Sodium incorporation into inorganic CaCO3 and implications for biogenic carbonates
Sodium incorporation into inorganic CaCO3 and implications for biogenic carbonates
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DOI：
10.1016/j.gca.2021.07.024
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发表时间：
2021-10-13
影响因子：
5
通讯作者：
Reichart, G-J
中科院分区：
文献类型：
--
作者：
Devriendt, L. S.;Mezger, E. M.;Reichart, G-J
生物碳酸盐的钠含量显示出潜在的古海洋代理盐度和/或钙浓度，但无机和生物方解石的Na+的掺入知之甚少。分类和同种的变化，在敏感性的碳酸盐钠/钙海水Na+/Ca 2+和盐度点的生物影响Na+分区和/或与其他环境参数的协变。在钙化过程中的生物控制的一个主要未知的是矿物沉淀的速度，它有一个很强的控制微量元素的无机碳酸盐系统的分区。我们进行了无机CaCO 3沉淀实验，其中溶液组成和晶体生长速率对碳酸盐晶体吸收Na+的影响进行了独立评估。方解石晶体以10（-6.）5 ~ 10（-4.5）mol/m（2）/s，而大于10（-4.5）mol/m（2）/s的生长速率导致文石和球文石的共沉淀。在一定的晶体生长速率下，溶液（Na+）（2）/Ca ~（2+）活度比每增加1%，方解石Na/Ca增加0.22%。然而，方解石钠/钙增加高达五倍，每增加一个数量级的晶体生长速率，这表明晶体生长速率和前体阶段可能是海洋碳酸盐钠/钙的主要控制。我们使用这些结果的框架中的DePaolo（2011年）模型的微量元素的方解石吸收，以评估变量（Na/Ca）（有孔虫）敏感性的起源[Ca 2 +]（海水）r和盐度。最后，根据已知的碳酸盐Na/Ca和海水的（Na+）（2）/Ca ~（2+）活度比，估算了一系列海相碳酸盐的最大矿物生长速率。估计速率从10（-5.6）（浮游有孔虫）到10（-4）（海胆）mol/m（2）/s不等。如此高的矿物生长速率意味着方解石的过饱和度很高（10至>100），支持了海洋生物碳酸盐中记录的元素分配和同位素分馏受动力学而不是平衡交换控制的观点。(C)2021作者（S）由爱思唯尔有限公司发布
The sodium content of biogenic carbonates shows potential as a palaeoceanographic proxy for salinity and/or calcium concentration but the incorporation of Na+ into inorganic and biogenic calcite is poorly understood. Taxonomic and conspecific variations in the sensitivity of carbonate Na/Ca to seawater Na+/Ca2+ and salinity point to a biological influence on Na+ partitioning and/or covariations with other environmental parameters. One major unknown of the biological control during calcification is the rate of mineral precipitation, which has a strong control on trace-element partitioning in inorganic carbonate systems. We conducted inorganic CaCO3 precipitation experiments where the effect of solution composition and crystal growth rate on Na+ uptake by carbonate crystals are independently assessed. Calcite crystals were precipitated at rates varying from 10(-6.)5 to 10(-4.5) mol/m(2)/s, while faster growth rate than 10(-4.5) mol/m(2)/s resulted in the coprecipitation of aragonite and vaterite. For a given crystal growth rate, calcite Na/Ca increases by 0.22% per % increase in solution (Na+)(2)/Ca2+ activity ratio. However, calcite Na/Ca increases up to fivefold per order of magnitude increase in crystal growth rate, suggesting crystal growth rate and precursor phases are likely dominant controls on marine carbonate Na/Ca. We use these results in the framework of the DePaolo (2011) model for trace element uptake by calcite to assess the origin of variable (Na/Ca)(foraminifer) sensitivities to [Ca2+](seawate)r and salinity. Last, maximum mineral growth rates are estimated for a range of marine carbonates based on known carbonate Na/Ca and the (Na+)(2)/Ca2+ activity ratio of seawater. Estimated rates vary from 10(-5.6) (planktic foraminifers) to above 10(-4) (sea urchins) mol/m(2)/s. Such high mineral growth rates imply high degrees of oversaturation with respect to calcite (10 to >100), supporting the idea that elemental partitioning and isotopic fractionation recorded in marine biogenic carbonates are controlled by kinetic rather than equilibrium exchanges. (C) 2021 The Author(s). Published by Elsevier Ltd.