In the past 50 years, the amount of water in the open ocean with zero oxygen has gone up more than fourfold. In coastal water bodies, including estuaries and seas, low-oxygen sites have increased more than 10-fold since 1950. Scientists expect oxygen to continue dropping even outside these zones as Earth warms. To halt the decline, the world needs to rein in both climate change and nutrient pollution. Approximately half of the oxygen on Earth comes from the ocean. However, combined effects of nutrient loading and climate change are greatly increasing the number and size of ‘dead zones’ in the open ocean and coastal waters, where oxygen is too low to support most marine life.
In areas traditionally called “dead zones,” like those in Chesapeake Bay and the Gulf of Mexico, oxygen plummets to levels so low many animals suffocate and die. As fish avoid these zones, their habitats shrink and they become more vulnerable to predators or fishing. But the problem goes far beyond “dead zones,” the authors point out. Even smaller oxygen declines can stunt growth in animals, hinder reproduction and lead to disease or even death. It also can trigger the
— source University of California – San Diego | Jan 4, 2018