Aren't these "dead zones" just like the ones in the Gulf of Mexico that have long been attributed to agriculture runoff from rivers? My (admittedly minimal) understanding is that the nitrates and phosphates that settle to the bottom and spur high concentrations of algae that consume oxygen faster than it can be replenished from the surface, subsequently killing most life in the zone.

There are areas of major pollution in areas such as the Gulf. Whether these are spreading because of global warming or additional pollutants, they are a problem of magnitude, especially to the millions dependent on seafood for protein.