Interaction of Holocene infilling processes between a tropical shallow lake system (Lake Ossa) and a nearby river system (Sanaga River) (South Cameroon)

Kossoni, Alice; Giresse, Pierre

doi:10.1016/j.jafrearsci.2009.05.012

Cited by 13 publications

(14 citation statements)

References 16 publications

(30 reference statements)

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“…The ITCZ is located around 5-10 • N and 15-20 • N in western Equatorial Africa during the boreal winter and boreal summer, respectively, in response to the northward migration of the maximum of received solar radiation energy. Large precipitation over western Equatorial Africa, around 3000 mm yr −1 (Kossoni et al, 2010), support the presence of evergreen rainforest and savannah (Foley et al, 2003).…”

Section: Oceanographic and Climatic Settingsmentioning

confidence: 95%

“…They cover a catchment area of ∼2 400 000 km 3 yr −1 and drive an annual riverine freshwater input of ∼277 km 3 (Weldeab et al, 2007a). More particularly, the drainage area of the Sanaga River is 133 000 km 2 and the mean annual discharge is 62 km 3 yr −1 (Kossoni et al, 2010). River discharges are minimal during the boreal winter-spring (February-April) and maximal during the boreal summer-autumn (JulyNovember), with peak runoffs in September and October (Weldeab et al, 2007a;Kossoni et al, 2010).…”

Section: Oceanographic and Climatic Settingsmentioning

confidence: 99%

“…More particularly, the drainage area of the Sanaga River is 133 000 km 2 and the mean annual discharge is 62 km 3 yr −1 (Kossoni et al, 2010). River discharges are minimal during the boreal winter-spring (February-April) and maximal during the boreal summer-autumn (JulyNovember), with peak runoffs in September and October (Weldeab et al, 2007a;Kossoni et al, 2010). Annual variations in the Sanaga discharge are determined by the yearly cycle of precipitations over Equatorial Africa, controlled by the West African monsoon (WAM).…”

Section: Oceanographic and Climatic Settingsmentioning

confidence: 99%

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Climatically-controlled siliceous productivity in the eastern Gulf of Guinea during the last 40 000 yr

et al. 2012

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Abstract. Opal content and diatom assemblages were analysed in core GeoB4905-4 to reconstruct siliceous productivity changes in the eastern Gulf of Guinea during the last 40 000 yr. Opal and total diatom accumulation rates presented low values over the considered period, except during the Last Glacial Maximum and between 15 000 calendar years Before Present (15 cal. ka BP) and 5.5 cal. ka BP, the so-called African Humid Period, when accumulation rates of brackish and freshwater diatoms at the core site were highest. Conversely, accumulation rates of windblown diatoms exhibited an opposite pattern with higher values before and after the African Humid Period and greatest values during Heinrich Events, the Younger Dryas and since 5.5 cal. ka BP.Our results demonstrate that siliceous productivity in the eastern Gulf of Guinea was directly driven by the nutrient load from local rivers, whose discharges were forced by precipitation changes over western Equatorial Africa and/or modification of the fluvio-deltaic systems forced by sea level changes. Precipitation in this region is controlled by the West African monsoon which is, in turn, partly dependent on the presence and intensity of the Atlantic Cold Tongue (ACT). Our results therefore suggest that the ACT was weakened, warmer trade winds were less vigorous, and cloud convection and precipitation were greater during the AHP though centennial-to-millennial timescale dry events were observed at ∼10 cal. ka BP, ∼8.5 cal. ka BP and ∼6 cal. ka BP. Conversely, the ACT was more intense, trade winds were more vigorous and African climate was more arid during H1, the Younger Dryas and after 5.5 cal. ka BP into the present.

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Section: Oceanographic and Climatic Settingsmentioning

confidence: 95%

Section: Oceanographic and Climatic Settingsmentioning

confidence: 99%

Section: Oceanographic and Climatic Settingsmentioning

confidence: 99%

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Climatically-controlled siliceous productivity in the eastern Gulf of Guinea during the last 40 000 yr

et al. 2012

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“…In central African subequatorial regions, proxy data inferred important disturbances in the periphery of the equatorial rain forest belt with possible appearance of included savannas (Ngomanda et al, 2009a, b) and complete dryness of lakes as Lake Sinnda in south Congo by 4400 yr BP (Vincens et al, 1994;Bertaux et al, 2000). In inner forest block, lakes were less affected by this climatic change (Vincens et al, 1999;Ngomanda et al, 2007;Kossoni et al, 2009). This period is characterised in Lake Mbalang by the maintenance of indicators of stable water table in agreement with the palynological and δ 13 C ORG.…”

Section: Middle To Late Holocene: From 7200 To 3600 Cal Yr Bpmentioning

confidence: 99%

“…Concordant data from low and high altitudes in western Cameroon (Maley and Brenac, 1998;Reynaud-Farrera et al, 1996;Nguetsop et al, 1998;Stager and Anfang-Sutter, 1999;Vincens et al, 1999;Ngomanda et al, 2007Ngomanda et al, , 2009b; Kossoni and Giresse, 2009) suggest that climatic changes were also controlled by modifications in the vertical structure of the atmosphere (Nguetsop et al, 2004). The present stable air layer situated at the base of the monsoon flux in JulyAugust could have extended on the western Cameroon lowlands and mid altitude areas during the greatest part of the year, entailing the almost suppression of convective rains before 3000 cal yr BP.…”

Section: Introductionmentioning

confidence: 96%

Past environmental and climatic changes during the last 7200 cal yr BP in Adamawa plateau (Northern-Cameroun) based on fossil diatoms and sedimentary carbon isotopic records from Lake Mbalang

et al. 2011

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Abstract. Past limnological conditions of Lake Mbalang (7 • 19 N, 13 • 44 E, altitude: 1130 m) and vegetation type were reconstructed from diatoms and sedimentary stable carbon isotope records (δ 13 C) since 7200 cal yr BP. The data showed that before 3600 cal yr BP, the water column was dominantly stable except around 5000-5300 cal yr BP where diatoms evidenced a mixed upper water layer and δ 13 C data suggest more forested vegetation in the landscape. These stable conditions can be explained by a strong monsoon flux and relatively northern position of the ITCZ that entailed high or low rainfall well distributed over the year, allowing the development of mountainous forest taxa. The decreasing trend of the monsoon flux towards the mid-Holocene was affected by several abrupt centennial to millennial-scale weakening at 6700, 5800-6000, 5000-5300, 4500 and 3600 cal yr BP. However, their impact on the vegetation is not visible, probably because rainfall distribution was favourable to forest maintenance or extension. After 3600 cal yr BP, the water column became very mixed as a result of more intense NE trade winds (Harmattan) that led at ∼3000 cal yr BP to the establishment of savannah in the vegetation landscape. At that time, rainfall was probably reduced following the southward shift of the ITCZ, and the distribution of yearly rainfall was not favourable anymore to forest development. A strong seasonality with a marked dry season was established, conditions that maintained the savannah vegetation until today.

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Geoelectrical imaging and spatial distribution of alluvial materials of the Sanaga River (Cameroon, Central Africa)

et al. 2022

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Interaction of Holocene infilling processes between a tropical shallow lake system (Lake Ossa) and a nearby river system (Sanaga River) (South Cameroon)

Cited by 13 publications

References 16 publications

Climatically-controlled siliceous productivity in the eastern Gulf of Guinea during the last 40 000 yr

Climatically-controlled siliceous productivity in the eastern Gulf of Guinea during the last 40 000 yr

Past environmental and climatic changes during the last 7200 cal yr BP in Adamawa plateau (Northern-Cameroun) based on fossil diatoms and sedimentary carbon isotopic records from Lake Mbalang

Geoelectrical imaging and spatial distribution of alluvial materials of the Sanaga River (Cameroon, Central Africa)

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