Ninth International Conference on Permafrost ... - IARC Research

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Soil Carbon Distribution in the Alaska Arctic Coastal PlainErik PullmanUniversity of Alaska Anchorage, Kachemak Bay Campus, 533 East Pioneer Ave., Homer, AK 99603M. Torre JorgensonABR, Inc. – Environmental Research and Services, P.O. Box 80410, Fairbanks, AK 99708Yuri ShurUniversity of Alaska Fairbanks, Civil and Environmental Engineering, P.O. Box 755900, Fairbanks, AK 99775IntroductionThe accumulation of soil carbon in arctic soils representsa globally significant sink of atmospheric carbon that isboth formed and maintained by development and accretionof permafrost. Much of this near-surface carbon currentlysequestered in permafrost can be incorporated into the activelayer through surface disturbance (Pullman et al. 2007) andthermokarst processes related to climate change (Jorgensonet al. 2006). Most recent estimates sample only the activelayers or top 100 cm of soil (however, see Bockheim &Hinkel 2007) or are based on samples taken from a limitednumber of geomorphological terrains.In this study, we have used a landscape-classificationapproach to sampling in an area of the North Slope CoastalPlain of Alaska covering 850 km 2 (Fig. 1). The terrain units,surface forms, and vegetation communities of the landscapein this area were classified through aerial photo interpretationand extensive field surveys. Samples for soil carbon weredistributed across the major terrain types identified acrossthe study area. Total soil carbon results for each terrainunit were then applied to the terrain map and a total carboninventory was calculated for the study area.MethodsSample collectionSoil cores were collected during the summer in 2001–2003in the NPR-A area. An intact soil plug was removed downto permafrost. Intact 3-inch (7.5 cm) soil cores in permafrostwere collected using a specially-designed soil corer attachedto a portable power head. At each location, we attemptedto core into the underlying sand sheet and locate sedimentswith less than 10% visible ice. We postulate that this mayrepresent the syngenetic/epigenetic boundary within theexisting permafrost. At each soil pit, soil stratigraphy,texture, and color were described from the intact, frozen soilcore. Cryogenic structures were described according to Shurand Jorgenson (1998). Visual ice content was estimated foreach stratigraphic section. Soil textures were grouped intolithofacies classes based on similarities on particle sizedistribution and depositional patterns (Pullman et al. 2007).Frozen soil samples were taken every 10–20 cm (withinstratigraphic sections) along the entire length of the core.Sample volumes were measured in the field by taking threemeasures of core length (at equidistant intervals around thecircumference) and three measures of core circumference(at the ends and midpoint of the core length). Unfrozencore material was removed prior to measurement. Meanlength and circumference values were used to calculate thecylindrical core volume. Core samples were then placed inlabeled ziplock freezer bags for transport. A total of 47 coresand bank exposures were included in this analysis, with totalsample depths ranging from 1.8 to 4 m. Most cores extendedto 2.7 m.Field samples were weighed and thawed at roomtemperature. Excess water was decanted off the sample onceall solids had settled to the bottom of the sample bag. Soilswere oven-dried to a constant weight at 60°C. A subsampleof the homogenized dried soil was submitted for total carbonand nitrogen analysis to the Palmer Soils Laboratory (Palmer,Alaska).Soil carbon calculationsSoil carbon content was calculated for each stratigraphicsection within individual cores, and then summed over 100cm and 200 cm. Stratigraphic sections that extended throughthe 100 cm and 200 cm depths were split for the purposesof calculating total carbon for these specific depths. Sincewe did not sample every stratigraphic section of everycore, estimates of the carbon content in unsampled sectionswere made to obtain total carbon stocks for each core. Astratigraphic method was used to reduce variability thatcould be introduced by a length-weighted mean method. Inthis study a total of 612 stratigraphic sections were identifiedin 46 cores. Of these sections, 476 were sampled for %Ccontent. Measurements on a majority of these sections (400)were made for sample volume, excess ice volume, dry soildensity, and water content. Using data from the sampledstratigraphic sections, we were able to calculate mean carboncontents for stratigraphic sections that were missing datafor either % carbon, dry density, or both. For stratigraphicsections missing % carbon measures, we used the mean%C of the section’s lithofacies class (Table 1). For sectionsmissing dry density measures, sample dry density wascalculated using a regression of dry density based on %C ofactive layer samples multiplied by the % excess ice (fromthe visual field estimate). For the minority of stratigraphicsections with neither density nor %C measures, we used avalue of both %C and dry density, based on calculated meansof the appropriate lithofacies class.Mean carbon stocks for each terrain type were applied to theterrain map of the study area to show the spatial distributionof carbon in the active layer, top 1 m, and top 2 m of soilacross the study area to produce a distribution pattern of total245
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 tcarbon in terrestrial areas of the landscape Terrain types thatwere not samples include water bodies (lakes, ponds, rivers,and streams) and some of the less-common terrain types.Results and DiscussionOverall, older surfaces with less-active depositionalenvironments had the largest soil carbon stocks (Fig. 1).Mean accumulation of surface organic material was leastin ice-poor thaw basin margins (8.0 cm), eolian inactivesands (11.3 cm), and alluvial-marine deposits (11.1 cm), andgreatest in ice-rich thaw basin centers (32.2 cm) and margins(48.8 cm).Carbon stocks were greatest in alluvial-marine depositsand thaw basin centers, and lowest in eolian inactivesands and basin margins. A general trend of increasing soilorganic carbon with decreasing depositional activity wasseen across the study area. Soil carbon stocks were lowestin riverine terrain units (active riverbeds, active overbank,and inactive overbank deposits) and highest in thaw basinand and alluvial-marine deposits. In riverine terrains, mean(± s.d.) carbon stocks in the top 1 m of soil ranged froma low of 10.2 ± 7.8 kg C/m² in meander active riverbeddeposits to 20.0 ± 2 kg C/m² in delta inactive overbankdeposits. In thaw basin terrains, the range was 37.8 ± 3.9kg C/m² in ice-poor margin deposits to 41.7 ± 13.4 kg C/m²in ice-rich center deposits. Alluvial-marine deposits, whichexperience minimal deposition or erosional activity, hadthe highest soil carbon stocks (58.2 ± 16.5 kg C/m²). Whencalculated in the top 2 m, large increases in carbon stockswere seen in all terrain units (Fig. 1). These data representconservative estimates of total soil carbon stocks, becauseadditional soil carbon may be present beyond our samplingdepths, especially in ice-rich thaw basin centers and alluvialmarineterrains. Our estimates of carbon stocks fall into therange of other recently published accounts (Ping et al. 2002,Bockheim & Hinkel 2007) of carbon stocks in the top 1 m(Ping et al. 2002) and 2 m (Bockheim & Hinkel 2007) of soilon the Arctic Coastal Plain. However, this study includes awider variety of terrain types and includes carbon-poor soiltypes that have not been previously sampled.Soil organic carbon data for sampled terrain units werecombined with an existing terrain unit map of a portion ofthe Western Beaufort Coastal Plain to produce a distributionmap of soil organic carbon. As additional terrain unit mapsin this area become available, we plan to expand the carbondistribution map and generate a regional soil carbon estimatebased on the current dataset. Based on previous soil surveysin the area, this data can be applied to approximately 7000km 2 of the Beaufort Coastal Plain. In addition, this data canbe combined with thaw settlement estimates across the samearea to identify terrain units where sequestered carbon maybe incorporated into the active layer under the conditions ofa warmer climate or human disturbance.Figure 1. Mean carbon content of soils in common terrain unitsof the Arctic Coastal Plain, Alaska. Error bars represent standarddeviation and numbers in parenthesis show the sample size (numberof cores) used to calculate 1 m and 2 m soil organic carbon.AcknowledgmentsThis research was funded by ConocoPhillips Alaska, Inc.and managed by Caryn Rae, Senior Biological Consultant.John Shook, Tim Cater, Gerald Frost, Luke Mcdonagh,and Jennifer Mitchell assisted with the fieldwork and soilprocessing.ReferencesBockheim, J.G. & Hinkel, K.M. 2007. The importance of“deep” organic carbon in permafrost-affected soilsof Arctic Alaska. Soil Science Society of AmericaJournal 71: 1889-1892.Jorgenson, M.T., Shur, Y. & Pullman, E.R. 2006. Abruptincrease in permafrost degradation in Arctic Alaska.Geophysical Research Letters 33: L022503.Ping, C.L., Michaelson, G.J., Kimble, J.M. & Everett, L.2002. Chap. 47. Soil organic carbon stores in Alaska.In: R. Lal, J.M. Kimble, & R. Follet (eds.), AgriculturalPractices and Policies of Carbon Sequestration inSoils. CRC Press LLC, 485-494.Pullman, E.R., Jorgenson, M.T., and Shur, Y. 2007. Thawsettlement in soils of the Arctic Coastal Plain, Alaska.Arctic, Antarctic, and Alpine Research, 39: 468-476.Shur, Y. & Jorgenson, M.T. 1998. Cryostructure developmenton the floodplain of the Colville River Delta, NorthernAlaska. Proceedings of the Seventh <strong>International</strong><strong>Conference</strong> on Permafrost, Yellowknife, Canada:993-999.246
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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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