Reconstruction of the Holocene Climate and Environmental changes of Niayes Peat Bog in Northern coast of Senegal (NW Africa) based on Stable Isotopes and Charcoals Analysis
Abstract
A core from a peat bog in the “Niayes” region, northwest of Senegal, provides a valuable insight into the evolution of the landscape and fire regime related to the West African Monsoon rainfall and to human impact over the Holocene. The high-resolution multiproxy approach based on stable carbon isotopic composition (δ13C), Rock-Eval® thermal analysis, and charcoal analysis, provides an understanding of vegetation composition (C3/C4) and fire regime in the continental watershed. The analysis of our data indicates a more woody landscape and a higher water table level, related to increased monsoonal rainfall during the African Humid period (AHP) between 9.5 and 5.5 cal kyr BP. High insolation and orbital changes account for a northward migration of the African Rain Belt and a reinforced West Africa monsoon. The amount of forest fires was low and most likely of natural occurrence, as human density was very low. A short dry event interrupts the AHP and gives rise to a weakly grassy landscape at around 8.2 cal kyr BP. This drought of centennial scale (400 years) occurring between 8.4 and 8 cal kyr BP is concomitant with the general cooling observed in the Northern Hemisphere. After a period of transition, the millennial-scale Late Holocene dry period begins at 4.8 cal kyr BP. The low water table level, resulting from a decrease in precipitation, coincides with the appearance of a grassy savanna landscape. Insolation decrease and reduced vegetation were likely driven by a southward migration of the African Rain Belt and a weakening of the monsoon. During the late Holocene the “Niayes” zone evolved into a phase of environmental stress often interrupted by Little Humid Periods (LHP) of centennial scale (500 and 600 years) respectively between 4.4 and 3.9 and between 1.1 and 0.5 cal kyr BP. After 0.5 cal kyr BP the decrease in precipitation and the increase in savanna fires, probaly of anthropogenic origin, favor the landscape opening.