Nico Fröhberg

Organic complexation of Zn and other trace metals (such as Fe and Cu) in geochemical transition zones by voltammetric methods

Within my PhD project, I am studying the behavior of trace metals, such as zinc (Zn), nickel (Ni), copper (Cu), and iron (Fe) at marine geochemical transition zones. Trace metals act as micro nutrients to marine phytoplankton and are present in such low concentrations in seawater that their availability can limit the growth of certain species, thus acting as a significant control parameter for the marine food web. At these transition zones, including estuaries, hydrothermal vents and the sediment-water interface, the investigated trace metals experience significant changes in the geochemical regime (like salinity, temperature, oxygen concentration and pH), affecting their chemical behavior as they are transported into the ocean or removed from the water column. Particularly the adsorption and desorption to/from particulate material and the complexation by organic ligands strongly affect the fate of trace metals entering the marine geochemical system.

I investigate these processes by analysis of different size fractions after sequential filtration and CLE-AdCSV (competitive ligand exchange – adsorptive cathodic stripping voltammetry) experiments for the determination of ligand concentrations and complexation constants (how strong the bond of the organic ligand to the metal ion is). My work focusses on the analysis of water samples from hydrothermal plumes of the Kermadec and Tonga arcs as well as the Amazon river estuary.

 Additionally, I am developing a low-cost open source potentiostat to reduce the cost of these electrochemical measurements and enable in-situ measurements of trace metal concentrations in anoxic systems as well as sulphide concentrations that are relevant as complexing agents for chalcophile elements.