Nico Fröhberg (PhD Student)

Research Interests:

Processes controlling the concentration and availability of biologically relevant trace elements to the ocean (e.g. Fe/Cu/Zn) including their behavior at transition zones like estuaries and hydrothermal systems with regards to particle adsorption, redox speciation and complexation by organic ligands.

Lowering barriers of access to scientific research through development of low-cost open source electrochemical methods i.e. for in-situ voltammetric measurements.

Research project:

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, 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. 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.

Participation in ongoing projects:

RV SONNE (SO289) research cruise to the South Pacific (GEOTRACES), February-April 2022

On board: Acquisition of seawater samples as well as sequential filtration and ultrafiltration for various parameters to be analyzed in the lab of Prof. Koschinsky.

Blog from the cruise:

RV METEOR (M174) research cruise to the Amazon Estuary, March-May 2021

On board: Acquisition of surface water, sediment, and porewater samples for analysis of concentrations and organic complexation of trace metals during estuarine mixing. Mixing experiment using seawater and Amazon river water endmembers.

Laboratory: Measurements of Ni-binding ligands in surface water and porewater samples using CLE-AdCSV.

Blog from the cruise:

RV MARIA S. MERIAN (MSM96) research cruise Metal-ML to the Porcupine & Iberian Abyssal Plains, October-November 2021

On board: Acquisition of sediment and porewater samples from the abyssal plains as well as surface water samples from the Weser estuary and North Atlantic. Voltammetric measurements of dissolved oxygen across the sediment water interface in sediment cores.

Laboratory: Mixing experiment using seawater and Weser river water endmembers. Measurements of Ni-binding ligands in porewater samples and samples from mixing experiment using CLE-AdCSV.

Blog from the cruise:

RV METEOR (M147) research cruise Amazon-Geotraces (DFG) to the Amazon Estuary, May 2018

Laboratory: Measurements of Ni-binding ligands in surface water samples using CLE-AdCSV.

Short cruise report:

Related work group publications:

  • Donald, H. K., Foster, G. L., Fröhberg, N., Swann, G. E. A., Poulton, A., Moore, C. M., & Humphreys, M. P. (2019). The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii). Biogeosciences Discuss., 2019, 1–27.

  • Kleint, C., Bach, W., Diehl, A., Fröhberg, N., Garbe-Schönberg, D., Hartmann, J.F., de Ronde, C.E.J., Sander, S.G., Strauss, H., Stucker, V., Thal, J., Zitoun, R. and Koschinsky, A. (2019): Geochemical characterization of highly diverse hydrothermal fluids from volcanic vent systems of the Kermadec intraoceanic arc, Chemical Geology. doi: 10.1016/j.chemgeo.2019.119289

Conference Presentations:

  • Fröhberg, N., Glazer, B. and Lio, S.: Development of a low-cost open-source potentiostat for in-situ electrochemical measurements (Talk); ICYMARE 2019, Bremen, Germany.