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Pierre Giresse Makaya Mvoubou Jean Maley Alfred Ngomanda 《Journal of Paleolimnology》2009,41(2):369-392
Seven vibro-cores were collected from three shallow lakes of the Gabon (Kamalété, Nguène, Maridor) along a 300-km west–east
transect close to the Equator. These lakes are located in very distinct landscapes: coastal forest-savanna mosaic, rain forest
and savanna with colonising forest, respectively. Core chronologies were established by radiocarbon dating. Study of these
lacustrine archives (textural variables, clay minerals, organic matter components, δ13C, pollen) allowed comparison of late Holocene environmental changes recorded at each site and with results from other studies.
Lake Kamalété indicates minor climatic deterioration (increased drying and greater seasonality) between 1,410 and 500 cal.
years BP, which is also recognised in southern Cameroon and east-central Africa. Lake Nguène was surrounded by dense moist
forest throughout the last 4,110 years, but shows significant deterioration from ~2,800 cal. years BP, a phenomenon seen at
nearby sites. Lake Maridor shows a decline of forest initiated a little after 3,800 cal. years BP, which indicates timing
that is distinct from the two other sites. This was probably a response to local conditions (i.e. outlet damming). Although
the three lakes display generally parallel climatic trends perhaps linked to SST oscillations, there is not perfect coherence
between these three sites. Differences among the three basins may be attributable to local factors like groundwater hydrology
and slope instabilities of such shallow lake systems in this equatorial region. 相似文献
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Alfred Ngomanda Dominique Jolly Ilhem Bentaleb Alex Chepstow-Lusty M'voubou Makaya Jean Maley Michel Fontugne Richard Oslisly Nicaise Rabenkogo 《Quaternary Research》2007,67(3):411-425
Pollen and δ13CTOM data obtained from two contrasting lake sequences (Lakes Kamalété and Nguène), located 200 km apart in the lowland rainforest of Gabon, provide complementary local and regional 1500-yr records of high resolution (15–30 yr) vegetation change. A combination of aquatic, semi-aquatic and terrestrial pollen showed in both records that the tropical rainforest increased during periods of high rainfall and decreased during drought intervals. The strong fluctuations of water balance at decadal scale during the “Medieval Warm Period” ( 1100–800 cal yr BP) coincided with a noticeable increase in shade-intolerant taxa, indicating recurring rainforest canopy disturbance. The δ13CTOM signal showed high-amplitude variations in both records, which positively correlates with the rainforest dynamics and local vegetation changes. The similar trends in both the pollen and the δ13CTOM signals between these sites demonstrate the regional broadly synchronous timing of shifting hydrological conditions. The largely positive co-variation between strong fluctuations of hydrological conditions and changes in rainforest structure and composition indicate that regional climatic change is probably the driving force for major rainforest dynamics in Gabon. Any significant anthropogenic impact on vegetation has not been clearly identified, and this issue still needs to be resolved independently by obtaining detailed archeological records across the interval 1400–800 BP, which currently seem to be extremely rare or not easily available. 相似文献
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