As oceans warm, microbes could pump more CO2 back into air, study warns

As oceans warm, microbes could pump more CO2 back into air, study warns
Aboard the German research vessel Sonne in the South Pacific, study author Frank Pavia (left, foreground) prepares pumping apparatus used to sample seawater for organic matter. Credit: Frank Pavia

The world's oceans soak up about a quarter of the carbon dioxide that humans pump into the air each year—a powerful brake on the greenhouse effect. In addition to purely physical and chemical processes, a large part of this is taken up by photosynthetic plankton as they incorporate carbon into their bodies. When plankton die, they sink, taking the carbon with them. Some part of this organic rain will end up locked into the deep ocean, insulated from the atmosphere for centuries or more. But what the ocean takes, the ocean also gives back. Before many of the remains get very far, they are consumed by aerobic bacteria. And, just like us, those bacteria respire by taking in oxygen and expelling carbon dioxide. Much of that regenerated CO2 thus ends up back in the air.

A new study suggests that CO2 regeneration may become faster in many regions of the world as the oceans warm with changing climate. This, in turn, may reduce the deep oceans' ability to keep locked up. The study shows that in many cases, bacteria are consuming more plankton at shallower depths than previously believed, and that the conditions under which they do this will spread as water temperatures rise. The study was published this week in the journal Proceedings of the National Academy of Sciences.

"The results are telling us that warming will cause faster recycling of carbon in many areas, and that means less carbon will reach the and get stored there," said study coauthor Robert Anderson, an oceanographer at Columbia University's Lamont-Doherty Earth Observatory.

Scientists believe that plankton produce about 40 billion to 50 billion tons of solid organic carbon each year. They estimate that, depending on the region and conditions, about 8 billion to 10 billion tons manage to sink out of the into greater depths, past about 100 meters, without getting eaten by bacteria. However, scientists have had a poor understanding of the depths at which CO2 is respired, and consequently, of the rate at which it is returned to the atmosphere. The new study zeroed in on this question, with surprising results.

Using data from a 2013 research cruise from Peru to Tahiti, the scientists looked at two distinct regions: the nutrient-rich, highly productive waters off South America, and the largely infertile waters that circle slowly in the central below the equator in a set of currents known as the South Pacific Gyre.

To measure how deep organic particles sink, many oceanographic studies use relatively primitive devices that passively trap particles as they sink. However, these devices can collect only a limited amount of data over the vast distances and depths of the ocean. For the new study, the researchers instead pumped large amounts of seawater at different depths and sifted through it. From these, they isolated particles of organic carbon and isotopes of the element thorium, which together enabled them to calculate the amount of carbon sinking through each depth that they sampled. This procedure yields far more data than traditional methods do.

As oceans warm, microbes could pump more CO2 back into air, study warns
Researchers prepare to lower pumps overboard to sample seawater. Credit: Frank Pavia

In the fertile zone, oxygen gets used up quickly near the surface, as bacteria and other organisms gobble up organic matter. At a depth of about 150 meters, oxygen content reaches near zero, halting aerobic activity. Once organic material reaches this layer, called the oxygen minimum zone (OMZ) it can sink untouched to the deeper ocean. The OMZ thus forms a sort of protective cap over any organic matter that sinks past it. In the deeps, oxygen levels pick up again and aerobic bacteria can go back to work; however, any CO2 produced down that far will take centuries to get back into the air via upwelling currents.

Up to now, many scientists have thought much of the organic matter produced near the surface makes it through the OMZ, and thus most CO2 regeneration would take place in the deep ocean. However, the researchers' measurements suggested that actually only about 15 percent makes it this far; the rest is converted back to CO2 above the OMZ.

"People did not think that much regeneration was taking place in the shallower zone," said the study's lead author, Frank Pavia, a graduate student at Lamont-Doherty. "The fact that it's happening at all shows that the model totally doesn't work in the way we thought it did."

This matters because researchers project that as the oceans warm, OMZs will both spread horizontally over wider areas, and vertically, toward the surface. Under the conventional paradigm, this would allow more organic matter to reach the deep ocean to get trapped there. However, the new study suggests that as OMZs spread, so will the vigorous CO2 regeneration above them. This would counteract any increased trapping of organic matter below the OMZ. Which effect—near surface regeneration or the cap provided by the OMZ—might win out is a question for more research, says Pavia. But the discovery implies that the spread of OMZs might not be as beneficial as previously thought. (At least not for carbon storage; OMZs are harmful, in that they kill off much marine life in what are now important fishing areas.)

Further out, in the South Pacific Gyre, the results were less ambiguous. There is less biologic activity here than above the OMZs because of lack of nutrients, and previous research using sediment traps has suggested that much of whatever does form on the surface sinks to the cold deeps. Some CO2 regeneration takes place there, but it would take centuries for the gas to resurface. However, the new study found the opposite: there is far more regeneration near the warmer surface than previously estimated by some studies.

This matters because, like OMZs, the South Pacific Gyre and similar current systems in other parts of the oceans are projected to grow as the oceans warm. The gyres will divide these regions into stratified layer cakes of warmer waters on top and colder waters below. And because, according to the study, so much CO2 regeneration will take place in the warm, shallower waters, more CO2 will end up going back into the air over wider regions. And unlike below the nearer-shore OMZs, "there is no counterbalancing effect in the gyres," said Anderson. "The story with the gyres is that over wide areas of the ocean, carbon storage is going to get less efficient." (There are four other major gyres: the north Pacific, the south and north Atlantic, and the Indian Ocean.)

The researchers point out that the processes they studied are only part of the ocean carbon cycle. Physical and chemical reactions independent of biology are responsible for much of the exchange of carbon between atmosphere and oceans, and these processes could interact with the biology in complex and unpredictable ways. "This [the study] gives us information that we didn't have before, that we can plug into future models to make better estimates," said Pavia.


Explore further

New view of how ocean 'pumps' impact climate change

More information: Frank J. Pavia el al., "Shallow particulate organic carbon regeneration in the South Pacific Ocean," PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1901863116
Citation: As oceans warm, microbes could pump more CO2 back into air, study warns (2019, April 29) retrieved 22 July 2019 from https://phys.org/news/2019-04-oceans-microbes-co2-air.html
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Apr 29, 2019
How can you say what will happen. Make an equation to take into account what will happen with 200,000 different species of viruses in the ocean. It is impossible. https://www.scien...r-oceans Almost 200,000 Never-Before-Seen Viruses Were Just Discovered Hidden in Our Oceans
Scientists are arrogant if they think their statistics can predict this.

Apr 30, 2019
How can you say what will happen
Isn't that the point of science? To study stuff, and try to understand what will happen?
Scientists are arrogant if they think their statistics can predict this
So what do you suggest? Just give up - and don't try to understand stuff? Models need data. As the data comes in - we can improve the models. We can check the models against reality. Climate is indeed complex - as we see from this one tiny piece of the puzzle. But the models have proven accurate.
Climate models published since 1973 have generally been quite skillful in projecting future warming
https://www.carbo...-warming

Apr 30, 2019
Hi green onions1,
Carbon dioxide is a molecule. There is history to show there that shows a direct mechanism between earth temperature and carbon dioxide levels. When it comes to biology, viruses replicate so fast that in one week they could take over the whole mass of the universe. Bacteria as well could take over the whole mass of the universe in one week. Trying to predict the interactions of all the bacteria, viruses, fungi, parasites, archaea , etc is impossible because it would take all the world computers an infinite amount of time to say what would happen in the next day. We are powerless to change things in a way that we could control, and even more difficult to figure out what is better.

Apr 30, 2019
O.. goodness Grandpa forgot his meds at home again, he actually thinks he's got it all worked out, spewing the most pathetic drivel i have seen in a long time posted on here...
Soz granpa, your monkey science only convinces your own sockpuppets, Real science convinces the normal people in the world living in this reality.. ;)

Apr 30, 2019
Why all the insults? Feynman said the following about the electron, nature is just as complicated.
…It always bothers me that, according to the laws as we understand them today, it takes a computing machine an infinite number of logical operations to figure out what goes on in no matter how tiny a region of space, and no matter how tiny a region of time. How can all that be going on in that tiny space? Why should it take an infinite amount of logic to figure out what one tiny piece of space/time is going to do? So I have often made the hypotheses that ultimately physics will not require a mathematical statement, that in the end the machinery will be revealed, and the laws will turn out to be simple, like the chequer board with all its apparent complexities.

Apr 30, 2019
grandpa
When it comes to biology, viruses replicate so fast that in one week they could take over the whole mass of the universe
Do you have a reference to support that assertion grandpa? Are you saying that we should not study this topic - as it is so unpredictable. I have a friend who is a microbiologist. He runs a lab that studies one specific bacteria. I am certain that he would disagree with you strongly. What do you think we should do grandpa? Throw up our hands - and declare that studying bacteria and viruses to be a fools errand?

May 01, 2019
grandpa
I have a friend who is a microbiologist. He runs a lab that studies one specific bacteria. I am certain that he would disagree with you strongly. What do you think we should do grandpa? Throw up our hands - and declare that studying bacteria and viruses to be a fools errand?
One can only study microbiology for specific purposes. One can find a bacteria that will turn plant cell walls into a useful product. Some bacteria can double in number every 20 minutes. If one doubles every 20 minutes for 7 days it is 2^504=5.27*10^151 bacteria. More particles than the whole universe by a long shot.

May 01, 2019
If one doubles every 20 minutes for 7 days it is 2^504=5.27*10^151 bacteria. More particles than the whole universe by a long shot
So why is the universe not overrun with bacteria? Maybe have something to do with food source? So again I ask - are you proposing that we not study these organisms - cuz the situation is too complex? What is your proposal?

May 02, 2019
Why all the insults? Feynman said the following about the electron, nature is just as complicated.
…It always bothers me that, according to the laws as we understand them today, it takes a computing machine an infinite number of logical operations to figure out what goes on in no matter how tiny a region of space, and no matter how tiny a region of time. How can all that be going on in that tiny space? Why should it take an infinite amount of logic to figure out what one tiny piece of space/time is going to do? So I have often made the hypotheses that ultimately physics will not require a mathematical statement, that in the end the machinery will be revealed, and the laws will turn out to be simple, like the chequer board with all its apparent complexities.


You (antigoracle sockpuppet) is an insult onto yourself everyday ;)

May 04, 2019


You (antigoracle sockpuppet) is an insult onto yourself everyday ;) I know not this antigoracle person. The ocean is full of bacteria, the only thing that keeps them in check is competition. It is a battle that keeps humans in check and will eventually bring humans to their knees as well. Fight global climate change is a fools errand. It is an enemy with less than a billionth the power of geometric progression of microbiology.

May 05, 2019
What I would like to know Grandpa, is how you became so brainwashed by extremist environmental points of view.? It's obvious that you have no clue about science or any aspect of the impending Environmental apocalypse from global warming nor care. Climb out of you fox hole and maybe you get a clue.

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