A late Holocene palaeoenvironmental record from Lake Tizong, northern Cameroon using diatom and carbon stable isotope analyses

2013

Article référencé dans le Web of Science WOS:000321685700004

Nguetsop V. F., Bentaleb I., Favier C., Bietrix S., Martin C., Servant Vildary Simone, Servant Michel

Quaternary Science Reviews, 2013, 72, p. 49-62 ISSN 0277-3791

A late Holocene record, based on diatom and stable carbon isotopes from Lake Tizong, northern Cameroon, provides a history of environmental changes over the last 4100 years. Several coarser sediment layers among which the two younger ones are of pyroclastic origin interrupt the fine clayey sediment of the core. The detailed chronology of the core supported by 24 radiocarbon C-14 dates and proxies data results revealed an erosive phase registered in the sedimentary column from 2200 to 1500 cal BP. The diatom ecological groups suggest that between 4100 and 2800 cal yrs BP, the lake level was much higher than after corresponding to a relatively greater precipitation minus evaporation (P E) ratio, as well as increased runoff in the lake catchment. These conditions were favourable to the development of C3 plants in the lake catchment as indicated by lower delta C-13 values and higher C/N ratios than after. This hydrological phase is also characterized by eutrophic, turbid and probably circum-neutral to alkaline waters. After this episode, higher delta C-13 values between 2800 and 2500 cal BP suggest increased water use efficiency of terrestrial plants and/or potentially more C4 plant debris input into the lake: an indication of savannas patches developing, due probably to changes in the rainfall distribution. Marked lake-level declines are recorded at 2500, 2200-2100, and at 1400-1000 cal yrs BP. These low-stands are characterized by higher inputs of windblown diatoms (up to 4.2%) than before, which confirms that the NE trade-winds were strengthening. This corresponds primarily to a reduction in the P E ratio, but probably also to greater inter-annual or seasonal variability when drier periods or seasons became more prolonged and intense than previously. Consequently, savannas were maintained as suggested by relatively higher than before delta C-13 values, as well as independently supported by regional pollen data. After 1000 cal BP, the lake-level rose towards sub-modern conditions, with a deep neutral and eutrophic water column. Carbon stable isotopes suggest a reduction of organic matter input, while savannas were maintained despite the return to more humid conditions. The trends of climatic changes observed in the Lake Tizong reveal the variability in timing, magnitude and regional extent of known climatic events.

Sciences du milieu [021] ; Géologie et formations superficielles [064]

CAMEROUN

Fonds IRD [F B010060494]

fdi:010060494