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

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.