[Coral-List] interesting BBC report

[Douglas Fenner]

The BBC article says "These are animals that lived in Megalake Chad, a
massive body of water that covered north-central Africa thousands of years
ago."  So you say it dried up in the late 1970's and early 80's when
Diadema and Acroporid corals "began to die."  Of course, the Diadema died
in 1983-1984, and white band disease killed the Acropora over a period of
more than those two years, African dust has been blowing to the Caribbean
for millenia, perhaps hundreds of millenia?  I took a look at the Wikipedia
page on Lake Chad and on the Bodele Depression where it is.  Seems that
Lake Chad has decreased in size, the Lake Chad article says "it shrank as
much as 95% from about 1963 to 1998, but "the 2007 (satellite) image shows
significant improvement over previous years."[4]
<http://en.wikipedia.org/wiki/Lake_Chad#cite_note-FOOTNOTEUnited_Nations2007-4>"
  It seems that "Lake Chad", the modern lake, and "Megalake Chad" are two
different things.  Megalake Chad was much larger, was in the Holocene, and
is now entirely dry.  It provides much of the area where the dust now
originates, and likely has the fish skeletons which the BBC article refers
to.  Note that that article was only talking about Megalake Chad.  The
present Lake Chad, is surrounded by wetlands, occupying much of the area of
the modern lake which has contracted by 95% since 1963.  The Wikipedia
article on Lake Chad has a map that shows both the present lake and the
much larger Holocene mega-lake which surrounds the present lake.  It also
has a 2001 satellite photo that shows that the area which the lake occupied
in 1963 but no longer occupies, is covered with green vegetation.  The
article refers to that area as wetlands.  So it appears that the 95% of the
modern lake that is no longer lake is mostly wetlands and covered with
vegetation.  Therefore it appears to be highly unlikely to be a source of
the dust.  The Bodele Depression article in Wikipedia says "The dry bowl
that forms the depression is marked by a series of ephemeral lakes
<http://en.wikipedia.org/wiki/Ephemeral_lake>, many of which were last
filled during wetter periods of the Holocene
<http://en.wikipedia.org/wiki/Holocene>.  Diatoms
<http://en.wikipedia.org/wiki/Diatom> from these fresh water lakes, once
part of Mega-Lake Chad, now make up the surface of the depression and are
the source material for the dust,[1]
<http://en.wikipedia.org/wiki/Bod%C3%A9l%C3%A9_Depression#cite_note-eo5-1>
which,
carried across the Atlantic Ocean, is an important source of nutrient
minerals for the Amazon rainforest
<http://en.wikipedia.org/wiki/Amazon_rainforest>."  So the much larger dry
lakebed of the Holocene Megalake Chad is surely the primary if not only,
source of that dust.  And most of it dried out thousands of years ago.
     Does that make a coincidence with the Diadema and Acropora dieoffs in
the Caribbean?

Cheers,  Doug

On Fri, Sep 26, 2014 at 6:12 AM, Eugene Shinn <eugeneshinn at mail.usf.edu>
wrote:

> Those of you who were around remember that algae became a problem (and
> continue to be so) on Caribbean coral reefs and Florida around the same
> time Diadema and Acroporid corals began to die (late 1970s-early 1980s.
> That was also when 100 mile-wide Lake Chad in north Africa was rapidly
> drying up. What you see in this BBC report is most interesting...Just a
> coincidence? Gene
>
> http://www.bbc.co.uk/news/science-environment-29361002
>
>
> --
>
>
> 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
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-- 
Douglas Fenner
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PO Box 7390
Pago Pago, American Samoa 96799  USA

phone 1 684 622-7084

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