制通常仍不清楚。在此，我们通过 1979 年至 2006 年期间的年轮氧同位素分析和基于过程的 δ18O 建模提供了机制理解。选取的树种为 ，其 δ18O 值与 6 月份相对湿度 (RH) 的线性关系最强。结果表明，6月相对湿度信号主要包含在树轮早材中，而不是晚材中。 δ18O 对 6 月相对湿度的强烈响应并不是由于遗留效应。使用 δ18O 代理系统模型（PSM），我们获得了建模的 δ18O 时间序列，该序列与测量的 δ18O 时间序列显着正相关。建模和测量的 δ18O 系列显示与每月相对湿度相似的关系。 PSM 灵敏度实验表明，6 月相对湿度信号源自源水和叶水的氧同位素。 6 月份纤维素的快速形成对增强 6 月份相对湿度信号起到了一定作用。我们的研究证明了 δ18O 如何从过程角度记录初夏水文气候信号，并且 PSM 可以有效地模拟梅雨地区 δ18O 年际变化。