Climate change

Climate change will deprive the oceans of precious oxygen

The emergence of deoxygenation is expected to be widespread in large areas of the oceans before 2080.

Photo: Pixabay/joker

When it comes to climate change, there is bad news and there is even worse news. Into this last category falls a new study in which scientists predict that more than two-thirds of the world’s oceans will be deprived of enough oxygen by 2080 due to warming temperatures.

This lack of oxygen will decimate fish stocks worldwide, likely leading to food shortages in many parts of the world. The trend is already being felt as increased oxygen loss driven by global warming passed a critical threshold last year.

According to scenarios devised by Chinese scientists in research who are the first to use climate models to predict how deoxygenation (the reduction in dissolved oxygen content in ocean water around the world outside its natural variability), “more than 72% of the global ocean is expected to experience an emergence of deoxygenation before 2080 for the three vertical zones”, explain the researchers.

“At the regional level, the emergence of deoxygenation is expected to be widespread under the epipelagic zone of the western North Pacific, North Atlantic and Southern Oceans before 2080,” they add.

As water temperature rises, seawater retains less dissolved oxygen, which reduces circulation between ocean layers. For their study, the researchers plotted the expected rates of deoxygenation in three areas of ocean depth (shallow, middle and deep) by examining when the loss of dissolved oxygen in the water will exceed natural fluctuations as the climate warms. will heat up in the decades to come.

“The middle layer of the ocean is particularly vulnerable to deoxygenation because it is not enriched in oxygen by the atmosphere and photosynthesis like the upper layer, and the greater decomposition of algae – a process that consumes energy. oxygen – occurs in this layer,” the scientists said. Remark.

This is why these so-called mesopelagic zones, which range from depths of around 200 meters to 1,000 meters, will be the first to lose significant amounts of oxygen in their two climate models with different carbon emission rates in the decades to come.

The finding is troubling because “this area is actually very important to us because a lot of commercial fish live there,” says Yuntao Zhou, an oceanographer at Shanghai Jiao Tong University and lead author of the study. “Deoxygenation also affects other marine resources, but fishing [are] perhaps the most related to our daily life.

In another finding, researchers found that parts of the oceans closer to the poles such as the western and northern Pacific as well as the southern seas are particularly vulnerable to deoxygenation, although the reason for this will need to be investigated further.

Meanwhile, tropical minimum oxygen zones, which are areas where dissolved oxygen levels are already low, appear to be spreading. “Zones of oxygen minimum actually spread into high latitude areas, both north and south,” Zhou said.

“Even if global warming were to reverse, allowing dissolved oxygen concentrations to rise, it is unclear whether dissolved oxygen would return to pre-industrial levels,” the scientists say.

Importantly, the new findings highlight the urgent need for effective climate change mitigation policies.

“Humanity is changing the metabolic state of the largest ecosystem on the planet, with truly unknown consequences for marine ecosystems,” said Matthew Long, an oceanographer at the National Center for Atmospheric Research who was not involved in the survey. the research. “This can manifest itself in significant impacts on the ability of the ocean to support important fisheries.”