[Coral-List] Thoughts on coral decline and the future.
Eugene Shinn
eugeneshinn at mail.usf.edu
Mon May 15 11:43:38 EDT 2017
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
--
--
No Rocks, No Water, No Ecosystem (EAS)
------------------------------------ -----------------------------------
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
---------------------------------- -----------------------------------
More information about the Coral-List
mailing list