Low Oxygen Hypoxia in Marine Waters
Dr. Denis Gilbert explains the impacts of marine hypoxia, or low oxygen “dead zones”, in marine environments. Some dead zones occur naturally, and others result from human activities. Certain hypoxic areas, including one that occurs on the Pacific continental shelf, are linked to climate change.
Transcript
Dr. Denis Gilbert
I’m heading a research project across the country, for Fisheries and Oceans Canada, on low oxygen areas.
By low oxygen areas, we mean those areas of the ocean where oxygen is so low that some fish are starting to have trouble breathing, which means in practice that they have to escape to other areas where there is more oxygen.
There can be a loss of habitat for fish, so some areas that were once good for living -- are no longer good for them to live in and they have to go away.
The first way in which climate change can affect oxygen has to do with the fact that the water is expected to warm at the surface.
In warm water, you have less possibility for dissolving gases, so that means you dissolve less oxygen.
The second factor has to do with the fact that with climate change, we’re expecting the surface water to warm faster than the waters that are beneath them, and that means that this water at the surface is getting lighter and lighter, and it becomes harder to mix this water with dense water at the bottom, and the fact that it becomes harder to mix water, means you will also be injecting less oxygen into those deeper waters.
We’ve noticed the change in oxygen largely through long terms monitoring programs conducted by Fisheries and Ocean Canada, both on the west coast in the Gulf of Alaska, and also on the east coast at various sites off Nova Scotia, Newfoundland, Quebec, New Brunswick, looking at how oxygen is changing.
Through the last decades, we’ve seen declining trends, a tendency for oxygen to go down over the years.
Some of the impacts we have started to study for cod, range from swimming ability - when there’s less oxygen, fish tend to swim less fast.
There’s also the issue of growth.
Some oxygen concentrations are not necessarily lethal in the sense that they will not kill the cod, but they can nevertheless have an effect on the growth.
A cod that is three years old with low oxygen, will be smaller that one that has lots of oxygen. In Canada, there’s been two main areas where we’ve seen stress in terms of oxygen in the marine waters.
One of those areas is off the coast of B.C.
We’ve seen these (areas) creep up the continental slope and reach shallower depths, which presents possibly a loss of habitat for certain ground fish species.
On the east coast, the deep waters that are in the Gulf of St. Lawrence, and in particular in the lower St. Lawrence Estuary, right in front of Rimouski, is a place where the levels of oxygen are considered so low that they are now inhospitable to cod.
So Fisheries and Oceans Canada is funding research at a number of labs across the country to figure out how fish are changing their distribution patterns with respect to oxygen; how those fish might redistribute in the future as oxygen is changing.
Through lab studies, we’ll try and figure out how certain species are reacting as a function of oxygen.
On the international stage, Canada has been, and remains, one of the leaders in the research on low oxygen areas, and we’re expecting that this will continue.
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