May 8, 2017

Carbon pollution is suffocating ocean life and speeding up the next mass extinction

by
Joe Romm
,
ThinkProgress
Much of the ocean is seeing sharp drops in oxygen levels (purple). Photo: Georgia Tech
Much of the ocean is seeing sharp drops in oxygen levels (purple). Photo: Georgia Tech

Depletion of dissolved oxygen in our oceans, which can cause dead zones, is occurring much faster than expected, a new study finds.

And by combining oxygen loss with ever-worsening ocean warming and acidification, humans are re-creating the conditions that led to the worst-ever extinction, which killed over 90 percent of marine life 252 million years ago.

Researchers at Georgia Institute of Technology reviewed ocean data going back to 1958 and “found that oxygen levels started dropping in the 1980s as ocean temperatures began to climb.”

Scientists have long predicted that as carbon pollution warms the globe, the amount of oxygen in our oceans would drop, since warmer water can’t hold as much dissolved gas as colder water. And, Georgia Tech researchers point out, falling oxygen levels have recently led to more frequent low-oxygen events that “killed or displaced populations of fish, crabs and many other organisms.”

But what is especially worrisome about this new research is how quickly it is happening. “The trend of oxygen falling is about two to three times faster than what we predicted from the decrease of solubility associated with the ocean warming,” said lead researcher Prof. Taka Ito. “This is most likely due to the changes in ocean circulation and mixing associated with the heating of the near-surface waters and melting of polar ice.”

Global warming drives ocean stratification — the separation of the ocean into relatively distinct layers. This in turn speeds up oxygen loss, as explained in this 2015 video.