Home Nature The oceans run out of oxygen

The oceans run out of oxygen

The levels in the lowest depths of the known Gulf of San Lorenzo (Canada) have decreased by 55% since 1930. What can happen?

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The oceans run out of oxygen
vast ocean

The ocean is running out of oxygen at high speed, and its exhaustion could lead to the death of most of the marine life that supports these waters. Now, a comprehensive review by international scientists and published in the journal Science, has documented the causes, consequences and possible solutions of what is technically known as “deoxygenation”.

The researchers discovered a 4- to 10-fold increase in oceanic areas with little or no oxygen; something alarming, since half of the Earth’s oxygen originates in the ocean.

Our data shows that in the last half century, the area of ​​the open ocean in which oxygen is lacking, has grown more than four times,” explains Andreas Oschlies of GEOMAR Helmholtz Center for Ocean Research Kiel, co-author of the work.

Oxygen is crucial for marine life in the oceans without oxygen, marine life will die or relocate, because it needs oxygen to breathe.

The team of scientists belongs to the working group of the Intergovernmental Oceanographic Commission of the United Nations, created in 2016 and called the Global Ocean Oxygen Network. They noted that the amount of water in the open ocean without oxygen has quadrupled in 50 years. It is worse for coastal waters, such as estuaries and seas. In these areas, areas with little oxygen have multiplied tenfold since 1950. This document is the first to analyze both ocean and coastal waters, which are often studied separately. 

The lack of oxygen in the oceans also directly affects the devastation of the human means of subsistence.

“There are many livelihoods that depend on a healthy ocean that does not smell and has a lot of dead things, when oxygen goes too low in the ocean, the animals leave if they can, those species will move or die of hunger,” says Lisa Levin. , co-author of the study.

The causes

This change is related to warmer ocean temperatures, because hot water contains less oxygen. In addition, the increase in  surface temperature makes it more difficult for oxygen to reach relatively deep areas of the ocean. The greatest loss of oxygen occurs between 90 and 670 meters deep (for reference, some parts of the ocean are 11 kilometers deep). Oxygen is usually replenished when the surface water mixes with the deeper water, but with the ocean warmer, there is less vertical mixing.

A second cause has to do with algae in coastal areas. This problem has nothing to do with the warmer waters caused by climate change induced by man, but excess nutrients from agriculture and wastewater cause an excessive growth of algae. The process of decomposition of algae consumes oxygen, having a new source of oceanic deoxygenation.

Areas with little or no oxygen reduce habitats for marine life, but scientists claim that even small reductions in oxygen can cause problems. Lack of sufficient oxygen can impede growth in animals, damage reproduction and cause disease or death. It can also cause the emission of a greenhouse gas called nitrous oxide into the air (up to 300 times more powerful than carbon dioxide).

“The decrease in ocean oxygen is among the most serious effects of human activities on  the Earth’s environment,” explains Denise Breitburg, leader of the study. “Stopping climate change requires a global effort, but even local actions can help with the decline of oxygen driven by nutrients.”

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