Methane bubbles trapped in the ice of a Siberian lake in 2003.
Mapping methane bubbles in the ice helps researchers estimate
how much methane escapes from lakes each year.
Photo: Katey Walter
Vast quantities of methane bubbled from Arctic lakes at the end of the Ice Age, triggering a dramatic spike in the concentration of the super-greenhouse gas in the atmosphere that in turn may have propelled further warming, according to research team led by scientist Katey Walter at the University of Alaska Fairbanks.
This ancient methane jolt — showing up in ice cores deposited between 14,000 and 11,700 years ago — had so far gone unexplained. But its source was almost certainly lakes amid the thermokarst of melting permafrost, Walter and her team argue.
The warming of these lakes could have produced up to 87 percent of the ancient methane spike, said Walter, lead author of a report published in the Oct. 26 issue of the journal of Science.
Walter and other scientists have found a similar process occurring in modern times, with far more methane bubbling out of Far North lakes than anyone realized.
The new insight into the ancient methane blast could help scientists pin down how Arctic warming will impact methane concentrations in the atmosphere during coming decades — and how this rise of methane may accelerate the greenhouse effect.
“It tells us that this isn’t just something that is ongoing now. It would have been a positive feedback to climate warming then, as it is today,” Walter says in a
UAF online story.
“We estimate that as much as 10 times the amount of methane that is currently in the atmosphere will come out of these lakes as permafrost thaws in the future.”
UAF writer Marmiam Grimes has more details:
Ice cores from Greenland and Antarctica have shown that during the early Holocene Period — about 14,000 to 11,500 years ago — the levels of methane in the atmosphere rose significantly, Walter said.
UAF researcher Katey Walter
lights a pocket of methane on
a thermokarst lake in Siberia
in March of 2007. Igniting the
gas is a way to demonstrate,
in the field, that it contains
methane.
Photo: Sergey Zimov -“They found that an unidentified northern source (of methane) appeared during that time.”
Previous hypotheses suggested that the increase came from gas hydrates or wetlands. This study’s findings indicate that methane bubbling from thermokarst lakes, which are formed when permafrost thaws rapidly, is likely a third and major source.
Walter’s research focused on areas of Siberia and Alaska that, during the last ice age, were dry grasslands atop ice-rich permafrost. As the climate warmed, Walter said, that permafrost thawed, forming thermokarst lakes.
“Lakes really flared up on this icy permafrost landscape, emitting huge amounts of methane,” she said.
As the permafrost around and under the lakes thaws, the organic material in it — dead plants and animals — can enter the lake bottom and become food for the bacteria that produce methane.
“All that carbon that had been locked up in the ground for thousands of years is converted to potent greenhouse gases: methane and carbon dioxide,” Walter said. Walter’s paper hypothesizes that methane from the lakes contributed 33 to 87 percent of the early Holocene methane increase.
To arrive at the hypothesis, Walter and her colleagues traveled to Siberia and northern Alaska to examine lakes that currently release methane. In addition, they gathered samples of permafrost and thawed them in the laboratory to study how much methane permafrost soil can produce immediately after thawing.
“We found that it produced a lot very quickly,” she said.
Finally, she and other researchers studied when existing lakes and lakes in the past formed and found that their formation coincided with the early Holocene Period northern methane spike.
“We came up with a new hypothesis,” she said. “Thermokarst lake formation is a source of atmospheric methane today, but it was even more important during early Holocene warming. This suggests that large releases from lakes may occur again in the future with global warming.”
Co-authors on the paper include Mary Edwards of the University of Southampton and the UAF College of Natural Science and Mathematics; Guido Grosse, an International Polar Year postdoctoral fellow with the UAF Geophysical Institute; Sergey Zimov of the Russian Academy of Sciences; and Terry Chapin of the UAF Institute of Arctic Biology.
