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Organic carbon transfer and ecosystem functionning in the terminal lobes of the Congo deep-sea fan – CONGOLOBE

The deep Congo Lobes : a unique ecosystem fed by river inputs

The terminal lobes of the Congo deep-sea fan are a unique area in the world ocean. Located at 750 km off the coast and at 5000 m depth, these lobes are directly fuelled by river material rich in organic matter delivered by the Congo River, which makes it the equivalent of an offshore river delta. These lobes host peculiar ecosystems characterized by large bivalves and bacterial mats, which functioning in such sedimentological context is unknown.

Understanding the link between Congo inputs to the deep-ocean and chemosynthetic fauna

The principal challenge of Congolobe is describing biodiversity and understanding the ecosystem functioning apparently based on chemosynthesis. Our project aims at establishing a link between organic inputs from the Congo canyon/channel, their diagenesis in the first meters of the sediment, the possible production of reduced fluids bearing sulphide and methane, and the presence of chemo-autotrophic bivalves and bacterial mats in the lobe zone.

A multidisciplinary approach gathers geologists specialists of this deep-sea fan, geochemists working on organic matter and the recycling of biogenic compounds, microbiologists assessing the nature of bacteria and archea of the sediment, and biologists studying biodiversity and functioning of the faunal communities. The experimental approach was largely based on in situ techniques deployed by the ROV Victor 6000 during the Congolobe and WACS cruises.

To come later

To come later

To come later

The terminal lobes of the Congo deep-sea fan are a unique area in the world ocean. These lobes are fuelled quasi-continuously by turbidites containing a large proportion of labile organic matter delivered by the Congo River (the second largest river in the world by its freshwater discharge) which is linked to its submarine canyon by an incision in the shelf. This connection between the river and the canyon is unique for large rivers on a global scale as all other large rivers (Amazon, Yangtze, Mississippi) are disconnected from their canyons since the increase of sea level linked to interglacial periods. The lobe zone is the receptacle of the organic inputs channelized by the canyon and covers an area of 3000 km2. The sedimentation of labile organic matter in the lobe zone located at 750 km from shore and at 5000 m depth which displays the same features as a river delta (high burial rate, fresh organic matter) allows the development of an exuberant ecosystems which is visualized by large bivalves, bacterial mats, mucus blankets of polychetes, an assemblage which has never been observed out of peculiar regions of active cold seeps.
Despite this specificity, the ecosystem from the terminal lobes of the Congo fan have been only poorly observed (preliminary pictures during ROV dives and rare multiple coring). This prevented the investigation of their exact composition, spatial extension and, furthermore, their functioning.
The Congolobe project aims at studying the ecosystems from the terminal lobes of the Congo deep-sea fan, which constitutes a hot spot for biology and biogeochemistry in the region. In addition to the biological description of the ecosystem in terms of biodiversity, we will test a hypothesis concerning the functioning of this ecosystem which composition seems to be close to chemosynthesis based ecosystems. Our hypothesis aims at establishing a link between organic imputs from the Congo canyon/channel, their diagenesis in the first meters of the sediment (or deeper), the possible production of reduced fluids bearing sulphide and methane, and the presence of chemo-autotrophic fauna and bacterial mats in the lobe zone.
In the heterogeneous context of the lobes, a multidiciplinary approach is needed, gathering geologists specialists of this deep-sea fan, organic geochemists capable of characterizing the origin and reactivity of organic matter, marine geochemists estimating the recycling and burial of biogenic compounds, microbiologists assessing the nature and activity of bacteria and archea of the sediment, and biologists studying biodiversity and functioning of the fauna of all size.
The working approach chosen is based on sea expeditions, such as those that IFREMER masters. One preliminary field campaign is already programmed in February 2011 with 5 days in the lobe zone (WACS leg 2) and will be occupied by a biogeochemical and biological survey of the zone. The second expedition which is already accepted by the French cruise committee (CNFE) will use the undersea equipment in order to characterize the diversity and heterogeneity of the ecosystem. Advanced technologies will be used: ROV Victor 6000 of IFREMER will allow the visualization and precise sampling of the biological and geological structures; in situ technologies will be fully employed with 3 landers (movable by the ROV) carrying either standard or polarographic micro-electrodes and benthic chambers.

Project coordinator

Monsieur Christophe RABOUILLE (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR SUD) – christophe.rabouille@lsce.ipsl.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

UPMC UNIVERSITE PARIS VI [PIERRE ET MARIE CURIE]
LSCE CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR SUD
IFREMER INSTITUT FRANCAIS DE RECHERCHE POUR L'EXPLOITATION DE LA MER (IFREMER)

Help of the ANR 800,000 euros
Beginning and duration of the scientific project: November 2011 - 48 Months

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