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Model, Proxy and Isotopic Perspectives on the East African Humid PeriodBoth North and East Africa experienced more humid conditions during the early and mid-Holocene epoch (11,000-5000yr BP; 11-5 ka) relative to today. The North African Humid Period has been a major focus of paleoclimatic study, and represents a response of the hydrological cycle to the increase in boreal summer insolation and associated ocean, atmosphere and land surface feedbacks. Meanwhile, the mechanisms that caused the coeval East African Humid Period are poorly understood. Here, we use results from isotopeenabled coupled climate modeling experiments to investigate the cause of the East African Humid Period. The modeling results are interpreted alongside proxy records of both water balance and the isotopic composition of rainfall. Our simulations show that the orbitally-induced increase in dry season precipitation and the subsequent reduction in precipitation seasonality can explain the East African Humid Period, and this scenario agrees well with regional lake level and pollen paleoclimate data. Changes in zonal moisture flux from both the Atlantic and Indian Ocean account for the simulated increase in precipitation from June through November. Isotopic paleoclimate data and simulated changes in moisture source demonstrate that the western East African Rift Valley in particular experienced more humid conditions due to the influx of Atlantic moisture and enhanced convergence along the Congo Air Boundary. Our study demonstrates that zonal changes in moisture advection are an important determinant of climate variability in the East African region.
Document ID
Document Type
Reprint (Version printed in journal)
Tierney, Jessica E.
(Lamont-Doherty Geological Observatory Palisades, NY, United States)
Lewis, Sophie C.
(Australian National Univ. Canberra, Australia)
Cook, Benjamin I.
(Lamont-Doherty Geological Observatory Palisades, NY, United States)
LeGrande, Allegra N.
(Columbia Univ. New York, NY, United States)
Schmidt, Gavin A.
(Columbia Univ. New York, NY, United States)
Date Acquired
August 25, 2013
Publication Date
May 23, 2011
Publication Information
Publication: Earth and Planetary Science Letters
Volume: 307
Issue: 2-Jan
Subject Category
Meteorology And Climatology
Report/Patent Number
Lamont Contribution No. 7467
Funding Number(s)
Distribution Limits

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