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The effects of solar irradiation changes on the migration of the Congo Air Boundary and water levels of paleo-Lake Suguta, Northern Kenya Rift, during the African Humid Period (15-5 ka BP)

  • The water-level record from the 300 m deep paleo-lake Suguta (Northern Kenya Rift) during the African Humid Period (AHP, 15-5 ka BP) helps to explain decadal to centennial intensity variations in the West African Monsoon (WAM) and the Indian Summer Monsoon (ISM). This water-level record was derived from three different sources: (1) grain size variations in radiocarbon dated and reservoir corrected lacustrine sediments, (2) the altitudes and ages of paleo-shorelines within the basin, and (3) the results of hydro-balance modeling, providing important insights into the character of water level variations (abrupt or gradual) in the amplifier paleo-Lake Suguta. The results of these comprehensive analyses suggest that the AHP highstand in the Suguta Valley was the direct consequence of a northeastwards shift in the Congo Air Boundary (CAB), which was in turn caused by an enhanced atmospheric pressure gradient between East Africa and India during a northern hemisphere insolation maximum. Rapidly decreasing water levels of up to 90 m overThe water-level record from the 300 m deep paleo-lake Suguta (Northern Kenya Rift) during the African Humid Period (AHP, 15-5 ka BP) helps to explain decadal to centennial intensity variations in the West African Monsoon (WAM) and the Indian Summer Monsoon (ISM). This water-level record was derived from three different sources: (1) grain size variations in radiocarbon dated and reservoir corrected lacustrine sediments, (2) the altitudes and ages of paleo-shorelines within the basin, and (3) the results of hydro-balance modeling, providing important insights into the character of water level variations (abrupt or gradual) in the amplifier paleo-Lake Suguta. The results of these comprehensive analyses suggest that the AHP highstand in the Suguta Valley was the direct consequence of a northeastwards shift in the Congo Air Boundary (CAB), which was in turn caused by an enhanced atmospheric pressure gradient between East Africa and India during a northern hemisphere insolation maximum. Rapidly decreasing water levels of up to 90 m over less than a hundred years are best explained by changes in solar irradiation either reducing the East African-Indian atmospheric pressure gradient and preventing the CAB from reaching the study area, or reducing the overall humidity in the atmosphere, or a combination of both these effects. In contrast, although not well documented in our record we hypothesize a gradual end of the AHP despite an abrupt change in the source of precipitation when a decreasing pressure gradient between Asia and Africa prevented the CAB from reaching the Suguta Valley. The abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during October. Whether or not this is the case, the water-level record from the Suguta Valley demonstrates the importance of both orbitally-controlled insolation variations and short-term changes in solar irradiation as factors affecting the significant water level variations in East African rift lakes.show moreshow less

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Metadaten
Author:Annett Junginger, Sybille Roller, Lydia A. Olaka, Martin H. Trauth
DOI:https://doi.org/10.1016/j.palaeo.2013.12.007
ISSN:0031-0182 (print)
ISSN:1872-616X (online)
Parent Title (English):Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences
Publisher:Elsevier
Place of publication:Amsterdam
Document Type:Article
Language:English
Year of first Publication:2014
Year of Completion:2014
Release Date:2017/03/27
Tag:African Humid Period; Congo Air Boundary; East African Rift System; Suguta Valley
Volume:396
Pagenumber:16
First Page:1
Last Page:16
Funder:German Research Foundation (DFG); DFG Graduate School [GRK1364]; Government of Kenya [MOST 13/001/30C 59/10, 59/18, 59/22, NCST/RRI/12/1/BS011/78]; University of Nairobi
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Erd- und Umweltwissenschaften
Peer Review:Referiert