Oxygen isotopes in stream water can serve as natural tracers of watershed dynamics. Freshwater pearl mussels provide δ18Owater estimates that overcome temporal and spatial limitations of instrumental records. The reliability of shell‐based δ18Owater reconstructions depends on understanding which shell layer biomineralizes closer to oxygen isotopic equilibrium with ambient water. To determine this, both the (outer) prismatic and (inner) nacreous sublayers of the outer shell layer were sampled. Over 2500 isotope values were obtained from shells collected from the Our River (Luxembourg) and from mussels cultured in tanks at constant temperature and monitored δ18Owater. Calculated δ18Owater from the prismatic portion was in excellent agreement with monitored δ18Owater, while δ18Oshell of the nacreous portion was systematically offset by +0.43‰, overestimating δ18Owater by +0.53‰. Although shell portions were formed simultaneously from the same extrapallial fluid, they underwent different fractionation mechanisms, presumably due to differences in carbonic anhydrase activity catalyzing mineralization processes.

中文翻译：

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淡水珍珠贻贝 (Margaritifera margaritifera) 超微结构不同壳部分的生物驱动同位素分馏：对溪流水 δ18O 重建的影响


溪水中的氧同位素可以作为流域动态的天然示踪剂。淡水珍珠贻贝提供 δ 18氧水克服仪器记录的时间和空间限制的估计。基于壳的δ的可靠性18氧水重建取决于了解哪个壳层生物矿化更接近与环境水的氧同位素平衡。为了确定这一点，对外壳层的（外）棱柱和（内）珠光亚层进行了取样。从我们河（卢森堡）收集的贝壳以及在恒温水箱中培养并监测 δ 的贻贝中获得了 2500 多个同位素值18氧水。计算值 δ 18氧水棱柱部分与监测到的 δ 非常一致18氧水，而 δ 18氧壳珠光部分的值被系统地抵消了 +0.43‰，高估了 δ 18氧水+0.53‰。尽管壳部分是由相同的外皮液体同时形成的，但它们经历了不同的分馏机制，这可能是由于催化矿化过程的碳酸酐酶活性的差异所致。