Long-term temporal characteristics of palaeomonsoon dynamics in equatorial Africa

Abstract

In this paper we examine the long-term temporal characteristics of palaeomonsoon dynamics in equatorial Africa from a continuous lacustrine sequence retrieved from Sacred Lake, Mount Kenya (0°03′N, 37°32′E, 2350 m a.s.l.), covering the last interglacial–glacial transition to the present. The trends in mineral magnetics and stable carbon isotopes are proxy indicators of changes in precipitation on the mountain over the last glacial–interglacial cycle. Spectral analysis by a fast fourier transform method revealed that the stable carbon isotope trend (δ13C) has strong signals at the 23,000 and 11,500 year frequencies. The mineral magnetic signature does not register the 23,000 year cycle observed in the δ13C signature. It has, however, a strong signal at an 11,500 year frequency, and sharp but relatively weak peaks at ca. 7500 and 5000 year frequencies are recorded. The dominant 23,000 year frequency recorded in the δ13C signature reflects the strong effect of the precessional cycle on tropical climate and ecosystems, and is most probably effected via global atmospheric pCO2 and temperature changes. The shorter cycles at 11,500 year (indicated by both mineral magnetics and δ13C trends), and 7500 and 5000 years BP (apparent in the mineral magnetic record) are attributed to precipitation variations, whose temporal cycles are dominated by the higher precessional harmonics.