Alaska’s North Slope is home to Arctic ground squirrels. Near the Atigun River their interlaced burrow network takes advantage of sandy soil. The burrows are so interconnected and the entrances so myriad that the scientists working there to decode Arctic ground squirrel mysteries carry a map denoting burrow entrance numbers so they can be certain to always return squirrels to their home burrows.
Arctic ground squirrel lifestyle
Why so much interest? Arctic ground squirrels are the only vertebrate known to man that can tolerate sustained sub-zero core body temperatures. They hibernate 8 months of the year underground in burrows surrounded by frozen ground, and actively expend energy just to heat their body temperature to a frigid 26.78°F [-2.9°C]. Average burrow temperatures near Atigun River measure 14°F [-10°C] during the hibernation season and have been recorded at -16.6°F [-27°C]. Arctic ground squirrels have a superpowered clock function, an internal clock that allows them to regulate their biological processes over 24-hour cycles and over the calendar year, despite lingering 8 months underground and spending their active days in the land of the midnight sun where normal day/night cues are jumbled. Decoding their remarkable clock function will help us one day treat a wide range of diseases or pathologies including cardiovascular disease, diabetes, seasonal defective disorder, and even alzheimers and old age senility. These are some of the reasons why Loren Buck, University of Alaska Anchorage Department of Biological Science professor, and his research team ‘Team Squirrel’ are undertaking Arctic ground squirrel research in Alaska.
The Polaris Project & Arctic ground squirrels
Across the Arctic on the Siberian tundra in the Kolyma River watershed near Cherskiy, Nigel Golden studied Arctic ground squirrels to learn about different impacts of their remarkable life. Golden, then a University of Wisconsin Stevens Point Biology and Wildlife Ecology undergraduate, was looking to understand how Arctic ground squirrel activities affect processes that influence carbon release from Arctic permafrost. He was able to do research in the Siberian Arctic with the support of The Polaris Project, an organization that describes itself as engaging young scientists, the public and decision makers in solving today’s scientific and societal challenges. Golden and Sue Natali, Ph.D., Polaris Project research coordinator, environmental scientist, and assistant scientist for the Woods Hole Research Center in Massachusetts, presented ‘Consequences of arctic ground squirrels on soil carbon loss from Siberian tundra’ at the American Geophysical Union 2014 Fall Meeting in San Francisco this December.
They found that Arctic ground squirrels, which are widely-distributed in the Arctic, create ecosystem changes as they build their burrow networks; they quantified some of those changes crafted by Arctic ground squirrels in the Siberian tundra. Digging burrows aerates the soil and mixes soil layers, redistributing soil nutrients. Inhabiting burrows warms the soil, changes soil moisture content and introduces nutrients through urine and feces. Vegetation cover in the Kolyma River watershed suffered; where Arctic ground squirrels burrowed 80% of the ground was un-vegetated, compared to 35% of ground un-vegetated on undisturbed sites. Soil from burrows seemed to contain plenty of nutrients (nitrogen) but little accessible carbon.
It’s about microbes
So what? you might be saying. And here’s where I have to admit that Arctic ground squirrels, with their cuddly fur and twitching noses and endearing love of carrots, are actually here to serve as ambassadors for the real topic of impact: dirt and the things that live in it. Microbes are considerably less photogenic than squirrels. Much like the Arctic Report Card uses polar bears (charismatic megafauna) to get people thinking about about Arctic sea ice, this study ‘Consequences of arctic ground squirrels on soil carbon loss from Siberian tundra’ uses Arctic ground squirrels to get us thinking about soil microbes in permafrost.
Dirt seems insignificant. Yet while the microorganisms that make their homes in soil aren’t much to look at, they’re incredibly important. In a teaspoon of permafrost you could feasibly find billions of single-celled microscopic organisms, thousands of different species. The possibilities are dizzying. Soil microbes in general serve to shuffle around nutrients and make vital building blocks of life like nitrogen available to plants and therefore to other species on up the food chain. They also serve as decomposers, eating up dead organic matter from plants and animals and then respiring (giving off as a byproduct) carbon. Soil respiration adds carbon (C) in the form of carbon dioxide (CO2) or methane (CH4) to the atmosphere.
So, what ‘Consequences of arctic ground squirrels on soil carbon loss from Siberian tundra’ is actually telling us is: Arctic ground squirrels’ activities promote conditions in which soil microbes can respire more carbon dioxide into the atmosphere than they would likely be able to were there no Arctic ground squirrels nearby.
Permafrost is a major player
A big part of that is in the word Arctic. Arctic land holds a lot of permafrost, or soil that has remained at or below freezing for two or more consecutive years. More than a quarter of the land in the Northern Hemisphere is composed of permafrost. Hugues Lantuit, coastal permafrost geomorphologist with the Alfred Wegener Institute for Polar and Marine Research, stated that “Permafrost underlies 44 percent of the land part of the northern hemisphere.” Parts of the land, including the sandy soil where these Arctic ground squirrels are digging, are indeed underlain by permafrost; a topsoil layer called the active layer thaws out every year during the warm season and then refreezes during winter, while the deeper permafrost layer remains frozen year-round. The very shallow depth common to the active layer means that deep root systems can’t take hold, and is one of the main reasons why Arctic tundra is characterized by plants that measure mere inches-high.
Over time, generations of those plants living and dying in the frigid Arctic have built up. Most permafrost began life during the Pleistocene, the most recent Ice Age, 1,800,000 to 10,000 years ago. Permafrost layers can measure up to 5,000 feet [1524 meters] thick. They’re not composed mainly of dirt or clay like you might imagine, but layer upon layer of dead organic matter: plants and even animals that died in the Arctic and became part of the ground you walk on. Because all that organic matter did not decay, the carbon (present in all life) that has been accumulating for tens of thousands of years is still there, waiting. Permafrost soils are estimated to contain 1,600 gigatons of carbon. That’s about twice as much as is currently aloft in the atmosphere.
Sink or source?
The Arctic has long served as a carbon sink, a place where carbon is taken in (mainly through photosynthesis) and then stored (as plants died but did not decompose). However when permafrost thaws that organic material begins to decompose. Soil microbes respire, adding carbon dioxide and even methane to the atmosphere. If more water is present in the tundra, microbes which produce methane are more likely to dominate emissions. If less water is present then the oxygen in the air allows microbes which produce carbon dioxide to flourish. Moisture is just one more variable in the grand equation, and serves to illustrate the complexity of the situation. In any case, both methane and carbon dioxide contain carbon, and both are greenhouse gasses. Methane is considerably more potent at trapping heat than carbon dioxide, but it remains in the atmosphere for a shorter duration of time. We don’t want large amounts of either of these gasses added to our atmosphere. But that might be what happens if permafrost thaw increases.
Carbon dioxide levels in the atmosphere have already far exceeded historical levels from the last 400 thousand years. Humans are adding carbon dioxide to the atmosphere as we burn fossil fuels, persist with deforestation, raise large populations of ruminant livestock, and more. (Ruminant livestock (i.e. cows) in the United States are estimated to generate 134 million tons of carbon dioxide every year.) And this is impacting the climate. Thirteen of the planet’s 14 hottest years on record occurred in the 21st century. The Intergovernmental Panel on Climate Change 2014 outlined that continued emissions will increase the likelihood of “Severe, pervasive and irreversible impacts for people and ecosystems.” Moving forward we can expect to see extreme weather conditions, water scarcity, and global food insecurity, impacts which will likely negatively impact developing nations far more than already-industrialized nations like the United States.
In the circumpolar far North, Arctic amplification is increasing temperatures drastically: Arctic air temperatures are warming at twice the rate of any other region of the world. “Melting permafrost is a canary in the coal mine, evidence of climate change,” said Breck Bowden, ecologist and watershed scientist at the University of Vermont, Burlington. “We are seeing more intense and rapid change in the Arctic than in any other biome on earth.”
One sign of the way climate warming is changing the Arctic is permafrost thaw. The thaw is evidenced by thermokarst events. Thermokarsts are places where warm temperatures have destabilized permafrost and resulted in collapsed landscapes. “In some locations, especially in Alaska, we see much greater erosion than there was before,” Lantuit described. Thermokarst events along the coast destabilize what was once solid ground; some land is lost to the sea. “There is oil and gas infrastructure on the coast, villages, people, also freshwater habitats for migrating caribou, so the coast has a tremendous social and ecological value in the Arctic, and coastal erosion is obviously a threat to settlements and to the features of this social and economical presence in the Arctic.” When thermokarst events happen ground buckles and slides downhill, often into waterways. This changes nutrient flow and availability, and drastically impacts Arctic ecosystems. It can strongly impact the atmosphere because soil microbes gain access to deeper stores of carbon, consume that carbon, and respire (emit) greenhouse gasses. It has even been shown that exposure to sunlight, common during thermokarst events, can increase microbial efficiency: they eat decaying organic matter and respire greenhouse gasses at a higher rate.
Positive feedback loop
This represents a potential feedback loop, a climate change amplifier. It’s called a positive feedback loop because positive feedback accelerates temperature rise, while negative feedback decelerates it. Greenhouse gasses released into the atmosphere promote warming, warming promotes permafrost thaw, permafrost thaw makes previously sequestered organic carbon available to soil microbes, soil microbes emit greenhouse gasses, greenhouse gasses promote warming. I’ve heard it called the ‘permafrost time bomb’. An alarmist way of phrasing it? Maybe. But maybe that’s what we need to hear to inspire us to push for reduced fossil fuel use and reduced deforestation. Charles Miller, principle investigator for the Carbon in Arctic Reservoirs Vulnerability Experiment and physical chemist for NASA’s Jet Propulsion Laboratory, underlined the importance of decoding Arctic processes. “The Arctic is critical to understanding global climate,” he explained. “Climate change is already happening in the Arctic, faster than its ecosystems can adapt.” And there’s that canary again: “Looking at the Arctic is like looking at the canary in the coal mine for the entire Earth system.” So part of understanding the integrated global climate system and predicting future climate change is understanding the future of permafrost.
We’re still not certain how vulnerable deep carbon reserves are to modern day climate change. And until fairly recently, the carbon stored in permafrost was not well accounted for in most climate models. Climate models are supercomputer-driven simulations, tools that can help scientists predict future conditions and simulate what will change if we use different mitigation strategies. The more we learn about different environmental processes, the more the findings can be used to improve climate model accuracy. Even small things (like Arctic ground squirrel burrows) can create significant impacts when they happen over and over again across entire landscapes. Ben Abbott, Ph.D. student, Department of Biology & Wildlife at University of Alaska Fairbanks said: “We know about a lot of processes that will affect the fate of arctic carbon, but we don’t yet know how to incorporate them into climate models.” He added, “We’re hoping to identify some of those processes and help the models catch up.”
So we’re back to Arctic ground squirrels and their burrows. “We saw an increase in soil temperature in the soils where the arctic ground squirrels were occupying,” Golden said. “As that permafrost begins to warm, now microbes can have access to these previously frozen carbons that were in the soil.” With access comes transformation, and the carbon is moved out of the soil into the atmosphere through the process of soil respiration.
“In the areas we looked at, there is less carbon in the soil, and the temperatures are higher,” Natali said. She emphasized an important point: “Human activities are the primary influence on climate. We do, however, need to understand how these activities are impacting natural ecosystems, and how these ecosystem responses will amplify or attenuate these human-driven impacts.”
“Even though we cannot alter wildlife activity, it’s important that we include greenhouse gas emissions from these activities into our accounting of carbon loss from the Arctic,” described Natali. The activities of Arctic ground squirrels serve as one more puzzle piece. We can use new knowledge about how they impact Arctic permafrost to help reduce uncertainty and refine our view of the future.
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
Arctic Ground Squirrel project
Climate Change Watch project
- ‘Amount and timing of permafrost carbon release in response to climate warming,’ Schaefer, K. Zhang, T., Bruhwiler, L. and Barrett, A. P. (2011), Tellus B, 63: 165–180. doi: 10.1111/j.1600-0889.2011.00527.x
- ‘Consequences of artic ground squirrels on soil carbon loss from Siberian tundra,’ Natali S., Golden, N. (2014) AGU Fall Meeting 2014, San Francisco, CA, Session B31G-0137
- ‘Differential mobilization of terrestrial carbon pools in Eurasian Arctic river basins,’ Xiaojuan Feng, Jorien E. Vonk, Bart E. van Dongen, Örjan Gustafsson, Igor P. Semiletov, Oleg V. Dudarev, Zhiheng Wang, Daniel B. Montluçon, Lukas Wacker, and Timothy I. Eglinton, (2013), PNAS 2013 110 (35) 14168-14173; published ahead of print August 12, 2013, doi:10.1073/pnas.1307031110
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- ‘Surface exposure to sunlight stimulates CO2 release from permafrost soil carbon in the Arctic’ Rose M. Cory, Byron C. Crump, Jason A. Dobkowski, and George W. Kling (2013), Proceedings of the National Academy of Sciences doi:10.1073/pnas.1214104110
- ‘Trends in CO2 exchange in a high Arctic tundra heath, 2000-2010. M. Lund et al. (2012), Journal of Geophysical Research, vol. 117, G02001, doi:10.1029/2011JG001901, 2012