ABSTRACT Freshwater bivalve shell oxygen isotope values (δ18OS) may act as a recorder of river δ18O variations that can then be interpreted in terms of hydrology (e.g. precipitation–evaporation balance, precipitation and river discharge patterns). We investigated the potential of this proxy measured across the hinge of South American unionid shells: Anodontites elongatus collected in Peru and A. trapesialis in Brazil. The isotopic signatures were reproducible between individuals of the same species. A. trapesialis clearly showed a strong δ18OS cyclicity in accordance with its growth patterns while A. elongatus presented less clear δ18OS with lower amplitude. We confirm that the deposition of successive growth lines and increments is annual, with growth line corresponding to the wet season. Also, we suggest that low amplitude of δ18OS in the A. elongatus shells indicates a habitat close to the river while large amplitude of δ18OS cycles observed in A. trapesialis shells would reflect a floodplain lake habitat, seasonally disconnected from the river and thus subjected to higher seasonal fluctuations in water δ18O. Considering these promising first results, future studies could be directed towards the use of fossil shells to reconstruct the past and present hydrological and geochemical conditions of the Amazon.

中文翻译：

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作为亚马逊河流水文地球化学记录器的淡水双壳贝壳中的季节性氧同位素变化

摘要淡水双壳贝壳氧同位素值 (δ18OS) 可以作为河流 δ18O 变化的记录器，然后可以根据水文（例如降水-蒸发平衡、降水和河流流量模式）进行解释。我们调查了在南美 unionid 贝壳铰链处测量的这种代理的潜力：在秘鲁收集的 Anodontites elongatus 和巴西的 A. trapesialis。同位素特征在同一物种的个体之间是可重复的。A. trapesialis 清楚地显示出与其生长模式一致的强烈 δ18OS 周期性，而 A. elongatus 则表现出不太清楚的 δ18OS 振幅较低。我们确认连续生长线和增量的沉积是年度的，生长线对应于雨季。此外，我们建议 A 中 δ18OS 的低振幅。elongatus 贝壳表明栖息地靠近河流，而在 A. trapesialis 贝壳中观察到的大振幅 δ18OS 循环将反映泛滥平原湖泊栖息地，季节性地与河流断开连接，因此受到水 δ18O 更高的季节性波动。考虑到这些有希望的初步结果，未来的研究可以针对使用化石贝壳来重建亚马逊过去和现在的水文和地球化学条件。