Iron and zinc enrichments in the northeastern subarctic Pacific: ligand production and zinc availability in response to phytoplankton growth

• Published in: Limnology and Oceanography
• Main Authors: Lohan, M.C., Crawford, D.W., Purdie, D.A., Statham, P.J.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2005
• Subjects: Pacific; Subarctic
• Online Access: https://eprints.soton.ac.uk/17746/

Iron- and zinc-enrichment experiments were carried out at Ocean Station Papa in the subarctic North Pacific. In iron-enriched treatments AI phytoplankton chlorophyll a (Chl a) increased 20-fold (9.7 mu g L-1) above the concentration on day zero. No stimulation of Chl a production or nitrate drawdown was observed on addition of zinc alone compared to the control. In the iron-enriched treatment, bioavailable zinc concentration decreased to 0.2 pmol L-1 lower than that which is known in culture experiments to limit some phytoplankton growth. Theoretical analyses suggest that this zinc concentration would cause diffusion-limited growth of large diatom cells present at the end of the incubation. Direct measurements of zinc-binding ligands indicate that the natural microbial planktonic assemblages have the ability to respond rapidly to conditions of high dissolved zinc concentrations. Rapid ligand production may be a mechanism by which certain phytoplankton reduce zinc toxicity or for maintaining zinc concentrations in the upper water column. Zinc-binding ligands were observed to be both produced and removed on the timescale of 1 d. We suggest that these zinc-binding ligands are produced to assist assimilation, particularly under iron-enriched conditions when concentrations of bioavailable zinc were extremely low, thereby alleviating the effects of zinc limitation.