Metal caps protect deep holes drilled in Alaskan permafrost ground from wanderers of the human and bear varieties. Permafrost, found across the Arctic, is subsurface soil which has remained frozen for two years or more.
Permafrost temperatures in Alaska are rapidly changing. Vladimir Romanovsky, professor of Geophysics at the University of Alaska Fairbanks and head of the UAF Geophysical Institute’s Permafrost Laboratory, reported “For the last 30 years the mean annual ground temperature at the top of permafrost on the North Slope has been rising.”
In Deadhorse, a stop along Alaska’s famous Dalton Highway– the haul road– average permafrost temperatures rose from -8°C [17.6°F] in 1988 to -2°C [28.5°F] (reported at the close of 2015). During that time, rising permafrost temperature trends closely mimicked rising local air temperatures. Romanovsky: “The warming of permafrost is following warming in air temperatures. So the main forcing which made permafrost warmer on the North Slope of Alaska is an increase in air temperature.”
Boreholes allow scientists to measure underground permafrost.
Permafrost boreholes dot Alaska, generally drilled 45 to 60 meters deep. William Cable, research professional and masters student at the University of Alaska Fairbanks Geophysical Institute, described “A network of deep boreholes that was established in the early 1980s by Dr. Tom Osterkamp.” Network boreholes “Begin down near Glenn Allen and follow the road North all the way to Prudhoe Bay;” additional holes have been added over the years. Through annual monitoring of the borehole network, scientists have a record of permafrost temperatures in Alaska.
In Barrow on Alaska’s northern coast, two boreholes provide access points to measure the permafrost. “When they were installed the temperature at 15 meters [deep] was approximately -9° Celsius and over the course of the last twelve, thirteen years, the temperature has risen to about -8.5° Celsius. So that’s about ½° Celsius in a decade, which is pretty rapid,” Cable told Frontier Scientists in 2016. Cable illuminated: “This matches pretty well with temperature increases with[in] our other Northern boreholes– like in Deadhorse, for example. It’s tied to an increase in air temperature that we’ve seen over this same time period.”
Romanovsky stated that permafrost temperature is influenced by Earth’s inner heat, changing 2 degrees Lucius every 100 meters. “You have heat coming from the inner part of the earth: geothermal heat flux. If you have everything in equilibrium, temperature is going to get warmer and warmer with depth, according to this geothermal gradient.” The change measures on “Average, usually 2 degrees every hundred meters. If it is according to gradient, you can calculate the thickness very easily. If it is -6° on the top, every 100 meters will be 2 degrees warmer, so 0° will be 300 meters [deep].”
At Alaska’s Prudhoe Bay, permafrost depth reaches 650 meters [2130 feet] deep. Internal temperature is influenced from below by the geothermal gradient warming (temperatures varying in temperature 13° Celsius due to Earth’s heat) while permafrost temperature is influenced from above by air temperatures.
The Arctic is warming twice as fast as any other region on earth. Rising temperatures are causing some permafrost areas to thaw, releasing carbon that was long locked away frozen underground back into the carbon cycle, including into the atmosphere as carbon dioxide and methane (greenhouse gasses). Cable said “That’s sort of the big concern with permafrost now. There’s a lot of research going on now to know how quickly this carbon– that’s locked up in permafrost– how quickly it can be transformed into carbon dioxide and methane.”
Now, patches of permafrost are thawing and the depth of the active layer– soil on top of permafrost which thaws every year– is deepening. Romanovsky explained: compared to its entirety, permafrost is thawing in “Limited locations.” He immediately added “It’s this kind of development of climate and warming. It will get more and more dramatic. We will see much more of this.”
One visit per year
While some boreholes have instruments installed year-round, most require scientists to actually visit the the hole to measure temperatures.
“We typically only measure these boreholes once per year because the method we use is a manual method. It involves lowering a temperature probe down the borehole, stopping at intervals,” Cable said. “The reason we can measure it this way,” he explained, is because “We only see change in temperature on an annual scale. And so we can measure the temperature below this point once per year, and that’s sufficient to record what is happening there.”
While “Close to the surface you have temperatures that fluctuate on a daily time scale, just like air temperature fluctuates on a daily cycle,” Cable outlined, “As you go deeper in the ground these temperature fluctuations become more of a seasonal fluctuation.” Cable: “As you get to about 15 meters, then you lose your seasonal fluctuations and you are left with decadal fluctuations.”
“We reach something we call the zero annual amplitude which means there are no more fluctuations on a seasonal scale,” Cable said, “The temperature is changing only on an annual time scale. That’s why we can measure it like this because it doesn’t change over one year.” Measuring once a year “Is high enough time resolution for us.”
Old impacts new
“Russia has the longest history of permafrost data collection. They have some of the longest [records] and some of the deepest boreholes,” Cable noted. “But here in Alaska the record of permafrost data is short; it starts in the 70’s, early 80’s. But even with this record we can still see that permafrost is warming in response to climate warming.”
Within a borehole, Cable noted, “The temperature at 20 or 15 meters usually lags the air temperature by about one year. So what we see at 15 to 20 meters [depth] is sort of representative of what happened last year, in terms of an annual average temperature. We don’t see the effect of a warm year until the following year at that depth.”
Why is underground temperature generally so stable? Cable explained when it comes to permafrost “You have such a large mass, and so this takes a long time to change temperature. It takes a lot of heat input.” All the more reason to be surprised when permafrost thaw creates events like the thermokarst slump Frontier Scientists explored at Wolverine Lake where thawed permafrost ground ran downslope, revealing and thawing more and more permafrost soils.
While air temperature has the heaviest influence on permafrost temperatures, there are also lesser influences. “So any change in ground temperatures is a combination of these other effects,” said Cable. “It’s not only air temperature but how effectively the air temperature can be transmitted to the ground.” Snow cover can insulate the ground; deep snow tends to keep the ground warmer, while sparse snow cover combined with a cold winter will lead to a colder ground. The depth of the active layer, and the amount of water which collected over the warm season, have an impact. Vegetation growing on the surface also plays a role. These factors help determine heat flux: the amount of heat moving into or out of the permafrost.
Info for simulations
The measurements permafrost scientists take are inputted into models: supercomputer-driven simulations which help predict the future of permafrost. The data is “Good for verification,” to make sure the model performs well, Cable said. “The data is used definitely for calibrating models and validating models. There’s a lot of other data that is used as well, but the temperature data is quite important.”
The Geophysical Institute Permafrost Laboratory (GIPL) at University of Alaska Fairbanks has a model ‘GIPL 1.0 – Spatially Distributed Model of Permafrost Dynamics in Alaska’ which holds information about permafrost distribution and active layer thickness in Alaska, including measurements of ground temperature, air temperature, weather conditions, topography, and vegetation. The scientists can enter different climate scenarios into the model to get results about potential future permafrost conditions.
Romanovsky: “A permafrost geophysicist is excited about the process of warming and thawing of permafrost. But other people around ask: So what? What will happen to the environment when permafrost is thawing?” Thawing permafrost has consequences: “Impact on infrastructure and not only roads but pipelines and airports and buildings,” Romanovsky said. It changes the landscape and ecosystems, influencing “How local people will need to change their hunting,” and even changes where people living in Alaska can have communities. Some have already had to move communities away from sinking coastlines. Romanovsky observed of questions and impacts like these– “And I think is the most interesting part for normal people, not geophysicists.”
Permafrost ground, especially the upper parts of permafrost, tend to contain a lot of ice content. Romanovsky reported: in the Fairbanks area, the upper 15 to 20 meters of permafrost is “Very ice-rich permafrost, it’s lots of ice.” Thawing permafrost means melting ice, and that destabilizes the ground.
Accurate information from the Alaska borehole network and the models temperature measurements contribute to are tools that can help people who build and maintain infrastructure on Alaska’s North Slope. In a future we will hopefully not see, one in which worldwide carbon dioxide emissions continue at today’s rates, by the year 2100 more than half of the permafrost on the North Slope will be thawing (Romanovsky reported at the American Geophysical Union fall meeting in December 2015). Infrastructure of roads, pipelines and buildings will be compromised. Engineering solutions for oil production on the North Slope “Were designed and infrastructure was built when the permafrost was much colder,” Romanovsky said.
Laura Nielsen 2016
Frontier Scientists: presenting scientific discovery in the Arctic and beyond