A team of researchers has identified two areas of the Pacific Ocean where oxygen levels are nearly zero. How is it possible? What are the consequences?
Oceans are environments rich in life, with the exception of some areas where there is a significant scarcity of oxygen, which for this reason become unlivable for most organisms that need this element.
These areas are called "Oxygen-Deficient Zones" (ODZ, oxygen-deficient zones), globally occupy an area of no more than one per cent of all oceans, and are also characterized by the fact that these are areas where a certain amount of nitrous oxide, a powerful greenhouse gas, is formed and enters the atmosphere.
Scientists at MIT have now created a highly detailed three-dimensional atlas describing the two large areas affected by the phenomenon, which are located in the tropical Pacific Ocean.
WHY? First of all, why do these areas exist and why does nitrous oxide form? To find an answer, it is worth bearing in mind that, near the surface of the seas, there is a real rain of organic matter precipitating from the atmosphere. The aerobic bacteria that live in the waters near the surface feed on this matter: oxygen is used as part of the bacterial metabolic process and this causes a decrease in the water.
It should also be emphasized that most of the oceanic areas are characterized by marine currents that continuously stir the waters, bringing oxygen back to where it is lacking. However, there are some areas characterized by a kind of water stagnation, where currents are lacking, and this prevents a quick mixing: the result is a drop in the oxygen level to very low values, sometimes even close to zero. To this is added another factor.
“Oceans have been shown to lose oxygen as the climate warms. In fact, warmer waters release the gases present in them more easily, "says Jarek Kwiecinski, who worked on the atlas together with Andrew Babbin, Cecil and Ida Green Career, from the Department of Earth, Atmosphere and Planetary Sciences of MIT. And the areas with little oxygen are the realm of anaerobic organisms which, with their metabolism, produce nitrous oxide which then spreads into the atmosphere. That's why these areas play such an important role in producing that very greenhouse gas.
The mapping of these areas required over 15 million measurements, made by scientific ships over many years of work. There are two areas with the least amount of oxygen: the first extends from the coast of South America to the ocean and involves approximately 600,000 cubic km of water - roughly the volume that would allow to fill 240 billion Olympic-sized swimming pools - while the other is located off the coast of Central America and is even three times larger.