In the initial phase the identification tool for S0-plumes was developed and validated. In the middle and end phase all data sets were processed and evaluated. One student from the University of Toulouse was trained in programming, numerical methods, and remote sensing. A field campaign with students took place at the Mediterranean coast. They were taught to measure different environmental variables. All results of the project were presented at the Benguela Symposium in Cape Town in 2016 (www.ma-re.uct.ac.za/benguela2016) the 3rd International Ocean Colour Science Meeting in Lisbon in 2017 (iocs.ioccg.org/iocs-2017-meeting) the Ocean Science Meeting in Portland in 2018 (osm.agu.org/2018) and the European Geosciences Union in Vienna in 2018 (www.egu2018.eu). The results were published in PlosONE (Ohde & Dadou, 2018).
Main results (Ohde & Dadou, 2018): “Our study illustrates that the main season is at the same time of increasing equatorward alongshore winds, so before the main upwelling season. Consequently, the coastal upwelling and offshore Ekman transport are increased which enhances the probability of the upwelling of H2S enriched bottom water. Furthermore, the activity of sulphur plumes is high during the seasonal oxygen minimum time period supporting the accumulation of H2S in the bottom water layer. The oxygen level in the bottom water is controlled by different local and remote-driven processes. Therefore, the main season of sulphur plumes is observed at the same time of the seasonal reduction of cross-shore ventilation of the bottom waters, the seasonal southernmost position of the ABFZ, the seasonal maximum of mass fractions of SACW and AGCW (sub-type of SACW) as well as the seasonal arrival of the downwelling coastal trapped waves. In contrast, the off-season is found during the upwelling season with maximum upwelling intensity and enhanced oxygen supply on the Namibian shelf. This higher oxygen level is associated with an increased ventilation of the bottom water by local processes (Ekman recirculation, mixing) as well as remote driven processes with the equatorward position of the ABFZ, the seasonal minimum of SACW mass fraction and upwelling coastal trapped waves.
… We conclude that the annual variability of sulphur plumes is characterized by years with very high activity interrupted by periods of lower activities ... For the first time this study highlights that the annual variability can be explained by the superposition of local and remote-driven processes. The sulphur plume activity is high in years with decreased yearly mean of the equatorward alongshore winds and increased coastal SST compared to normal years. It means years with a lower yearly mean of upwelling intensity probably supporting the deceleration of the depletion of the yearly H2S pool. There is a higher probability for an enhanced sulphur plume activity in years with a decreased oxygen supply promoting the formation of H2S. The years with higher sulphur plume activity are associated with decreased lateral ventilation of bottom waters by local processes as mixing and Ekman recirculation. Furthermore, the remote-driven processes like the displacement of the ABFZ, the interaction of SACW with the ESACW and the coastal trapped waves play also a strong role for the oxygen water content on the Namibian Benguela shelf. Therefore, the probability of the occurrence of strong sulphur plume activity is enhanced in years with a more southern position of the ABFZ, an increased mass fraction of SACW and stronger downwelling coastal trapped waves.”
The TOXIC-RISK project guarantees the exploitation of the results to the end-users by their open-access publication:
1. PANGAEA, doi.pangaea.de/10.1594/PANGAEA.887243
2. PlosONE, doi.org/10.1371/journal.pone.0192140
The results were disseminated in:
1. PlosONE, doi.org/10.1371/journal.pone.0192140
2. HAL, hal.archives-ouvertes.fr/hal-01713215
3. ZENODO, www.zenodo.org
4. ResearchGate, www.researchgate.net/project/Systematic-investigation-of-the-spatiotemporal-variability-of-TOXIC-hydrogen-sulphide-events-and-their-potential-RISKs-for-the-Namibian-fishing-and-aquaculture-industry-TOXIC-RISK
5. IOCCG, ioccg.org/2018/05/may-201
6. CNRS, www.insu.cnrs.fr/node/9051
7. LEGOS, www.legos.obs-mip.fr/actualites/actualites-scientifiques/emissions-toxiques-de-sulfure-dhydrogene-detectees-par-satellite-et-leur-forcage-en-milieu-cotier www.legos.obs-mip.fr/members/ohde/toxic_risk_project/overview
