Deep-sea terrigenous organic carbon transfer and accumulation: Impact of sea-level variations and sedimentation processes off the Ogooue River (Gabon)

Mignard, Salomé; Mulder, Thierry; Martinez, Philippe; Charlier, Karine; Rossignol, Louise; Garlan, Thierry

doi:10.1016/j.marpetgeo.2017.04.009

Cited by 21 publications

(17 citation statements)

References 61 publications

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“…to its mouth in the southern part of the Atlantic coast of Gabon. The Ogooué river flows northwestward in upstream until the confluence with the Ivindo and southwestward from the confluence with the Ivindo river to a 100 km long and 100 km width delta it forms in the south of Port Gentil where it discharges into the Atlantic ocean [30]. The Ogooué river basin (ORB) is located between 9 • and 15 • E, and 3 • S and 2.5 • N (Figure 1) stretching on about 80% of the total area of Gabon and It is bounded on the east by the Congo basin, on the south by the Niari and Nyanga basins, on the west and north-west by the coastal river basins [31].…”

Section: Study Areamentioning

confidence: 99%

“…Due to its location crossing the Equator, the ORB receives the largest annual precipitation in Africa (1600-2200 mm yr −1 ), making the annual discharge of the river of 4750 m 3 •s −1 , the third along the African West Coast after the Congo River (40,000 m 3 •s −1 ) and the Niger River (5590 m 3 •s −1 ) [30,32]. The annual variation of the discharge of the Ogooué river passes by two maximum : in spring and autumn corresponding to the rainy seasons [31].…”

Section: Radar Altimetry Datamentioning

confidence: 99%

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Monitoring Water Levels and Discharges Using Radar Altimetry in an Ungauged River Basin: The Case of the Ogooué

et al. 2018

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Radar altimetry is now commonly used for the monitoring of water levels in large river basins. In this study, an altimetry-based network of virtual stations was defined in the quasi ungauged Ogooué river basin, located in Gabon, Central Africa, using data from seven altimetry missions (Jason-2 and 3, ERS-2, ENVISAT, Cryosat-2, SARAL, Sentinel-3A) from 1995 to 2017. The performance of the five latter altimetry missions to retrieve water stages and discharges was assessed through comparisons against gauge station records. All missions exhibited a good agreement with gauge records, but the most recent missions showed an increase of data availability (only 6 virtual stations (VS) with ERS-2 compared to 16 VS for ENVISAT and SARAL) and accuracy (RMSE lower than 1.05, 0.48 and 0.33 and R 2 higher than 0.55, 0.83 and 0.91 for ERS-2, ENVISAT and SARAL respectively). The concept of VS is extended to the case of drifting orbits using the data from Cryosat-2 in several close locations. Good agreement was also found with the gauge station in Lambaréné (RMSE = 0.25 m and R 2 = 0.96). Very good results were obtained using only one year and a half of Sentinel-3 data (RMSE < 0.41 m and R 2 > 0.89). The combination of data from all the radar altimetry missions near Lamabréné resulted in a long-term (May 1995 to August 2017) and significantly improved water-level time series (R 2 = 0.96 and RMSE = 0.38 m). The increase in data sampling in the river basin leads to a better water level peak to peak characterization and hence to a more accurate annual discharge over the common observation period with only a 1.4 m 3 •s −1 difference (i.e., 0.03%) between the altimetry-based and the in situ mean annual discharge.

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Section: Study Areamentioning

confidence: 99%

Section: Radar Altimetry Datamentioning

confidence: 99%

Monitoring Water Levels and Discharges Using Radar Altimetry in an Ungauged River Basin: The Case of the Ogooué

et al. 2018

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“…The twelve Küllenberg cores presented here were collected during the cruise MOCOSED 2010. Five of these cores have already been presented in (Mignard et al, 2017) (Table 1). Visual descriptions of the cores distinguished the dominant grain size (clay, silty clay, silt, and fine sand) and vertical successions of sedimentary facies.…”

Section: Methodsmentioning

confidence: 99%

“…Subsamples were regularly taken in order to measure carbonate content using a gasometric calcimeter and grain size using a Malvern Mastersizer S. The stratigraphic framework is based on the previous work of (Mignard et al, 2017)), new AMS 14 C dating and facies correlation to determine the boundary between Marine Isotopic Stage 1 (MIS1) and Marine Isotopic…”

Section: Methodsmentioning

confidence: 99%

“…They display a variety of bedding structures: normally-graded or massive. The composition varies from terrigenous (quartz and mica) to biogenic (foraminifera), some sequences are highly enriched in organic debris (Mignard et al, 2017). They are interpreted as being deposited by turbidity currents initiated on the Gabonese continental shelf.…”

Section: Sedimentary Faciesmentioning

confidence: 99%

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The Ogooue Fan (Gabon): a modern example of deep-sea system on a complex sea-floor topography

Mignard

Mulder

Martinez

et al. 2018

Preprint

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Abstract. The Ogooue deep-sea Fan located in the northeastern part of the Gulf of Guinea expands over more than 550 km westwards of the Gabonese shelf and passes through the Cameroun volcanic line. Here are presented the first study of acoustic data (multibeam echosounder and 3.5 kHz seismic data) and piston cores covering the deep-sea part of this West African system. This study led to the construction of the sedimentary processes map of this area. The overall system corresponds to a well-developed mud-sand rich deep-sea fan, fed by the Ogooue River 'sedimentary load. This system presents the typical morphological elements of clastic slope apron: tributary canyons, distributary channel-levees systems and lobes elements. However, variations on the slope gradient cumulated with the presence of numerous seamounts, including volcanic islands and mud volcanoes, led to a more complex fan architecture and sedimentary facies distribution. In particular, turbidity currents derived from the Gabonese shelf deposit across several interconnected sedimentary sub-basins located on the low gradient segments of the margin. The repeated spill-overs of the most energetic turbidite flows have notably led to the incision of a large distal valley connecting an intermediate sedimentary basin to the more distal lobe area. The sedimentary facies repartition over the fan indicates that pelagic to hemipelagic sedimentation is dominant across the area. Distribution and thickness of turbidite sand beds is highly variable along the system, however turbidite sands preferentially deposit in the bottom of channel-levee systems and on the most proximal depositional areas. The most distal depocenters receive only the upper parts of the flows, which are composed of fine-grained sediments. The Ogooue deep-sea system is predominantly active during periods of low sea-level because canyon heads are separated from terrestrial sediment sources by the broad shelf. However, the northern part of this system appears active during sea-level highstands. This feature is one deeply incised canyon, the Cape Lopez canyon, located on a narrower part of the continental shelf has a different behaviour and receives sediments transported by the longshore drift.

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Long‐Term Hydrological Variations of the Ogooué River Basin

Bogning

Frappart

Mahé

et al. 2022

Congo Basin Hydrology, Climate, and Biogeochemistry

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Deep-sea terrigenous organic carbon transfer and accumulation: Impact of sea-level variations and sedimentation processes off the Ogooue River (Gabon)

Cited by 21 publications

References 61 publications

Monitoring Water Levels and Discharges Using Radar Altimetry in an Ungauged River Basin: The Case of the Ogooué

Monitoring Water Levels and Discharges Using Radar Altimetry in an Ungauged River Basin: The Case of the Ogooué

The Ogooue Fan (Gabon): a modern example of deep-sea system on a complex sea-floor topography

Long‐Term Hydrological Variations of the Ogooué River Basin

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