Ninth International Conference on Permafrost ... - IARC Research

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The Effect of Spatially Distributed Snow Cover on Soil Temperatures:A Field and Modeling StudyIntroductionAnna LiljedahlUniversity of Alaska Fairbanks, USALarry HinzmanUniversity of Alaska Fairbanks, USASergei MarchenkoUniversity of Alaska Fairbanks, USASvetlana BerezovskayaUniversity of Alaska Fairbanks, USADue to its insulative properties, snow cover has beenshown to play a significant role in the 20 th century warmingof permafrost (Osterkamp 2007, Stieglitz et al. 2003) andthermokarst formation (Osterkamp 2007). Although theeffects of snow cover characteristics on soil temperatureshave been studied by others (Ling & Zhang 2003, Osterkamp2007, Overduin et al. 2007, Stieglitz et al. 2003), small-scalegeographical variations have been given limited attention.The combination of snow redistribution, hydraulic gradientsinduced by polygonal features, nutrient limited vegetation,soil mineralization, and respiration impaired by the cold soilscalls for a fine-scale analysis to understand the interactionsamong the Arctic systems and how they would respond toany changes in air temperature and precipitation.We examine the effects of snow depth and soil thermalproperties on micro-scale (>0.6 m horizontal, >0.01 m vertical)soil temperature distribution through field measurementsand computer modeling across a single polygon.Study siteThe study site is located inside the boundaries of theBarrow Environmental Observatory (BEO) close to Barrowon the North Slope of Alaska (Fig. 1). The BEO hosts anintensively monitored area called the Biocomplexity site(71°16′47ʺN, 156°36′2ʺW), which is a 1 km 2 watershedcontaining a drained lake basin and low- and high-centeredpolygons. Sedges and sphagnum moss represent the majorvegetation at the Biocomplexity site.The mean annual air temperature in Barrow during theyears 1973–2006 was -12°C with 32% of mean daily airtemperatures colder than -20°C. The latter ranged from-45°C to 16°C yr 1973–2006. Adjusted precipitation (Yanget al. 1998) averaged 168 mm/yr with 72 mm falling June–August (1973–2006). Summer 2007 was a warm summer(5.4°C compared to 3.3°C yr 1973–2007) with a low amountof precipitation (24 mm), resulting in unusually dry soilsprior to freezing. The Circumpolar Active Layer Monitoringsite (Brown et al. 2000), located at the northern end of theBEO, experienced a mean active layer depth of 35 cm yr1995–2007. The area of focus for this study is a low-centeredpolygon represented by relatively high (0.5 m) and wide (5m) rims.Figure 1. The location of the Biocomplexity site inside theboundaries of the Barrow Environmental Observatory. Originalimage courtesy of K.M. Hinkel.MethodsWe combined distributed modeling and field observationsof snow depth and soil temperatures, focusing on the activelayer thermal regime. Output from a snow distributionmodel was used as input to a soil thermal regime modelin both daily and hourly time steps. SnowTran-3D (Listonet al. 2007) provided wind-driven snow depth evolutionover topographically variable terrain. Required modelinputs include topography, vegetation, and weather data(precipitation, air temperature, humidity, wind speed anddirection). In order to simulate the spatially distributedtemperatures of permafrost and active layer thickness forthe investigated area, both equilibrium and transient modelshave been applied. The equilibrium model is a spatiallydistributed permafrost model based on an approximateanalytical solution of soil freezing and thawing, whichincludes an estimation of thermal offset due to the differenceof frozen and thawed soil thermal properties (Romanovsky &Osterkamp 1995). The numerical (transient) model simulatessoil temperature dynamics and depth of seasonal freezingand thawing by solving nonlinear heat equation with a phasechange. In this model, the process of soil freezing/thawingoccurs in accordance with the unfrozen water content curveand soil thermal properties, which are specific for each soillayer (Marchenko et al. 2008). The model requires input of183
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 tupper (air temperature, snow, and vegetation) and lower(geothermal heat flux) boundary conditions, initial conditions(temperature distribution with depth), soil water content, andsoil thermal properties. Topography was resolved in 1 m and0.04 m horizontal and vertical scale, respectively, with finerpixels available in the near future. Vegetation was mappedinto 2.8 m horizontal resolution.The simulations were validated with field measurementsof soil temperature and snow depth. An installation of 116thermistors (YSI model 44033 and Hobo U23-004) and 29water content reflectometers (CS616, Campbell Scientific)was made in late September 2007 across the polygon. Thethermistors were placed 0.6–20 m apart at three depths persite (1) at the interface of living and dead organic, (2) 7–10cm below the interface, and (3) at the bottom of the activelayer. One soil moisture sensor was placed in the organiclayer 7–10 cm below the living and dead organic interface.Thermal conductivity, volumetric specific heat, diffusivity,and temperature were measured with a Kd2Pro sensor(Decagon) throughout the different soil layers in fall 2007.Results and DiscussionActive layer depths ranged from 18 (troughs) to 46 cm(rims) in 2007 with a mean of 31 cm across the studiedpolygon. In the thawed polygon soil profile a 2–10 cm thicklive moss layer (mean 4 cm) overlaid a 5–25 cm organiclayer (mean 10 cm). The thicker moss layers were foundin troughs, while the thickest thawed organic layers werefound at the inner edge of the rim. Organic layer thermalconductivity in fall 2007 varied between 0.16–0.60 W m -1K -1 (n = 68) with moss thermal conductivity from 0.11 to0.91 W m -1 K -1 (n = 6). Measurements of moss thermalconductivity could only be obtained at a limited number ofsites where ice formation had not occurred. However, five ofthe six measurements were obtained at the same day, wherefour sites showed higher thermal conductivities in the mosslayer than in the organic layer below (ratio 2.3 to 5.6).Field measurements showed large variation in near-surfacesoil thermal properties on short horizontal and verticalscales. Despite relatively small differences in vegetationand topography, a heterogeneous snow accumulation is tobe expected due to redistribution by wind. The distributionof winter soil temperatures across the polygon are likely tovary significantly due to the combined effects of snow depthand soil thermal characteristics.ReferencesBrown, J., Hinkel, K.M. & Nelson, F.E. 2000. The circumpolaractive layer monitoring (CALM) program: Researchdesigns and initial results. Polar Geogr. 24(3): 165-258.Ling, F. & Zhang, T. 2003. Impact of the timing andduration of seasonal snow cover on the active layerand permafrost in the Alaskan arctic. Permafrost andPeriglac. Process. 14: 141-150.Liston, G.E., Haehnel, R.B., Sturm, M., Hiemstra, C.A.,Berezovskaya, S. & Tabler, R.D. 2007. Simulatingcomplex snow distribution in windy environmentsusing SnowTran-3D. J. of Glaciol. 53(181): 241-256.Marchenko, S.S., Romanovsky, V.E. & Tipenko, G.S. 2008.Numerical modeling of spatial permafrost dynamicsin Alaska. Proceedings of the <strong>Ninth</strong> <strong>International</strong><strong>Conference</strong> on Permafrost, Fairbanks, Alaska, June29–July 3, 2008.Osterkamp, T.E. 2007. Causes of warming and thawingpermafrost in Alaska. Eos Trans. 88(48): 522-523.Overduin, P.P., Boike, J., Kane, D.L. & Westermann, S.2007. Soil temperatures under a rage of organic andsnow covers. Eos Trans. 88(52), Fall Meet. Suppl.,Abstract C12A-0061, 31:737-747.Romanovsky, V.E. & Osterkamp, T.E. 1995. Interannualvariations of the thermal regime of the active layerand near surface permafrost in Northern Alaska.Permafrost and Periglac. Process. 6(3): 313-335.Stieglitz, M., Déry, S.J., Romanovsky, V.E. & Osterkamp,T.E. 2003. The role of snow cover in the warming ofarctic permafrost. Geophys. Res. Lett., 30(13): 1721,doi:10.1029/2003GL017337.Yang, D., Goodison, B.E. & Ishida, S. 1998. Adjustmentof daily precipitation data at 10 climate stations inAlaska: Application of WMO intercomparison results.Water Resours. Res. 34(2): 241-256.AcknowledgmentsThe authors are grateful to Matthew Sturm, Robert Busey,Steve Hastings, and B.A.S.C. for field assistance. Financialsupport was provided by Gålö Foundation, Center for GlobalChange and Arctic System Research, and the National ScienceFoundation through the <strong>International</strong> Arctic Research Center(Grant number 0327664).184
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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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