Less and less oxygen in the oceans: biodiversity is at risk

"As the oceans lose oxygen, warming up, the delicate balance of marine life weakens," he says Grethel Aguilar, interim general director of the organization. "To limit the loss of oxygen in the oceans, as well as other dramatic climate change affects, world leaders must commit to reducing their emissions immediately and substantially," he urged, while the COP25 is underway in Madrid. Chile, which chairs the conference in Madrid, has promised to focus on the situation in the oceans.
Deoxygenation is mainly explained by two phenomena: eutrophication (proliferation of some vegetables, usually algae) "due to the outflow of nutrients from the continents and nitrogen deposits from the use of fossil fuels, and water heating due to of global warming ", whereby the oceans partly absorb the greenhouse gas emissions generated by humans. On a global scale, the oxygen level in the oceans has fallen by around 2% from 1960 to 2010, according to the report. It could fall by another 3-4 points by 2100, if emissions continue to grow at the current rate, "most of the loss is concentrated in the first thousand meters of the water column, where wealth and the abbonandaza of species are more high, "the report warns. There are about 700 points on the globe, often near the coasts and in semi-enclosed seas, which suffer from a low quantity of oxygen, while in 1960 they were 45. In the same period, the volume of anoxic waters (ie without oxygen) has quadrupled.All this has already begun "to modify the balance of marine life, favoring hypoxia-tolerant species such as microbes, jellyfish and some squid to the detriment of species sensitive to hypoxia like various marine species, mostly fish", notes the IUCN. Species such as tuna, marlin and sharks are "particularly sensitive to low amounts of oxygen, due to their large size and high energy needs," the report states. They therefore risk having to move to more oxygenated surface waters, where they would be even more exposed to the risks of overfishing. There will be consequences, although it is more difficult to measure them even on species such as those that live on the seabed, corals, macroalgae, mangroves, fish, plankton, marine mammals.

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