An international team of scientists, sponsored in part by NOAA’s National Centers for Coastal Ocean Science, has published the broadest view yet of declining oxygen in the world’s oceans. The article in the journal Science is the first to take a global perspective on the causes, consequences, and solutions for low oxygen in the oceans.
Declining oxygen in the world’s oceans is a growing problem, with a four-fold increase in areas with zero dissolved oxygen and a ten-fold increase in areas with low-oxygen since 1950. Often called “dead zones,” such as those that occur each summer in the Chesapeake Bay and Gulf of Mexico, these areas of little or no dissolved oxygen are harmful to marine life. Fish often avoid these zones, which can cause widespread loss of habitat, harm reproduction and growth, and overall biodiversity decline.
“Oxygen is fundamental to life in the oceans,” said Denise Breitburg, lead author with the Smithsonian Environmental Research Center. “The decline in ocean oxygen ranks among the most serious effects of human activities on the Earth’s environment.”
In the open ocean, rising ocean temperatures is often the key cause. Warming surface waters make it harder for oxygen to reach the ocean interior. Furthermore, as the ocean as a whole gets warmer, it holds less oxygen. In coastal waters, excess nutrient pollution from land creates algal blooms, which drain oxygen as they die and decompose.
To combat the problem, the authors suggest addressing three factors. First, address the dual causes of nutrient pollution and climate change. In the United States, groups such as the Gulf of Mexico/Mississippi Watershed Nutrient Task Force have been leading efforts to reduce nutrient pollution. The team of scientists also recommends protecting marine life, such as through protected areas, and enhancing efforts to monitor dissolved oxygen globally.
“This is a problem we can solve,” Breitburg said. “Halting climate change requires a global effort, but even local actions can help with nutrient-driven oxygen decline.” As proof Breitburg points to the ongoing recovery of Chesapeake Bay, where nitrogen pollution has dropped 24 percent since its peak thanks to better sewage treatment and improved farming practices. While some low-oxygen zones persist, the area of the Chesapeake with zero oxygen has almost disappeared.
The study was conducted through the GO2NE (Global Ocean Oxygen Network), a new working group created in 2016 by the United Nation’s Intergovernmental Oceanographic Commission. NOAA NCCOS support was provided through the Coastal Hypoxia Research Program.