Calibration of Na partitioning in the calcitic foraminifer Operculina ammonoides under variable Ca concentration: Toward reconstructing past seawater composition
Calibration of Na partitioning in the calcitic foraminifer Operculina ammonoides under variable Ca concentration: Toward reconstructing past seawater composition
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DOI：
10.1016/j.epsl.2018.06.004
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发表时间：
2018-09-01
影响因子：
5.3
通讯作者：
Erez, Jonathan
中科院分区：
文献类型：
--
作者：
Hauzer, Hagar;Evans, David;Erez, Jonathan
海水钙浓度（Ca-sw）过去变化的重建对于理解海洋化学、碳循环的长期变化以及有孔虫中元素替代物（EI/Ca-CaCO 3）的准确应用至关重要（例如，Mg/Ca作为温度的代表）。在这里，我们表明，在有孔虫壳的Na/Ca比值可以用于重建Ca-sw和Mg/Ca在过去的海洋。Ca在海洋中的停留时间很短（类似于1 My），而Na在海水中的停留时间类似于100 My。因此，它可以合理地假设，钠SW是不变的新生代，使海洋钙的变化，从有孔虫的Na/Ca（Na/Ca壳）推断，如果Na掺入有孔虫壳取决于海水中的Na/Ca。此外，其他主要和次要元素的古浓度，然后可以计算相对于在壳中的钙，提供其他环境或生物因素不存在进一步的复杂性。为了评估这一假设，我们培养的底栖有孔虫Operculina ammonoides，现存的始新世钱币石的亲戚，在不同的钙SW和温度。有孔虫在实验条件下生长良好，增重40- 90%。通过激光烧蚀ICP-MS分析新生长的方解石（在实验海水中使用Ba-135标记鉴定）的Li、Na、Mg和Sr与Ca的比率。壳层中Na/Ca和Mg/Ca与溶液中Na/Ca和Mg/Ca比值的关系可用幂函数表示，瞬时分配系数是El/Ca壳层与El/Ca-sw的幂函数的导数。我们的结论是，有孔虫壳中的Na/Ca可以用来计算海洋中的古钙浓度，以及其他可能相对于钙发生变化的元素（例如，Mg、Sr、Li和其它）。(C)2018爱思唯尔B. V.保留所有权利。
Reconstructions of past changes in the seawater calcium concentration (Ca-sw) are critical for understanding the long-term changes in ocean chemistry, the carbon cycle and for accurate application of elemental proxies (EI/Ca-CaCO3) in foraminifera (e.g., Mg/Ca as proxy of temperature). Here we show that Na/Ca ratios in foraminiferal shells could be used for reconstructing Ca-sw and Mg/Ca in the past oceans. Ca has a short residence time in the ocean (similar to 1 My), whereas Na in seawater has a residence time of similar to 100 My. Hence it may be reasonably assumed that Na-sw is invariant over the Cenozoic, enabling variations in oceanic Ca to be deduced from foraminiferal Na/Ca (Na/Ca-shell) if Na incorporation into foraminiferal shells depends on Na/Ca in seawater. Furthermore, the paleo-concentrations of other major and minor elements may then be calculated relative to the Ca in the shells, provided that other environmental or biological factors do not present a further complication. To evaluate this hypothesis, we cultured the benthic foraminifer Operculina ammonoides, an extant relative of the Eocene Nummulites, under varying Ca-sw and temperature. The foraminifera grew well under the experimental conditions and increased their weight by 40-90%. The newly grown calcite (identified using a Ba-135 labeling in the experimental seawater) was analyzed by Laser-Ablation ICP-MS for Li, Na, Mg and Sr to Ca ratios. The relationship between Na/Ca and Mg/Ca in the shell and their ratio in the solution are best described as a power function, where the instantaneous distribution coefficient is the derivative of the power fit to the El/Ca-shell versus El/Ca-sw. In contrast, D-sr and D-Li are invariant with El/Ca-sw. The influence of temperature on Li, Na and Sr incorporation was smaller than the uncertainty of our measurements. We conclude that Na/Ca in foraminiferal shells can be used to calculate paleo-calcium concentrations in the oceans and also other elements that may change relative to calcium (e.g., Mg, Sr, Li and others). (C) 2018 Elsevier B.V. All rights reserved.