Trapped by deep ocean pressure and cold temperatures along continental shelves, methane hydrates could be an energy windfall or a looming disaster. Norway is spending millions to discover whether this ice-like form of natural gas will prove boon or bane.
The landers lashed to the aft deck of the R/V Helmer Hanssen held firm as waves crashed into the ship. The two golf-cart-sized crafts, stocked with scientific instruments, appeared ready for planetary exploration, but in a few hours, they would be winched down to the seafloor off the coast of Svalbard, about 1,300 kilometers (800 miles) from the North Pole. If all went well, the landers would stay there for a year, powered by half a tonne of lithium batteries, monitoring the methane bubbles seeping from the seabed.
As a greenhouse gas, methane is 25 times more potent than carbon dioxide (CO2). Scientists have found that oceans absorb much of the methane bubbling up from seafloor seeps, but they don’t quite know how much. And their real worry is the 10,000 gigatonnes of methane trapped worldwide as a solid beneath the seafloor in the form of methane hydrate. With ocean temperatures on the rise, methane hydrates pose a threat far greater than the seeps. Although hydrates also exist on land beneath permafrost, 99 percent of known reserves are buried beneath the seafloor. Some of Norway’s largest reservoirs lie right along the continental shelf, where a slight rise in temperature could thaw the methane hydrates — and unleash vast quantities of the gas, slowly over time — or possibly quite quickly.
“Methane hydrates serve as a kind of cement of the sediments. Our fear is that if the cement gets dissolved, sediment might slide down the [continental shelf] slope,” Peter Linke told me in the instrument room of the Hanssen. Linke, a marine biologist from the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, works closely with researchers from Norway’s Centre for Arctic Gas Hydrate, Environment and Climate (CAGE), and was aboard the research cruise to supervise the deployment of the two landers, worth a half million dollars each. “If a large volume of sediment is moving, this might cause a tsunami, which has happened before.” Some 8,000 years ago, an earthquake along Norway’s southern coast triggered a catastrophic expansion of methane hydrates, unleashing a tsunami that washed over a landmass the size of Iceland.
Where climatologists see great peril, energy companies see great promise. Methane hydrate can expand 160 times its volume when it is transformed to methane, a gas. Japanese scientists have succeeded in extracting methane from seafloor hydrates, but like oil extraction, this could be a risky business. Disturbing hydrates in the seafloor could destabilize them and initiate a vicious cycle: More methane in the atmosphere creates warmer oceans, which, in turn, further destabilize hydrates.
In a methane hydrate, the gas molecule is actually trapped in a “cage” of water molecules. Hydrates look and feel like ice, but are not a frozen gas. They are actually more akin to minerals because they have a geometric architecture rather than a random structure like true ice. Another distinction: Unlike frozen water, a lump of methane hydrate can be set on fire.
The deep sea’s low temperatures and high pressure keep hydrates safely locked away, but along Svalbard’s continental shelf, they occur in relatively shallow waters near the top of the seabed. Even a small change in water temperature near the seafloor there could initiate a meltdown. No one is sure how much methane the oceans can absorb before releasing excess gas into the atmosphere. It’s an important question the scientists on board the Hanssen hope to answer by studying the dynamics of methane in the water column.
Surprisingly, some scientists say that, in certain cases, methane seeps might even be associated with removing other greenhouse gases from the atmosphere. John Pohlman, a biogeochemist at the U.S. Geological Survey at Woods Hole, calls it the Seep Fertilization Hypothesis. “On this same survey last year, I noticed that where methane content was highest at the surface, there was also a depletion of carbon dioxide in the water,” he said. “The release of methane bubbles from the seafloor seems to stimulate uptake of CO2 from the water, which leads to uptake of CO2 from the overlying atmosphere.”
Pohlman and his colleagues, including biochemist Helge Niemann of the University of Basel in Switzerland, are running experiments to measure the dynamics of methane and carbon dioxide along our survey route to better understand the fate of these greenhouse gases, and what might happen if methane hydrates buried in the sea floor become destabilized.
According to Pohlman’s hypothesis, as methane bubbles upward, it pumps nutrient-rich deep water to the surface that encourages the algae there to grow. The algae consume carbon dioxide (as plants do), removing carbon dioxide from the ocean, which then absorbs more carbon dioxide from the atmosphere.
But not all of the methane makes it to the surface. Bacteria on the seafloor, called methanotrophs, consume some of the gas – and Niemann wants to know how much. “Think of it like a dinner table and our guests are methanotrophs,” Niemann explained. “We want to know how hungry they are, how many they are, and who they are.”
To measure how much methane the bacteria can eat, Niemann and his assistant added radioactive methane to vials of methanotrophs throughout the week. When active, methanotrophs produce carbon dioxide and water. The amount of radioactive water produced in such samples reveals how much the bacteria eat.
To tally his “guests,” Niemann added a fluorescing solution that lights up the bacteria’s DNA and allows him to count them under a fluorescence microscope. Later, he reconstructed his “guest list” by cloning tiny bits of DNA to identify individual species.
Once we were in position off the coast of Spitsbergen island, Linke and several German engineers lowered the landers to the seafloor. Each machine held three separate sensors for measuring methane, carbon dioxide and pH (acidity), plus sonars to monitor gas bubbles, a meter to detect algal blooms and an instrument to track ocean currents.
Each deployment seemed like a moon landing. As we watched live video from the ship’s command center, a screen of blue nothingness suddenly came to life with images of a rocky seafloor punctuated by the escape of methane bubbles.
The challenge for Linke and his engineers was to position each lander among the methane seeps rather than on top of them so it could make the best observations. With a click of the computer keyboard, the explosives detonated, separating each launcher from its payload and allowing it to settle onto the seafloor.
Over the next four days, scientists pulled deep water samples at 65 separate points, working continuously in rotating shifts, catching sleep when they could. By the end of the week, exhausted and bleary eyed, Pohlman had found several clear instances where the carbon dioxide levels noticeably dropped above methane seeps.
Whether such seeps prove to be greenhouse gas sponges or not, the bigger concern remains their cousins, methane hydrates. Just a few miles further offshore, in deeper waters, CAGE has also been investigating methane hydrates along the continental shelf edge and found that they lie so close to the seabed surface under relatively marginal pressure, that the slightest rise in ocean temperature could destabilize them.
Scientists have already seen this happen off Washington and Oregon. Last October, scientists at the University of Washington published a study showing that methane bubble plumes off the coast were emanating from depths where only methane hydrates occur. They speculated that anomalous warm currents from Siberia, which they had previously identified in the same location, might be melting the hydrates.
As the oceans warm, researchers are racing to make informed predictions – and provide possible solutions. Linke and his colleagues at GEOMAR have a proposal. They have developed a way to replace the methane in the hydrate with carbon dioxide. They call it SUGAR, since the cage-like structure of that sweet molecule resembles the gas hydrate molecule. GEOMAR has successfully tested the method in their labs and is now running trials in the Black Sea. If successful, the swap would allow energy companies to harvest methane and bury carbon dioxide beneath the seafloor. The process also forms a compound that is more stable and heat tolerant than its original – the methane hydrate. If SUGAR bears fruit, hydrates could sweeten the energy pot for nations worldwide rather than wreak havoc on the atmosphere.
As Arctic coal and oil lose their glow and petroleum giants like Royal Dutch Shell walk away from billions of dollars of investment in Arctic oil exploration, natural gas grows ever more attractive. It is widely seen as a cleaner fossil fuel used increasingly in power plants, home heating and vehicles. If extraction of methane hydrates on an industrial scale becomes viable, many nations will have access to substantial reserves along their coasts. With the Arctic warming twice as fast as the global average, Norwegian research on methane hydrates is very much on the front burner.
Randall Hyman was a 2015 Alicia Patterson Foundation Fellow.