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Tropical mangrove forests as a source of dissolved rare earth elements and yttrium to the ocean
Chemical Geology ( IF 3.6 ) Pub Date : 2021-04-24 , DOI: 10.1016/j.chemgeo.2021.120278
Duc Huy Dang , Zhirou Zhang , Wei Wang , Benjamin Oursel , Farid Juillot , Cecile Dupouy , Hugues Lemonnier , Stephane Mounier

Rare earth elements (REEs) and Y, or REYs, are commonly used as geochemical proxies for water chemistry, history of the continental crust and provenance studies. At the continent-ocean interface, the estuarine geochemistry of REYs is commonly thought to be driven by large-scale removal of the dissolved fraction. Consequently, contributions of river-borne dissolved REYs to the marine budget are assumed to represent a minor fraction of the total flux. Here, we report a significant release of dissolved REYs, together with a fractionation between light REEs, heavy REEs and Y, in the tropical mangrove estuaries of New Caledonia. These observations were associated with biogeochemical processes of the redox-dynamic mangrove system, rather than a possible contribution of REYs from a fresh groundwater source, based on stable water isotope compositions. These findings imply that tropical mangrove estuaries may act as a sizeable source of REYs to the ocean rather than buffer zones, at least for the dissolved fraction. We also extrapolated our data to compute the contributions of dissolved REY fluxes from the mangroves to global oceans. This preliminary calculation suggests that the mangrove system supplies 2.6-5% of global river-borne dissolved Nd, an REE with the most comprehensive mass balance. Therefore, given that the ocean mass budget of REYs remains unbalanced with fluxes missing on a global scale, considering the mangrove system as an input of oceanic mass balance models may help balance the global distribution of REYs.



中文翻译:

热带红树林森林是海洋中溶解的稀土元素和钇的来源

稀土元素(REE)和Y或REY通常用作水化学,大陆结壳历史和物源研究的地球化学替代物。在大陆与海洋的交界处,人们普遍认为REYs的河口地球化学是由大规模去除溶解部分驱动的。因此,假定河流溶解的REY对海洋预算的贡献仅占总通量的一小部分。在这里,我们报告了新喀里多尼亚热带红树林河口中溶解的REY的大量释放,以及轻稀土,重稀土和Y之间的分离。这些观察结果与氧化还原动力红树林系统的生物地球化学过程有关,而不是基于稳定的水同位素组成,来自新鲜地下水源的REY的可能贡献。这些发现暗示,至少对于溶解部分而言,热带红树林河口可以作为向海洋而不是缓冲区带提供大量REY的来源。我们还推断了我们的数据,以计算从红树林到全球海洋的溶解REY通量的贡献。这一初步计算表明,红树林系统提供了全球河流传播的溶解Nd的2.6%至5%,这是一种最全面的质量平衡的REE。因此,鉴于REYs的海洋质量预算仍然不平衡,并且全球范围内缺少通量,因此将红树林系统作为海洋质量平衡模型的输入可以帮助平衡REYs的全球分布。我们还推断了我们的数据,以计算从红树林到全球海洋的溶解REY通量的贡献。这一初步计算表明,红树林系统提供了全球河流传播的溶解Nd的2.6%至5%,这是一种最全面的质量平衡的REE。因此,鉴于REYs的海洋质量预算仍然不平衡,并且全球范围内缺少通量,因此将红树林系统作为海洋质量平衡模型的输入可以帮助平衡REYs的全球分布。我们还推断了我们的数据,以计算从红树林到全球海洋的溶解REY通量的贡献。此初步计算表明,红树林系统提供了全球河道溶解Nd的2.6-5%,这是一种质量平衡最全面的REE。因此,鉴于REYs的海洋质量预算仍然不平衡,并且全球范围内缺少通量,因此将红树林系统作为海洋质量平衡模型的输入可以帮助平衡REYs的全球分布。

更新日期:2021-04-24
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