Stepwise drying of Lake Turkana at the end of the African Humid Period: a forced regression modulated by solar activity variations?
Résumé
Although the timing of the termination of the
African Humid Period (AHP) is now relatively well estab-
lished, the modes and controlling factors of this drying are
still debated. Here, through a geomorphological approach,
we characterize the regression of Lake Turkana at the end
of the AHP. We show that lake level fall during this period
was not continuous but rather stepwise and consisted of five
episodes of rapid lake level fall separated by episodes marked
by slower rates of lake level fall. Whereas the overall regres-
sive trend reflects a decrease in regional precipitations linked
to the gradual reduction in Northern Hemisphere summer in-
solation, itself controlled by orbital precession, we focus dis-
cussion on the origin of the five periods of accelerated lake
level fall. We propose that these periods are due to temporary
reductions in rainfall across the Lake Turkana area associ-
ated with repeated westward displacement of the Congo Air
Boundary (CAB) during solar activity minima.
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