Rare earth element (REE)–silicic acid complexes in seawater to explain the incorporation of REEs in opal and the “leftover” REEs in surface water: New interpretation of dissolved REE distribution profiles
Rare earth element (REE)–silicic acid complexes in seawater to explain the incorporation of REEs in opal and the “leftover” REEs in surface water: New interpretation of dissolved REE distribution profiles
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DOI：
10.1016/j.gca.2013.03.014
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发表时间：
2013-07
影响因子：
5
通讯作者：
T. Akagi
中科院分区：
文献类型：
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作者：
T. Akagi
鉴于硅藻蛋白石携带稀土元素 (REE) 的量超过了可以解释公海柱中 REE/Si 比率的新发现，人们对 REE 与硅酸的复合形成以及随后将复合物掺入硅藻蛋白石进行了探索。在物种计算中采用了报道的 EuH3SiO42+ 络合物形成常数以及常数与水解常数的经验线性关系。计算表明，稀土元素-硅酸复合物是溶解稀土元素的主要种类，尤其是在太平洋和大西洋的深层。复合物形成的程度取决于溶解的二氧化硅浓度、pH 值和 pCO2。假设只有 REEH3SiO42+ 形式的 REE 与溶解的二氧化硅一起从深水扩散/平流到地表水，才被纳入硅藻蛋白石中，因此开发了 REE 掺入理论。该理论将地表水中硅藻摄入的 REE 和二氧化硅与其在深水中的浓度联系起来，并提出了硅藻蛋白石中 REE 的两个分配系数 (D)，即针对地表水的常规 D 和针对深水的柱状 D，它们是 pH 和溶解二氧化硅浓度的函数。该理论成功解释了海洋表层水中显着的 REE 浓度水平（“剩余 REE”），并重现了硅藻蛋白石中的 REE 浓度，该浓度与在北太平洋硅藻蛋白石中观察到的浓度一致。海洋深水的稀土元素组成主要由两个分馏过程来解释：稀土元素掺入蛋白石和稀土元素的碳酸盐/氧化物清除。
In light of a new finding that diatom opal carries rare earth elements (REEs) at an amount exceeding that which would explain the REEs/Si ratio in open ocean columns, the complex formation of REEs with silicic acid and subsequent incorporation of the complex into diatom opal has been explored. Reported complex formation constants of EuH3SiO42+ and an empirical linear relationship of the constants with hydrolysis constants were employed in the species calculation. The calculation reveals that REE–silicic acid complex is the dominant species of dissolved REEs especially in deep layers of the Pacific and the Atlantic Oceans. The degree of complex formation varies depending on dissolved silica concentration, pH, and pCO2. Assuming that only REEs in the form of REEH3SiO42+, which is diffused/advected from deep water to surface water together with dissolved silica, are incorporated into diatom opal, a REE incorporation theory has been developed. The theory links the intake of REEs and silica by diatoms in surface water and their concentrations in deep water and presents two distribution coefficients (Ds) of REEs in diatom opal, conventional D against surface water and columnar D against deep water as functions of pH and dissolved silica concentration. The theory successfully explains the significant REE concentration level (“leftover REEs”) in the surface water of the oceans and reproduces a concentration of REEs in diatom opal that is consistent with that observed in diatom opal in the North Pacific Ocean. The REE composition of oceanic deep water is largely explained by two fractionation processes: REE incorporation into opal and carbonate/oxide scavenging of REEs.