Assessing influence of diagenetic carbonate dissolution on planktonic foraminiferal Mg/Ca in the southeastern Arabian Sea over the past 450 ka: Comparison between Globigerinoides ruber and Globigerinoides sacculifer
Assessing influence of diagenetic carbonate dissolution on planktonic foraminiferal Mg/Ca in the southeastern Arabian Sea over the past 450 ka: Comparison between Globigerinoides ruber and Globigerinoides sacculifer
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DOI：
10.1029/2007gc001904
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发表时间：
2008-04
期刊：
影响因子：
3.7
通讯作者：
K. Tachikawa;Sophie Sepulcre;T. Toyofuku;E. Bard
中科院分区：
文献类型：
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作者：
K. Tachikawa;Sophie Sepulcre;T. Toyofuku;E. Bard
利用阿拉伯海东部一个岩芯站点的红拟抱球虫（Globigerinoides ruber）和袋拟抱球虫（Globigerinoides sacculifer），评估了过去450千年期间超溶跃面方解石溶解对Mg/Ca温度计的影响。所研究的站点具有岁差循环的古生产力变化特征，这种变化导致了沉积物中方解石的溶解，尽管该岩芯仍含有40 - 80%的碳酸钙。在高生产力时期，两种有孔虫物种的窄尺寸测试重量往往随着Mn/Ca比值的增加而降低，这表明孔隙水具有腐蚀性条件。扫描电子显微镜观察表明，袋拟抱球虫比红拟抱球虫能更好地保持测试超微结构。微探针图谱显示，尽管钙含量降低，但红拟抱球虫房室壁中的富镁带得以保存。假设袋拟抱球虫和红拟抱球虫之间的低测试重量以及Mg/Ca温度的偏差完全是由方解石溶解造成的，那么Mg/Ca温度测定的偏差估计约为1°C，与该测温法的不确定性相当。尽管有测试溶解的证据，但在研究条件下，有孔虫的Mg/Ca似乎仍保留了初始温度信号。
The influence of supralysoclinal calcite dissolution on the Mg/Ca thermometer over the last 450 ka is assessed using Globigerinoides ruber and Globigerinoides sacculifer from a core site in the eastern Arabian Sea. The studied site is characterized by precession‐cycled paleoproductivity changes that have induced calcite dissolution in the sediments, although the core still contains 40–80% CaCO3. During high‐productivity periods, the narrow‐sized test weights of both foraminiferal species tend to decrease with increasing Mn/Ca ratio, indicating corrosive pore water conditions. Scanning electron microscope observations show that G. sacculifer maintains a better preserved test ultrastructure than G. ruber. Microprobe mapping reveals that Mg‐rich bands in G. ruber chamber walls are preserved despite reduced Ca content. Assuming that the low test weight and offset in Mg/Ca temperature between G. sacculifer and G. ruber are exclusively produced by calcite dissolution, the bias in Mg/Ca temperature determination can be estimated at around 1°C, comparable to uncertainty of this thermometry. Despite the evidence for test dissolution, foraminiferal Mg/Ca seems to preserve initial temperature signals under the studied conditions.