Dr. Natasha van Horsten

Research interests

  • Distribution of trace metals in the marine water column
  • Sources and sinks of trace metals to the marine environment
  • Method development for Cr redox speciation with voltammetry

Research project:

The research I am currently undertaking is part of the international GEOTRACES program, focusing on the biogeochemical cycling of trace elements in the global ocean, specifically looking at Chromium (Cr) redox speciation.

The redox speciation of Cr has been studied as a possible tracer of hydrothermal influence in the marine environment. Throughout the marine water column, Cr is mainly present as two redox species, Cr(III) or Cr(VI). Processes such as photoreduction or hydrothermal activity can affect the fractionation of these Cr redox species. We aim to shed more light on the fractionation of Cr into its two dominant redox species to improve the understanding of the behaviour of Cr in the marine environment.

I will be participating in the GEOTRACES research cruise SO298 (GP11) transect along the Equatorial Pacific Ocean from April to June 2023. During which samples will be collected for trace metals, redox-sensitive metals and bioactive metal ligands. We aim to gain information on the distribution of these various metals in their different size fractions, as well as fluxes and removal processes that ultimately result in the observed distributions throughout the water column of the Equatorial Pacific Ocean. My research, specifically, aims to gain more knowledge on the biogeochemical behaviour of Cr in seawater as a possible proxy for hydrothermal activity in the Equatorial Pacific Ocean.

Current project:

GEOTRACES process study across the Equatorial Pacific: participation in cruise (SO298), measurements and data evaluation and publication


  • van Horsten, N. R., Planquette, H., Sarthou, G., Ryan-Keogh, T. J., Mtshali, T. N., Roychoudhury, A., and Bucciarelli, E. (2022) Early winter barium excess in the southern Indian Ocean as an annual remineralisation proxy (GEOTRACES GIPr07 cruise), Biogeosciences. https://doi.org/10.5194/bg-2021-42.
  • Viljoen, J. J., Philibert, R., Van Horsten, N., Mtshali, T., Roychoudhury, A. N., Thomalla, S., et al. (2018). Phytoplankton response in growth, photophysiology and community structure to iron and light in the Polar Frontal Zone and Antarctic waters. Deep Res. Part I Oceanogr. Res. Pap. 141, 118–129. doi: 10.1016/j.dsr.2018.09.006
  • Ryan‐Keogh, T. J., Thomalla, S. J., Mtshali, T. N., van Horsten, N. R., & Little, H. (2018). Seasonal development of iron limitation in the sub‐ Antarctic zone. Biogeosciences, 15(14), 4647–4660. https://doi.org/10.5194/bg‐15‐4647‐2018
  • Mtshali, T. N., van Horsten, N. R., Thomalla, S. J., Ryan‐Keogh, T. J., Nicholson, S.‐A., Roychoudhury, A. N., et al. (2019). Seasonal depletion of the dissolved iron reservoirs in the sub‐Antarctic Zone of the Southern Atlantic Ocean. Geophysical Research Letters, 46. https://doi.org/10.1029/ 2018GL081355
  • Cloete, R., Loock, J. C., van Horsten, N. R., Fietz, S., Mtshali, T. N., Planquette, H., & Roychoudhury, A. N. (2021). Winter Biogeochemical Cycling of Dissolved and Particulate Cadmium in the Indian Sector of the Southern Ocean (GEOTRACES GIpr07 Transect). Frontiers in Marine Science, 8. https://doi.org/10.3389/FMARS.2021.656321/FULL
  • Cloete, R., Loock, J. C., van Horsten, N. R., Menzel Barraqueta, J. L., Fietz, S., Mtshali, T. N., Planquette, H., García-Ibáñez, M. I., & Roychoudhury, A. N. (2021). Winter dissolved and particulate zinc in the Indian Sector of the Southern Ocean: Distribution and relation to major nutrients (GEOTRACES GIpr07 transect). Marine Chemistry, 236, 104031. https://doi.org/10.1016/J.MARCHEM.2021.104031
  • Mdutyana, M., Burger, J., Smith, S., Flynn, R., van Horsten, N.R.,  Thomalla, S.J., Sun, X., Ward, B.B., Fawcett, S.E. (2022). The kinetics of ammonium uptake and oxidation during winter across the Indian sector of the Southern Ocean. Limnology and Oceanography. https://doi.org/10.1002/lno.12050