Ninth International Conference on Permafrost ... - IARC Research

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Variable Peat Accumulation Rates in Stable Subarctic Peat Plateaus,West-Central CanadaA.B.K. SannelDepartment of Physical Geography and Quaternary Geology, Stockholm University, SwedenP. KuhryDepartment of Physical Geography and Quaternary Geology, Stockholm University, SwedenIntroductionPeatland ecosystems located in the boreal forest andtundra biomes contain a large and significant pool of soilorganic carbon. The carbon storage in boreal and subarcticpeat deposits is approximately 455 Pg C, representing onethirdof the total world pool of soil carbon (Gorham 1991).As a result of global warming, the highest increases intemperature are predicted to take place at high northernlatitudes. For most permafrost regions a reductionin permafrost area and an increase in thaw depth areexpected (ACIA 2004, IPCC 2007). Permafrost peatlandsare sensitive ecosystems expected to respond rapidly tochanges in climate. Since perennially frozen peatlands inthe sporadic and discontinuous permafrost zones are alreadynear thawing, they are most sensitive to climate changes(Tarnocai 2006). Climate warming may affect permafrostpeatlands in many ways: permafrost degradation, formationof thaw lakes, increased thaw depth, drier peat surfaces,changes in carbon accumulation, methane emissions, plantcommunities, hydrology, and fire frequency (e.g., Gorham1991, Zoltai 1995, ACIA 2004).An increased knowledge of permafrost conditions andcarbon accumulation rates in subarctic permafrost peatlandsthroughout the Holocene is important for understanding howthese ecosystems might respond to the predicted future climatechanges.Figure 1. Location of Selwyn Lake and Ennadai Lake, permafrostzonation, and ecoclimatic regions in west-central Canada. CPZ =continuous permafrost zone, DPZ = discontinuous permafrost zoneand SPZ = sporadic permafrost zone (after Zoltai 1995). LA = lowarctic, HS = high subarctic, LS = low subarctic, HBs = subhumidhigh boreal and MBs = subhumid mid-boreal ecoclimatic region(after Ecoregions Working Group 1989).Aim, Study Area, and MethodsThe aim of this study is to better understand the long-termcarbon dynamics in subarctic peat plateaus in relation tovegetation and permafrost conditions.Selwyn Lake and Ennadai Lake are located within the lowsubarctic ecoclimatic region in west-central Canada, wherethe climate is characterized by very cold winters and short,warm summers (Fig. 1).The peat profile SL1 (59º53′N, 104º12′W) was collected inthe discontinuous permafrost zone from a treed peat plateaubog calving into Selwyn Lake (Fig. 2). The peat profile EL1(60º50′N, 101º33′W) was collected in the continuous permafrostzone from a polygonal peat plateau on the western shoreof a small lake located 1 km west of Ennadai Lake (Fig. 3).In both peat profiles (SL1 and EL1), vegetation successionand high-resolution peat and carbon accumulation rateshave been studied through plant macrofossil analyses andextensive AMS radiocarbon dating. Bulk densities weremeasured throughout the profiles as well as carbon (C) andnitrogen (N) content.Figure 2. The collection site of peat profile SL1 at a forested peatplateau calving into Selwyn Lake (Photo: © P. Kuhry).Results and DiscussionPeat formation at the two sites began around 6600–5900cal yr BP, and permafrost conditions have prevailed inthe peat plateaus since permafrost aggradation occurredbetween 5600–4500 cal yr BP (Sannel & Kuhry in press).An important characteristic of these peat plateaus are thealternating layers of Sphagnum fuscum and rootlet peatlayers. Sphagnum stages represent slightly more moistsurface conditions than rootlet stages, which mainly containroots, Picea needles, and leaves from ericaceous shrubs. Thelong-term peat and carbon accumulation rates for both thestudied peat profiles are 0.30–0.31 mm/yr and 12.5–12.7267
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tFigure 3. The collection site of peat profile EL1 at a polygonal peatplateau near Ennadai Lake (Photo: © P. Kuhry).gC/m 2 yr, which is coherent with previously reported datafrom subarctic Canadian peatlands by Tarnocai (1988) andGorham (1991).Extensive radiocarbon dating of the peat profile SL1shows that accumulation rates are variable over time andthat abrupt shifts in accumulation rates occur when thevegetation composition in the peat changes. Vertical peatgrowth is generally 4–5 times higher in Sphagnum peat thanin rootlet peat. Also, the net carbon accumulation is 3–4 timeshigher in Sphagnum peat. The lowest accumulation rates arerecorded in rootlet layers that have been subjected to fires.Sphagnum peat represents 78% of the peat profile height, butonly 44% of the time since the peatland was formed (Sannel& Kuhry submitted).In both EL1 and SL1, C/N ratios in Sphagnum peat arerelatively high (around 90–140) and remain rather stablethroughout most of the profiles, indicating that the organicmaterial that has been incorporated into the permafrost has alow degree of decomposition (Sannel & Kuhry submitted).Persistently dry surfaces as a result of stable permafrostconditions since the peat plateaus developed suggest thatthese peatlands have been negligible as methane sourcesthroughout their history. Therefore, generally they haverepresented a negative net radiative climatic forcing overtime. However in a future warmer climate, permafrostdegradation may cause wetter surface conditions, formationof collapse scars, and thermokarst lakes, and turn these areasinto methane sources.Ecoregions Working Group. 1989. Ecoclimatic regionsof Canada, First Approximation. Ecological LandClassification Series, No. 23. Canada, Ottawa:Sustainable Development Branch, Wildlife Service,Environment, 118 pp.Gorham, E. 1991. Northern peatlands – role in the carboncycleand probable responses to climatic warming.Ecological Applications 1(2): 182-195.IPCC (Intergovernmental Panel on Climate Change). 2007.Climate Change 2007: The Scientific Basis. Summaryfor Policymakers. Geneva: IPCC Secretariat, 21 pp.Sannel, A.B.K. & Kuhry, P. in press. Long-term stability ofpermafrost in subarctic peat plateaus, west-centralCanada. The Holocene 18(4).Sannel, A.B.K. & Kuhry, P. submitted. Peat growth anddecay dynamics in subarctic peat plateaus, westcentralCanada. Boreas.Tarnocai, C. 1988. Wetlands in Canada: Distribution andcharacteristics. In: H.I. Schiff & L.A. Barrie (eds.),Global change, Canadian Wetlands Study, WorkshopReport and Research Plan. York University, NewYork: Canadian Institute for Research in AtmosphericChemistry, 21-25.Tarnocai, C. 2006. The effect of climate change on carbonin Canadian peatlands. Global and Planetary Change53(4): 222-232.Zoltai, S.C. 1995. Permafrost distribution in peatlands ofwest-central Canada during the Holocene warm period6000 years BP. Geographie Physique et Quaternaire49(1): 45-54.AcknowledgmentsFinancial support has been given by the K&A WallenbergFoundation, Ymer-80 Foundation, Royal Swedish Academyof Science, Ahlmann Foundation, Vice-President CentralResearch Fund, EU GLIMPSE project, and SwedishResearch Council.ReferencesACIA (Arctic Climate Impact Assessment). 2004. Impactsof a Warming Arctic, 1st ed. Cambridge UniversityPress, 139 pp.268
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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