Oxygen is becoming increasingly scarce in the world’s oceans, threatening the ability of plants and animals to survive, Scientific American reports.
Some marine environments have seen oxygen levels plummet by 40% over the past five decades, while the decline in other areas has been more modest. Overall, the oceans have 2% less oxygen in them than they did five decades ago, according to readings by the Helmholtz Center for Ocean Research.
“We were surprised by the intensity of the changes we saw, how rapidly oxygen is going down in the ocean and how large the effects on marine ecosystems are,” Andreas Oschlies, an oceanographer at the Helmholtz Center, told Scientific American.
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Even a slight decline in oxygen is catastrophic for marine creatures that depend on the element to function, Scientific American notes.
Zooplankton, which support the marine food chain, are extremely sensitive to shifts in oxygen levels and have been made more susceptible to predators as they migrate in response to changing conditions.
Other animals have begun to limit their movements to conserve energy, and fish such as Tuna that are critical to the global seafood industry have been forced to migrate to new areas as their traditional habitats become deprived of oxygen. These mass migrations, in turn, can unravel long-established ecosystems.
The world’s oceans are losing oxygen for a few reasons, Scientific American reports.
First, excess heat from greenhouse gas emissions in the atmosphere is being absorbed by the oceans, and warmer water is less able to hold oxygen. Next, melting sea ice is causing warm layers of water to sit atop colder, saltier waters, preventing oxygen in the atmosphere from being absorbed by the oceans. Finally, runoff such as fertilizer from industrial agricultural operations is creating algae blooms in coastal areas that consume large quantities of oxygen.
The loss of oxygen is expected to accelerate in the years ahead and scientists are urging governments around the world to take action to address this problem. The Kiel Declaration on Ocean Deoxygenation, for example, is a declaration from various experts urging countries to mitigate climate change and stop industrial runoff.
The oceans are threatened by a range of other developments including ocean acidification, overfishing, and plastic pollution.
Noise pollution from boats searching for oil has been shown to seriously harm the web of sound that marine creatures depend upon, and even kill animals. As the world’s oceans warm, heat-sensitive coral reef are being killed, destroying ecosystems that sustain thousands of species.
All of these problems are linked and require a globally coordinated response, according to the United Nations.
For example, countries can adopt rules on fishing quotas to help rehabilitate depleted animal populations, actively police pollution throughout open waters, and work to limit greenhouse gas emissions.