A new study published on April 16, 2021, in the scientific journal Nature Communications says that even if all CO2 emissions stopped right away, the amount of oxygen in the oceans would still go down for hundreds of years.
The author, Prof. Dr. Andreas Oschlies from the GEOMAR Helmholtz Centre for Ocean Research in Kiel, says that this is caused by the slowing of ocean circulation and the gradual warming of deeper water layers.
Almost all ocean animals need oxygen, which is a gas that dissolves in seawater and is needed for life. But for a long time, the ocean has been losing oxygen all the time. In the last 50 years, about 2% of the total amount of oxygen has been lost around the world.
The primary cause for this is global warming, which makes it harder for gases, like oxygen, to dissolve in water. It also slows down the ocean’s circulation and mixing of water from top to bottom. Even if all CO2 emissions and warming at the surface of the Earth stop right now, a new study published in the scientific journal Nature Communications shows that this process will keep going for hundreds of years (Oschlies 2021).
“In the study, a model of the Earth’s system was used to figure out what would happen to the ocean over time if all CO2 emissions stopped right away,” says Professor Andreas Oschlies from the GEOMAR Helmholtz Centre for Ocean Research in Kiel, who led the research. “The results show that even in this worst-case scenario, oxygen loss will continue for hundreds of years, which is more than four times as much as we’ve seen in the ocean so far,” Oschlies says.
Most of the long-term loss of oxygen happens in the deeper layers. Prof. Oschlies says that this also affects ecosystems in the ocean. A “metabolic index,” which measures the most oxygen-breathing organisms can do, shows a drop of up to 25% in many places, especially in the deep sea (below 2000 meters).
The oceanographer says that this is likely to cause big changes in this habitat, which was once thought to be very stable. Our past CO2 emissions have already caused these changes, which are now on their way to the deep ocean. He thinks that the habitat of the deep ocean, which has only been studied in small pieces so far, should be studied in depth before this environment, which is thought to have been stable for thousands of years, changes a lot because of the expected decrease in oxygen.
The model shows that climate change has a much faster effect on the upper parts of the ocean. There, if the emissions stopped, the oxygen minimum zones close to the surface would stop growing within a few years. So, an ambitious climate policy can help stop the gradual loss of oxygen from putting even more stress on ecosystems close to the surface.