Transcript Aerosols ----desert dust ---

Aerosols
----desert dust
----an ocean fertilizer
The members for this presentation are:
Sarah, Helen, Amy, Sasa, Peizhen,
Rachelle
Introduction
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desertification increased the natural process of
desert dust by…
Lake Chad, once one of the African continent's
largest bodies of fresh water, has dramatically
decreased in size due to climate change and
human demand for water.
1/20th of the size it was 35 years ago.
source of water for massive irrigation projects. In
addition, the region has suffered from an
increasingly dry climate, experiencing a significant
decline in rainfall since the early 1960s.
• Lake Chad, Africa.
http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?i
mg_id=4714
Pathway of dust
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Storm activity in the Sahara Desert region kicks up fine particles from
the arid topsoil there, generating vast clouds of dust. Easterly trade
winds carry the dust across the Atlantic Ocean and into the Gulf of
Mexico.
Our planet's atmosphere provides a transcontinental highway for dust
that's been stirred up from dry soils by strong winds. Because dust
particles are so small -- often less than 0.002 mm across -- they can
remain aloft for days as they ride global rivers of air. Larger sand
grains don't get airborne as often or for as long, but they can be
pushed along the ground by the wind or washed away by water
erosion.
African dust plumes begin their trans-Atlantic journey with storm
activity in the Sahara Desert region. The dust, originating from fine
particles in the arid topsoil, is transported into the atmosphere by
winds and may be carried more than 10,000 feet high. Dust clouds
cross the Atlantic Ocean and reach the Caribbean and the Americas in
about 5 to 7 days.
Dust being picked up over the
Sahara desert, Africa
(http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3
?img_id=4714)
Bacteria on dust…
During the transportation of dust from North African to the
Atlantic some of the microbes die because of exposure to ultraviolet
(UV) rays
Some microbes embedded in the cracks and crevasses of dust
particles can be shielded from the harmful UV rays.
It is thought that the upper altitudes of the dust clouds deflect
harmful UV rays therefore enabling the shielding and survival of
microbes at lower altitudes.
The moderate temperatures and high humidity found over water
enhance the microbial survival at lower altitudes.
There is a mixture of harmless and harmful microbes that survive
the trans-Atlantic journey.
Research into their impact on arrival in this new environment is
on-going today.
Dust cloud transporting bacteria.
Dust cloud moving over the Atlantic ocean from Africa.
http://antwrp.gsfc.nasa.gov/apod/ap000303.html
pro’s…
• The Saharan dust reached the West Florida shelf around July 1st,
increasing iron concentrations in the surface waters by 300 percent.
As a result, Trichodesmium counts shot up to 10 times what they
had been prior to this event. Through a complex process involving a
special enzyme called nitrogenase, the Trichodesmium used the iron
to convert nitrogen in the water to a form more usable for other
marine life.
• Iron is an essential nutrient for all organisms, used in a variety of
enzyme systems, including those for photosynthesis, respiration,
and nitrogen fixation. However, iron is very insoluble under oxidizing
conditions above pH 4. For marine phytoplankton, separated from
the iron-rich sediment of the ocean floor by considerable water
depths, physiological iron requirements must be met from within the
water column. Iron supply is a limiting factor on phytoplankton
growth over vast areas of the modern ocean, although this may not
have been so in the distant past, when prokaryotes first evolved in a
less oxic ocean.
• In a vicious cycle, particles landing in the seas encourage plankton
growth, which absorb carbon dioxide – a major greenhouse gas –
and so cool the ocean surface. This leads to fewer clouds and less
rain – the perfect conditions for creating more dust storms.
con’s…
 The new study shows that these clouds fertilize the water off the West
Florida coast with iron. Plant-like bacteria use that iron to set the stage for
red tides. When iron levels go up, these bacteria, called Trichodesmium, fix
nitrogen in the water, converting it to a form usable by other marine life. The
addition of biologically usable nitrogen in the water makes the Gulf of Mexico
a friendlier environment for toxic algae.
 In October, after a 300 percent increase of this biologically-accessible
nitrogen, a huge bloom of toxic red algae (Karenia brevis) had formed within
the study area, an 8,100 square mile region between Tampa Bay and Fort
Myers, Florida.
 Humans who swim in the Gulf during a red tide can experience respiratory
problems by breathing toxins from K. brevis that get in the air. Also, eating
shellfish poisoned by red tides can lead to paralysis and memory problems.
 Red tides (algae) bloomed late this summer along a 300-mile stretch of
Texas' Gulf Coast, killing millions of fish and shellfish as well as making
some people sick. State officials are calling this the worst red tide bloom in
14 years. The algae produces a poison that paralyzes fish and prevents
them from breathing. There is concern that the deadly algae could impact or
even wipe out this year's oyster harvest in Texas, which usually peaks during
the Thanksgiving and Christmas holidays.
Red tides
The dark reddish discoloration indicates the red tide.
http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id
=4332
conclusion
The end
The photographs for this presentation have been
extracted from the science NASA web site
(www.science.nasa.gov) which houses a number
of up-to-date satellite images.
Thank you very much for listening.