African dust research

Gene Shinn eshinn at
Thu Oct 12 14:06:57 EDT 2000

 Hi coral-listers, I see that someone released the Washington post article
about our paper in Geophysical Research Letters to the coral-list group.
Since it was released in conjunction with comments about Dick Barber and
his work on Iron I thought you might want to hear the rest of the story.

    First I thank Dick Barber for getting me into this in the first
place (he is also a co-author on The GRL paper published by American
Geophysical Union). For more information the article, African dust and
the Demise of Caribbean coral reefs, is in Vol. 27, No. 19 p.
3029-3032, Oct 1, of Geophysical Research Letters. This research was
stimulated when Richard Barber gave a lecture here in St. Pete in 1996
on the Iron Ex experiments. In that experiment a 75 square kilometer
section of the deep Pacific was dosed with iron sulfate. The resulting
diatom bloom turned the clear blue water to pea soup, dramatically
proving that iron was the limiting nutrient. The experiment was
intended to evaluate a method for reducing atmospheric Co2 should it be
needed sometime in the future. A few years before Barbers visit I had
become aware that the Amazon rain forest receives its essential
nutrients from African dust, (About 1/2 lb. of phosphate per acre per
year). The dust also supports a robust bromeliad-based ecosystem high
in the tree canopy. More recent work has shown that the Hawaiian rain
forest receives its essential nutrients from Asian dust. Geologists had
known for many years that the iron-and clay-rich red soils upon which
agriculture depends in the Bahamas had settled as dust from Africa over
the past few thousand years. We also knew that Joe Prospero had been
monitoring African dust in Barbados since 1965 and had shown dramatic
increases in dust flux beginning with the onset of the ongoing drought
in North Africa that started in 1970

      The peak years for African dust flux in the Caribbean, as shown
by Prospero, were 1983 and 1987, and as Caribbean reef workers we all
know these were significant years for coral mortality, seafan disease,
and the demise of Diadema. It was Barber's talk on iron nutrification
that got my attention and after I showed him Joe Propero's dust flux
data from Barbados he convinced me stick my neck out and present the
hypothesis at the 1996 annual meeting of the Oceanographic Society
(significantly it was on April fools day!). We both realized that the
most consistent component of the dust was iron (about 6 percent). Well
that's how I got into it. Since then, however, we have learned a lot
more and today it appears that microbes and other components may be
equally important. As Hans Pearl recently pointed out, the composition
of the dust ( Fe, Al, P, Si, and sulfates) makes it like "Geritol for
bugs". Phil Dustan had suspected dust from the Florida Keys might
affect reefs in the 1970 and later Pam Muller-Halock and John Hallas
listed African dust as a possible source of nutrients in a National Geo
Publication. As we speak, Barber's student, Marshall Hayes, is
finishing his dissertation at Duke on the effects of iron/dust on

    As many of you know, Garriet Smith and others at U. of South
Carolina identified Aspergillus (soil fungus) as the cause of the
seafan disease and realized that a constant supply of spores was needed
to explain the on-going nature of the disease. Aspergillus does not
reproduce in sea water. We talked about the supply problem and
speculated that dust might be the main carrier. Since then Garriet was
then able to isolate A.sydowii from the dust. Later he and Juliana Weir
cultured it from dust samples and inoculated healthy seafans with the
culture. He also mentioned that there were many many other bugs in the
dust that they had to push them out of the way to do the isolations.
That led us to the second step.

    With NASA funding we were able to bring in a post-doc
microbiologist. Dale Griffin came on board June 1. Many of you in the
Florida Keys may remember that it was his dissertation work that found
coliforms and viruses in nearshore waters. The work led to the closing
of Beaches in Key West. Last week Dale submitted a paper to Science. He
worked on dust samples that had been filtered from the air in the
Virgin Islands by Ginger Garrison during dust storms. Garriet Smith did
his work on similar samples. We can't tell you more because Science has
a policy against pre publication publicity. I can say that if you ask
most any microbiologist you will get a knee-jerk response. "UV would
kill any bugs making the 5-day journey". I suppose that's why agencies
like the CDC, NIH, EPA and dept of Agriculture, have not paid
attention. Just goes to show how paradigms can control our thinking
(and research agencies). So stay tuned. Now here is the third step in
this work. 

     Thanks to Chuck Holmes, we now know that the dust is loaded with
Be-7 (half-life of only 43 days.) The dust also contains high levels of
Pb-210. Chuck will present his work at the up coming American
Geophysical Union meeting in December. Be-7 is produced naturally in
the atmosphere by solar and cosmic-ray bombardment of Oxygen and
Nitrogen atoms but the levels are usually quite low. It appears,
however, that it is adhering to the dust and somehow being concentrated
during transport. Because of its short half-life one has to collect and
analyze the samples quickly. We obtained samples from the Feb 26
African dust event (see Sept National Geographic or cover of Oct 1
Geophysical Research Letters) from a researcher at the University. of
the Azores. Before that we had collected dust from the bottom of water
cisterns in the Caribbean and wondering why Be-7 and mercury could be
so high) We had been finding levels as high at 500 dpm/g in cistern
samples. The usual levels one finds in marine sediments ranges from
4-10 dpm/g. The sample from the Azores (collected on a filter pad)
emitted gamma radiation up to 45,000 dpm/g! (roughly 3 times the
radiation allowed in the work place!) Not only that, the sample
contained 2-ppm mercury. Mercury usually occurs in the ppb (parts per
billion) range. Mercury is mined (open pits) in Algeria and may be the

     Finally, there is also DDT and other pesticides in the dust that
we no longer use in the US. They use pesticides in huge amounts at the
first sign of a Locust plagues in N. Africa. Because of the pesticides,
microbes, Be-7, mercury, and potential health effects on humans, NASA
is now funding much of our work. We also learned that about half the
kids in Puerto Rico and Trinidad have asthma. And, anyone in the Virgin
Islands with sinus problems will attest to their distress when the dust
blows in and visibility is reduced to a few miles. You have to live in
the Virgin Islands to really appreciate the red dust people clean from
boat sails, decks, window screens, etc. Airports have been closed
temporarily due to haze when the dust clouds arrive. One has to wonder
what 1-micron size particles emitting gamma radiation do when imbedded
in lung tissue? One might even wonder what it could do to coral tissue
once ingested. We know corals ingest the particles. Lisa Merman
defended her thesis at the University of South Florida on Oct 10. She
had isolated not only African dust from Monstastrea faveolata
skeletons, but was also able to isolate and distinguish volcanic dust
from the 1883 eruption of Krakatau in Indonesia. She did the work on
one of these 100+ year coral cores that Harold Hudson drilled in
Biscayne National Park, Florida in 1986. She presented some of the data
last year at AGU and will give another presentation this year. One
might even wonder, are zooxanthelle repelled by gamma radiation?
Someone should find out (the dust season in the Caribbean and Florida
is June-Oct).

    I think that now you can appreciate why we are so excited about the
potential for this new direction of coral research. There are so many
bacteria, fungi, chemicals, isotopes, and nutrients and so much work to
be done that we will be adding another microbiologist to the project. 

    The most difficult philosophical problem we have had to contend
with is the knowledge that this hypothesis, even if only half correct,
will undermine, or appear to undermine, a lot of ongoing research,
including research I have done in the past. Various agencies and
universities have spent millions on coral reef research over the past
15 years and as noted by Phil Dustan at the last Technical Advisory
Committee meeting in the Florida Keys, "we still can't prove
scientifically why the corals are dying." At the same meeting Ron Jones
pointed out that during 5 years of monitoring nutrients in the Florida
Keys Marine Sanctuary, phosphorus levels had continued to rise even "in
areas too remote to have come from septic tanks and disposal wells." 

     Most distressing are the powerful environmental politics at play.
I don't have to remind anyone that anthropogenic causes, proven or
unproven, can be used to stop development near coral reefs so while
this hypothesis may be loved by some it will be hated by others. Here
is an example of how the information has already has been used in the
political arena. Boats US, a boaters rights advocacy group in
Washington DC, used the hypothesis in a recent publication. They said
that Sanctuary restrictions on boat access are based on the assumption
that boats and people are the main problem while, "the real problem may
be African dust!" Another example, When Ginger Garrison unveiled the
National Parks plans to expand Virgin Islands National park about 2
weeks ago at a public hearing, someone in the audience questioned the
need for more protection since "the real problem was African dust"!
Amazing how environmental science can become politicized. I must say,
however, that work on human health is rewarding because it is
appreciated by more people. It does not seem to upset anyone, yet! You
can bet that the various Tourism boards and chambers of commerce on
Caribbean Islands will be concerned about the potential effects of this
research on tourism to the sunny Caribbean. 

     I must say it was not easy for me to stick my neck out. I had been
sitting on much of this information for about 4 years before Dick
Barber came along and "pushed me over the edge." I thank him for giving
me the courage. A young researcher without tenure probably would not do
it. It is unfortunate but that's the way it is. I did it because of the
millions that were been spent on coral research and because although we
knew microbes were causing coral disease the sources were unknown or at
least unproven. Meanwhile, many of us continue to monitor and map coral
reefs while the corals continue to die. It just seemed that a lot of
coral reef research could be on the wrong track. As Dennis Hubbard
likes to say, "When you are on the wrong train every stop is the wrong

     So the bottom-line might be that maybe we need to do something
about global warming and at the same time do something to help people
in the overgrazed and farmed Sahel region of North Africa. They have a
real food problem. What's going on there appears similar to what
happened here in the US during the "Dust Bowl Years." In the 1930 the
government encouraged farmers to go west and plow the land and grow
grain. They did and then it stopped raining between 1931 and 1939.
Significantly, we didn't get legislation to help farmers switch to
no-till farming until a dust cloud actually reached Washington, DC.

     One final thought. We have only focused on African Dust but if you
look at the TOMS satellite data,
<<>, or
the animated display of 6 months data at
<<>you will see that Pacific reefs also get
dusted on a regular basis. The source is Asia. I don't know that much
about reef conditions in the Pacific other than what I have read about
bleaching and the Crown of Thorns problem. I do know that Korean
farmers are told to bring their livestock inside the barn when the
yellow dust is blowing out of Asia because it brings hoof and mouth
disease. It may carry microbes etc that also impact corals. This is
something to think about as we travel to the 9th international Coral
Reef Symposium.

     I look forward to seeing you all in Bali and hope we have a good
time. Gene

"If we knew what we were doing it wouldn't be called Science would it?"
Albert Einstein

E. A. Shinn

email  eshinn at
USGS Center for Coastal Geology     | 
600 4th St. South                   | voice  (727) 803-8747 x3030
St.Petersburg, FL  33701            | fax    (727) 803-2032

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