“Oxygen minimum zones” (OMZs) are areas of low-oxygen water that stretch for thousands of miles through the world’s oceans. They have deleterious effects on ecosystems because the low oxygen levels they contain impact many species' reproduction and feeding strategies. OMZs are also a significant source of nitrous oxide, a major greenhouse gas. Until recently, climate models have been unable to say whether OMZs will grow or shrink from climate change, in part because OMZs result from two opposing processes: oxygen supplied by ocean circulation and oxygen used by sea life.
Now, a team led by Princeton’s Laure Resplandy has confidently predicted that the boundaries of the Pacific OMZ, the planet’s largest, will expand by as much as 2 million additional cubic miles (8 million cubic kilometers) — both upward toward the sea surface and outward toward the coast — by the end of the century.
The key insight of the research, Resplandy said, was understanding that the OMZ isn’t uniform but has layers “like an onion” that respond differently to rising greenhouse gases. OMZs are made up of an outer layer and an inner core, and the new models show that the core will shrink while the outer layer will expand.
The research shows that if high greenhouse gas emissions continue, the tropical Pacific OMZ will grow 6 to 8 million cubic kilometers — about 1.4 to 2 billion cubic miles, or about 0.6% of the volume of the world’s oceans — by 2100. Over much of its area, it will likely expand toward the surface by 5 to 50 meters (16 to 160 feet).