Stable barium isotopes are a potential proxy for riverine inputs into the ocean that reflect monsoon variability and climate change. However, dissolved Ba isotope (δ¹³⁸Ba_DBa) geochemistry in river estuaries, a dynamic land to ocean transition zone, has rarely been systematically examined to date. Here, we show that significant Ba isotope fractionation occurs at near-zero salinities in the Yangtze and Pearl River Estuary, whereas conservative mixing dominates δ¹³⁸Ba_DBa distributions beyond low salinities, which are well predicted by an ion exchange model. Elevated δ¹³⁸Ba_DBa in the river endmember results from preferential removal of light Ba isotopes by adsorption to fluvial particles. Subsequently, δ¹³⁸Ba_DBa rapidly drops to minimum signatures at increased salinities indicating particle desorption of isotopically light Ba. Nevertheless, the apparently conservative δ¹³⁸Ba_DBa-salinity relationship beyond the low-salinity minimum in both estuaries provides a modern calibration for using Ba isotopes as a proxy for paleosalinity and river water inputs into the ocean.

中文翻译：

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河口混合过程中稳定的钡同位素动力学

稳定的钡同位素是反映季风变率和气候变化的河流输入海洋的潜在代表。然而，迄今为止，河流河口（一个动态的陆地到海洋的过渡带）中溶解的 Ba 同位素 (δ ¹³⁸ Ba _DBa ) 地球化学很少被系统地研究过。在这里，我们表明在长江和珠江口的接近零盐度处发生显着的 Ba 同位素分馏，而保守混合在低盐度以外的δ ¹³⁸ Ba _DBa分布中占主导地位，这可以通过离子交换模型很好地预测。升高的 δ ¹³⁸ Ba _DBa在河流端元中，由于吸附到河流颗粒上优先去除轻 Ba 同位素。随后，δ ¹³⁸ Ba _DBa在盐度增加时迅速下降到最小特征，表明同位素轻 Ba 的粒子解吸。然而，明显保守的 δ ¹³⁸ Ba _DBa - 盐度关系超出了两个河口的低盐度最小值，为使用 Ba 同位素作为古盐度和河水输入海洋的代理提供了现代校准。