Gulf of Guinea

The morphology of the deep Congo submarine channel and the sedimentological structures of the deep-sea fan were established during the geological ZAIANGO project and helped to select study sites ranging from 350 to 4800 m water depth inside or near the channel and away from its influence. Ifremer conducted eight deep-sea cruises on board research vessels between 2000 and 2005. Standardized methods of sampling together with new technologies such as the ROV Victor 6000 and its associated instrumentation were used to investigate this poorly known continental margin. In addition to the study of sedimentary environments more or less influenced by turbidity events, the discovery of one of the largest cold seeps near the Congo channel and deep coral reefs extends our knowledge of the different habitats of this margin.
With the expansion of deep offshore oil and gas industry, there was a need for baseline studies to assess possible ecological impacts. The BIOZAIRE Program developed regional and local surveys to identify and analyze environmental variables, benthic processes and the scales of variability of benthic communities necessary to predict their response to deep-sea industrial activities.
With its multiple objectives, the BIOZAIRE Program aimed to gain a better understanding of the regional and local variables, along with the influence of habitats and different sources of energy on the structure of the communities. The objectives were:
1. To determine the influence of the Congo River discharge, both in the surface layer and in the near-bottom layers; particularly, to explain the presence and extent of deep anomalies in oxygen (deficit) and nutrient (excess) concentrations near 4000 m depth already revealed by previous studies near the Congo channel;
2. To monitor the deep-layer currents at a regional scale during the duration of the project with a specific focus on turbidity currents in the Congo submarine channel;
3. To evaluate the trophic resources by measuring the organic carbon flux and its temporal variability as well as the mineralization processes on selected sites;
4. To identify the benthic fauna and define the species composition and the diversity of the different size categories at the same sites: the megafauna, the macrofauna and the meiofauna;
5. To determine the abundance and the biomass of the different faunal components;
6. To evaluate the spatial variability of the biological compounds together with the physical and chemical characteristics at the water-sediment interface;
7. To undertake and compare long-term in situ colonization experiments at bathyal (1300 m depth) and abyssal depths (4000 m depth);
8. To characterize the bacterial activity in relation with hydrocarbon and methane seeps;
9. To locate and identify chemosynthetic-based communities, symbiotic associations and the accompanying fauna in relation with local environmental variables (i.e. methane concentrations);
10. To identify coral mounds fauna and explain their presence.