Gulf of Mexico Dead Zone


By Michael J. Lynch, University of South Florida, FL


The Gulf of Mexico dead zone is an example of the consequences of nutrient rich land run-off into ocean waters and is an example of the kinds of pollution addressed by the Global Programme of Action for the Protection of the Marine Environment from Land-based Activities.

The National Oceanic and Atmospheric Administration of the United State Department of Commerce recently competed a study mapping the Gulf of Mexico dead zone (NOAA Study). The study notes that the dead zone is approximately 5,025 square miles (13017.28 square kilometers), an area the size of the state of Connecticut, which is less than 1 percent of the total area in the Gulf of Mexico. Nevertheless, despite its limited size, this dead zone has importance. NOAA set a goal of limiting the Gulf dead zone to 1,900 square miles, or less than 40% of its current size.

The dead zone is the result of nutrient rich waters that reach the Gulf of Mexico primarily from the Mississippi River. Those nutrients produce hypoxia in waterways, that is oxygen deficiency in part of the Gulf’s waters. In this sense, hypoxia is caused by eutrophication, or the response of waterways to excessive nutrient loads from fertilizers, sewage, phosphates, and detergents.

NOAA notes in its report that the Gulf of Mexico dead zone is one of about 550 known dead zones globally. A map of the Gulf of Mexico dead zone may be viewed here. A map of the world’s most serious global dead zones can be viewed here.

Dead zones, especially in smaller waterways, can cause fish kills as oxygen is depleted from waterways. Low oxygen levels associated with dead zone can also produce a decline in fish reproduction, affect the development of fish reproductive organs, lead to a decline in spawning and a reduced egg count (Diaz and Roseenberg, 2008; Rabalais, Turner and Wiseman, 2002).

Dead zones are reversible, and efforts to reduce land-based pollution of waterways are important in reducing the scope of marine dead zones.

Further Reading


Diaz, Robert J., and Rutger Rosenberg. (2008). “Spreading dead zones and consequences for marine ecosystems.” Science 321, 5891: 926-929.

Rabalais, Nancy N., R. Eugene Turner, and William J. Wiseman Jr. (2002). “Gulf of Mexico hypoxia, AKA” The dead zone”.” Annual Review of Ecology and Systematics 33: 235-263.

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