The Southern Ocean hosts complex connections between ocean physics, chemistry, and biology. Changes in these connections are hypothesized to be responsible for significant alterations of ocean biogeochemistry and carbon storage both on glacial‐interglacial timescales and in the future due to anthropogenic forcing. Isotopes of thorium (²³⁰Th and ²³²Th) and protactinium (²³¹Pa) have been widely applied as tools to study paleoceanographic conditions in the Southern Ocean. However, understanding of the chemical behavior of these isotopes in the modern Southern Ocean has been limited by a paucity of high‐resolution observations. In this study, we present measurements of dissolved ²³⁰Th, ²³¹Pa, and ²³²Th on a meridional transect along 170°W from 67°S to 54°S in the Pacific sector of the Southern Ocean, with high vertical and meridional sampling resolution. We find Th/Pa fractionation factors below 1, highlighting the preferential removal of Pa relative to Th in a region with low lithogenic inputs where the particle flux is dominated by biogenic opal. We also find steep gradients in all three of these isotopes along neutral density surfaces from north to south, demonstrating the importance of isopycnal mixing in transporting these nuclides to the Southern Ocean. Our results suggest that ²³¹Pa and ²³⁰Th in the Southern Ocean are highly sensitive tracers of physical transport that may find use in studies of Southern Ocean biogeochemical‐physical connections in the past, present, and future.

中文翻译：

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太平洋南部大洋中230Th和231Pa的等渗运移和清除

南大洋在海洋物理学，化学和生物学之间有着复杂的联系。这些联系的变化被认为是造成冰川生物间时间尺度上以及未来由于人为强迫而导致海洋生物地球化学和碳储存发生重大变化的原因。²³⁰（²³⁰ Th和²³² Th）和pro（²³¹ Pa）的同位素已被广泛用作研究南大洋古海洋条件的工具。但是，由于缺乏高分辨率的观测资料，对现代同位素在现代南大洋中化学行为的了解受到了限制。在这项研究中，我们介绍了溶解的²³⁰ Th，²³¹ Pa和在南大洋太平洋扇形断面中，从67°S到54°S在170°W上的²³² Th具有高的垂直和子午采样分辨率。我们发现Th / Pa的分馏因子低于1，这突出说明了在具有低成岩作用输入的区域（相对于Th而言），Pa优先去除，在该区域中，颗粒通量由生物蛋白石控制。我们还在中性密度表面上从北到南在所有这三种同位素中发现了陡峭的梯度，这说明了等密度混合在将这些核素运输到南大洋的重要性。我们的结果表明²³¹ Pa和²³⁰在南大洋中，物理运输的高灵敏度示踪剂可能在过去，现在和未来的南洋生物地球化学与物理联系的研究中有用。