FunNature & AnimalThe oceans run out of oxygen

The oceans run out of oxygen

The ocean is running out of oxygen at high speed, and its depletion could lead to the death of most of the marine life that supports these waters. Now, an extensive 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 found a 4 to 10-fold increase in oceanic areas with little or no oxygen; something alarming, since half of the oxygen on Earth originates from the ocean.

Our data show 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 the 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, needing oxygen to breathe.

The team of scientists belongs to the working group of the United Nations Intergovernmental Oceanographic Commission, created in 2016 and called the Global Ocean Oxygen Network. They observed 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, oxygen-poor areas have increased tenfold since 1950. This paper is the first to analyze both oceanic and coastal waters, which are often studied separately.

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

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

The causes

This change is related to warmer ocean temperatures, as warm water contains less oxygen. Also, rising surface temperatures make 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 surface water mixes with deeper water, but as the ocean is warmer, there is less vertical mixing.

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

Areas with little or no oxygen reduce habitats for marine life, but scientists say that even small reductions in oxygen can cause problems. Lack of sufficient oxygen can stunt growth in animals, damage reproduction, and lead to illness 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 oxygen from the ocean 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 nutrient-driven oxygen depletion.”

Reference: Declining oxygen in the global ocean and coastal waters. Science 2018: Vol. 359, Issue 6371, eaam7240. DOI: 10.1126 / science.aam7240

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