干旱区生态环境知识资源中心

Sucessive samples of fossil pear from a 450 cm core, spanning past 6 kyr in Senegal (Touba Ndiaye, 15 degrees 08 N-16 degrees 97 E) were analyzed. The delta(13)C in fibrous pears show variations indicating changes from humid periods (delta(13)C similar to -28 parts per thousand) to dry periods (delta(13)C similar to -22 parts per thousand). An exceptional shift of delta(13)C around 4.5 kyr is in accordance with pollen and macro-rest curves which suggests regression of water level in peat bog basin. This dry period is followed by a short but very wet phase between 3.5 kyr and 2.6 kyr BP. Then after about 2 kyr BP a second delta(13)C Shift occurs showing the onset of present-day semi-arid conditions. The arid phase around 4.5 kyr BP and the following wet phase around 3.5 kyr BP show the past monsoon rainfall fluctuations over Sahelian areas previously described in West African coastal sediments and connected with astronomical change of orbital insolation.