[Coral-List] Thoughts on coral decline and the future.

[Eugene Shinn]

Thanks Thomas. Your question comes up often.  Within the first 100 ft 
there are several unconformities in the Pleistocene limestone of the 
Florida Keys. Each one records changes in sea level and exposure of old 
coral reefs and or oolitic limestone. Each zone of exposure is capped by 
red brown caliche (peleo-soil) containing silica and clay minerals that 
crossed the Atlantic Ocean. In those cases the corals had already died 
from exposure to air when sea level went down. Cores in the Pleistocene 
on the Bahama bank reveal many more minor unconformities capped by 
caliche (often associated with blackened angular limestone pebbles----a 
product of paleo fires).
There may have been coral deaths associated with dust in the past but it 
would be difficult to prove either way. For certain the reefs died when 
sea level drops exposed them. However, what we are experiencing now is 
unique. There were no man-made pesticides and fertilizers during the 
Pleistocene. As I have noted before DDT is still legal and used in 
Africa to fight mosquitoes and locusts. Many other kinds of pesticides 
are also used there and they end up in the dust. There was also little 
agriculture in the past and certainly no 4-wheel-drive autos racing 
around stirring up dust along with herds of goats.
And the big one---History shows the Sahara was greener 10,000 tears ago, 
Earlier during the Pleistocene glacial and inter glacial periods, the 
area was likely intermittently dry and arid and moist and wet. Such 
changes in climate are well documented in deep-sea cores and reflected 
in stable isotope data.

Nevertheless, the platform on which the Florida Holocene reefs have 
grown has been flooded for a little more than 6,000 years. There are 
stretches of platform edge areas (that’s where the reefs normally would 
be growing) where no reefs have accumulated. These areas will be more 
thoroughly discussed in our book, “The Geology of the Florida Keys” by 
Shinn and Lidz which will be in print later this year. Pleas excuse the 
shameless advertisement. Gene

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No Rocks, No Water, No Ecosystem (EAS)
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E. A. Shinn, Courtesy Professor
University of South Florida
College of Marine Science Room 221A
140 Seventh Avenue South
St. Petersburg, FL 33701
<eugeneshinn at mail.usf.edu>
Tel 727 553-1158
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