Oceans Are Running Out of Oxygen Due to Climate Change
by Stephanie MlotThe world’s oceans—and their inhabitants—are being choked to death by climate change and nutrient pollution.
Ocean oxygen loss, according to a new report by the International Union for Conservation of Nature (IUCN), is a growing menace to fisheries and species like tuna, marlin, and sharks.
Titled “Ocean deoxygenation: Everyone’s problem,” the peer-reviewed study highlights causes of, impacts to, and solutions for marine suffocation.
Ocean regions with low oxygen concentrations are expanding, IUCN warned, citing some 700 sites worldwide now affected by poor conditions—up from 45 in the 1960s.
Over the same six-decade period, the volume of anoxic waters—areas completely depleted of oxygen—in the global ocean has quadrupled.
“As the warming ocean loses oxygen, the delicate balance of marine life is thrown into disarray,” IUCN Acting Director General Grethel Aguilar said in a statement.
The adverse process favors low-oxygen-tolerant species (microbes, jellyfish, some squid) at the expense of low-oxygen-sensitives ones (many marine species, most fish).
Particularly susceptible to low oxygen (because of their large size and high energy demands), tuna, marlin, and sharks are being driven into increasingly shallow surface layers of oxygen-rich water, making them vulnerable to overfishing.
“Ocean oxygen depletion is menacing marine ecosystems already under stress from ocean warming and acidification,” study co-editor Dan Laffoley, senior advisor of marine science and conservation in IUCN’s Global Marine and Polar Program, explained.
“To stop the worrying expansion of oxygen-poor areas,” he continued, “we need to decisively curb greenhouse gas emissions as well as nutrient pollution from agriculture and other sources.”
Very low ocean oxygen can also affect basic processes like the cycling of elements including nitrogen and phosphorous, which are crucial for life on Earth, the report warned.
Under a business-as-usual model, the ocean is expected to lose 3 to 4 percent of its global oxygen inventory by 2100.
But while a single-digit decrease may not seem dire, that average masks more severe local changes.
“Urgent global action to overcome and reverse the effects of ocean deoxygenation is needed,” IUCN Global Marine and Polar Program Director Minna Epps said.
“Decisions taken at the ongoing [2019 United Nations Climate Change Conference in Madrid] will determine whether our ocean continues to sustain a rich variety of life, or whether habitable, oxygen-rich marine areas are increasingly, progressively, and irrevocably lost,” Epps added.
Read IUCN’s full report (and summary) online.
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