Dead zones have been found in deep waters of the Atlantic Ocean, where these formations, devoid of oxygen, are rarely observed.
Life either flees these regions or dies, leaving behind a nearly barren aquatic environment. These formations are usually found near the coast, where chemical pollutants and fertilizers from farms, homes and businesses reach the water.
The newly discovered lifeless regions were found several hundred miles from the coast of West Africa and north of the island chain of Cape Verde. This could cause serious problems if the dead zone were to strike the collection of volcanic islands.
Oxygen levels in these newly discovered zones are the lowest ever recorded in the open waters of the Atlantic Ocean. The formations are marked by the presence of large whirlpools, which slowly move westward. Oxygen levels in these eddies can be just 20 percent that in average deep sea waters. When these dead zones encounter an island, it can lead to mass deaths in the local marine environment.
"The fast rotation of the eddies makes it very difficult to exchange oxygen across the boundary between the rotating current and the surrounding ocean. Moreover, the circulation creates a very shallow layer — of a few tens of meters — on top of the swirling water that supports intense plant growth," Johannes Karstensen of the Helmholtz Centre for Ocean Research Kiel in Germany said.
Fertilizers entering coastal waters can lead to the proliferation of algae, known as an algal bloom. As these microorganisms die, they sink to the bottom of the ocean, where they are consumed by bacteria. These tiny beings use up the oxygen in the region, producing the dead zone. These regions can be pulled out to sea, but this discovery marks the first time one of these low-oxygen areas has been recorded in deep ocean waters.
Intense plant growth in the newly discovered dead zones acts in the place of algae in smaller coastal systems, investigators believe.
The dead zones can cause economic, as well as environmental, damage. Commercial fisheries saw significant losses from these events in the Baltic Sea as well as other regions. The Cape Verde archipelago is close enough to some of the newly discovered eddies that the regions could soon pass through waters surrounding the island.
"This could cause the coast to be flooded with low-oxygen water, which may put severe stress on the coastal ecosystems and may even provoke fish kills and the die-off of other marine life," Karstensen said.
Discovery and analysis of the dead zones in the deep waters of the Atlantic Ocean was detailed in the journal Biogeosciences.
Photo: Ben Brophy | Flickr
