Climate change is starving the oceans of oxygen, what is the risk?

The ocean's oxygen levels have reached a dangerously low state, as confirmed by a recent study published in the prestigious journal Nature. The study establishes a compelling comparison between the present condition of our seas and that of over 14 million years ago.

One of the results showed that the oxygen level in the world's oceans has actually decreased by about 2% since 1960. Why? Much of it is responsible for global warming since the water that is heated contains less oxygen

Nancy Rabalais, a professor and chair of oceanography and wetland studies at Louisiana State University, explained to PopScience that alterations in marine ecosystems and biodiversity can be induced by this phenomenon. She emphasized the significance of oxygen concentrations in influencing the rates of organic matter decomposition, which consequently impacts the productivity of both coastal and oceanic ecosystems.

Impact on Marine life and oxygen concentration predictions

Marine animals and microbes would also be affected, as this phenomenon could affect their abundance, as well as reduce the quality and quantity of suitable habitats for them to live and reproduce.

But the study published by Nature has not been the only one that warns what will happen. Other research from Global Biochemical Cycles, in 2018, talks about how oxygen in some regions of the ocean can concentrate and leave the rest with reduced numbers between the years 2150 and 2300.

“I don't think we should wait to see if deoxygenation reverses as the climate continues to warm,” says Anya Hess, a doctoral candidate at Rutgers University who studies ocean oxygenation.

The scientist also points out that not only ecosystems would be affected, but also the ocean food industries for humans. This would result in a decrease in fishing and, ultimately, in a direct problem for the populations that depend on this activity.

That is why, in the words of Hess, one of the solutions to implement would be to reduce greenhouse gas emissions. Also, according to the scientist, the public policies of the most affected countries could focus on measuring the oxygen in their seas to help identify patterns and predict biological responses.

Coastal eutrophication and hypoxic environments

Nancy Rabalais, a distinguished professor and chair of oceanography and wetland studies at Louisiana State University, dedicates herself to advancing research on coastal eutrophication and hypoxic environments. As highlighted by Rabalais, the harmful consequences of deoxygenation are far-reaching, impacting essential biogeochemical processes and precious living resources.

Consequently, deoxygenation can give rise to enhanced phosphorus recycling, diminished nitrogen losses, and heightened availability of iron initially. Each of these occurrences holds the potential to greatly influence the productivity and sustainability of coastal and ocean ecosystems.

The decrease in oxygen content significantly affects marine microbes and animals. Deoxygenation alters their abundance, diversity, and suitable habitats and interferes with reproduction. Even minor decreases in oxygen levels can have drastic impacts, particularly in oxygen minimum zones that are already close to physiological thresholds.

The stress caused by the loss of oxygen forces marine organisms to adapt, if possible, in order to survive. As the oxygen-deficient zones expand, they are pushing species highly sensitive to changes in oxygenation, such as tuna and sharks, into shallower habitats. Deoxygenation also poses a threat to the ocean's ability to provide food for humans, which could lead to reduced fish catches and collapse of regional populations.

Recent research indicates that deoxygenation may eventually reverse, but experts do not expect the reversal of this phenomenon to occur until the distant future.

Understanding oceans during warm periods

A study published in Nature explored the Miocene warm period, roughly 16 to 14 million years ago, to gain insight into how oceans behave during long warm periods.

However, current climate models predict that oxygen concentrations may start to rise and oxygen-starved regions of the ocean could shrink between 2150 and 2300. Scientists attribute this projection to a decrease in tropical export production, an increase in oceanic ventilation, and the transport of surface waters into the ocean interior.

Marine ecosystems are already experiencing various impacts today, and recovery is challenging due to reconfiguration of food webs caused by deoxygenation and torpor or death of organisms unable to tolerate low oxygen levels.

Anya Hess, a doctoral candidate at Rutgers University specializing in ocean oxygenation, emphasizes the urgency of addressing deoxygenation.

Hess says, "We should not wait around to see whether deoxygenation will reverse as the climate continues to warm. We know that rising temperatures are causing ocean deoxygenation, so if we want to stop it, we know what we need to do—reduce greenhouse gas emissions."

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