Climate change is going to wreak havoc on the world’s oceans, according to two new studies, depleting the warming waters of the oxygen that fish and other sea life depend on to survive.
Around 70% of the oceans of the planet will be affected by a lack oxygen from warmer temperatures by 2080. A study published in November by researchers with the American Geophysical Union’s journal Geophysical Research Letters concluded. The study found that significant deoxygenation of middle ocean depths, where large amounts of fish are found, began in 2021.
“This zone is actually very important to us because a lot of commercial fish live in this zone,” Yuntao Zhou, an oceanographer at Shanghai Jiao Tong University and lead author of the study, said in A statement.
The study’s models show deoxygenation will begin affecting all ocean depth zones by 2080, and that deoxygenation may be irreversible. Even if humans stopped emitting greenhouse gases and reversed global warming by sucking carbon dioxide from the air, the question of “whether dissolved oxygen would return to pre-industrial levels remains unknown,” Zhou said. This underscores the importance of halting climate change — and the resulting ocean deoxygenation — as quickly as possible, according to scientists.
The reason ocean oxygen levels are declining is because warmer waters hold less oxygen, and ocean temperatures continue to rise at alarming rates. According to another, new study released this week and published in the scientific journal PLOS Climate, a majority of the world’s ocean surface has consistently exceeded the normal range since 2014.
High water temperatures pose a threat to ecosystems like coral reefs and the kelp forests which fish depend on. Monterey Bay Aquarium in Monterey (Calif.) used 150 years of sea-surface temperatures to determine the average temperature ranges. They discovered that 2014 was the first year when ocean surface temperatures rose above historical norms. This benchmark has been broken every year since, making extreme heat the new norm.
“Climate change is not a future event,” Dr. Kyle Van Houtan, who led the research team when he was chief scientist for the aquarium, Statement. “The reality is that it’s been affecting us for a while. Our research shows that for the last seven years more than half of the ocean has experienced extreme heat.”
Heat is not enough to threaten marine life. However, decreasing oxygen levels pose a further threat. The middle ocean depths are most at risk because they lack additional oxygen sources. The ocean surface absorbs oxygen, while the lower sea depths get oxygen from the algal decomposition. But the ocean’s middle depths, which are from about 600 feet to 3,300 feet below the surface and are called mesopelagic zones, will be the first area to lose large amounts of oxygen because they do not get oxygen from either of those sources. They are also home to many of the world’s commercially fished species, including tuna, swordfish and anchovies.
The loss of these fish species could lead to deoxygenation, which could cause havoc in fishing-based economies as well as a shortage of seafood for communities that depend on it. “Deoxygenation affects other marine resources as well, but fisheries [are] maybe most related to our daily life,” Zhou said.
The researchers also discovered that oceans closer the poles, where warming occurs faster, also lose oxygen much more quickly.