'Dead zones' found in Atlantic open waters

A team of German and Canadian researchers have discovered areas with extremely low levels of oxygen, called dead zones, in the tropical North Atlantic, off the coast of West Africa.

The levels measured in these 'dead zones', inhabitable for most marine animals, are the lowest ever recorded in Atlantic open waters.

Dead zones are areas of the ocean depleted of oxygen and most marine animals, like fish cannot live there, where only certain microorganisms can survive.

"The few eddies we observed in greater detail may be thought of as rotating cylinders of 100 to 150 km in diameter and a height of several hundred metres, with the dead zone taking up the upper 100 metres or so," said lead-author Johannes Karstensen from Helmholtz Centre for Ocean Research Kiel, Germany.

To study the dead zones, the team used several tools, including drifting floats that often got trapped within the eddies and to measure plant growth, they used satellite observations of ocean surface colour.

Apart from environmental impact, dead zones are an economic concern for commercial fishing also.

With very low oxygen concentrations, the areas are linked to reduced fish yields.

The dead zones are created in eddies, large swirling masses of water that slowly move westward.

Encountering an island, they could potentially lead to mass fish kills.

The study appeared in the journal Biogeosciences.