Ja. Holmes et al., HOLOCENE PALEOLIMNOLOGY OF KAJEMARUM OASIS, NORTHERN NIGERIA - AN ISOTOPIC STUDY OF OSTRACODES, BULK CARBONATE AND ORGANIC-CARBON, Journal of the Geological Society, 154, 1997, pp. 311-319
A high-resolution 5500 year palaeolimnological record from Kajemarum O
asis, a closed basin in the Manga Grasslands of northern Nigeria, prov
ides evidence of environmental change in Subsaharan Africa during the
Holocene. Palaeohydrological variations, mainly changes in the balance
between precipitation and evaporation, are recorded by stable oxygen
isotope ratios in bulk carbonate and ostracod calcite and by the Sr/Ca
ratio in ostracode shells. Variations in the carbon isotope ratios in
carbonates indicate changes in primary productivity in the lake, wher
eas the carbon isotope composition of organic carbon reflects ecophysi
ological processes within the lake and its surrounding catchment. Resu
lts indicate that there have been marked environmental changes in the
Manga Grasslands over the last 5500 years. A more variable climate set
in around 1500 cai. a sp. A prolonged drought between 1200 and 1000 c
al. a sp. with reduced aquatic productivity, was followed by a switch
to a wetter, but still unstable climate: moist conditions prevailed du
ring the Little Ice Age. The results indicate that drought has affecte
d the Sahel episodically over the last 1500 years and is not solely a
twentieth-century phenomenon.