Ocean Dead Zones

The ocean has been place of mystery and adventure since ancient times, but in our present age it has become a giant dump for our industrial emissions and garbage, as well as a huge carbon sink. The ocean might seem endless and eternal, but our activities and excesses have an effect on the ocean’s equilibrium and health. One of the ways these effects can manifest is through ocean dead zones.

A ocean dead zone is an area in a body of water with low oxygen levels insufficient to support marine life. Ocean dead zones are caused by a spike in algae growth known as the phenomenon algal bloom. As massive quantities of these algae die, bacteria in the water feed on them, using up available oxygen in the water. Oxygen levels become so low that marine animals exhibit behavioral mechanisms such as swimming away from the area and standing upright to reach higher levels. Animals which are slow moving or are unable to escape the area, die. Ocean dead zones decrease the habitats of fish and other marine life. As they are forced to seek more oxygen rich areas, they crowd with other local species. They are also more prone to predators and fishing. In addition to the marine life casualties, the water turns dirty brown and inhabitable.

Ocean dead zones can and have been formed by natural causes, as seen in the chemical record on earstones or otoliths of some fishes. But human activities and industrial waste aggravate the situation. Excessive fertilizer from intensive farming, sewage, and phosphorus and nitrogen containing pollutants are great fare for algae. According to a NOAA study, climate change is also a key factor in the expansion of dead zones in recent years. A rising global temperature means warmer oceans, translating into a decreased capacity to hold oxygen. Certain ocean dead zones have been increasing in size over the years. One example is the famous Gulf of Mexico, which has a recurring marine dead zone several thousand square miles wide. On 2006, an ocean dead zone appeared measured at 6,662 square miles. In 2007, it was measured at 7,900 miles. These pale in comparison with the 8,495 square mile marine dead zone that appeared in 2002. Whether the reports in 2006 and 2007 were good news is hard to say.

In other areas, marine dead zones are also recurrent events. In the US, marine dead zones have been recorded in the outfall of the Mississippi river, Elizabethriverof Virginia beach, Lake Erie, and Pacific Northwest coastal regions. Similar marine dead zones have been recurring in different parts of the world – China, New Zealand, Japan, and South America. In the UN’s GEO (Global Environment Outlook Year Book) 2003 report, 146 dead zones were recorded. In 2008, it more than doubled at 405.

There is hope, however, as marine dead zones can be reversible. The former largest marine dead zone in the world, the Black Sea, was reversed in the years between 1991 and 2001. Fertilizer in those times became too expensive after the collapse of the Soviet Union. This shows that a decrease in industrial emissions can erase or at least minimize marine dead zones around the world. With the demand for biofuels increasing pressure on farmlands however, as well as the continuing practice of dumping human waste and garbage in the ocean, we might be seeing more ocean dead zones in future years.

Photo Credit: Some rights reserved by  Alan Vernon via Flickr.

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Estel (303 Posts)

Estel Grace Masangkay is a freelance creative writer who enjoys outdoor trips and activities in natural settings. She is passionate about animal welfare and environment conservation. Follow Me @Em23me.

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