With the combination of the aggressive warming occurring in the Arctic and the shallow water depths, any released methane has a short journey from emission at the seafloor to release into the atmosphere.
The researchers used radiocarbon dating to fingerprint the origin of methane from their samples.
Up to 2500 ppb CO in the air samples was quantitatively removed using the Sofnocat reagent.
14C procedural blanks were greatly reduced through the construction of a new CH4 conversion line utilizing platinized quartz wool for CH4 combustion and the use of an ultra-high-purity iron catalyst for graphitization.
In addition to methane hydrates, carbon-rich permafrost that is tens of thousands of years old—and found throughout the Arctic on land and in seafloor sediments—can produce methane once this material thaws in response to warming.
Exponentially less methane would be able to reach the atmosphere in waters that are thousands of feet deep at the very edge of the shallow seas near continents, which is the area of the ocean where the bulk of methane hydrates are," Sparrow says.
"Our data suggest that even if increasing amounts of methane are released from degrading hydrates as climate change proceeds, catastrophic emission to the atmosphere is not an inherent outcome." Sparrow and Kessler's results on the role of ancient methane sources are consistent with the findings of their Rochester colleague Vasilii Petrenko, an associate professor of earth and environmental sciences, who also radiocarbon dated methane.
By employing a technique they developed that involves collecting methane from roughly ten thousand gallons of seawater per sample, they made a surprising discovery: ancient-sourced methane is indeed being released into the ocean; but very little survives to be emitted to the atmosphere, even at surprisingly shallow depths.
"We do observe ancient methane being emitted from the seafloor to the overlying seawater, confirming past suspicions," Kessler says.
Credit: University of Rochester photo / John Kessler Trapped in ocean sediments near continents lie ancient reservoirs of methane called methane hydrates.