This is really cool but I find it very hard to believe that this has the effect they are supposing here. We're talking about an area that's ~50% of Europe, so I believe microclimates can help much more than the dust from the other side of the world. It would be like saying the Europe only exists the way it is because of the gulfstream, be it in Ireland or Romania.

Also keep in mind that rhe Amazon rainforest is much more dense on the area around the Equator line, which happens on all over the world at this latitude, so there's nothing unique about Amazon here.

Another intriguing thing about this is that if this dust is so fertile then it's hard to believe that it would not impact in a positive way the african coast line around the Sahara.