The incorporation of zinc and iron into the frustule of the marine diatom Thalassiosira pseudonana

Zinc and iron uptake experiments were conducted with the marine diatom Thalassosira pseudonana, to investigate whether Zn and Fe are incorporated into the frustule of this diatom. Our results show that the uptake and deposition of Zn into opal has a sigmoidal relationship with the free Zn2+ concentration of the culture medium. The amount of Zn incorporated into the opal represents only 1–3% of the total amount of Zn taken up by the diatom; however, the exact reasons for Zn incorporation into the opal are not known. Even so, the consistent relationship between Zn levels in the opal and the culture medium suggests that fossil diatoms may be used as a recorder for historical changes in oceanic free Zn2+ concentrations. These results also demonstrate that the Zn:Si(OH)4 relationship observed in the Pacific and Antarctic Oceans is not a result of Zn released from biogenic opal. Fe uptake experiments also revealed that Fe is incorporated into diatom opal; however, the amount incorporated appears to be regulated by the diatom and did not increase with increasing Fe concentration within the diatom culture medium. This therefore eliminates the use of Fe incorporated within diatom opal as a possible proxy for dissolved Fe concentrations.