Beryllium isotopes (stable 9Be and cosmogenic meteoric 10Be) enter the oceans through distinct pathways – i.e., from the continents and the atmosphere respectively – and display non-conservative behaviour in seawater. This isotope system has served as a powerful tool for quantifying a variety of processes, including geomagnetism, sedimentation, continental input, and ocean circulation. However, processes at land–ocean boundaries and within the ocean interior may either amplify or buffer the seawater isotope response to environmental changes. In the last decade, substantial effort has been invested in understanding external sources and internal cycling of Be isotopes, offering an excellent opportunity to revisit their modern oceanic cycle. Here, we investigate the controls on the modern oceanic cycling of Be isotopes using a three-dimensional ocean model, constrained by observational data on input fluxes and water-column distributions of 9Be and 10Be. In addition to modelling the previously known controls, we highlight the key role of marine benthic fluxes and scavenging onto particulate organic matter and opal in determining the mass balance and spatial distribution of Be isotopes. Inter-basin Be transport by the circulation is less important than external inputs at continent/atmosphere–ocean boundaries, except in the South Pacific. Therefore, the distribution of seawater 10Be/9Be ratios largely reflects that of the external inputs in most basins in the modern ocean. Finally, we apply our data-constrained mechanistic model to test the sensitivity of basin-wide 10Be/9Be ratios to changes of external sources and internal cycling. This analysis shows that seawater 10Be/9Be ratios are to some extent buffered against changes in continental denudation. For example, a 50 % decrease in denudation rates results in a 13–48 % increase in ocean-wide 10Be/9Be ratios. Moreover, the interplay between particle scavenging and ocean circulation can cause divergent responses in 10Be/9Be ratios in different basins. Weaker scavenging (e.g., 50 % decrease in intensity) would increase the homogenising effect of ocean circulation, making North Atlantic and North Pacific 10Be/9Be ratios converge (∼20 % change in isotope ratios). The mechanistic understanding developed from this Be cycling model provides important insights into the various applications of marine Be isotopes, and offers additional tools to assess the causes of spatio-temporal Be isotope variations. We also identify the key oceanic processes that require further constraints to achieve a complete understanding of Be cycling in the modern ocean and back through time.

中文翻译：

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使用数据受限的生物地球化学模型评估铍同位素的现代海洋循环


铍同位素（稳定的 9Be 和宇宙成因陨石 10Be）通过不同的途径进入海洋——即分别从大陆和大气中进入——并在海水中表现出非保守的行为。这种同位素系统已成为量化各种过程的强大工具，包括地磁、沉积、大陆输入和海洋环流。然而，陆地-海洋边界和海洋内部的过程可能会放大或缓冲海水同位素对环境变化的反应。在过去的十年中，人们投入了大量精力来了解铍同位素的外部来源和内部循环，为重新审视其现代海洋循环提供了绝佳的机会。在这里，我们使用三维海洋模型研究了对 Be 同位素现代海洋循环的控制，该模型受 9Be 和 10Be 的输入通量和水柱分布的观测数据的约束。除了对以前已知的控制措施进行建模外，我们还强调了海洋底栖通量和对颗粒有机物和蛋白石的清除在确定 Be 同位素的质量平衡和空间分布方面的关键作用。除南太平洋外，环流的流域间运输不如大陆/大气-海洋边界的外部输入重要。因此，海水 10Be/9Be 比率的分布在很大程度上反映了现代海洋中大多数流域的外部输入分布。最后，我们应用数据约束的机理模型来测试流域范围的 10Be/9Be 比率对外部来源和内部循环变化的敏感性。该分析表明，海水 10Be/9Be 比率在一定程度上缓冲了大陆剥蚀的变化。 例如，剥蚀率降低 50% 会导致全洋 10Be/9Be 比率增加 13-48%。此外，颗粒清除和海洋环流之间的相互作用会导致不同流域中 10Be/9Be 比率的响应不同。较弱的清除（例如，强度降低 50%）会增加海洋环流的均质化效应，使北大西洋和北太平洋的 10Be/9Be 比率趋同（同位素比率变化约 20%）。从该 Be 循环模型中发展出的机理理解为海洋 Be 同位素的各种应用提供了重要见解，并为评估时空 Be 同位素变化的原因提供了额外的工具。我们还确定了需要进一步约束才能全面理解 Be 在现代海洋中循环和返回时间的关键海洋过程。