Late Quaternary behavior of the East African monsoon and the importance of the Congo Air Boundary
Tierney, J.; Russell, J.M.; Sinninghe Damsté, J.S.; Huang, Y.S.; Verschuren, D. (2011). Late Quaternary behavior of the East African monsoon and the importance of the Congo Air Boundary. Quat. Sci. Rev. 30(7-8): 798-807. dx.doi.org/10.1016/j.quascirev.2011.01.017
In: Quaternary Science Reviews. Pergamon Press: Oxford; New York. ISSN 0277-3791; e-ISSN 1873-457X, more
Both Atlantic and Indian Ocean climate dynamics exert influence over tropical African hydroclimate, producing complex patterns of convergence and precipitation. To isolate the Indian Ocean influence on African paleohydrology, we analyzed the deuterium/hydrogen ratio of higher plant leaf waxes (delta D-wax) in a 25 000-year sediment record from Lake Challa (3 degrees S, 38 degrees E) in the easternmost area of the African tropics. Whereas both the seismic record of inferred lake level fluctuations and the Branched and Isoprenoidal Tetraether (BIT) index proxy record changes in hydrology within the Challa basin, delta D-wax, as a proxy for the isotopic composition of precipitation (delta D-p) is interpreted as a tracer of large-scale atmospheric circulation that integrates the history of the moisture transported to the Lake Challa area. Specifically, based on modern-day isotope-rainfall relationships, we argue that Lake Challa delta D-wax reflects the intensity of East African monsoon circulation. The three hydrological proxy records show generally similar trends for the last 25 000 years, but there are important differences between them, primarily during the middle Holocene. We interpret this deviation of delta D-wax from local hydrological history as a decoupling of East African monsoon intensity - which heavily influences the isotopes of precipitation in East Africa today - from rainfall amount in the Challa basin. In combination, the hydrological proxy data from Lake Challa singularly highlight zonal gradients in tropical African climate that occur over a variety of timescales, suggesting that the Congo Air Boundary plays a fundamental role in controlling hydroclimate in the African tropics.
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