Mg/Ca ratio, Sr/Ca ratio and stable isotopes of the foraminifera Oridorsalis umbonatus in surface sediment samples

We investigate the influence of carbonate system parameters (carbonate ion concentration, [CO3**2-]; carbonate ion saturation, Delta [CO3**2-]) on the trace element and stable isotope ratios in the endobenthic foraminifera Oridorsalis umbonatus. Data from modern core top samples from the Namibian continental slope suggest that the shell composition of this species is influenced by the chemistry of the pore-water. For these organic-rich sediments, the impact of ocean bottom water properties on both pore-water and shell chemistry is surprisingly small. Sr/Ca correlates positively with [CO3**2-] and to a lesser extent with Delta [CO3**2-], which is opposed to previous results. A [CO3**2-] decrease of 10 µmol/kg leads to an increase of 0.05 mmol/mol in Sr/Ca. We observe a correlation between shell d18O (corrected for temperature and d18O seawater) and [CO3**2-], however, the variability of the corrected d18O is close to the analytical limit. No clear dependences were observed for d13C and Mg/Ca.

我们研究了碳酸盐系统参数（碳酸根离子浓度[CO₃²⁻]、碳酸根离子饱和度Δ[CO₃²⁻]）对底栖有孔虫（endobenthic foraminifera）Oridorsalis umbonatus体内微量元素及稳定同位素比值的影响。来自纳米比亚大陆坡的现代岩心顶部样品数据表明，该物种的壳体组成受孔隙水（pore-water）化学性质的影响。对于这些富含有机质的沉积物，海洋底层水（ocean bottom water）性质对孔隙水及壳体化学性质的影响出乎意料地小。锶钙比（Sr/Ca）与[CO₃²⁻]呈正相关，与Δ[CO₃²⁻]的相关性较弱，这与先前的研究结果相反。当[CO₃²⁻]降低10 µmol/kg时，Sr/Ca会增加0.05 mmol/mol。我们观察到壳体δ¹⁸O（d¹⁸O，经温度和海水δ¹⁸O校正）与[CO₃²⁻]之间存在相关性，但校正后的δ¹⁸O变异性接近分析极限。未观察到δ¹³C（d¹³C）与镁钙比（Mg/Ca）存在明显相关性。