Nearly twenty scientists from around the world are issuing a warning about a little known side effect of climate change and pollution.
According to an article published this week in the journal Science, oxygen disappears from the oceans in increasingly large proportions, which threatens marine life.
The study, which was funded by an international organization affiliated to UNESCO (the United Nations Educational, Scientific and Cultural Organization), reports that this problem has been worsening since the 1950s.
In the last 50 years, the area of oceans affected has increased from 4.5 million to 32 million square kilometers in nearshore and high seas waters.
Rivers on the west coast of Canada and on the St. Lawrence Seaway would be affected.
“We believe that this issue should be examined and that it should attract more attention,” said Denis Gilbert, one of the 22 authors who co-authored the research.
“All animals must breathe oxygen and we know that areas of the ocean that are losing oxygen are becoming more prevalent. We are seeing marine animals leaving these places, “said Gilbert, who is also a scientist with the Department of Fisheries and Oceans.
The article, which summarizes recent research, found several oxygen-depleted streams around the world. The waters near major rivers and urban centers would be particularly affected. However, the researchers found other cases on the high seas.
A “huge” increase
The volume of water completely devoid of oxygen has quadrupled since the 1950s, according to a study. Marine animal populations and diversity have declined significantly in coastal areas.
In the deepest waters of the Gulf of St. Lawrence, the oxygen rate has dropped by 55 percent since the 1930s.
“It is enormous. We are already losing cod in deep waters, “said Gilbert.
A similar phenomenon has been observed in northern British Columbia, according to the scientist.
Several factors play a role in this problem.
Industries and the agricultural sector release their nitrates into the ocean, creating algal blooms similar to those that can affect freshwater systems. But at sea, it is certainly climate change that is the main culprit, by far.
Climate change brings a “triple offensive,” Gilbert said.
First, warmer waters can not absorb as much oxygen.
Then, the different layers of the ocean do not mix as much if the upper part is warmer – the deep layers are not so aerated by being exposed to the surface, so, gradually, the oxygen they contain is nibbled by bacteria.
Finally, warmer waters force marine animals to breathe more quickly, causing them to use available oxygen more quickly.
“One of the reasons why (marine animals) can not tolerate very hot water is that they have to breathe more. In these waters where they have to breathe more, there is less oxygen, “said the researcher.
A little studied issue
In comparison with other climate change issues, including ocean acidification, the impacts of lack of oxygen in water are poorly studied, according to Denis Gilbert.
“It’s very little understood,” Gilbert said.
And the problem is not likely to be resolved in the short term, says the scientist.
“Global warming models predict that oxygen depletion will be even worse by 2100 and will continue to worsen.”
Even with ambitious targets for reducing greenhouse gases, there will be a decline in oxygen in the water, depending on the model. But that does not mean that they are useless, according to Gilbert.
“Acting on fossil fuels will have benefits not only for sea ice and ocean acidification, but also for oxygen,” he concluded.