Oceanic Dead Zones Infographic

oceanic dead zones infographic


The Death of An Ocean
Less oxygen dissolved in the water is often referred to as a “dead zone.” A dead zones occur when marine life dies and fish settle elsewhere. In other words, dead-zone habitats that would normally be teeming with life transform into biological deserts.

Wikipedia defines dead zones as hypoxic (low-oxygen) areas in the world’s oceans and large lakes, caused by excessive nutrient pollution from human activities coupled with other factors that deplete the oxygen required to support most marine life in bottom and near-bottom water.

The Earth currently has more than 500 oceanic dead zones, with the count doubling every decade. A single dead zone may cover tens of thousands of square miles. Hypoxic zones can occur naturally, but scientists are concerned about the areas affected by human activity.

Damaging, Dead Zone Facts
What are the causes of oceanic conditions? The most likely culprits are eutrophication, agricultural run-offs/interferences and sewage, vehicular and industrial emissions. According to the NY Times, “the global proliferation of dead zones, once mainly a problem of the developed world, had been fueled by industrialization, changing eating habits and population growth, which has led to more fertilizer use and more waste in the world’s watersheds.”

There are an estimated 530 aquatic dead zones (including 166 in US waters) which result in 95,000 total square miles. Dead zones lead to the loss of about 1.3 million metric tons of fish food each year in the Baltic Sea. Dead zones are estimated to prevent the production of 75,000 metric tons of fish food. The largest recorded dead zone measured 8,481 square miles in 2002. The most famous U.S. dead zone is a 6,765 square mile swath off the Gulf of Mexico that has tripled in nitrogen levels over the past 50 years due to human activities ( which increases the size of the dead zone).

Types of Dead Zones
Scientists classify water bodies in four categories: permanent, temporary, seasonal and diel cycling.

1). Permanent Hypoxia: occurs in deep waters, when oxygen rarely rises about 2 milligrams per liter
2.) Temporary Hypoxia: exists for hours and/or days
3.) Seasonal Hypoxia: occurs every year, but only during warm seasons
4.) Diel Cycling Hypoxia: occurs in warm nights, but only at nighttime

According to Dr. Robert J. Diaz of the Virginia Institute of Marine Science, “we have to realize that hypoxia is not a local problem[…] it is a global problem and it has severe consequences for ecosystems.”

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