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Oceans Face Oxygen Loss, Acidification as Warming Challenges Ability to Absorb Carbon

With the Earth’s oceans rapidly and dangerously losing oxygen due to a combination of global warming and pollution, Greenpeace is urging countries to restore and protect the planet’s marine ecosystems, both for their own sake and because a healthy ocean is vital to fighting the climate emergency.

“The world’s oceans are gasping for breath,” reports the New York Times, citing an internationally-authored report released last week at the UN climate conference in Madrid by the Gland, Switzerland-based International Union for Conservation of Nature (IUCN). The report found that “oxygen levels in the world’s oceans declined by roughly 2% between 1960 and 2010,” a depletion that researchers attribute largely to ocean warming—and the reality that warm water holds less oxygen than cool.

It also takes up more space, notes the Times, citing NASA’s estimate that such thermal expansion “has caused roughly a third of existing sea level rise.”

Oxygen-sucking algal blooms caused by nutrient runoff from agriculture also emerge as a driver of the loss.

While a 2% seepage of oxygen from ocean waters may seem very small, it is enough to “affect the planetary cycling of elements such as nitrogen and phosphorus,” writes the Times, elements essential for life to exist on Earth. “We lower these oxygen levels at our peril,” said report co-author Dan Laffoley, principal advisor in IUCN’s global marine and polar program.

Depleting oxygen levels are just one of myriad threats to the Earth’s oceans, notes the Times. Powerful absorbers of CO2, the oceans are becoming ever more acidic, a change that eats away at the calcium carbonate skeletons and shells of many marine creatures. As mass absorbers of “93% of the heat associated with human-caused greenhouse gas emissions” for the past 70 years, the oceans have also seen mass bleaching of coral reefs.

All of which helps make the case that “ocean protection is climate action—if we can save our ocean, it can save us,” said Greenpeace UK oceans campaigner Louisa Casson. It’s the world’s biggest carbon sink, and with life forms from the tiny krill crustacean to the giant baleen whale, “the ocean’s biology is one of our best allies in the fight against climate change.” 

However, “we are rapidly reaching the limits of the oceans’ absorptive capacity,” writes the Times. Already, overfishing and marine plastic pollution are disrupting an ocean mechanism known as the “biological carbon pump,” in which gravity drives the carbon in marine life of all sizes down to the sea bottom after they die, to be buried in sediment.

With the planet’s krill populations “in long-term decline since the 1970s due to pollution, overfishing and climate change,” and with baleen whales “estimated to store 910 million tonnes less carbon than they did before commercial whaling began,” Greenpeace is urging governments to create ocean sanctuaries and forge a new treaty for ocean protection.

“Safeguarding at least 30% of the oceans by 2030 could restore many areas to health and combat global heating,” the Times writes, citing the Greenpeace report. “Protecting the oceans can also help make coastal communities more resilient against the impacts of climate chaos.”