The number of open ocean ‘dead zones’ — in which oxygen levels are too low to support marine life — has quadrupled in the past 50 years. The only way to stop this phenomenon is to curb climate change and nutrient pollution, according to a new paper published last week in the journal Science.
The study came from a team of researchers at the Global Ocean Oxygen Network (GO2NE), a working group created in 2016 by the United Nations’ Intergovernmental Oceanographic Commission. Their results also showed that low-oxygen sites have increased more than 10-fold in coastal water bodies, including seas and estuaries, since 1950.
In these so-called dead zones, oxygen concentrations fall so significantly that marine animals suffocate. As fish come to avoid these locations, their habitats shrink and they become increasingly vulnerable to predation and fishing. Even small oxygen reductions can result in stunted growth and disease in wildlife.
Climate change is the key contributing factor to oxygen loss in the open ocean, with warmer surface waters making it difficult for oxygen to reach the ocean interior. As the ocean heats up, it is also less capable of holding oxygen.
In coastal waters, nutrient pollution acts as a fertilizer and promotes the excessive growth of algal blooms. The algae then drain oxygen from the surrounding area as they die and decompose.
The GO2NE scientists suggest that the issue of low oxygen can be solved using a three-pronged approach. As low oxygen becomes inevitable, vulnerable marine life must be protected and oxygen monitoring enhanced worldwide. Most importantly, pollution and fossil fuel emissions must be addressed.
“This is a problem we can solve,” says Denise Breitburg, the study’s lead author and marine ecologist with the Smithsonian Environmental Research Center. “Halting climate change requires a global effort, but even local actions can help with nutrient-driven oxygen decline.”
As proof, Breitburg highlights the recovery of the Chesapeake Bay on the East Coast of the United States, where better sewage treatment, improved farming practices, and successful environmental legislation have led to a 24% reduction in nitrogen pollution.