Delta #130 Feb 19 / 2015

#1
I was watching the Maritimes of Canada last night, when I noticed Delta Flight #130 (Boeing 767-400) suddenly slow down, descend, then turn 180 degrees over Cape Breton Island. This flight originated in Mexico City, stopped in Atlanta, then was heading to Munich.

I thought perhaps it had an emergency, and was going to land in Halifax Nova Scotia, but it went back up to speed and returned to Hartsfield-Jackson International in Atlanta.

What would cause a flight crew to do this? I don't see anything in the news.