Keywords: Congo fan, hydrocarbons, NAH, hopanes, hopenes, sediments, turbidite system

)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, C 21 to C 26 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.

Introduction

The effort to quantitatively understand and predict the carbon cycle includes the assessment of the inventory of marine reservoirs of organic carbon and the prediction of its oxidation and transfer back to atmospheric CO 2 . However part of the terrestrial organic carbon escapes degradation and is buried in sedimentary horizons where no more oxidation occurs. Marine sediments are among the largest sinks of organic carbon, and half of this organic carbon reservoir is sourced by terrestrial plants and organisms [START_REF] Blair | The fate of terrestrial organic carbon in the marine environment[END_REF][START_REF] Burdige | Burial of terrestrial organic matter in marine sediments: A re-assessment[END_REF][START_REF] Burdige | Preservation of Organic Matter in Marine Sediments: Controls, Mechanisms, and an Imbalance in Sediment Organic Carbon Budgets?[END_REF]. This preserved organic carbon accounts for less than half the rivers inputs (Burdige, 2007 and references therein) which pictures the ocean margins as efficient in both remineralizing terrestrial organic matter and sequestering it (Middelburg et al., 1993). The organic carbon budget bridges processes on different times scales. The water column biogeochemical cycling and early diagenesis processes integrate annual to decadal time scales. In contrast, the cycle of organic carbon that is ultimately preserved in marine sediments as geopolymers, kerogen or source rocks eroded from the continent, may exert feedbacks on atmospheric CO 2 over thousand years to geologic time scale, with enhanced carbon burial during low sea level glacial ages [START_REF] Cartapanis | Global pulses of organic carbon burial in deep-sea sediments during glacial maxima[END_REF].

The Congo River (ex-Zaire) has a large intertropical watershed mainly covered by C3 rain forest vegetation. It delivers a large flux of higher plant debris and fine particles eroded from soils to the Atlantic Ocean, while it carries a minor contribution of riverine planktonic organic matter [START_REF] Spencer | An initial investigation into the organic matter biogeochemistry of the Congo River[END_REF]. The particulate organic carbon exported to the Atlantic Ocean by the Congo River accounts for an input of 2 Tg organic carbon per year [START_REF] Coynel | Spatial and seasonal dynamics of total suspended sediment and organic carbon species in the Congo River[END_REF]. The Congo River is connected to a sinuous submarine canyon that starts within the river mouth, deeply incises in the shelf and slope and further extends in the deep basin through an active channel-levees-lobe system. The active terminal lobe complex is located at 4750 m depth, 760 km away from the river mouth [START_REF] Savoye | Geological overview of the Angola-Congo Margin, the Congo deep-sea fan and its submarine valleys[END_REF][START_REF] Vangriesheim | Turbidity events observed in situ along the Congo submarine channel[END_REF].

Overload of river sediments and sliding of sediment at the canyon head can initiate energetic gravity currents that transport most of the river particles to the terminal lobe complex. Besides terrestrial organic matter, sediments of the Congo-Angola margin also comprise a remarkable contribution of marine organic matter sourced by the coastal upwelling North and South the Congo River plume and within the plume itself [START_REF] Schefuß | Lipid biomarkers as major source and preservation indicators in SE Atlantic surface sediments[END_REF]. As a result, the gravity currents may transport an admixture of organic carbon sourced by this coastal autochthonous production together with the river inputs. Times series studies have captured very energetic turbidity events upstream the terminal lobe complex [START_REF] Khripounoff | Direct observation of intense turbidity current activity in the Zaire submarine valley at 4000 m water depth[END_REF][START_REF] Vangriesheim | Turbidity events observed in situ along the Congo submarine channel[END_REF]. For example, a turbiditic event in 2001 caused a massive particle flux within the canyon but also spilled over its edge thereby yielding a high pulse of terrestrial clay on the levee, 18 km away from the canyon channel, in an area otherwise characterized by marine pelagic particle flux [START_REF] Khripounoff | Direct observation of intense turbidity current activity in the Zaire submarine valley at 4000 m water depth[END_REF]. In 2004, two intense events were recorded by intense peaks in turbidity and in particle flux, and by mooring breaking [START_REF] Vangriesheim | Turbidity events observed in situ along the Congo submarine channel[END_REF]. When reaching the terminal lobe system, even though the current looses velocity, it can still deliver intense particle flux [START_REF] Vangriesheim | Turbidity events observed in situ along the Congo submarine channel[END_REF]. Besides turbitic currents smaller pulses in particle flux with no current increase were also recorded, and indicate local sliding of sediment accumulated on the walls or terraces on the sides of the channel [START_REF] Vangriesheim | Turbidity events observed in situ along the Congo submarine channel[END_REF].

The Congolobe project aims at studying the geology, geochemistry and ecology of the Congo terminal deepsea fan system [START_REF] Rabouille | The Congolobe project, a multidisciplinary study of Congo deep-sea fan lobe complex: Overview of methods, strategies, observations and sampling[END_REF], a hotspot of terrestrial carbon burial (Baudin et al., 2017b). The sediments of the lobe complex are organic-rich silts and silty-clays, their C/N and δ 13 C values indicated that 70-80% of the OM was terrestrial in origin [START_REF] Baudin | Distribution of the organic matter in the channel-levees systems of the Congo mud-rich deep sea fan (West Africa). Implication for deep offshore petroleum source rocks and global carbon cycle[END_REF][START_REF] Stetten | 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[END_REF], and was mostly composed by river particles conveyed from the Congo mouth by turbiditic currents. Sediment palynofacies revealed predominant well preserved particles derived from plant structures. In addition, amorphous organic matter was relatively more abundant in the studied levee whereas the denser well preserved wood fragments and transparent intact phytoclasts were enriched in the channel sediment, suggesting a general sorting of particles according to the density of particle [START_REF] Schnyder | Palynofacies reveal fresh terrestrial organic matter inputs in the terminal lobes of the Congo deep-sea fan[END_REF]. Palynofacies also evidenced a vertical gradient in the upper 20 cm of the cores. Amorphous organic matter is relatively enriched upcore with respect to denser terrestrial components, which further supports hydraulic sorting of particles in the turbiditic deposits.

Molecular geochemistry brings complementary views to bulk geochemical information. Terrestrial molecular biomarkers fall into extractable lipids or non extractable macromolecules. Typical terrestrial biomarkers such as lignin phenols for instance, have revealed selective sorting of higher plant debris and soil particles [START_REF] Cathalot | The fate of river organic carbon in coastal areas: A study in the Rhone River delta using multiple isotopic (delta C-13, Delta C-14) and organic tracers[END_REF][START_REF] Gordon | Controls on the distribution and accumulation of terrigenous organic matter in sediments from the Mississippi and Atchafalaya river margin[END_REF][START_REF] Rezende | Lignin phenols used to infer organic matter sources to Sepetiba Bay -RJ, Brasil[END_REF]. Branched glycerol dialkyl glycerol tetraethers (DGDT) are used to trace soil inputs to aquatic sediments [START_REF] Kim | Tracing soil organic carbon in the lower Amazon River and its tributaries using GDGT distributions and bulk organic matter properties[END_REF][START_REF] Lopes Dos Santos | Signatures of tetraether lipids reveal anthropogenic overprinting of natural organic matter in sediments of the Thames Estuary, UK[END_REF]. Even if lipids comprise less than 1% of the bulk terrestrial organic pool, terrestrial lipid biomarkers are routinely used to detect variations in terrestrial inputs and in their preservation in sediments. Odd long-chained (C 25 -C 35 ) alkanes are higher plant biomarkers resistant to degradation and are commonly used as vascular plant proxy, in present day environments as well as in paleoreconstruction studies [START_REF] Castañeda | Organic geochemical records from Lake Malawi (East Africa) of the last 700 years, part II: Biomarker[END_REF][START_REF] Gogou | Marine organic geochemistry of the Eastern Mediterranean: 1. Aliphatic and polyaromatic hydrocarbons in Cretan Sea surficial sediments[END_REF][START_REF] Mangelsdorf | Climatic and oceanographic variations on the California continental margin during the last 160 kyr[END_REF][START_REF] Romero-Viana | Lipid biomarker signatures in a hypersaline lake on Isabel Island (Eastern Pacific) as a proxy for past rainfall anomaly (1942-2006 AD)[END_REF]. A 3 year survey of n-alkanes in suspended particles from the Congo River showed that they integrate the catchment signal with minimal seasonality [START_REF] Hemingway | Multiple plant-wax compounds record differential sources and ecosystem structure in large river catchments[END_REF].

The present contribution examines the hydrocarbon composition of sediments of the lobe complex, of Congo River sediments and of sediment traps in order to complement bulk proxies and palynofacies evidences. It aims at bringing information on the source of the organic matter preserved in the lobe sediments and questions whether the spatial distribution of terrestrial hydrocarbon biomarkers reflects the variability evidenced by palynofacies. Concentrations of both aliphatic and terpenic hydrocarbons in recent marine sediments are very seldom reported in the literature and concentrations of both aliphatic and terpenic hydrocarbons presented here provides original reference data for this region, displaying uncommon terpene abundances. In addition, fluxes have seldom been reported previously. Comparing sedimentary mass accumulation rates and water column fluxes of aliphatic and terpenic hydrocarbons brings new understanding of the importance of terrestrial hydrocarbon inputs.

Five sites representative of an upstream-downstream gradient in the lobe complex, including both the active lobe system and an abandoned lobe, and a site in the Congo River were selected for sedimentary hydrocarbon molecular study. This sample set has been previously characterized for grain size, organic carbon concentration (OC), δ 13 C, C/N ratio, Rock-Eval and other geochemical approaches (Baudin et al., 2017a;[START_REF] Stetten | 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[END_REF][START_REF] Schnyder | Palynofacies reveal fresh terrestrial organic matter inputs in the terminal lobes of the Congo deep-sea fan[END_REF]. Particles collected by sediment trap moored 40 m above the lobe sediment beds were also analyzed to understand the contribution of sinking particles.

Material and methods

Sampling strategy

The samples were collected during two cruises that took place in 2011 on the RV Pourquoi Pas? The first one, WACS [START_REF] Olu | WACS cruise[END_REF] was conducted in February 2011 and the second one, Congolobe, was performed between Fig. 1. Study area. Red dots on the top figure shows the locations of the Congo River sediments K1, K2 and K3, at the entrance to the Malebo Pool. Sediment trap moorings at the Regab site (Tr R1 and Tr R2) at the site WACS Tr C (Tr C1,Tr C2 and Tr C4) are indicated by blue triangles. The lower panel shows the general bathymetric map of the Congo River deep-sea fan. The boundaries of the terminal lobe complex are outlined by a black line, while dotted lines outline distinct lobes, from the older lobe 1 to the youngest lobe 5. The presently active channel fuels the lobe 5. The locations of coring sites are indicated by black dots. The Site E is located at the end of the abandoned channel. The location of the sediment trap mooring at site A (A-WPPART03) is indicated by a blue triangle.

Table 1 reports the locations and depths of the analyzed sample set. Sites A, F and C are located along an upstream -downstream gradient along the active southern channel. Site A is located in lobe 2 (A), where the canyon is a 45 m deep channel in which the sediment core CoL-A-MTB03 was recovered. This core was collected on the southern levee displaying gentle flanks [START_REF] Rabouille | The Congolobe project, a multidisciplinary study of Congo deep-sea fan lobe complex: Overview of methods, strategies, observations and sampling[END_REF]. Site F is located at the onset of lobe 4, 40 km downstream of site A and the sediment core CoL-F-MTB-04 was collected on the northern levee of this site. At site F, the canyon is a 45 m deep and 2500 m wide channel. Site C is located 25 km downstream of site F, at the distal part of the lobe 5, where the canyon structure fades into a 11 m deep channel, as a result of the accumulation of recent particle deposits. At this site, the sediment core CoL-C-MTB-06 was collected on the levee and CoL-C-MTB-11 on the channel. CoL-B-MTB-12 was sampled on lobe 3 at site B, located on the northern levee in the vicinity of the inactive channel. At the coring location the presently inactive channel leading to lobe 3 is only a few meters deep. Site E characterizes an abandoned northern lobe complex, 45 km north of the active channel that receives little turbiditic matter since at least 4 ka BP [START_REF] Rabouille | The Congolobe project, a multidisciplinary study of Congo deep-sea fan lobe complex: Overview of methods, strategies, observations and sampling[END_REF][START_REF] Stetten | 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[END_REF]. This site refers to conditions where mainly pelagic inputs build up the sediments, as opposed to the other sites where turbidites are the main deposit types. The sediment core CoL-E-MTB-14 was collected at this site.

In order to characterize the Congo River particulate inputs, sediments from the river floodplain were analyzed (Table 1). They were collected at three sites at the Malebo Pool, permanently flooded, inundated during high discharge months, and recently exposed, and were donated from H. Talbot and R. Spencer (Talbot et al., 2014, Supplementary Table 2). At these sites the particulate organic carbon composition compares well to that in the estuary and these 3 river sediments are considered as representative of the Congo particulate export to the Atlantic [START_REF] Spencer | An initial investigation into the organic matter biogeochemistry of the Congo River[END_REF].

In order to characterize the vertical rain of pelagic particles, a limited set of sediment trap samples from 3 sites were considered (Table 1). Two sediment traps were located at a mid distance between the canyon head and the lobe complex, one is located 10 km north of the canyon channel and is located above a large cold seep pockmark (samples TrR1 and TrR2), the other is above the canyon itself (TrC1,TrC2 and TrC4). The third trap was moored at the entrance of the lobe complex above the site A (TrA1 and TrA2).

Hydrocarbon molecular analyses

Known amounts of C 24 D 50 were added to the lyophilised samples prior to extraction as a surrogate for non aromatic hydrocarbons. The lyophilised sediment samples (ca. 0.2 to 6 g d.w.) were extracted using accelerated solvent extraction. The samples were homogenised with diatomeous powder previously combusted at 450 o C and sequentially extracted using accelerated solvent extraction (Dionex ASE 350). The first extraction, with acetone at 100 o C and 1500psi for 1 static cycle of 5 min. and 60% of flush, was followed by 3 static cycles of 5 min. with acetone/dichloromethane (1:1) at 100 o C and under a pressure of 140 bars. The sequence was previously optimized using coastal sediments to ensure no cross-contamination. The lipid extracts were treated with acid-activated copper to remove elemental sulfur. The extracts were concentrated using rotary evaporation, solvent exchanged to iso-octane and concentrated down to 200 l. They were purified into different fractions on a dual silica/alumina column made of 5g of silica deactivated at 5% and 3 g of alumina deactivated at 3%. The first fraction, eluded by 25 ml of hexane, contained the aliphatic and cyclic hydrocarbons.

This fraction was first analyzed for aliphatic compounds by gas chromatography (GC) coupled to a flame ionization detector (FID) equipped with a DB-5MS capillary column (J&W, 30m x 0.249 mm i.d. x 0.25 µm thick phase film). The carrier gas was helium at a pressure of 110 kPa. The oven temperature, initially at 60°C was brought to 100°C at a rate of 25°C/min, then to 310°C at a rate of 2°C/min. The final isotherm of 310°C was held for 60 minutes. The FID was kept at 330°C. Aliphatic hydrocarbons were quantified relatively to the internal standard added prior to extraction. For river and trap samples the quantity of available material (0.2 to 1g) did not allow a proper quantification by GC-FID. These samples were quantified by GC-Mass Spectrometry (GC-MS) on an Agilent 6890 Series GC system coupled to an Agilent 5973 Network Mass Selective Detector. A DB-5MS capillary column (Agilent DB5, 30m x 0.25 mm i.d. x 0.25 µm thick phase film) was used. The carrier gas was helium at a flow of 1.2 ml/min. The initial oven temperature of 60°C was held for 5 minutes, then brought from 60°C to 160°C at a rate of 25°C/min, then increased to 310°C at a rate of 3°C/min with a final isotherm of 10 minutes. Full acquisition program scan (from 40 to 600 amu) under electron impact ionization at 70eV was used. Individual hydrocarbons were quantified relatively to the surrogate (C 24 D 50 ) and corrected with relative response factors (RRFs). Calibration solutions containing 25 target n-alkanes (prepared from Alkane mix 10, Dr Erhenstorfer GmD), chosen to bracket the sample concentrations, were used to derive the RRFs of the analytes. Carbon Preference Index (CPI) was calculated as:

) ) C C C C C (C ) C C C C C (C ) C C C C C (C ) C C C C C (C (
                      
Hopanes and other triterpenes were semi-quantified by integrating peaks on the ion current at m/z 191. The major hopanoid, hop-17(21)-ene, was quantified by GC-FID, and the other triterpene abundances were calculated by relating their area to that of the hop-17(21)-ene. In a few samples, hop-17(21)-ene could not be quantified on the GC-FID trace. In those few samples, the hopane abundances were calculated by relating their area to that of the n-C 31 n-alkane, and correcting with response factors determined from the samples where both n-C 31 and hop-17(21)-ene were unequivocally quantified by GC-FID responses.

Procedural blanks were processed and analyzed. They were clear of contamination. The method was also tested for reproducibility and repeatability. The disparity was less than 5%.

Sedimentary accumulation fluxes of the given hydrocarbons were calculated as :

4 alk alk 10 p) (1 d AR C Φ       With alk
Φ the mass accumulation rate of the hydrocarbon in ng m -2 yr -1 , alk C the concentration of a given hydrocarbon in ng.g -1 of dry weight, AR the sediment accumulation rate in cm yr -1 , d the sediment density in g cm -3 , p the sediment porosity.

Results

n-alkanes molecular profiles and concentrations

A total of 31 n-alkanes ranging from C 10 to C 40 , and 8 isoprenoid hydrocarbons were identified and quantified in the samples. The dominant biomarkers in most sediments of the lobe complex sediments are a suite of n-alkanes dominated by high-MW compounds (> C 24 ) with predominance of odd over even carbon chain alkanes (CPI values from 4.0 to 9.6) (Fig. 2, Table S1 Supplementary material, p. 40-47). They derive from higher plant waxes (Table 2). Their concentrations in the lobe sediments varied from 50 to 6070 ng g DW -1

, from 320 to 1150 ng g DW -1 in Congo River banks and from 470 to 2040 ng g DW -1 in sediment traps. Their range compares well with other river deltas (Table 3). [START_REF] Bravo | Novel methylated triterpenoids of the gammacerane series from the nitrogen-fixing bacterium Bradyrhizobium japonicum USDA 110[END_REF][START_REF] Hamed | Unusual Fernane and Gammacerane Glycosides from the Aerial Parts of Spergula fallax[END_REF][START_REF] Kleemann | Tetrahymanol from the phototrophic bacterium Rhodopseudomonas palustris: first report of a gammacerane triterpene from a prokaryote[END_REF][START_REF] Banta | A distinct pathway for tetrahymanol synthesis in bacteria[END_REF] Oleanene, ursene angiosperms terrestrial [START_REF] Peters | The biomarker Guide[END_REF] Fernenes ferns terrestrial [START_REF] Ageta | Fern constituents: Pentacyclic triterpenoids isolated from Polypodium niponicum and P. formosanum[END_REF][START_REF] Paull | Fernenes and other triterpenoid hydrocarbons in Dicroidium-bearing Triassic mudstones and coals from South Australia[END_REF] anaerobic bacteria Marine [START_REF] Volkman | Bacterial and algal hydrocarbons in sediments from a saline Antarctic lake, Ace Lake[END_REF]Marynowski et al., 2007b bacteria

Brassel and Eglinton1893

Diploptene and bacteria marine [START_REF] Rohmer | Distribution of hopanoid triterpenes in prokaryotes[END_REF][START_REF] Talbot | Variability in aerobic methane oxidation over the past 1.2Myrs recorded in microbial biomarker signatures from Congo fan sediments[END_REF][START_REF] Banta | A distinct pathway for tetrahymanol synthesis in bacteria[END_REF] hop-21-ene soil bacteria terrestrial [START_REF] Prahl | Diploptene: an indicator of terrigeneous organic carbon in Washington coastal sediments[END_REF] Hop-17(21)-ene ferns terrestrial [START_REF] Patitucci | Analysis of crude extracts and fractions of Brazilian Polypodiaceae by high resolution gas chromatography mass-spectrometry. I. Triterpenes[END_REF]Shiojima and Ageta, 1990 Neohop-13(18) ) and fluxes ( g m -2 yr -1 ) of terrestrial alkanes, Short-chain alkanes, UCM and terpenoids in marine, lacustrine and continental sediments in comparison with sediments from the terminal Congo lobe system.

Study location

Reference ng g DW -1

g g OC -1 g m -2 yr-1 ng g DW -1 g g OC -1 g m -2 yr-1 ng g DW -1 g m -2 yr -1 ng g DW -1 g g OC -1
g m -2 yr-1 The three sediments from the Congo River show an identical hydrocarbon composition, maximizing at n-C 29 , and with the n-C 23 to n-C 35 mode accounting from 91% to 95% of total non cyclic hydrocarbons. These patterns are consistent with the molecular composition described for suspended particles in the Congo River [START_REF] Hemingway | Multiple plant-wax compounds record differential sources and ecosystem structure in large river catchments[END_REF]. This strong higher plant signature is mirrored in alkane molecular patterns from many of the studied sediments: the levee of site A, the channel at site C, and in the deeper part of the site E (>10 cm horizons), confirming that the Congo River is the primary supply of the organic matter accumulated in the lobe complex (Fig. 3). In the sinking particles collected by sediment traps, the higher plant fingerprint is faint at the Regab site, located away from the active channel, marked at the canyon site, and variable at site A (Fig. 3). ). Carbon Preference Index (CPI) calculated from C 25 to C 35 is plotted on the right axis. Bottom panels show the vertical profiles of terrestrial nalkane concentrations and CPI in two cores, from the channel at site C, and from site E.

Atlantic Ocean

In sediments from the channel of site A, the levee of site F, the levee and upper horizons of the channel at site C and of site E, the terrestrial imprint co-occurs with a low molecular weight mode of n-alkanes, with even predominance maximizing at n-C 14 and n-C 16 (Fig. 2, right middle and bottom panels; Fig. 4). The phytoplanktonic biomarker n-C 17 indicates recent input of phytoplanktonic biomass (Table 2; [START_REF] Marty | Particulate fluxes of organic compounds and their relationship to zooplankton fecal pellets in the northwestern Mediterranean Sea[END_REF]. Its higher contribution in sediment trap particles than in sediments and soils underlines the predominantly marine origin of the sinking particles, in line with Rock-Eval assessment (Baudin et al., 2017a). Chromatographically unresolved hydrocarbons were detected in 12 samples. The unresolved complex mixture (UCM), potentially composed of over 250 000 cyclic and branched hydrocarbons [START_REF] Sutton | Isolation of individual hydrocarbons from the unresolved complex hydrocarbon mixture of a biodegraded crude oil using preparative capillary gas chromatography[END_REF] brings evidence for the occurrence of petrogenic hydrocarbons (Table 2). UCM concentration was the highest in the surface sediments of site E (10 500 ng g DW -1

), and took lower values in some sediments of the sites A and B (up to 8 000 ng g DW -1 and up to 1 500 ng g DW -1

, respectively). Three phytadiene isomers were the dominant isoprenoids in the vast majority of sediment samples, but they were absent in river sediments and nearly absent in sinking particles (Fig. 5). The concentrations of the three isomers were similar and that of the third one took a maximum value 202 ng g DW -1 in the surface sediment of the levee at site C, and of 1 ng g DW -1 in the sole trap sample where phytadienes could be identified. -1 . Bottom panels show the vertical profiles of concentration of phytadienes, in two cores, from the channel at site C, and from site E.

Triterpene molecular profiles

Substantial amounts of triterpenes were present in the sediment extracts from the terminal lobe, in particular at site C. The hopane and hopene mass spectra interpretation was inferred from retention times and published spectra. Representative m/z=191 hopanograms and mass spectra of the major hopanoids are presented in the Supplementary material (Figs. S2,S3,S4 and S5,.

Triterpene distribution patterns within the lobe complex sediments shared common features such as the predominance of C 30 and C 31 hopanes in the 17β(H),21β(H) (ββ) and 17β(H),21α(H) (βα) configurations, and of unsaturated hopanoids . Both characteristics are a clear signature of recent immature organic matter, as opposed to oil contamination. Hopane and C 31 homohopane having retained their precursor ββ configuration are abundant in terrestrial clays and sediments [START_REF] Kvenvolden | Hydrocarbons in sediments of the Weddell Sea, Antarctica[END_REF]Marynowski et al., 2007a). In the lobe complex sediments, they likely traced soil inputs (Fig. 7). A few samples showed contrasting composition: in surficial sediments (0-0.5 cm and 0.5-and 1 cm) of the disconnected E site, tricyclic diterpanes with 20, 21, 23, 24 and 25 carbon atoms were the dominant homologues, and hopenes were less abundant or non detected (Fig. 6, Fig. S2 in Supplementary material, p. 59). Tricyclic diterpanes have been described as the major homologues in saline lacustrine and marine crude oils [START_REF] Tao | Geochemical application of tricyclic and tetracyclic terpanes biomarkers in crude oils of NW China[END_REF], and their occurrence points to oil contamination of site E surficial sediment, in agreement with the UCM concentrations and CPI values. However the hopane profile in the lobe complex sediments did not show the characteristics of a mature oil (αβ and moretane dominance over ββ-hopanes), as the hopene profile was the same as in the other non-contaminated sites, and as in the non-contaminated deeper horizons at site E (hop-17(21)-ene, ββ-C 30 hopane and ββ-C 31 -homohopane (Fig. 6) (Fig. 8). In most lobe sediments, hop-17(21)-ene, ββ-hopane and diploptene (hop-22(29)-ene) were the dominant homologues (Figs. 9 and 10). Diploptene is present in various types of bacteria and is related to the membrane constituent bacterihopanetetraol (Table 2). In contemporary sediments, its diagenesis starts with double bond migration into hop-21-ene, then into hop-17(21)-ene, and further proceeds by rearrangement and migration of the methyl at C-18 to the position C-17 forming norneohop-13(18)-ene [START_REF] Simoneit | A review of current applications of mass spectrometry for biomarker/molecular tracer elucidations[END_REF]. In the present sample set, the four isomers were detected in variable proportions. Hop-17(21)-ene prevailed in most sediments, in particular at the site C, and also in the sinking particles collected by sediment traps. Hop-17(21)-ene concentrations were from non detected to 9 ng g DW -1 in the Congo River sediments, maximized at 335 ng g DW -1 in some sediments of the site C and varied from non detected to 303 ng g DW -1 in the sediment trap samples.

In river samples and in a few samples (site A levee, site C surficial layers), diploptene was equally prominent in the m/z 191 fragmentograms. Diploptene concentrations reached 25 ng g DW -1 in the Congo River sediments, 294 ng g DW -1 in some sediments of the site C and 215 ng g DW -1 in the sediment trap samples. Neohop-13(18)-ene seldomly prevailed, for instance in surficial sediment of the levee of the site A (Fig. 6). A C 27 22,29,30trisnorhop-13(18)-ene was also detected in most samples (Figs. S3 and S4, Supplementary material, p. 60). Gammacerene was the most abundant non-hopanoid triterpene in the lobe sediments. It differs from hopanoid by a six-, instead of 5-, membered E ring. Other non-hopanoid triterpenes produced by higher plants were detected in the lobe sediments: oleanene, lupene, ursene and fernenes (Fig. 6).

The ursane and oleanane skeletons derive from α-and β-amyrins and are the most frequently encountered in recent sediments [START_REF] Simoneit | A review of current applications of mass spectrometry for biomarker/molecular tracer elucidations[END_REF]. Oleanene accounted for a higher portion of triterpenes at the levee of site A, and was less abundant at the other sites (Fig. 6). Even though bulk indices showed a rather homogeneous, mostly terrestrial, organic matter at the sites A, F and C of the lobe, the contribution of vascular plants and soil bacterial biomarkers may differ by as much as one order of magnitude in the terminal lobe sediments (Figs. 2, 7 and 8). Oleanene, ursenes, and hop-17(21)-ene are reported in shelf sediments at other locations worldwide and in terrestrial clays [START_REF] Brassell | Aliphatic Hydrocarbons of a Cretaceous Black Shale and Its Adjacent Green Claystone From the Southern Angola Basin[END_REF]Ten Havens and Rullkötter, 1989;[START_REF] Van Dongen | Well preserved Palaeogene and Cretaceous biomarkers from the Kilwa area, Tanzania[END_REF]Marynowski et al., 2007a). ββ-homohopane is also one of the dominant terpenoids in immature terrestrial organic matter [START_REF] Kvenvolden | Hydrocarbons in sediments of the Weddell Sea, Antarctica[END_REF]. The saturated homologues of higher plant triterpenes were not detected, nor gammacerane, bringing another evidence of the immaturity of the soil and plant organic matter present in the sediments. Pearson correlations show that gammacerene is related to the bulk terrestrial indicator δ 13 C, suggesting that it quantitatively contributed to the bulk terrestrial matter, while oleanene and fernenes did not, and may represent a less abundant higher plant contribution (Table S2, Supplementary material, p. 48-58). Des-A-triterpenoids are formed by A-ring degradation under anoxic conditions [START_REF] Van Bree | Des-A-lupane in an East African lake sedimentary record as a new proxy for the stable carbon isotopic composition of C 3 plants[END_REF]. They are detected in low levels in the terminal lobe system and indicate the occurrence of degraded C3/C4 plants (Table S1, Supplementary material, p. 40-47).

Steranes, sterenes and diasterenes showed a minor contribution to the Congo River and lobe sediments. Higher C 29 sterene concentrations characterized the sediment trap samples. They more probably stem from the degradation of higher plant and phytoplankton sterols.

Discussion

Organic matter sources and degradation by microorganisms, spatial heterogeneity

Sedimentary hydrocarbons in the terminal lobe complex show a conspicuous dominance of terrestrial n-alkanes, and of terrestrial and microbial triterpenes. Their dominance evidences the primary terrigenous source of the organic matter, which is already established by δ 13 C and C/N values of the same sediments [START_REF] Stetten | 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[END_REF], and by their Rock-Eval characterization (Baudin et al., 2017a(Baudin et al., , 2007b)). Rock-Eval results typified the organic matter as non mature Type III kerogen, sourced by terrestrial biomass and soils. The CPI values confirm that the lobe complex is a site of large accumulation of terrestrial organic carbon exported from the Congo catchment area to the deep ocean. The concentrations of terrestrial n-alkanes were in the same range as other marine coastal and marginal locations such as the Mediterranean Rhône and Ebro prodelta (Table 3), showing that the massive export of terrestrial organic matter through the Congo canyon results in similar terrestrial fingerprint as coastal shallow deposition sites, but at an abyssal location.

On top of this general homogeneous trend, terrestrial biomarker concentrations show some degree of variability (Figs. 3 and8), which will be discussed in the present section.

Site B is located in the lobe 3 where a branch of the northern channel is only a few meter deep and is supposed to convey much less turbiditic inputs than the active southern channel ending at site C.

Terrestrial n-alkane signatures at site B and site C are however comparable, revealing that B receives the same organic matter as C, either from the northern channel or from overspilling of the turbidites going through the southern active channel.

At disconnected site E, δ 13 C values show a dominance of marine organic matter (-22.8 to -24.2‰, Stetten et al., 2015). Phytadienes reflect the decay of recent algal remains in anaerobic conditions. Other phytoplanktonic fingerprints (n-C 17 dominance) were not present. The lower accumulation rate (0.1 cm yr -1 ) and the larger oxic layer (6.6 cm, [START_REF] Pozzato | Early diagenesis in the Congo deep-sea fan sediments dominated by massive terrigenous deposits: Part I -Oxygen consumption and organic carbon mineralization using a micro-electrode approach[END_REF] than at the other studied sites involve a more extensive degradation at this site. The first centimetre of sediment has been accumulated during at least 20 years and the reported degradation rates of marine short-chain nalkanes are coherent with their decay during this time period [START_REF] Cheng | Progressive Degradation of Crude Oil n-Alkanes Coupled to Methane Production under Mesophilic and Thermophilic Conditions[END_REF][START_REF] Grossi | Burial, exportation and degradation of acyclic petroleum hydrocarbons following a simulated oil spill in bioturbated Mediterranean coastal sediments[END_REF][START_REF] Miralles | Alkane biodegradation and dynamics of phylogenetic subgroups of sulfate-reducing bacteria in an anoxic coastal marine sediment artificially contaminated with oil[END_REF]. The sediment core collected at site E has been deposited in less than a thousand years, while the corresponding channel ceased to fuel river particles to the lobe ca 4 kyr ago [START_REF] Rabouille | The Congolobe project, a multidisciplinary study of Congo deep-sea fan lobe complex: Overview of methods, strategies, observations and sampling[END_REF]. A striking characteristic of the upper 13 cm of the sediments at site E is that its higher plant biomarker content compares well to that of sites A, F, or B, presently connected to the active canyon, despite the large difference in δ 13 C opposing the site to the others (Fig. S1, Supplementary material, p. 59). Given the hemipelagic source of the organic matter at E, a marked contribution of n-C 17 , a planktonic alkane, would be expected, but is not found (Fig. 2). A plausible explanation to this mismatch is the faster degradation of short-chain marine alkanes, relatively to more refractory terrestrial hydrocarbons. The molecular fingerprint (proportions in n-C 29 , gammacerene and hop-17(21)-ene) of the terrestrial organic matter at site E reflects the same origin as at sites connected to the Congo canyon, and can be ascribed to Congo River inputs rather than from atmospheric aerosol deposition, the dominant source of terrestrial hydrocarbons at other open sea locations [START_REF] Gogou | Marine organic geochemistry of the Eastern Mediterranean: 1. Aliphatic and polyaromatic hydrocarbons in Cretan Sea surficial sediments[END_REF]. This is a striking evidence that significant river matter is admixed to the pelagic particles at site E, 45 km away from the active channel. The deeper sedimentary horizons of site E showed an increase in several higher plant indicators, a feature also observed in the deeper horizon of the channel at site C. These signals seem to reveal an input of higher plant detritus in these horizons, in line with the slightly higher grain size and terrestrial phytoclasts [START_REF] Stetten | 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[END_REF][START_REF] Schnyder | Palynofacies reveal fresh terrestrial organic matter inputs in the terminal lobes of the Congo deep-sea fan[END_REF].

Pearson correlations of hydrocarbons concentrations normalized to organic carbon are shown in Table S2 (Supplementary material, p. 48-58). They indicated that hydrocarbons with similar structures covaried, for instance, long-chain homologues on one hand, and short-chain homologues on the other, pointing to common source and comparable sensitivity to degradation (Table S2, Supplementary material, p. 48-58). The Spearman correlations show that vascular plant n-alkanes covaried with some hopanes with αβ (C 20 ) and βα (C 30 ) configurations, but vascular plant alkane concentrations showed no covariation neither with those of gammacerene nor fernene, biomarkers of ferns, nor with concentrations of oleanene and ursene, biomarkers of angiosperms. This suggests the occurrence of terrestrial remains from distinct types of vegetation and from soils. Palynofacies also showed variable relative abundances of amorphous organic matter (AmOM) and terrestrial phytoclasts (T-Phyt), however they did not allow to distinguish fern and angiosperm remains [START_REF] Schnyder | Palynofacies reveal fresh terrestrial organic matter inputs in the terminal lobes of the Congo deep-sea fan[END_REF]. The denser T-Phyt were enriched in the channel of station A relatively to the less dense AmOM, whereas AmOM was enriched in the levee sediments at station A and C, suggesting hydraulic sorting of the turbiditic particles. In the sediments enriched in AmOM, hydrocarbon concentrations are higher. It could be hypothesized that the lighter particles may be enriched in hydrocarbons. The enrichment in terrestrial alkanes in the deepest (19-22 cm) horizons of the channel of station C and of station E corresponds to the highest T-Phyt palynomorphs and a more terrestrial organic matter as seen by δ 13 C values (Fig. S1, Supplementary material, p. 59). It suggests either a physical sorting of particles within the same turbidite, or the occurrence of a second turbidite in the deepest layers, enriched in coarser terrestrial particles.

Interestingly, δ 13 C and CPI, both classical indicators of higher plant contribution, showed no significant covariation in the present data set (Table S2, Supplementary material, p. 48-58). δ 13 C did not covary significantly with any of the concentrations of aliphatic nor terpenoid terrestrial indicators. In the channel of site C, δ 13 C of the organic matter is shifted towards more negative values, and the proportion of terrestrial phytoclasts in the palynofacies is higher. Both signals agree to indicate a higher fraction of non degraded terrestrial matter at this site.

Hydrocarbons are effectively degraded under oxic conditions. Experiments in coastal sediments have showed that alkanes having less than 25 C atoms were degraded within one year. For example, between 29% and 84% of n-C 17 alkane was degraded in 500 days [START_REF] Grossi | Burial, exportation and degradation of acyclic petroleum hydrocarbons following a simulated oil spill in bioturbated Mediterranean coastal sediments[END_REF][START_REF] Miralles | Alkane biodegradation and dynamics of phylogenetic subgroups of sulfate-reducing bacteria in an anoxic coastal marine sediment artificially contaminated with oil[END_REF]. The degradation of longer chain hydrocarbons is slower but also effective (80% in one year, [START_REF] Grossi | Burial, exportation and degradation of acyclic petroleum hydrocarbons following a simulated oil spill in bioturbated Mediterranean coastal sediments[END_REF]20-88% in 500 days, Miralles et al., 2007). The efficient mineralization of longchain alkanols, another class of terrestrial lipids, was previously evidenced at a site located closer to the canyon head [START_REF] Treignier | Terrestrial and marine n-alcohol inputs and degradation processes relating to a sudden turbidity current in the Zaire canyon[END_REF]. Diffusive oxygen uptake values showed that organic carbon was actively remineralized in the first centimeters of the Congo lobe sediments [START_REF] Pozzato | Early diagenesis in the Congo deep-sea fan sediments dominated by massive terrigenous deposits: Part I -Oxygen consumption and organic carbon mineralization using a micro-electrode approach[END_REF].

The average sediment accumulation at site C was exceptionally high, with a turbidite layer (of 10-20 cm) being deposited every 2-3 years, while the sediment accumulation at A and F is one order of magnitude lower [START_REF] Rabouille | The Congolobe project, a multidisciplinary study of Congo deep-sea fan lobe complex: Overview of methods, strategies, observations and sampling[END_REF]. Therefore the organic matter at station C remains in the oxic layer ca 10 times less than at A and F. This shorter exposure to oxic degradation may result in less degraded terrestrial material at the distal site C than at site A.

Phytadienes are produced by degradation of the phytyl side chain of chlorophylls during early diagenesis, while they are not produced during water column degradation processes [START_REF] Grossi | Formation et devenir des phytadiènes dans le milieu marin: implication de ces hydrocarbures dans les processus de dégradation des chlorophylles à chaîne phytyle. Origin and fate of phytadienes in the marine environment: implication of these hydrocarbons in degradation processes of chlorophylls with a phytyl side chain[END_REF][START_REF] Grossi | Biotransformation pathways of phytol in recent anoxic sediments[END_REF]. They have been shown to be readily degraded in aerobic sediments while low oxygen exposure favoured their preservation in cyanobacterial mats [START_REF] Grossi | Formation et devenir des phytadiènes dans le milieu marin: implication de ces hydrocarbures dans les processus de dégradation des chlorophylles à chaîne phytyle. Origin and fate of phytadienes in the marine environment: implication of these hydrocarbons in degradation processes of chlorophylls with a phytyl side chain[END_REF][START_REF] Pagès | Characterizing microbial communities and processes in a modern stromatolite (Shark Bay) using lipid biomarkers and two-dimensional distributions of porewater solutes[END_REF][START_REF] Slowakiewicz | Holocene intertidal microbial mats of Qatar and their implications for petroleum source rock formation in carbonate-siliciclastic-evaporite systems[END_REF]. The spatial distribution pattern of phytadienes in the Congo lobe system contrasts with that of terrestrial n-alkanes and terpenoids (gammacerene, fernene, diploptene) by their absence in the river sediments and sediment traps and their marked enrichment at the site C where they almost reach the concentrations of terrestrial n-alkanes. Phytadienes' occurrence confirms a greater input of labile chlorophylls, present in fresh plants or algae, to the sites C and B, followed by their hydrolysis into phytadienes and the preservation of phytadienes under anaerobic conditions. The longer residence of turbidite particles in the oxic layer at sites A and F may have resulted in chlorophyll hydrolysis before they reached the anaerobic layer and explain the low abundance of phytadienes in these cores. Whereas covariation was observed for hydrocarbons with similar structures (short-chain and long-chain alkanes, short-chain even hydrocarbons, hopenes, phytadienes), phytadienes and terpenoids, of markedly difference structures, show significant covariation (Table S2, Supplementary material, p. 48-58). It evidences that phytadienes and terpenoids share a common source and shows that terpenoids are associated with recent inputs of terrestrial matter.

The bulk terrestrial signature at all sites is equivalent, but all aliphatic and terpenoid terrestrial hydrocarbons have higher concentrations at sites C and B, normalized to organic carbon or to dry weight. The higher concentrations at site C could indicate that terrestrial hydrocarbons have been exposed to degradation for a shorter time within the sediments of site C relatively to sites A and F, and that terrestrial hydrocarbons decay faster than bulk terrestrial organic matter. According to its location at the end of an inactive channel, site B has a low sediment accumulation rate (0.3 cm yr -1 , [START_REF] Rabouille | The Congolobe project, a multidisciplinary study of Congo deep-sea fan lobe complex: Overview of methods, strategies, observations and sampling[END_REF], comparable to that of site A. Therefore its hydrocarbon content was expected to be in the same range as that of site A. Surprisingly, concentrations of terrestrial n-alkanes, of terrestrial terpenes, and of phytadienes at site B are similar to those of site C and in turn, much higher than those of sites A and F (Figs. 3,5,7,8 and 9). Amongst the studies carried out by the Congolobe consortium, only palynofacies characterization evidenced differences in the contribution of terrestrial organic matter pools between stations A and C, but station B was not considered [START_REF] Schnyder | Palynofacies reveal fresh terrestrial organic matter inputs in the terminal lobes of the Congo deep-sea fan[END_REF]. Bulk characteristics, like δ 13 C and C/N did not differenciate sediments from sites A, F, B and C. The enrichment in phytadienes and terrestrial hydrocarbons indicates a larger fraction of recent terrestrial organic matter at sites C and B, within an organic matter that is equally predominantly terrestrial at all sites A, F, C and B. Site B is located 10 km away from the active channel. In march 2001 sediment overspilling over the channel levees caused a significant flux of particles at site ZD, located 13 km off the channel [START_REF] Khripounoff | Direct observation of intense turbidity current activity in the Zaire submarine valley at 4000 m water depth[END_REF][START_REF] Vangriesheim | Turbidity events observed in situ along the Congo submarine channel[END_REF]. The sedimentation rate recorded at site B [START_REF] Rabouille | The Congolobe project, a multidisciplinary study of Congo deep-sea fan lobe complex: Overview of methods, strategies, observations and sampling[END_REF] is consistent with aggradation due to spillover from the feeding channel, and the less dense upper part of the turbidity currrents may reach site B (Dennielou et al., 2017). Therefore the larger proportion of terrestrial hydrocarbons at site B may reflect deposition of labile terrestrial organic matter having recently overflown the levee. The morphology of the sediments at sites A and F showed blocks and headscars (Dennielou et al., 2017) and indicates that sediments are eroded by sliding and levee dismantling. The lower proportion of phytadienes at sites A and F may be linked to the erosion of recent turbiditic deposits at these sites.

Processes driving the hopene and triterpene spatial and temporal variabilities

The prevalence of hopanes and hopenes over steranes and sterenes indicates some contribution of microbiota as source of organic matter [START_REF] Peters | The biomarker Guide[END_REF][START_REF] Simoneit | A review of current applications of mass spectrometry for biomarker/molecular tracer elucidations[END_REF][START_REF] Volkman | Bacterial and algal hydrocarbons in sediments from a saline Antarctic lake, Ace Lake[END_REF][START_REF] Volkman | Sterols and other triterpenoids: source specificity and evolution of biosynthetic pathways[END_REF]. The biological sources of the dominant triterpenes in the lobe sediments, hop-17(21)-ene, ββ-hopane and diploptene (hop-22(29)-ene) are microorganisms and ferns [START_REF] Douka | Structural diversity of the triterpenic hydrocarbons from the bacterium Zymomonas mobilis: the signature of defective squalene cyclization by the squalene/hopene cyclase[END_REF][START_REF] Innes | Preservation and diagenesis of hopanoids in Recent lacustrine sediments of Priest Pot, England[END_REF][START_REF] Innes | Early diagenesis of bacteriohopanoids in Recent sediments of Lake Pollen, Norway[END_REF][START_REF] Patitucci | Analysis of crude extracts and fractions of Brazilian Polypodiaceae by high resolution gas chromatography mass-spectrometry. I. Triterpenes[END_REF][START_REF] Rohmer | Distribution of hopanoid triterpenes in prokaryotes[END_REF][START_REF] Rohmer | The biosynthesis of triterpenoids of the hopane series in the eubacteria -a mine of new enzyme reactions[END_REF][START_REF] Rontani | Lipid characterization of coastal hypersaline cyanobacterial mats from the Camargue (France)[END_REF][START_REF] Sinninghe-Damsté | C 27 -C 30 neohop-13(18)-enes and their saturated and aromatic derivatives in sediments: Indicators for diagenesis and water column stratification[END_REF][START_REF] Welander | Identification of a methylase required for 2-methylhopanoid production and implications for the interpretation of sedimentary hopanes[END_REF]. They are dominant triterpenes in terrestrial environments with low maturity of the organic matter [START_REF] Garel | High frequency floral changes at the Paleocene-Eocene Boundary revealed by comparative biomarker and palynological studies[END_REF]. Their predominance in the Congo River sediments suggests that the export of land particles to the lobe complex is a significant source of these triterpenes (Fig. 6). The three river samples showed a larger abundance of the C 30 moretane (αβ-hopane) than lobe sediments, suggesting that other inputs than river sediment contribute to hopenes in the lobe sediments.

Diploptene is a well-recognized terrestrial biomarker [START_REF] Prahl | Diploptene: an indicator of terrigeneous organic carbon in Washington coastal sediments[END_REF] and gammacerene is a constituent of ciliates, ferns, purple non-sulfur bacteria and N-fixing symbionts of plant roots [START_REF] Bravo | Novel methylated triterpenoids of the gammacerane series from the nitrogen-fixing bacterium Bradyrhizobium japonicum USDA 110[END_REF][START_REF] Hamed | Unusual Fernane and Gammacerane Glycosides from the Aerial Parts of Spergula fallax[END_REF][START_REF] Kleemann | Tetrahymanol from the phototrophic bacterium Rhodopseudomonas palustris: first report of a gammacerane triterpene from a prokaryote[END_REF]. Both are the only hydrocarbons covarying with the bulk terrestrial indicator δ 13 C (Table S2, Supplementary material, p. 48-58), which shows that their spatial variability is related to the dominant fraction of terrestrial organic carbon. Both marine and terrestrial lineages of aerobic methane-oxidizing bacteria were characterized in the studied sediments [START_REF] Bessette | ToffinRelative Abundance and diversity of bacterial methanotrophs at the oxic-anoxic interface of the Congo deep-sea fan[END_REF] and diploptene and gammacerene variations may reflect alive bacteria associated to soil and river organic matter.

Spearman correlations discriminate fern-8-ene, β,α-hopane and hop-21-ene from the other terpenoids because in addition to covarying with other terpenoids, they also show significant covariance with terrestrial n-alkanes. Most terpenoids of Congo River sediments were transferred to the lobe sediments in similar relative proportions (Ts, hop-17(21)-ene, gammacerene, αβ-and ββhopane, ββ-C 31 homohopane). In contrast, hop-17(21)-ene and diploptene showed a variable contribution to total terpenoids (some sediments are devoid of diploptene), and both dominate at site C (Fig. 6). Diploptene and hop-21-ene are constituents of anaerobic Geobacter and Zygomonas bacteria [START_REF] Douka | Structural diversity of the triterpenic hydrocarbons from the bacterium Zymomonas mobilis: the signature of defective squalene cyclization by the squalene/hopene cyclase[END_REF]Hartner et al., 2005), and the similarity in their vertical profiles favors the interpretation of a common anaerobic bacterial source for these isomers (Fig. 9). Clay-catalyzed isomerisation of diploptene into hop-21-ene, further isomerisation into hop-17(21)-ene, and further degradation into neohop-13(18)-ene occur in immature sediments and may alter the precursor signature [START_REF] Simoneit | A review of current applications of mass spectrometry for biomarker/molecular tracer elucidations[END_REF][START_REF] Sinninghe-Damsté | C 27 -C 30 neohop-13(18)-enes and their saturated and aromatic derivatives in sediments: Indicators for diagenesis and water column stratification[END_REF]. The interplay between the soil contribution and the prediagenetic production of diploptene is illustrated by plotting the selected terpenoids concentrations versus that of gammacerene, synthesized by ciliates and bacteria, and generally considered as a terrestrial biomarker. In the present set of samples gammacerene covaries with δ 13 C and is therefore considered to stem from terrestrial bacteria or ciliates (Table S2, Supplementary material, p. 48-58). The covariation of gammacerene with C 27 18(H)-22,29,30trisnorhopane (Ts) shown in the cross plot of their concentrations is consistent with a same continental source of both compounds (Fig. 10). In contrast, the scatter in the plots of neohop-13(18)-ene and hop-17(21)-ene versus gammacerene suggests additional contributions of organic matter than those from terrestrial origin (Fig. 10). The plot of diplotene versus gammacerene concentrations shows some degree of scatter but still with a clear covariance, suggesting the existence of a mixture of terrestrial organic matter inputs with other inputs of organic matter, more likely a contribution from marine bacteria added to terrestrial soil microorganisms.

Diploptene and its Δ21 isomer show identical subsurface peaks at site E (Fig. 9). In the upper sediment layers of site E, palynofacies and δ 13 C values indicate low proportion of higher plant remains and bacteria may be major contributors to these hopenes. Almost identical vertical profiles of hop-17(21)-ene and neohop-13(18)-ene at sites C and E suggest either common precursor organisms or sequential isomerisation of hop-21-ene into hop-17(21)-ene and further transformation into neohop-13(18)-ene (Fig. 11). Similar correlations were observed in a more mature terrestrial set of samples [START_REF] Garel | High frequency floral changes at the Paleocene-Eocene Boundary revealed by comparative biomarker and palynological studies[END_REF]. In a large set of immature marine and lacustrine samples, matching δ 13 C values of both compounds evidenced a diagenetic relationship or a common source [START_REF] Sinninghe-Damsté | C 27 -C 30 neohop-13(18)-enes and their saturated and aromatic derivatives in sediments: Indicators for diagenesis and water column stratification[END_REF]. The series of neohop-13(18)-enes identified in a range of recent and ancient sediments included C 27 to C 30 homologues. In the Congo lobe sediments, the series was limited to the C 30 and C 27 neohop-13(18)-enes, and corresponds to the composition of recent sediments from other locations [START_REF] Sinninghe-Damsté | C 27 -C 30 neohop-13(18)-enes and their saturated and aromatic derivatives in sediments: Indicators for diagenesis and water column stratification[END_REF].

Petroleum contamination

The occurrence of oil hydrocarbons (UCM, C 23 and C 24 tricyclic triterpanes) indicate a notable petroleum contamination of the first surface centimetre of the sediment at site E, but absent underneath (Table S1, Supplementary material, p.40-47). Below the contaminated layers, the CPI is consistent with a higher plant source of the high molecular weight alkanes, alike at the other studied sites. Oil hydrocarbons are also evidenced in lower concentrations at site A and C. A strong petroleum odour was noted when slicing the top of contaminated cores (site E, site C). UCM and alkanes concentrations remained on the same order of magnitude as moderately contaminated coastal sites [START_REF] Bouloubassi | Hydrocarbons in surface sediments from the changjiang (Yangtze River) estuary, East China Sea[END_REF][START_REF] Tolosa | Aliphatic and polycyclic aromatic hydrocarbons and sulfur/oxygen derivatives in northwestern Mediterranean sediments: spatial and temporal variability, fluxes, and budgets[END_REF] and are at least one order of magnitude less abundant than in heavily contaminated coastal areas such as Alexandria harbor, the Rhine estuary and hydrocarbon seepage area (Aboul-Kassim and [START_REF] Aboul-Kassim | Aliphatic and Aromatic Hydrocarbons in Particulate Fallout of Alexandria, Egypt: Sources and Implications[END_REF][START_REF] Burns | Fluxes and fate of petroleum hydrocarbons in the Timor Sea ecosystem with special reference to active natural hydrocarbon seepage[END_REF][START_REF] Stronkhorst | Contaminants of Concern in Dutch Marine Harbor Sediments[END_REF]. UCM covariates with short-chain alkanes in the range C 15 -C 18 , with pristane, phytane, and C 23 and C 24 tricyclic diterpanes, suggesting a fossil source for these compounds (Table S2, Supplementary material, p. 48-58). Another molecular evidence for petroleum occurrence is the series of tricyclic diterpanes from C 21 to C 26 dominating over other terpanes and terpenes on the m/z=191 fragmentogram of the surficial sediment of site E and absent in noncontaminated location nearby (Fig. S3, Supplementary material, p. 60).

The origin of this crude oil contamination is difficult to assert with certainty. The background oil occurrence characterized in sediments along the end of the canyon may come from soil particles from Kinshasa, from hydrocarbon accidental release from Matadi and Boma harbours and from the Banana oil terminal. Crude oil is extracted from the offshore blocks located close to the coast on the Northern side of the canyon (Congo-brazzaville-hydrocarbons-blocks: ©Copyright, 2017) and the possibility that accidental oil spills may have reached the lobe area cannot be ruled out.

The striking enrichment in short chain alkanes with an even predominance at the levee of site C is difficult to explain. These compounds are unusual in marine systems, and are consistent with several sources of organic matter. They were first characterized in evaporitic environments in which the highly reducing conditions favor reduction of fatty acids rather than their β-decarboxylation [START_REF] Moldowan | Relationship between petroleum composition and depositional environment of petroleum source rocks[END_REF][START_REF] Zhang | Geochemical characteristics of saturate hydrocarbons in crude oils and source rocks of the Qaidam, Tarim, Tupran basins, NW[END_REF]. They were also observed in oxygenated environments and were interpreted as a direct microbiota inputs generated by β -decarboxylation of bacterial odd fatty acids [START_REF] Grimalt | Sources and occurrence of C12-C22 n-alkane distributions with even carbon-number preference in sedimentary environments[END_REF][START_REF] Nishimura | Possible origin of n-alkanes with a remarkable even-to-odd predominance in recent marine sediments[END_REF]. The predominance of C 18 in lacustrine sediments was considered to be inherited from planktonic and/or bacterial cells [START_REF] Affouri | The sedimentary organic matter from a Lake Ichkeul core (far northern Tunisia): Rock-Eval and biomarker approach[END_REF]. A short chain mode of even alkanes was observed in C3 trees and C4 grasses, woodland and grassland soils (Table 2). It was also identified in charred biomass and in soils with a coal fraction, however maximizing at C 16 and C 18 [START_REF] Eckmeier | Short-chain n-alkanes (C16-20) in ancient soil are useful molecular markers for prehistoric biomass burning[END_REF]. Finally, Δ 14 C values of hydrocarbons from sediments from the China East margin Sea showed that C 16 and C 18 had a fossil origin [START_REF] Tao | Geochemical application of tricyclic and tetracyclic terpanes biomarkers in crude oils of NW China[END_REF]. In the sedimentary context of Congo lobe complex, this signature is consistent with a higher plant, a bacterial and a fossil contribution. It is present in most of the samples from the lobe system, in the river sediments and even in some sediment trap samples. However the fainter C 16 and C 18 fingerprint in the river sediment samples argues for another origin than higher plants (Fig. 4). C 14 , C 16 and C 18 n-alkanes were correlated to the chromatographically unresolved hydrocarbons (UCM) (Table S2, Supplementary material, p. 48-58). However, these alkanes were more abundant than their odd counterparts in many samples where UCM cannot be quantified. The last likely sources expected to yield a broad repartition of short-chain alkanes are soil bacteria, shown to contribute to alive microbial communities of aerobic methane-oxidizing bacteria [START_REF] Bessette | ToffinRelative Abundance and diversity of bacterial methanotrophs at the oxic-anoxic interface of the Congo deep-sea fan[END_REF]. The degradation products of diploptene, hop-21-ene and neoho-13(18)-ene also displayed their highest concentrations at the levee of site C (Figs. 4 and 11). The occurrence of this group of hopenes in bacteria (Table 3) evokes a possible bacterial source for both groups of hydrocarbons. 14 C isotopic ratios of alkanes would unequivocally ascribe the source of even shortchain alkanes but they were not available in the present study.

Dynamics of terrestrial organic matter inputs

Fluxes of alkanes are seldom reported, and the highest values of terrestrial alkanes are measured in subtropical shelf [START_REF] Sikes | Sources of organic matter in a coastal marine environment: Evidence from n-alkanes and their δ 13 C distributions in the Hauraki Gulf, New Zealand[END_REF]. The accumulation fluxes of terrestrial alkanes measured in the Congo terminal lobe are in the upper range of previous measurements in deep marine environments (Table 3). Terrestrial n-alkanes and triterpenes fingerprint two different sources of terrestrial organic matter, as shown by the Pearson correlation of δ 13 C to gammacerene and diploptene, and not to odd n-alkanes in the range C 25 -C 37 (Table S2, Supplementary material, p. One-year time series of sediment trap sampling in the lobe complex and at sites located upstream showed a typical pelagic flux for most of the year (Khripounoff, personal communication) with 2 peaks of particles at the site located upstream in the channel (Regab Z′, Tr C1 February 2011, Tr C4 from the 29th of March to the 13th of April 2011). Mass flux peak at Tr C1 and Tr C4 showed likely erosion of the flanks or of the levees of the channel (124 and 877 g m -2 yr -1 ). Except for these events, mass flux was within a range consistent with pelagic sinking fluxes of particles (25-49 g m -2 yr -1 ). The sinking particles were enriched in the planktonic n-C 17 in relation to others alkanes (Fig. S2, Supplementary Material, p. 59). The sedimentation of particles 40 m above the sediment fuels about one tenth of the terrestrial n-alkanes flux accumulated in the sediments at site C (Fig. 12). It clearly shows that the vertical rain of particles contributes a minor fraction of the organic matter preserved in the sediments at site C, and that the sediment is controlled by lateral transport of particles through the canyon (Fig. 12). When the canyon flanks and levees are destabilized, a massive input of particle is captured by the sediment trap (Tr C4), yielding unusually high sedimentation of terrestrial alkanes, reaching the high alkane sedimentary accumulation rates at C. At sites A, B and E the similar order of magnitude of sediment accumulation rates in one hand, and of vertical flux supported by sinking particles on the other, evidences that river inputs are not preserved into these sediments, either they are degraded by the microorganisms or they are further transported towards site C. Eventhough site B, receiving overspilling particles from the active channel, shows a similar proportion of labile hydrocarbons sourced by higher plant debris as site C sediments, their sedimentary accumulation rates at B show that these inputs are little significant in terms of fluxes.

Conclusions

Hydrocarbons of the Congo lobe complex have a marked higher plant fingerprint, in agreement with the bulk geochemical characteristics showing the dominance of terrestrial matter. Terrestrial biomarkers from higher plants, ferns, bacteria and angiosperms show ample variations in their contributions, indicating heterogeneous sources of the soil and vegetation detritus delivered to the sediments of the terminal lobe system at the end of the Congo submarine canyon. Hydrocarbon composition variations may reflect both different sources of the organic matter and different exposure to degradation, implied by the two-fold difference in mass accumulation rates of sediments of the terminal lobe complex.

At the more distal site C, the sediment accumulation is higher and the sediments spend less time in the oxic layer than at other sites. These sediments displayed higher organic carbon-normalized concentrations of terrestrial hydrocarbons than those where the exposure to oxic degradation is longer, suggesting that bulk organic carbon degrades faster than terrestrial hydrocarbons in the first steps of the pre-diagenesis. Despite their much smaller concentrations, terrestrial hydrocarbons and terrestrial terpenes are still present at the site disconnected from the active channel (site E) bringing evidences for the admixture of some river particles to the planktonic organic matter, dominant at this site.

The occurrence of a minor terrestrial signal in the sediment traps shows that some sediment from the levees may be destabilized, and form nepheloid layers that are admixted to the vertical flux of pelagic sinking particles. Corresponding vertical flux may produce pulses of terrestrial hydrocarbons but the general vertical fluxes of terrestrial hydrocarbons are one order of magnitude lower than hydrocarbon accumulation fluxes in the sediment at site C. It evidences the magnitude of the inputs delivered by turbidites through the active channel and clearly demonstrates that lateral transport controls the supply of organic matter to the terminal lobe complex.

Aliphatic hydrocarbons and triterpenes of the Congo deep sea fan -Supplementary material -

Laurence Méjanelle (1)* , Béatrice Rivière (1) , Laurence Pinturier (2) , Alexis Khripounoff (3) , François Baudin (4) and Jordi Dachs (5) List of supplementary materials: . Table S1. Concentrations of aliphatic hydrocarbons in ng.( g of dry weight) -1 in River and lobe sediments. To be continued.

Sample K1 K2 K3

A L 0-0.5 AL 0.5-1 AC 0-0.5 AC 0.5-1 FL 0-0.5 FL 0.5-1 CL 0-0.5 CL 0.5-1 Table S1. Concentrations of aliphatic hydrocarbons in ng.( g of dry weight) -1 in the Congo lobe sediments. To be continued.

Alkanes

------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ C10 0 1 1 2 1 5 1 9 C11 0.
Sample CC 0-0.5 CC 0.5-1 CC 1-2cm CC 3-5cm CC 5-7cm CC 7-10cmCC 10-13cm CC 13-16cCC 16-19cm CC 19-22cm B 0-0.5 B 0.5-1 Table S1. Concentrations of terpenoid hydrocarbons in ng.( g of dry weight) -1 in sediments from the Congo River and from the Congo canyon terminal lobe system. To be continued.

Alkanes

------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ C10 10
------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ C 1 0 4 5
------ ------ ------ ------ ------ ------ ------ C10 C11

Sample K1 K2 K3

A L 0-0.5 AL 0.5-1 AC 0-0.5 AC 0.5-1 FL 0-0.5 FL 0.5-1 CL 0-0.5 CL 0.5-1

C20H36 Tricyclic

3.5 0.6 . For each pair of compound, the correlation is given on the first line, and N, the number of samples used for the calculation, is given on the second line. The compounds that were detected in most samples have been selected for this analysis, and the compound occasionally detected were not considered. *: the correlation is significant at the 0.05 level (2-tailed). **: the correlation is significant at the 0.01 level (2-tailed).

C21H38

Fig. 2 .

 2 Fig. 2. Molecular profiles of n-alkanes in River sediments (K1), in sediment traps collected during WACS at 3420 m (TrC1) and at the site A (TrA1), and in surficial (0-0.5 cm) sediments collected in the terminal lobe complex, in the levee of site C (CL 0-0.5), in the channel of site C (CC 0-0.5) and at site E (E 0-0.5). n-Alkane homologues are assigned by their carbon number, and their abundance is expressed as concentrations, in ng per gram of dry weight (ng g DW-1 ).

Fig. 4 .

 4 Fig. 4. Top panel shows the spatial distribution of C 16 n-alkane concentrations normalized to organic carbon, in sediments from the Congo River (grey bars), in surficial sediments collected from the Congo deep-sea fan (black bars, Lev: levee, Cha: channel, sediment layers from 0 to 0.5 cm and from 0.5 to 1 cm), and in sediment trap samples (white bars). C 16 levels are expressed in ng g OC -1 . Bottom panels show the vertical profiles of C 16 concentration in two cores, from the channel at site C, and from site E. The star indicates petroleum contamination, in this sample the low molecular mode of alkane showed no even predominance.

Fig. 5 .

 5 Fig. 5. Top panel shows the spatial distribution of phytadiene concentrations normalized to organic carbon, in sediments from the Congo River (grey bars), in surficial sediments collected from the Congo deep-sea fan (black bars, Lev: levee, Cha: channel, sediment layers from 0 to 0.5 cm and from 0.5 to 1 cm), and in sediment trap samples (white bars). The sum of three phytadiene levels are expressed in ng g OC -1 . Bottom panels show the

Fig. 6 .

 6 Fig. 6. Molecular profiles of dominant triterpenes in River sediments (K1), in sediment traps collected during WACS at 3420 m (TrC1) and at the site A (TrA1), and in surficial (0-0.5 cm) sediments collected in the terminal lobe complex, in the levee of site A (AL 0-0.5), in the channel of site C (CC 0-0.5) and at site E (E 0-0.5). Hopanes, hopenes and other triterpenes are quantified as peak area in the fragmentogram m/z= 191, and by relating their area to the area of hop-17(21)-ene, quantified by GC-FID. Triterpene levels are expressed in ng g DW -1 .

Fig. 8 .

 8 Fig. 8. The top panel shows the spatial distribution of the concentrations of C 31 ββ-homohopane normalized to organic carbon, in sediments from the Congo River (grey bars), in surficial sediments collected from the Congo deep-sea fan (black bars, Lev: levee, Cha: channel, sediment layers from 0 to 0.5 cm and from 0.5 to 1 cm), and in sediment trap samples (white bars). C 31 ββ-homohopane levels are expressed in ng g OC -1 . White circles represent the mean grain size of the lobe complex sediment, in μm and is plotted on the right axis. Bottom panels show the vertical profiles of concentration of C 31 ββ-homohopane and of mean grain size, in two cores: from the channel at site C, and from site E.

Fig. 9 .

 9 Fig. 9. Top panel shows the spatial distribution of diploptene concentrations normalized to organic carbon, in sediments from the Congo River (grey bars), in surficial sediments collected from the Congo deep-sea fan (black bars, sediment layers from 0 to 0.5 cm and from 0.5 to 1 cm), and in sediment trap samples (white bars). Hop-21-ene concentration is represented by white circles, plotted on the right axis. Diploptene is a terrestrial biomarker (soil microorganisms), and marine bacteria can also be its biological precursor. Diploptene and hop-21-ene levels are expressed in ng g OC -1 . Bottom panels show the vertical profiles of concentration of diploptene and hop-21-ene, in two cores: from the channel at site C, and from site E.

Fig. 10 .

 10 Fig. 10. Scatter plots of OC-normalized concentrations of selected terpenoids versus gammacerene concentration. Gammacerene is a synthesized by ferns and bacteria. In the Congo terminal lobe system, it covariates with δ 13 C, therefore have a terrestrial origin.

Fig. 11 .

 11 Fig. 11. The top panel shows the spatial distribution of neohop-13(18)-ene concentrations normalized to organic carbon, in sediments from the Congo River (grey bars), in surficial sediments collected from the Congo deep-sea fan (black bars, Lev: levee, Cha: channel. sediment layers from 0 to 0.5 cm and from 0.5 to 1 cm), and in sediment trap samples (white bars). Concentrations of hop-17(21)-ene are represented by white circles plotted on the right axis. Diploptene and hop-17(21)-ene levels are expressed in ng g OC -1 . Bottom panels show the vertical profiles of concentration of neohop-13(18)-ene and hop-17(21)-ene, in two cores: from the channel at site C, and from site E.

  [48][49][50][51][52][53][54][55][56][57][58]. However the dynamics of both terrestrial components in the terminal lobe sediments is equally driven by the accumulation of particles fuelled by the canyon. This overwhelming lateral input of particles masks the contribution of atmospheric deposition, which generally dominates abyssal fluxes of terrestrial n-alkanes in the open ocean. The concentration gradient of terrestrial n-C 29 and gammacerene at the different sites (Sites C and B> Site B > Site E) combines with the mass accumulation rates (Site C > Site A and B > Site E) to yield a decreasing magnitude of accumulation fluxes from site C, sites A and B, and the disconnected site E (Fig.12).

Fig. 12 .

 12 Fig. 12. Hydrocarbon accumulation rates in sediments from sites A, F and C are represented by back bars. Hydrocarbon sedimentation fluxes, measured by sediment traps 40 m above the sediment are showed by white bars. Selected hydrocarbons are the dominant terrestrial alkane, n-C 29 , an terrestrial indicator,

Figure S1, page 59 :

 59 Figure S1, page 59: Variation of organic carbon percent, plotted on the left axis and of  13 C, plotted on the right axis, in the surficial sediments of the studied sample set Figure S2, page 59: Distribution of terpenoids (Selected Ionc Current m/z = 191) in the most contaminated sediment of the studied area, on the bottom panel. This sediment layer, collected at site E (0-0.5cm layer) showed the highest UCM concentrations. The m/z fragmentogram of a noncontaminated sample, the 0-0.5cm sediment layer at the channel of site C, is presented on the top panel. A series of tricyclic terpanes from C 20 to C 26 is indicated on the bottom m/z=191 current by shorthand notation TC 20 , TC 21 , … etc. These compounds are present in petroleum but not in recent organic matter.

Figure S3, page 60 :

 60 Figure S3, page 60: Distribution of terpenoids (Selected Ionc Current m/z = 191) in the 0-0.5 cm layer at the channel of site C. Peaks are labeled by their structural identification. Ts is the shorthand denomination for 18-22,29,30-trisnorhopane and G stands for gammacerene.

Figure S4, page 60 :

 60 Figure S4, page 60: Distribution of terpenoids (Selected Ionc Current m/z = 191) in the 0-0.5 cm layer at the levee of site A. Peaks are labeled by their structural identification. Fgure S5, page 61 to 62: Mass spectra of dominant hopanoids and non-hopanoid triterpenes.

Figure S1 .Figure S2 .Figure S3 .

 S1S2S3 Figure S1. Variation of organic carbon percent, plotted on the left axis and of  13 C, plotted on the 14 right axis, in the surficial sediments of the studied sample set (Data previously published in Stetten et 15 al., 2015). 16

Figure S4 .Figure S5 .Fernene

 S4S5 Figure S4. Distribution of terpenoids (Selected Ionc Current m/z = 191) in the 0-0.5 cm layer at the levee of site A. Peaks are labeled by their structural identification. Ts stands for 18-22,29,30trisnorhopane. O, L and G are shorthand denominations for oleanene, lupene and gammacerene, respectively.

Table 2 .

 2 Source assignment of hydrocarbon biomarkers detected in the present study.

	Biomarker	Source organisms	Source environment	References
	C 25 -C 35 odd alkanes	waxes of higher plants	terrestrial inputs	Eglinton et al., 1962; Eglinton and Hamilton, 1967
	C 17	phytoplankton	marine	Clark and Blumer, 1967
	C 16 , C 18	bacteria	marine	Grimalt and Albaigés, 1987; Nishimura and Baker, 1986
	grass	terrestrial	Kuhn et al., 2010
	sedimentary rocks	terrestrial	Tao et al., 2016
	petroleum	oil input	Tao et al., 2016
	Phytadienes	reducing environment	marine	Grossi et al., 1998
	UCM	petroleum	oil input	Broman et al., 1987
	Gammacerene	ciliates, ferns, bacteria	terrestrial, marine

Table 3 .

 3 Concentration levels (ng g DW -1 and ng OC

	-1

Table S1 , pages 40 to 47:

 S1 Concentrations of aliphatic hydrocarbons in ng.( g of dry weight) -1 in the Congo lobe sediments.

	Table S2, pages 48 to 58: Non parametric Spearman correlation of biomarker concentrations
	expressed in ng g OC -1

Table S1 .

 S1 Concentrations of the compounds in ng.( g of dry weight) -1 in Congo terminal lobe sediments. To be continued.

	Sample	E 0-0.5	E 0.5-1	E 1-2		E 2-3	E 3-5	E 5-7	E 7-10	E 10-13	E 13-16	E 16-19	E 19-22
	Alkanes
			1.1	1.8	3.2	1.8	2.2	1.0	2.0	0.6	1.2		1.4	1.9
	C11	3	2.5	5.3	6.1		2.5		3.4	1.1	3.0		4.4	6.1
	C 1 2	9	6	7	6	4	4	5	4	2	8		1 4	1 4
	C 1 3	2	3	7	6		4	7	4	3	5
	C14	22	22	19	6	6	7	13	6	5	23		52	28
	C15	8	8	6	6		5	9	7	5	15		10
	C16	19	41	30	6	5	7	25	8	6	29		62	19
	C 1 7	3 2	3 6	2 5	2 1	4 2	4 4	6 4	4 5	4 2	1 6 9		2 4	2
	Pristane	5		3	1			4	2		12
	C18	13	30	19	6	9	0	25	12	12	42		31	11
	Phytane	2	17	9		3		4	4	3	14		5
	Phytadiene1	145	127	37	55	136	229	124	110	99	101		79	59
	Phytadiene2	130	95	22	28	110	165	80	59	67	55		105	52
	Phytadiene3	202	138	33	45	169	240	130	102	112	92		129	89
	C 1 9	1 4	1 8	9	6	1 5	2 9	2 0	1 7	1 6	4 6		2 6	1 3
	C 2 0	1 1	1 9	1 2		1 3	1 3	2 1	1 5	1 7	4 8		1 4	1 1
	C21	21	6	15	9	23	1	29	25	2	86		19	5
	C22	15	17	10	6	15	13	20	18	20	58		13	16
	C 2 3	5 1	5 8	3 5	2 3	5 6	4 4	6 9	6 2	7 0	2 0 7		4 4	5 3
	C24	20	24	14	9	22	18	27	24	28	84		18	22
	C25	68	76	52	34	82	60	100	93	96	298		62	72
	C 2 6	2 5	3 0	2 1	1 3	3 3	2 4	3 9	3 6	3 8	1 2 4		2 5	2 9
	Squalane	12	14	9	5	14	11	17	14	17	57		10	14
	C27	116	126	106	67	166	119	198	198	183	604		116	135
	C28	48	52	43	21	51	3	77	77	2	250		3	59
	Squalene	23	28	15	11	23	49	28	25	27	64			16
	C29	377	427	406	252	582	459	740	825	652	2424		448	517
	C30	20	57	57	33	85	61	96	104	86	316		69	70
	C31	232	292	301	179	418	349	526	579	456	1701		308	351
	C 3 2	4 4	5 4	4 9	2 9	7 3	5 9	8 4	8 5	7 5	2 6 4		4 8	5 2
	C33	78	101	121	74	171	132	197	221	174	669		118	65
	C 3 4	6	8	1 0	1 0	1 4	1 1	1 6	1 7	1 3	6 5		2 6	1 0
	Lycopane	7	2				3		4		13
	C 3 5	2 6	3 5	4 4	2 9	6 3	4 6	7 4	8 2	6 2	2 3 9		4 0	4 8
	C 3 6	3	5	6	4	9	5	9	1 2	7	3 2		5	7
	C 3 7	1 1	1 3	1 7	1 1	2 6	1 7	2 9	3 3	2 4	8 9		1 6	1 8
	C38	4	6	7	4	10	7	12	15	11	37		6	8
	C39	5	7	9	6	12	8	16	19	13	48		7	9
	C40										10
	UCM		1540	248				201	150
	CPI	5.7	4.8	5.3	5.5	5.4	6.7	5.5	5.7	6.8	5.4	5.8	5.0

Table S1 .

 S1 Concentrations of aliphatic hydrocarbons in ng.( g of dry weight) -1 in sediment traps moored 40m above the sediments in the Congo terminal lobe system. To be continued.

	Sample	Tr1		Tr 2	Tr C1		Tr C2	Tr C4	Tr L1		Tr L2
	Alkanes
				4	6	1 6	4	1	4	4	0 . 9	0 . 3
	C11	4	3.2	1.0	1.4	5.8	0.4	0.7	0.2	0.4		0.6
	C12	16	4.9	2.8	3.4	10.0	0.8	1.3	0.4	0.6	0.5	1.7
	C13	7		1.2	0.9	3.4	0.5	0.8		0.5		1.1
	C 1 4	6 2	1 1	8	7	1 4	1	2	0 . 6	1 . 0	0 . 6	3 . 4
	C15	42				3	1	1				1.6
	C16	132	14	6	5	11	1	2		0.9		2.8
	C17	61		2	2	5		1		1.2	0.5	5.2
	Pristane	17
	C18	124		3.4	2.3	6.6	0.7	1.0				3.1
	Phytane	53
	Phytadiene1	24		5.4	4.4		2.2	4.3	4.4	3.5	6.9	2.6
	Phytadiene2	36		3.3	3.1		1.8	3.7	3.5	1.9	3.8	1.0
	Phytadiene3	18		5.5	5.4		3.1	5.5	5.3	2.8	6.2	1.8
	C19	117		2.4	1.5	4.2	0.6	1.0		1.1	0.5	4.8
	C 2 0	2 4 1		3	2	5	1	1	1	1		5
	C 2 1	5 0 2		5	3	8	1	2	1	3	1	1 5
	C22	518		4	3	7	1	1		2	1	10
	C 2 3	4 2 4		1 0	7	1 5	2	3	1	6	4	3 9
	C 2 4	8 3		6	4	9	1	1		2	1	1 5
	C 2 5			1 4	9	2 0	2	4	2	8	5	5 4
	C 2 6	8 4		7	5	1 0	1	2	1	3	2	2 1
	Squalane						0	1	0	2	0	2
	C27			24	16	32	4	7	3	15	9	100
	C 2 8	4 6		1 1	7	1 6	2	2	1	6	3	4 2
	Squalene			5	4	5	1	1		0	1	4
	C29	188	27	79	49	105	12	25	12	55	34	410
	C 3 0	5 0		1 1	6	1 5	2	3	0	6	4	5 3
	C 3 1	8 7	2 1	6 1	3 7	7 9	9	1 7	8	3 6	2 2	2 8 3
	C 3 2			1 0	6	1 3	2	3	1	6	3	4 4
	C33	7		25	15	35	4	7	3	14	8	108
	C34	59		2	2	4		2		1	2	11
	Lycopane	7										2
	C35	4		8.3	4.6	12.9	1.3	2.4	1.1	4.5	2.5	33
	C36			1.5						0.8		5
	C37			2.7	1.1	3.1	0.3	0.7	0.2	1.7	1.0	15
	C38			1.0						0.7		5.7
	C39			0.6						0.7		7.9
	C40											1.6
	UCM	10471	276	86
	CPI	3.8		4.6	4.8	4.6	5.3	4.8	9.6	5.4	5.4	5.3

Table S1 .

 S1 Concentrations of terpenoid hydrocarbons in ng.( g of dry weight) -1 in sediments from the Congo River and from the Congo canyon terminal lobe system. To be continued.

	Sample			CC 0-0.5 CC 0.5-1 CC 1-2cm CC 3-5cm CC 5-7cm CC 7-10cmCC 10-13cm CC 13-16cm CC 16-19cm CC 19-22cm	B 0-0.5	B 0.5-1
	C20H36 Tricyclic					22.8	2.5		5.6	7.4	3.0			10.2
	Tricyclic C21H38 Tricyclic	1.2		4.9	21.5	6.9	2.0		1.7	1.1 11.9	4.6		0.2	16.5
	C21H36 Triterpene C21H36 Triterpene			5.8	4.8	7.7	4.1	5.7	10.6	0.1 7.9	6.9	5.2
	C23H42 Tricyclic 1 C23H42 Tricyclic 1				5.7		2.9			0.2				14.6
	C24H44 Tricyclic 1 C24H44 Tricyclic 1					15.2								9.6
	C23H42 Tricyclic 2 C23H42 Tricyclic 2	0.3		4.0	15.8		1.9	2.6	2.2 3.7	1.2 10.5	5.5
	C23H42 Tricyclic 3 C23H42 Tricyclic 3	0.3
	C23H40 Tri-terpene C23H40 Tri-terpene	0.5
	C24H44 Tricyclic 2 C24H44 Tricyclic 2				6.3	5.2 3.9	1.1			32.8 3.9	2.7			6.8	5.5
	des-A-Olean-13(18)-ene des-A-Olean-13(18)-ene										1.2
	des-A-Oleanediene des-A-Oleanediene des-A-lupane des-A-lupane des-A-terpene des-A-terpene C25H44 Tri-terpene C25H44 Tri-terpene C25H46 Tricyclic 1 C25H46 Tricyclic 1 C25H46 Tricyclic 2 C24H42 Tri-terpene 2 C25H46 Tricyclic 2 C24H42 Tri-terpene 3 C24H42 Tri-terpene 2 C24H42 Tri-terpene 4 C24H42 Tri-terpene 3 C27sterane C24H42 Tri-terpene 4 C27sterane C28sterene 1 C26sterene C28sterene 1 C26sterene C28sterene 2 C29sterene C28sterene 2 C27 Trisnorhopene C29sterene C27 Trisnorhopene C27 Trisnorhopene C28sterane C27 Trisnorhopene 22,29,30-trisnorneohop-13(18)-ene 3.8 0.7 0.9 0.4 C28sterane 22,29,30-trisnorneohop-13(18)-ene C27sterane 2 C27sterane 2 C27 Trisnorhopene 1 C27 Trisnorhopene 1 C27 Trisnorhopene 2 22,29,30-trisnorneohop-17(21)-ene C27 Trisnorhopene 2 Cholestene 0.7 22,29,30-trisnorneohop-17(21)-ene C30hop-di-ene Cholestene C28sterene 3 C30hop-di-ene 0.6 C28sterene 3 C29diasterene C29diasterene 18(H)-22,29,30-trisnorhop 7.8 18(H)-22,29,30-trisnorhopane (Ts) C29 Tri-terpene 17(H)-22,29,30-trisnorhop 8.6 C29 Tri-terpene	8.8 2.5 41.1	19.7 20.0 3.2 62.7 24.4 50.2 42.2 7.7	21.9 68.4 17.0 43.2 6.2	5.4 22.0 3.9 4.2 4.0 15.0 63.6 16.3 3.1 44.6 7.3	1.8 11.4 1.7 3.7 36.3 0.9 4.6 1.2 20.7 2.4	18.5 2.3 72.9 12.2 38.8 6.1	2.3 40.7 5.4 2.8 6.1 0.5 0.6 6.9 117.8 13.5 0.7 78.3 5.9 18.8	12.6 22.4 0.19 0.13 0.08 0.02 1.8 0.03 1.7 0.16 0.06 0.03 0.28 2.2 1.2 1.6 3.2 69.5 0.04 0.02 8.6 0.44 0.06 45.9 7.3	2.2 5.1 69.5 21.6 65.1 12.2	17.7 0.4 3.1 1.4 1.4 2.5 69.3 14.5 0.7 0.1 41.8 9.5	4.8 1.2 1.6 8.2 2.4 1.8 10.7 2.5 6.9 0.3	15.8 22.5 5.1 10.0 44.2 27.7 17.6 4.3 39.3 7.6 34.1 10.3	18.8 15.8 3.1 10.0 43.1 47.0 17.8 41.6 7.9 44.5 8.1
	Adiantene 1 17(H)-22,29,30-trisnorhopane (Tm)
	Oleanene Adiantene 1					34.2	1.2		4.1	1.34		1.6	13.4
	C29 -norhopane S Oleanene C29 -norhopane R C29 -norhopane S C29 sterene C29 -norhopane R	9.0		4.3 17.2	5.5 19.1	19.6	1.4		1.6			0.2	4.1	15.0 12.5 14.6	16.9 1.9 14.7
	C29 sterene C29 sterene	1.7	19.0	5.1		9.7			1.8	0.13		0.2	12.0	7.0	8.1
	Lupene C29 sterene			7.6	6.4	21.3 5.3	1.2 9.7	19.3	7.0	0.31 24.4	33.0	0.6 22.7	1.9	13.4	2.0 5.3
	C30 hop-7(21)-ene Lupene	6.4		9.2		5.3	26.4		15.6	0.11		0.1	37.3	231 23.4	290
	Adiantene 2 C30 hop-7(21)-ene			210	233	29	19	144	129	0.13 335	86	0.2 296	2.1	228	197
	C 30 -hopane R Adiantene 2	1.5				8.6	2.1		2.6	0.27				18.0	20.6
	C 30 -hopane S C 30 -hopane R			18.7	21.2	18.6	7.7	11.8	34.4	21.8	24.6		1.7	19.4	22.1
	neohop-13(18)-ene C 30 -hopane S	2.9	6.7	8.7		40.3			7.8	0.69		0.9	4.6	43	69
	Adiantane or -C29 hopan 2.8 neohop-13(18)-ene		22	30	18	4.8 6	16	27	0.35 34	26	0.6 19	19.4 0.6	25.4
	Gammacerene Adiantane or -C29 hopane	6.5	17.0	31.5		16.2	4.8		5.9	0.05		36	12.2	78	52 29.1
	Fern-8-ene Gammacerene	0.7		57	74	80	1.0 33	73	148	89	149	0.1 90	1.3 4.8	37 42.5	20 84.5
	Fern-7-ene Fern-8-ene C31 -homohopane Fern-7-ene C30 hopane C31 -homohopane C31 -homohopane C30 hopane C30 -hopane C31 -homohopane C30 -hopane C30 -hopane	1.5 7.3 6.0	6.2 27.1 14.1	26 7.4 16.9 38.3 66.2 32.1	41 20.2 69	11 13.0 6.5 25.8 67 32.6	6.4 1.7 7.2 31 9.1	54 11.4 52	55 31.5 2.0 9.8 118 11.6	86 16.4 0.12 0.63 69	21 20.1 95	68 12.9 0.2 0.9 60	1.4 3.6 16.8 21.7	12.8 6.7 12.4 56 54 79.6	15.7 11.8 15.7 69.9 67
	C31Hopene C30 -hopane			83.7	87.9	85.0	0.7 37.1	60.1	9.6 135.1	0.02 80.6	120.3	0.1 73.6	2.2 5.7	73	85
	Diploptene C31Hopene	6.4	22.0	33.8		3.2								101	11
	Hop-21-ene Diploptene C31 methyl-hopene Hop-21-ene C32 -homohopane C31 methyl-hopene C31homohopene C32 -homohopane ab/baC32 C31homohopene C31-homohopane C32-homohopane ab/baC32 C31-homohopane	1.9 3.7	6.0 12.0	161 41 6.9 9.4 24.7 70	187 42 10.5 75	202 4 2.8 10.8 27.9 2.2 73	99 6.0 7.4 0.7 29	201 29 4.7 52.5	303 17.6 1.0 6.3 120	172 8 10.4 71.3 0.7 0.1 7	294 3.9 16.1 107	146 19 4.9 8.0 62.9 1.1 0.2 6.2	4.7 2.9 19.0 1.8 1.2	40 7.4 4.9 65 4.7 59.4	28 76.8 19.1 7.8 3.3 8.7 6.6 71.6
	C32-homohopane			7.0	6.1				13.4		10.1		3.5	5.5	10.1

Table S1 .

 S1 Concentrations of terpenoid hydrocarbons in ng.( g of dry weight) -1 in sediments from the Congo River and from the Congo canyon terminal lobe system. To be continued.

	Sample	E 0-0.5	E 0.5-1	E 1-2	E 2-3	E 3-5	E 5-7	E 7-10	E 10-13	E 13-16	E 16-19	E 19-22
	C20H36 Tricyclic	60	12.2
	C21H38 Tricyclic	129	26.4			0.3
	C21H36 Triterpene	39										4.3
	C23H42 Tricyclic 1	37	7.9
	C24H44 Tricyclic 1
	C23H42 Tricyclic 2	322	7.6			0.4						0.5
	C23H42 Tricyclic 3		65.7
	C23H40 Tri-terpene		2.9
	C24H44 Tricyclic 2	177	36.2			0.3
	des-A-Olean-13(18)-ene	12.8	2.6
	des-A-Oleanediene
	des-A-lupane			0.5	0.2			0.7	0.2	0.2	0.9	2.5
	des-A-terpene											1.3
	C25H44 Tri-terpene											3.9
	C25H46 Tricyclic 1	83	16.9
	C25H46 Tricyclic 2	70	14.4
	C24H42 Tri-terpene 2		4.3
	C24H42 Tri-terpene 3		6.9
	C24H42 Tri-terpene 4	21.1	7.7
	C27sterane		2.0									1.9
	C28sterene 1		2.1
	C26sterene		1.5
	C28sterene 2		2.0
	C29sterene	37.7
	C27 Trisnorhopene
	C27 Trisnorhopene
	C28sterane
	22,29,30-trisnorneohop-13(18)-ene	6.6		0.9
	C27sterane 2	9.7
	C27 Trisnorhopene 1
	C27 Trisnorhopene 2
	22,29,30-trisnorneohop-17(21)-ene	7.5	2.6	13.4	10.0	4.2	3.6	3.7	1.4	0.4	2.3	14
	Cholestene	10.0
	C30hop-di-ene
	C28sterene 3			1.5	0.9			1.0	0.6	0.3	0.8
	C29diasterene	5.5										4
	18(H)-22,29,30-trisnorhopane (Ts)	13.0	0.9	3.3	2.2	1.3	0.8	2.4	1.4	0.6	2.4	34
	C29 Tri-terpene			0.6	0.7					0.1	0.5	9
	17(H)-22,29,30-trisnorhopane (Tm)
	Adiantene 1
	Oleanene	5.6			0.3							2
	C29 -norhopane S	7.9	2.2	0.7	0.2
	C29 -norhopane R	10.8		2.3	1.2	0.9		0.9		0.2		9
	C29 sterene
	C29 sterene			17.7
	Lupene										0.9
	C30 hop-7(21)-ene	39.5	8.1	18.0	14.6	4.7	4.4	6.9	4.6	0.1	8.6	16
	Adiantene 2	1.2	0.3
	C 30 -hopane R	14.9	3.0	3.4	2.4	1.3		0.8	0.5	0.2	0.9	9
	C 30 -hopane S
	neohop-13(18)-ene	8.2	1.7						1.0		1.0
	Adiantane or -C29 hopane			5 . 4	4 . 2	1 . 8	1 . 0	1 . 0				8
	Gammacerene	7.7	1.6	5.1	4.2	2.3	0.9	3.5	1.1	1.1	5.7	71
	Fern-8-ene	2.0	0.4					0.4				3
	Fern-7-ene			1.9	1.5	0.7		0.8		0.2		7
	C31 -homohopane
	C30 hopane	4.4	0.9	8.4	5.6	3.0	1.7	3.0	1.4	0.8	3.4	42
	C31 -homohopane	12.3	2.5
	C30 -hopane
	C30 -hopane	11.5	2.4	9.5	6.4	3.1	1.8	4.3	2.1	1.2	6.0	66
	C31Hopene
	Diploptene			8.8	3.9	2.4		1.4	0.9	1.5	4.9	30
	Hop-21-ene			1.5	1.3	0.6				0.1		1
	C31 methyl-hopene
	C32 -homohopane
	C31homohopene			0.7				0.3	1.2	0.1
	ab/baC32				0.7							7
	C31-homohopane	10.5	2.1	9.7	6.2			4.0		1.0		54
	C32-homohopane			0.8

Table S1 .

 S1 Concentrations of terpenoid hydrocarbons in ng.( g of dry weight) -1 in sediment traps particles sinking 40m above the sediment bed, in the Congo River terminal lobe system.

	Sample	Tr1	Tr 2	Tr C1	Tr C2	Tr C4	Tr L1	Tr L2
	C20H36 Tricyclic
	C21H38 Tricyclic						57.6	54.2
	C21H36 Triterpene			2.4
	C23H42 Tricyclic 1
	C24H44 Tricyclic 1
	C23H42 Tricyclic 2			2.2
	C23H42 Tricyclic 3
	C23H40 Tri-terpene
	C24H44 Tricyclic 2
	des-A-Olean-13(18)-ene
	des-A-Oleanediene
	des-A-lupane		15.3	17.0
	des-A-terpene		1.3
	C25H44 Tri-terpene
	C25H46 Tricyclic 1
	C25H46 Tricyclic 2
	C24H42 Tri-terpene 2						91.6	98.3
	C24H42 Tri-terpene 3			2.6			22.8	38.6
	C24H42 Tri-terpene 4						36.0	38.5
	C27sterane			2.1
	C28sterene 1
	C26sterene
	C28sterene 2
	C29sterene
	C27 Trisnorhopene
	C27 Trisnorhopene
	C28sterane
	22,29,30-trisnorneohop-13(18)-ene
	C27sterane 2
	C27 Trisnorhopene 1			2.9
	C27 Trisnorhopene 2
	22,29,30-trisnorneohop-17(21)-ene		27.7	16.7
	Cholestene	1.8					16.2
	C30hop-di-ene
	C28sterene 3				31.4	37.0	41.3	43.2
	C29diasterene						30.0	19.7
	18(H)-22,29,30-trisnorhopane (Ts)	36.3	47.6	38.5			37.9	52.4
	C29 Tri-terpene	6.5	7.5	6.3
	17(H)-22,29,30-trisnorhopane (Tm)
	Adiantene 1						97.8
	Oleanene
	C29 -norhopane S						48.4	33.7
	C29 -norhopane R
	C29 sterene						440	433
	C29 sterene	22.0	14.0	15.5			33.5	11.9
	Lupene
	C30 hop-7(21)-ene	35	38	10			303	263
	Adiantene 2
	C 30 -hopane R						87	116
	C 30 -hopane S						61	88
	neohop-13(18)-ene	16	22	14	35	13	87	88
	Adiantane or -C29 hopane	11	17	8
	Gammacerene	47	55	53			52	85
	Fern-8-ene	3		4
	Fern-7-ene		13	9			40	41
	C31 -homohopane							40
	C30 hopane		65	51	12	8	28	47
	C31 -homohopane	9					50
	C30 -hopane						29
	C30 -hopane	59	77	62			54	47
	C31Hopene
	Diploptene	66		6	35	15	58	215
	Hop-21-ene	46
	C31 methyl-hopene
	C32 -homohopane	4			7	42	15	17
	C31homohopene	60	8	56		10	43	44
	ab/baC32		55	6
	C31-homohopane

6

C32-homohopane

Table S2 .

 S2 Non parametric Spearman correlation of biomarker concentrations expressed in ng g OC

	-1

Table S2 continued.

 S2

			Phytadie	Phytadie	Phytadie
			ne1	ne2	ne3	C19	C20	C21	C22	C23	C24	C25	C26	Squalane	C27	C28
	median grain size d 0.5 µm	Pearson correlation	.190	.177	.142	.097	.248	.253	.250	.278	.278	.270	.315	.330	.298	.216
		N	29	30	30	29	28	30	29	30	29	29	30	26	29	30
	OC	Pearson correlation	.398 *	.194	.326	-.196	-.186	-.193	-.203	-.175	.009	.319 *	.017	.213	.282	.118
		N	30	31	31	39	38	40	39	40	39	39	40	29	39	40
	 15 N ‰	Pearson correlation	-.492 **	-.369 *	-.448 *	-.011	.192	.213	.220	.187	.194	-.262	.141	-.499 **	-.310	-.058
		N	29	30	30	29	28	30	29	30	29	29	30	26	29	30
	13C ‰	Pearson correlation	-.405 *	-.225	-.359	.199	.333	.348	.365	.323	.349	-.221	.281	-.356	-.267	.054
		N	29	30	30	29	28	30	29	30	29	29	30	26	29	30
	C/N molar	Pearson correlation	.231	.075	.189	-.277	-.312	-.324	-.342	-.301	-.332	.197	-.261	.294	.251	-.050
		N	29	30	30	29	28	30	29	30	29	29	30	26	29	30
	C10	Pearson correlation	-.117	-.049	-.115	.065	.093	.095	.092	.098	.172	.136	.161	.055	.069	.208
		N	29	29	29	28	27	29	28	29	28	28	29	25	28	29
	C11	Pearson correlation	.486 *	.580 **	.470 *	.482 **	.165	.122	.114	.142	.187	.315	.203	.245	.275	.330
		N	2 6	2 7	2 7	3 3	3 3	3 4	3 3	3 4	3 3	3 3	3 4	2 6	3 3	3 4
	C12	Pearson correlation	.335	.415 *	.400 *	.759 **	.241	.222	.214	.239	.328 *	.335 *	.358 *	.171	.260	.364 *
		N	29	30	30	37	36	38	37	38	37	37	38	29	37	38
	C13	Pearson correlation	.476 *	.528 **	.565 **	.707 **	.032	-.002	-.005	.016	.031	.207	.042	.099	.185	.174
		N	24	24	24	32	31	32	32	32	32	31	32	23	31	32
	C14	Pearson correlation	.484 **	.619 **	.460 **	.579 **		.238	.231	.256	.251	.236	.266	.121	.210	.306
		N	30	31	31	39	38	40	39	40	39	39	40	29	39	40
	C15	Pearson correlation	.385	.594 **	.322	.845 **	.814 **	.785 **	.781 **	.790 **	.764 **	.274	.740 **	.140	.248	.525 **
		N	22	23	23	32	31	32	32	32	32	31	32	24	31	32
	C16	Pearson correlation	.395 *	.602 **	.346	.831 **	.722 **	.690 **	.685 **	.698 **	.638 **	.218	.637 **	.091	.192	.445 **
		N	28	29	29	38	37	38	38	38	38	37	38	27	37	38
	C17	Pearson correlation	.451 *	.557 **	.319	.539 **	.741 **	.719 **	.711 **	.752 **	.772 **	.641 **	.794 **	.413 *	.639 **	.708 **
		N	28	29	29	38	36	38	38	38	38	37	38	27	37	38
	Pristane	Pearson correlation	.551 *	.764 **	.441	.776 **	.791 **	.761 **	.757 **	.774 **	.771 **	.381	.769 **	.245	.338	.587 **
		N	1 5	1 5	1 5	2 2	2 1	2 2	2 2	2 2	2 2	2 1	2 2	1 6	2 1	2 2
	C18	Pearson correlation	.322	.527 **	.251	.867 **	.879 **	.855 **	.852 **	.860 **	.800 **	.269	.785 **	.122	.245	.515 **
		N	27	28	28	37	36	37	37	37	37	36	37	26	36	37
	Phytane	Pearson correlation	.156	.366	.043	.732 **	.994 **	.988 **	.986 **	.987 **	.952 **	.463 *	.918 **	.234	.425 *	.552 **
		N	18	19	19	23	23	23	23	23	23	22	23	18	22	23
	Phytadiene1	Pearson correlation	1	.937 **	.968 **	.387 *	.131	.107	.101	.154	.193	.492 **	.245	.579 **	.475 **	.302
		N	30	30	30	29	28	30	29	30	29	29	30	25	29	30
	Phytadiene2	Pearson correlation	.937 **	1	.935 **	.506 **	.312	.285	.280	.324	.358	.446 *	.392 *	.519 **	.420 *	.319
		N	30	31	31	30	29	31	30	31	30	30	31	26	30	31
	Phytadiene3	Pearson correlation	.968 **	.935 **	1	.371 *	.035	.014	.007	.061	.105	.478 **	.157	.552 **	.454 *	.223
		N	30	31	31	30	29	31	30	31	30	30	31	26	30	31
	C19	Pearson correlation	.387 *	.506 **	.371 *	1	.703 **	.682 **	.680 **	.691 **	.655 **	.241	.644 **	.137	.223	.453 **
		N	29	30	30	39	37	39	39	39	39	38	39	28	38	39
	C20	Pearson correlation	.131	.312	.035	.703 **	1	.998 **	.998 **	.994 **	.927 **	.564 **	.900 **	.343	.500 **	.507 **
		N	28	29	29	37	38	38	37	38	37	37	38	27	37	38
	C21	Pearson correlation	.107	.285	.014	.682 **	.998 **	1	.999 **	.995 **	.921 **	.664 **	.897 **	.566 **	.589 **	.503 **
		N	30	31	31	39	38	40	39	40	39	39	40	29	39	40
	C22	Pearson correlation	.101	.280	.007	.680 **	.998 **	.999 **	1	.994 **	.918 **	.515 **	.893 **	.532 **	.429 **	.490 **
		N	29	30	30	39	37	39	39	39	39	38	39	28	38	39

Table S2 continued.

 S2

												Lycopan
			C29	C30		C31		C32	C33	C34		e		C35	C36		C37		C38	C39		UCM		CPI
	median grain size d 0.5 µm	Pearson correlation	.337	.439 *	.293	.309	.219	.285	.371	.255	.130	.329	.196	.165	.357	-.229
		N	31	30	31	29	30	28	11	30	22	29	23	22	26	30
	OC	Pearson correlation	.146	.179	.168	.259	.196	-.030	-.527	.302	.493 **	.429 *	.498 **	.395	-.238	-.233
		N	41	40	41	39	40	38	11	40	27	33	26	25	26	39
	 15 N ‰	Pearson correlation	-.317	-.142	-.341	-.331	-.309	.192	.567	-.333	-.255	-.402 *	-.341	-.402	.183	-.265
		N	31	30	31	29	30	28	11	30	22	29	23	22	26	30
	13C ‰	Pearson correlation	-.254	-.057	-.280	-.295	-.290	.355	.704	*	-.286	-.184	-.354	-.278	-.346	.285	-.305
		N	31	30	31	29	30	28	11	30	22	29	23	22	26	30
	C/N molar	Pearson correlation	.248	.088	.271	.278	.267	-.361	-.685	*	.281	.181	.345	.273	.335	-.246	.232
		N	31	30	31	29	30	28	11	30	22	29	23	22	26	30
	C10	Pearson correlation	.010	.008	.024	.047	.067	.122	.411	.060	.037	-.047	.001	-.084	.030	-.146
		N	30	29	30	28	29	27	10	29	21	28	22	21	25	29
	C11	Pearson correlation	.257	.089	.282	.281	.253	.189	.114	.170	.133	.260	.150	.174	.072	.005
		N	35	34	35	33	34	32	11	34	23	29	23	22	23	33
	C12	Pearson correlation	.177	.303	.181	.204	.162	.278	.778 **	.125	.177	.185	.071	.124	.240	-.271
		N	39	38	39	37	38	36	11	38	26	32	25	24	26	37
	C13	Pearson correlation	.203	.110	.222	.189	.191	.095	-.024	.075	.054	.199	.077	.146	-.009	.067
		N	32	32	32	31	32	31	10	32	22	26	21	20	21	31
	C14	Pearson correlation	.248	.093	.250	.246	.173	.247	.215	.037	.073	.201	.105	.127	.226	.000
		N	41	40	41	39	40	38	11	40	27	33	26	25	26	39
	C15	Pearson correlation	.266	.360 *	.189	.269	.020	.749 **	.802 **	-.027	.176	.273	.209	.210	.764 **	-.354
		N	32	32	32	31	32	31	11	32	22	25	21	20	19	31
	C16	Pearson correlation	.245	.290	.185	.233	.038	.612 **	.717 *	-.078	.038	.167	.069	.111	.696 **	-.225
		N	39	38	39	37	38	37	11	38	27	31	26	25	24	37
	C17	Pearson correlation	.547 **	.611	**	.476	**	.704 **	.347 *	.740	**	.861 **	.243	.666	**	.705	**	.744 **	.709	**	.778	**	-.338	*
		N	38	38	38	37	38	38	11	38	27	31	26	25	23	37
	Pristane	Pearson correlation	.307	.381	.230	.360	.057	.775 **	.743	-.028	.175	.269	.219	.213	.735 **	-.351
		N	22	22	22	21	22	22	7	22	16	17	16	15	12	21
	C18	Pearson correlation	.250	.389 *	.165	.286	-.006	.774 **	.855 **	-.077	.080	.229	.123	.170	.843 **	-.368 *
		N	37	37	37	36	37	36	11	37	26	30	25	24	22	36
	Phytane	Pearson correlation	.178	.453 *	.056	.439 *	-.138	.962 **	.913 **	-.131	.302	.340	.327	.310	.960 **	-.666 **
		N	23	23	23	22	23	23	9	23	20	20	19	18	15	23
	Phytadiene1	Pearson correlation	.466 **	.347	.463 **	.492 **	.399 *	.206	.127	.397 *	.213	.400 *	.312	.270	.094	.107
		N	30	30	30	29	30	28	10	30	22	29	23	22	24	30
	Phytadiene2	Pearson correlation	.413 *	.348	.393 *	.428 *	.301	.386 *	.388	.303	.180	.343	.255	.209	.307	-.009
		N	31	31	31	30	31	29	11	31	23	30	24	23	25	31
	Phytadiene3	Pearson correlation	.431 *	.308	.433 *	.455 *	.376 *	.135	.077	.380 *	.204	.373 *	.290	.247	.006	.155
		N	31	31	31	30	31	29	11	31	23	30	24	23	25	31
	C19	Pearson correlation	.267	.429 **	.200	.224	.069	.684 **	.933 **	.011	.093	.224	.115	.190	.673 **	-.337 *
		N	39	39	39	38	39	38	11	39	27	32	26	25	24	38
	C20	Pearson correlation	.173	.443	**	.062	.475 **	-.108	.868	**	.920 **	-.085	.656	**	.604	**	.649 **	.568	**	.969	**	-.476 **
		N	38	38	38	37	38	36	11	38	26	31	25	24	23	37
	C21	Pearson correlation	.169	.445	**	.060	.504 **	-.104	.854	**	.921 **	-.080	.853	**	.719	**	.837 **	.711	**	.968	**	-.475 **
		N	40	40	40	39	40	38	11	40	27	33	26	25	25	39
	C22	Pearson correlation	.155	.436 **	.044	.337 *	-.125	.853 **	.916 **	-.097	.853 **	.726 **	.851 **	.703 **	.966 **	-.529 **
		N	39	39	39	38	39	38	11	39	27	32	26	25	24	38

Table S2 continued.

 S2

			C 24	C 24	Trisnorneoh		C 28		C 29			C 29
			Tricyclic	Triterpen	op-13(18)-	Trisnorhop-	sterene	Trisnor	Triterpen	Oleanen		sterene		Hop-17(21)-
			2	e 1	ene	17(21)-ene	3	C 27 Ts	e	e	C 29 R	A	Lupene	ene	 C 30 S
	median grain size d 0.5 µm	Pearson correlation	.287	.387	.165	.170	.406	.204	.031	.476	.408	-.200	.502	.183	.358
		N	12	23	14	26	16	31	24	12	16	19	8	31	27
	OC	Pearson correlation	-.519	.342	-.499	.265	.611 **	.156	.069	-.142	-.001	-.369	-.586	.124	.356
		N	12	28	14	28	20	39	27	12	16	27	8	38	30
	 15 N ‰	Pearson correlation	.431	-.574 **	.200	-.390 *	-.565 *	-.458 **	-.275	-.088	-.034	.698 **	.135	-.343	-.102
		N	12	23	14	26	16	31	24	12	16	19	8	31	27
	13C ‰	Pearson correlation	.595 *	-.456 *	.432	-.347	-.432	-.396 *	-.225	.176	.056	.657 **	.556	-.211	.086
		N	12	23	14	26	16	31	24	12	16	19	8	31	27
	C/N molar	Pearson correlation	-.576 *	.316	-.478	.267	.397	.312	.111	-.148	-.133	-.555 *	-.542	.121	-.138
		N	12	23	14	26	16	31	24	12	16	19	8	31	27
	C10	Pearson correlation	.022	-.099	.473	-.123	-.138	-.165	.001	.009	-.077	.428	-.120	-.049	.013
		N	11	22	13	26	16	30	23	11	16	18	7	30	26
	C11	Pearson correlation	.041	.382	.225	.209	.410	.270	.324	.191	.324	-.059	-.219	.561 **	.219
		N	11	23	12	23	16	34	22	12	16	23	7	33	27
	C12	Pearson correlation	.681 *	.265	.181	.128	.357	.190	.228	.152	.364	-.109	.050	.327 *	.220
		N	12	27	14	27	19	38	26	12	16	26	8	37	30
	C13	Pearson correlation	-.019	.328	.150	.277	.336	.270	.389	.778 **	.271	-.067	-.064	.569 **	.140
		N	9	2 1	1 1	2 1	1 4	3 1	2 1	1 0	1 4	2 2	5	3 0	2 3
	C14	Pearson correlation	.202	.319	.323	.232	.320	.238	.308	.170	.499 *	-.095	-.186	.562 **	.225
		N	12	28	14	28	20	39	27	12	16	27	8	38	30
	C15	Pearson correlation	.854 **	.337	.594 *	.100	.454	.221	.303	.211	.789 **	-.045	-.233	.445 *	.418
		N	1 1	2 1	1 2	2 0	1 2	3 1	2 1	1 1	1 2	2 4	7	3 0	2 2
	C16	Pearson correlation	.763 **	.349	.579 *	.111	.243	.216	.304	.219	.735 **	-.121	-.230	.456 **	.330
		N	12	26	14	26	18	37	26	12	16	27	7	36	28
	C17	Pearson correlation	.819 **	.513 **	.589 *	-.005	.459 *	.174	.127	.235	.794 **	-.167	-.076	.309	.459 *
		N	11	27	14	25	19	36	27	12	16	27	8	35	28
	Pristane	Pearson correlation	.788 *	.569 *	.817 **	.089	.268	.291	.525	.664	.938 **	-.065	-.114	.542 *	.438
		N	7	1 3	9	1 1	7	2 0	1 4	7	7	1 8	5	1 9	1 4
	C18	Pearson correlation	.925 **	.338	.634 *	.008	.284	.193	.275	.237	.757 **	-.112	-.224	.363 *	.389 *
		N	11	25	14	24	17	35	25	12	15	27	7	34	26
	Phytane	Pearson correlation	.991 **	.537 *	.642 *	-.152	.215	.236	.335	.195	.791 *	-.225	-.171	.131	.773 **
		N	10	16	13	15	10	21	18	10	9	19	7	21	15
	Phytadiene1	Pearson correlation	.078	.888 **	.343	.747 **	.422	.825 **	.709 **	.402	.734 **	-.052	.452	.787 **	.656 **
		N	10	22	13	25	17	29	23	11	16	18	7	29	25
	Phytadiene2	Pearson correlation	.327	.885 **	.434	.613 **	.387	.795 **	.743 **	.208	.830 **	-.054	.371	.846 **	.761 **
		N	11	23	14	25	17	30	24	12	16	19	8	30	26
	Phytadiene3	Pearson correlation	-.042	.895 **	.145	.729 **	.449	.809 **	.751 **	.075	.632 **	-.033	.452	.847 **	.614 **
		N	11	23	14	25	17	30	24	12	16	19	8	30	26
	C19	Pearson correlation	.993 **	.297	.465	.133	.315	.266	.331	.256	.683 **	-.052	.387	.393 *	.386 *
		N	11	27	14	26	19	37	27	12	16	27	8	36	28
	C20	Pearson correlation	.997 **	.500 **	.631 *	-.080	.642 **	.133	.118	.239	.720 **	-.103	-.169	.107	.405 *
		N	11	26	14	25	19	36	25	12	16	26	7	35	27
	C21	Pearson correlation	.998 **	.288	.627 *	-.086	.627 **	.128	-.044	.242	.708 **	-.017	.294	.073	.382 *
		N	11	28	14	27	20	38	27	12	16	27	8	37	29
	C22	Pearson correlation	.998 **	.244	.626 *	-.097	.724 **	.126	.059	.241	.709 **	.019	.331	.073	.388 *
		N	11	27	14	26	19	37	27	12	16	27	8	36	28

Table S2 continued.

 S2

			Gammac	Fern-8-		Fern-7-						Diplopte	Hop-21-	 C 31
			erene			ene		ene	 C 30		C 30			ne		ene		hopene C 31
	median grain size d 0.5 µm	Pearson correlation	.189	-.099	.345	.170	.341	.242	.192	.299	-.028
		N	30	19	20	28	28	25	20	17	25
	OC	Pearson correlation	.350	*	.375	.357	.261	.287	.486	**	.434	*	.445	*	.081
		N	38	22	24	37	36	34	21	23	29
	 15 N ‰	Pearson correlation	-.545	**	-.484	*	-.442	-.426	*	-.483	**	-.612	**	-.608	**	-.362	-.210
		N	30	19	20	28	28	25	20	17	25
	13C ‰	Pearson correlation	-.498	**	-.558	*	-.374	-.423	*	-.431	*	-.642	**	-.464	*	-.469	-.198
		N	30	19	20	28	28	25	20	17	25
	C/N molar	Pearson correlation	.434	*	.350	.310	.349	.380	*	.604	**	.346	.458	.096
		N	30	19	20	28	28	25	20	17	25
	C10	Pearson correlation	-.235	-.129	-.247	-.201	-.257	-.374	-.144	-.373	-.021
		N	29	19	20	27	27	24	20	17	24
	C11	Pearson correlation	.249	.310	.204	.244	.266	-.073	.479 *	-.028	.372
		N	33	19	20	31	31	29	18	18	28
	C12	Pearson correlation	.247	.242	.088	.233	.314	.073	.555 **	-.143	.343
		N	37	21	23	35	35	32	21	21	29
	C13	Pearson correlation	.414 *	.375	.249	.353	.453 *	.138	.698 **	-.076	.424 *
		N	30	17	20	28	28	26	16	17	25
	C14	Pearson correlation	.239	.168	.255	.183	.351 *	-.059	.519 *	-.111	.311
		N	38	22	24	37	36	34	21	23	29
	C15	Pearson correlation	.107	.072	.318	.009	.137	-.188	.200	-.080	.168
		N	30	19	19	28	28	25	13	17	24
	C16	Pearson correlation	.133	.073	.266	.045	.212	-.119	.290	-.149	.198
		N	36	22	24	35	34	32	19	22	29
	C17	Pearson correlation	.044	.066	.194	.067	-.007	-.092	.093	.230	-.036
		N	35	21	24	34	33	31	18	22	28
	Pristane	Pearson correlation	.138	.151	.318	.084	.185	-.307	-.012	-.174	.256
		N	19	13	10	18	17	17	7	11	17
	C18	Pearson correlation	.070	.024	.266	-.011	.122	-.157	.120	-.131	.130
		N	34	21	23	33	32	30	17	21	27
	Phytane	Pearson correlation	-.083	-.167	.387	-.081	-.057	-.299	-.380	-.490	.064
		N	20	15	13	20	18	16	9	13	17
	Phytadiene1	Pearson correlation	.714 **	.658 **	.805 **	.836 **	.760 **	.640 **	.875 **	.316	.662 **
		N	28	18	20	27	26	24	19	18	23
	Phytadiene2	Pearson correlation	.595 **	.423	.789 **	.730 **	.720 **	.463 *	.788 **	.205	.649 **
		N	29	18	20	28	27	25	19	18	24
	Phytadiene3	Pearson correlation	.716 **	.611 **	.811 **	.853 **	.787 **	.655 **	.937 **	.249	.700 **
		N	29	18	20	28	27	25	19	18	24
	C19	Pearson correlation	.241	.197	.247	.188	.286	.035	.338	-.075	.295
		N	36	21	24	35	34	32	19	22	28
	C20	Pearson correlation	-.059	-.125	.361	-.088	-.018	-.172	-.159	.176	.010
		N	35	21	23	34	33	31	19	22	27
	C21	Pearson correlation	-.070	-.146	-.042	-.092	-.025	-.178	-.177	.169	.000
		N	37	21	24	36	35	33	20	23	28
	C22	Pearson correlation	-.071	-.146	.099	-.097	-.029	-.184	-.194	.262	.007
		N	36	21	24	35	34	32	19	22	28

Table S2 continued. 1

 S2

			Phytadie	Phytadie	Phytadie
			ne1	ne2	ne3	C19	C20	C21	C22	C23	C24	C25	C26	Squalane	C27	C28
	C23	Pearson correlation	.154	.324	.061	.691 **	.994 **	.995 **	.994 **	1	.930 **	.958 **	.923 **	.535 **	.915 **	.565 **
		N	30	31	31	39	38	40	39	40	39	39	40	29	39	40
	C24	Pearson correlation	.193	.358	.105	.655 **	.927 **	.921 **	.918 **	.930 **	1	.700 **	.971 **	.555 **	.615 **	.673 **
		N	29	30	30	39	37	39	39	39	39	38	39	28	38	39
	C25	Pearson correlation	.492 **	.446 *	.478 **	.241	.564 **	.664 **	.515 **	.958 **	.700 **	1	.907 **	.585 **	.982 **	.915 **
		N	29	30	30	38	37	39	38	39	38	39	39	29	39	39
	C26	Pearson correlation	.245	.392 *	.157	.644 **	.900 **	.897 **	.893 **	.923 **	.971 **	.907 **	1	.582 **	.841 **	.770 **
		N	30	31	31	39	38	40	39	40	39	39	40	29	39	40
	squalane	Pearson correlation	.579 **	.519 **	.552 **	.137	.343	.566 **	.532 **	.535 **	.555 **	.585 **	.582 **	1	.618 **	.534 **
		N	25	26	26	28	27	29	28	29	28	29	29	29	29	29
	C27	Pearson correlation	.475 **	.420 *	.454 *	.223	.500 **	.589 **	.429 **	.915 **	.615 **	.982 **	.841 **	.618 **	1	.905 **
		N	29	30	30	38	37	39	38	39	38	39	39	29	39	39
	C28	Pearson correlation	.302	.319	.223	.453 **	.507 **	.503 **	.490 **	.565 **	.673 **	.915 **	.770 **	.534 **	.905 **	1
		N	3 0	3 1	3 1	3 9	3 8	4 0	3 9	4 0	3 9	3 9	4 0	2 9	3 9	4 0
	squalene	Pearson correlation	.681 **	.575 **	.639 **	.215	.565 **	.654 **	.845 **	.866 **	.853 **	.860 **	.855 **	.870 **	.847 **	.732 **
		N	25	26	26	26	24	26	26	26	26	26	26	23	26	26
	C29	Pearson correlation	.466 **	.413 *	.431 *	.267	.173	.169	.155	.254	.312	.901 **	.441 **	.554 **	.947 **	.793 **
		N	30	31	31	39	38	40	39	40	39	39	40	29	39	40
	C30	Pearson correlation	.347	.348	.308	.429 **	.443 **	.445 **	.436 **	.517 **	.610 **	.926 **	.718 **	.555 **	.942 **	.866 **
		N	30	31	31	39	38	40	39	40	39	39	40	29	39	40
	C31	Pearson correlation	.463 **	.393 *	.433 *	.200	.062	.060	.044	.147	.215	.910 **	.355 *	.588 **	.957 **	.760 **
		N	30	31	31	39	38	40	39	40	39	39	40	29	39	40
	C32	Pearson correlation	.492 **	.428 *	.455 *	.224	.475 **	.504 **	.337 *	.881 **	.532 **	.944 **	.750 **	.546 **	.958 **	.865 **
		N	29	30	30	38	37	39	38	39	38	39	39	29	39	39
	C33	Pearson correlation	.399 *	.301	.376 *	.069	-.108	-.104	-.125	-.023	.076	.909 **	.224	.653 **	.958 **	.675 **
		N	30	31	31	39	38	40	39	40	39	39	40	29	39	40
	C34	Pearson correlation	.206	.386 *	.135	.684 **	.868 **	.854 **	.853 **	.848 **	.903 **	.311	.821 **	.506 **	.318	.526 **
		N	2 8	2 9	2 9	3 8	3 6	3 8	3 8	3 8	3 8	3 7	3 8	2 7	3 7	3 8
	Lycopane	Pearson correlation	.127	.388	.077	.933 **	.920 **	.921 **	.916 **	.940 **	.965 **	.879 **	.977 **	.896 **	.874 **	.780 **
		N	10	11	11	11	11	11	11	11	11	10	11	10	10	11
	C35	Pearson correlation	.397 *	.303	.380 *	.011	-.085	-.080	-.097	-.032	.157	.732 **	.225	.722 **	.790 **	.565 **
		N	30	31	31	39	38	40	39	40	39	39	40	29	39	40
	C36	Pearson correlation	.213	.180	.204	.093	.656 **	.853 **	.853 **	.946 **	.862 **	.925 **	.902 **	.546 **	.914 **	.878 **
		N	22	23	23	27	26	27	27	27	27	27	27	22	27	27
	C37	Pearson correlation	.400 *	.343	.373 *	.224	.604 **	.719 **	.726 **	.911 **	.712 **	.934 **	.832 **	.643 **	.962 **	.856 **
		N	29	30	30	32	31	33	32	33	32	33	33	27	33	33
	C38	Pearson correlation	.312	.255	.290	.115	.649 **	.837 **	.851 **	.958 **	.878 **	.945 **	.949 **	.950 **	.948 **	.873 **
		N	23	24	24	26	25	26	26	26	26	26	26	22	26	26
	C39	Pearson correlation	.270	.209	.247	.190	.568 **	.711 **	.703 **	.925 **	.727 **	.947 **	.845 **	.938 **	.971 **	.881 **
		N	22	23	23	25	24	25	25	25	25	25	25	21	25	25
	UCM	Pearson correlation	.094	.307	.006	.673 **	.969 **	.968 **	.966 **	.963 **	.944 **	-.087	.932 **	-.056	-.092	.692 **
		N	24	25	25	24	23	25	24	25	24	24	25	21	24	25
	CPI	Pearson correlation	.107	-.009	.155	-.337 *	-.476 **	-.475 **	-.529 **	-.456 **	-.651 **	-.094	-.533 **	.140	-.021	-.357 *
		N	30	31	31	38	37	39	38	39	38	38	39	28	38	39
	C 23 Tricyclic_2	Pearson correlation	.069	.424	-.064	.999 ** 1.000 **	.999 **	.999 **	.999 **	.991 **	.318	.990 **	.655 *	.297	.837 **
		N	12	12	12	14	13	14	14	14	14	13	14	11	13	14

Acknowledgments

We are indebted to the captains and crews of the N.O. Pourquoi Pas? who operated the ship and her equipment during WACS and Congolobe cruises, and to K. Olu and C. Rabouille who were the Chief scientists for the WACS and Congolobe cruises respectively. We acknowledge B. Bombled and P. Noel for operating the multicore on board. G. Vetion and S. Bourgeois conditioned the samples onboard, and C. Senyarich and E. Stetten weighted and lyophilised them back at the laboratory. We thank Rob Spencer and Helen Talbot who shared their samples from the Congo River. This research was funded by ANR Congolobe (ANR Blanc 601 SIMI5-6, n°11 BS56 030) and IFREMER (Project "Biodiversité et dynamique des écosystèmes profonds, impacts"). We thank the PI of Congolobe, Christophe Rabouille, for stimulating exchange of data and ideas though regular meetings.

We would like to thank two anonymous reviewers for their valuable comments and helpful suggestions on an earlier version of the manuscript.