Ocean absorption of carbon dioxide compensates for emissions from seafloor methane seeps

Ocean absorption of carbon dioxide compensates for emissions from seafloor methane seeps
USGS geochemist John Pohlman monitoring data from the USGS Gas Analysis System (GAS) that continuously measured carbon dioxide and methane concentrations in near-surface waters and in the air on the western Svalbard margin. Credit: United States Geological Survey

The ocean waters near the surface of the Arctic Ocean absorbed 2,000 times more carbon dioxide from the atmosphere than the amount of methane that escaped into the atmosphere from the same waters, according to a study by the USGS Gas Hydrates Project and collaborators in Germany and Norway. The study was conducted near Norway's Svalbard Islands, above several seafloor methane seeps.

Methane is a more potent greenhouse gas than carbon dioxide, but the removal of carbon dioxide from the atmosphere where the study was conducted more than offset the potential warming effect of the that were observed.

"If what we observed near Svalbard occurs more broadly at similar locations around the world, it could mean that have a net cooling effect on climate, not a warming effect as we previously thought," said USGS biogeochemist John Pohlman, who is the paper's lead author. "We are looking forward to testing the hypothesis that shallow-water methane seeps are net greenhouse gas sinks in other locations."

During the study, scientists continuously measured the concentrations of methane and carbon dioxide in near-surface waters and in the air just above the ocean surface. The measurements were taken over methane seeps fields at water depths ranging from 260 to 8530 feet (80 to 2600 meters).

Analysis of the data confirmed that methane was entering the atmosphere above the shallowest ( depth of 260-295 feet or 80-90 meters) Svalbard margin seeps. However, the data also showed that significant amounts of carbon dioxide were being absorbed by the waters near the ocean surface, and that the cooling effect resulting from carbon dioxide uptake is up to 230 times greater than the warming effect expected from the methane emitted.

Ocean absorption of carbon dioxide compensates for emissions from seafloor methane seeps
Research vessel Helmer Hanssen of UiT – The Arctic University of Norway offshore of the Svalbard Islands. Credit: Randall Hyman

Most previous studies have focused only on the sea-air flux of methane overlying seafloor seep sites and have not accounted for the drawdown of carbon dioxide that could offset some of the atmospheric warming potential of the methane.

Photosynthetic algae (marine phytoplankton) appeared to be more active in the near-surface waters overlying the seafloor methane seeps, a phenomenon that would explain why so much carbon dioxide was being absorbed. Previous research has shown that when cold, nutrient-rich waters come up from the depths, algae near the surface can use the nutrients to enhance their photosynthetic processes, resulting in more dioxide being absorbed from the atmosphere. However, this study is the first to make this observation where methane-rich waters rise to the surface.

Jurgen Mienert, the director of the Centre for Arctic Gas Hydrate, Environment and Climate (CAGE) at the University of Tromso, Norway, said, "At CAGE, we are fortunate to have access to expertise, equipment, and a ship platform that allow us to launch sustained research focused on the Arctic Ocean. Collaborating with the USGS Gas Hydrates Project and GEOMAR on the important issue of sea-air flux of greenhouse gases above seafloor methane seeps has been rewarding for all of the researchers involved."

Ocean absorption of carbon dioxide compensates for emissions from seafloor methane seeps
Ocean waters overlying shallow-water (260-295 feet; 80-90 meters) methane seeps (white dots) offshore the western margin of the Svalbard Islands absorb substantially more atmospheric carbon dioxide than the methane that they emit to the atmosphere.  Colors indicate the strength of the negative greenhouse warming potential associated with carbon dioxide influx to these surface waters relative to the positive greenhouse warming potential associated with the methane emissions.  Gray shiptracks have background values for the relative greenhouse warming potential.  Credit: United States Geological Survey

The research was conducted during a research expedition sponsored by CAGE, and supplementary data was collected by researchers from CAGE and the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany. USGS involvement in the Svalbard margin expeditions was partially supported by the U.S. Department of Energy.

The USGS Gas Hydrates Project is an international leader in the study of methane dynamics related to environmental and energy issues. In addition to the expeditions on the Svalbard margin, USGS has studied the interchange between and at the in Alaska's Beaufort and Bering Seas, on the U.S. Atlantic margin, and in the Baltic and North Seas.

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More information: John W. Pohlman et al. Enhanced CO uptake at a shallow Arctic Ocean seep field overwhelms the positive warming potential of emitted methane, Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1618926114
Citation: Ocean absorption of carbon dioxide compensates for emissions from seafloor methane seeps (2017, May 9) retrieved 17 October 2019 from https://phys.org/news/2017-05-ocean-absorption-carbon-dioxide-compensates.html
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May 09, 2017
Earthling - you seem to be saying that unless we already understand everything about a topic - we should not study it. Of course climate science is emergent - and as new information comes in - models are adjusted. It does not mean "we have no idea." Models have proven critical in predicting where we are today - unless you deny the fact that we are in a warming trend.

May 09, 2017
If we stopped researching such topics and just claim ignorance as you say, it might be good for the cavemen wanting die happy and ignorant. I believe though you will find most tax payers are not just cavemen, but understand researching and understanding our environment in fact is a worthy project for the tiny fraction of the tax we pay.

Only about 2% of all US collected tax money go to "Science and medical research", see: http://www.cbpp.o...llars-go

May 10, 2017
Glad to see several recent studies confirm something that seems intuitive/common sense to me. A planet where life has existed for billions of years has built-in mechanisms to deal with changing conditions. One of the flaws in the way that climate change has been presented to the public is the assumption that Nature cannot deal with change, and change is inherently "bad". This is not justification for inaction but it's a call for toning down the alarmist rhetoric. People are justified in their mistrust of those who are willing to hyperbolize facts and narratives to suit their own purposes.

May 10, 2017
Earthling - then why do you use terms such as "we have no idea?" We do have an idea. We have a huge volume of research - that gives us a lot of information. It is the people who deny the science - that I label anti science. I am not up for 'let's roll the dice - and see what happens'. I would rather we paid attention to the formidable body of knowledge that we have developed.

May 12, 2017
I am not discounting science
Yes you are. Re-read this one statement - "The "huge volume of research" that you refer to has not told us anything definitive." You are the one politicizing. The research into the climate has given us volumes of definitive information. Study up on Milankovich cycles - and see how much definitive information there is in that one topic.

May 16, 2017
I am not discounting science; I am merely saying that with politicized topics such as climate change, the cart has been placed several miles ahead of the horse
1- you are discounting science because you fear the application of it's research

2- there is no politicized debate about the facts (the science), there is only politicized debate about what to do about it
he "huge volume of research" that you refer to has not told us anything definitive

you are either not reading the science or you're not paying attention to anything you don't like because of your political or other motivations and that comment proves it

a validated study is a scientific fact, yet you're ignoring validated studies all over PO climate threads because ... why?
We need to back up, analyze things more closely
people like you politicizing the results of studies while blatantly misrepresenting facts like above are the reason there are deniers, BTW

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