Aerosols ----desert dust ----an ocean fertilizer The members for this presentation are: Sarah, Helen, Amy, Sasa, Peizhen, Rachelle

Introduction 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. Lake Chad, Africa. mg_id=4714

Pathway of dust 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. 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 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. 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 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. 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 ( ?img_id=4714) ?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.

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… 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. =4332

conclusionconclusion

The end The photographs for this presentation have been extracted from the science NASA web site ( which houses a number of up-to-date satellite images. Thank you very much for listening.