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by Thomas Ohde — last modified Jan 18, 2017 12:42 PM


TOXIC RISK is a joint project funded by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Action (No 706426).


The project is focused on the systematic investigation of the spatiotemporal variability of TOXIC hydrogen sulphide events and their potential RISKs for the Namibian fishing and aquaculture industry.

The project is an integrated study combining different disciplines and methods.

Funding Period

01.07.2016 – 30.06.2018


In the Namibian upwelling system, hydrogen sulphide (H2S) outbreaks and their sulfur plumes are unique events not found anywhere else in global ocean with such intensity. When H2S is produced and consumed in the oxygen minimum zone, several biogeochemical reactions take place and have direct impacts on the C, N, O cycles especially with the consumption of O2, the release of N2O and CO2 greenhouse gases and the nitrogen-fixed loss (Lavik et al., 2008). The H2S enriched bottom water is upwelled at the coast during the onset of upwelling favorable wind forces. The H2S is oxidized to colloidal sulfur producing localized sulfur plumes at the sea surface which can be observed with satellite sensors (Weeks et al., 2002, 2004, Ohde et al., 2007, 2011).


Figure: Sulphur plumes at the Namibian coast in blue/turquoise colors. The pictures were provided by the ocean color satellite sensors MERIS of ESA and MODIS of NASA. MODIS RGB images are courtesy of MODIS Rapid Response Project.

The local fishing and aquaculture industry, an important Namibian economic factor, is threatened (Little, 2008). Hydrogen sulphide can decrease the amount of benthos, fish stocks and other marine organisms or can cause mass mortality of commercially important fishes, oysters, crabs, shrimps and prawns (Matthews and Pitcher, 1996; Cockcroft, 2001). Moreover, the local population is inured to the unpleasant smell and corrosive effects of these sulfur emissions (Weeks et al., 2002). The tourism activity is also impacted by the accumulations of dead marine organisms on the coastal areas.

At present, there are large gaps in the knowledge of these sporadic events. So far there are no comprehensive long-term studies on their temporal and spatial variability and no statistical analyses exist. It is unclear when and how often the Namibian waters are affected, which coastal areas are more or less impacted and which oceanic and atmospheric conditions support or limit these events. No hazard analysis and risk assessment were done before. The TOXIC RISK project will contribute to fill these gaps.
The sporadic occurrence of sulfur plumes and their mostly coastal location offshore of Namibian desert regions make it impossible to examine them systematically using in-situ observations. But their milky turquoise patches at the sea surface can be identified with ocean color sensors on satellites (Weeks et al., 2002, Ohde et al., 2007). The TOXIC RISK project will use remote sensing methods combined with physical-biogeochemical modeling to investigate these events.

Cockcroft, A.C., Marine Freshwater Research, 52, 1085-1094, 2001.
Lavik, G., Stuhrmann, T., Bruchert, V., Van der Plas, A., Mohrholz, V., Lam, P., et al.., Nature, 457, 581–584, 2008.
Little, D., History and development of shellfish cultivation in Walvis Bay, Namibia., 2008.
Matthews, S.G., Pitcher, G.C., In: Harmful and Toxic Algal Blooms. UNESCO, Paris, 1996.
Ohde, T., Siegel, H., Reißmann, J., Gerth, M., Continental Shelf Research, 27(6), 744-756, 2007.
Ohde, T., Mohrholz, V., International Journal of Remote Sensing, 32(24), 9327-9342, 2011.
Weeks, S.J., Currie, B., Bakun, A., Nature, 415, 493-494, 2002.
Weeks, S.J., Currie, B., Bakun, A., Peard, K.R., Deep-Sea Research I, 51, 153-172, 2004.



    European Union’s Horizon 2020
    Marie Skłodowska-Curie Individual Fellowship

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