Rare earth elements (REEs) in the tropical South Atlantic and quantitative deconvolution of their non-conservative behavior
Rare earth elements (REEs) in the tropical South Atlantic and quantitative deconvolution of their non-conservative behavior
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DOI：
10.1016/j.gca.2016.01.018
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发表时间：
2016-03
影响因子：
5
通讯作者：
Xin-Yuan Zheng;Y. Plancherel;M. Saito;Peter Scott;G. Henderson
中科院分区：
文献类型：
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作者：
Xin-Yuan Zheng;Y. Plancherel;M. Saito;Peter Scott;G. Henderson
本研究提出了新的溶解稀土元素（dREE）的浓度测量沿整个深度横跨热带南大西洋（沿着，并使用这些数据来调查海洋循环的稀土元素。富集dREE，与铁锰氧化物的氧化还原循环，观察在最低限度的氧区（OMZ）非洲大陆架。对于深水，开发了一个多参数混合模型，以反卷积物理迁移的相对重要性（即，水团混合）对深大西洋dREE分布的地球化学控制。这种方法使稀土元素循环中涉及的化学过程，不明显的单独测量，被区分和量化。结果表明，1000 m以下测得的稀土元素浓度主要受水团混合产生的稀土元素浓度控制（>75%）。这一结果表明，在大西洋深水沃茨中观测到的REE和溶解Si之间的线性相关性是由于这些示踪剂的主要保守行为，而不是由于影响REE和Si的类似化学过程。在巴西盆地深部（> 4000 m）观察到少量dREE的增加（dNd约10%，dYb约5%），这是由于颗粒原位或沿沿着的矿化作用所致，在靠近非洲大陆边缘的安哥拉盆地，dREE的增加在1500 m和4000 m以下，dNd约25%，dYb约20%。铈异常表明，不同的来源是负责这些dREE添加羽。1500米的过量是最有可能归因于dREE从铁氧化物的释放，而4000米的过量可能是由于方解石的矿化。安哥拉盆地中较高的颗粒通量和较缓慢的海洋环流可以解释为什么该盆地中的dREE过量显著高于巴西盆地中观察到的。大西洋中脊热液喷流对轻稀土元素起到区域性净汇的作用，但对重稀土元素的净收支影响不大。密集的REE测量与水团反褶积相结合，提供定量评估的相对作用的物理和地球化学过程中的海洋稀土元素循环。
This study presents new concentration measurements of dissolved rare earth elements (dREEs) along a full-depth east–west section across the tropical South Atlantic (∼12°S), and uses these data to investigate the oceanic cycling of the REEs. Enrichment ofdREEs, associated with the redox cycling of Fe–Mn oxides, is observed in the oxygen minimum zone (OMZ) off the African shelf. For deeper-waters, a multi-parameter mixing model was developed to deconvolve the relative importance of physical transport (i.e., water mass mixing) from biogeochemical controls on thedREE distribution in the deep Atlantic. This approach enables chemical processes involved in REE cycling, not apparent from the measurements alone, to be distinguished and quantified. Results show that the measureddREE concentrations below ∼1000 m are dominantly controlled (>75%) by preformed REE concentrations resulting from water mass mixing. This result indicates that the linear correlation betweendREEs and dissolved Si observed in Atlantic deep waters results from the dominantly conservative behavior of these tracers, rather than from similar chemical processes influencing bothdREEs and Si. Minor addition ofdREEs (∼10% ofdNd and ∼5% ofdYb) is observed in the deep (>∼4000 m) Brazil Basin, resulting from either remineralization of particlesin-situor along the flow path. Greater addition ofdREEs (up to 25% fordNd and 20% fordYb) is found at ∼1500 m and below ∼4000 m in the Angola Basin near the African continental margin. Cerium anomalies suggest that different sources are responsible for thesedREE addition plumes. The 1500 m excess is most likely attributed todREE release from Fe oxides, whereas the 4000 m excess may be due to remineralization of calcite. Higher particulate fluxes and a more sluggish ocean circulation in the Angola Basin may explain why thedREE excesses in this basin are significantly higher than that observed in the Brazil Basin. Hydrothermal venting over the mid-Atlantic ridge acts as a regional net sink for light REEs, but has little influence on the net budget of heavy REEs. The combination of dense REE measurements with water mass deconvolution is shown to provide quantitative assessment of the relative roles of physical and biogeochemical processes in the oceanic cycling of REEs.