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A looming oxygen crisis and its impact on our oceans

By Climate Guest Contributor on August 15, 2010 at 10:42 am

"A looming oxygen crisis and its impact on our oceans"


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We’ve known for a while that we are poisoning the oceans and that human emissions of carbon dioxide, left unchecked, would likely have devastating consequences.  A 2010 study found that oceans are acidifying 10 times faster today than 55 million years ago when a mass extinction of marine species occurred.

And we’ve known those impacts might last a long, long time “”a 2009 study concluded ocean dead zones “devoid of fish and seafood” are poised to expand and “remain for thousands of years.” Worse, a Nature study just found that global warming is already the likely cause of a 40% decline in the ocean’s phytoplankton:  “Microscopic life crucial to the marine food chain is dying out. The consequences could be catastrophic.”

Carl Zimmer, a noted science writer and winner of the 2007 NAS Communication Award, reveals some more chilling facts about the path our oceans may be on in this repost from Yale’s Environment 360 online magazine.

As warming intensifies, scientists warn, the oxygen content of oceans across the planet could be more and more diminished, with serious consequences for the future of fish and other sea life.

The Deepwater Horizon oil spill is overshadowing another catastrophe that’s also unfolding in the Gulf of Mexico this summer: The oxygen dissolved in the Gulf waters is disappearing. In some places, the oxygen is getting so scarce that fish and other animals cannot survive. They can either leave the oxygen-free waters or die. The Louisiana Universities Marine Consortium reported this week that this year’s so-called “dead zone” covers 7,722 square miles.

Unlike the Deepwater Horizon disaster, this summer’s dead zone is not a new phenomenon in the Gulf. It first appeared in the 1970s, and each summer it has returned, growing bigger as the years have passed. Its expansion reflects the rising level of fertilizers that farmers in the U.S. Midwest have spread across their fields. Rain carries much of that fertilizer into the Mississippi River, which then delivers it to the sea. Once the fertilizer reaches the Gulf, it spurs algae to grow, providing a feast for bacteria, which grow so fast they use up all the oxygen in their neighborhood. The same phenomenon is repeating itself along many coastlines around the world. This summer, a 377,000-square-kilometer (145,000-square-mile) dead zone appeared in the Baltic Sea. In 2008, scientists reported that new dead zones have been popping up at an alarming rate for the past 50 years. There are now more than 400 coastal dead zones around the world.

As serious as these dead zones are, however, they may be just a foreshadowing of a much more severe crisis to come. Agricultural runoff can only strip oxygen from the ocean around the mouths of fertilizer-rich rivers. But global warming has the potential to reduce the ocean’s oxygen content across the entire planet. Combined with acidification “” another global impact of our carbon emissions “” the loss of oxygen could have a major impact on marine life.

Scientists point to two reasons to expect a worldwide drop in ocean oxygen. One is the simple fact that as water gets warmer, it can hold less dissolved oxygen. The other reason is subtler. The entire ocean gets its oxygen from the surface “” either from the atmosphere, or from photosynthesizing algae floating at the top of the sea. The oxygen then spreads to the deep ocean as the surface waters slowly sink.

Global warming is expected to reduce the mixing of the ocean by making surface seawater lighter. That’s because in a warmer world we can expect more rainfall and more melting of glaciers, icebergs, and ice sheets. Since freshwater is less dense than salt water, the water at the ocean’s surface will become lighter. The extra heat from the warming atmosphere will also make surface waters expand “” and thus make them lighter still. The light surface water will be less likely to sink “” and thus the deep ocean will get less oxygen. Instead, more of the oxygen will linger near the surface, where it will be used up by oxygen-breathing organisms.

The prospect that global warming could reduce the ocean’s oxygen has led some scientists to wonder if the predicted decline has already begun. It’s a maddeningly hard thing to determine, however. We can be very confident that humans have driven up the concentration of carbon dioxide in the atmosphere because scientists have recorded a steady increase over the course of decades. The signal of human-produced carbon dioxide is stronger than the noise of nature’s ups and downs.

Fluctuations in oxygen levels, on the other hand, are a lot noisier. As ocean currents oscillate naturally, upwellings of deep-ocean water can deliver nutrients to coastal waters, triggering an explosion of growth and driving down oxygen levels. Volcanoes can alter oxygen levels, too, by creating a haze that blocks sunlight, thus temporarily cooling the ocean’s surface and allowing more oxygen to dissolve into the water.

In recent years some worrying signals have started to emerge from the noise. In 2006, for example, oxygen levels off the coast of Oregon dropped to record lows. Reefs that had been packed with rockfish and other animals suddenly became ecological ghost towns. Instead of agricultural run-off, studies on the Oregon dead zone suggest that global warming was partly responsible. Higher temperatures have reduced the oxygen in the ocean currents that deliver water to the Oregon coast.

It’s much harder for scientists to figure out what’s happening in the open ocean than along the coastlines, because the records are far spottier. But some recent studies have also offered cause for worry. In April, for example, Lothar Stramma of the University of Kiel and his colleagues published a study in Deep Sea Research in which they compared records of oxygen levels in the tropical ocean from two periods: from 1960 to 1974 and from 1990 to 2008. In some regions, the oxygen levels have gone up, the scientists found, but in most places they’ve gone down. In fact, the area of the global ocean without enough oxygen for animals to survive (less than 70 micromoles per kilogram to be exact) expanded by 4.5 million square kilometers (1.7 million square miles). That’s an area about half the size of the United States.

Because the records of oxygen levels in the past are so incomplete, many scientists are calling for a push for more research. An international collaboration started in 1995, the Climate Variability and Predictability Repeat Hydrography Program “” CLIVAR for short “” is beginning to gather better data. But in the latest issue of Annual Review of Marine Science , Ralph Keeling of Scripps Institution of Oceanography and his colleagues warn that the CLIVAR program may need 20 to 30 years to establish long-term trends of oxygen levels. To speed up the process, they call for a global network of floating sensors known as Argo to be brought into the effort. If scientists put oxygen sensors on a few hundred of the 3,000 Argo floats, Keeling and his colleagues predict that a clear pattern would emerge in as little as five years. Keeling and his colleagues believe that it’s urgent to speed up this research, because the deoxygenation of the oceans could have a major impact on marine life.

In order to project how global warming will alter oxygen in the oceans, climate scientists are developing a new generation of computer models. The models are still too crude to capture some important features of the real world, such as the way winds can change how deep water rises in upwellings. But the models are good enough to replicate some of the changes in oxygen levels that have already been recorded. And they all predict that the oxygen in the world’s oceans will drop; depending on the model, the next century will see a drop of between 1 and 7 percent.

That could be enough to have a profound effect on life in the ocean, according to Daniel Pauly, a fisheries biologist at the University of British Columbia. In his new book, Gasping Fish and Panting Squids: Oxygen, Temperature and the Growth of Water-Breathing Animals, Pauly argues that getting oxygen is the most important constraint on the growth of fishes and many other marine animals. That’s because it takes a lot of energy to extract oxygen from water, and the bigger animals get, the more energy they have to invest.

Pauly and his colleagues are working on computer models to project how global warming will affect the world’s fisheries. Many species of fishes will shift their ranges away from water that’s too warm for them. But this flight from heat may force them into regions of the ocean with low levels of oxygen, where their growth will be limited. Pauly and his colleagues predict that the drop in the ocean’s oxygen and pH levels will together reduce the world’s fish catch by 20 to 30 percent by 2050.

While fishes and other animals with high oxygen demands suffer, jellyfish may thrive. Jellyfish can tolerate lower oxygen levels than fish, in part because they can store reserves of the gas in their jelly. Free from competition and predators, jellyfish will be able to feast on the microscopic animals and protozoans that feed on algae. They may thus leave more food for bacteria, spurring a further drop in oxygen levels.

A drop in oxygen may also cause the ocean’s bacteria to change. Bacteria that need oxygen will no longer be able to thrive in oxygen-free zones of the ocean. But these dead zones will foster the growth of many species of bacteria for whom oxygen is toxic. Some of these oxygen-hating microbes produce nitrogen compounds that are among the most potent greenhouse gases ever measured. In other words, a drop in oxygen levels could further intensify global warming.

Unless we find a way to rein in our carbon emissions very soon, a low-oxygen ocean may become an inescapable feature of our planet. A team of Danish researchers published a particularly sobering study last year. They wondered how long oxygen levels would drop if we could somehow reduce our carbon dioxide emissions to zero by 2100. They determined that over the next few thousand years oxygen levels would continue to fall, until they declined by 30 percent. The oxygen would slowly return to the oceans, but even 100,000 years from now they will not have fully recovered. If they’re right, fish will be gasping and squid will be panting for a long time to come.

Carl Zimmer

Related Posts:

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New York Times front-page story: In Weather Chaos, a Case for Global Warming!

30 Responses to A looming oxygen crisis and its impact on our oceans

  1. AH1 says:

    Jellyfish blooms are appearing all over the world. Nomura’s Jellyfish up to two metres long are invading the beaches off eastern China and Japan.

  2. fj2 says:

    This is not good. There is stuff people in power can do to initiate timely action.

  3. K. Nockels says:

    We are taking so much seafood out of the oceans that never even makes it to shore (by-catch) that any more reduction in marine life added to what humans are now consuming will finish off most species that are already in trouble. Which will leave the oceans to only those that we don’t or can’t eat. Jellies seem on the rise, I have been hearing about the increase in them over the last four maybe five years. They were one of the first creatures to evolve in the sea and we don’t eat them which is one reason I’m sure that they are not in decline. We are walking a very fine line now, and could end up not being able to survive on the planet that we evolved on.

  4. anonymous says:

    http://www.treehugger.com/files/2010/08/melting-arctic-sea-ice-wont-expand-ocean-carbon-storage-potential.php As there have also been reports of methane escaping to the atmosphere in the Arctic, and not turning into CO2 while it rises, it is likely the effects of climate change will speed up from this year forward. I’m (now) expecting climate refugees to become an issue during this decade and not in 2030s as previously.

  5. Mike says:

    @ AH1 says:
    August 15, 2010 at 10:54 am

    “Jellyfish blooms are appearing all over the world. Nomura’s Jellyfish up to two metres long are invading the beaches off eastern China and Japan.”

    A literary note. Gunter Grass wrote a doomsday novel about the end of the world, or at least humanity, called The Rat in 1980′s – Oscar from The Tin Drum is all grown up and produces videos. Jellyfish blooms play a prominent role although it was the neutron bombs that finished us off.

  6. Paulm says:


    Jersey Shore: Dead Fish Wash Ashore In Thousands For Second Time This Week On East Coast (VIDEO)
    First Posted: 08-12-10 01:28 PM   |   Updated: 08-12-10 05:43 PM

  7. Abe says:

    On the plus side, we can create more tidal power turbines without fear of killing sea life, since there won’t be anything big enough to be effected by them.

  8. Edward says:

    30% decrease in oxygen won’t be enough to allow sulfur bacteria to take over the whole ocean, but see:

    H2S is coming out of the ocean off the coast of Namibia.
    See:”Under a Green Sky” by Peter D. Ward, Ph.D., 2007.
    Does anybody know if we will see more places like the coast of Namibia? How many and how much H2S?

  9. Frank Zaski says:

    Something to monitor closely is the declining percentage of oxygen in the air we breath. With continuing deforestation and CO2 creation, the percent continues to drop. Do climate models indicate what the level will be 40 years from now? A few snips from an article:

    “According to a study conducted by scientists from the Scripps Institute there is less oxygen in the atmosphere today than there used to be. The ongoing study, which accumulated and interpreted data from NOAA monitoring stations all over the world…the conclusion of that 20 year study is that, as carbon dioxide (produced primarily by burning fossil fuels) accumulates in the atmosphere, available oxygen is decreasing.”

    “Carbon dioxide seems to be almost the total focus of attention in the climate change model as it exists today. After reviewing the results of this study and talking with Dr. Ralph Keeling (one of the lead scientists on the study), it seemed to me that the consequences of atmospheric oxygen depletion should be included in any discussion of atmospheric change.”

    “In conclusion, it seems that the depletion of atmospheric oxygen will continue until such time as we stop burning hydrocarbons faster than the environment can absorb the byproducts of the reaction and replenish the oxygen.” http://blogcritics.org/scitech/article/atmospheric-oxygen-levels-fall-as-carbon/

    Another article concludes the oxygen decline was considerable over the past 100 years.

  10. Sasparilla says:

    For an excellent book detailing past events in the archeological record related to low or no oxygen parts (or all) of the oceans (anoxic areas) there is Peter Ward’s excellent book:

    Under a Green Sky


    The suggested studies listed in the article should be done ASAP as well as one detailing the constant state of the ocean conveyer.

    The short version from the book…regarding these bacteria..

    The nasty bacteria that don’t need oxygen and don’t make oxygen (and thrive in these anoxic environments) – make a sulphur based gas that is poisonous (not just a little bit) to oxygen based life (besides being a potent greenhouse gas as mentioned in the article) – this has the effect of clearing their local environment of oxygen based life for their continued growth, i.e. we really don’t want that ball to start rolling in our oceans (much more of a long term effect, but once it starts going it would be hard to imagine how to stop it).

    The geologic record lists multiple instances of (sections and entire) oceans switching over to an anoxic state populated by these bacteria. It appears that the main indication of it happening (in the geologic record) was the ocean conveyer switching to bringing low/no oxygen level water to the depths (instead of the cold high oxygen water that its currently doing, more slowly at this point, now). The book mentions that it appears that the conveyer might stop, but then (if it stops) starts back up but is diving much earlier in its path bringing warm low oxygen water down to the depths, providing the environment these little buggers need (they start at the depths and gradually work their way up and apparently really get going once they get to sunlight – there are types of non oxygen producing algae that they work with when they get sun).

    There are several current aquatic environments that are in this anoxic state in the world today and scientists have (and are continuing to) study. One of those crazy things that’s just out there that most of us are not aware of. Please check out the book for more details as its an excellent read.

  11. Gord says:

    From what I understand Jellyfish can survive in water with a substantially lower oxygen content than regular fish. So Jellyfish swarms, I would assume, are the ‘canary’ in the coal mine for identifying oxygen depleted waters.

    That Nature paper identifying a loss of 40% of our phytoplankton since 1950 and an ongoing decrease of 1% a year, to me, is astonishing. From what I understand the yearly decrease is most probably a function of ocean surface heating … causing more stable lamina to form which decrease mixing with cooler, food-rich, lower layers of the ocean.

    Considering the amount of CO2 we have in the atmosphere and considering the amount of extra heat this represents (eventually) in the surface waters of the oceans, we can only conclude that the 1% decline can only increase in magnitude going forward.

    So these are brutal numbers we have to deal with: we are down 40%, decreasing by 1% (and soon more) a year, and we are facing an unknown tipping point for oceanic life.

    It makes me want to research, design, build and test a (proof of concept) prototype of an ocean anchored, wave powered, seawater upwelling device just to have it ready to go for future use.

    A technical mitigation? It may come to that.

  12. catman306 says:

    Gord, Please do design such devices. I suggest that you think small, and cheap. Millions of these devices may be needed. But that’s no sweat for our modern manufacturing techniques.

    If someone can design it, someone else will want to fund and manufacture these devices. But it’s just an idea for now. I doubt if pumps can move water from the bottom all the way up to the top or air from the surface down to the bottom. Too much pressure differential. Sooo…..
    Why not build many small pumps that can pump water downward a couple of hundred feet. Suspend them on cables from floats that house the power supply, either solar, wave, wind, or some other non-polluting electric power supply. Scores of these small pumps could be attached at intervals along the length a cable and move the water downward in many stages. The cable would be anchored to the bottom to keep the assembly in place and not a become hazard to navigation. I’m thinking that garden hose size but a million times over is the cheap and efficient way to go.
    All of this assumes that the water near the surface HAS oxygen in it.
    Good luck!

  13. homunq says:

    The easiest energy to use for mixing the ocean is hydropower. That is, instead of making hundreds of millions of Gord’s “upwellers”, we need to put 2/3 of the Amazon in a pipe just before it hits the sea, then run all that freshwater deep under the ocean where it will mix with high-nutrient water before upwelling on its own (due to its lower salt content). I honestly think that if I live out my current life expectancy (about another 50 years), I’ll probably see this happen; it is a giant, ugly interference with nature, but unless humanity is embracing such lesser evils, I probably won’t survive that long.

  14. homunq says:

    note: 2/3 of the amazon is as much flow as the next 3 biggest rivers combined.

  15. Rabid Doomsayer says:

    You know I am more than a little pessimistic. But this far worse, far sooner, than my worst nightmares.

    “Here we report new observations, however, that indicate dramatic changes in the oceanographic characteristics of the anoxic interface of the Black Sea over decadal or shorter timescales. The anoxic, sulphide-containing interface has moved up in the water column since the last US cruises in 1969 and 1975. In addition, a suboxic zone overlays the sulphide-containing deep water.”

    The above refers to the Black Sea, how long before we see a similar one for one of our oceans?

  16. Leif says:

    Moving water from the deep ocean? #2 & 3. Floating wind mills with a low pressure compressor pumping air into the upper part of a long “straw.” The rising air will start a syphon bringing up deep water with it. We just need to get the flow moving and only need to add a little energy as we are only trying to overcome the difference in density, not trying to lift the water above the surface level. Not many moving parts. Machine parts all stay above the surface.

    Water invented man so it could go up hill.

  17. Lewis Cleverdon says:

    Rabid D -

    sorry to say that googling : nasa modis image gallery
    will bring up an archive that includes recent satellite images of hydrogen sulphide “eruptions” off the coast of Namibia in the south Atlantic.

    I’d no idea the issue was that far advanced.

    For me it affirms the fact that we need to get much more ruthless intellectually in identifying the necessary path to resolving the warming problem.

    Chin up!



  18. Chris Winter says:

    Gord wrote: “Why not build many small pumps that can pump water downward a couple of hundred feet. Suspend them on cables from floats that house the power supply, either solar, wave, wind, or some other non-polluting electric power supply. Scores of these small pumps could be attached at intervals along the length a cable and move the water downward in many stages. The cable would be anchored to the bottom to keep the assembly in place and not a become hazard to navigation. I’m thinking that garden hose size but a million times over is the cheap and efficient way to go.”

    Picture a large cylinder in a tube that’s hundreds of feet long. The cylinder could be made of anything that’s sturdy and won’t corrode. Overall, it has to be denser than water. Hang it from a cable and it can be lowered to push the column of surface water into the depths. If it has louvers on top and bottom, open these before winching it back up. Repeat as necessary. Size and scale as necessary.

  19. Here is another paper on the subject that is available to all:


  20. Mike says:

    An interesting resource on marine issues.

    Marine Climate Change Impacts Partnership

  21. Mike says:

    @#15: The paper is from 1989 and is about the likely reduced flow of fresh water into the Black Sea. I don’t see how it is related to climate change.

  22. mike roddy says:

    Thanks to the excellent comments and links.

    Peter Ward gave the Faculty Lecture at UW this year, and I was lucky enough to briefly chat with him afterwards. He’s a fascinating guy, with wide interests, and does a lot of fieldwork, too. All of his books are good, and my own favorite is Rare Earth.

  23. DrD says:

    Several posts have mentioned Dr. Peter Ward. I also read Under a Green Sky a year or so ago and came away impressed and convinced that widespread species extinction is possible (likely?) in the next millenium. This weekend I read Ward’s newest book, The Flooded Earth: Our Future in a World Without Ice Caps. I highly recommend it. Ward repeatedly points out that many models that try to predict the next 100 years or so often fail to account for sea level rise, not only in its impact on the human and built environment but also its impact in increasing the rate of global warming and sea level rise. That is, sea level rise will create more sea level rise as heat absorbing water replaces energy reflecting land and leads to more melting of the Greenland and Anartic ice sheets. Much more to it than what I’ve mentioned here, but I strongly recommend Ward’s new work. One warning: Don’t expect to come away from the book feeling very optimistic about your grandchildren’s future. (We added another granddaughter this weekend. Good luck little Juliette Lauren.)

  24. DrD says:

    #23 Anarctic ice sheets

  25. Gord says:

    Thanks for your encouragement.

    Here’s my top level design.

    Each upweller consists of five parts: a tethering device, a covered flexible cylindrical container looking somewhat like an overturned water glass which separates the water column from its surroundings, pumps located at the top to empty the water column, an electronics package and the power supply. The covered top will contain buoyancy devices which will stretch the container to prevent collapse as the water is pumped out at the top. Everything can be located below the surface to save it from wave action.

    If the power supply is required to be on the surface then it must have the capability to be submerged by remote command to avoid damage in storms.

    There it is.

    The unit mass production cost goal should be somewhere in the neighbourhood of $100k. We should set a goal of having a final pre-production prototype ready to go by 2020 with massive deployment by 2025.

    It would be nice to have a foundation offer prizes for the best designs. The Internet could be leveraged to crowd-source them.

    World wide brain power at work!!

  26. James Newberry says:

    So let me get this straight. Soon we will have lost half of all ocean phytoplankton, even as as most marine life crashes. Even as we have destroyed tropical forests over the past few decades at the rate of one acre per second, we will soon witness the collapse of world forests.

    What will we breath? Those phytoplankton and trees make atmospheric OXYGEN.

    The human economic organism has become . . . (insane, suicidal, genocidal, murderous, a sickly myth)? And we worry about health care!

  27. catman306 says:

    Leif, I think your ‘straw’ idea will honestly work. It works in countless designs of aquarium filters. I had the thought of piping major rivers to the bottom of the deep sea and didn’t like the engineering myself.

    Do we really want to bring up cold water from the bottom of the oceans?
    Actually, that sounds like a really good idea. It might lower sea surface temperatures as well as upwelling nutrients.

    Millions of 4 inch straws, anchored in place, fixing the ocean that we’ve broken and helping cool the planet. Excellent!

  28. Prokaryotes says:

    Ocean pipes could help the Earth to cure itself

    We propose a way to stimulate the Earth’s capacity to cure itself, as an emergency treatment for the pathology of global warming.Measurements of the climate system show that the Earth is fast becoming a hotter planet than anything yet experienced by humans. http://www.nature.com/nature/journal/v449/n7161/full/449403a.html

  29. Leif says:

    catman306, @ 24. Actually I was thinking of much bigger “straws.” They would not need to be very heavily built Something like wire coil Dryer hose many feet in diameter. Perhaps 50 feet below the top place ring of perforated pipe around the inside perimeter to bubble low pressure air in. 50 psi would get you ~100 feet down. There would be no need for heavy construction as there is no suction to speak of. I do not believe that the bottoms would even need to be that deep as a field perhaps a thousand feet deep would draw water from much deeper if properly placed to take advantage of natural up welling. One decent sized wind mill in the center of a ring of tubes would move a lot of water. Proper engineering should even get the center un-straw water to up well as well. This is the oceans we are talking about. Big area! The key would be to work with nature as much as possible.

    In reality however keeping it all together in an ocean environment??? …

  30. Ken says:

    CEPD (Chronic Earth Pulmonary Disease)

    Forests provide us with essential oxygen, and are referred to as “the lungs of the earth”. In the year 1800, there were about 23,000,000,000 hectares of forest for earth’s 980,000,000 population. For 2011, earth’s population of 7,000,000,000 will share about 5,000,000,000 hectares of forest. This represents a decline of 97%, from 23.4 hectares of forest per person in 1800, to 0.7 hectares per person in 2011. An average tree absorbs ten pounds of pollutants from the air each year, including four pounds of ozone and three pounds of particulates. Robert Sloan, Professor Department of Geology and Geophysics University of Minnesota, found the percentage of oxygen in air samples from dinosaur-era amber at 28% – 35%. Currently, dry air contains about 20.94% oxygen. An Australian government research organization calculated recent declines in atmospheric oxygen at about 0.15% per century.