Climate Change Depleting Ocean Oxygen

April 28, 2016

New study profiles decreasing oxygen levels in oceans.

Above, scientists tell us about what’s happened in Earth’s deep past  when the process went to extremes.

Washington Post:

The oceans are getting warmer — they are, after all, where 90 percent of global warming actually ends up. And when they warm up they expand, because that’s what warm water does. This raises our sea levels, but it also has another effect — it reduces the amount of oxygen dissolved in the water. That’s simply physics: Warmer water contains less oxygen.

But it’s worse: If surface water is warmer, it doesn’t mix down as much into the ocean depths any longer. It’s less dense, and so less capable of doing that. That means that oxygen that enters the ocean in its upper layers — either through exchange with the atmosphere, or because it is generated by tiny photosynthesizing microorganisms, called phytoplankton, that hang out up there — won’t mix down into the deep as often.

“What’s happening is, there’s a physical mechanism that impedes the delivery of surface waters into the interior,” said Matthew Long, an oceanographer with the National Center for Atmospheric Research who is lead author of a troubling new study on what scientists call the “deoxygenation” of the oceans. The work appeared in Global Biogeochemical Cycles, co-authored with Curtis Deutsch of the University of Washington and Taka Ito of the Georgia Institute of Technology.

The problem is that marine life needs oxygen. If there’s less of it, that could expand the number of areas sometimes called “oxygen minimum zones” where plants, fish, and other organisms would struggle to survive.

Now, in the new study, Long and his colleagues have found that some parts of the ocean are already likely showing an oxygen deficiency, due to the effects of global warming. And by around the year 2030, their model suggests, the human role in driving widespread ocean oxygen loss will be even more apparent if greenhouse gas emissions continue unchecked.

“Its fairly widespread detection….is basically evident in the 2030s to 2040s decade,” Long said.

Phil Plait in Slate:

What they found is sobering. Deoxygenation due to human-made global warming is already detectable in the southern Indian Ocean, and in some regions in the eastern tropical Pacific and Atlantic. By 2030 to 2040—two decades from now—they expect to see more and more widespread deoxygenation over the globe. By the year 2100 (which is how far into the future they ran the models) a significant fraction of the global oceans will see some deoxygenation due to human activity.

This is, obviously, bad. The amount of deoxygenation may not be very much, just a drop of a few percent. But as we learned with increasing carbon dioxide levels in the atmosphere, and rising temperatures, it doesn’t take much change to destabilize a system.

The worst effects will come from areas already low in oxygen, called hypoxic zones, where the levels can be as much as 70–90 percent lower than average, and in suboxic zones, where it’s even lower. In those regions, a few percent drop can mean the difference between life barely holding on, and death.

Even when the change isn’t so dramatic, it can be devastating. You might think of the ocean as one big fish tank, but it’s actually incredibly diverse, depending on water temperatures, currents, pressure, and more. Changes in oxygen levels in the water reduce marine life habitats, stressing the inhabitants there. Changes in regional oxygen levels have caused migrations of fish, and even massive die-offs. Besides the effect on the life there, this has an impact on human activity including fishing, on which many countries depend.

Mind you, about half the oxygen we breathe comes from ocean phytoplankton. Messing with their habitat is like setting fire to your own house. Which is pretty much what we’re doing.

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11 Responses to “Climate Change Depleting Ocean Oxygen”


  1. Low Dose Radiation, CO2 Causing Oxygen Depletion Globally, Increases Jellyfish, Toxic Algae Numbers, Killing Trees, Corals, Fish, Plankton
    http://agreenroad.blogspot.com/2013/07/low-dose-radiation-causes-oxygen.html


  2. Reminds me of the end of the Permian: http://www.nature.com/articles/srep04132

    Not good….

  3. brucehparker Says:

    If the warmer ocean surface is not mixing as much oxygen, it’s also not mixing as much CO2. Does this mean that the oceans will absorb less of our future CO2 emissions? Any idea how much of a difference this will make? And will that also mean more heat for hurricanes?


    • Someone will correct me if I’m wrong but I would have thought the process of O2 and CO2 “mixing” are different processes. O2 dissolution is dependent on heat and the process ends up with a solution. CO2 absorption involves CO2 molecules bonding with H2O to form carbonic acid H2CO3 which is a whole new molecule…so…different processes with the end result being that O2 can decrease while CO2 uptake can increase. For your last question, yes.

      • dumboldguy Says:

        It’s a bit more complicated than that. The word “dissolve” is a bit confusing, in that anything that “disappears” into the ocean has “dissolved” in the mind of the layman. You’re correct that most oxygen does simply go into solution, while carbon dioxide both dissolves and remains a “gas” (a small part) and reacts (most of it) to form new molecules.

        The same factors that cause the ocean to hold less oxygen also decrease its ability to hold CO2. One factor is temperature, another is the stratification and “mixing failure” that Bruce posits.

        https://en.wikipedia.org/wiki/Solubility_pump
        https://en.wikipedia.org/wiki/Biological_pump

        Warming of the oceans at any depth decreases their ability to “dissolve” both O2 and CO2. Have you got any link that talks about “….O2 can decrease while CO2 uptake can increase”?

  4. Andy Lee Robinson Says:

    Apart from reigning in carbon emissions, the solution to this is simple – oxygenate the water the same way that aquaria are oxygenated…

    Big pipes carrying compressed air into the oceans to a couple of hundred metres depth… of course, this would require lots of them, and a lot of energy which can be intermittent using solar or wind.

    It couldn’t do all the oceans, but a pilot experiment would be interesting to see the extent of the effect.

    It would also help against stratification.

    Perhaps ships could carry one to oxygenate instead of pollute?

    • mboli Says:

      But of course! The difference between an ocean and a home aquarium is merely scale.


    • The sheer genius
      Rather than tax CO2 which would be a minor financial impact or reduce consumption of fossil fuels.
      Play the denial misinform cards until it becomes critical to economic and human survival at which point those that have ensured this situation will offer the very expensive geo engineering solutions that will bleed the economies and individuals completely dry , which they out of desperation will pay.

      Humans can be so dumb and gullible

    • dumboldguy Says:

      Great idea! And of course, that compressed air will be quite hot from being compressed, and piping it down to the depths will heat up the water and diminish its capacity to hold the oxygen from the air being pumped down. Which horse will win the race? Another geoengineering idea that may have unintended consequences.

      (And while we’re at it, why don’t we install tens of thousands of big solar or wind powered ice-makers around the shores of the arctic to dump house-sized ice cubes in the ocean to counter the loss of arctic sea ice).

    • andrewfez Says:

      I’d rather have the extra oxygen in the atmosphere to breath, especially if the phytoplankton take an early retirement.


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