The hydrology of Amazonia is changing due to climate and land-use changes, especially in the southern region, which has warmed and dried faster than other tropical regions. Yet there are no long-term hydrological records to put these changes in a historical perspective. Here we investigate the use of tree-ring carbon (δ¹³C) and oxygen isotopes (δ¹⁸O) to assess the seasonal variation in climate for the southern Amazonia basin. We analysed the intra-annual variation of δ¹³C and δ¹⁸O in 10 segments of each tree ring from 2013 to 2017 from individuals of Hymenaea courbaril, a long-lived and widespread neotropical tree species. We find strong seasonal patterns of tree-ring δ¹³C supporting previous observations of annual growth rhythms for this species. The intra-annual variation in δ¹⁸O shows that the lowest values generally occur just after the middle point of ring formation, corresponding to the peak rainy season. We find strong correlations between the δ¹⁸O in the middle of the growth ring and vapour pressure deficit (r = 0.92, P = 0.02) and precipitation (r = −0.93, P = 0.02). We further find associations between the oxygen isotopic series and the discharge of the Araguaia basin’s main rivers during the rainy period. Our results show that these δ¹⁸O records are sensitive to fluctuations in rainfall and humidity, and thus to river discharge in the region. Longer reconstructions of based on tree-ring δ¹⁸O of Hymenaea courbaril could provide a novel proxy to assess past hydrological changes.

由于气候和土地利用的变化，亚马逊流域的水文正在发生变化，特别是在南部地区，其变暖和干燥的速度比其他热带地区更快。然而，没有长期的水文记录可以从历史的角度来看待这些变化。在这里，我们研究使用树木年轮碳 (δ ¹³ C) 和氧同位素 (δ ¹⁸ O) 来评估亚马逊流域南部气候的季节性变化。我们分析了2013 年至 2017 年每个树轮 10 个节段的 δ 13 C 和 δ 18 O的^年内变化^，该树种是长寿且广泛分布的新热带树种。我们发现树木年轮 δ ¹³ C 的强烈季节性模式支持了先前对该物种年度生长节律的观察。^{δ 18} O的年内变化表明，最低值一般出现在环形成的中点之后，对应于雨季的高峰期。我们发现年轮中部的δ ^{18 O 与}水汽压差 (r = 0.92, P  = 0.02) 和降水量 (r = -0.93, P  = 0.02) 之间存在很强的相关性。我们进一步发现氧同位素系列与雨季阿拉瓜亚盆地主要河流的流量之间的关联。我们的结果表明，这些 δ ¹⁸ O 记录对降雨和湿度的波动敏感，因此对该地区的河流流量敏感。基于Hymenaea cobaril树轮 δ ¹⁸ O的较长重建可以为评估过去的水文变化提供新的代理。