Studies on the biogeochemistry of zinc in the subartic North Pacific

Lohan, Maeve Carroll (2003) Studies on the biogeochemistry of zinc in the subartic North Pacific. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

This research involves a study on the distributions and speciation of Zn in the NE Pacific Ocean and its interactions with phytoplankton species present. Total dissolved Zn and Zn speciation was measured using AdCSV. A clear gradient is evident in the total dissolved Zn concentrations within the mixed layer, decreasing offshore along an E - W transect from a shelf station (0.9 nM) out into the High Low Chlorophyll (HNLC) area at Ocean Station Papa (OSP; 0.04 nM) in both summer and winter. Dissolved Zn/Si ratios in the upper 200m decrease with distance from shore, which infers a decoupling between dissolved Zn and silicic acid in the upper ocean. It is hypothesised that the profile of dissolved Zn in deeper water is a result of recycling from relatively biologically resistance organic particulate phases, that leads to profiles very similar to those of silicic acid.

Zinc speciation was dominated by complexation to a natural organic ligand reducing the free Zn²⁺ concentration to 0.72 pM at OSP. Below 200m the total dissolved Zn concentration exceeds the concentration of the Zn-binding ligand and therefore the speciation of Zn is not dominated by organic complexation in the deep waters of the NE Pacific. No relationship between the Zn-binding ligands and chlorophyll fluorescence was observed.

The addition of Fe to surface waters containing a natural phytoplankton assemblage dramatically increased the growth rate and abundance of diatoms and other phytoplankton species at OSP. Addition of Fe increased the uptake of total dissolved Zn and in combination with the production of organic ligands reduces the [Zn²⁺] to 0.2 pM, well below the limit suggested in laboratory cultures that can limit phytoplankton growth. At these low bioavailable Zn concentrations ligand production may be a mechanism by which phytoplankton can access Zn bound to these ligands. Zinc concentrations observed at OSP in this study were not limiting phytoplankton growth as the addition of Zn showed no significant increase in phytoplankton biomass. Production of Zn-binding ligands was observed on the addition of Zn, indicating a rapid response from phytoplankton and specificity for Zn.

Text

887061.pdf - Version of Record

Available under License University of Southampton Thesis Licence.

Download (25MB)