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Millennial-Scale Variations in West African Precipitation
Nguetsop, V.F., Servant-Vildary, S. and Servant, M.  2004.  Late Holocene climatic changes in west Africa, a high resolution diatom record from equatorial Cameroon.  Quaternary Science Reviews 23: 591-609.

What was done
The authors developed a high-resolution proxy record of West African precipitation based on analyses of diatoms recovered from a 5.5-m sediment core retrieved from Lake Ossa, West Cameroon, which rainfall history they describe as "the first paleohydrological record for the last 5500 years in the equatorial near-coastal area, east of the Guinean Gulf."

What was learned
Nguetsop et al. say the Lake Ossa record provides evidence for alternating periods of increasing and decreasing precipitation "at a millennial time scale for the last 5500 years," which oscillatory behavior they interpret as being "a result of south/northward shifts of the ITCZ [Intertropical Convergence Zone]."  Specifically, they report that "a southward shift of the ITCZ, combined with strengthened northern trade winds, was marked by low and high precipitation at the northern subtropics and the subequatorial zone, respectively," and that "these events occurred in coincidence with cold spells in the northern Atlantic."  They thus conclude that "the climatic evolution in the tropical zone of Africa [is] essentially driven by interactions between the northern and southern hemispheres."

What it means
As with so many other temperature and precipitation records from around the world, the data of Nguetsop et al. for West Africa add to the growing body of evidence for the existence of a millennial-scale oscillation of climate that alternately brings either warmer or cooler temperatures or wetter or drier conditions to each of the locations it influences as it reverberates down through the ages.

Reviewed 23 June 2004