Widespread and sometimes drastic marine oxygen declines are stressing sensitive species—a trend that will continue with climate change
Climate change already poses serious problems for marine life, such as ocean acidification, but deoxygenation is the most pressing issue facing sea animals today, Andreas Oschlies.
After all, he says, “they all have to breathe.”
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As oxygen-rich regions become scarcer, current fish habitats will also shrink and force economically important species—such as tuna, which globally generate an estimated $42 billion annually—into new ranges. In the northeastern tropical Atlantic researchers have found habitat for tuna as well as billfish fisheries shrank by 15 percent from 1960 to 2010 (pdf) due to oxygen loss.
“Oxygen levels in some tropical regions have dropped by a startling 40 percent in the last 50 years”
In the past decade ocean oxygen levels have taken a dive—an alarming trend that is linked to climate change, says Andreas Oschlies , an oceanographer at the Helmholtz Center for Ocean Research Kiel in Germany, whose team tracks ocean oxygen levels worldwide. “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,” he says.
It is no surprise to scientists that warming oceans are losing oxygen, but the scale of the dip calls for urgent attention, Oschlies says.
Levels have dropped more subtly elsewhere, with an average loss of 2 percent globally.
To address the overall deoxygenation problem, Oschlies helped organize an international conference on the subject in Kiel last September. Attendees drafted an impromptu declaration called the Kiel Declaration on Ocean Deoxygenation to raise awareness among international governments, the United Nations and the public as well as to call for immediate action. They want governments and international groups to make more serious strides to slow climate change and cut back on the coastal runoff pollution that exacerbates oxygen decline. The researchers modeled the new declaration after the Monaco Declaration (pdf), which Oschlies thinks successfully helped raise international awareness around ocean acidification in 2008.
“It’s really intended to be an alert to both the public and the various governmental and international agencies that this is a significant issue,” says Wishner, one of the more than 300 scientists from more than 30 countries who signed the declaration.
Brad Seibel, also a signatory, minces no words on the matter: “I think it’s potentially very dire.”