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Half-precessional dynamics of monsoon rainfall near the East African equator: Implications for Indian Ocean ITCZ migration over the past 25,000 years

Dirk Verschuren UGent, JSS Damste, Jasper Moernaut UGent, I Kristen, M Blaauw, Maureen Fagot UGent and GH Haug (2009) GEOCHIMICA ET COSMOCHIMICA ACTA. 73(13). p.A1380-A1380
abstract
We present a detailed reconstruction of hydrological changes near the equator in East Africa from before the LGM to the present, using proxies extracted from the sediment record of Lake Challa on the lower east slope of Mt. Kilimanjaro (3° S, 36° E). Our results show that monsoon rainfall in this region varied at half-precessional (~11,500-year) intervals, because the southeasterly and northeasterly Indian Ocean monsoons, which together create the bimodal seasonal distribution of equatorial rainfall, were strengthened in alternation when the inter-hemispheric insolation gradient was maximized. Dry conditions prevailed when neither monsoon was particularly strong, and minima in local March or September insolation weakened the rain season that followed. The distinct timing of late-glacial drought on the equator (20.5-16.5 ka BP) does not fit well with NH glaciation being its primary driver. It is best attributed to partial failure of the short rain season due to modest local September insolation, perhaps exacerbated by the southeasterly monsoon being weakened by northern cooling still affecting the North African land mass. Our data further highlight that orbital-scale ITCZ ‘migration’, or shifts in its mean annual latitudinal position, mainly relates to variation in how far the ITCZ is displaced into the NH or SH during summer and winter; the cross-equatorial position of the East African region with twice-annual ITCZ passage is not much affected. On (sub)millennial time scales the temporal pattern of hydrological change on the East African equator bears clear signatures of northern high-latitude climate variability, but on the orbital time scale it mainly responded to low-latitude insolation forcing. Important keys to this history are the low-latitude position of its continental regions of convergence and its relative isolation from the Atlantic Ocean domain, where strong meridional overturning circulation more tightly coupled tropical climate regimes to high-latitude climate dynamics.
Please use this url to cite or link to this publication:
author
organization
year
type
conference
publication status
published
subject
in
GEOCHIMICA ET COSMOCHIMICA ACTA
Geochim. Cosmochim. Acta
volume
73
issue
13
pages
1 pages
publisher
PERGAMON-ELSEVIER SCIENCE LTD
place of publication
OXFORD
Web of Science type
Meeting Abstract
Web of Science id
000267229903448
JCR category
GEOCHEMISTRY & GEOPHYSICS
JCR impact factor
4.385 (2009)
JCR rank
2/74 (2009)
JCR quartile
1 (2009)
ISSN
0016-7037
language
English
UGent publication?
yes
classification
C3
id
1008642
handle
http://hdl.handle.net/1854/LU-1008642
date created
2010-07-12 00:06:55
date last changed
2010-07-14 09:31:32
@inproceedings{1008642,
  abstract     = {We present a detailed reconstruction of hydrological changes near the equator in East Africa from before the LGM to the present, using proxies extracted from the sediment record of Lake Challa on the lower east slope of Mt. Kilimanjaro (3{\textdegree} S, 36{\textdegree} E). Our results show that monsoon rainfall in this region varied at half-precessional ({\texttildelow}11,500-year) intervals, because the southeasterly and northeasterly Indian Ocean monsoons, which together create the bimodal seasonal distribution of equatorial rainfall, were strengthened in alternation when the inter-hemispheric insolation gradient was maximized. Dry conditions prevailed when neither monsoon was particularly strong, and minima in local March or September insolation weakened the rain season that followed. The distinct timing of late-glacial drought on the equator (20.5-16.5 ka BP) does not fit well with NH glaciation being its primary driver. It is best attributed to partial failure of the short rain season due to modest local September insolation, perhaps exacerbated by the southeasterly monsoon being weakened by northern cooling still affecting the North African land mass. Our data further highlight that orbital-scale ITCZ {\textquoteleft}migration{\textquoteright}, or shifts in its mean annual latitudinal position, mainly relates to variation in how far the ITCZ is displaced into the NH or SH during summer and winter; the cross-equatorial position of the East African region with twice-annual ITCZ passage is not much affected. On (sub)millennial time scales the temporal pattern of hydrological change on the East African equator bears clear signatures of northern high-latitude climate variability, but on the orbital time scale it mainly responded to low-latitude insolation forcing. Important keys to this history are the low-latitude position of its continental regions of convergence and its relative isolation from the Atlantic Ocean domain, where strong meridional overturning circulation more tightly coupled tropical climate regimes to high-latitude climate dynamics.},
  author       = {Verschuren, Dirk and Damste, JSS and Moernaut, Jasper and Kristen, I and Blaauw, M and Fagot, Maureen and Haug, GH},
  booktitle    = {GEOCHIMICA ET COSMOCHIMICA ACTA},
  issn         = {0016-7037},
  language     = {eng},
  number       = {13},
  pages        = {A1380--A1380},
  publisher    = {PERGAMON-ELSEVIER SCIENCE LTD},
  title        = {Half-precessional dynamics of monsoon rainfall near the East African equator: Implications for Indian Ocean ITCZ migration over the past 25,000 years},
  volume       = {73},
  year         = {2009},
}

Chicago
Verschuren, Dirk, JSS Damste, Jasper Moernaut, I Kristen, M Blaauw, Maureen Fagot, and GH Haug. 2009. “Half-precessional Dynamics of Monsoon Rainfall Near the East African Equator: Implications for Indian Ocean ITCZ Migration over the Past 25,000 Years.” In Geochimica Et Cosmochimica Acta, 73:A1380–A1380. OXFORD: PERGAMON-ELSEVIER SCIENCE LTD.
APA
Verschuren, D., Damste, J., Moernaut, J., Kristen, I., Blaauw, M., Fagot, M., & Haug, G. (2009). Half-precessional dynamics of monsoon rainfall near the East African equator: Implications for Indian Ocean ITCZ migration over the past 25,000 years. GEOCHIMICA ET COSMOCHIMICA ACTA (Vol. 73, pp. A1380–A1380). OXFORD: PERGAMON-ELSEVIER SCIENCE LTD.
Vancouver
1.
Verschuren D, Damste J, Moernaut J, Kristen I, Blaauw M, Fagot M, et al. Half-precessional dynamics of monsoon rainfall near the East African equator: Implications for Indian Ocean ITCZ migration over the past 25,000 years. GEOCHIMICA ET COSMOCHIMICA ACTA. OXFORD: PERGAMON-ELSEVIER SCIENCE LTD; 2009. p. A1380–A1380.
MLA
Verschuren, Dirk, JSS Damste, Jasper Moernaut, et al. “Half-precessional Dynamics of Monsoon Rainfall Near the East African Equator: Implications for Indian Ocean ITCZ Migration over the Past 25,000 Years.” Geochimica Et Cosmochimica Acta. Vol. 73. OXFORD: PERGAMON-ELSEVIER SCIENCE LTD, 2009. A1380–A1380. Print.