Climate Change in the Arctic – Permafrost, Thermokarst, and Why They Matter to the Non-Arctic World

Climate Change in the Arctic – Permafrost, Thermokarst,and Why They Matter to the Non-Arctic World

William B. Bowden*Rubenstein School of Environment and Natural Resources, University of Vermont

Abstract

Thermokarst terrain develops when some forms of permafrost – or so-called frozen ground – thawand the soil subsides under its own mass. The processes that create thermokarst terrain alter theArctic landscape substantially. The formation of thermokarst terrain is a natural phenomenon thatincreases or decreases as the climate warms or cools. There is now strong evidence that permafrosthas been warming for several decades and that the rate of thermokarst formation has accelerated inmany parts of the Arctic. Based on predictions of future climate in Arctic regions, a substantialportion of the permafrost that exists today will disappear in the next 50–100 years. The increasein thermokarst activity observed recently is likely to be an early indicator of permafrost retreat.Taken individually a particular thermokarst feature is perhaps merely an interesting oddity. How-ever, taking a longer temporal and larger spatial perspective, it is reasonable to conclude that ther-mokarst formation has important impacts on the hydrology, geomorphology, biogeochemistry andecology of the Arctic landscape. If the rate of thermokarst formation increases as expected, then itis possible that important aspects of the structure and function of the Arctic landscape will changerapidly as well. It is of particular concern that permafrost contains more total carbon than is cur-rently in circulation in the modern atmosphere. New experimental evidence suggests that whenpermafrost thaws, the carbon it contains will become available for microbial processing and muchof the carbon may end up as carbon dioxide or methane in the atmosphere. It is important thatwe understand these interacting process to better understand how climate change will affect theArctic environment as well as the global climate, in the future.

Introduction

In recent years scientific and public interest in the Arctic region has grown considerablyas the potential effects of climate change have become clearer. This interest has beenspurred in part by the fourth International Polar Year (IPY 2007) and by recent summa-ries of our current state of knowledge about the Arctic system and possible effects ofclimate change (e.g. Christensen et al. 2007; Hinzman et al. 2005; Lemke et al. 2007;Walsh et al. 2005). The Arctic is particularly vulnerable to climate change due to thepositive feedback loop connecting solar radiation, snow and ice, albedo (reflection) andwarming. The Arctic is not an isolated system. It is currently responding to driving forcesthat originate around the globe. Furthermore, continued warming of the Arctic couldcause important changes, not just locally, but globally. As the Arctic warms, snow andsurface ice melt, which lowers the albedo of the Arctic surface, warming it further.

At some point Arctic soils that are currently colder than 0 �C (permafrost) will warmabove this critical threshold. Enormous quantities of ice and carbon are currently immobi-lized in permafrost. When ice-rich permafrost thaws the ice it contains melts, oftencreating distortions in the land surface called thermokarst terrain. The formation of

Geography Compass 4/10 (2010): 1553–1566, 10.1111/j.1749-8198.2010.00390.x

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thermokarst terrain can, by itself, have important impacts on the ecology, biogeochemis-try, hydrology and geomorphology of the Arctic landscape (Bowden et al. 2008; Hinzmanet al. 2005; Jorgensen & Osterkamp 2005). However, the combined effects of permafrostwarming and formation of thermokarst terrain may accelerate the rates of production ofvarious greenhouse gases, further warming the Arctic region.

This review article describes key characteristics of the Arctic as they relate to perma-frost and the particular role that thermokarst features play as indicators of current climatechange and as possible agents of future change. A sound scientific understanding of howand why the Arctic system is changing is important to guide future policy and manage-ment decisions.

The Arctic Environment and Characteristics of Permafrost

The Greek origin of the word ‘Arctic’ (arktikos) refers to ‘northern’. Many people thinkof the Arctic as any area lying above the Arctic Circle at 66� 34¢ N latitude, the lowestlatitude in the northern hemisphere at which sun does not set on the summer solstice inJune and so the ‘land of the midnight sun’. A more ecologically-based definition of theArctic region takes into consideration the fact that only well-adapted plants and animalsare able to survive in the Arctic and may be specialized to live there. And so, anotherdefinition of the Arctic includes areas of the north that lie above the region that can sup-port extensive forests; i.e. the tree line. Yet other definitions are based on temperaturecriteria; e.g. regions where the average temperature of the warmest month never exceeds10 �C [National Snow and Ice Data Center (NSIDC) 2010]. By these various definitions,‘Arctic’ regions may lie above or below the Arctic Circle. Viewing the earth from apolar-centric viewpoint rather than from an equator-centric viewpoint (Figure 1) showsthat the Arctic is a vast, interconnected region. In total the Arctic biome covers7 567 000 km2 (Bliss and Matveyeva 1992) – about 5% of the total land mass of the earth– that span every longitude on earth. This is more than just an interesting observation.As a pan-Arctic system, knowledge that scientists generate in one part of the Arctic is rel-evant to other parts of the Arctic.

By any definition the Arctic is an area dominated by snow and ice. But unlike its Ant-arctic counterpart there are many places in the Arctic where summer temperatures can bewell above freezing for several weeks or even several months at a time. However, atanyplace where the annual average temperature falls below 0 �C there is the potential toform permafrost (French 1999). Permafrost is defined as soil or rock that stays below 0 �Cfor over 2–3 years at a time. It is interesting to note that the definition of permafrost isbased on temperature and not water content or state (van Everdingen 2005). Thus, it ispossible to have permafrost that is not frozen, as in the case where the concentration ofmineral solutes depresses the freezing point of the soil water which remains liquid. How-ever, the focus of this article will be on areas of permafrost that do contain frozen water;so called frozen ground. In many places ice in permafrost may have been frozen for muchlonger than the 2–3 years minimum required by the definition. For example, it is notunusual to find ice that may have been frozen for centuries and even millennia (Dmitrievet al. 1997; Froese et al. 2008).

Permafrost may contain a lot of frozen water, or ground ice. Massive ice is common inpermafrost and may have formed for a variety of reasons. Some massive ice forms as aconsequence of fairly recent and regular freeze-thaw cycles near the soil surface, whicheventually form vertical ice wedges that self-organize into a honeycomb structure ofslightly raised ridges with central ponds called patterned ground (Figure 2). These

1554 Climate change in the Arctic: why it matters

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formations can cover a few hectares to hundreds of square kilometers in some areas, espe-cially in flat, wet terrain like the Arctic coastal plain (Davis 2001).

In other cases, massive ice may be a relic of glaciers that covered the land long agoduring earlier ice ages. As the environment warmed and the glaciers retreated, largemasses of ice were left behind and were covered by eroding sediment from the retreatingglaciers. In lower latitudes these relic ice masses melted and the overlying sediment col-lapsed into the resultant void, creating the pothole lakes that are characteristics of somenorthern temperate regions like Minnesota in the USA, Canada and the Siberian steppes.But in higher latitudes cold temperatures may have kept this ice frozen during the winterand the overlying sediment insulated it during the warmer summers, so the ice nevermelted.

Much of the frozen water in permafrost exists as individual crystals in the pores of soilor isolated lens created by ice segregation, a physical process by which water vapor is drawnto frozen areas of the soil. This process of reverse sublimation – sometimes referred to ascryosuction – can produce lens of ice ranging in thickness from fractions of a millimeter tometers (Davis 2001).

As noted above, the formation and maintenance of permafrost is entirely dependent onsoil temperatures that remain below 0 �C. The southern extent of permafrost is bounded,

PermafrostContinousDiscontinousSporadicIsolated

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Fig. 1. Polar projection of the northern hemisphere showing the current extent of continuous, discontinuous, spo-radic and isolated permafrost. Based on data from the US National Snow and Ice Data Center as rendered usingthe United Nations Environment Programme’s Arctic Environmental Atlas Utility (UNEP ⁄ GRID-Arendal 2010). Theblack line indicates the Arctic Circle. The green line indicates the approximate location of tree-line.

Climate change in the Arctic: why it matters 1555


therefore, by conditions that lead to sub-zero soil temperatures. Thick permafrost canonly form under conditions in which the annual energy balance is such that the soil losesmore energy in the colder months than it gains energy in the warmer months. In thehigher latitudes where average annual temperatures are below )6 �C to )8 �C, perma-frost is usually continuous. At lower latitudes the energy balance swings in favor of greatergain than loss over the annual seasons. This transition is gradual and therefore, furthersouth in the Arctic, permafrost becomes discontinuous, distributed in patches (Brown et al.1998; and Figure 1).

The lower boundary of permafrost thickness is defined by another energy balance. Thisbalance is dictated by the rate at which the soil can lose energy through the surface andthe rate at which thermal energy wells up from the geothermal depths of the earth (Davis2001; Zhang et al. 2003). As in the latitudinal gradient, when the rate of thermal energyinput from below exceeds the rate of thermal energy loss to the surface the permafrostthaws from below. Permafrost thickness varies widely, depending on local conditions(e.g. climate and geology). However, it is not uncommon for permafrost to be severalhundreds meter thick with some permafrost in Siberia reported to be 1500 m thick(Nelson 2003; Walsh et al. 2005).

These seasonal balances of energy in and out are delicately poised. Even in the highArctic large rivers and lakes deeper than about 2 m will contain liquid water at about4 �C, below a cap of ice and snow. Although cold, this 4 �C water is well above freezingand so it radiates energy to the colder sediment and substrata below the lake, which pre-vents permafrost from forming. The thaw basin that develops below large, deep lakes mayextend many tens to hundreds of meters in depth, often extending through the entirethickness of permafrost. Similar conditions prevail under large and deep rivers that retainliquid and possibly flowing water throughout the winter. Thus, in reality continuous per-mafrost is naturally deformed by thermal energy carried in flowing rivers and is puncturedby the thermal energy radiating from unfrozen water in deep lakes (Delisle 1998).

Fig. 2. Patterned ground north of Atigun Pass on the North Slope of Alaska. The largest of the polygonal structuresin the foreground of this image are roughly 20 m (65 feet) across. Photo credit: W.B. Bowden.



Of greatest interest to this article, however, is the upper surface boundary. Every sum-mer the upper few centimeters to a few meters of soil thaw in response to energy inputsfrom the sun. The depth of this active layer of thawed soil is defined by several factorsincluding the amount and intensity of the solar radiation, the surface albedo (reflectivity)and the thermal conductivity of the soil, that is, the ease with which the soil will conductthermal energy. Rocky soils or soils with a high mineral content typically conduct thermalenergy more easily than organic or peaty soils and so the active layer tends to be deeper inmineral soils than in organic soils. Below the active layer, however, the soil remains below0 �C and any ice it contains will normally remain frozen all year long. Liquid water maypersist in permafrost that is less than 0 �C. This freezing-point depression may be caused byseveral factors, including capillary forces in fine-textured soils and high concentrations ofdissolved solids in soil water.

Permafrost Degradation and Thermokarst Formation

When exposed, permafrost looks like ordinary soil, but has the consistency of concrete.Ground ice within the permafrost can impart considerable strength and structure as longas the soil stays frozen. As noted above, the occurrence of permafrost is bounded spatiallyby increasingly positive energy balance as one moves south, deeper into the soil and clo-ser to the soil surface in the summer. These boundaries are all somewhat indistinct,occurring over a gradient. However, there is one boundary that is immutable: the bound-ary between frozen water and liquid water at 0 �C. Permafrost temperatures track long-term, mean annual air temperatures (MAAT) and not individual daily highs and lows.For example, at Toolik Field Station on the North Slope of Arctic Alaska it might benearly 20 �C on a sunny day in the summer, but the energy input on this day will bemore than offset by days in the winter in which it is )60 �C or colder and the soil losesenergy content to the air. Over the long-term the MAAT at the Toolik Lake site is –8.4 �C (Hobbie et al. 1999) and as a consequence this is in an area of continuous perma-frost. Even under conditions where temperature changes on an annual basis (either coolingor warming), there can be long lag times between local, short-term (e.g. decadal) MAATand the temperature of the underlying permafrost (Delisle 1998; Osterkamp and Gosink1991). So under normal conditions one would expect that even inter-annual changes intemperature should not have large, immediate impacts on the state of permafrost. It mighttake thousands of years to completely eliminate thick permafrost from particularly coldregions.

Nevertheless, anything that disturbs the balance of energy losses and inputs at the soilsurface for a sufficiently long time has the potential to thaw shallow permafrost. This iswhy civil infrastructure such as building, roads and pipelines must be specially engineeredin the Arctic where the ice-content of the soil is high so that that the structures are com-pletely insulated from the frozen ground on which they are built (US Arctic ResearchCommission Permafrost Task Force 2003). Otherwise these structures will slowly thawthe permafrost beneath and they will sink into the soil. Ma et al. (2009), for example,reported damage rates of up to 45% for the Trans-Siberian Railway in Russia and theQinghai-Tibet Highway and Railway in China, which were all constructed in a mannerthat did not adequately protect underlying permafrost. The Trans-Alaska Pipeline build inthe early 1970s was designed to transport warm (40–60 �C) crude oil through areas ofcontinuous and discontinuous permafrost and is a good example of engineering designedto protect sensitive permafrost with high ice content, through passive refrigeration devicesand simple insulation (Alyeska Pipeline Service Company 2008).



Climate change in the Arctic presents an entirely different threat to the integrity of per-mafrost. Climate change is diffuse and persistent. The origins of climate change are notlocal to the Arctic but come instead from developed regions much further to the south.Nevertheless, these remote and subtle stressors may have profound effects on the futurestructure of the Arctic landscape. Already scientists from around the world have confirmedthat in almost every place we look, permafrost is warming (Deming 1995; Lemke et al.2007; Osterkamp 2005). For decades scientists in Russia, northern Europe, Canada andAlaska have drilled bore holes deep into permafrost and installed thermistors or thermocouplesto measure and record temperature electronically. In most places these simple long-termrecords show definitively that permafrost is getting warmer (Figure 3). And in manyplaces, the shallow permafrost is very near 0 �C; i.e. the point at which it will thaw.

When the permafrost thaws the soil loses internal structure and can subside unevenlyunder its own mass. This phenomenon is called thermokarst. The word karst is used bygeologists to describe rugged, often dry, limestone-dominated landscapes that have fre-quent caves and sinkholes. Cryologists – scientists who study snow and ice – appropriatedand modified the term with the suffix thermo- to refer to formerly frozen ground that hasthawed and subsided, becoming uneven (van Everdingen 2005).

It is important to note that the formation of thermokarst terrain is a natural phenom-enon that has proceeded at faster or slower rates throughout time. Currently there is no

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Fig. 3. Long-term records of the temperature of permafrost from boreholes drilled at several locations near the‘haul road’ that connects Fairbanks to Prudhoe Bay, Alaska. These locations are on the North Slope, in the vicinityof Toolik Lake. From north to south the locations are: WD: West Dock at Prudhoe Bay, DH: Deadhorse Airport, FB:Franklin Bluffs, HV: Happy Valley, GL: Galbraith Lake. From Osterkamp (2003). Related data can be found inOsterkamp and Romanovsky (1999), Osterkamp (2005, 2007) and Hinzman et al. (2005).



way to reliably age thermokarst terrains, though there are indicators in the structure andtexture of soils in the Arctic and elsewhere that can be interpreted as past thermokarstterrain (French 2008). It seems reasonable to assume, however, that the rate at whichthermokarst terrain formed was faster during warm interglacial periods and slower dur-ing glacial maxima. It well known that there is a strong correlation between historicatmospheric carbon dioxide concentrations and measured or inferred global mean tem-peratures. Given the conclusion from the Fourth Assessment Report of the InternationalProtocol on Climate Change, that current carbon dioxide levels are higher than anylevel thought to have occurred over the last 650 000 years and that these levels will cer-tainly rise further (Solomon et al. 2007), it is inevitable that global temperatures willcontinue to rise, particularly in the Arctic. Christensen et al. (2007) concluded thatannual average temperatures in the Arctic region will increase by 5 �C with a rangefrom 2.8 �C to 7.8 �C. Warming in the winter will be especially dramatic with a pro-jected range of +4.3 �C to +11.4 �C. Thus, it is highly likely that vast areas of continuouspermafrost will become discontinuous or will disappear altogether. In the recent ArcticClimate Impact Assessment, Walsh et al. (2005) reported that a quarter of all permafrostand up to half of the continuous permafrost could be gone by the end of the century.At the same time the active layer may have deepened by 30–50% in large areas of theArctic. These are conditions that are likely to lead to extensive formation of thermokarstterrain.

Examples of Thermokarst Terrain

Thermokarst terrain has been a subject of study for decades (e.g. Davis 2001; Lemkeet al. 2007), primarily in relation to civil infrastructure, as noted above (US ARC 2003).However, the long-term and large-scale consequences of thermokarst terrain on the ecol-ogy and biogeochemistry of Arctic landscape are poorly understood and have onlyrecently become the subject of scientific study. Thermokarst terrain takes on a variety offorms depending on the local geology, topography, vegetation and climate. Jorgensonand Osterkamp (2005) describe sixteen different forms of thermokarst features in borealecosystems. Most of these forms can also be found in Arctic landscapes as well.

In flat areas such as Arctic coastal plains around Point Barrow, Alaska, USA and nearthe MacKenzie Delta, Yukon Territory, Canada there are often numerous, aligned ther-mokarst or thaw lakes. These lakes form and re-form, due to the action of winds thatcome from a prevailing direction. Wind-driven currents in these lakes most effectivelyerode the lake margins at right angles to the wind direction, elongating the lakes laterally(Davis 2001). The striking form of these lakes is the combined result of wind and watermovement that thaw permafrost around the lake shore. Results from recent studies sug-gest that in some areas climate change is causing these lakes to dry up through increasedevapotranspiration (Smol and Douglas 2007). Alternatively, Smith et al. (2005) utilizedremote sensing imagery of the Siberian Arctic in the vicinity of the Yamal Peninsula andconcluded that in areas of continuous permafrost the number of thaw lakes had increasedbetween 1997–2004 apparently due to thermokarst development and ground subsidencethat then filled with water. However, in areas of discontinuous permafrost to the south,the number of thaw lakes had decreased. Smith et al. (2005) concluded that many ofthese lakes drained through the bottom after the thaw basin beneath the lakes penetratedentirely through the permafrost, opening a new flow path to deeper groundwater. Morelakes drained and disappeared in the south than formed in the north. But in both casesthe changes were driven by changes in the thermokarst terrain.



Thermokarst terrain also develops in hilly and mountainous terrain with results thatrange from subtle to dramatic. Solifluction lobes and cryoturbation steps are two subtleand unusual features of surface soils in the Arctic, formed by slow and repeated freezingand thawing of soil (Davis 2001). However, true thermokarst formation occurs when thepermafrost thaws and the formerly frozen ground destabilizes. Subsequently, an event likea large or persistent rainfall event may initiate mass movement of the soil downslope.Glacial thermokarst features (Figure 4A) occur where massive ground ice preserved as arelic of previous glacial events is finally exposed to conditions that cause the ice to thaw.These conditions often prevail on sides of hillslope in kame and kettle topography. Thesefeatures remain active only as long as there is massive ice to thaw.

Retrogressive thaw slumps (Figure 4B) take a number of forms that are superficially simi-lar to glacial thermokarst features. However, these features form when less massive forms ofground ice (e.g. lenticular, reticulate and ataxitic ice) melt. These features often form onriver banks and bluffs. The particular feature shown in Figure 4B is on the Itkillik River onthe North Slope of Alaska. It has remnant ‘islands’ or ‘rafts’ of the original vegetation distrib-uted in a regular pattern across the surface of the feature suggesting that the underlying min-eral soil destabilized and washed away, leaving the original surface nearly intact. The specificfactors that initiate these features are not clear, though fluvial and then thermal erosion ofriver banks is certainly indicated. It is even less clear why and how they stop growing.

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Fig. 4. Examples of hillslope failures induced by thermokarst terrain, including (a) glacial thermokarst, (b) retrogres-sive thaw slumps, (c) gully thermokarst and (d) active layer detachments slides. Photos credits: (A–C) by W. B. Bow-den, (d) by A.W. Balser.



Gully thermokarsts (Figure 4C) form when ice wedges on moderate hillslopes in siltysoils begin to fail. Liquid water apparently begins to accumulate at the base of the icewedges and then migrates downslope. Over time the flowing water can create large tun-nels in the soil. At some point the ice wedge or the soil around it will weaken to thepoint that the tunnel ceiling collapses forming a long, irregular gully. The exposed soilhas a lower albedo than the surrounding vegetation and so will continue to thaw, increas-ing the depth and especially the width of the feature. These features appear to stabilizeonce vegetation re-establishes on the bare soils and increases the albedo and shading ofthe surface. Bowden et al. (2008) describe the conditions leading up to the developmentof a particularly well-formed gully thermokarst near the Toolik Field Station and the sub-sequent evolution of this feature over several years.

Active layer detachment slides (ALDS, Figure 4D) occur when the active layerdetaches from the underlying permafrost and slides downslope. The vegetation mat that isdisplaced downslope has the appearance of a carpet that has been pushed up against a wallat the bottom of the slope. Though the exact mechanisms that form these features arepoorly understood, it is likely that they form as a consequence of positive soil pore pres-sure after large rain or melt events. The positive pore pressure lessens the soil strength,allowing the shallow soil of the active layer to slide over the permafrost table under theforce of gravity. Some argue that ALDS are not really thermokarst features because theyare restricted to the active layer and do not involve substantial thawing of the underlyingpermafrost. However, it is appropriate to include them here because these features are insome way dependent on an interaction with permafrost and lead to many of the sameenvironmental impacts as other forms of thermokarst features. Furthermore, the formationof an ALDS promotes subsequent permafrost thaw. ALDS are very common in someparts of the Arctic and appear to be more numerous now than was the case in the past(Bowden et al. 2008; Gooseff et al. 2009).

Why is Thermokarst Terrain Important?

All of these thermokarst features have the potential to cause important changes to theland surface. For example, thermokarst-induced hillslope failures move tons of soil acrossthe landscape, as well as the carbon, nitrogen and phosphorus associated with the soil. Atthe very least, these events are responsible for reshaping the local landscape. But whenthese thermokarst failures happen to intersect lakes and rivers, as they often do, they caninject massive quantities of sediment and nutrients directly into these waterbodies, whichmay be subsequently transported downstream. In addition, the injected sediments andnutrients may alter the community structure and ecological function of the lakes andrivers, themselves, in ways that have not yet been fully quantified (Bowden et al. 2008).

Thermokarst failures expose large areas of fresh mineral soil that were once covered bytundra vegetation. Little is known about the successional sequence of vegetation in thisnew primary habitat (Osterkamp et al. 2009). One possibility is that these areas are ulti-mately ideal habitat for shrubs, where previously the habitat may have been grasses andforbs. Shrubs have a number of different and interesting impacts on the Arctic landscape.The tender leaves and new twigs of shrubs are excellent food for moose, which wereonce rare in Arctic Alaska but have become increasing common. Shrubs also tend to holdand collect snow in the winter and consequently insulate the soil around them, whichmaintains microbial processing rates in the soil for longer periods and higher ratesthan would have been the case in the past. This connection between snow, shrubs and



microbial activity could have important impacts on carbon and nutrient processing inArctic soils (Sturm et al. 2005).

The changes noted above are local in nature but could have important impacts onnon-Arctic biomes and communities. In particular permafrost contains high concen-trations of carbon and nitrogen that if liberated, could substantially increase the atmo-spheric concentration of important greenhouse gasses. Furthermore, thermokarst failuresaccelerate physical processes that initially liberate these elements and microbial processesthat subsequently produce the greenhouse gasses, thus facilitating the transfer of theseelements from an inactive storage reservoir to an active component of the globalatmosphere.

Zimov et al. (2006) estimated that there are about 1000 gigatons (1000 petagrams or1018 g) of carbon stored in permafrost soils. Almost half of this total is stored in ice- andcarbon-rich yedoma soils in Siberia. The total carbon stored in permafrost is, therefore,about 1.4 times greater than the amount of carbon currently in circulation in the atmo-sphere and 1.5 times greater than the carbon currently stored in all vegetation on earth.Dutta et al. (2006) extracted Pleistocene-aged permafrost soils from four Siberian sitesand thawed them in the laboratory to determine whether the carbon in this soil waslabile, i.e. could be used by microbes. They found that on thawing, the carbon in thispermafrost decomposed rapidly. They concluded that if just 10% of the Siberian yedomasoils thawed they could add 41 gigatons of carbon to atmospheric CO2 burden, a 5%increase over levels today. Schuur et al. (2009) used field measurements to conclude thatrecently thawed areas emitted less old (pre-modern) CO2 than areas that had thawedabout 15 years earlier. However, the total carbon balance was more complicated. The15-year-old sites tended to accumulate carbon overall, primarily in new plant growth. Inturn, the oldest sites they examined, which thawed decades earlier, not only emittedmore old carbon but emitted more total carbon overall; i.e. they were a net source ofcarbon. Thus, it appears that thermokarst features might follow a complicated pattern ofcarbon emission driven by a fast release (a net source) of old and new carbon from easilydecomposable materials made available just after the thermokarst forms, followed by aperiod of continued release of old carbon but more rapid uptake by re-growing vegeta-tion (a net sink), followed finally by a longer period of old and new carbon release (a netsource).

The estimates reported by Dutta et al. (2006) do not include the other half of non-yedoma permafrost soils in the Arctic and neither of these studies included the potentialemissions of methane and nitrous oxide from thermokarst features. These two greenhousegases could be produced if carbon and nitrogen from thawed permafrost are processedunder anerobic, waterlogged conditions (Schuur et al. 2008). For example, Walter et al.(2007) have reported intense methane ebullition (bubbling) from thermokarst thaw lakesacross the Alaskan and Siberian Arctic and have estimated that this previously unac-counted source of methane contributes 24.2 ± 10.5 Tg CH4 ⁄year to the global methanebudget. It is less clear whether other thermokarst features are also important sources ofradiatively active trace gases, but it seems likely. It is worth noting that the global warm-ing potential (GWP) of methane is 72 times greater than carbon dioxide over a 20-yeartimeframe and 25 times greater over a 100-year timeframe. The GWP for nitrous oxideis nearly 300 times that of carbon dioxide over timeframes upto 100 years (Forster et al.2007). Thus, even relatively small emissions of methane or nitrous oxide to the atmo-sphere may be more important than larger emissions of carbon dioxide. The potential forfuture warming due to these emissions is considerable and is a matter of concern not justfor the Arctic region but for the globe as a whole.



Thermokarst in the Changing Arctic – A Systems Perspective

The processes and mechanisms noted above do not operate in isolation; the Arctic is asystem with numerous interconnections and teleconnections. Thus, thermokarst forma-tion may play a central role in the evolution of the Arctic landscape and in the behaviorof the earth system in a warmer and wetter future climate (Figure 5). Increasing temper-ature and winter rainfall will directly warm Arctic soils. Snow plays a more complicatedrole in that more snow decreases energy loss from the soil by insulation but increasesalbedo which reduces energy input to the soil. Overall indicators are, however, that soilhas been warming and if this continues, permafrost will thaw, forming thermokarst ter-rain that will have all of the consequences described above. The warmer soil directlystimulates microbial activity which accelerates the production of nutrients and tracegases. Increased trace gas emissions stimulate further climate change, creating a positivefeedback. Increased nutrients from permafrost thaw and thermokarst formation maystimulate vegetation growth and change community composition, perhaps to shrubs.

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Fig. 5. The central role of thermokarst in the evolution of the arctic landscape in a warmer and wetter climate. Thesolid lines connect drivers (ovals) and system components (rectangles) for which a value, magnitude or directioncan be identified as either increasing (+) or decreasing ()). The dotted lines connect drivers and components forwhich a value, magnitude, or direction is less evident. For example, though thermokarst features clearly affect thevegetation community it is not clear that this effect is positive or negative and the direction of the effect mightdepend on the specific metric used (e.g. biomass, diversity, height, value to consumers, value to humans). Similarly,it is not clear that changes to the vegetation community have positive or negative effects on human communities.The magnitude and direction of effect would depend on the specific interaction between the vegetation andhuman communities.



This vegetation change will have direct, stabilizing influences on thermokarst formationand will have indirect influences on further soil warming through impacts on snowaccumulation and albedo. The sediment and nutrients generated from thermokarst ter-rain may enter aquatic ecosystems. Sediments will most likely depress primary produc-tion while nutrients should increase primary production. The relative strengths of theseinfluences are not well known but it is possible that the stimulatory effects of nutrientswill persist longer than the inhibitory effects of sediment. The landform (e.g. flat coastalplain versus foothills) will strongly modify the terrestrial and aquatic ecosystems dynamicsand will itself be influenced over the long-term by the formation of thermokarst terrain.These shifts in landform, vegetation and aquatic resources will influence the deliverymaterials to coastal ecosystems, which will in turn influence the regional climate forcingfunctions. Finally, landform, vegetation, aquatic and coastal resources all affect humanuses and ecosystem services. These uses and services range from subsistence harvestingthat primarily affects local communities to greenhouse gas emissions that affect the globalcommunity.

There is still much that we do not know about how these components function indi-vidually and much less about how they function in concert with one another. The Arctic– like any biome – is a complex system with feedbacks, non-linearities, emergent proper-ties, hysteresis and ill-defined boundaries. Thus, we should expect that the formation ofthermokarst terrain in the Arctic will create complex responses. This complexity presentschallenges for policy and management, but also presents opportunities for exciting newresearch to inform policy and management.

Acknowledgement

This paper is a contribution the Arctic Systems Science Thermokarst project. The mate-rial presented in this paper is based on work supported, in part, by the National ScienceFoundation under grant ARC-08-06394. Any opinions, findings and conclusions or rec-ommendations expressed in this material are those of the author and do not necessarilyreflect the views of the National Science Foundation. The author thanks the ArcticSystems Science Thermokarst Project team and the broader Arctic Systems Science com-munity for discussions and insights that contributed directly to this paper. The final man-uscript was greatly improved by detailed and thoughtful comments from two anonymousreviewers and by guidance from Associate Editor Doerthe Tetzlaff.

Short Biography

William (Breck) Bowden teaches and conducts research on the influences of land coverand land use on aquatic ecosystems, especially streams. His work focuses on interactionsamong ecology, hydrology, biogeochemistry, policy and management. Bowden has beencontinuously involved in arctic research since 1987, primarily on the North slope of Arc-tic Alaska. He is a founding member of the Arctic Long-Term Ecological Research(ArcLTER) Project and currently serves as the co-ordinator for the ‘Streams’ researchtheme for this project. Bowden currently directs research on the influences of thermok-arst terrain on the evolution of the arctic landscape, the influences of changing seasonalityin the Arctic on stream biogeochemical processing and the influences of fire as a newform of disturbance in the Arctic region. Bowden is currently the Robert and GenevievePatrick Professor of Watershed Science and Planning in the Rubenstein School of Envi-ronment and Natural Resources at the University of Vermont, in Burlington, Vermont,



USA. When not in the Arctic Bowden teaches in the Environmental Sciences programand directs research on the influences of urban and suburban development on stream hab-itat quality. He is the Director of the Vermont Water Resources and Lake Studies Centerand Director of the Socioeconomic Theme (Theme 1) in the Northeastern StatesResearch Cooperative. Bowden received his B.Sc. with majors in Zoology and Chemis-try from the University of Georgia. He holds an M.Sc. and Ph.D. from North CarolinaState University. Before moving to the University of Vermont in 2002 Bowden was theProgramme Leader for Integrated Catchment Management at Manaaki Whenua – Land-care Research in Lincoln, New Zealand and was for 10 years prior to that an Assistantand Associate Professor for Water Resources Management at the University of NewHampshire, Durham, New Hampshire, USA where he founded the Water ResourcesManagement Program.

Note

* Correspondence address: William B. Bowden, Rubenstein School of Environment and Natural Resources, Uni-versity of Vermont, Burlington, VT 05405, USA. E-mail: [email protected]

References

Alyeska Pipeline Service Company (2008). Pipeline facts. [Online]. Retrieved on 18 April 2010 from: http://www.alyeska-pipe.com/pipelinefacts.html.

Bliss, LC and Matveyeva, N. V. (1992). Circumpolar arctic vegetation. In: Chapin, F. S. III, Jefferies, R. L., Rey-nolds, J. F., Shaver, G. R. and Svoboda, J., (eds.) Arctic ecosystems in a changing climate: an ecophysiological perspective.New York: Academic Press, pp. 59–89.

Bowden, W. B., et al. (2008). Sediment and nutrient delivery from thermokarst features in the foothills of the NorthSlope, Alaska: Potential impacts on headwater stream ecosystems. Journal of Geophysical Research-Biogeosciences 113,pp. G02026.

Brown, J., Ferrians, O. J., Heginbottom, J. A. and Melnikov, E. S. (1998). Circum-arctic map of permafrost and ground-ice conditions. [Online]. Retrieved on 20 April 2010 from: http://nsidc.org/data/ggd318.html.

Christensen, J. H., et al. (2007). Chapter 11: Regional climate projections. In: Solomon, S., Qin, D., Manning,M., et al. (eds) Climate change 2007: the physical science basis. Contribution of Working Group I to the Fourth AssessmentReport of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, pp. [Online]Retrieved on 18 April 2010 from: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch11.html.

Davis, N. (2001). Permafrost: A guide to frozen ground in transition. Fairbanks: University of Alaska Press.Delisle, G. (1998). Numerical simulation of permafrost growth and decay. Journal of Quaternary Science 13, pp. 325–333.Deming, D. (1995). Climatic warming in North-America: analysis of borehole temperatures. Science 268, pp. 1576–

1577.Dmitriev, V. V., et al. (1997). Detection of viable yeast in 3-million-year-old permafrost soils of Siberia. Microbiology

66, pp. 546–550.Dutta, K., Schuur, E. A. G., Neff, J. C. and Zimov, S. A. (2006). Potential carbon release from permafrost soils of

Northeastern Siberia. Global Change Biology 12, pp. 2336–2351.van Everdingen, R. (2005). Multi-language glossary of permafrost and related ground-ice terms. [Online] Retrieved on 18

April 2010 from: http://nsidc.org/fgdc/glossary/english.html#T.Forster, P., et al. (2007). Changes in atmospheric constituents and in radiative forcing. Chapter 2. In: Solomon, S.,

Qin, D., Manning, M., et al. (eds) Climate Change 2007: The Physical Science Basis. Contribution of Working GroupI to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge UniversityPress, pp. [Online] Retrieved on 18 April 2010 from: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2.html.

French, H. (1999). Past and present permafrost as an indicator of climate change. Polar Research 18, pp. 269–274.French, H. (2008). Recent contributions to the study of past permafrost. Permafrost and Periglacial Processes 19, pp.

179–194.Froese, D. G., et al. (2008). Ancient permafrost and a future, warmer arctic. Science 321, p. 1648.Gooseff, M. N., Balser, A., Bowden, W. B. and Jones, J. B. (2009). Effects of hillslope thermokarst in northern

Alaska. EOS 90, pp. 29–36.Hinzman, L. D., et al. (2005). Evidence and implications of recent climate change in northern Alaska and other

arctic regions. Climatic Change 72, pp. 251–298.



Hobbie, J. E., et al. (1999). Impact of global change on the biogeochemistry and ecology of an Arctic freshwater sys-tem. Polar Research 18, pp. 207–214.

IPY. (2007). Internatinal Polar Year homepage. [Online] Retrieved on 3 June 2010 from: http://www.ipy.org/.Jorgenson, M. T. and Osterkamp, T. E. (2005). Response of boreal ecosystems to varying modes of permafrost deg-

radation. Canadian Journal of Forest Research-Revue Canadienne de Recherche Forestiere 35, pp. 2100–2111.Lemke, P., et al. (2007). Chapter 4: Observations: changes in snow, ice and frozen ground. In: Solomon, S.,

D.Qin, D., Manning, M., et al. (eds) Climate Change 2007: The Physical Science Basis. Contribution of WorkingGroup I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: CambridgeUniversity Press, pp. [Online] Retrieved on 18 April 2010 from: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch4.html.

Ma, W., Cheng, G. D. and Wu, Q. B. (2009). Construction on permafrost foundations: Lessons learned from theQinghai-Tibet railroad. Cold Regions Science and Technology 59, pp. 3–11.

Nelson, F. E. (2003). (Un)frozen in time. Science 299, pp. 1673–1675.NSIDC (2010). What is the arctic? [Online]. Retrieved on 18 April 2010b from: http://nsidc.org/arcticmet/basics/

arctic_definition.htmlOsterkamp, T. E. (2003). A thermal history of permafrost in Alaska. Proceedings of Eighth International Confer-

ence on Permafrost (Zurich). Potsdam: International Permafrost Association, pp. 863–868. [Online] Retrieved on18 April 2010 from: http://research.iarc.uaf.edu/NICOP/DVD/ICOP%202003%20Permafrost/Pdf/Chapter_151.pdf.

Osterkamp, T. E. (2005). The recent warming of permafrost in Alaska. Global and Planetary Change 49, pp. 187–202.Osterkamp, T. E. (2007). Characteristics of the recent warming of permafrost in Alaska. Journal of Geophysical

Research-Earth Surface 112, F02S02, 10 pp. doi: 10.1029/2006JF000578.Osterkamp, T. E. and Gosink, J. P. (1991). Variations in permafrost thickness in response to changes in paleocli-

mate. Journal of Geophysical Research-Solid Earth and Planets 96, pp. 4423–4434.Osterkamp, T. E and Romanovsky, V. E. (1999). Evidence for warming and thawing of discontinuous permafrost

in Alaska. Permafrost and Periglacial Processes 10, pp. 17–37.Osterkamp, T. E, et al. (2009). Physical and ecological changes associated with warming permafrost and thermokarst

in interior Alaska. Permafrost and Periglacial Processes 20, pp. 235–256.Schuur, E. A. G., et al. (2008). Vulnerability of permafrost carbon to climate change: Implications for the global

carbon cycle. BioScience 58, pp. 701–714.Schuur, E. A. G., et al. (2009). The effect of permafrost thaw on old carbon release and net carbon exchange from

tundra. Nature 459, pp. 556–559.Smith, L. C., Sheng, Y., MacDonald, G. M. and Hinzman, L. D. (2005). Disappearing Arctic lakes. Science 308,

p. 1429.Smol, J. P. and Douglas, M. S. V. (2007). Crossing the final ecological threshold in high Arctic ponds. Proceedings of

the National Academy of Sciences of the USA 104, pp. 12395–12397.Solomon, S., et al. (2007). Technical summary. In: Solomon, S., Qin, D., Manning, M., et al. (eds) Climate Change

2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovern-mental Panel on Climate Change. New York: Cambridge University Press, pp. [Online] Retrieved on 18 April2010 from: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ts.html.

Sturm, M., et al. (2005). Winter biological processes could help convert arctic tundra to shrubland. BioScience 55,pp. 17–26.

UNEP ⁄ GRID-Arendal. (2010) Arctic Environmental Atas. United Nations Environment Programme and the GRID-Aren-dal Norwegian Foundation. [Online] Retrieved 3 June 2010 from: http://maps.grida.no/arctic/.

US ARC. (2003). Climate change, permafrost, and impacts on civil infrastructure. Special Report 01-03. Arlington,Virginia: U.S. Arctic Research Commission, Permafrost Task Force, p. 63.

Walsh, J. E., et al. (2005). Chapter 6: Cryosphere and hydrology. In: Symon, C., Arris, L. and Heal, B., (eds.) .New York: Cambridge University Press, pp. 183–242. [Online] Retrieved 18 April 2010 from: http://www.a-cia.uaf.edu/PDFs/ACIA_Science_Chapters_Final/ACIA_Ch06_Final.pdf.

Walter, K. M., Smith, L. C. and Chapin, F. S. (2007). Methane bubbling from northern lakes: present and futurecontributions to the global methane budget. Philosophical Transactions of the Royal Society Series A: MathematicalPhysical and Engineering Sciences 365, pp. 1657–1676.

Zhang, Y., Chen, W. J. and Cihlar, J. (2003). A process-based model for quantifying the impact of climate changeon permafrost thermal regimes. Journal of Geophysical Research-Atmospheres 108, 4695, 16 pp. doi: 10.1029/2002JD003354.

Zimov, S. A., Schuur, E. A. G. and Chapin, F. S. (2006). Permafrost and the global carbon budget. Science 312, pp.1612–1613.



Documents

Climate Change in the Arctic – Permafrost, Thermokarst, and Why They Matter to the Non-Arctic World