Abrupt onset and termination of the African Humid Period:
Identifieur interne : 000B67 ( Main/Exploration ); précédent : 000B66; suivant : 000B68Abrupt onset and termination of the African Humid Period:
Auteurs : Peter Demenocal [États-Unis] ; Joseph Ortiz [États-Unis] ; Tom Guilderson [États-Unis] ; Jess Adkins [États-Unis] ; Michael Sarnthein [Allemagne] ; Linda Baker [États-Unis] ; Martha Yarusinsky [États-Unis]Source :
- Quaternary Science Reviews [ 0277-3791 ] ; 1999.
Abstract
A detailed (ca. 100yr resolution) and well-dated (18 AMS 14C dates to 23 cal. ka BP) record of latest Pleistocene–Holocene variations in terrigenous (eolian) sediment deposition at ODP Site 658C off Cap Blanc, Mauritania documents very abrupt, large-scale changes in subtropical North African climate. The terrigenous record exhibits a well-defined period of low influx between 14.8 and 5.5 cal. ka BP associated with the African Humid Period, when the Sahara was nearly completely vegetated and supported numerous perennial lakes; an arid interval corresponding to the Younger Dryas Chronozone punctuates this humid period. The African Humid Period has been attributed to a strengthening of the African monsoon due to gradual orbital increases in summer season insolation. However, the onset and termination of this humid period were very abrupt, occurring within decades to centuries. Both transitions occurred when summer season insolation crossed a nearly identical threshold value, which was 4.2% greater than present. These abrupt climate responses to gradual insolation forcing require strongly non-linear feedback processes, and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non-linear climate sensitivity. The African monsoon climate system is thus a low-latitude corollary to the bi-stable behavior of high-latitude deep ocean thermohaline circulation, which is similarly capable of rapid and large-amplitude climate transitions.
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DOI: 10.1016/S0277-3791(99)00081-5
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deposition at ODP Site 658C off Cap Blanc, Mauritania documents very abrupt, large-scale changes in subtropical North African climate. The terrigenous record exhibits a well-defined period of low influx between 14.8 and 5.5 cal. ka BP associated with the African Humid Period, when the Sahara was nearly completely vegetated and supported numerous perennial lakes; an arid interval corresponding to the Younger Dryas Chronozone punctuates this humid period. The African Humid Period has been attributed to a strengthening of the African monsoon due to gradual orbital increases in summer season insolation. However, the onset and termination of this humid period were very abrupt, occurring within decades to centuries. Both transitions occurred when summer season insolation crossed a nearly identical threshold value, which was 4.2% greater than present. These abrupt climate responses to gradual insolation forcing require strongly non-linear feedback processes, and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non-linear climate sensitivity. The African monsoon climate system is thus a low-latitude corollary to the bi-stable behavior of high-latitude deep ocean thermohaline circulation, which is similarly capable of rapid and large-amplitude climate transitions.</div></front></TEI><affiliations><list><country><li>Allemagne</li><li>États-Unis</li></country><region><li>Schleswig-Holstein</li><li>État de New York</li></region><settlement><li>Kiel</li></settlement></list><tree><country name="États-Unis"><noRegion><name sortKey="Demenocal, Peter" sort="Demenocal, Peter" uniqKey="Demenocal P" first="Peter" last="Demenocal">Peter Demenocal</name></noRegion><name sortKey="Adkins, Jess" sort="Adkins, Jess" uniqKey="Adkins J" first="Jess" last="Adkins">Jess Adkins</name><name sortKey="Baker, Linda" sort="Baker, Linda" uniqKey="Baker L" first="Linda" last="Baker">Linda Baker</name><name sortKey="Demenocal, Peter" sort="Demenocal, Peter" uniqKey="Demenocal P" first="Peter" last="Demenocal">Peter Demenocal</name><name sortKey="Guilderson, Tom" sort="Guilderson, Tom" uniqKey="Guilderson T" first="Tom" last="Guilderson">Tom Guilderson</name><name sortKey="Ortiz, Joseph" sort="Ortiz, Joseph" uniqKey="Ortiz J" first="Joseph" last="Ortiz">Joseph Ortiz</name><name sortKey="Yarusinsky, Martha" sort="Yarusinsky, Martha" uniqKey="Yarusinsky M" first="Martha" last="Yarusinsky">Martha Yarusinsky</name></country><country name="Allemagne"><region name="Schleswig-Holstein"><name sortKey="Sarnthein, Michael" sort="Sarnthein, Michael" uniqKey="Sarnthein M" first="Michael" last="Sarnthein">Michael Sarnthein</name></region></country></tree></affiliations></record>Pour manipuler ce document sous Unix (Dilib)
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