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

作者：Tachikawa Kazuyo^*; Sepulcre Sophie; Toyofuku Takashi; Bard Edouard

来源：Geochemistry Geophysics Geosystems, 2008, 9: Q04037.

DOI：10.1029/2007GC001904

• supralysoclinal calcite dissolution
• foraminiferal Mg/Ca
• seawater temperature

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 degrees 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.

• 出版日期2008-4-26