New study measures permafrost changes with impacts to carbon cycle
Global warming is limiting the growth of seasonal ice on Arctic lakes, which could have implications for the global carbon cycle. new study accepted for publication in Geophysical Research Letters, permafrost beneath shallow Arctic lakes is starting to thaw — another sign of the widespread Arctic meltdown due to climate change.
Another recent study found that Arctic lakes in Canada’s northern archipelago are drying at an unprecedented rate. The findings also support previous University of Waterloo research on Arctic lake ice.
The changes stem from warmer winter temperatures and increased snowfall during the past 30 years. Lakebed temperatures of Arctic lakes less than 1 meter (3 feet) deep have warmed by 2.4 degrees Celsius (4.3 degrees Fahrenheit) during the past three decades, and during five of the last seven years, the mean annual lakebed temperature has been above freezing, the study found.
The rate of warming is similar to those observed in terrestrial permafrost. But since those soil temperatures are still well below freezing, widespread thawing is not expected for another 70 years. But the permafrost beneath lakes is generally warmer, making them more susceptible to thawing. These lakes may cover 20 to 40 percent of the landscape in vast areas of Arctic lowlands.
“During the 1970s, late winter lake ice thickness measurements commonly exceeded 2 meters (6.5 feet) in northern Alaska. Such thick ice growth helps to limit sub-lake permafrost thaw by freezing the sediments solid each winter,” said Christopher Arp, research assistant professor at the University of Alaska Fairbanks. “However, during winter field surveys over the last decade, lake ice has typically only grown to 1.5 meters (5 feet) thick, and has been as thin as 1.2 meters (4 feet),” Arp said.
The study findings are another example of the complex interaction in the Arctic climate system. The permafrost thaw could unlock a portion of the permafrost carbon pool and potentially release this carbon in the form of greenhouse gases.
These findings also highlight the importance of conducting winter fieldwork in the Arctic.
“Arctic lakes and ponds are typically ice covered for nine months of the year, but research on them typically occurs during the short Arctic summer. To more fully understand Arctic lake dynamics and to document the changes we have observed requires also doing fieldwork under often harsh conditions during the cold and dark arctic winter,” said Benjamin Jones of the U.S. Geological Survey in Anchorage and co-author of the new study.
The thawing could also lead to ground subsidence, which will increase lake depth and accelerate melting, said Vladimir Romanovsky of the UAF Geophysical Institute and co-author of the new study.
“In contrast, the warming on the land may increase the protective vegetation layer and delay thawing of permafrost outside of lakes,” Romanovsky said.
With increasingly warmer and snowier winters yielding thinner lake ice, shallow lakes will likely continue to warm, Arp said.