Aliphatic hydrocarbons and triterpenes of the Congo deep-sea fan

Abstract

Hydrocarbons were analyzed in sediments from the Congo River deep-sea fan, from the Congo River, and in sinking particles collected by sediment traps 40 m above the sediment. Studied sites encompassed three lobes of decreasing age of formation along the canyon: sites A, F and C and a another lobe system, disconnected from the active channel since 4 ka, Site E. Terrestrial long-chain odd n-alkanes were dominant in all sediments of the lobe system. Unsaturated terpenoids sourced by higher plants, such as gammacerene, lupene, ursene and oleanene, were also detected. At site C, characterized by high accumulation rates (10-20 cm yr−1), the organic matter spends less time in the oxic layer than at other sites and high phytadiene concentrations (10 to 17 μg gOC−1) evidenced recent terrestrial and phytoplanktonic remains reworked in anaerobic conditions. In these sediments, organic carbon-normalized concentrations of terrestrial alkanes and terpenoids were several fold higher than in the lobe sediments with lower accumulation rates (sites A and F), arguing for a more rapid degradation of terrestrial hydrocarbons than bulk organic carbon in the first steps of pre-diagenesis. Ample variations in the contributions of biomarkers from higher plants, ferns, bacteria and angiosperms, indicate an heterogeneous contribution of the soil and vegetation detritus delivered to the Congo lobe sediments. Lower concentrations in terrestrial hydrocarbons at site E, 45 km away from the active canyon, indicated that river particles are still admixed to the dominant marine organic matter. Diploptene and hop-7(21)ene have a dual origin, from terrestrial and marine microorganisms. Scatter in their relationship to gammacerene argues for a contribution of marine microorganisms, in addition to soils-sourced microorganisms. The close distribution patterns of diploptene, hop-21-ene, hop-7(21)ene and neohop-13(18)-ene is in line with the hypothesis of sequential clay-catalyzed isomerisation of bacterial hopenes. Terrestrial biomarker accumulation fluxes at site C are one order of magnitude higher than vertical pelagic flux, demonstrating the magnitude of the inputs delivered through turbiditic transport in the submarine canyon. Crude oil contamination was evidenced at the disconnected site E (UCM, C21 to Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. C26 tricyclic diterpanes, CPI) and, in smaller amounts, in some sediments from sites A and C. It may be related to marine crude oil extraction and transport. A short-chain mode of alkanes with an even predominance is evidenced in sediments of the lobe complex and likely sources, crude oil, microorganisms and ferns, are discussed.

Nuclear magnetic resonance assignment strategy for pentacyclic triterpenes, using lup-20(29)-ene from Pilotrichella flexilis as model system, combining spectrally filtered proton-to-carbon schemes and DFT–GIAO approach

“…As part of our ongoing research to identify bioactive substances from native mosses [18], we have recently isolated and identified for the first time a pentacyclic triterpene lup-20(29)-ene coming from Pilotrichella flexilis, which is a common species broadly distributed along Mexico [19], and barely one phytochemical study of an oversea species has been reported until now [20]. Structures related to this type of PTs mainly comprised in higher plants, have also been observed in other ecosystems, including deep-sea fan, ancient sediments from high-moor peats as well as in several geological sources [21,22].…”

Routing of terrestrial organic matter from the Congo River to the ultimate sink in the abyss: a mass balance approach (André Dumont medallist lecture 2017)

“…Additionally, numerous sedimentological and organic geochemical data were obtained during the shore-based studies on the 145 sediment cores collected in different parts of the Congo turbidite system, from the canyon head to the terminal lobe complex, by ca. 5000 m of water depth (Droz et al, 1996(Droz et al, , 2003Gervais et al, 2001;Babonneau, 2002;Babonneau et al, 2002Babonneau et al, , 2004Babonneau et al, , 2010Ferry et al, 2004;Migeon et al, 2004;Bonnel, 2005;Treignier, 2005;Marsset et al, 2009;Rabouille et al, 2009Rabouille et al, , 2017aRabouille et al, , 2017bBaudin et al, 2010Baudin et al, , 2017aBaudin et al, , 2017bPicot, 2015;Stetten et al, 2015;Picot et al, 2016Picot et al, , 2019Croguennec et al, 2017;Méjanelle et al, 2017;Pastor et al, 2017;Pozzato et al, 2017;Schnyder et al, 2017;Taillefert et al, 2017). The resulting data allows a good description and understanding of the entire Congo turbidite system.…”

“…5). Detailed organic geochemical investigations, including molecular signatures and palynofacies observations, were conducted in the upper and lower channellevee areas (Baudin et al, 2010) and in the terminal lobe complex (Stetten et al, 2015;Baudin et al, 2017b;Méjanelle et al, 2017;Pruski et al, 2017;Schnyder et al, 2017). All geochemical and palynological proxies suggest that at least 80-90% of the organic matter preserved in marine sediment along the turbidite channel has a terrestrial origin.…”

“…All the analyses confirm that the origin of organic matter is a mixture of terrestrial higher-plant debris, soil organic matter and deeply oxidized phytoplanktonic material. Nevertheless, variations in the contributions of biomarkers from higher plants, ferns, bacteria and angiosperms, indicate a heterogeneous contribution of the soil and vegetation detritus delivered by the Congo River (Méjanelle et al, 2017). Fine structures of higher plant, cuticle fragments and vegetal cellular material are generally well preserved, emphasizing the efficiency of turbidity currents to rapidly transfer terrestrial organic matter to the seafloor (Schnyder et al, 2017).…”