Organic matter characterization and distribution in sediments of the terminal lobes of the Congo deep-sea fan: Evidence for the direct influence of the Congo River

Type Article
Date 2015-11
Language English
Author(s) Stetten Elsa1, 2, Baudin Francois1, Reyss Jean-Louis3, Martinez Philippe4, Charlier Karine4, Schnyder Johann5, 6, Rabouille Christophe3, Dennielou BernardORCID7, Coston-Guarini Jennifer8, Pruski Audrey M.2, 9
Affiliation(s) 1 : Univ Paris 06, Univ Paris 04, Inst Sci Terre Paris ISTeP, CNRS, F-75005 Paris, France.
2 : Univ Paris 06, Univ Paris 04, Stn Marine Banyuls Mer, Observ Oceanol,LECOB,UMR 8222, F-66650 Banyuls Sur Mer, France.
3 : Domaine CNRS, Lab Sci Climat & Environm, CEA CNRS UVSQ IPSL UMR 8212, F-91198 Gif Sur Yvette, France.
4 : Univ Bordeaux 1, Environm & Paleoenvironm Ocean & Continentaux, CNRS UMR C 5805, F-33405 Talence, France.
5 : Univ Paris 06, Univ Paris 04, ISTeP, UMR 7193, F-75005 Paris, France.
6 : CNRS, UMR 7193, ISTeP, F-75005 Paris, France.
7 : IFREMER, UR Geosci Marines, F-29280 Plouzane, France.
8 : Univ Bretagne Occidentale, UMR LEMAR 6539, IUEM, F-29280 Plouzane, France.
9 : CNRS, UMR 8222, Lab Ecogeochim Environm Benth, F-66650 Banyuls Sur Mer, France.
Source Marine Geology (0025-3227) (Elsevier Science Bv), 2015-11 , Vol. 369 , P. 182-195
DOI 10.1016/j.margeo.2015.08.020
WOS© Times Cited 37
Keyword(s) Congo River, Turbiditic system, Recent lobe complex, Terrestrial organic matter, Preservation
Abstract The terminal lobe complex of the Congo River submarine fan sits on the abyssal Atlantic plain, at 5000 m water depth, 760 km offshore from the river mouth estuarine area. While most rivers deliver particulate material to the continental shelf, particulate matter from the Congo River largely bypasses the shelf and is transported by turbidity currents through the Congo submarine canyon system. We determined the quantity and quality of the organic matter reaching the terminal lobe complex at five sites with marked morphological differences that may influence the distribution of organic matter. A suite of bulk geochemical (% OC, δ13Corg, δ15N, C: N), 137Cs and palynofacies analyses were done on cores collected from the terminal lobe area. These results were also compared to the composition of sediments collected upstream at the Malebo Pool (Congo River).

Distal lobe complex sediments contain high amounts of terrestrial organic carbon (3–5 wt.%) that is homogeneously distributed in surficial (22 cm) and deeper sediments (580 cm) silty–clay facies. Strongly altered soil-derived organic matter with well-preserved land plant detritus from the Congo River predominates. A terrestrial soil origin for the particulate load was confirmed by the elevated 137Cs activity in lobe sediments. The vertical distribution of the 137Cs signal suggests that there has been a massive arrival of terrestrial sediments since 1963, consistent with a turbiditic origin. From the locations surveyed, we estimate a maximum accumulation of terrestrial organic carbon of ca. 1 kg OC m− 2 y− 1 for the distal lobe. However, transport modifies the organic matter both in terms of quantity and quality. Observed differences were attributed to preferential degradation of nitrogenous matter during diagenesis and to the addition of highly remineralized marine organic matter.

Results from our temporal reference site (E) suggest that organic matter may be preserved in turbidite facies for thousands of years. The good preservation state of the accumulated organic matter shows that turbiditic lobe complexes should be considered as a sink for terrestrial organic carbon in the deep ocean.
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Stetten Elsa, Baudin Francois, Reyss Jean-Louis, Martinez Philippe, Charlier Karine, Schnyder Johann, Rabouille Christophe, Dennielou Bernard, Coston-Guarini Jennifer, Pruski Audrey M. (2015). Organic matter characterization and distribution in sediments of the terminal lobes of the Congo deep-sea fan: Evidence for the direct influence of the Congo River. Marine Geology, 369, 182-195. Publisher's official version : https://doi.org/10.1016/j.margeo.2015.08.020 , Open Access version : https://archimer.ifremer.fr/doc/00278/38958/