Abrupt onset and termination of the African Humid Period:

Abrupt onset and termination of the African Humid Period: A detailed (ca. 100 yr resolution) and well-dated (18 AMS 14 C 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. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Quaternary Science Reviews Elsevier

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Publisher
Elsevier
Copyright
Copyright © 1999 Elsevier Science Ltd
ISSN
0277-3791
eISSN
1873-457X
D.O.I.
10.1016/S0277-3791(99)00081-5
Publisher site
See Article on Publisher Site

Abstract

A detailed (ca. 100 yr resolution) and well-dated (18 AMS 14 C 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.

Journal

Quaternary Science ReviewsElsevier

Published: Jan 1, 2000

References

  • Late Pleistocene variability of Arabian Sea summer monsoon winds and continental aridity
    Clemens, S.C.; Prell, W.L.
  • The sensitivity of the terrestrial biosphere to climatic change
    Foley, J.A.
  • West African rainfall deficits and sea-surface temperatures
    Fontaine, B.; Bigot, S.
  • Saharan wind regimes traced by the Sr-Nd isotopic composition of subtropical Atlantic sediments
    Grousset, F.E.; Parra, M.; Bory, A.; Martinez, P.; Bertrand, P.; Shimmield, G.; Ellam, R.M.
  • A fully coupled GCM simulation of the climate of the mid-Holocene
    Hewitt, C.D.; Mitchell, J.F.B.H.
  • Energetics of the 6000-yr BP atmospheric circulation in Boreal summer, from large-scale to monsoon areas
    Masson, V.; Joussaume, S.
  • Current directions in West African prehistory
    McIntosh, S.K.; McIntosh, R.J.
  • Surface water response of the equatorial Atlantic Ocean to orbital forcing
    McIntyre, A.; Ruddiman, W.F.; Karlin, K.; Mix, A.C.

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