Brings to mind a report I read last year of trash collecting in ocean current eddies. Perhaps that's what these debris spots are turning out to be.
That was probably about "Garbage Island" which is located in the Pacific. There have been a lot of articles on that recently as well as a few documentaries. If a plane went down there they would have a lot of trouble figuring out what is from the accident and what is just garbage floating out there.
Just a quick search shows that there are a few similar "oceanic gyres" in the Atlantic, though as yet there do not seem to be reports of garbage islands forming there -
Oceanic Gyres - of course that does not mean they are not there.