Radium-228 as a tracer of dissolved trace element inputs from the Peruvian continental margin
Radium-228 as a tracer of dissolved trace element inputs from the Peruvian continental margin
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DOI：
10.1016/j.marchem.2017.05.008
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发表时间：
2017-05
期刊：
影响因子：
3
通讯作者：
V. Sanial;L. Kipp;P. Henderson;P. Beek;J. Reyss;D. Hammond;N. Hawco;M. Saito;J. Resing;P. Sedwick;W. Moore;M. Charette
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作者：
V. Sanial;L. Kipp;P. Henderson;P. Beek;J. Reyss;D. Hammond;N. Hawco;M. Saito;J. Resing;P. Sedwick;W. Moore;M. Charette
大陆边是海洋生态系统运作所必需的微量元素的重要来源，因此在海水的组成方面发挥着核心作用。在这里，我们测量了长寿命镭同位素（226 Ra，228 Ra）沿着12°S（美国GEOTRACES GP 16）在热带南太平洋东部的纬向样带。我们使用228 Ra来量化从秘鲁大陆架i）和ii）斜坡输送的微量元素和同位素（TEI）通量（DMn、DFe和DCo）。首先，在整个断面（~ 8500 km）的地表水中测量到了228 Ra的活动，这表明大陆架不仅是沿海地区，而且也是中太平洋沃茨沉积物来源的TEI的重要来源。模拟的228 Ra陆架通量结合水柱溶解TEI/228 Ra比率被用来量化DMn（3.3 × 103μmol m− 2 y − 1）、DFe（1.5 × 103μ mol m − 2 y − 1）和DCo（1.0 × 102μmol m − 2 y − 1）的陆架-海洋输入率（归一化为陆架面积）。第二，228 Ra，DFe和DMn的共同发生的羽状物从边缘延伸超过1800公里，深度为1000-2500米，表明大陆坡沉积物TEI输入到中间水柱。228 Ra梯度使我们能够推导出46 m2 s − 1的有效水平涡动扩散系数（Kh），这反过来又允许根据其近海浓度梯度计算坡面沉积物DMn（6.4 μmol m− 2 y − 1）和DFe（5.9 × 102μmol m− 2 y − 1）通量。在0-20°S的南太平洋大陆边缘尺度上，DMn陆架通量比陆坡通量约高2-3个数量级，而DFe陆架/陆坡通量约为3：1。大陆架和斜坡沉积物衍生DMn被运送到海洋内部的一个显着的距离，而DFe浓度梯度是陡峭的，与较长的水柱停留时间DMn相一致，在海洋系统中的DFe。这些发现突出了在海洋生物重要微量元素预算中考虑大陆坡-海洋边界的重要性。
Continental margins play a central role in the composition of seawater by being an important source of trace element essentials to the functioning of the ocean ecosystems. Here, we measured long-lived radium isotopes (226Ra,228Ra) along a zonal transect at 12°S (US GEOTRACES GP16) in the eastern tropical South Pacific Ocean. We used228Ra to quantify the trace element and isotope (TEI) fluxes (DMn, DFe, and DCo) delivered from the Peruvian continental i) shelf and ii) slope. First, elevated228Ra activities were measured in surface water over the entire transect (~ 8500 km), evidence that the continental shelf is an important source of sediment-derived TEIs not only to coastal areas, but to central Pacific Ocean waters. Modeled228Ra shelf fluxes combined with water column dissolved TEI/228Ra ratios were used to quantify the shelf-ocean input rates (normalized to shelf-area) for DMn (3.3 × 103μmol m− 2y− 1), DFe (1.5 × 103μmol m− 2y− 1), and DCo (1.0 × 102μmol m− 2y− 1). Second, co-occurring plumes of228Ra, DFe, and DMn extended over 1800 km from the margin at 1000–2500 m depth, indicative of a continental slope sediment TEI input to the intermediate water column. The228Ra gradient allowed us to derive an effective horizontal eddy diffusion coefficient (Kh) of 46 m2s− 1, which in turn permitted the calculation of slope sediment DMn (6.4 μmol m− 2y− 1) and DFe (5.9 × 102μmol m− 2y− 1) fluxes based on their offshore concentration gradients. On the scale of the South Pacific continental margin between 0–20°S, the DMn shelf flux is approximately 2–3 orders of magnitude higher than the slope flux, while the DFe shelf/slope flux is ~ 3:1. Both shelf and slope sediment derived DMn was transported over a significant distance towards the ocean interior, while DFe concentration gradients were steep, consistent with longer water column residence time for DMn as compared to DFe in marine systems. These findings highlight the importance of considering the continental slope-ocean boundary in the oceanic budgets of biologically-important trace elements.