Elemental systematics of the calcitic skeleton of Corallium rubrum and implications for the Mg/Ca temperature proxy
Elemental systematics of the calcitic skeleton of Corallium rubrum and implications for the Mg/Ca temperature proxy
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DOI：
10.1016/j.chemgeo.2019.06.008
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发表时间：
2019-10-05
期刊：
影响因子：
3.9
通讯作者：
Montagna, P.
中科院分区：
文献类型：
--
作者：
Chaabane, S.;Correa, Lopez M.;Montagna, P.
高镁方解石骨架的珊瑚红进行了分析，从生活的殖民地收集了广泛的深度（15米至607米）和环境设置在地中海。一个总体目标是更好地了解钙化过程，并将元素纳入浅水和深水标本的缓慢生长的骨架中，更具体地说，是为了澄清重建海水温度的地球化学代用品的准确性。珊瑚的内部结构，包括生长带的扫描电子显微镜（SEM）和岩相技术确定。采用溶液法和激光烧蚀电感耦合等离子体质谱法（ICP-MS）测定了珊瑚骨骼的微量元素（Li、B、Mg、Sr和Ba）组成。结果表明，深水标本的骨骼具有类似于浅水菌落的内部微观结构，在浅水和深水标本中，髓区和环形区清晰可辨。一般来说，深水样品的条带非常薄，与浅水样品的不规则条带相比，条带的距离是相等的。带状差异与对比鲜明的环境动态，浅水标本暴露于大的季节性波动相比，那些居住在半深海深处的相对稳定的条件。内髓和外环部分不同的微量元素浓度：镁/钙，锶/钙和锂/钙比较高的髓区，似乎是由生长动力学的影响，而B/钙和Ba/钙是相似的，在这两个区域，因此不受生长速度。深水样品中元素比值的变异性较低。生长带与Mg/Ca、Sr/Ca和Li/Ca高度相关，表明控制这些元素并入珊瑚骨骼的共同机制。Mg/Ca比值在暗带中尤其耗尽。虽然每个样本的平均镁/钙是正相关的环境海水温度，年际变化和振幅不同，并不相关的带宽。这些研究结果表明，下和年际变化的Mg/Ca不能用来重建一个连续的时间序列的长期季节性温度记录。然而，平均镁/钙组合物可以作为一个有价值的代理估计平均古海水温度在地中海内的一个给定的网站。
The high-Mg calcite skeleton of Corallium rubrum was analyzed from living colonies collected from a wide range of depths (15 m to 607 m) and environmental settings in the Mediterranean Sea. An overarching goal was to better understand the calcification process and incorporation of elements into the slow-growing skeleton of both shallow and deep-water specimens, and more specifically, to clarify the veracity of geochemical proxies for reconstructing seawater temperatures. The coral internal structure including growth bands were determined by scanning electronic microscopy (SEM) and petrographic techniques. Trace elements (Li, B, Mg, Sr and Ba) compositions of the coral skeleton were obtained by solution and laser ablation inductively coupled plasma mass spectrometry (ICP-MS). Results show that the skeleton of the deep-water specimens has an internal microstructure similar to shallow-water colonies, with the medullar and the annular zones clearly distinguishable in both shallow and deep-water specimens. In general, the bands of the deep-water samples are very thin and equidistant compared to the irregular banding of the shallow-water specimens. Banding differences relate to the contrasting environmental dynamics, with the shallow-water specimens being exposed to large seasonal fluctuations compared to the relative stable conditions of those inhabiting bathyal depths. The inner medullar and outer annular portions differ in their trace element concentrations: Mg/Ca, Sr/Ca and Li/Ca ratios are higher in the medullar zone and seem to be influenced by growth kinetics, whereas B/Ca and Ba/Ca are similar in both zones and hence unaffected by growth rate. The variability of elemental ratios is lower in the deep-water specimens. Growth bands are highly correlated to Mg/Ca, Sr/Ca and Li/Ca, suggesting common mechanism(s) controlling the incorporation of these elements into the coral skeleton. Mg/Ca ratios were especially depleted in the dark bands. Although the mean Mg/Ca of each specimen is positively correlated to ambient seawater temperature, the infra-annual variations and amplitudes differ and do not correlate to the band widths. These findings suggest that infra- and inter-annual variations of Mg/Ca cannot be used to reconstruct a continuous time-series of long-term seasonal temperature records. However, the mean Mg/Ca composition can serve as a valuable proxy to estimate mean palaeoseawater temperature at a given site within the Mediterranean.