Water And Oceanography

Ocean Oxygen Depletion

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Ocean dead zones are getting bigger. Dead zones are regions of oxygen-deprived ocean where fish, clams, crabs, and other undersea creatures cannot survive. Ocean oxygen depletion, also known as hypoxia, is the result of a decrease in the soluble oxygen concentration of ocean water. According to new data, dead zones are increasing in both number and size. Findings from two recent scientific studies highlight the growing problem of ocean oxygen depletion. One study used computer models to evaluate the long-term effect of continued fossil fuel consumption on the vitality of ocean ecosystems, concluding that a substantial reduction in greenhouse emissions would provide the best chance for preventing sustained damage from oxygen depletion. Another study found that low-oxygen zones have expanded during the last 50 years, particularly in the tropical Atlantic Ocean. The results of these studies provide more evidence of the damage caused by fossil fuel emissions and water pollution from fertilizers and sewage. Oxygen depletion threatens the long-term survival of ocean life.

Over 400 ocean dead zones have been identified worldwide. A dead zone develops as the result of a decrease in the concentration of dissolved oxygen in ocean water. Rising temperatures cause surface warming, and water becomes less dense. Oxygenated water at the surface is prevented from circulating into deeper layers of ocean. Runoff into coastal waters is also a problem, because fertilizers and sewage add nutrients that ecourage the growth of oxygen-sucking organic matter. Without oxygen, fish, and other mobile undersea creatures flee the area. Species like plankton could thrive in such an environment, and the composition and framework of the underwater ecosystem could experience significant long-term transformation.

A group of researchers publishing in Nature Geoscience studied computer models to determine ocean climate changes over a period of 100,000 years. Data from the study are predictive of a grim future for ocean life, with serious oxygen depletion and expanded dead zones. Another research team publishing in Science created a 50-year timeline showing trends in tropical ocean oxygen concentrations. Results showed that dead zones have expanded, particularly in the tropical regions of the Atlantic, but also in the Pacific and northern Indian oceans over the last 50 years.

A declining fish population resulting from oxygen depletion will have a tremendous impact on the commercial fishing industry, as well as seafood, restaurant, and grocery businesses. Deep Atlantic tuna, for example, could be cut off from their own habitat, and other types of seafood would be affected as well.

The long-term consequences of global warming are still unknown. Recent research provides even more evidence that substantial reduction of fossil fuel emissions may be the only hope for avoiding the kind of damage that will take thousands of years to repair. Oxygen depletion will not only impact ocean life, but humanity as well. Dead zones are just a part of the problem with global warming and other types of pollution. Some dead zones can most likely be recovered, but time is running short. Dead zones are a cry for help from our oceans. Hopefully enough of us will hear, and soon, before it's too late.


Diaz, R., Rosenberg, R. Spreading Dead Zones and Consequences for Marine Ecosystems. Science

Shafer, G, Olsen, S., Pedersen, J. Long-term ocean oxygen depletion in response to carbon dioxide emissions from fossil fuels. Nature Geoscience

Stramma, L., Johnson, G., Sprintall, J., Mohrholz, V. Expanding Oxygen-Minimum Zones in the Tropical Oceans. Science

More about this author: Debbie Luyo

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