New Permafrost Forms Around Shrinking Arctic Lakes
11.06.2014 16:10 Age: 21 days
There is new permafrost forming around Twelvemile Lake in the interior of Alaska, according to researchers from McGill University and the U.S. Geological Survey.
By Katherine Gombay, McGill University
Researchers from McGill University and the U.S. Geological Survey, more used to measuring thawing permafrost than its expansion, have made a surprising discovery. There is new permafrost forming around Twelvemile Lake in the interior of Alaska. But they have also quickly concluded that, given the current rate of climate change, it won’t last beyond the end of this century.
Twelvemile Lake is sometimes called the disappearing lake. That’s because over the past thirty years, as a result of climate change and thawing permafrost, the lake water has been receding at an alarming rate. It is now 5 metres or 15 feet shallower than it would have been three decades ago. This is a big change in a very short time.
As the lake recedes, bands of willow shrubs have grown up on the newly exposed lake shores over the past twenty years. What Martin Briggs from the U.S. Geological Survey and Prof. Jeffrey McKenzie from McGill’s Dept. of Earth and Planetary Science have just discovered is that the extra shade provided by these willow shrubs has both cooled and dried the surrounding soil, allowing new permafrost to expand beneath them.
The researchers were initially very excited by this find. But after analyzing the thickness of the new permafrost and projecting how it will be affected by continued climate change and the expected rise in temperature in the Arctic of 3°C, they arrived at the conclusion that the new permafrost won’t last beyond the end of the century.
Widespread lake shrinkage in cold regions has been linked to climate warming and permafrost thaw. Permafrost aggradation, however, has been observed within the margins of recently receded lakes, in seeming contradiction of climate warming. Here permafrost aggradation dynamics are examined at Twelvemile Lake, a retreating lake in interior Alaska. Observations reveal patches of recently formed permafrost within the dried lake margin, colocated with discrete bands of willow shrub. We test ecological succession, which alters shading, infiltration, and heat transport, as the driver of aggradation using numerical simulation of variably saturated groundwater flow and heat transport with phase change (i.e., freeze‐thaw). Simulations support permafrost development under current climatic conditions, but only when net effects of vegetation on soil conditions are incorporated, thus pointing to the role of ecological succession. Furthermore, model results indicate that permafrost aggradation is transitory with further climate warming, as new permafrost thaws within seven decades.
New permafrost is forming around shrinking Arctic lakes, but will it last? by Martin A. Briggs,Michelle A. Walvoord,Jeffrey M. McKenzie,Clifford I. Voss,Frederick D. Day‐Lewis,John W. Lane published in Geophysical Research Letters doi 10.1002/2014GL059251
Read the abstract and get the paper here.
McGill University news release here.