Climate change is driving oxygen out of the world's warming oceans at unnatural rates, likely suffocating many of the world's fisheries, according to a new study in Geophysical Research Letters.
Credit: Paul Einerhand
The new findings are deeply concerning and adds to the urgency to engage meaningfully in mitigating climate change, says Matthew Long, an oceanographer at NCAR who was not involved in the study.
"Humanity is currently changing the metabolic state of the largest ecosystem on the planet, with really unknown consequences for marine ecosystems," he said. "That may manifest in significant impacts on the ocean's ability to sustain important fisheries."
Evaluating vulnerability
The researchers identified the beginning of the deoxygenation process in three ocean depth zones - shallow, middle and deep - by modeling when the loss of oxygen from the water exceeds natural fluctuations in oxygen levels. The study predicted when deoxygenation would occur in global ocean basins using data from two climate model simulations: one representing a high emissions scenario and the other representing a low emissions scenario.
In both simulations, the mesopelagic zone lost oxygen at the fastest rate and across the largest area of the global oceans, although the process begins about 20 years later in the low emissions scenario. This indicates that lowering carbon dioxide and other greenhouse gas emissions could help delay the degradation of global marine environments.
The researchers also found that oceans closer to the poles, like the west and north Pacific and the southern oceans, are particularly vulnerable to deoxygenation. They're not yet sure why, although accelerated warming could be the culprit. Areas in the tropics known for having low levels of dissolved oxygen, called oxygen minimum zones, also seem to be spreading, according to Zhou.
"The oxygen minimum zones actually are spreading into high latitude areas, both to the north and the south. That's something we need to pay more attention to," she says. Even if global warming were to reverse, allowing concentrations of dissolved oxygen to increase, "whether dissolved oxygen would return to pre-industrial levels remains unknown."
