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.
A 2011 study, “Rapid expansion of oceanic anoxia immediately before the end-Permian mass extinction,” found that rapid and widespread anoxia (absence of oxygen) preceded “the largest mass extinction in Earth history, with the demise of an estimated 90 percent of all marine species.”
As National Geographic reported in 2015, we’re already starting to see the impacts of anoxia. “The waters of the Pacific Northwest, starting in 2002, intermittently have gotten so low in oxygen that at times they’ve smothered sea cucumbers, sea stars, anemones, and Dungeness crabs,” the magazine reported.
Finally, a 2015 study found there is no techno-fix to prevent a catastrophic collapse of ocean life for centuries if not millennia if we continue current CO2 emissions trends through 2050.
If we don’t start slashing carbon pollution, then, as co-author John Schellnhuber put it, “we will not be able to preserve ocean life as we know it.”