West African Monsoon Variability from a High-Resolution Paleolimnological Record (Lake Bosumtwi, Ghana)

Persistent Link:
http://hdl.handle.net/10150/194712
Title:
West African Monsoon Variability from a High-Resolution Paleolimnological Record (Lake Bosumtwi, Ghana)
Author:
Shanahan, Timothy Michael
Issue Date:
2006
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Instrumental and observational records of climate in West Africa suggest that this region may be susceptible to abrupt, decades-long drought events, with potentially catastrophic impacts for the people living in this region. However, because of the dearth of long, continuous and high quality climate records from sub-Saharan Africa, little is known about the long-term frequency and persistence of drought events in this region. It is also unclear whether observed 20th century droughts are natural or due to human impacts. In the present study, we use several complementary approaches to develop a high-resolution record of paleoclimatic changes in West Africa from the geological record preserved at Lake Bosumtwi, Ghana.Our results suggest that West Africa has undergone significant hydrologic variations over the last ca. 10,000 years. The dominant influence on hydrologic changes over this interval was changes in northern hemisphere summer insolation and the associated feedback processes acting in the oceans and on land. This led to a more northerly position of the Intertropical Convergence Zone (ITCZ) and increased precipitation during the early to mid-Holocene. In the late Holocene, a second increase in precipitation occurred along the Guinea coast as a result of the southward migration of the ITCZ from its northern position. This maximum was followed by an abrupt decrease in precipitation at ca. 2.5-3 kyr.The West African monsoon also varies on timescales from millennia to decades. Millennial and century-scale variations appear to be partly paced by changes in solar irradiance, either directly or indirectly. On decadal timescales, variability appears to be dominated by changes in Atlantic sea surface temperatures. The dominant mode is a ca. 40 year oscillation, which in strongly coherent and in phase with the Atlantic Multidecadal Oscillation (AMO). It is unclear from this study, however, if drought conditions over the last century are related to this multidecadal oscillation, or if they are forced by anthropogenic changes.
Type:
text; Electronic Dissertation
Keywords:
West Africa; Monsoon; Lake; Varve; Paleoclimate
Degree Name:
PhD
Degree Level:
doctoral
Degree Program:
Geosciences; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Overpeck, Jonathan T.
Committee Chair:
Overpeck, Jonathan T.

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titleWest African Monsoon Variability from a High-Resolution Paleolimnological Record (Lake Bosumtwi, Ghana)en_US
dc.creatorShanahan, Timothy Michaelen_US
dc.contributor.authorShanahan, Timothy Michaelen_US
dc.date.issued2006en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractInstrumental and observational records of climate in West Africa suggest that this region may be susceptible to abrupt, decades-long drought events, with potentially catastrophic impacts for the people living in this region. However, because of the dearth of long, continuous and high quality climate records from sub-Saharan Africa, little is known about the long-term frequency and persistence of drought events in this region. It is also unclear whether observed 20th century droughts are natural or due to human impacts. In the present study, we use several complementary approaches to develop a high-resolution record of paleoclimatic changes in West Africa from the geological record preserved at Lake Bosumtwi, Ghana.Our results suggest that West Africa has undergone significant hydrologic variations over the last ca. 10,000 years. The dominant influence on hydrologic changes over this interval was changes in northern hemisphere summer insolation and the associated feedback processes acting in the oceans and on land. This led to a more northerly position of the Intertropical Convergence Zone (ITCZ) and increased precipitation during the early to mid-Holocene. In the late Holocene, a second increase in precipitation occurred along the Guinea coast as a result of the southward migration of the ITCZ from its northern position. This maximum was followed by an abrupt decrease in precipitation at ca. 2.5-3 kyr.The West African monsoon also varies on timescales from millennia to decades. Millennial and century-scale variations appear to be partly paced by changes in solar irradiance, either directly or indirectly. On decadal timescales, variability appears to be dominated by changes in Atlantic sea surface temperatures. The dominant mode is a ca. 40 year oscillation, which in strongly coherent and in phase with the Atlantic Multidecadal Oscillation (AMO). It is unclear from this study, however, if drought conditions over the last century are related to this multidecadal oscillation, or if they are forced by anthropogenic changes.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectWest Africaen_US
dc.subjectMonsoonen_US
dc.subjectLakeen_US
dc.subjectVarveen_US
dc.subjectPaleoclimateen_US
thesis.degree.namePhDen_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorOverpeck, Jonathan T.en_US
dc.contributor.chairOverpeck, Jonathan T.en_US
dc.contributor.committeememberOverpeck, Jonathan T.en_US
dc.contributor.committeememberCole, Juliaen_US
dc.contributor.committeememberBeck, J. Warrenen_US
dc.identifier.proquest1934en_US
dc.identifier.oclc659746501en_US
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