Ocean ‘Dead Zones’ Have Quadrupled Since 1950

Our oceans are running out of air.

A new report, published this week, says that ocean dead zones—regions starved of oxygen—have increased by millions of square miles and quadrupled in size since 1950. Coastal regions with low levels of oxygen, caused by fertilizer and sewage runoff, have multiplied tenfold. Climate change is a likely culprit, as warmer waters carry less oxygen.

Oceans have some natural low oxygen regions, but they’re usually off the west coast of continents due to the coriolis effect. The dead zones in question are different—at least 500 dead zones have been reported near coasts, in particular. In 1950, that number was below 50.

Algal blooms, like this one in the South Atlantic Ocean, draw oxygen out of water.

Here’s Damian Carrington, reporting for The Guardian:

The analysis, published in the journal Science, is the first comprehensive analysis of the areas and states: “Major extinction events in Earth’s history have been associated with warm climates and oxygen-deficient oceans.” Denise Breitburg, at the Smithsonian Environmental Research Center in the US and who led the analysis, said: “Under the current trajectory that is where we would be headed. But the consequences to humans of staying on that trajectory are so dire that it is hard to imagine we would go quite that far down that path.”

“This is a problem we can solve,” Breitburg said. “Halting climate change requires a global effort, but even local actions can help with nutrient-driven oxygen decline.” She pointed to recoveries in Chesapeake Bay in the US and the Thames river in the UK, where better farm and sewage practices led to dead zones disappearing.

Low oxygen levels are difficult to reverse—in suffocating environments, marine organisms have to breathe faster, using up oxygen more quickly. On top of that, microbes that reproduce in low oxygen regions produce nitrous oxide, a greenhouse gas. Thus, ocean dead zones risk sending our planet spiraling into further climate extremes. They also threaten ocean animals and the people who spend on them for their livelihood.

There’s some evidence that the global meat industry could be fueling ocean dead zones by channeling toxins from manure and fertilizers into waterways. It’s an ironic circular system: the production of meat designed to feed the world’s people may be contributing to the rapid demise of another major source of food, sending a ripple through the supply chain.

 

 

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