Dead Zones are areas where the water at the sea floor is anoxic, meaning that it has very low (or zero) concentrations of dissolved oxygen. These dead zones are occurring in many areas along the coasts of major continents. They are spreading over larger areas of the sea floor. Because very few organisms can tolerate the lack of oxygen, dead zones can destroy the habitat in which numerous organisms make their home.
BNI researchers report that the dead zones in the Baltic Sea have increased 10-fold over the last 115 years, growing from approximately 5,000 km² in 1900 to more than 60,000 km² in recent years.
Dead zones can be caused naturally but more often they are the result of humans polluting the waterways. They have long been the concern of scientists and environmental activists because of the loss of aquatic life. They are difficult to rehabilitate. As oxygen levels in the water decrease production of nitrous oxide increases.
Nitrous oxide is 300 times more potent as a greenhouse gas than carbon dioxide.
“The dead zone has been a frustrating thing to work on,” Matt Rota, senior policy director for the Gulf Restoration Network, told The Daily Beast. “It’s such a big problem and there are so many ways for people to point fingers.”
Many of the areas where increasing bottom water anoxia has recently been observed are near the mouths of major river systems. While Satellite images can’t see the bottom of the ocean, they can see the surface, where sediments from rivers mix with ocean waters.