Joseph Prospero, PhD (Miami FL). U. of Miami Professor Emeritus of Marine and Atmospheric Chemistry, "Sediments and trace substances in the polar regions."
Dr. Prospero's studies of sediment began with deep sea sediment in the 1960's. Scientists were wondering where deep sea sediments came from since there is no erosion underwater. The theory had been that they were carried in runoff from the continents. It is now believed that they are composed of dust carried from land into the prevailing large weather systems and deposited into the ocean.
His studies later turned to atmospheric dust deposits on land. Most interesting is the huge amount of African dust deposited in the West Indies. Dust deposits show great variability and reflect patterns of drought at the point of origin.
Dust is studied by filtering the air and analyzing the filtrate. Typically, in the West Indies, you get sea salt, iron and dust from numerous sources, including skin flora and cloth (although transoceanic dust differs from house dust and is mostly minerals). Iron deposited into the ocean is important to marine life but too much dust deposits can make the ocean unhealthy.
Airborne African dust is caused by poor farming practices that makes the soil unstable. When it reaches the Caribbean, it can cause health issues.
The human impact on airborne soil particles in well known. The dust storms in the US in the 1930's were caused by extended draught and by agricultural practices that did not anchor the soil to the ground and allowed it to be picked up by the wind.
These types of poor agricultural practices are expanding in Africa, China and India, which strongly affects downwind countries such as South Korea and Japan.
When Sharon asked about dams, Dr. Prospero acknowledged their many benefits to humans but also noted that they tend to disrupt an area's natural ecosystem. He also noted, with regard to the Louisiana oil spill, that oil in the water equals oil in the air and is not healthy.