Zirconium on Benthic Foraminiferal Tests in the Arctic: A Plausible Shield towards Ocean Acidification

Abstract

Foraminiferal samples from Kongsfjorden (Arctic Ocean) were analysed for elemental ratios using Energy Dispersive spectrometry (EDS), along with sediment organic carbon, grain size and trace metals (Zr and Hf). EDS results on benthic foraminifera N. labradorica tests surface indicated presence of zirconium (Zr), whereas other foraminiferal species like Elphidium excavatum, Cassidulina reniforme and Quinqueloculina stalkeri were devoid of any Zr traces. Both foraminiferal analysis (EDS) as well as sediment analysis (ICP-MS) indicated highest Zr percentage at the inner fjord station 4. Concentration of Zr showed opposite trend to salinity, temperature and organic carbon indicating that the source of Zr is through weathering of continental zircon. Zr showed close association with Hafnium (Hf) and the average Zr/Hf ratio within Kongsfjorden was 43. Benthic foraminiferal shells did not show any signs of dissolution. As Zr is resistant to any acid corrosion; it could possibly be protecting the foraminifera from dissolution. Hence, in the present study we conducted lab experiment on the benthic foraminifera from outer/ inner fjord by pH manipulation, to identify the possible effects on benthic foraminiferal tests in absence/presence of zirconium coating towards dissolution. Interestingly, at pH 6 foraminifera from inner fjord having Zr coating (as evidenced by EDS) did not show any dissolution, whereas outer fjord ones which are devoid of Zr shielding showed dissolution. These preliminary results indicate that with the continuing increase in atmospheric CO 2 it may be interesting to study the test structure of Zr encrusted foraminiferal tests in Kongsfjorden.