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The ``African humid period'' and the record of marine upwelling from excess 230
 

Summary: The ``African humid period'' and the record of marine upwelling
from excess 230
Th in Ocean Drilling Program Hole 658C
Jess Adkins,1
Peter deMenocal,2
and Gidon Eshel3
Received 26 August 2005; revised 4 February 2006; accepted 13 June 2006; published 20 October 2006.
[1] Using a high-resolution 230
Th normalized record of sediment flux, we document the deglacial and Holocene
history of North African aridity and coastal upwelling at Ocean Drilling Program Hole 658C. At both the end of
the Younger Dryas and after the 8.2 ka event, there are significant drops in terrigenous accumulation at our site,
indicating an increase in the monsoon moisture flux over Africa at this time. At 5.5 ka, there is an abrupt end to
the ``African humid period'' and a return to stronger upwelling conditions. For carbonate and opal fluxes the
230
Th normalization completely changes the shape of each record based on percentage variations alone. This site
is a clear example of how variations in one sediment component can obscure changes in the others, and it
demonstrates the need for radionuclide measurements more generally in paleoceanography. By taking our new
records and a large amount of previous data from this site we conclude that increases in African moisture are
tightly coupled to decreases in coastal upwelling intensity.
Citation: Adkins, J., P. deMenocal, and G. Eshel (2006), The ``African humid period'' and the record of marine upwelling from

  

Source: Adkins, Jess F. - Division of Geological and Planetary Sciences, California Institute of Technology
deMenocal, Peter B. - Lamont-Doherty Earth Observatory & Department of Earth and Environmental Sciences, Columbia University

 

Collections: Environmental Sciences and Ecology; Geosciences