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Marine Biology: More and more dead zones in the sea

Marine Biology: More and more dead zones in the sea

The number of these areas increased from more than 400 to about 700 between 2008 and 2019, according to the second United Nations’ World Ocean Assessment on the state of the seas, which was presented in New York on Wednesday. In addition to the Gulf of Mexico and the South China Sea, the Baltic and North Seas are particularly affected.

This phenomenon occurs naturally in some marine areas. One reason is algal blooms. After they die, the algae slowly sink and are decomposed by bacteria that consume oxygen. In this way, huge areas can form at the depths, sometimes where there is hardly any oxygen in the water. The entry of nutrients like nitrogen and phosphorous into the oceans aids algal blooms.