1517
Limnol. Oceanogr., 45(7), 2000, 1517–1524
q 2000, by the American Society of Limnology and Oceanography, Inc.
The incorporation of zinc and iron into the frustule of the marine diatom Thalassiosira
pseudonana
Michael J. Ellwood1 and Keith A. Hunter
Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand
Abstract
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 Zn21 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 Zn21 concentrations. These results also demonstrate that the Zn : Si(OH)4 relationship ob-
served 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 concentra-
tions.
It is well known that biological uptake and regeneration
processes control the concentrations of the major nutrients
in seawater. Macronutrients such as NO32, PO432, and
Si(OH)4 are frequently considered to limit phytoplankton
growth in the surface waters of the ocean because of their
low concentrations. There is now mounting evidence to sug-
gest that low surface-water concentrations of certain micro-
nutrients can also limit phytoplankton growth