Initiated on December 1st 2011 and set to run for a 4-year period, the ANR Congolobe project is a joint effort involving the LSCE laboratories, Ifremer (deep-sea ecosystem research and marine geoscience) and the UPMC.
Its main objective is to study deep-sea ecosystems in the terminal lobes of the Congo deep-sea fan, a hot spot within the region and in the global ocean due to its considerable deposits of terrigenous material at very great depths (5000m). Our project seeks to establish a link between the nature and magnitude of organic material originating from the Congo River and the benthic ecosystems in the canyon’s terminal zone. The latter seem to be characterised by a high degree of spatial heterogeneity with chemosynthesis-based communities similar to those associated with the region’s pockmarks.
Against this backdrop, the geological, geochemical and microbiological processes at the root of reducing environments promoting the development of these ecosystems are unknown. They will be studied by adopting a multidisciplinary approach incorporating a range of spatial scales. The evolution of the Congo’s organic deposits as a direct or indirect source for their metabolism will be quantified.
The Congolobe project hinges on two campaigns: the WACS campaigns (February 2011) was used as an opportunity to carry out explorations and take initial samples in the lobe area, and the Congolobe campaign which took place from the 12/12/2011 to the 10/01/2012 on board the oceanographic research vessel “Pourquoi pas” with the Victor ROV. Around fifteen Ifremer scientists, engineers, and technicians representing the various disciplines actively contributed to the success of this campaign. In total, 5 sites were explored at depths ranging from 4700 to 5000 metres; three are located along the main axis of the currently active lobe, the fourth on a lobe that seems to have received more deposits over the past decades and finally, the last on a lobe that has been disconnected for several millennia. The latter will be used to establish the persistence of biological assemblies and the long-term influence of channel deposits.
Dives using the Victor’s monitoring module were carried out in order to produce microbathymetric maps, followed by a series of deep-sea images to understand the link between surface biological observations and geomorphology, as well as to select sampling targets. Other subsequently analysed data, such as acoustic imaging, will help to gain a better understanding of the links between sedimentary and biological processes. In addition to the sampling and monitoring facilities typically used by Victor, in situ measurements were taken using tools developed more recently by Ifremer, including the micro-profiler and the CALMAR benthic chamber that were used successfully in spite of exceptional depths and extremely loose sediment. Multi-core tubes and Calypso will be used for in-depth analysis of geochemical and microbiological processes and gradients inside the sediments. Use of the stand-alone respirometer, along with the recovery of particle traps and current meters deployed during the WACS campaign last year will help to evaluate the flow of carbon and other elements, as well as their intra-annual variability.