The concentration of oxygen in the lower layers of the waters of the Gulf of Oman has declined sharply in recent years, which created a giant “dead spot” at its bottom, where life is absent in principle, oceanologists say in an article published in the journal Geophysical Research Letters.
“The Arabian Sea has long been considered one of the largest” dead zones “in the world’s oceans, but so far no one has been able to verify it because of pirates and constant conflicts in the region.We have found that the situation is worse than everyone feared – huge size and continues to grow rapidly, “said Bastien Queste of the University of East Anglia in Norwich, UK.
Areas of oceans with a low oxygen content, the so-called “death zones”, are formed as a result of pollution of water with fertilizers and industrial wastes. The ingress of nitrates and other compounds into the rivers and then to the coastal regions of the sea leads to a rapid multiplication of unicellular algae in the ocean, the death and decomposition of which in the water column absorbs most of the oxygen. Most animals do not survive in such conditions.
In recent years, ecologists and oceanologists have found more and more hints that global warming and some bacteria accelerate the growth of such “dead spots” in the waters of the world’s oceans, especially in the tropical and equatorial zones. Today, a similar fate befell about 7% of the total area of the oceans and seas of the Earth.
Keste and his colleagues at the university found that one of the biggest and most dangerous for living beings “death zones” is at the bottom of the Gulf of Oman, which is washing the shores of Iran, Pakistan and the countries of the Arabian Peninsula.
As the scientists say, because of constant wars and the threat of a clash with pirates, they knew practically nothing about the condition of the bottom of the Arabian Sea, whose composition includes the Gulf of Oman. This problem was solved by oceanologists using a fleet of autonomous deep-water robots that independently measured the oxygen concentration in the Gulf waters and transmitted data via communication satellites.
When the authors of the article combined their measurements in a single map of the bottom of the Gulf of Oman, they found that a huge part of it, comparable in size to the average country in Europe, was completely devoid of oxygen, and in the rest of its corners it was almost nonexistent.
Such changes, as the scientists note, should have an extremely negative impact on the lives of many commercial fish species, whose forage base has declined sharply due to the almost total disappearance of oxygen at depths exceeding 170-200 meters. In addition, the “death zones” migrated at the onset of spring and autumn, which made the fish move with them or lead to their mass death.
An even more serious problem was that the disappearance of oxygen from the waters of the Gulf of Oman turned it into one of the largest sources of nitrous oxide and other strong greenhouse gases that occur during the anoxic decomposition of the remains of living creatures falling to the bottom of the sea.
All this, according to oceanologists, will only contribute to the further growth of the “death zone” and may lead to the complete extinction of most species of fish and other multicellular creatures in the Arabian Sea by the end of the century.