The Global Ocean Oxygen Network noted that in the oceans, low-oxygen areas have increased in open ocean and in coastal water such as estuaries and seas since 1950.
In 50 years, the amount of water without oxygen has quadrupled in open ocean and it is eight times worse in estuaries!
Alarming? Well, the pace is alarming!
http://www.newsweek.com/oxygen-disappearing-worlds-oceans-alarmingly-rapid-pace-771406
