In the Arctic Ocean, between Norway and the North Pole, is a small archipelago called Svalbard. Covered mostly with glaciers, the people of Svalbard have snowmobiles, not cars. However, off the coast of these islands, the shallow ocean is warming and releasing methane into the atmosphere. Something strange is also happening.
In the summer of 2014, from onboard the research vessel Helmer Hanssen, a group of researchers obtained the surface water concentrations of two greenhouse gases – carbon dioxide and methane – over a 1,600-km-long stretch on the western Svalbard coast. They found the methane seeping into the atmosphere, as they had anticipated. However, the amount of carbon dioxide took them by surprise. It was almost as if it wasn’t there.
Methane is a powerful greenhouse gas: it can hold 30-times as much heat as carbon dioxide. Large quantities of methane are stored in seabeds in natural gas reservoirs, the permafrost and methane clathrates (crystals containing relatively large quantities of methane). These sources release the trapped methane gradually and the quantities released have varied over time.
With the global mean temperature on the rise, however, there has been an especially high increase in the amount of methane released because of the melting permafrost. While scientists continue to debate if this is a recent phenomenon or if it has been happening for a long time, there is also a fear of an abrupt and catastrophic change in the climate if the rates of emission continue to climb. And greater the amount of methane released, more of the trapped heat is freed as well, making the world warmer, melting more ice and leading to a runaway chain of events.
At this juncture, a new study stands to offer a ray of hope. “We wondered to what extent carbon dioxide contributed to the total greenhouse gas input in areas of methane seepage,” John Pohlman, of the US Geological Survey and an author of the study, told The Wire. Published last month, the study found that while methane is being released into the atmosphere from the shallow ocean-bed off the coast of Svalbard, almost 2,000-times as much carbon dioxide has been absorbed by the ocean.
In other words, if the methane seeps caused X units of warming, then the carbon dioxide uptake resulted in 230X units of cooling.
Additionally, the amount of carbon dioxide absorbed over the methane seeps was twice as much as what was absorbed in other areas. This could have big implications for global warming – but let’s not get ahead of ourselves. M.M. Sarin, who studies atmospheric chemistry at the Physical Research Laboratory, Ahmedabad, cautioned, “You cannot say one-to-one, you have to look at the [whole] scenario.”
There are only two natural sinks for carbon dioxide: land and water. They absorb about 55% of the carbon dioxide emitted by humans; the ocean accounts for 25% and land, about 30%. The remaining 45% of the gas stays in the atmosphere. Starting from about 280 ppm in the pre-industrial age, the atmospheric carbon dioxide content today is just above 400 ppm. Scientists have estimated that it will continue to rise until emissions are cut down to nearly zero.
Back in Svalbard, the researchers were curious about why such vast amounts of carbon dioxide were being absorbed in regions over the methane seeps.
“Carbon dioxide uptake is enhanced in the areas of the seep, but it is probably not related directly to the presence of methane,” Pohlman explained. “The likely relationship is that the same physical process transporting methane from the seafloor to the surface also transports nutrients utilised by algae in the sunlit surface waters.”
“We know this because where the surface waters were depleted in carbon dioxide and enriched with methane, they are also significantly colder, which is a certain indicator that deep – and presumably nutrient-rich – water was upwelled to the surface.”
Such a phenomenon has been observed in the western side of continents thanks to the broad and slow-moving oceanic eastern boundary currents – but it had not been seen before with methane seeps. The carbon dioxide depletion was also accompanied by a small increase in the pH (from 8.1 to 8.2), indicating that the dissolved gas had been removed by photosynthesis and hadn’t been absorbed by the waters.
Although the algae have used up the carbon dioxide, it may not mean cooling over the long-term. “The most important point here is how long the absorbed carbon dioxide remains in the waters,” said V.V.V.S. Sarma, who studies the biogeochemical cycling of carbon and nitrogen in oceans at the National institute of Oceanography, Visakhapatnam. The respiration or decomposition of such organisms leads to carbon dioxide production over a few days to a few weeks, which was not considered in the study, he said.
The Arctic is warming twice as fast as other regions by some estimates and scientists have been busy trying to get a grip on the implications. Most reports on the topic originate from the Siberian Arctic, indicating large quantities of methane have been bubbling from the seabed into the atmosphere around this area. The eastern Siberian Arctic is a shallow shelf, around 5.1 million square km in area mostly covered in permafrost, so methane doesn’t have to travel far to reach its surface.
Although there have been no studies on carbon dioxide absorption in the Siberian seas yet, Pohlman thinks the same enhanced uptake of the gas will be seen there as well.
As does its net effect on warming at a global scale. Although new methane seeps are being discovered regularly, and while there is usually an upward revision in the amount of gas emitted, estimates say the methane released into the atmosphere from all possible seeps will only be about 0.03% of the total methane emissions (natural + man-made). What is unknown is if all of the seafloor methane will be released abruptly or gradually. Gradual release has always been happening, but if all the methane is released abruptly, there are fears of rapid warming in an extremely short time, with disastrous consequences.
The ocean’s waters have always been carbon dioxide sinks.? “When you talk about the global scenario you cannot say the Arctic is going to be the next available sink for carbon dioxide, so let us keep on pumping more carbon dioxide,” said Sarin.
In addition, Jürgen Mienert, the director of the Centre for Arctic Gas Hydrate, Environment and Climate (CAGE) at the University of Tromsø, Norway, which was part of the study, sounded a cautionary note in a press release: “But we do need to keep in mind that these studies are very local to this area of Svalbard. More global research and international collaboration is needed to see if these are global trends.”
Pohlman also agrees that it is too early to say how the magnitude of the increased absorption of carbon dioxide will affect the global greenhouse gas balance. A question also remains as to what will happen in the winter, when the amount of sunlight will be minimal.
This study is just a piece in the complex balance of different gases being emitted and absorbed on Earth’s surface. Additional investigations will necessary before we can fully understand its impact on a global scale.
Lakshmi Supriya is a freelance science writer based in Bangalore.