This is great new photo from the European Space Agency of the dust flux from western Africa across the Atlantic - a significant proportion of which end up deposited over the Amazon basin (see this article:

This dust flux is very important in fertilising the Amazon rainforests which naturally lose nutrients due via the Amazon River, particularly as a consequence of the annual flood. This loss of nutrients cannot be matched by mineral input from the eroding Andes, and so without the dust flux from Africa the nutrient status of Amazon soils would be progressively reduced (with significant consequences for productivity).