Iodate in calcite, aragonite and vaterite CaCO3: Insights from first-principles calculations and implications for the I/Ca geochemical proxy
Iodate in calcite, aragonite and vaterite CaCO3: Insights from first-principles calculations and implications for the I/Ca geochemical proxy
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DOI：
10.1016/j.gca.2018.02.017
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发表时间：
2018-09
影响因子：
5
通讯作者：
Xiaolei Feng;S. Redfern
中科院分区：
文献类型：
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作者：
Xiaolei Feng;S. Redfern
采用第一性原理计算模拟的三个多晶型的碳酸钙-方解石，文石和球文石，碘的掺入进行了比较。在每种情况下，碘最容易以碘酸盐（IO 3 −）的形式被容纳在碳酸盐位点上。碘酸盐溶质原子周围的局部应变场显示在对分布函数的松弛结构，这表明文石显示最大程度的局部结构畸变，而球文石是相对不受影响。碘酸盐掺入的能量损失在球霰石中最小，在文石中最大，这意味着碘将以球霰石>方解石>文石的顺序在碳酸钙多晶型物之间显示出显著的分配。此外，我们发现，微量碘掺入球霰石赋予改善的机械强度球霰石晶体。我们的研究结果支持的假设，碘被纳入碘酸盐内的生物碳酸盐，重要的应用程序中的I/Ca数据在古海洋氧代研究。我们的观察，碘酸盐是最容易容纳到球文石意味着球文石的存在下，在任何生物钙化过程中，无论是作为最终产品或前体，应考虑到当应用的I/Ca地球化学代理。
The incorporation of iodine into each of the three polymorphs of CaCO3– calcite, aragonite and vaterite, is compared using first-principles computational simulation. In each case iodine is most easily accommodated as iodate (IO3−) onto the carbonate site. Local strain fields around the iodate solute atom are revealed in the pair distribution functions for the relaxed structures, which indicate that aragonite displays the greatest degree of local structural distortion while vaterite is relatively unaffected. The energy penalty for iodate incorporation is least significant in vaterite, and greatest in aragonite, with the implication that iodine will display significant partitioning between calcium carbonate polymorphs in the order vaterite > calcite > aragonite. Furthermore, we find that trace iodine incorporation into vaterite confers improved mechanical strength to vaterite crystals. Our results support the supposition that iodine is incorporated as iodate within biogenic carbonates, important in the application of I/Ca data in palaeoproxy studies of ocean oxygenation. Our observation that iodate is most easily accommodated into vaterite implies that the presence of vaterite in any biocalcification process, be it as an end-product or a precursor, should be taken into account when applying the I/Ca geochemical proxy.