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Multi-Century Climatic Cycles of Equatorial Africa
Reference
Russell, J.M and Johnson, T.C. 2005. Late Holocene climate change in the North Atlantic and equatorial Africa: Millennial-scale ITCZ migration. Geophysical Research Letters 32: 10.1029/2005GL023295.

What was done
Working with three sediment cores extracted from Lake Edward (0N, 30E) in Africa, the authors developed a continuous 5400-year record of Mg concentration and isotopic composition of authigenic inorganic calcite as proxies for the lake's water balance, which is itself a proxy for regional drought conditions in equatorial Africa.

What was learned
Russell and Johnson report that "the geochemical record from Lake Edward demonstrates a consistent pattern of equatorial drought during both cold and warm phases of the North Atlantic's '1500-year cycle' during the late Holocene," noting that similar "725-year climate cycles" are found in several records from the Indian and western Pacific Oceans and the South China Sea, citing as authority for the latter statement the studies of von Rad et al. (1999), Wang et al. (1999), Russell et al. (2003) and Staubwasser et al. (2003).

What it means
The two scientists say their results "show that millennial-scale high-latitude climate events are linked to changes in equatorial terrestrial climate ... during the late Holocene," or as they phrase it in another place, that their results "suggest a spatial footprint in the tropics for the '1500-year cycle' that may help to provide clues to discern the cycle's origin," noting there is already reason to believe that it may be solar-induced.

References
Russell, J.M., Johnson, T.C. and Talbot, M.R. 2003. A 725-year cycle in the Indian and African monsoons. Geology 31: 677-680.

Staubwasser, M., Sirocko, F., Grootes, P. and Segl, M. 2003. Climate change at the 4.2 ka BP termination of the Indus valley civilization and Holocene south Asian monsoon variability. Geophysical Research Letters 30: 10.1029/2002GL016822.

von Rad, U., et al. 1999. A 5000-yr record of climate changes in varved sediments from the oxygen minimum zone off Pakistan, northeastern Arabian Sea. Quaternary Research 51: 39-53.

Wang, L., et al. 1999. East Asian monsoon climate during the late Pleistocene: High resolution sediment records from the South China Sea. Marine Geology 156: 245-284.

Reviewed 15 March 2006