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Sample records for high arctic tundra

  1. Diversification of Nitrogen Sources in Various Tundra Vegetation Types in the High Arctic.

    PubMed

    Skrzypek, Grzegorz; Wojtuń, Bronisław; Richter, Dorota; Jakubas, Dariusz; Wojczulanis-Jakubas, Katarzyna; Samecka-Cymerman, Aleksandra

    2015-01-01

    Low nitrogen availability in the high Arctic represents a major constraint for plant growth, which limits the tundra capacity for carbon retention and determines tundra vegetation types. The limited terrestrial nitrogen (N) pool in the tundra is augmented significantly by nesting seabirds, such as the planktivorous Little Auk (Alle alle). Therefore, N delivered by these birds may significantly influence the N cycling in the tundra locally and the carbon budget more globally. Moreover, should these birds experience substantial negative environmental pressure associated with climate change, this will adversely influence the tundra N-budget. Hence, assessment of bird-originated N-input to the tundra is important for understanding biological cycles in polar regions. This study analyzed the stable nitrogen composition of the three main N-sources in the High Arctic and in numerous plants that access different N-pools in ten tundra vegetation types in an experimental catchment in Hornsund (Svalbard). The percentage of the total tundra N-pool provided by birds, ranged from 0-21% in Patterned-ground tundra to 100% in Ornithocoprophilous tundra. The total N-pool utilized by tundra plants in the studied catchment was built in 36% by birds, 38% by atmospheric deposition, and 26% by atmospheric N2-fixation. The stable nitrogen isotope mixing mass balance, in contrast to direct methods that measure actual deposition, indicates the ratio between the actual N-loads acquired by plants from different N-sources. Our results enhance our understanding of the importance of different N-sources in the Arctic tundra and the used methodological approach can be applied elsewhere.

  2. Diversification of Nitrogen Sources in Various Tundra Vegetation Types in the High Arctic

    PubMed Central

    Skrzypek, Grzegorz; Wojtuń, Bronisław; Richter, Dorota; Jakubas, Dariusz; Wojczulanis-Jakubas, Katarzyna; Samecka-Cymerman, Aleksandra

    2015-01-01

    Low nitrogen availability in the high Arctic represents a major constraint for plant growth, which limits the tundra capacity for carbon retention and determines tundra vegetation types. The limited terrestrial nitrogen (N) pool in the tundra is augmented significantly by nesting seabirds, such as the planktivorous Little Auk (Alle alle). Therefore, N delivered by these birds may significantly influence the N cycling in the tundra locally and the carbon budget more globally. Moreover, should these birds experience substantial negative environmental pressure associated with climate change, this will adversely influence the tundra N-budget. Hence, assessment of bird-originated N-input to the tundra is important for understanding biological cycles in polar regions. This study analyzed the stable nitrogen composition of the three main N-sources in the High Arctic and in numerous plants that access different N-pools in ten tundra vegetation types in an experimental catchment in Hornsund (Svalbard). The percentage of the total tundra N-pool provided by birds, ranged from 0–21% in Patterned-ground tundra to 100% in Ornithocoprophilous tundra. The total N-pool utilized by tundra plants in the studied catchment was built in 36% by birds, 38% by atmospheric deposition, and 26% by atmospheric N2-fixation. The stable nitrogen isotope mixing mass balance, in contrast to direct methods that measure actual deposition, indicates the ratio between the actual N-loads acquired by plants from different N-sources. Our results enhance our understanding of the importance of different N-sources in the Arctic tundra and the used methodological approach can be applied elsewhere. PMID:26376204

  3. Sunlight stimulates methane uptake and nitrous oxide emission from the High Arctic tundra.

    PubMed

    Li, Fangfang; Zhu, Renbin; Bao, Tao; Wang, Qing; Xu, Hua

    2016-12-01

    Many environmental factors affecting methane (CH4) and nitrous oxide (N2O) fluxes have been investigated during the processes of carbon and nitrogen transformation in the boreal tundra. However, effects of sunlight on CH4 and N2O fluxes and their budgets were neglected in the boreal tundra. Here, summertime CH4 and N2O fluxes in the presence and total absence of sunlight were investigated at the six tundra sites (DM1-DM6) on Ny-Ålesund in the High Arctic. The mean CH4 fluxes at the tundra sites ranged from -4.7 to -158.6μg CH4 m(-2)h(-1) in the presence of light, indicating that a large CH4 sink occurred in the tundra soils. However, enhanced CH4 emission in total absence of light occurred at all the tundra sites. The mean N2O fluxes ranged from 7.4 to 14.6μg N2O m(-2)h(-1) in the presence of light, whereas in the absence of light all the tundra sites generally released less N2O, and even significant N2O uptake occurred there. Soil temperature, chamber temperature and soil moisture showed no significant correlations with tundra CH4 and N2O flux. The presence of sunlight increased tundra CH4 uptake by 114.2μg CH4 m(-2)h(-1) and N2O emission by 10.9μg N2O m(-2)h(-1) compared with total absence of light. Overall our results showed that tundra ecosystem switched from CH4 sink and N2O emission source in the presence of light to CH4 emission source and N2O sink in the absence of light. Therefore sunlight had an important effect on CH4 and N2O budgets in the High Arctic tundra. The exclusion of sunlight might overestimate CH4 budgets, but underestimate N2O budgets in the Arctic tundra ecosystem.

  4. Importance of Marine-Derived Nutrients Supplied by Planktivorous Seabirds to High Arctic Tundra Plant Communities

    PubMed Central

    Zwolicki, Adrian; Zmudczyńska-Skarbek, Katarzyna; Richard, Pierre; Stempniewicz, Lech

    2016-01-01

    We studied the relative importance of several environmental factors for tundra plant communities in five locations across Svalbard (High Arctic) that differed in geographical location, oceanographic and climatic influence, and soil characteristics. The amount of marine-derived nitrogen in the soil supplied by seabirds was locally the most important of the studied environmental factors influencing the tundra plant community. We found a strong positive correlation between δ15N isotopic values and total N content in the soil, confirming the fundamental role of marine-derived matter to the generally nutrient-poor Arctic tundra ecosystem. We also recorded a strong correlation between the δ15N values of soil and of the tissues of vascular plants and mosses, but not of lichens. The relationship between soil δ15N values and vascular plant cover was linear. In the case of mosses, the percentage ground cover reached maximum around a soil δ 15N value of 8‰, as did plant community diversity. This soil δ15N value clearly separated the occurrence of plants with low nitrogen tolerance (e.g. Salix polaris) from those predominating on high N content soils (e.g. Cerastium arcticum, Poa alpina). Large colonies of planktivorous little auks have a great influence on Arctic tundra vegetation, either through enhancing plant abundance or in shaping plant community composition at a local scale. PMID:27149113

  5. Importance of Marine-Derived Nutrients Supplied by Planktivorous Seabirds to High Arctic Tundra Plant Communities.

    PubMed

    Zwolicki, Adrian; Zmudczyńska-Skarbek, Katarzyna; Richard, Pierre; Stempniewicz, Lech

    2016-01-01

    We studied the relative importance of several environmental factors for tundra plant communities in five locations across Svalbard (High Arctic) that differed in geographical location, oceanographic and climatic influence, and soil characteristics. The amount of marine-derived nitrogen in the soil supplied by seabirds was locally the most important of the studied environmental factors influencing the tundra plant community. We found a strong positive correlation between δ15N isotopic values and total N content in the soil, confirming the fundamental role of marine-derived matter to the generally nutrient-poor Arctic tundra ecosystem. We also recorded a strong correlation between the δ15N values of soil and of the tissues of vascular plants and mosses, but not of lichens. The relationship between soil δ15N values and vascular plant cover was linear. In the case of mosses, the percentage ground cover reached maximum around a soil δ 15N value of 8‰, as did plant community diversity. This soil δ15N value clearly separated the occurrence of plants with low nitrogen tolerance (e.g. Salix polaris) from those predominating on high N content soils (e.g. Cerastium arcticum, Poa alpina). Large colonies of planktivorous little auks have a great influence on Arctic tundra vegetation, either through enhancing plant abundance or in shaping plant community composition at a local scale.

  6. Nitrogen Accumulation and Partitioning in High Arctic Tundra from Extreme Atmospheric N Deposition Events

    NASA Astrophysics Data System (ADS)

    Phoenix, G. K.; Osborn, A.; Blaud, A.; Press, M. C.; Choudhary, S.

    2013-12-01

    Arctic ecosystems are threatened by pollution from extreme atmospheric nitrogen (N) deposition events. These events occur from the long-range transport of reactive N from pollution sources at lower latitudes and can deposit up to 80% of the annual N deposition in just a few days. To date, the fate and impacts of these extreme pollutant events has remained unknown. Using a field simulation study, we undertook the first assessment of the fate of acutely deposited N on arctic tundra. Extreme N deposition events were simulated on field plots at Ny-Ålesund, Svalbard (79oN) at rates of 0, 0.04, 0.4 and 1.2 g N m-2 yr-1 applied as NH4NO3 solution over 4 days, with 15N tracers used in the second year to quantify the fate of the deposited N in the plant, soil, microbial and leachate pools. Separate applications of 15NO3- and 15NH4+ were also made to determine the importance of N form in the fate of N. Recovery of the 15N tracer at the end of the first growing season approached 100% of the 15N applied irrespective of treatment level, demonstrating the considerable capacity of High Arctic tundra to capture pollutant N from extreme deposition events. Most incorporation of the 15N was found in bryophytes, followed by the dominant vascular plant (Salix polaris) and the microbial biomass of the soil organic layer. Total recovery remained high in the second growing season (average of 90%), indicating highly conservative N retention. Between the two N forms, recovery of 15NO3- and 15NH4+ were equal in the non-vascular plants, whereas in the vascular plants (particularly Salix polaris) recovery of 15NO3- was four times higher than of 15NH4+. Overall, these findings show that High Arctic tundra has considerable capacity to capture and retain the pollutant N deposited in acute extreme deposition events. Given they can represent much of the annual N deposition, extreme deposition events may be more important than increased chronic N deposition as a pollution source. Furthermore

  7. Variation in bird's originating nitrogen availability limits High Arctic tundra development over last 2000 year (Hornsund, Svalbard)

    NASA Astrophysics Data System (ADS)

    Skrzypek, Grzegorz; Wojtuń, Bronisław; Hua, Quan; Richter, Dorota; Jakubas, Dariusz; Wojczulanis-Jakubas, Katarzyna; Samecka-Cymerman, Aleksandra

    2016-04-01

    Arctic and subarctic regions play important roles in the global carbon balance. However, nitrogen (N) deficiency is a major constraint for organic carbon sequestration in the High Arctic. Hence, the identification of the relative contributions from different N-sources is critical for understanding the constraints that limit tundra growth. The stable nitrogen composition of the three main N-sources and numerous plants were analyzed in ten tundra types (including those influenced by seabirds) in the Fuglebekken catchment (Hornsund, Svalbard, 77°N 15°E). The percentage of the total tundra N-pool provided by seabirds' feces (from planktivorous colonially breeding little auks Alle alle), ranged from 0-21% in Patterned-ground tundra to 100% in Ornithocoprophilous tundra. The total N-pool utilized by tundra plants in the studied catchment originated from birds (36%), atmospheric deposition (38%), and N2-fixation (26%). The results clearly show that N-pool in the tundra is significantly supplemented by nesting seabirds. Thus, if they experienced climate change induced substantial negative environmental pressure, it would adversely influence the tundra N-budget (Skrzypek et al. 2015). The growth rates and the sediment thickness (<15cm) in different tundra types varied considerably but the tundra age was similar in the whole area, <450 cal BP. The only exception was Ornithocoprophilous bird-N rich tundra with very diverse ages ranging from 235 to 2300 cal BP and thickness up to 110 cm. The growth rates for this tundra (62 cm core, 18 AMS 14C dates) were high (1.5-3.0 mm/yr) between 1568 and 1804 AD and then substantially declined for the period between 1804 and 1929 AD (0.2 mm/yr). These findings deliver an additional argument, that the organic matter accumulation is driven not only directly by climatic conditions but also by birds' contribution to the tundra N-pool. Skrzypek G, Wojtuń B, Richter D, Jakubas D, Wojczulanis-Jakubas K, Samecka-Cymerman A, 2015

  8. Nitrogen accumulation and partitioning in a High Arctic tundra ecosystem from extreme atmospheric N deposition events.

    PubMed

    Choudhary, Sonal; Blaud, Aimeric; Osborn, A Mark; Press, Malcolm C; Phoenix, Gareth K

    2016-06-01

    Arctic ecosystems are threatened by pollution from recently detected extreme atmospheric nitrogen (N) deposition events in which up to 90% of the annual N deposition can occur in just a few days. We undertook the first assessment of the fate of N from extreme deposition in High Arctic tundra and are presenting the results from the whole ecosystem (15)N labelling experiment. In 2010, we simulated N depositions at rates of 0, 0.04, 0.4 and 1.2 g Nm(-2)yr(-1), applied as (15)NH4(15)NO3 in Svalbard (79(°)N), during the summer. Separate applications of (15)NO3(-) and (15)NH4(+) were also made to determine the importance of N form in their retention. More than 95% of the total (15)N applied was recovered after one growing season (~90% after two), demonstrating a considerable capacity of Arctic tundra to retain N from these deposition events. Important sinks for the deposited N, regardless of its application rate or form, were non-vascular plants>vascular plants>organic soil>litter>mineral soil, suggesting that non-vascular plants could be the primary component of this ecosystem to undergo measurable changes due to N enrichment from extreme deposition events. Substantial retention of N by soil microbial biomass (70% and 39% of (15)N in organic and mineral horizon, respectively) during the initial partitioning demonstrated their capacity to act as effective buffers for N leaching. Between the two N forms, vascular plants (Salix polaris) in particular showed difference in their N recovery, incorporating four times greater (15)NO3(-) than (15)NH4(+), suggesting deposition rich in nitrate will impact them more. Overall, these findings show that despite the deposition rates being extreme in statistical terms, biologically they do not exceed the capacity of tundra to sequester pollutant N during the growing season. Therefore, current and future extreme events may represent a major source of eutrophication.

  9. Short-term herbivory has long-term consequences in warmed and ambient high Arctic tundra

    NASA Astrophysics Data System (ADS)

    Little, Chelsea J.; Cutting, Helen; Alatalo, Juha; Cooper, Elisabeth

    2017-02-01

    Climate change is occurring across the world, with effects varying by ecosystem and region but already occurring quickly in high-latitude and high-altitude regions. Biotic interactions are important in determining ecosystem response to such changes, but few studies have been long-term in nature, especially in the High Arctic. Mesic tundra plots on Svalbard, Norway, were subjected to grazing at two different intensities by captive Barnacle geese from 2003–2005, in a factorial design with warming by Open Top Chambers. Warming manipulations were continued through 2014, when we measured vegetation structure and composition as well as growth and reproduction of three dominant species in the mesic meadow. Significantly more dead vascular plant material was found in warmed compared to ambient plots, regardless of grazing history, but in contrast to many short-term experiments no difference in the amount of living material was found. This has strong implications for nutrient and carbon cycling and could feed back into community productivity. Dominant species showed increased flowering in warmed plots, especially in those plots where grazing had been applied. However, this added sexual reproduction did not translate to substantial shifts in vegetative cover. Forbs and rushes increased slightly in warmed plots regardless of grazing, while the dominant shrub, Salix polaris, generally declined with effects dependent on grazing, and the evergreen shrub Dryas octopetala declined with previous intensive grazing. There were no treatment effects on community diversity or evenness. Thus despite no changes in total live abundance, a typical short-term response to environmental conditions, we found pronounced changes in dead biomass indicating that tundra ecosystem processes respond to medium- to long-term changes in conditions caused by 12 seasons of summer warming. We suggest that while high arctic tundra plant communities are fairly resistant to current levels of climate warming

  10. Snowpack fluxes of methane and carbon dioxide from high Arctic tundra

    NASA Astrophysics Data System (ADS)

    Pirk, Norbert; Tamstorf, Mikkel P.; Lund, Magnus; Mastepanov, Mikhail; Pedersen, Stine H.; Mylius, Maria R.; Parmentier, Frans-Jan W.; Christiansen, Hanne H.; Christensen, Torben R.

    2016-11-01

    Measurements of the land-atmosphere exchange of the greenhouse gases methane (CH4) and carbon dioxide (CO2) in high Arctic tundra ecosystems are particularly difficult in the cold season, resulting in large uncertainty on flux magnitudes and their controlling factors during this long, frozen period. We conducted snowpack measurements of these gases at permafrost-underlain wetland sites in Zackenberg Valley (NE Greenland, 74°N) and Adventdalen Valley (Svalbard, 78°N), both of which also feature automatic closed chamber flux measurements during the snow-free period. At Zackenberg, cold season emissions were 1 to 2 orders of magnitude lower than growing season fluxes. Perennially, CH4 fluxes resembled the same spatial pattern, which was largely attributed to differences in soil wetness controlling substrate accumulation and microbial activity. We found no significant gas sinks or sources inside the snowpack but detected a pulse in the δ13C-CH4 stable isotopic signature of the soil's CH4 source during snowmelt, which suggests the release of a CH4 reservoir that was strongly affected by methanotrophic microorganisms. In the polygonal tundra of Adventdalen, the snowpack featured several ice layers, which suppressed the expected gas emissions to the atmosphere, and conversely lead to snowpack gas accumulations of up to 86 ppm CH4 and 3800 ppm CO2 by late winter. CH4 to CO2 ratios indicated distinctly different source characteristics in the rampart of ice-wedge polygons compared to elsewhere on the measured transect, possibly due to geomorphological soil cracks. Collectively, these findings suggest important ties between growing season and cold season greenhouse gas emissions from high Arctic tundra.

  11. The effect of a permafrost disturbance on growing-season carbon-dioxide fluxes in a high Arctic tundra ecosystem

    NASA Astrophysics Data System (ADS)

    Cassidy, Alison E.; Christen, Andreas; Henry, Gregory H. R.

    2016-04-01

    Soil carbon stored in high-latitude permafrost landscapes is threatened by warming and could contribute significant amounts of carbon to the atmosphere and hydrosphere as permafrost thaws. Thermokarst and permafrost disturbances, especially active layer detachments and retrogressive thaw slumps, are present across the Fosheim Peninsula, Ellesmere Island, Canada. To determine the effects of retrogressive thaw slumps on net ecosystem exchange (NEE) of CO2 in high Arctic tundra, we used two eddy covariance (EC) tower systems to simultaneously and continuously measure CO2 fluxes from a disturbed site and the surrounding undisturbed tundra. During the 32-day measurement period in the 2014 growing season, the undisturbed tundra was a small net sink (NEE = -0.1 g C m-2 d-1); however, the disturbed terrain of the retrogressive thaw slump was a net source (NEE = +0.4 g C m-2 d-1). Over the measurement period, the undisturbed tundra sequestered 3.8 g C m-2, while the disturbed tundra released 12.5 g C m-2. Before full leaf-out in early July, the undisturbed tundra was a small source of CO2 but shifted to a sink for the remainder of the sampling season (July), whereas the disturbed tundra remained a source of CO2 throughout the season. A static chamber system was also used to measure daytime fluxes in the footprints of the two towers, in both disturbed and undisturbed tundra, and fluxes were partitioned into ecosystem respiration (Re) and gross primary production (GPP). Average GPP and Re found in disturbed tundra were smaller (+0.40 µmol m-2 s-1 and +0.55 µmol m-2 s-1, respectively) than those found in undisturbed tundra (+1.19 µmol m-2 s-1 and +1.04 µmol m-2 s-1, respectively). Our measurements indicated clearly that the permafrost disturbance changed the high Arctic tundra system from a sink to a source for CO2 during the majority of the growing season (late June and July).

  12. The effect of a permafrost disturbance on growing-season carbon-dioxide fluxes in a high Arctic tundra ecosystem

    NASA Astrophysics Data System (ADS)

    Cassidy, A. E.; Christen, A.; Henry, G. H. R.

    2015-12-01

    Soil carbon stored in high-latitude permafrost landscapes is threatened by warming, and could contribute significant amounts of carbon to the atmosphere and hydrosphere as permafrost thaws. Permafrost disturbances, especially active layer detachments and retrogressive thaw slumps, have increased in frequency and magnitude across the Fosheim Peninsula, Ellesmere Island, Canada. To determine the effects of retrogressive thaw slumps on net ecosystem exchange (NEE) of CO2 in high Arctic tundra, we used two eddy covariance (EC) tower systems to simultaneously and continuously measure CO2 fluxes from a disturbed site and the surrounding undisturbed tundra. During the 32-day measurement period in the 2014 growing season the undisturbed tundra was a small net sink (NEE = -0.12 g C m-2 d-1); however, the disturbed terrain of the retrogressive thaw slump was a net source (NEE = +0.39 g C m-2 d-1). Over the measurement period, the undisturbed tundra sequestered 3.84 g C m-2, while the disturbed tundra released 12.48 g C m-2. Before full leaf out in early July, the undisturbed tundra was a small source of CO2, but shifted to a sink for the remainder of the sampling season (July), whereas the disturbed tundra remained a source of CO2 throughout the season. A static chamber system was also used to measure fluxes in the footprints of the two towers, in both disturbed and undisturbed tundra, and fluxes were partitioned into ecosystem respiration (Re) and gross primary production (GPP). Average GPP and Re found in disturbed tundra were smaller (+0.41 μmol m-2 s-1 and +0.50 μmol m-2 s-1, respectively) than those found in undisturbed tundra (+1.21 μmol m-2 s-1 and +1.00 μmol m-2 s-1, respectively). Our measurements indicated clearly that the permafrost disturbance changed the high Arctic tundra system from a sink to a source for CO2 during the growing season.

  13. Energy fluxes in a high Arctic tundra heath subjected to strong climate warming

    NASA Astrophysics Data System (ADS)

    Lund, M.; Hansen, B. U.; Pedersen, S. H.; Stiegler, C.; Tamstorf, M. P.

    2012-12-01

    During recent decades the observed warming in the Arctic has been almost twice as large as the global average. The implications of such strong warming on surface energy balance, regulating permafrost thaw, hydrology, soil stability and carbon mineralization, need to be assessed. In Zackenberg, northeast Greenland, measurements of energy balance components in various environments have been performed since late 90's, coordinated by Zackenberg Ecological Research Operations. During 1996-2009, mean annual temperature in the area has increased by ca. 0.15 °C yr-1; while maximum thaw depth has increased by 1.4-1.8 cm yr-1. Eddy covariance measurements of energy fluxes have been performed in a Cassiope heath plant community, a commonly occurring tundra ecosystem type in circumpolar middle and high Arctic areas, in Zackenberg allowing for detailed investigations of relationships between energy fluxes and meteorological and soil physical characteristics. As the available data set spans more than a decade, possible trends in energy flux components resulting from warming related changes such as earlier snow melt, increased active layer depth and higher temperatures can be investigated. This presentation will focus on the mid-summer period from which eddy covariance measurements are available. The summer-time energy partitioning at the Zackenberg tundra heath site will be characterized using ratios of sensible, latent and ground heat flux to net radiation and Bowen ratio, whereas the surface characteristics will be described using surface resistance, McNaughton and Jarvis Ω value and Priestley-Taylor α coefficient. Furthermore, we aim to estimate the full year, all energy balance components for the tundra heath site using Snow Model (Liston and Elder 2006) for the dark winter period during which no eddy covariance measurements are available. The snow cover duration in the area is a major regulator of the energy partitioning. Early results point towards high summer

  14. 100% Retention of Snowpack Derived Nitrogen Over 10 Years in High Arctic Tundra

    NASA Astrophysics Data System (ADS)

    Choudhary, S.; Tye, A. M.; Young, S. D.; West, H. M.; Phoenix, G. K.

    2013-12-01

    ecosystem sinks for the 15N tracer in the long-term were organic humus soil, followed by bryophytes and then vascular plants, it is concluded that greater N deposition resulting in greater released of N from melting snowpack could significantly enrich the plant N pool and possibly enhance plant growth (with a potential to increase C storage) in the future. Overall, this study shows that high arctic tundra has considerable short- and long term- capacity for retention of snow-melt deposited N, with very tight internal recycling that allows 100% of the initially sequestered N to be retained over 10 years. Such capacity for pollutant N retention may exacerbate the impact that increased N deposition has on high arctic tundra.

  15. Methane and nitrous oxide fluxes from four tundra ecotopes in Ny-Ålesund of the High Arctic.

    PubMed

    Chen, Qingqing; Zhu, Renbin; Wang, Qing; Xu, Hua

    2014-07-01

    During the summers of 2008 and 2009, net methane (CH₄) and nitrous oxide (N₂O) fluxes were investigated from 4 tundra ecotopes: normal lowland tundra (LT), bird sanctuary tundra (BT), the tundra in an abandoned coal mine (CT) and the tundra in scientific bases (ST) in Ny-Ålesund of the High Arctic. Tundra soils in CT (184.5 ± 40.0 μg CH4/(m²·hr)) and ST (367.6 ± 92.3μg CH4/(m²·hr)) showed high CH4 emissions due to the effects of human activities, whereas high CH4 uptake or low emission occurred in the soils of LT and BT. The lowland tundra soils (mean, -4.4-4.3μg N₂O/(m²·hr)) were weak N₂O sources and even sinks. Bird activity increased N₂O emissions from BT with the mean flux of 7.9μgN2O/(m(2)·hr). The mean N₂O fluxes from CT (45.4 ± 10.2 μg N₂O/(m²·hr)) and ST (78.8 ± 18.5μg N₂O/(m²·hr)) were one order of magnitude higher than those from LT and BT, indicating that human activities significantly increased N₂O emissions from tundra soils. Soil total carbon and water regime were important factors affecting CH₄ fluxes from tundra soils. The N₂O fluxes showed a significant positive correlation with ammonia nitrogen (NH₄(+)-N) contents (r=0.66, p<0.001) at all the observation sites, indicating that ammonia nitrogen (NH₄(+)-N) content acted as a strong predictor for N₂O emissions from tundra soils. The CH4 and N₂O fluxes did not correspond to the temperature variations of soil at 0-15 cm depths. Overall our results implied that human activities might have greater effects on soil CH₄ and N₂O emissions than current climate warming in Ny-Ålesund, High Arctic.

  16. The growth of shrubs on high Arctic tundra at Bylot Island: impact on snow physical properties and permafrost thermal regime

    NASA Astrophysics Data System (ADS)

    Domine, Florent; Barrere, Mathieu; Morin, Samuel

    2016-12-01

    With climate warming, shrubs have been observed to grow on Arctic tundra. Their presence is known to increase snow height and is expected to increase the thermal insulating effect of the snowpack. An important consequence would be the warming of the ground, which will accelerate permafrost thaw, providing an important positive feedback to warming. At Bylot Island (73° N, 80° W) in the Canadian high Arctic where bushes of willows (Salix richardsonii Hook) are growing, we have observed the snow stratigraphy and measured the vertical profiles of snow density, thermal conductivity and specific surface area (SSA) in over 20 sites of high Arctic tundra and in willow bushes 20 to 40 cm high. We find that shrubs increase snow height, but only up to their own height. In shrubs, snow density, thermal conductivity and SSA are all significantly lower than on herb tundra. In shrubs, depth hoar which has a low thermal conductivity was observed to grow up to shrub height, while on herb tundra, depth hoar only developed to 5 to 10 cm high. The thermal resistance of the snowpack was in general higher in shrubs than on herb tundra. More signs of melting were observed in shrubs, presumably because stems absorb radiation and provide hotspots that initiate melting. When melting was extensive, thermal conductivity was increased and thermal resistance was reduced, counteracting the observed effect of shrubs in the absence of melting. Simulations of the effect of shrubs on snow properties and on the ground thermal regime were made with the Crocus snow physics model and the ISBA (Interactions between Soil-Biosphere-Atmosphere) land surface scheme, driven by in situ and reanalysis meteorological data. These simulations did not take into account the summer impact of shrubs. They predict that the ground at 5 cm depth at Bylot Island during the 2014-2015 winter would be up to 13 °C warmer in the presence of shrubs. Such warming may however be mitigated by summer effects.

  17. Disentangling trophic relationships in a High Arctic tundra ecosystem through food web modeling.

    PubMed

    Legagneux, P; Gauthier, G; Berteaux, D; Bêty, J; Cadieux, M C; Bilodeau, F; Bolduc, E; McKinnon, L; Tarroux, A; Therrien, J F; Morissette, L; Krebs, C J

    2012-07-01

    Determining the manner in which food webs will respond to environmental changes is difficult because the relative importance of top-down vs. bottom-up forces in controlling ecosystems is still debated. This is especially true in the Arctic tundra where, despite relatively simple food webs, it is still unclear which forces dominate in this ecosystem. Our primary goal was to assess the extent to which a tundra food web was dominated by plant-herbivore or predator-prey interactions. Based on a 17-year (1993-2009) study of terrestrial wildlife on Bylot Island, Nunavut, Canada, we developed trophic mass balance models to address this question. Snow Geese were the dominant herbivores in this ecosystem, followed by two sympatric lemming species (brown and collared lemmings). Arctic foxes, weasels, and several species of birds of prey were the dominant predators. Results of our trophic models encompassing 19 functional groups showed that <10% of the annual primary production was consumed by herbivores in most years despite the presence of a large Snow Goose colony, but that 20-100% of the annual herbivore production was consumed by predators. The impact of herbivores on vegetation has also weakened over time, probably due to an increase in primary production. The impact of predators was highest on lemmings, intermediate on passerines, and lowest on geese and shorebirds, but it varied with lemming abundance. Predation of collared lemmings exceeded production in most years and may explain why this species remained at low density. In contrast, the predation rate on brown lemmings varied with prey density and may have contributed to the high-amplitude, periodic fluctuations in the abundance of this species. Our analysis provided little evidence that herbivores are limited by primary production on Bylot Island. In contrast, we measured strong predator-prey interactions, which supports the hypothesis that this food web is primarily controlled by top-down forces. The presence of

  18. Impact of seabird activity on nitrous oxide and methane fluxes from High Arctic tundra in Svalbard, Norway

    NASA Astrophysics Data System (ADS)

    Zhu, Renbin; Chen, Qingqing; Ding, Wei; Xu, Hua

    2012-12-01

    In this study, tundra N2O and CH4 fluxes were measured from one seabird sanctuary (SBT) and two non-seabird colonies (NST-I and NST-II) in Ny-Ålesund (79°55'N, 11°56'E), Svalbard during the summers of 2008 and 2009. N2O and CH4 fluxes from SBT showed large temporal and spatial variations depending on the intensity of seabird activity. High seabird activity sites showed large N2O and CH4 emissions while low N2O and CH4 emissions, even CH4 uptake occurred at medium and low seabird activity sites. Overall the mean fluxes were 18.3 ± 3.6 μg N2O m-2 h-1 and 53.5 ± 20.3 μg CH4 m-2 h-1 from tundra SBT whereas tundra NST-I and NST-II represented a relatively weak N2O source (8.3 ± 13.2 μg N2O m-2 h-1) and strong CH4 sink (-82.8 ± 22.3 μg CH4 m-2 h-1). Seabird activity was the strongest control of N2O and CH4 fluxes compared with soil temperature and moisture, and high N2O and CH4 emissions were created by soil physical and chemical processes (the sufficient supply of nutrients NH4+-N, NO3--N, total nitrogen, total phosphorus and total carbon from seabird guano, seabird tramp and appropriate water content) related to the seabird activity. Our work suggests that tundra ecosystems impacted by seabird activity are the potential "hotspots" for N2O and CH4 emissions although these sources have been largely neglected at present. Furthermore the combination of seabird activity and warming climate will likely further enhance N2O and CH4 emissions from the High Arctic tundra.

  19. Tundra Rehabilitation in Alaska's Arctic

    NASA Astrophysics Data System (ADS)

    Lynn, L. A.

    2012-12-01

    Oil exploration in Alaska's Arctic has been conducted for more than 40 years, resulting in over 3,640 ha of gravel fill placed for roads, pads, and airstrips to support the industry. Likewise, tundra disturbance from burying power lines and by tundra vehicle travel are also common. Rehabilitation of disturbed sites began around 2002, with well over 150 ha that has been previously treated or is currently being rehabilitated. Two primary goals of rehabilitation efforts have been 1) revegetation by indigenous species, and 2) limiting thermokarst. Early efforts were concerned that removing gravel and having exposed bare ground would lead to extensive subsidence and eolian erosion. Native grass cultivars (e.g. Poa glauca, Arctagrostis latifolia, and Festuca rubra) were seeded to create vegetation cover quickly with the expectation that these grasses would survive only temporarily. The root masses and leaf litter were also expected to trap indigenous seed to enhance natural recolonization by indigenous plants. Due to the remote location of these sites, many of which are only accessible by helicopter, most are visited only two to three times following cultivation treatments, providing a limited data pool. At many sites, the total live seeded grass cover declined about 15% over the first 5¬-6 years (from around 30% to 15% cover), while total live indigenous vascular cover increased from no or trace cover to an average of 10% cover in that time. Cover of indigenous vascular plants at sites that were not seeded with native grass cultivars averaged just less than 10% after 10 years, showing no appreciable difference between the two approaches. Final surface elevations at the sites affect local hydrology and soil moisture. Other factors that influence the success of vegetation cover are proximity to the Arctic coast (salt effects), depth of remaining gravel, and changes in characteristics of the near-surface soil. Further development of rehabilitation techniques and the

  20. Timing, Magnitude and Sources of Ecosystem Respiration in High Arctic Tundra of NW Greenland

    NASA Astrophysics Data System (ADS)

    Lupascu, M.; Xu, X.; Lett, C.; Maseyk, K. S.; Lindsey, D. S.; Thomas, J. S.; Welker, J. M.; Czimczik, C. I.

    2011-12-01

    High arctic ecosystems with low vegetation density contain significant stocks of organic carbon (C) in the form of soil organic matter that range in age from modern to ancient. How rapidly these C pools can be mineralized and lost to the atmosphere as CO2 (ecosystem respiration, ER) as a consequence of warming and, or changes in precipitation is a major uncertainty in our understanding of current and future arctic biogeochemistry and for predicting future levels of atmospheric CO2. In a 2-year study (2010-2011), we monitored seasonal changes in the magnitude, timing and sources of ER and soil pore space CO2 in the High Arctic of NW Greenland under current and simulated, future climate conditions. Measurements were taken from May to August at a multi-factorial, long-term climate change experiment in prostrate dwarf-shrub tundra on patterned ground with 5 treatments: (T1) +2oC warming, (T2) +4oC warming, (W) +50% summer precipitation, (T2W) +4oC + 50% summer precipitation, and (C) control. ER (using opaque chambers) and soil CO2 concentrations (wells) were monitored daily via infrared spectroscopy (LI-COR 800 & 840). The source of CO2 was inferred from its radiocarbon (14C) content analyzed at the AMS facility in UCI. CO2 was sampled monthly using molecular sieve traps (chambers) or evacuated canisters (wells). Highest rates of ER are observed on vegetated ground with a maximum in mid summer - reflecting a peak in plant productivity and soil temperature. Respiration rates from bare ground remain similar throughout the summer. Additional soil moisture, administered or due to precipitation events, strongly enhances ER from both vegetated and bare ground. Daily ER budget for the sampling period was of 53.1 mmol C m-2 day-1 for the (C) vegetated areas compared to the 60.0 for the (T2), 68.1 for the (T2W) or the 79.9 for the (W) treatment. ER was highly correlated to temperature (eg. C = 0.8; T2W = 0.8) until middle of July, when heavy precipitation started to occur. In

  1. Long-term experimentally deepened snow decreases growing-season respiration in a low- and high-arctic tundra ecosystem

    NASA Astrophysics Data System (ADS)

    Semenchuk, Philipp R.; Christiansen, Casper T.; Grogan, Paul; Elberling, Bo; Cooper, Elisabeth J.

    2016-05-01

    Tundra soils store large amounts of carbon (C) that could be released through enhanced ecosystem respiration (ER) as the arctic warms. Over time, this may change the quantity and quality of available soil C pools, which in-turn may feedback and regulate ER responses to climate warming. Therefore, short-term increases in ER rates due to experimental warming may not be sustained over longer periods, as observed in other studies. One important aspect, which is often overlooked, is how climatic changes affecting ER in one season may carry-over and determine ER in following seasons. Using snow fences, we increased snow depth and thereby winter soil temperatures in a high-arctic site in Svalbard (78°N) and a low-arctic site in the Northwest Territories, Canada (64°N), for 5 and 9 years, respectively. Deepened snow enhanced winter ER while having negligible effect on growing-season soil temperatures and soil moisture. Growing-season ER at the high-arctic site was not affected by the snow treatment after 2 years. However, surprisingly, the deepened snow treatments significantly reduced growing-season ER rates after 5 years at the high-arctic site and after 8-9 years at the low-arctic site. We speculate that the reduction in ER rates, that became apparent only after several years of experimental manipulation, may, at least in part, be due to prolonged depletion of labile C substrate as a result of warmer soils over multiple cold seasons. Long-term changes in winter climate may therefore significantly influence annual net C balance not just because of increased wintertime C loss but also because of "legacy" effects on ER rates during the following growing seasons.

  2. Stochastic daily modeling of arctic tundra ecosystems

    NASA Astrophysics Data System (ADS)

    Erler, A.; Epstein, H. E.; Frazier, J.

    2011-12-01

    ArcVeg is a dynamic vegetation model that has simulated interannual variability of production and abundance of arctic tundra plant types in previous studies. In order to address the effects of changing seasonality on tundra plant community composition and productivity, we have uniquely adapted the model to operate on the daily timescale. Each section of the model-weather generation, nitrogen mineralization, and plant growth dynamics-are driven by daily fluctuations in simulated temperature conditions. These simulation dynamics are achieved by calibrating stochastic iterative loops and mathematical functions with raw field data. Air temperature is the fundamental driver in the model, parameterized by climate data collected in the field across numerous arctic tundra sites, and key daily statistics are extracted (mean and standard deviation of temperature for each day of the year). Nitrogen mineralization is calculated as an exponential function from the simulated temperature. The seasonality of plant growth is driven by the availability of nitrogen and constrained by historical patterns and dynamics of the remotely sensed normalized difference vegetation index (NDVI), as they pertain to the seasonal onset of growth. Here we describe the methods used for daily weather generation, nitrogen mineralization, and the daily competition among twelve plant functional types for nitrogen and subsequent growth. This still rather simple approach to vegetation dynamics has the capacity to generate complex relationships between seasonal patterns of temperature and arctic tundra vegetation community structure and function.

  3. High Arctic tundra greenhouse gas fluxes: new insights from Adventdalen, Svalbard

    NASA Astrophysics Data System (ADS)

    Pirk, N.; Parmentier, F. J. W.; Mastepanov, M.; Christiansen, H. H.; Christensen, T. R.

    2014-12-01

    Data on greenhouse gas (GHG) exchange in high Arctic environments is rare but badly needed, as the environment in these places will likely respond early and most rapidly to climate warming. Also, the high Arctic holds carbon stocks in permafrost that is most likely to be made vulnerable to decomposition as ecosystems get warmer. In 2011 we established a long-term GHG flux-monitoring site in the Adventdalen valley on the Svalbard archipelago. The site is characterised by little precipitation (about 200 mm/year), a strong marine influence (summer air temperatures predominantly around 5 degrees Celsius), and a continuous permafrost ground with low-centered ice wedge polygons at the surface. The measurement equipment features an eddy-covariance tower and an automatic chamber system, both set up in accordance with already existing monitoring programs (INTERACT, ICOS and the Greenland Ecosystem Monitoring program). Here, we present the first results of this multi-year campaign, such as the pattern of carbon dioxide and methane fluxes during the growing and shoulder seasons, including the recently discovered autumn burst, as well as carbon dioxide fluxes during wintertime. Carbon dioxide fluxes measured with eddy-covariance agree well with the automatic chamber data, and indicate that the site acts as a sink for carbon dioxide. Methane fluxes measured by the automatic chamber system indicate a significant methane source, which is, however, weaker than at comparable sites in Greenland. There is a high degree of inter-annual variation in methane emissions, which seems to be driven by the amount of precipitation in summer. On top of that, there is a strong spatial variability resembling the polygonal ground pattern. This variability is also reflected in the occurrence of the methane autumn burst, which could be detected and is spatially and temporally distributed at a few locations and years.

  4. How will Shrub Expansion Impact Soil Carbon Sequestration in Arctic Tundra?

    NASA Astrophysics Data System (ADS)

    Czimczik, C. I.; Holden, S. R.; He, Y.; Randerson, J. T.

    2015-12-01

    Multiple lines of evidence suggest that plant productivity, and especially shrub abundance, is increasing in the Arctic in response to climate change. This greening is substantiated by increases in the Normalized Difference Vegetation Index, repeat photography and field observations. The implications of a greener Arctic on carbon sequestration by tundra ecosystems remain poorly understood. Here, we explore existing datasets of plant productivity and soil carbon stocks to quantify how greening, and in particular an expansion of woody shrubs, may translate to the sequestration of carbon in arctic soils. As an estimate of carbon storage in arctic tundra soils, we used the Northern Circumpolar Soil Carbon Database v2. As estimates of tundra type and productivity, we used the Circumpolar Arctic Vegetation map as well as the MODIS and Landsat Vegetation Continuous Fields, and MODIS GPP/NPP (MOD17) products. Preliminary findings suggest that in graminoid tundra and erect-shrub tundra higher shrub abundance is associated with greater soil carbon stocks. However, this relationship between shrub abundance and soil carbon is not apparent in prostrate-shrub tundra, or when comparing across graminoid tundra, erect-shrub tundra and prostrate-shrub tundra. Uncertainties originate from the extreme spatial (vertical and horizontal) heterogeneity of organic matter distribution in cryoturbated soils, the fact that (some) permafrost carbon stocks, e.g. yedoma, reflect previous rather than current vegetative cover, and small sample sizes, esp. in the High Arctic. Using Vegetation Continuous Fields and MODIS GPP/NPP (MOD17), we develop quantitative trajectories of soil carbon storage as a function of shrub cover and plant productivity in the Arctic (>60°N). We then compare our greening-derived carbon sequestration estimates to projected losses of carbon from thawing permafrost. Our findings will reduce uncertainties in the magnitude and timing of the carbon-climate feedback from the

  5. Dynamics of Aboveground Phytomass of the Circumpolar Arctic Tundra During the Past Three Decades

    NASA Technical Reports Server (NTRS)

    Epstein, Howard E.; Raynolds, Martha K.; Walker, Donald A.; Bhatt, Uma S.; Tucker, Compton J.; Pinzon, Jorge E.

    2012-01-01

    Numerous studies have evaluated the dynamics of Arctic tundra vegetation throughout the past few decades, using remotely sensed proxies of vegetation, such as the normalized difference vegetation index (NDVI). While extremely useful, these coarse-scale satellite-derived measurements give us minimal information with regard to how these changes are being expressed on the ground, in terms of tundra structure and function. In this analysis, we used a strong regression model between NDVI and aboveground tundra phytomass, developed from extensive field-harvested measurements of vegetation biomass, to estimate the biomass dynamics of the circumpolar Arctic tundra over the period of continuous satellite records (1982-2010). We found that the southernmost tundra subzones (C-E) dominate the increases in biomass, ranging from 20 to 26%, although there was a high degree of heterogeneity across regions, floristic provinces, and vegetation types. The estimated increase in carbon of the aboveground live vegetation of 0.40 Pg C over the past three decades is substantial, although quite small relative to anthropogenic C emissions. However, a 19.8% average increase in aboveground biomass has major implications for nearly all aspects of tundra ecosystems including hydrology, active layer depths, permafrost regimes, wildlife and human use of Arctic landscapes. While spatially extensive on-the-ground measurements of tundra biomass were conducted in the development of this analysis, validation is still impossible without more repeated, long-term monitoring of Arctic tundra biomass in the field.

  6. CO2, CH4, and DOC Flux During Long Term Thaw of High Arctic Tundra

    NASA Astrophysics Data System (ADS)

    Stackhouse, B. T.; Vishnivetskaya, T. A.; Layton, A.; Bennett, P.; Mykytczuk, N.; Lau, C. M.; Whyte, L.; Onstott, T. C.

    2013-12-01

    Arctic regions are expected to experience temperature increases of >4° C by the end of this century. This warming is projected to cause a drastic reduction in the extent of permafrost at high northern latitudes, affecting an estimated 1000 Pg of SOC in the top 3 m. Determining the effects of this temperature change on CO2 and CH4 emissions is critical for defining source constraints to global climate models. To investigate this problem, 18 cores of 1 m length were collected in late spring 2011 before the thawing of the seasonal active layer from an ice-wedge polygon near the McGill Arctic Research Station (MARS) on Axel Heiberg Island, Nunavut, Canada (N79°24, W90°45). Cores were collected from acidic soil (pH 5.5) with low SOC (~1%), summertime active layer depth between 40-70 cm (2010-2013), and sparse vegetation consisting primarily of small shrubs and sedges. Cores were progressively thawed from the surface over the course of 14 weeks to a final temperature of 4.5° C and held at that temperature for 15 months under the following conditions: in situ water saturation conditions versus fully water saturated conditions using artificial rain fall, surface light versus no surface light, cores from the polygon edge, and control cores with a permafrost table maintained at 70 cm depth. Core headspaces were measured weekly for CO2, CH4, H2, CO, and O2 flux during the 18 month thaw experiment. After ~20 weeks of thawing maximum, CO2 flux for the polygon edge and dark treatment cores were 3.0×0.7 and 1.7×0.4 mmol CO2 m-2 hr-1, respectively. The CO2 flux for the control, saturated, and in situ saturation cores reached maximums of 0.6×0.2, 0.9×0.5, and 0.9×0.1 mmol CO2 m-2 hr-1, respectively. Field measurements of CO2 flux from an adjacent polygon during the mid-summer of 2011 to 2013 ranged from 0.3 to 3.7 mmol CO2 m-2 hr-1. Cores from all treatments except water saturated were found to consistently oxidize CH4 at ~atmospheric concentrations (2 ppmv) with a maximum

  7. Two years with extreme and little snowfall: effects on energy partitioning and surface energy exchange in a high-Arctic tundra ecosystem

    NASA Astrophysics Data System (ADS)

    Stiegler, Christian; Lund, Magnus; Røjle Christensen, Torben; Mastepanov, Mikhail; Lindroth, Anders

    2016-07-01

    Snow cover is one of the key factors controlling Arctic ecosystem functioning and productivity. In this study we assess the impact of strong variability in snow accumulation during 2 subsequent years (2013-2014) on the land-atmosphere interactions and surface energy exchange in two high-Arctic tundra ecosystems (wet fen and dry heath) in Zackenberg, Northeast Greenland. We observed that record-low snow cover during the winter 2012/2013 resulted in a strong response of the heath ecosystem towards low evaporative capacity and substantial surface heat loss by sensible heat fluxes (H) during the subsequent snowmelt period and growing season. Above-average snow accumulation during the winter 2013/2014 promoted summertime ground heat fluxes (G) and latent heat fluxes (LE) at the cost of H. At the fen ecosystem a more muted response of LE, H and G was observed in response to the variability in snow accumulation. Overall, the differences in flux partitioning and in the length of the snowmelt periods and growing seasons during the 2 years had a strong impact on the total accumulation of the surface energy balance components. We suggest that in a changing climate with higher temperature and more precipitation the surface energy balance of this high-Arctic tundra ecosystem may experience a further increase in the variability of energy accumulation, partitioning and redistribution.

  8. Determining Regional Arctic Tundra Carbon Exchange: A Bottom-Up Approach

    NASA Technical Reports Server (NTRS)

    Huemmrich, Fred

    2006-01-01

    This viewgraph presentation reviews the carbon atmospheric exchange with Arctic tundra. In the Arctic the ecosystem has been a net carbon sink. The project investigates the question of how might climate warming effect high latitude ecosystems and the Earth ecosystems and how to measure the changes.

  9. Fourfold higher tundra volatile emissions due to arctic summer warming

    NASA Astrophysics Data System (ADS)

    Lindwall, Frida; Schollert, Michelle; Michelsen, Anders; Blok, Daan; Rinnan, Riikka

    2016-03-01

    Biogenic volatile organic compounds (BVOCs), which are mainly emitted by vegetation, may create either positive or negative climate forcing feedbacks. In the Subarctic, BVOC emissions are highly responsive to temperature, but the effects of climatic warming on BVOC emissions have not been assessed in more extreme arctic ecosystems. The Arctic undergoes rapid climate change, with air temperatures increasing at twice the rate of the global mean. Also, the amount of winter precipitation is projected to increase in large areas of the Arctic, and it is unknown how winter snow depth affects BVOC emissions during summer. Here we examine the responses of BVOC emissions to experimental summer warming and winter snow addition—each treatment alone and in combination—in an arctic heath during two growing seasons. We observed a 280% increase relative to ambient in BVOC emissions in response to a 4°C summer warming. Snow addition had minor effects on growing season BVOC emissions after one winter but decreased BVOC emissions after the second winter. We also examined differences between canopy and air temperatures and found that the tundra canopy surface was on average 7.7°C and maximum 21.6°C warmer than air. This large difference suggests that the tundra surface temperature is an important driver for emissions of BVOCs, which are temperature dependent. Our results demonstrate a strong response of BVOC emissions to increasing temperatures in the Arctic, suggesting that emission rates will increase with climate warming and thereby feed back to regional climate change.

  10. Recent Arctic tundra fire initiates widespread thermokarst development

    DOE PAGES

    Jones, Benjamin M.; Grosse, Guido; Arp, Christopher D.; ...

    2015-10-29

    Fire-induced permafrost degradation is well documented in boreal forests, but the role of fires in initiating thermokarst development in Arctic tundra is less well understood. Here we show that Arctic tundra fires may induce widespread thaw subsidence of permafrost terrain in the first seven years following the disturbance. Quantitative analysis of airborne LiDAR data acquired two and seven years post-fire, detected permafrost thaw subsidence across 34% of the burned tundra area studied, compared to less than 1% in similar undisturbed, ice-rich tundra terrain units. The variability in thermokarst development appears to be influenced by the interaction of tundra fire burnmore » severity and near-surface, ground-ice content. Subsidence was greatest in severely burned, ice-rich upland terrain (yedoma), accounting for -50% of the detected subsidence, despite representing only 30% of the fire disturbed study area. Microtopography increased by 340% in this terrain unit as a result of ice wedge degradation. Increases in the frequency, magnitude, and severity of tundra fires will contribute to future thermokarst development and associated landscape change in Arctic tundra regions.« less

  11. Recent Arctic tundra fire initiates widespread thermokarst development

    SciTech Connect

    Jones, Benjamin M.; Grosse, Guido; Arp, Christopher D.; Miller, Eric; Liu, Lin; Hayes, Daniel J.; Larsen, Christopher F.

    2015-10-29

    Fire-induced permafrost degradation is well documented in boreal forests, but the role of fires in initiating thermokarst development in Arctic tundra is less well understood. Here we show that Arctic tundra fires may induce widespread thaw subsidence of permafrost terrain in the first seven years following the disturbance. Quantitative analysis of airborne LiDAR data acquired two and seven years post-fire, detected permafrost thaw subsidence across 34% of the burned tundra area studied, compared to less than 1% in similar undisturbed, ice-rich tundra terrain units. The variability in thermokarst development appears to be influenced by the interaction of tundra fire burn severity and near-surface, ground-ice content. Subsidence was greatest in severely burned, ice-rich upland terrain (yedoma), accounting for -50% of the detected subsidence, despite representing only 30% of the fire disturbed study area. Microtopography increased by 340% in this terrain unit as a result of ice wedge degradation. Increases in the frequency, magnitude, and severity of tundra fires will contribute to future thermokarst development and associated landscape change in Arctic tundra regions.

  12. Recent Arctic tundra fire initiates widespread thermokarst development

    NASA Astrophysics Data System (ADS)

    Jones, Benjamin M.; Grosse, Guido; Arp, Christopher D.; Miller, Eric; Liu, Lin; Hayes, Daniel J.; Larsen, Christopher F.

    2015-10-01

    Fire-induced permafrost degradation is well documented in boreal forests, but the role of fires in initiating thermokarst development in Arctic tundra is less well understood. Here we show that Arctic tundra fires may induce widespread thaw subsidence of permafrost terrain in the first seven years following the disturbance. Quantitative analysis of airborne LiDAR data acquired two and seven years post-fire, detected permafrost thaw subsidence across 34% of the burned tundra area studied, compared to less than 1% in similar undisturbed, ice-rich tundra terrain units. The variability in thermokarst development appears to be influenced by the interaction of tundra fire burn severity and near-surface, ground-ice content. Subsidence was greatest in severely burned, ice-rich upland terrain (yedoma), accounting for ~50% of the detected subsidence, despite representing only 30% of the fire disturbed study area. Microtopography increased by 340% in this terrain unit as a result of ice wedge degradation. Increases in the frequency, magnitude, and severity of tundra fires will contribute to future thermokarst development and associated landscape change in Arctic tundra regions.

  13. The unseen iceberg: plant roots in arctic tundra

    DOE PAGES

    Iversen, Colleen M.; Sloan, Victoria L.; Sullivan, Patrick F.; ...

    2014-09-10

    Arctic tundra is characterized by short-statured plant communities underlain by carbon (C)-rich soils and permafrost. Ecosystem C and nutrient cycles in tundra are driven by complex interactions between plants and their environment. However, root dynamics are one of the least understood aspects of plant growth in the Arctic. We synthesized available literature on tundra roots and discussed their representation in terrestrial biosphere models. Belowground biomass in tundra ecosystems can be an order of magnitude larger than aboveground biomass. Data on root production and turnover in tundra is sparse, limiting our understanding of the controls over root dynamics in these systems.more » Roots are shallowly distributed in the thin layer of soil that thaws each year, and are often found in the organic horizon at the soil surface. Species-specific differences in root distribution, mycorrhizal colonization, and resource partitioning may affect plant species competition under changing climatic conditions. Model representation of belowground processes has increased in complexity over recent years, but data are desperately needed to fill the gaps in model treatment of tundra roots. Future research should focus on estimates of root production and lifespan, and interactions between roots and the surrounding soil across the diversity of tundra ecosystems in the Arctic.« less

  14. Recent Arctic tundra fire initiates widespread thermokarst development.

    PubMed

    Jones, Benjamin M; Grosse, Guido; Arp, Christopher D; Miller, Eric; Liu, Lin; Hayes, Daniel J; Larsen, Christopher F

    2015-10-29

    Fire-induced permafrost degradation is well documented in boreal forests, but the role of fires in initiating thermokarst development in Arctic tundra is less well understood. Here we show that Arctic tundra fires may induce widespread thaw subsidence of permafrost terrain in the first seven years following the disturbance. Quantitative analysis of airborne LiDAR data acquired two and seven years post-fire, detected permafrost thaw subsidence across 34% of the burned tundra area studied, compared to less than 1% in similar undisturbed, ice-rich tundra terrain units. The variability in thermokarst development appears to be influenced by the interaction of tundra fire burn severity and near-surface, ground-ice content. Subsidence was greatest in severely burned, ice-rich upland terrain (yedoma), accounting for ~50% of the detected subsidence, despite representing only 30% of the fire disturbed study area. Microtopography increased by 340% in this terrain unit as a result of ice wedge degradation. Increases in the frequency, magnitude, and severity of tundra fires will contribute to future thermokarst development and associated landscape change in Arctic tundra regions.

  15. Recent Arctic tundra fire initiates widespread thermokarst development

    PubMed Central

    Jones, Benjamin M.; Grosse, Guido; Arp, Christopher D.; Miller, Eric; Liu, Lin; Hayes, Daniel J.; Larsen, Christopher F.

    2015-01-01

    Fire-induced permafrost degradation is well documented in boreal forests, but the role of fires in initiating thermokarst development in Arctic tundra is less well understood. Here we show that Arctic tundra fires may induce widespread thaw subsidence of permafrost terrain in the first seven years following the disturbance. Quantitative analysis of airborne LiDAR data acquired two and seven years post-fire, detected permafrost thaw subsidence across 34% of the burned tundra area studied, compared to less than 1% in similar undisturbed, ice-rich tundra terrain units. The variability in thermokarst development appears to be influenced by the interaction of tundra fire burn severity and near-surface, ground-ice content. Subsidence was greatest in severely burned, ice-rich upland terrain (yedoma), accounting for ~50% of the detected subsidence, despite representing only 30% of the fire disturbed study area. Microtopography increased by 340% in this terrain unit as a result of ice wedge degradation. Increases in the frequency, magnitude, and severity of tundra fires will contribute to future thermokarst development and associated landscape change in Arctic tundra regions. PMID:26511650

  16. The unseen iceberg: plant roots in arctic tundra

    SciTech Connect

    Iversen, Colleen M.; Sloan, Victoria L.; Sullivan, Patrick F.; Euskirchen, Eugenie S.; McGuire, A. David; Norby, Richard J.; Walker, Anthony P.; Warren, Jeffrey M.; Wullschleger, Stan D.

    2014-09-10

    Arctic tundra is characterized by short-statured plant communities underlain by carbon (C)-rich soils and permafrost. Ecosystem C and nutrient cycles in tundra are driven by complex interactions between plants and their environment. However, root dynamics are one of the least understood aspects of plant growth in the Arctic. We synthesized available literature on tundra roots and discussed their representation in terrestrial biosphere models. Belowground biomass in tundra ecosystems can be an order of magnitude larger than aboveground biomass. Data on root production and turnover in tundra is sparse, limiting our understanding of the controls over root dynamics in these systems. Roots are shallowly distributed in the thin layer of soil that thaws each year, and are often found in the organic horizon at the soil surface. Species-specific differences in root distribution, mycorrhizal colonization, and resource partitioning may affect plant species competition under changing climatic conditions. Model representation of belowground processes has increased in complexity over recent years, but data are desperately needed to fill the gaps in model treatment of tundra roots. Future research should focus on estimates of root production and lifespan, and interactions between roots and the surrounding soil across the diversity of tundra ecosystems in the Arctic.

  17. Recent Arctic tundra fire initiates widespread thermokarst development

    USGS Publications Warehouse

    Jones, Benjamin M.; Grosse, Guido; Arp, Christopher D.; Miller, Eric K.; Liu, Lingli; Hayes, Daniel J.; Larsen, Christopher F.

    2015-01-01

    Fire-induced permafrost degradation is well documented in boreal forests, but the role of fires in initiating thermokarst development in Arctic tundra is less well understood. Here we show that Arctic tundra fires may induce widespread thaw subsidence of permafrost terrain in the first seven years following the disturbance. Quantitative analysis of airborne LiDAR data acquired two and seven years post-fire, detected permafrost thaw subsidence across 34% of the burned tundra area studied, compared to less than 1% in similar undisturbed, ice-rich tundra terrain units. The variability in thermokarst development appears to be influenced by the interaction of tundra fire burn severity and near-surface, ground-ice content. Subsidence was greatest in severely burned, ice-rich upland terrain (yedoma), accounting for ~50% of the detected subsidence, despite representing only 30% of the fire disturbed study area. Microtopography increased by 340% in this terrain unit as a result of ice wedge degradation. Increases in the frequency, magnitude, and severity of tundra fires will contribute to future thermokarst development and associated landscape change in Arctic tundra regions.

  18. Airborne Spectral Measurements of Surface-Atmosphere Anisotropy for Arctic Sea Ice and Tundra

    NASA Technical Reports Server (NTRS)

    Arnold, G. Thomas; Tsay, Si-Chee; King, Michael D.; Li, Jason Y.; Soulen, Peter F.

    1999-01-01

    Angular distributions of spectral reflectance for four common arctic surfaces: snow-covered sea ice, melt-season sea ice, snow-covered tundra, and tundra shortly after snowmelt were measured using an aircraft based, high angular resolution (1-degree) multispectral radiometer. Results indicate bidirectional reflectance is higher for snow-covered sea ice than melt-season sea ice at all wavelengths between 0.47 and 2.3 pm, with the difference increasing with wavelength. Bidirectional reflectance of snow-covered tundra is higher than for snow-free tundra for measurements less than 1.64 pm, with the difference decreasing with wavelength. Bidirectional reflectance patterns of all measured surfaces show maximum reflectance in the forward scattering direction of the principal plane, with identifiable specular reflection for the melt-season sea ice and snow-free tundra cases. The snow-free tundra had the most significant backscatter, and the melt-season sea ice the least. For sea ice, bidirectional reflectance changes due to snowmelt were more significant than differences among the different types of melt-season sea ice. Also the spectral-hemispherical (plane) albedo of each measured arctic surface was computed. Comparing measured nadir reflectance to albedo for sea ice and snow-covered tundra shows albedo underestimated 5-40%, with the largest bias at wavelengths beyond 1 pm. For snow-free tundra, nadir reflectance underestimates plane albedo by about 30-50%.

  19. The unseen iceberg: plant roots in arctic tundra.

    PubMed

    Iversen, Colleen M; Sloan, Victoria L; Sullivan, Patrick F; Euskirchen, Eugenie S; McGuire, A David; Norby, Richard J; Walker, Anthony P; Warren, Jeffrey M; Wullschleger, Stan D

    2015-01-01

    Plant roots play a critical role in ecosystem function in arctic tundra, but root dynamics in these ecosystems are poorly understood. To address this knowledge gap, we synthesized available literature on tundra roots, including their distribution, dynamics and contribution to ecosystem carbon and nutrient fluxes, and highlighted key aspects of their representation in terrestrial biosphere models. Across all tundra ecosystems, belowground plant biomass exceeded aboveground biomass, with the exception of polar desert tundra. Roots were shallowly distributed in the thin layer of soil that thaws annually, and were often found in surface organic soil horizons. Root traits - including distribution, chemistry, anatomy and resource partitioning - play an important role in controlling plant species competition, and therefore ecosystem carbon and nutrient fluxes, under changing climatic conditions, but have only been quantified for a small fraction of tundra plants. Further, the annual production and mortality of fine roots are key components of ecosystem processes in tundra, but extant data are sparse. Tundra root traits and dynamics should be the focus of future research efforts. Better representation of the dynamics and characteristics of tundra roots will improve the utility of models for the evaluation of the responses of tundra ecosystems to changing environmental conditions.

  20. The unseen iceberg: Plant roots in arctic tundra

    USGS Publications Warehouse

    Iverson, Colleen M.; Sloan, Victoria L.; Sullivan, Patrick F.; Euskirchen, E.S.; McGuire, Anthony; Norby, Richard J.; Walker, Anthony P.; Warren, Jeffrey M.; Wullschleger, Stan D.

    2015-01-01

    Plant roots play a critical role in ecosystem function in arctic tundra, but root dynamics in these ecosystems are poorly understood. To address this knowledge gap, we synthesized available literature on tundra roots, including their distribution, dynamics and contribution to ecosystem carbon and nutrient fluxes, and highlighted key aspects of their representation in terrestrial biosphere models. Across all tundra ecosystems, belowground plant biomass exceeded aboveground biomass, with the exception of polar desert tundra. Roots were shallowly distributed in the thin layer of soil that thaws annually, and were often found in surface organic soil horizons. Root traits – including distribution, chemistry, anatomy and resource partitioning – play an important role in controlling plant species competition, and therefore ecosystem carbon and nutrient fluxes, under changing climatic conditions, but have only been quantified for a small fraction of tundra plants. Further, the annual production and mortality of fine roots are key components of ecosystem processes in tundra, but extant data are sparse. Tundra root traits and dynamics should be the focus of future research efforts. Better representation of the dynamics and characteristics of tundra roots will improve the utility of models for the evaluation of the responses of tundra ecosystems to changing environmental conditions.

  1. Identifying nitrogen limitations to organic sediments accumulation in various vegetation types of arctic tundra (Hornsund, Svalbard)

    NASA Astrophysics Data System (ADS)

    Skrzypek, G.; Wojtuń, B.; Hua, Q.; Richter, D.; Jakubas, D.; Wojczulanis-Jakubas, K.; Samecka-Cymerman, A.

    2015-12-01

    Arctic and subarctic regions play important roles in the global carbon balance. However, nitrogen (N) deficiency is a major constraint for organic carbon sequestration in the High Arctic. Hence, the identification of the relative contributions from different N-sources is critical for understanding the constraints that limit tundra growth. The stable nitrogen composition of the three main N-sources and numerous plants were analyzed in ten tundra types in the Fuglebekken catchment (Hornsund Fjord, Svalbard, 77°N 15°E). The percentage of the total tundra N-pool provided by seabirds' feces (colonially breeding, planktivorous Alle alle), ranged from 0-21% in Patterned-ground tundra to 100% in Ornithocoprophilous tundra. The total N-pool utilized by tundra plants in the studied catchment was built in 36% by birds, 38% by atmospheric deposition, and 26% by N2-fixation. The results clearly show that N-pool in the tundra is significantly supplemented by nesting seabirds. Thus, if they experienced substantial negative environmental pressure associated with climate change, it would adversely influence the tundra N-budget [1]. The growth rates and the sediment thickness (<15 cm) in different tundra types varied considerably but the tundra age was similar, <450 cal BP. The only exception was Ornithocoprophilous tundra with very diverse ages ranging from 235 to 2300 cal BP and thickness up to 110cm. The growth rates for this tundra (62 cm core, 18 AMS 14C dates) were high (1.5-3.0 mm/yr) between 1568 and 1804 AD and then substantially declined for the period between 1804 and 1929 AD (0.2 mm/yr). These findings deliver an additional argument, that the organic matter accumulation is driven not only directly by climatic conditions but also by birds' contribution to the tundra N-pool. [1] Skrzypek G, Wojtuń B, Richter D, Jakubas D, Wojczulanis-Jakubas K, Samecka-Cymerman A, 2015. Diversification of nitrogen sources in various tundra vegetation types in the high Arctic. PLoS ONE

  2. Carbon loss from an unprecedented Arctic tundra wildfire.

    PubMed

    Mack, Michelle C; Bret-Harte, M Syndonia; Hollingsworth, Teresa N; Jandt, Randi R; Schuur, Edward A G; Shaver, Gaius R; Verbyla, David L

    2011-07-27

    Arctic tundra soils store large amounts of carbon (C) in organic soil layers hundreds to thousands of years old that insulate, and in some cases maintain, permafrost soils. Fire has been largely absent from most of this biome since the early Holocene epoch, but its frequency and extent are increasing, probably in response to climate warming. The effect of fires on the C balance of tundra landscapes, however, remains largely unknown. The Anaktuvuk River fire in 2007 burned 1,039 square kilometres of Alaska's Arctic slope, making it the largest fire on record for the tundra biome and doubling the cumulative area burned since 1950 (ref. 5). Here we report that tundra ecosystems lost 2,016 ± 435 g C m(-2) in the fire, an amount two orders of magnitude larger than annual net C exchange in undisturbed tundra. Sixty per cent of this C loss was from soil organic matter, and radiocarbon dating of residual soil layers revealed that the maximum age of soil C lost was 50 years. Scaled to the entire burned area, the fire released approximately 2.1 teragrams of C to the atmosphere, an amount similar in magnitude to the annual net C sink for the entire Arctic tundra biome averaged over the last quarter of the twentieth century. The magnitude of ecosystem C lost by fire, relative to both ecosystem and biome-scale fluxes, demonstrates that a climate-driven increase in tundra fire disturbance may represent a positive feedback, potentially offsetting Arctic greening and influencing the net C balance of the tundra biome.

  3. Arctic lakes and streams as gas conduits to the atmosphere: Implications for tundra carbon budgets

    SciTech Connect

    Kling, G.W. ); Kipphut, G.W. ); Miller, M.C. )

    1991-01-01

    Arctic tundra has large amounts of stored carbon and is thought to be a sink for atmospheric carbon dioxide (CO{sub 2}) (0.1 to 0.3 petagram of carbon per year) (1 petagram = 10{sup 15} grams). But this estimate of carbon balance is only for terrestrial ecosystems. Measurements of the partial pressure of CO{sub 2} in 29 aquatic ecosystems across arctic Alaska showed that in most cases (27 of 29) CO{sub 2} was released to the atmosphere. This CO{sub 2} probably originates in terrestrial environments; erosion of particulate carbon plus ground-water transport of dissolved carbon from tundra contribute to the CO{sub 2} flux from surface waters to the atmosphere. If this mechanism is typical of that of other tundra areas, then current estimates of the arctic terrestrial sink for atmospheric CO{sub 2} may be 20 percent too high. 1 table, 2 figs., 21 refs.

  4. Willow Shrub Expansion Following Tundra Fires in Arctic Alaska

    NASA Astrophysics Data System (ADS)

    Racine, C.

    2010-12-01

    Climate warming in the Arctic is predicted to result in the expansion of woody shrubs and increased frequency and size of tundra fires. How will fire influence this shrub expansion? Over a period of 32 years, following a 1977 tundra fire in the central Seward Peninsula, we sampled seven times the post-fire vegetation at eight permanently marked sites on a long (2 Km) hillslope (Nimrod Hill). We had previously sampled vegetation here in 1973 prior to the fire. By 2001, 24 years post-fire conspicuous willow shrubs (mostly Salix pulchra) had increased in numbers, size and cover over the entire slope in moist tussock-shrub tundra, well-drained heath, and wet meadow. Prior to fire, willow on this slope was largely restricted to small drainages or watertracks. Willows here have originated from both seed and vegetative resprouting - the latter mostly in moist tussock-shrub tundra from willows resprouting within one to three years post-fire. With fire-induced removal of vascular plant competition and Spagnum moss cover and litter in tussock-shrub tundra, both seedling and resprouting willows have grown rapidly to overtop tussocks by 30-40 cm. Similar rapid post-fire resprouting of willows has been observed in tussock-shrub tundra after the 2007 Anaktuvuk River tundra fire and after the 1977 tundra fires in the Noatak River basin. On Nimrod Hill the most striking willow expansion has occurred on the severely burned and well-drained backslope where willow establishment from seed 5-10 years after fire has resulted in up to 40% cover of rapidly growing willows of both upright and spreading growth form. At several sites along the slope there is evidence of continuing willow expansion from seedlings 24 to 32 years post-fire, when we might expect the effects of fire on seedbeds would have ceased. We conclude that tundra fire may promote shrub expansion in the Arctic.

  5. Long-term experimental warming alters nitrogen-cycling communities but site factors remain the primary drivers of community structure in high arctic tundra soils.

    PubMed

    Walker, Jennifer K M; Egger, Keith N; Henry, Gregory H R

    2008-09-01

    Arctic air temperatures are expected to rise significantly over the next century. Experimental warming of arctic tundra has been shown to increase plant productivity and cause community shifts and may also alter microbial community structure. Hence, the objective of this study was to determine whether experimental warming caused shifts in soil microbial communities by measuring changes in the frequency, relative abundance and/or richness of nosZ and nifH genotypes. Five sites at a high arctic coastal lowland were subjected to a 13-year warming experiment using open-top chambers (OTCs). Sites differed by dominant plant community, soil parent material and/or moisture regimen. Six soil cores were collected from each of four replicate OTC and ambient plots at each site and subdivided into upper and lower samples. Differences in frequency and relative abundance of terminal restriction fragments were assessed graphically by two-way cluster analysis and tested statistically with permutational multivariate analysis of variance (ANOVA). Genotypic richness was compared using factorial ANOVA. The genotype frequency, relative abundance and genotype richness of both nosZ and nifH communities differed significantly by site, and by OTC treatment and/or depth at some sites. The site that showed the most pronounced treatment effect was a wet sedge meadow, where community structure and genotype richness of both nosZ and nifH were significantly affected by warming. Although warming was an important factor affecting these communities at some sites at this high arctic lowland, overall, site factors were the main determinants of community structure.

  6. Recognition and characterization of networks of water bodies in the Arctic ice-wedge polygonal tundra using high-resolution satellite imagery

    NASA Astrophysics Data System (ADS)

    Skurikhin, A. N.; Gangodagamage, C.; Rowland, J. C.; Wilson, C. J.

    2013-12-01

    Arctic lowland landscapes underlain by permafrost are often characterized by polygon-like patterns such as ice-wedge polygons outlined by networks of ice wedges and complemented with polygon rims, troughs, shallow ponds and thermokarst lakes. Polygonal patterns and corresponding features are relatively easy to recognize in high spatial resolution satellite imagery by a human, but their automated recognition is challenging due to the variability in their spectral appearance, the irregularity of individual trough spacing and orientation within the patterns, and a lack of unique spectral response attributable to troughs with widths commonly between 1 m and 2 m. Accurate identification of fine scale elements of ice-wedge polygonal tundra is important as their imprecise recognition may bias estimates of water, heat and carbon fluxes in large-scale climate models. Our focus is on the problem of identification of Arctic polygonal tundra fine-scale landscape elements (as small as 1 m - 2 m width). The challenge of the considered problem is that while large water bodies (e.g. lakes and rivers) can be recognized based on spectral response, reliable recognition of troughs is more difficult. Troughs do not have unique spectral signature, their appearance is noisy (edges are not strong), their width is small, and they often form connected networks with ponds and lakes, and thus they have overlapping spectral response with other water bodies and surrounding non-water bodies. We present a semi-automated approach to identify and classify Arctic polygonal tundra landscape components across the range of spatial scales, such as troughs, ponds, river- and lake-like objects, using high spatial resolution satellite imagery. The novelty of the approach lies in: (1) the combined use of segmentation and shape-based classification to identify a broad range of water bodies, including troughs, and (2) the use of high-resolution WorldView-2 satellite imagery (with resolution of 0.6 m) for this

  7. Climate adaptation is not enough: warming does not facilitate success of southern tundra plant populations in the high Arctic.

    PubMed

    Bjorkman, Anne D; Vellend, Mark; Frei, Esther R; Henry, Gregory H R

    2017-04-01

    Rapidly rising temperatures are expected to cause latitudinal and elevational range shifts as species track their optimal climate north and upward. However, a lack of adaptation to environmental conditions other than climate - for example photoperiod, biotic interactions, or edaphic conditions - might limit the success of immigrants in a new location despite hospitable climatic conditions. Here, we present one of the first direct experimental tests of the hypothesis that warmer temperatures at northern latitudes will confer a fitness advantage to southern immigrants relative to native populations. As rates of warming in the Arctic are more than double the global average, understanding the impacts of warming in Arctic ecosystems is especially urgent. We established experimentally warmed and nonwarmed common garden plots at Alexandra Fiord, Ellesmere Island in the Canadian High Arctic with seeds of two forb species (Oxyria digyna and Papaver radicatum) originating from three to five populations at different latitudes across the Arctic. We found that plants from the local populations generally had higher survival and obtained a greater maximum size than foreign individuals, regardless of warming treatment. Phenological traits varied with latitude of the source population, such that southern populations demonstrated substantially delayed leaf-out and senescence relative to northern populations. Our results suggest that environmental conditions other than temperature may influence the ability of foreign populations and species to establish at more northerly latitudes as the climate warms, potentially leading to lags in northward range shifts for some species.

  8. Changing trends in carbon dioxide exchange components in three Arctic tundra sites

    NASA Astrophysics Data System (ADS)

    Mbufong, Herbert; Lund, Magnus; Christensen, Torben; Jackowicz-Korczynski, Marcin; Parmentier, Frans-Jan; Dolman, Han; van der Molen, Michiel; Tamstorf, Mikkel

    2014-05-01

    This paper aims to investigate the interannual variability in carbon flux components in a High, Low and Sub Arctic tundra site. By identifying trends in different tundra types, we can better understand the possible future response of Arctic tundra under climatic change. The timing and length of seasons, alongside environmental controls, have been examined to assess their effect on the seasonal carbon budgets of these sites. Data was collected using the micrometeorological eddy covariance technique from three Arctic tundra sites in Greenland (74.47 °N), Siberia (70.82 °N) and Sweden (68.33 °N). We have hypothesized that the interannual trends in net ecosystem exchange (NEE) components will vary between the different tundra types in this study and will most likely be driven by temperature, vegetation characteristics (NDVI) and season phenology (start and length of seasons). Our results will present the evolution of the seasonal budgets (Thaw, pre-green, green, post-green seasons) of NEE components; and the drivers of these trends over 6 years (2003 - 2008) in these three sites. These and more will be presented at the conference.

  9. Shrub expansion and climate feedbacks in Arctic tundra

    NASA Astrophysics Data System (ADS)

    Loranty, Michael M.; Goetz, Scott J.

    2012-03-01

    Arctic tundra ecosystems stand to play a substantial role in both the magnitude and rate of global climate warming over the coming decades and centuries. The exact nature of this role will be determined by the combined effects of currently amplified rates of climate warming in the Arctic (Serreze et al 2000) and a series of related positive climate feedbacks that include mobilization of permafrost carbon (Schuur et al 2008), decreases in surface albedo (Chapin et al 2005) and evapotranspiration (ET) mediated increases in atmospheric water vapor (Swann et al 2010). Conceptually, these feedback mechanisms are intuitive and readily comprehensible: warming-induced permafrost thaw will make new soil carbon pools accessible for microbial respiration, and increased vegetation productivity, expansion of shrubs in particular, will lower surface reflectance and increase ET. However, our current understanding of these feedback mechanisms relies largely on limited and local field studies and, as such, the quantitative estimates of feedback effects on regional and global climate require spatial upscaling and uncertainty estimates derived from models. Moreover, the feedback mechanisms interact and their combined net effect on climate is highly variable and not well characterized. A recent study by Bonfils et al (2012) is among the first to explicitly examine how shrub expansion in tundra ecosystems will impact regional climate. Using an Earth system model, Bonfils et al find that an idealized 20% increase in shrub cover north of 60°N latitude will lead to annual temperature increases of 0.66 °C and 1.84 °C, respectively, when the shrubs are 0.5 m and 2 m tall. The modeled temperature increases arise from atmospheric heating as a combined consequence of decreased albedo and increased ET. The primary difference between the two cases is associated with the fact that tall shrubs protrude above the snow, thus reducing albedo year round, whereas short shrubs are completely

  10. Assessing the Utility of Alternate Digital Image Color Space for Deriving Phenological Dynamics in a High-Arctic Tundra Ecosystem

    NASA Astrophysics Data System (ADS)

    Vargas, S. A., Jr.; Oberbauer, S. F.; Ramirez, G.; Ramirez, G. A.; Tweedie, C. E.; Hollister, R. D.; Escarzaga, S. M.; Ochoa, E.

    2015-12-01

    The need to improve the spatial and temporal scaling and extrapolation of plot level ecosystem properties and processes to the landscape level remains a persistent research challenge in the Arctic. Plant and landscape phenology is sensitive to a number of spatiotemporally variable environmental factors such as soil moisture, temperature, and radiation. Seasonal and inter-annual differences in phenology can affect surface energy balance and land-atmosphere carbon flux. Considering the relative importance of the Arctic to global carbon balance, improved scaling and extrapolation of phenological dynamics from the plot level to the landscape level is important for advancing our understanding of the impact of climate and other environmental change in arctic terrestrial ecosystems. Seasonal and interannual landscape phenology was observed over the Mobile Instrumented Sensor Platform (MISP) grid (2 x 50 meters) located in Barrow and Atqasuk, Alaska using imagery acquired from kite aerial photography (KAP), a hyperspectral ground-based spectrometer, and a phenocam. These data were analyzed in RGB and non-traditional HSV and l*a*b*color spaces to determine site, plant community seasonal, and inter annual phenological dynamics. Results were also compared to high spatial resolution satellite imagery to determine optimal indices for scaling vegetation dynamics from plot to landscape level. These results show that greenness indices similar to those acquired from hyperspectral remote sensing platforms can be derived using low-cost and low-tech techniques that could be deployed at multiple sites at low cost.

  11. Geochemical drivers of organic matter decomposition in Arctic tundra soils

    SciTech Connect

    Herndon, Elizabeth M.; Yang, Ziming; Graham, David E.; Wullschleger, Stan D.; Gu, Baohua; Liang, Liyuan; Bargar, John; Janot, Noemie; Regier, Tom Z.

    2015-12-07

    Climate change is warming tundra ecosystems in the Arctic, resulting in the decomposition of previously-frozen soil organic matter (SOM) and release of carbon (C) to the atmosphere; however, the processes that control SOM decomposition and C emissions remain highly uncertain. In this study, we evaluate geochemical factors that influence anaerobic production of carbon dioxide (CO2) and methane (CH4) in the active layers of four ice-wedge polygons. Surface and soil pore waters were collected during the annual thaw season over a two-year period in an area containing waterlogged, low-centered polygons and well-drained, high-centered polygons. We report spatial and seasonal patterns of dissolved gases in relation to the geochemical properties of Fe and organic C as determined using spectroscopic and chromatographic techniques. Iron was present as Fe(II) in soil solution near the permafrost boundary but enriched as Fe(III) in the middle of the active layer, similar to dissolved aromatic-C and organic acids. Dissolved CH4 increased relative to dissolved CO2 with depth and varied with soil moisture in the middle of the active layer in patterns that were positively correlated with the proportion of dissolved Fe(III) in transitional and low-centered polygon soils but negatively correlated in the drier flat- and high-centered polygons. These results suggest that microbial-mediated Fe oxidation and reduction influence respiration/fermentation of SOM and production of substrates (e.g., low-molecular-weight organic acids) for methanogenesis. As a result, we infer that geochemical differences induced by water saturation dictate microbial products of SOM decomposition, and Fe geochemistry is an important factor regulating methanogenesis in anoxic tundra soils.

  12. Geochemical drivers of organic matter decomposition in Arctic tundra soils

    DOE PAGES

    Herndon, Elizabeth M.; Yang, Ziming; Graham, David E.; ...

    2015-12-07

    Climate change is warming tundra ecosystems in the Arctic, resulting in the decomposition of previously-frozen soil organic matter (SOM) and release of carbon (C) to the atmosphere; however, the processes that control SOM decomposition and C emissions remain highly uncertain. In this study, we evaluate geochemical factors that influence anaerobic production of carbon dioxide (CO2) and methane (CH4) in the active layers of four ice-wedge polygons. Surface and soil pore waters were collected during the annual thaw season over a two-year period in an area containing waterlogged, low-centered polygons and well-drained, high-centered polygons. We report spatial and seasonal patterns ofmore » dissolved gases in relation to the geochemical properties of Fe and organic C as determined using spectroscopic and chromatographic techniques. Iron was present as Fe(II) in soil solution near the permafrost boundary but enriched as Fe(III) in the middle of the active layer, similar to dissolved aromatic-C and organic acids. Dissolved CH4 increased relative to dissolved CO2 with depth and varied with soil moisture in the middle of the active layer in patterns that were positively correlated with the proportion of dissolved Fe(III) in transitional and low-centered polygon soils but negatively correlated in the drier flat- and high-centered polygons. These results suggest that microbial-mediated Fe oxidation and reduction influence respiration/fermentation of SOM and production of substrates (e.g., low-molecular-weight organic acids) for methanogenesis. As a result, we infer that geochemical differences induced by water saturation dictate microbial products of SOM decomposition, and Fe geochemistry is an important factor regulating methanogenesis in anoxic tundra soils.« less

  13. Cold season emissions dominate the Arctic tundra methane budget

    PubMed Central

    Zona, Donatella; Gioli, Beniamino; Lindaas, Jakob; Wofsy, Steven C.; Miller, Charles E.; Dinardo, Steven J.; Dengel, Sigrid; Sweeney, Colm; Karion, Anna; Chang, Rachel Y.-W.; Henderson, John M.; Murphy, Patrick C.; Goodrich, Jordan P.; Moreaux, Virginie; Liljedahl, Anna; Watts, Jennifer D.; Kimball, John S.; Lipson, David A.; Oechel, Walter C.

    2016-01-01

    Arctic terrestrial ecosystems are major global sources of methane (CH4); hence, it is important to understand the seasonal and climatic controls on CH4 emissions from these systems. Here, we report year-round CH4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for ≥50% of the annual CH4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the “zero curtain” period, when subsurface soil temperatures are poised near 0 °C. The zero curtain may persist longer than the growing season, and CH4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH4 derived from aircraft data demonstrate the large spatial extent of late season CH4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 ± 5 (95% confidence interval) Tg CH4 y−1, ∼25% of global emissions from extratropical wetlands, or ∼6% of total global wetland methane emissions. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming. PMID:26699476

  14. Cold season emissions dominate the Arctic tundra methane budget

    NASA Astrophysics Data System (ADS)

    Zona, Donatella; Gioli, Beniamino; Commane, Róisín; Lindaas, Jakob; Wofsy, Steven C.; Miller, Charles E.; Dinardo, Steven J.; Dengel, Sigrid; Sweeney, Colm; Karion, Anna; Chang, Rachel Y.-W.; Henderson, John M.; Murphy, Patrick C.; Goodrich, Jordan P.; Moreaux, Virginie; Liljedahl, Anna; Watts, Jennifer D.; Kimball, John S.; Lipson, David A.; Oechel, Walter C.

    2016-01-01

    Arctic terrestrial ecosystems are major global sources of methane (CH4); hence, it is important to understand the seasonal and climatic controls on CH4 emissions from these systems. Here, we report year-round CH4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for ≥50% of the annual CH4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the "zero curtain" period, when subsurface soil temperatures are poised near 0 °C. The zero curtain may persist longer than the growing season, and CH4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH4 derived from aircraft data demonstrate the large spatial extent of late season CH4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 ± 5 (95% confidence interval) Tg CH4 y-1, ∼25% of global emissions from extratropical wetlands, or ∼6% of total global wetland methane emissions. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming.

  15. Cold season emissions dominate the Arctic tundra methane budget.

    PubMed

    Zona, Donatella; Gioli, Beniamino; Commane, Róisín; Lindaas, Jakob; Wofsy, Steven C; Miller, Charles E; Dinardo, Steven J; Dengel, Sigrid; Sweeney, Colm; Karion, Anna; Chang, Rachel Y-W; Henderson, John M; Murphy, Patrick C; Goodrich, Jordan P; Moreaux, Virginie; Liljedahl, Anna; Watts, Jennifer D; Kimball, John S; Lipson, David A; Oechel, Walter C

    2016-01-05

    Arctic terrestrial ecosystems are major global sources of methane (CH4); hence, it is important to understand the seasonal and climatic controls on CH4 emissions from these systems. Here, we report year-round CH4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for ≥ 50% of the annual CH4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the "zero curtain" period, when subsurface soil temperatures are poised near 0 °C. The zero curtain may persist longer than the growing season, and CH4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH4 derived from aircraft data demonstrate the large spatial extent of late season CH4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 ± 5 (95% confidence interval) Tg CH4 y(-1), ∼ 25% of global emissions from extratropical wetlands, or ∼ 6% of total global wetland methane emissions. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming.

  16. Wetting increases respiration loss from the Arctic tundra

    NASA Astrophysics Data System (ADS)

    Zona, Donatella; Lipson, David; Barott, Katie; Tha Paw U, Kyaw; Oberbauer, Steven; Olivas, Paulo; Hastings, Steven; Hinzman, Larry; Oechel, Walter

    2010-05-01

    Numerous studies (Billings et al. 1982; Peterson et al. 1984; Oberbauer et al. 1991; Funk et al., 1994; Oechel et al., 1998) have demonstrated that decreasing soil moisture and increasing soil oxygen increase respiration loss in the Arctic tundra. Warming and drying of tundra soils due to climate change are assumed to increase greenhouse gas emissions and the potential for strong positive feedbacks on the climate of the Arctic. However, here we show that an increase in the water table can lead to the same result, increasing respiration. In the largest scale water table manipulation experiment ever performed in the Arctic tundra, we showed that increasing the water table to 7.5 cm above the surface caused the ecosystem to more than half its net C uptake (9 gCm-2season-1) compared to the 23 gCm-2season-1 of a control site where water table was about 2 cm below the surface. Standing water saturated the moss layer, increased the heat conduction into the soil, and lead to higher soil temperature, deeper thaw and, surprisingly, to higher respiration rates in the most anaerobic area of the manipulation experiment. Probably, the increase in thaw depth increased substrate availability and freed sufficient Fe(III) to act as an electron acceptor in place of oxygen for respiration and CO2 production in these anaerobic soils (Zehnder and Stumm 1988, Kappler et al. 2004, Lipson et al. in review). In contrast to the general assumption that aerobic peat soils release more CO2 than soils under anaerobic conditions (Billing et al., 1982; Funk et al., 1994; Bridgham et al., 1998), here we show that this is not always the case. That the increase in the water table can result in increased respiration, even under nearly fully anaerobic conditions, through previously underestimated pathways, highlights yet another unexpected positive feedback on climate change of carbon exchange in the Arctic. That anaerobic conditions do not necessarily prevent CO2 loss in permafrost areas has major

  17. Topographic Variation and Methane Production in Siberian Arctic Tundra

    NASA Astrophysics Data System (ADS)

    Eason, J.; Kuhn, M. A.; Dunn, S.; Spawn, S.; Schade, J. D.

    2014-12-01

    Understanding the fate of soil carbon when permafrost soils begin to thaw is critical for predicting the impact of permafrost thaw on global climate change. Microbial metabolism of soil carbon can produce carbon dioxide or methane, depending on soil conditions, and which pathway dominates has great significance for the strength of climate feedbacks since methane is a much more powerful greenhouse gas than carbon dioxide. In Arctic ecosystems, methane production from upland environments is not well understood and generally assumed to be low because conditions there are generally not favorable for methanogenesis. Small changes in topography, however, can lead to great heterogeneity in soil conditions at small scales that may lead to higher methane flux than generally recognized. In this study, we investigated patterns in methane, carbon dioxide, and oxygen concentrations in in surface waters of 15 small ponds in the Kolyma River watershed in Northeast Siberia. The ponds were distributed across a topographic gradient from upland tundra high in the landscape to low-lying ponds in the floodplain of the Kolyma River. In addition, we used chambers to measured methane fluxes from a variety of topographic depressions that ranged from pools to moss-dominated saturated soils lacking surface water, to dry soils dominated by sedges. Dissolved carbon dioxide concentrations in ponds showed no trend down the topographic gradient while methane concentrations decreased downslope. The decrease in methane production may be the result of a switch from green moss to brown moss, which may act as a host for methanotrophic bacteria. Ponds with green moss had significantly higher concentrations of methane than the ponds with brown moss. In addition, we found significantly higher methane fluxes from pools and saturated soils then from drier soils, which showed very low fluxes. These results suggest that upland tundra may be a significant source of methane, and that methane fluxes are driven

  18. Will Arctic ground squirrels impede or accelerate climate-induced vegetation changes to the Arctic tundra?

    NASA Astrophysics Data System (ADS)

    Dalton, J.; Flower, C. E.; Brown, J.; Gonzalez-Meler, M. A.; Whelan, C.

    2014-12-01

    Considerable attention has been given to the climate feedbacks associated with predicted vegetation shifts in the Arctic tundra in response to global environmental change. However, little is known regarding the extent to which consumers can facilitate or respond to shrub expansion. Arctic ground squirrels, the largest and most northern ground squirrel, are abundant and widespread throughout the North American tundra. Their broad diet of seeds, flowers, herbage, bird's eggs and meat speaks to the need to breed, feed, and fatten in a span of some 12-16 weeks that separate their 8-9 month bouts of hibernation with the potential consequence to impact ecosystem dynamics. Therefore Arctic ground squirrels are a good candidate to evaluate whether consumers are mere responders (bottom-up effects) or drivers (top-down) of the observed and predicted vegetation changes. As a start towards this question, we measured the foraging intensity (giving-up densities) of Arctic ground squirrels in experimental food patches within which the squirrels experience diminishing returns as they seek the raisins and peanuts that we provided at the Toolik Lake field station in northern Alaska. If the squirrels show their highest feeding intensity in the shrubs, they may impede vegetation shifts by slowing the establishment and expansion of shrubs in the tundra. Conversely, if they show their lowest feeding intensity within shrub dominated areas, they may accelerate vegetation shifts. We found neither. Feeding intensity varied most among transects and times of day, and least along a tundra-to-shrub vegetation gradient. This suggests that the impacts of squirrels will be heterogeneous - in places responders and in others drivers. We should not be surprised then to see patches of accelerated and impeded vegetation changes in the tundra ecosystem. Some of these patterns may be predictable from the foraging behavior of Arctic ground squirrels.

  19. Luteolibacter arcticus sp. nov., isolated from high Arctic tundra soil, and emended description of the genus Luteolibacter.

    PubMed

    Kim, MyongChol; Pak, SeHong; Rim, SongGuk; Ren, Lvzhi; Jiang, Fan; Chang, Xulu; Liu, Ping; Zhang, Yumin; Fang, Chengxiang; Zheng, Congyi; Peng, Fang

    2015-06-01

    A pale yellow, Gram-reaction-negative, non-motile, aerobic bacterium, designated MC 3726T, was isolated from a tundra soil near Ny-Ålesund, Svalbard Archipelago, Norway (78 °N). Growth occurred at 4-37 °C (optimum 25-30 °C) and at pH 5.0-9.0 (optimum pH 8.0). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain MC 3726T belonged to the genus Luteolibacter in the family Verrucomicrobiaceae. The 16S rRNA gene sequence of this strain showed 93.18, 92.54 and 92.44 % similarity to those of Luteolibacter cuticulihirudinis E100T, Luteolibacter pohnpeiensis A4T-83T and Luteolibacter yonseiensis EBTL01T, respectively. The cell wall of strain MC 3726T contained meso-diaminopimelic acid as the diagnostic amino acid. Strain MC 3726T contained iso-C14:0 (38.28 %), C16:0 (15.89 %), C16:1ω9c (14.24 %), iso-C16:0 (10.42 %) and anteiso-C15:0 (5.75 %) as the predominant cellular fatty acids, MK-9 and MK-10 as the major respiratory quinones, and phosphatidylethanolamine, phosphatidylmethylethanolamine, phosphatidylglycerol and diphosphatidylglycerol as the main polar lipids. The DNA G+C content was 60.7 mol %. On the basis of phenotypic, chemotaxonomic and phylogenetic data, strain MC 3726T is considered to represent a novel species of the genus Luteolibacter, for which the name Luteolibacter arcticus sp. nov. is proposed. The type strain is MC 3726T ( = CCTCC AB 2014275T = LMG 28638T). An emended description of the genus Luteolibacter is also provided, along with emended descriptions of Luteolibacter cuticulihirudinis, Luteolibacter yonseiensis and Luteolibacter pohnpeiensis.

  20. Vegetation shifts observed in arctic tundra 17 years after fire

    USGS Publications Warehouse

    Barrett, Kirsten; Rocha, Adrian V.; van de Weg, Martine Janet; Shaver, Gaius

    2012-01-01

    With anticipated climate change, tundra fires are expected to occur more frequently in the future, but data on the long-term effects of fire on tundra vegetation composition are scarce. This study addresses changes in vegetation structure that have persisted for 17 years after a tundra fire on the North Slope of Alaska. Fire-related shifts in vegetation composition were assessed from remote-sensing imagery and ground observations of the burn scar and an adjacent control site. Early-season remotely sensed imagery from the burn scar exhibits a low vegetation index compared with the control site, whereas the late-season signal is slightly higher. The range and maximum vegetation index are greater in the burn scar, although the mean annual values do not differ among the sites. Ground observations revealed a greater abundance of moss in the unburned site, which may account for the high early growing season normalized difference vegetation index (NDVI) anomaly relative to the burn. The abundance of graminoid species and an absence of Betula nana in the post-fire tundra sites may also be responsible for the spectral differences observed in the remotely sensed imagery. The partial replacement of tundra by graminoid-dominated ecosystems has been predicted by the ALFRESCO model of disturbance, climate and vegetation succession.

  1. Shrub Abundance Mapping in Arctic Tundra with Misr

    NASA Astrophysics Data System (ADS)

    Duchesne, R.; Chopping, M. J.; Wang, Z.; Schaaf, C.; Tape, K. D.

    2013-12-01

    Over the last 60 years an increase in shrub abundance has been observed in the Arctic tundra in connection with a rapid surface warming trend. Rapid shrub expansion may have consequences in terms of ecosystem structure and function, albedo, and feedbacks to climate; however, its rate is not yet known. The goal of this research effort is thus to map large scale changes in Arctic tundra vegetation by exploiting the structural signal in moderate resolution satellite remote sensing images from NASA's Multiangle Imaging SpectroRadiometer (MISR), mapped onto a 250m Albers Conic Equal Area grid. We present here large area shrub mapping supported by reference data collated using extensive field inventory data and high resolution panchromatic imagery. MISR Level 1B2 Terrain radiance scenes from the Terra satellite from 15 June-31 July, 2000 - 2010 were converted to surface bidirectional reflectance factors (BRF) using MISR Toolkit routines and the MISR 1 km LAND product BRFs. The red band data in all available cameras were used to invert the RossThick-LiSparse-Reciprocal BRDF model to retrieve kernel weights, model-fitting RMSE, and Weights of Determination. The reference database was constructed using aerial survey, three field campaigns (field inventory for shrub count, cover, mean radius and height), and high resolution imagery. Tall shrub number, mean crown radius, cover, and mean height estimates were obtained from QuickBird and GeoEye panchromatic image chips using the CANAPI algorithm, and calibrated using field-based estimates, thus extending the database to over eight hundred locations. Tall shrub fractional cover maps for the North Slope of Alaska were constructed using the bootstrap forest machine learning algorithm that exploits the surface information provided by MISR. The reference database was divided into two datasets for training and validation. The model derived used a set of 19 independent variables(the three kernel weights, ratios and interaction terms

  2. Potential enzyme activities altered by increased nutrient availability in Arctic tundra soils

    NASA Astrophysics Data System (ADS)

    Koyama, A.; Wallenstein, M. D.; Moore, J. C.; Simpson, R. T.

    2012-12-01

    The Arctic tundra is a biome affected most by global warming predicted in the future. Such warming is expected to increase nutrient availability to soil microbes which, in turn, may accelerate soil organic matter decomposition. We investigated how extra-cellular enzyme activities in soils were affected by increasing nutrient availability in an Arctic tundra ecosystem. Specifically, we measured potential activities of seven enzymes at three profiles (organic, organic/mineral interface, and mineral) of soils which had been fertilized in long- (23 years) and short-terms (six years), assayed at four temperatures. The long-term site had a high fertilization treatment (10g N m-2 year-1 and 5g P m-2 year-1) and control, and the short-term site had a low fertilization treatment (5g N m-2 year-1 and 2.5g P m-2 year-1) in addition to the high fertilization treatment and control. The fertilization treatments significantly altered most of the enzyme activities in both sites. The fertilization treatments increased activities of enzymes hydrolyzing products for C and nitrogen N sources, but decreased phosphatase activities. Such alterations were most pronounced in the organic soils. The fertilization treatments also increased ratios of total enzyme activities involved in hydrolysis for C products to those for N products. This result is consistent with an observation that long-term N and P fertilization decreased soil organic C in the same tundra ecosystem. Altered enzymatic stoichiometry with increased nutrient availability should be considered when modeling biogeochemical cycles in Arctic tundra ecosystems in response to warming predicted in the future.

  3. Remote sensing of vegetation and land-cover change in Arctic tundra ecosystems

    USGS Publications Warehouse

    Checkstow, D.A.; Hope, A.; McGuire, D.; Verbyla, D.; Gamon, J.; Huemmrich, F.; Houston, S.; Racine, C.; Sturm, M.; Tape, K.; Hinzman, L.; Yoshikawa, K.; Tweedie, C.

    2004-01-01

    The objective of this paper is to review research conducted over the past decade on the application of multi-temporal remote sensing for monitoring changes of Arctic tundra lands. Emphasis is placed on results from the National Science Foundation Land-Air-Ice Interactions (LAII) program and on optical remote sensing techniques. Case studies demonstrate that ground-level sensors on stationary or moving track platforms and wide-swath imaging sensors on polar orbiting satellites are particularly useful for capturing optical remote sensing data at sufficient frequency to study tundra vegetation dynamics and changes for the cloud prone Arctic. Less frequent imaging with high spatial resolution instruments on aircraft and lower orbiting satellites enable more detailed analyses of land cover change and calibration/validation of coarser resolution observations. The strongest signals of ecosystem change detected thus far appear to correspond to expansion of tundra shrubs and changes in the amount and extent of thaw lakes and ponds. Changes in shrub cover and extent have been documented by modern repeat imaging that matches archived historical aerial photography. NOAA Advanced Very High Resolution Radiometer (AVHRR) time series provide a 20-year record for determining changes in greenness that relates to photosynthetic activity, net primary production, and growing season length. The strong contrast between land materials and surface waters enables changes in lake and pond extent to be readily measured and monitored.

  4. Remote sensing of vegetation and land-cover change in Arctic Tundra Ecosystems

    USGS Publications Warehouse

    Stow, D.A.; Hope, A.; McGuire, D.; Verbyla, D.; Gamon, J.; Huemmrich, F.; Houston, S.; Racine, C.; Sturm, M.; Tape, K.; Hinzman, L.; Yoshikawa, K.; Tweedie, C.; Noyle, B.; Silapaswan, C.; Douglas, D.; Griffith, B.; Jia, G.; Epstein, H.; Walker, D.; Daeschner, S.; Petersen, A.; Zhou, L.; Myneni, R.

    2004-01-01

    The objective of this paper is to review research conducted over the past decade on the application of multi-temporal remote sensing for monitoring changes of Arctic tundra lands. Emphasis is placed on results from the National Science Foundation Land-Air-Ice Interactions (LAII) program and on optical remote sensing techniques. Case studies demonstrate that ground-level sensors on stationary or moving track platforms and wide-swath imaging sensors on polar orbiting satellites are particularly useful for capturing optical remote sensing data at sufficient frequency to study tundra vegetation dynamics and changes for the cloud prone Arctic. Less frequent imaging with high spatial resolution instruments on aircraft and lower orbiting satellites enable more detailed analyses of land cover change and calibration/validation of coarser resolution observations. The strongest signals of ecosystem change detected thus far appear to correspond to expansion of tundra shrubs and changes in the amount and extent of thaw lakes and ponds. Changes in shrub cover and extent have been documented by modern repeat imaging that matches archived historical aerial photography. NOAA Advanced Very High Resolution Radiometer (AVHRR) time series provide a 20-year record for determining changes in greenness that relates to photosynthetic activity, net primary production, and growing season length. The strong contrast between land materials and surface waters enables changes in lake and pond extent to be readily measured and monitored. ?? 2003 Elsevier Inc. All rights reserved.

  5. Long-term recovery patterns of arctic tundra after winter seismic exploration.

    PubMed

    Jorgenson, Janet C; Ver Hoef, Jay M; Jorgenson, M T

    2010-01-01

    In response to the increasing global demand for energy, oil exploration and development are expanding into frontier areas of the Arctic, where slow-growing tundra vegetation and the underlying permafrost soils are very sensitive to disturbance. The creation of vehicle trails on the tundra from seismic exploration for oil has accelerated in the past decade, and the cumulative impact represents a geographic footprint that covers a greater extent of Alaska's North Slope tundra than all other direct human impacts combined. Seismic exploration for oil and gas was conducted on the coastal plain of the Arctic National Wildlife Refuge, Alaska, USA, in the winters of 1984 and 1985. This study documents recovery of vegetation and permafrost soils over a two-decade period after vehicle traffic on snow-covered tundra. Paired permanent vegetation plots (disturbed vs. reference) were monitored six times from 1984 to 2002. Data were collected on percent vegetative cover by plant species and on soil and ground ice characteristics. We developed Bayesian hierarchical models, with temporally and spatially autocorrelated errors, to analyze the effects of vegetation type and initial disturbance levels on recovery patterns of the different plant growth forms as well as soil thaw depth. Plant community composition was altered on the trails by species-specific responses to initial disturbance and subsequent changes in substrate. Long-term changes included increased cover of graminoids and decreased cover of evergreen shrubs and mosses. Trails with low levels of initial disturbance usually improved well over time, whereas those with medium to high levels of initial disturbance recovered slowly. Trails on ice-poor, gravel substrates of riparian areas recovered better than those on ice-rich loamy soils of the uplands, even after severe initial damage. Recovery to pre-disturbance communities was not possible where trail subsidence occurred due to thawing of ground ice. Previous studies of

  6. Controls over nutrient flow through plants and microbes in Arctic tundra. Final report

    SciTech Connect

    Schimel, J.

    1994-02-01

    Ecosystem productivity in the Arctic is strongly controlled by N availability to plants. Thus, disturbances to the Arctic system are likely to have their greatest impacts by altering the supply of nutrients to plants. Thus, to understand the dynamics of Arctic tundra, a complete understanding of the controls on N cycling in tundra soils is necessary. This project focused on understanding nutrient dynamics in arctic tussock tundra, specifically evaluating the role of microbial uptake and competition for nutrients as a control on plant N-uptake. The project consisted of several major components: Short- and long-term partitioning of NH{sub 4}{sup +} in tussock tundra (1990--1991); Measurement of NH{sub 4}{sup +} uptake rates by Eriophorum vaginatum and by soil microbes; Determination of microbial NH{sub 4}{sup +} and NO{sub 3}{minus} uptake kinetics; and Determination of the partitioning of NH{sub 4}{sup +} and amino acids between E. vaginatum and soil microbes.

  7. Rough-Legged Buzzards, Arctic Foxes and Red Foxes in a Tundra Ecosystem without Rodents

    PubMed Central

    Pokrovsky, Ivan; Ehrich, Dorothée; Ims, Rolf A.; Kondratyev, Alexander V.; Kruckenberg, Helmut; Kulikova, Olga; Mihnevich, Julia; Pokrovskaya, Liya; Shienok, Alexander

    2015-01-01

    Small rodents with multi-annual population cycles strongly influence the dynamics of food webs, and in particular predator-prey interactions, across most of the tundra biome. Rodents are however absent from some arctic islands, and studies on performance of arctic predators under such circumstances may be very instructive since rodent cycles have been predicted to collapse in a warming Arctic. Here we document for the first time how three normally rodent-dependent predator species—rough-legged buzzard, arctic fox and red fox – perform in a low-arctic ecosystem with no rodents. During six years (in 2006-2008 and 2011-2013) we studied diet and breeding performance of these predators in the rodent-free Kolguev Island in Arctic Russia. The rough-legged buzzards, previously known to be a small rodent specialist, have only during the last two decades become established on Kolguev Island. The buzzards successfully breed on the island at stable low density, but with high productivity based on goslings and willow ptarmigan as their main prey – altogether representing a novel ecological situation for this species. Breeding density of arctic fox varied from year to year, but with stable productivity based on mainly geese as prey. The density dynamic of the arctic fox appeared to be correlated with the date of spring arrival of the geese. Red foxes breed regularly on the island but in very low numbers that appear to have been unchanged over a long period – a situation that resemble what has been recently documented from Arctic America. Our study suggests that the three predators found breeding on Kolguev Island possess capacities for shifting to changing circumstances in low-arctic ecosystem as long as other small - medium sized terrestrial herbivores are present in good numbers. PMID:25692786

  8. Rough-legged buzzards, Arctic foxes and red foxes in a tundra ecosystem without rodents.

    PubMed

    Pokrovsky, Ivan; Ehrich, Dorothée; Ims, Rolf A; Kondratyev, Alexander V; Kruckenberg, Helmut; Kulikova, Olga; Mihnevich, Julia; Pokrovskaya, Liya; Shienok, Alexander

    2015-01-01

    Small rodents with multi-annual population cycles strongly influence the dynamics of food webs, and in particular predator-prey interactions, across most of the tundra biome. Rodents are however absent from some arctic islands, and studies on performance of arctic predators under such circumstances may be very instructive since rodent cycles have been predicted to collapse in a warming Arctic. Here we document for the first time how three normally rodent-dependent predator species-rough-legged buzzard, arctic fox and red fox - perform in a low-arctic ecosystem with no rodents. During six years (in 2006-2008 and 2011-2013) we studied diet and breeding performance of these predators in the rodent-free Kolguev Island in Arctic Russia. The rough-legged buzzards, previously known to be a small rodent specialist, have only during the last two decades become established on Kolguev Island. The buzzards successfully breed on the island at stable low density, but with high productivity based on goslings and willow ptarmigan as their main prey - altogether representing a novel ecological situation for this species. Breeding density of arctic fox varied from year to year, but with stable productivity based on mainly geese as prey. The density dynamic of the arctic fox appeared to be correlated with the date of spring arrival of the geese. Red foxes breed regularly on the island but in very low numbers that appear to have been unchanged over a long period - a situation that resemble what has been recently documented from Arctic America. Our study suggests that the three predators found breeding on Kolguev Island possess capacities for shifting to changing circumstances in low-arctic ecosystem as long as other small - medium sized terrestrial herbivores are present in good numbers.

  9. Vegetation biomass, leaf area index, and NDVI patterns and relationships along two latitudinal transects in arctic tundra

    NASA Astrophysics Data System (ADS)

    Epstein, H. E.; Walker, D. A.; Raynolds, M. K.; Kelley, A. M.; Jia, G.; Ping, C.; Michaelson, G.; Leibman, M. O.; Kaarlejärvi, E.; Khomutov, A.; Kuss, P.; Moskalenko, N.; Orekhov, P.; Matyshak, G.; Forbes, B. C.; Yu, Q.

    2009-12-01

    Analyses of vegetation properties along climatic gradients provide first order approximations as to how vegetation might respond to a temporally dynamic climate. Until recently, no systematic study of tundra vegetation had been conducted along bioclimatic transects that represent the full latitudinal extent of the arctic tundra biome. Since 1999, we have been collecting data on arctic tundra vegetation and soil properties along two such transects, the North American Arctic Transect (NAAT) and the Yamal Arctic Transect (YAT). The NAAT spans the arctic tundra from the Low Arctic of the North Slope of Alaska to the polar desert of Cape Isachsen on Ellef Ringnes Island in the Canadian Archipelago. The Yamal Arctic Transect located in northwest Siberia, Russia, presently ranges from the forest-tundra transition at Nadym to the High Arctic tundra on Belyy Ostrov off the north coast of the Yamal Peninsula. The summer warmth indices (SWI - sum of mean monthly temperatures greater than 0°C) range from approximately 40 °C months to 3 °C months from south to north. For largely zonal sites along these transects, we systematically collected leaf area index (LAI-2000 Plant Canopy Analyzer), normalized difference vegetation index (NDVI - PSII hand-held spectro-radiometer), and vegetation biomass (clip harvests). Site-averaged LAI ranges from 1.08 to 0 along the transects, yet can be highly variable at the landscape scale. Site-averaged NDVI ranges from 0.67 to 0.26 along the transects, and is less variable than LAI at the landscape scale. Total aboveground live biomass ranges from approximately 700 g m-2 to < 50 g m-2 along the NAAT, and from approximately 1100 g m-2 to < 400 g m-2 along the YAT (not including tree biomass at Nadym). LAI and NDVI are highly correlated logarithmically (r = 0.80) for the entire dataset. LAI is significantly related to total aboveground (live plus dead) vascular plant biomass, although there is some variability in the data (r = 0.63). NDVI is

  10. Russian Arctic warming and ‘greening’ are closely tracked by tundra shrub willows

    NASA Astrophysics Data System (ADS)

    Forbes, B. C.; Macias Fauria, M.; Zetterberg, P.

    2009-12-01

    Growth in arctic vegetation is generally expected to increase under a warming climate, particularly among deciduous shrubs. We analyzed annual ring growth for an abundant and nearly circumpolar erect willow (Salix lanata L.) from the coastal zone of the northwest Russian Arctic (Nenets Autonomous Okrug). The resulting chronology is strongly related to summer temperature for the period 1942-2005. Remarkably high correlations occur at long distances (>1600 km) across the tundra and taiga zones of West Siberia and Eastern Europe. We also found a clear relationship with photosynthetic activity for upland vegetation at a regional scale for the period 1981-2005, confirming a parallel ‘greening’ trend reported for similarly warming North American portions of the tundra biome. The standardized growth curve suggests a significant increase in shrub willow growth over the last six decades. These findings are in line with field and remote sensing studies that have assigned a strong shrub component to the reported greening signal since the early 1980s. Furthermore, the growth trend agrees with qualitative observations by nomadic Nenets reindeer herders of recent increases in willow size in the region. The quality of the chronology as a climate proxy is exceptional. Given its wide geographic distribution and the ready preservation of wood in permafrost, S. lanata L. has great potential for extended temperature reconstructions in remote areas across the Arctic.

  11. On site bioremediation of hydrocarbon-contaminated Arctic tundra soils in inoculated biopiles.

    PubMed

    Mohn, W W; Radziminski, C Z; Fortin, M C; Reimer, K J

    2001-10-01

    There is a need to develop technology to allow the remediation of soil in polar regions that have been contaminated by hydrocarbon fuel spills. Bioremediation is potentially useful for this purpose, but has not been well demonstrated in polar regions. We investigated biopiles for on-site bioremediation of soil contaminated with Arctic diesel fuel in two independent small-scale field experiments at different sites on the Arctic tundra. The results were highly consistent with one another. In biopiles at both sites, extensive hydrocarbon removal occurred after one summer. After 1 year in treatments with optimal conditions, total petroleum hydrocarbons were reduced from 196 to below 10 mg per kg of soil at one site, and from 2,109 to 195 mg per kg of soil at the other site. Addition of ammonium chloride and sodium phosphate greatly stimulated hydrocarbon removal and indicates that biodegradation was the primary mechanism by which this was achieved. Inoculation with cold-adapted, mixed microbial cultures further stimulated hydrocarbon removal during the summer immediately following inoculation. At one site, soil temperature was monitored during the summer season, and a clear plastic cover increased biopile soil temperature, measured as degree-day accumulation, by 30-49%. Our results show that on-site bioremediation of fuel-contaminated soil at Arctic tundra sites is feasible.

  12. Migration potential of tundra plant species in a warming Arctic: Responses of southern ecotypes of three species to experimental warming in the High Arctic

    NASA Astrophysics Data System (ADS)

    Bjorkman, Anne; Henry, Greg; Vellend, Mark

    2013-04-01

    Climatic changes due to anthropogenic activity are predicted to have a profound effect on the world's biodiversity and ecosystem functioning. The response of natural communities to climate change will depend primarily on two factors: 1) the ability of species to adapt quickly to changing temperatures and precipitation trends, and 2) the ability of species and populations from southern latitudes to migrate northward and establish in new environments. The assumption is often made that species and populations will track their optimal climate northward as the earth warms, but this assumption ignores a host of other potentially important factors, including the lack of adaptation to photoperiod, soil moisture, and biotic interactions at higher latitudes. In this study, we aim to better understand the ability of southern populations to establish and grow at northern latitudes under warmer temperatures. We collected seeds or ramets of three Arctic plant species (Papaver radicatum, Oxyria digyna, and Arctagrostis latifolia) from Alexandra Fiord on Ellesmere Island, Canada and from southern populations at Cornwallis Island, Canada, Barrow, Alaska, and Latnjajaure, Sweden. These seeds were planted into experimentally warmed and control plots at Alexandra Fiord in 2011. We have tracked their survival, phenology, and growth over two growing seasons. Here, we will present the preliminary results of these experiments. In particular, we will discuss whether individuals originating from southern latitudes exhibit higher growth rates in warm plots than control plots, and whether southern populations survive and grow as well as or better than individuals from Alexandra Fiord in the warmed plots. In both cases, a positive response would indicate that a warming climate may facilitate a migration northward of more southerly species or populations, and that the lack of adaptation to local conditions (soil chemistry, microhabitat, etc.) will not limit this migration. Alternately, a

  13. Effects of Landscape Position on Carbon Cycling in Siberian Arctic Tundra

    NASA Astrophysics Data System (ADS)

    Curasi, S. R.; Weber, L. R.; Loranty, M. M.

    2014-12-01

    High latitude carbon cycling is important because shifts in climatic conditions are thawing permafrost and altering carbon uptake in ways that will impact global climate. Within arctic ecosystems variation in slope and topography lead to flows of water beneath the soil surface that increase ecosystem moisture and nutrient availability. Consequently, such differences in landscape position often alter ecosystem structure, increase vegetation productivity, and more generally alter carbon cycling, relative to adjacent upland areas. Such differences will likely result in altered ecosystem responses to continued climate change. Understanding this variability in ecosystem function will be necessary in order to accurately understand the future of the arctic carbon cycle. The objective of this study is to characterize differences in biological and environmental conditions associated with landscape position in Siberian arctic tundra, and to understand how these differences impact ecosystem carbon cycling. To quantify the impact of landscape position on tundra ecosystem carbon cycling, we selected pairs of plots in upland and low lying landscape positions with high and low shrub density. We measured CO2 flux, permafrost thaw depth, soil moisture, soil temperature, and meteorological conditions. These variables were compared relative to shrub density and landscape position in order to determine differences in gross primary productivity and ecosystem respiration associated with vegetation type and landscape position. Low-lying wet areas were more productive than adjacent upland areas, irrespective of vegetation type. We also observed shallower permafrost thaw depth, lower soil temperature, greater soil moisture, and higher ecosystem respiration in the low lying plots. The observation of higher ecosystem respiration despite lower permafrost thaw depths and soil temperatures in the low-lying areas highlights the challenges associated with understanding the arctic carbon cycle

  14. Can antibrowsing defense regulate the spread of woody vegetation in arctic tundra?

    USGS Publications Warehouse

    Bryant, John P.; Joly, Kyle; Chapin, F. Stuart; DeAngelis, Donald L.; Kielland, Knut

    2014-01-01

    Global climate warming is projected to promote the increase of woody plants, especially shrubs, in arctic tundra. Many factors may affect the extent of this increase, including browsing by mammals. We hypothesize that across the Arctic the effect of browsing will vary because of regional variation in antibrowsing chemical defense. Using birch (Betula) as a case study, we propose that browsing is unlikely to retard birch expansion in the region extending eastward from the Lena River in central Siberia across Beringia and the continental tundra of central and eastern Canada where the more effectively defended resin birches predominate. Browsing is more likely to retard birch expansion in tundra west of the Lena to Fennoscandia, Iceland, Greenland and South Baffin Island where the less effectively defended non-resin birches predominate. Evidence from the literature supports this hypothesis. We further suggest that the effect of warming on the supply of plant-available nitrogen will not significantly change either this pan-Arctic pattern of variation in antibrowsing defense or the resultant effect that browsing has on birch expansion in tundra. However, within central and east Beringia warming-caused increases in plant-available nitrogen combined with wildfire could initiate amplifying feedback loops that could accelerate shrubification of tundra by the more effectively defended resin birches. This accelerated shrubification of tundra by resin birch, if extensive, could reduce the food supply of caribou causing population declines. We conclude with a brief discussion of modeling methods that show promise in projecting invasion of tundra by woody plants.

  15. Estimating carbon and energy fluxes in arctic tundra

    NASA Astrophysics Data System (ADS)

    Gokkaya, K.; Jiang, Y.; Rastetter, E.; Shaver, G. R.; Rocha, A. V.

    2013-12-01

    Arctic ecosystems are undergoing a very rapid change due to climate change and their response to climate change has important implications for the global energy budget and carbon (C) cycling. Therefore, it is important to understand how (C) and energy fluxes in the Arctic will respond to climate change. However, attribution of these responses to climate is challenging because measured fluxes are the sum of multiple processes that respond differently to environmental factors. For example, net ecosystem exchange of CO2 (NEE) is the net result of gross (C) uptake by plant photosynthesis (GPP) and (C) loss by ecosystem respiration (ER) and similarly, evapotranspiration (i.e. latent energy, LE) is the sum of transpiration and evaporation. Partitioning of NEE into GPP and ER requires nighttime measurements of NEE, when photosynthesis does not take place, to be extrapolated to daytime. This is challenging in the Arctic because of the long photoperiod during the growing season and the errors involved during the extrapolation. Transpiration (energy), photosynthesis (carbon), and vegetation phenology are inherently coupled because leaf stomata are the primary regulators of gas exchange. Our objectives in this study are to i) estimate canopy resistance (Rc) based on a light use efficiency model, ii) utilize the estimated Rc to predict GPP and transpiration using a coupled C and energy model and thus improve the partitioning of NEE and LE, and iii) to test ensemble Kalman filter (EnKF) to estimate model parameters and improve model predictions. Results from one growing season showed that the model predictions can explain 75 and 71% of the variance in GPP and LE in the Arctic tundra ecosystem, respectively. When the model was embedded within the EnKF for estimating Rc, the amount of variance explained for GPP increased to 81% but there was no improvement for the prediction of LE. This suggests that the factors controlling LE are not fully integrated in the model such as the

  16. Summertime surface O3 behavior and deposition to tundra in the Alaskan Arctic

    NASA Astrophysics Data System (ADS)

    Van Dam, Brie; Helmig, Detlev; Doskey, Paul V.; Oltmans, Samuel J.

    2016-07-01

    Atmospheric turbulence quantities, boundary layer ozone (O3) levels, and O3 deposition to the tundra surface were investigated at Toolik Lake, AK, during the 2011 summer season. Beginning immediately after snowmelt, a diurnal cycle of O3 in the atmospheric surface layer developed with daytime O3 maxima, and minima during low-light hours, resulting in a mean amplitude of 13 ppbv. This diurnal O3 cycle is far larger than observed at other high Arctic locations during the snow-free season. During the snow-free months of June, July, and August, O3 deposition velocities were ˜3 to 5 times faster than during May, when snow covered the ground most of the month. The overall mean O3 deposition velocity between June and August was 0.10 cm s-1. The month of June had the highest diurnal variation, with a median O3 deposition velocity of 0.2 cm s-1 during the daytime and 0.08 cm s-1 during low-light conditions. These values are slightly lower than previously reported summertime deposition velocities in northern latitudes over tundra or fen. O3 loss during low-light periods was attributed to a combination of surface deposition to the tundra and stable boundary layer conditions. We also hypothesize that emissions of reactive biogenic volatile organic compounds into the shallow boundary layer may contribute to nighttime O3 loss.

  17. Arctic shrubification mediates the impacts of warming climate on changes to tundra vegetation

    NASA Astrophysics Data System (ADS)

    Mod, Heidi K.; Luoto, Miska

    2016-12-01

    Climate change has been observed to expand distributions of woody plants in many areas of arctic and alpine environments—a phenomenon called shrubification. New spatial arrangements of shrubs cause further changes in vegetation via changing dynamics of biotic interactions. However, the mediating influence of shrubification is rarely acknowledged in predictions of tundra vegetation change. Here, we examine possible warming-induced landscape-level vegetation changes in a high-latitude environment using species distribution modelling (SDM), specifically concentrating on the impacts of shrubification on ambient vegetation. First, we produced estimates of current shrub and tree cover and forecasts of their expansion under climate change scenarios to be incorporated to SDMs of 116 vascular plants. Second, the predictions of vegetation change based on the models including only abiotic predictors and the models including abiotic, shrub and tree predictors were compared in a representative test area. Based on our model predictions, abundance of woody plants will expand, thus decreasing predicted species richness, amplifying species turnover and increasing the local extinction risk for ambient vegetation. However, the spatial variation demonstrated in our predictions highlights that tundra vegetation can be expected to show a wide variety of different responses to the combined effects of warming and shrubification, depending on the original plant species pool and environmental conditions. We conclude that realistic forecasts of the future require acknowledging the role of shrubification in warming-induced tundra vegetation change.

  18. Phenological dynamics of arctic tundra vegetation and its implications on satellite imagery interpretation

    NASA Astrophysics Data System (ADS)

    Juutinen, Sari; Aurela, Mika; Mikola, Juha; Räsänen, Aleksi; Virtanen, Tarmo

    2016-04-01

    Remote sensing is a key methodology when monitoring the responses of arctic ecosystems to climatic warming. The short growing season and rapid vegetation development, however, set demands to the timing of image acquisition in the arctic. We used multispectral very high spatial resolution satellite images to study the effect of vegetation phenology on the spectral reflectance and image interpretation in the low arctic tundra in coastal Siberia (Tiksi, 71°35'39"N, 128°53'17"E). The study site mainly consists of peatlands, tussock, dwarf shrub, and grass tundra, and stony areas with some lichen and shrub patches. We tested the hypotheses that (1) plant phenology is responsive to the interannual weather variation and (2) the phenological state of vegetation has an impact on satellite image interpretation and the ability to distinguish between the plant communities. We used an empirical transfer function with temperature sums as drivers to reconstruct daily leaf area index (LAI) for the different plant communities for years 2005, and 2010-2014 based on measured LAI development in summer 2014. Satellite images, taken during growing seasons, were acquired for two years having late and early spring, and short and long growing season, respectively. LAI dynamics showed considerable interannual variation due to weather variation, and particularly the relative contribution of graminoid dominated communities was sensitive to these phenology shifts. We have also analyzed the differences in the reflectance values between the two satellite images taking account the LAI dynamics. These results will increase our understanding of the pitfalls that may arise from the timing of image acquisition when interpreting the vegetation structure in a heterogeneous tundra landscape. Very high spatial resolution multispectral images are available at reasonable cost, but not in high temporal resolution, which may lead to compromises when matching ground truth and the imagery. On the other hand

  19. Frequent fires in ancient shrub tundra: implications of paleorecords for arctic environmental change.

    PubMed

    Higuera, Philip E; Brubaker, Linda B; Anderson, Patricia M; Brown, Thomas A; Kennedy, Alison T; Hu, Feng Sheng

    2008-03-05

    Understanding feedbacks between terrestrial and atmospheric systems is vital for predicting the consequences of global change, particularly in the rapidly changing Arctic. Fire is a key process in this context, but the consequences of altered fire regimes in tundra ecosystems are rarely considered, largely because tundra fires occur infrequently on the modern landscape. We present paleoecological data that indicate frequent tundra fires in northcentral Alaska between 14,000 and 10,000 years ago. Charcoal and pollen from lake sediments reveal that ancient birch-dominated shrub tundra burned as often as modern boreal forests in the region, every 144 years on average (+/- 90 s.d.; n = 44). Although paleoclimate interpretations and data from modern tundra fires suggest that increased burning was aided by low effective moisture, vegetation cover clearly played a critical role in facilitating the paleofires by creating an abundance of fine fuels. These records suggest that greater fire activity will likely accompany temperature-related increases in shrub-dominated tundra predicted for the 21(st) century and beyond. Increased tundra burning will have broad impacts on physical and biological systems as well as on land-atmosphere interactions in the Arctic, including the potential to release stored organic carbon to the atmosphere.

  20. Frequent Fires in Ancient Shrub Tundra: Implications of Paleorecords for Arctic Environmental Change

    PubMed Central

    Higuera, Philip E.; Brubaker, Linda B.; Anderson, Patricia M.; Brown, Thomas A.; Kennedy, Alison T.; Hu, Feng Sheng

    2008-01-01

    Understanding feedbacks between terrestrial and atmospheric systems is vital for predicting the consequences of global change, particularly in the rapidly changing Arctic. Fire is a key process in this context, but the consequences of altered fire regimes in tundra ecosystems are rarely considered, largely because tundra fires occur infrequently on the modern landscape. We present paleoecological data that indicate frequent tundra fires in northcentral Alaska between 14,000 and 10,000 years ago. Charcoal and pollen from lake sediments reveal that ancient birch-dominated shrub tundra burned as often as modern boreal forests in the region, every 144 years on average (+/− 90 s.d.; n = 44). Although paleoclimate interpretations and data from modern tundra fires suggest that increased burning was aided by low effective moisture, vegetation cover clearly played a critical role in facilitating the paleofires by creating an abundance of fine fuels. These records suggest that greater fire activity will likely accompany temperature-related increases in shrub-dominated tundra predicted for the 21st century and beyond. Increased tundra burning will have broad impacts on physical and biological systems as well as on land-atmosphere interactions in the Arctic, including the potential to release stored organic carbon to the atmosphere. PMID:18320025

  1. Changing snow cover in tundra ecosystems tips the Arctic carbon balance

    NASA Astrophysics Data System (ADS)

    Zona, D.; Hufkens, K.; Gioli, B.; Kalhori, A. A. M.; Oechel, W. C.

    2014-12-01

    The Arctic environment has witnessed important changes due to global warming, resulting in increased surface air temperatures and rain events which both exacerbate snow cover deterioration (Semmens et al, 2013; Rennert et al, 2009; White et al, 2007; Min et al, 2008; Sharp et al, 2013; Schaeffer et al, 2013). Snow cover duration is declining by almost 20% per decade, a far higher rate than model estimates (Derksen and Brown, 2012). Concomitant with increasing temperatures and decreasing snow cover duration, the length of the arctic growing season is reported to have increased by 1.1 - 4.9 days per decade since 1951 (Menzel et al, 2006), and, plant productivity and CO2 uptake from arctic vegetation are strongly influenced by changes in growing season length (Myneni et al., 1997; Schaefer et al., 2005; Euskirchen et al., 2006). Based on more than a decade of eddy flux measurements in Arctic tundra ecosystems across the North slope of Alaska, and remotely sensed snow cover data, we show that earlier snow melt in the spring increase C uptake while an extended snow free period in autumn is associated with a higher C loss. Here we present the impacts of changes in snow cover dynamics between spring and autumn in arctic tundra ecosystems on the carbon dynamics and net C balance of the Alaskan Arctic. ReferencesDerksen, C., Brown R. (2012) Geophys. Res. Lett., doi:10.1029/2012GL053387 Euskirchen, E.S., et al. (2006) Glob. Change Biol., 12, 731-750. Menzel, A., et al. 2006. Glob. Change Biol., 12, 1969-1976. Min SK, Zhang X, Zweirs F (2008) Science 320: 518-520. Rennert K J, Roe G, Putkonen J and Bitz C M (2009) J. Clim. 22 2302-15. Schaefer, K., Denning A.S., Leonard O. (2005) Global Biogeochem. Cycles, 19, GB3017. Schaeffer, S. M., Sharp, E., Schimel, J. P. & Welker, J. M. (2013). Soil- plant N processes in a High Arctic ecosystem, NW Greenland are altered by long-term experimental warming and higher rainfall. Glob. Change Biol., 11, 3529-39. doi: 10.1111/gcb.12318

  2. Development of an Energy-based Runoff Generation Model in Arctic Tundra Regions

    NASA Astrophysics Data System (ADS)

    Thorne, R.; Quinton, W. L.

    2009-05-01

    Recently, the demand for improved predictive models of runoff in arctic tundra regions has increased, given uncertainties regarding the future availability of northern freshwater resources related to climate change and expanding resource development. Hydrological characteristics of the arctic tundra are substantially different from those of temperate regions in which traditional runoff generation theories were based. Therefore, theories that apply specifically to the arctic tundra need to be incorporated into a robust runoff model to improve predictions for this region. In addition, the topographically based contributing areas described by source area concepts in the model can be combined with or superseded by an energy-based contributing area. The goal of this project is to design an energy-based runoff generation model to simulate characteristics influencing the aerodynamic and radiation regimes at the surface, including surface roughness, slope aspect and angle in tundra landscapes. Through the model, the frost table topography can be derived, which is a critical step toward predicting the rate and direction of flow. As most arctic tundra catchments in Canada are ungauged, understanding the impact of observed climate warming and unprecedented resource extraction activities can only be achieved through improved conceptualization of hydrological processes. Thus, an energy-based runoff generation model may lead to improved predictions of streamflow in both the present and future.

  3. Effects of experimentally-warmed tundra on diurnal gas exchange in Salix-, Carex, and Eriophorum in a high-arctic lowland oasis

    SciTech Connect

    Jones, M.H.; MacDonald, S.E. ); Henry, G.H.R. )

    1994-06-01

    Gas exchange was measured for the willow Salix arctica and two sede species. Carex qauatilus stans and Eriophorum angustifolium triste, at Alexandra Fiord, Ellesmere Island (78[degrees]52'N) in an experiment designed to stimulate climate change. The tundra was warmed using passive, open-topped experimental chambers that raised daily mean temperatures approx. 2[degrees] over two seasons. The chambers are part of the International Tundra Experiment (ITEX), the objective of which is to assess potential impacts of global warming on tundra plant communities. Salix arctica was measured in dry tundra and on adjacent wet meadow hummocks. The sedges were measured on hummocks and in hollows in the wet meadow only. Gas exchange was measured every four hours for 48 hours for each species. For S arctica, experimental warming had no effect in the dry tundra, but appeared to depress net assimilation (NA) in the wet meadow. Gas exchange parameters were slightly higher overall in the dry tundra for this species. For the sedges, the warming treatment had no major effect, although it caused some reduction of NA for Eriophorum on the hummocks. Gas exchange parameters were generally higher for Carex than for Eriophorum. No regular diurnal patterns of gas exchange were observed for any species.

  4. Succession Stages of Tundra Plant Communities Following Wildfire Disturbance in Arctic Alaska

    NASA Astrophysics Data System (ADS)

    Breen, A. L.; Hollingsworth, T. N.; Mack, M. C.; Jones, B. M.

    2015-12-01

    Rapid climate change is affecting climate-sensitive disturbance regimes throughout the world. In particular, the impacts of climate change on Arctic disturbance regimes are poorly understood because landscape-scale disturbances are infrequent or occur in remote localities. Wildfire in Arctic Alaska is presently limited by ignition source and favorable burn weather. With rapid climate change, a lengthening growing season, and subsequent increase in plant biomass and productivity, wildfire frequency and annual area burned in tundra ecosystems is expected to increase over the next century. Yet, post-fire tundra vegetation succession is inadequately characterized except at a few point locations. We identify succession stages of tussock tundra communities following wildfire using a chronosequence of 65 relevés in 10 tundra fire scars (1971-2011) and nearby unburned tundra from sites on the Seward Peninsula and northern foothills of the Brooks Range. We used the Braun-Blanquét approach to classify plant communities, and applied nonmetric multidimentional scaling (NMDS) to identify ecological gradients underlying community differentiation. The ordination revealed a clear differentiation between unburned and burned tundra communities. Ecological gradients, reflected by ordination axes, correspond to fire history (e.g., time since last fire, number of times burned, burn severity) and a complex productivity gradient. Post-fire species richness is less than unburned tundra; primarily reflected as a decrease in lichen species and turnover of bryophyte species immediately post-fire. Species richness of grasses increases post-fire and is greatest in communities that burned more than once in the past 30 years. Shrub cover and total aboveground biomass are greatest in repeat burn sites. We review and discuss our results focusing on the implications of a changing tundra fire regime, its effect on vegetation succession trajectories, and subsequent rates of carbon sequestration and

  5. Shrub encroachment in Arctic tundra: Betula nana effects on above- and belowground litter decomposition.

    PubMed

    McLaren, Jennie R; Buckeridge, Kate M; van de Weg, Martine J; Shaver, Gaius R; Schimel, Joshua P; Gough, Laura

    2017-03-06

    Rapid arctic vegetation change as a result of global warming includes an increase in the cover and biomass of deciduous shrubs. Increases in shrub abundance will result in a proportional increase of shrub litter in the litter community, potentially affecting carbon turnover rates in arctic ecosystems. We investigated the effects of leaf and root litter of a deciduous shrub, Betula nana, on decomposition, by examining species-specific decomposition patterns, as well as effects of Betula litter on the decomposition of other species. We conducted a 2-yr decomposition experiment in moist acidic tundra in northern Alaska, where we decomposed three tundra species (Vaccinium vitis-idaea, Rhododendron palustre, and Eriophorum vaginatum) alone and in combination with Betula litter. Decomposition patterns for leaf and root litter were determined using three different measures of decomposition (mass loss, respiration, extracellular enzyme activity). We report faster decomposition of Betula leaf litter compared to other species, with support for species differences coming from all three measures of decomposition. Mixing effects were less consistent among the measures, with negative mixing effects shown only for mass loss. In contrast, there were few species differences or mixing effects for root decomposition. Overall, we attribute longer-term litter mass loss patterns to patterns created by early decomposition processes in the first winter. We note numerous differences for species patterns between leaf and root decomposition, indicating that conclusions from leaf litter experiments should not be extrapolated to below-ground decomposition. The high decomposition rates of Betula leaf litter aboveground, and relatively similar decomposition rates of multiple species below, suggest a potential for increases in turnover in the fast-decomposing carbon pool of leaves and fine roots as the dominance of deciduous shrubs in the Arctic increases, but this outcome may be tempered by

  6. Regional-Scale Vegetation Dynamics in Patterned-Ground Ecosystems of Arctic Tundra

    NASA Astrophysics Data System (ADS)

    Epstein, H. E.; Kelley, A. M.; Walker, D. A.; Jia, G. J.; Raynolds, M. K.

    2006-12-01

    Regional-scale patterns of vegetation have been analyzed along a number of climate gradients throughout the world; these spatial dynamics provide important insights into the controlling factors of vegetation and the potential plant responses to environmental change. Only a few studies to date have collectively examined the vegetation biomass and production of arctic tundra ecosystems and their relationships to broadly ranging climate variables. No prior study has taken a systematic and consistent approach to examining vegetation biomass patterns along the full temperature gradient of the arctic biome. An additional complicating factor for studying vegetation of arctic tundra is the high spatial variability associated with small patterned-ground features (e.g. non-sorted circles and small non-sorted polygons), resulting from intense freeze-thaw processes. In this study, we sampled and analyzed the aboveground plant biomass components of patterned-ground ecosystems in the Arctic of northern Alaska and Canada along an 1800-km north-south gradient that spans approximately 11 degrees C of mean July temperatures. At each of ten locations along the regional temperature gradient, we ran several 50-m transects and harvested the aboveground biomass of three 20 x 50 cm plots for each transect. Vegetation biomass was dried, sorted by plant functional groups and tissue types, weighed, and analyzed as functions of the summer warmth index (SWI sum of mean monthly temperatures > 0). The absolute biomass (g/m2) of shrubs and graminoids increased exponentially with SWI, whereas forb and lichen biomass showed no change along the gradient. Moss biomass increased linearly with SWI, but with greater variabiliy than the other types. Relative aboveground biomass (% of total) of shrubs and graminoids increased with SWI, whereas percent lichen biomass decreased, and forbs again exhibited no significant change. Percentage of moss biomass was a parabolic function of SWI, with high relative

  7. NDVI as a predictor of canopy arthropod biomass in the Alaskan arctic tundra.

    PubMed

    Sweet, Shannan K; Asmus, Ashley; Rich, Matthew E; Wingfield, John; Gough, Laura; Boelman, Natalie T

    2015-04-01

    The physical and biological responses to rapid arctic warming are proving acute, and as such, there is a need to monitor, understand, and predict ecological responses over large spatial and temporal scales. The use of the normalized difference vegetation index (NDVI) acquired from airborne and satellite sensors addresses this need, as it is widely used as a tool for detecting and quantifying spatial and temporal dynamics of tundra vegetation cover, productivity, and phenology. Such extensive use of the NDVI to quantify vegetation characteristics suggests that it may be similarly applied to characterizing primary and secondary consumer communities. Here, we develop empirical models to predict canopy arthropod biomass with canopy-level measurements of the NDVI both across and within distinct tundra vegetation communities over four growing seasons in the Arctic Foothills region of the Brooks Range, Alaska, USA. When canopy arthropod biomass is predicted with the NDVI across all four growing seasons, our overall model that includes all four vegetation communities explains 63% of the variance in canopy arthropod biomass, whereas our models specific to each of the four vegetation communities explain 74% (moist tussock tundra), 82% (erect shrub tundra), 84% (riparian shrub tundra), and 87% (dwarf shrub tundra) of the observed variation in canopy arthropod biomass. Our field-based study suggests that measurements of the NDVI made from air- and spaceborne sensors may be able to quantify spatial and temporal variation in canopy arthropod biomass at landscape to regional scales.

  8. Winter precipitation and snow accumulation drive the methane sink or source strength of Arctic tussock tundra.

    PubMed

    Blanc-Betes, Elena; Welker, Jeffrey M; Sturchio, Neil C; Chanton, Jeffrey P; Gonzalez-Meler, Miquel A

    2016-08-01

    Arctic winter precipitation is projected to increase with global warming, but some areas will experience decreases in snow accumulation. Although Arctic CH4 emissions may represent a significant climate forcing feedback, long-term impacts of changes in snow accumulation on CH4 fluxes remain uncertain. We measured ecosystem CH4 fluxes and soil CH4 and CO2 concentrations and (13) C composition to investigate the metabolic pathways and transport mechanisms driving moist acidic tundra CH4 flux over the growing season (Jun-Aug) after 18 years of experimental snow depth increases and decreases. Deeper snow increased soil wetness and warming, reducing soil %O2 levels and increasing thaw depth. Soil moisture, through changes in soil %O2 saturation, determined predominance of methanotrophy or methanogenesis, with soil temperature regulating the ecosystem CH4 sink or source strength. Reduced snow (RS) increased the fraction of oxidized CH4 (Fox) by 75-120% compared to Ambient, switching the system from a small source to a net CH4 sink (21 ± 2 and -31 ± 1 mg CH4  m(-2)  season(-1) at Ambient and RS). Deeper snow reduced Fox by 35-40% and 90-100% in medium- (MS) and high- (HS) snow additions relative to Ambient, contributing to increasing the CH4 source strength of moist acidic tundra (464 ± 15 and 3561 ± 97 mg CH4  m(-2)  season(-1) at MS and HS). Decreases in Fox with deeper snow were partly due to increases in plant-mediated CH4 transport associated with the expansion of tall graminoids. Deeper snow enhanced CH4 production within newly thawed soils, responding mainly to soil warming rather than to increases in acetate fermentation expected from thaw-induced increases in SOC availability. Our results suggest that increased winter precipitation will increase the CH4 source strength of Arctic tundra, but the resulting positive feedback on climate change will depend on the balance between areas with more or less snow accumulation than they are currently

  9. Sea ice, rain-on-snow and tundra reindeer nomadism in Arctic Russia.

    PubMed

    Forbes, Bruce C; Kumpula, Timo; Meschtyb, Nina; Laptander, Roza; Macias-Fauria, Marc; Zetterberg, Pentti; Verdonen, Mariana; Skarin, Anna; Kim, Kwang-Yul; Boisvert, Linette N; Stroeve, Julienne C; Bartsch, Annett

    2016-11-01

    Sea ice loss is accelerating in the Barents and Kara Seas (BKS). Assessing potential linkages between sea ice retreat/thinning and the region's ancient and unique social-ecological systems is a pressing task. Tundra nomadism remains a vitally important livelihood for indigenous Nenets and their large reindeer herds. Warming summer air temperatures have been linked to more frequent and sustained summer high-pressure systems over West Siberia, Russia, but not to sea ice retreat. At the same time, autumn/winter rain-on-snow (ROS) events have become more frequent and intense. Here, we review evidence for autumn atmospheric warming and precipitation increases over Arctic coastal lands in proximity to BKS ice loss. Two major ROS events during November 2006 and 2013 led to massive winter reindeer mortality episodes on the Yamal Peninsula. Fieldwork with migratory herders has revealed that the ecological and socio-economic impacts from the catastrophic 2013 event will unfold for years to come. The suggested link between sea ice loss, more frequent and intense ROS events and high reindeer mortality has serious implications for the future of tundra Nenets nomadism.

  10. Sea ice, rain-on-snow and tundra reindeer nomadism in Arctic Russia

    PubMed Central

    Kumpula, Timo; Meschtyb, Nina; Laptander, Roza; Macias-Fauria, Marc; Zetterberg, Pentti; Verdonen, Mariana; Kim, Kwang-Yul; Boisvert, Linette N.; Stroeve, Julienne C.; Bartsch, Annett

    2016-01-01

    Sea ice loss is accelerating in the Barents and Kara Seas (BKS). Assessing potential linkages between sea ice retreat/thinning and the region's ancient and unique social–ecological systems is a pressing task. Tundra nomadism remains a vitally important livelihood for indigenous Nenets and their large reindeer herds. Warming summer air temperatures have been linked to more frequent and sustained summer high-pressure systems over West Siberia, Russia, but not to sea ice retreat. At the same time, autumn/winter rain-on-snow (ROS) events have become more frequent and intense. Here, we review evidence for autumn atmospheric warming and precipitation increases over Arctic coastal lands in proximity to BKS ice loss. Two major ROS events during November 2006 and 2013 led to massive winter reindeer mortality episodes on the Yamal Peninsula. Fieldwork with migratory herders has revealed that the ecological and socio-economic impacts from the catastrophic 2013 event will unfold for years to come. The suggested link between sea ice loss, more frequent and intense ROS events and high reindeer mortality has serious implications for the future of tundra Nenets nomadism. PMID:27852939

  11. Isotopic insights into methane production, oxidation, and emissions in Arctic polygon tundra.

    PubMed

    Vaughn, Lydia J S; Conrad, Mark E; Bill, Markus; Torn, Margaret S

    2016-10-01

    Arctic wetlands are currently net sources of atmospheric CH4 . Due to their complex biogeochemical controls and high spatial and temporal variability, current net CH4 emissions and gross CH4 processes have been difficult to quantify, and their predicted responses to climate change remain uncertain. We investigated CH4 production, oxidation, and surface emissions in Arctic polygon tundra, across a wet-to-dry permafrost degradation gradient from low-centered (intact) to flat- and high-centered (degraded) polygons. From 3 microtopographic positions (polygon centers, rims, and troughs) along the permafrost degradation gradient, we measured surface CH4 and CO2 fluxes, concentrations and stable isotope compositions of CH4 and DIC at three depths in the soil, and soil moisture and temperature. More degraded sites had lower CH4 emissions, a different primary methanogenic pathway, and greater CH4 oxidation than did intact permafrost sites, to a greater degree than soil moisture or temperature could explain. Surface CH4 flux decreased from 64 nmol m(-2)  s(-1) in intact polygons to 7 nmol m(-2)  s(-1) in degraded polygons, and stable isotope signatures of CH4 and DIC showed that acetate cleavage dominated CH4 production in low-centered polygons, while CO2 reduction was the primary pathway in degraded polygons. We see evidence that differences in water flow and vegetation between intact and degraded polygons contributed to these observations. In contrast to many previous studies, these findings document a mechanism whereby permafrost degradation can lead to local decreases in tundra CH4 emissions.

  12. Organic layer serves as a hotspot of microbial activity and abundance in Arctic tundra soils.

    PubMed

    Lee, Seung-Hoon; Jang, Inyoung; Chae, Namyi; Choi, Taejin; Kang, Hojeong

    2013-02-01

    Tundra ecosystem is of importance for its high accumulation of organic carbon and vulnerability to future climate change. Microorganisms play a key role in carbon dynamics of the tundra ecosystem by mineralizing organic carbon. We assessed both ecosystem process rates and community structure of Bacteria, Archaea, and Fungi in different soil layers (surface organic layer and subsurface mineral soil) in an Arctic soil ecosystem located at Spitsbergen, Svalbard during the summer of 2008 by using biochemical and molecular analyses, such as enzymatic assay, terminal restriction fragment length polymorphism (T-RFLP), quantitative polymerase chain reaction (qPCR), and pyrosequencing. Activity of hydrolytic enzymes showed difference according to soil type. For all three microbial communities, the average gene copy number did not significantly differ between soil types. However, archaeal diversities appeared to differ according to soil type, whereas bacterial and fungal diversity indices did not show any variation. Correlation analysis between biogeochemical and microbial parameters exhibited a discriminating pattern according to microbial or soil types. Analysis of the microbial community structure showed that bacterial and archaeal communities have different profiles with unique phylotypes in terms of soil types. Water content and hydrolytic enzymes were found to be related with the structure of bacterial and archaeal communities, whereas soil organic matter (SOM) and total organic carbon (TOC) were related with bacterial communities. The overall results of this study indicate that microbial enzyme activity were generally higher in the organic layer than in mineral soils and that bacterial and archaeal communities differed between the organic layer and mineral soils in the Arctic region. Compared to mineral soil, peat-covered organic layer may represent a hotspot for secondary productivity and nutrient cycling in this ecosystem.

  13. Below-ground carbon transfer among Betula nana may increase with warming in Arctic tundra.

    PubMed

    Deslippe, Julie R; Simard, Suzanne W

    2011-11-01

    • Shrubs are expanding in Arctic tundra, but the role of mycorrhizal fungi in this process is unknown. We tested the hypothesis that mycorrhizal networks are involved in interplant carbon (C) transfer within a tundra plant community. • Here, we installed below-ground treatments to control for C transfer pathways and conducted a (13)CO(2)-pulse-chase labelling experiment to examine C transfer among and within plant species. • We showed that mycorrhizal networks exist in tundra, and facilitate below-ground transfer of C among Betula nana individuals, but not between or within the other tundra species examined. Total C transfer among conspecific B. nana pairs was 10.7 ± 2.4% of photosynthesis, with the majority of C transferred through rhizomes or root grafts (5.2 ± 5.3%) and mycorrhizal network pathways (4.1 ± 3.3%) and very little through soil pathways (1.4 ± 0.35%). • Below-ground C transfer was of sufficient magnitude to potentially alter plant interactions in Arctic tundra, increasing the competitive ability and mono-dominance of B. nana. C transfer was significantly positively related to ambient temperatures, suggesting that it may act as a positive feedback to ecosystem change as climate warms.

  14. Water Status of Arctic Tundra Plants During the Winter-Spring Transition

    NASA Astrophysics Data System (ADS)

    Oberbauer, S. F.; Olivas, P. C.; Moser, J.; Starr, G.; Mortazavi, B.

    2012-12-01

    The arctic winter-spring transition when full snow cover rapidly changes to snow-free conditions potentially represents a time of physiological stress for tundra plants. Plants that have been subjected to freezing temperatures for several months over winter are suddenly exposed to high radiation loads from clear skies and reflection from unmelted snow. Water uptake at this time may be limited by low stem temperatures and cold or even frozen soils. Because of these potential stresses it may be advantageous for plants to delay photosynthetic activity and water loss until soils are warmer. However, given the short length of the growing season, the optimal strategy for plants may be to maximize carbon uptake and begin photosynthesis and growth as soon as possible after snowmelt. Some tundra evergreens even photosynthesize under snow cover. To test the hypothesis that plant water stress increases immediately following loss of snow cover, we investigated xylem and leaf osmotic potentials of evergreen tundra species before and immediately after snowmelt. We also compared these measurements with summer and winter measurements. Our study was conducted in moist acidic tundra near Toolik Field Station in the northern foothills of the Brooks Range, Alaska. Xylem water potentials were measured by Scholander pressure chamber and osmotic potentials by psychrometry of cell sap expressed from frozen (-80 °C) leaf tissue. Xylem water potentials under snow were generally higher than those of plants recently released from snow. Osmotic potentials measured before and after snowmelt did not show evidence of strong changes. Some species, such as Ledum palustre, maintained high water potentials both under snow and shortly after snow melt. With only a few exceptions, water potentials just after melt out were generally higher than those after soils had warmed and plants had greened up. Low water potentials (< -3 MPa) were most commonly found in Cassiope tetragona, a snowbed

  15. Seasonal evolution of the effective thermal conductivity of the snow and the soil in high Arctic herb tundra at Bylot Island, Canada

    NASA Astrophysics Data System (ADS)

    Domine, Florent; Barrere, Mathieu; Sarrazin, Denis

    2016-11-01

    The values of the snow and soil thermal conductivity, ksnow and ksoil, strongly impact the thermal regime of the ground in the Arctic, but very few data are available to test model predictions for these variables. We have monitored ksnow and ksoil using heated needle probes at Bylot Island in the Canadian High Arctic (73° N, 80° W) between July 2013 and July 2015. Few ksnow data were obtained during the 2013-2014 winter, because little snow was present. During the 2014-2015 winter ksnow monitoring at 2, 12 and 22 cm heights and field observations show that a depth hoar layer with ksnow around 0.02 W m-1 K-1 rapidly formed. At 12 and 22 cm, wind slabs with ksnow around 0.2 to 0.3 W m-1 K-1 formed. The monitoring of ksoil at 10 cm depth shows that in thawed soil ksoil was around 0.7 W m-1 K-1, while in frozen soil it was around 1.9 W m-1 K-1. The transition between both values took place within a few days, with faster thawing than freezing and a hysteresis effect evidenced in the thermal conductivity-liquid water content relationship. The fast transitions suggest that the use of a bimodal distribution of ksoil for modelling may be an interesting option that deserves further testing. Simulations of ksnow using the snow physics model Crocus were performed. Contrary to observations, Crocus predicts high ksnow values at the base of the snowpack (0.12-0.27 W m-1 K-1) and low ones in its upper parts (0.02-0.12 W m-1 K-1). We diagnose that this is because Crocus does not describe the large upward water vapour fluxes caused by the temperature gradient in the snow and soil. These fluxes produce mass transfer between the soil and lower snow layers to the upper snow layers and the atmosphere. Finally, we discuss the importance of the structure and properties of the Arctic snowpack on subnivean life, as species such as lemmings live under the snow most of the year and must travel in the lower snow layer in search of food.

  16. Initial Conceptualization and Simulation of Arctic Tundra Landscape Evolution Using the Alaska Thermokarst Model

    NASA Astrophysics Data System (ADS)

    Bolton, W. R.; Romanovsky, V. E.; McGuire, A. D.; Grosse, G.; Lara, M. J.

    2014-12-01

    Thermokarst topography forms whenever ice-rich permafrost thaws and the ground subsides due to the volume loss when excess ground ice transitions to water. The Alaska Thermokarst Model (ATM) is a large-scale, state-and-transition model designed to simulate transitions between [non-]thermokarst landscape units, or cohorts. The ATM uses a frame-based methodology to track transitions and proportion of cohorts within a 1-km2 grid cell. In the arctic tundra environment, the ATM tracks thermokarst-related transitions between wetland tundra, graminoid tundra, shrub tundra, and thermokarst lakes. The transition from one cohort to another due to thermokarst processes can take place if thaw reaches ice-rich ground layers either due to pulse disturbance events such as a large precipitation event or fires or due to gradual active layer deepening that eventually results in penetration of the protective layer. The protective layer buffers the ice-rich soils from the land surface and is critical to determine how susceptible an area is to thermokarst degradation. The rate of terrain transition in our model is determined by the ice-content of the soil, the drainage efficiency (or ability of the landscape to store or transport water), and a cumulative probability of thermokarst initiation. Tundra types are allowed to transition from one type to another (ie wetland tundra to a graminoid tundra) under favorable climatic conditions. In this study, we present our conceptualization and initial simulation results from the ATM model for an 1792 km2 area on the Barrow Peninsula, Alaska. The area selected for simulation is located in a polygonal tundra landscape under varying degrees of thermokarst degradation. The goal of this modeling study is to simulate landscape evolution in response to thermokarst disturbance as a result of climate change. The ATM will eventually be incorporated into the Integrated Ecosystem Model (IEM) for Alaska and Northwest Canada for use in management decisions

  17. DOES NITROGEN PARTITIONING PROMOTE SPECIES DIVERSITY IN ARCTIC TUSSOCK TUNDRA?

    EPA Science Inventory

    We used 15N soil-labeling techniques to examine how the dominant species in a N-limited, tussock tundra plant community partitioned soil N, and how such partitioning may contribute to community organization. The five most productive species were well differentiated with respect ...

  18. Estimated storage of amorphous silica in soils of the circum-Arctic tundra region

    NASA Astrophysics Data System (ADS)

    Alfredsson, H.; Clymans, W.; Hugelius, G.; Kuhry, P.; Conley, D. J.

    2016-03-01

    We investigated the vertical distribution, storage, landscape partitioning, and spatial variability of soil amorphous silica (ASi) at four different sites underlain by continuous permafrost and representative of mountainous and lowland tundra, in the circum-Arctic region. Based on a larger set of data, we present the first estimate of the ASi soil reservoir (0-1 m depth) in circum-Arctic tundra terrain. At all sites, the vertical distribution of ASi concentrations followed the pattern of either (1) declining concentrations with depth (most common) or (2) increasing/maximum concentrations with depth. Our results suggest that a set of processes, including biological control, solifluction and other slope processes, cryoturbation, and formation of inorganic precipitates influence vertical distributions of ASi in permafrost terrain, with the capacity to retain stored ASi on millennial timescales. At the four study sites, areal ASi storage (0-1 m) is generally higher in graminoid tundra compared to wetlands. Our circum-Arctic upscaling estimates, based on both vegetation and soil classification separately, suggest a storage amounting to 219 ± 28 and 274 ± 33 Tmol Si, respectively, of which at least 30% is stored in permafrost. This estimate would account for about 3% of the global soil ASi storage while occupying an equal portion of the global land area. This result does not support the hypothesis that the circum-Arctic tundra soil ASi reservoir contains relatively higher amounts of ASi than other biomes globally as demonstrated for carbon. Nevertheless, climate warming has the potential to significantly alter ASi storage and terrestrial Si cycling in the Arctic.

  19. Sea Ice, Hydrocarbon Extraction, Rain-on-Snow and Tundra Reindeer Nomadism in Arctic Russia

    NASA Astrophysics Data System (ADS)

    Forbes, B. C.; Kumpula, T.; Meschtyb, N.; Laptander, R.; Macias-Fauria, M.; Zetterberg, P.; Verdonen, M.

    2015-12-01

    It is assumed that retreating sea ice in the Eurasian Arctic will accelerate hydrocarbon development and associated tanker traffic along Russia's Northern Sea Route. However, oil and gas extraction along the Kara and Barents Sea coasts will likely keep developing rapidly regardless of whether the Northwest Eurasian climate continues to warm. Less certain are the real and potential linkages to regional biota and social-ecological systems. Reindeer nomadism continues to be a vitally important livelihood for indigenous tundra Nenets and their large herds of semi-domestic reindeer. Warming summer air temperatures over the NW Russian Arctic have been linked to increases in tundra productivity, longer growing seasons, and accelerated growth of tall deciduous shrubs. These temperature increases have, in turn, been linked to more frequent and sustained summer high-pressure systems over West Siberia, but not to sea ice retreat. At the same time, winters have been warming and rain-on-snow (ROS) events have become more frequent and intense, leading to record-breaking winter and spring mortality of reindeer. What is driving this increase in ROS frequency and intensity is not clear. Recent modelling and simulation have found statistically significant near-surface atmospheric warming and precipitation increases during autumn and winter over Arctic coastal lands in proximity to regions of sea-ice loss. During the winter of 2013-14 an extensive and lasting ROS event led to the starvation of 61,000 reindeer out of a population of ca. 300,000 animals on Yamal Peninsula, West Siberia. Historically, this is the region's largest recorded mortality episode. More than a year later, participatory fieldwork with nomadic herders during spring-summer 2015 revealed that the ecological and socio-economic impacts from this extreme event will unfold for years to come. There is an urgent need to understand whether and how ongoing Barents and Kara Sea ice retreat may affect the region's ancient

  20. Modelling carbon responses of tundra ecosystems to historical and projected climate: Sensitivity of pan-Arctic carbon storage to temporal and spatial variation in climate

    USGS Publications Warehouse

    McGuire, A.D.; Clein, J.S.; Melillo, J.M.; Kicklighter, D.W.; Meier, R.A.; Vorosmarty, C.J.; Serreze, M.C.

    2000-01-01

    Historical and projected climate trends for high latitudes show substantial temporal and spatial variability. To identify uncertainties in simulating carbon (C) dynamics for pan-Arctic tundra, we compare the historical and projected responses of tundra C storage from 1921 to 2100 between simulations by the Terrestrial Ecosystem Model (TEM) for the pan-Arctic and the Kuparuk River Basin, which was the focus of an integrated study of C dynamics from 1994 to 1996. In the historical period from 1921 to 1994, the responses of net primary production (NPP) and heterotrophic respiration (RH) simulated for the Kuparuk River Basin and the pan-Arctic are correlated with the same factors; NPP is positively correlated with net nitrogen mineralization (NMIN) and RH is negatively correlated with mean annual soil moisture. In comparison to the historical period, the spatially aggregated responses of NPP and RH for the Kuparuk River Basin and the pan-Arctic in our simulations for the projected period have different sensitivities to temperature, soil moisture and NMIN. In addition to being sensitive to soil moisture during the projected period, RH is also sensitive to temperature and there is a significant correlation between RH and NMIN. We interpret the increases in NPP during the projected period as being driven primarily by increases in NMIN, and that the correlation between NPP and temperature in the projected period is a result primarily of the causal linkage between temperature, RH, and NMIN. Although similar factors appear to be controlling simulated regional-and biome-scale C dynamics, simulated C dynamics at the two scales differ in magnitude with higher increases in C storage simulated for the Kuparuk River Basin than for the pan-Arctic at the end of the historical period and throughout the projected period. Also, the results of the simulations indicate that responses of C storage show different climate sensitivities at regional and pan-Arctic spatial scales and that

  1. Long-term Nutrient Fertilization Increases CO2 Loss in Arctic Tundra

    NASA Astrophysics Data System (ADS)

    Graham, L. M.; Natali, S.; Rastetter, E. B.; Shaver, G. R.; Risk, D. A.; Loranty, M. M.; Jastrow, J. D.

    2015-12-01

    As anthropogenic climate change warms the Arctic, organic carbon (C) trapped in permafrost is at an increased risk of being released to the atmosphere as carbon dioxide (CO2). At the same time, higher rates of decomposition may increase nutrient availability and enhance plant growth, leading to an uptake of C that may offset respiratory losses. Arctic tundra ecosystems are highly nitrogen (N) limited, and the indirect effects of warming on nutrient availability will be the most likely outcome of increased temperature on plant productivity. This study aims to understand the effects of nutrient addition on arctic CO2 and H2O exchange in a tundra ecosystem at Toolik Lake Field Station, Alaska. The nutrient addition experiment, which began in 2006, is comprised of 7 fertilization treatments: 0.5, 1, 2, 5, and 10 g m-2 of N as NO3- and NH4+ (1:1) with 0.25, 0.5, 1, 2.5, and 5 g m-2 of phosphorus as PO43-; 5 g m-2 of N as NO3-; 5 g m-2 of N as NH4+, and one control plot. Plot-level CO2 and H2O exchange was measured at 5 light levels 7 times over a four-week period in June and July 2015. We measured ecosystem CO2 and H2O exchange using a rectangular plexiglass chamber (0.49 m2) that was connected to an infrared gas analyzer (LI-840). Other ecosystem variables measured include thaw depth, soil moisture and temperature, and normalized difference vegetation index. After 10 years of nutrient addition, fertilization significantly altered ecosystem C cycling. Soil respiration was greatest in the highest fertilization treatment (2.97 μmol m-2 s-1), increasing linearly with nutrient level at a rate of 0.133 μmol m-2 s-1 per g m-2 of N added (R2=0.914). Net CO2 uptake was greatest under highest fertilization (-2.06 μmol m-2 s-1), decreasing linearly with nutrient addition at a rate of -0.068 μmol m-2 s-1 per g m-2 of N added (R2=0.687). These results suggest that as nutrients become more available under a warmer climate, plant productivity increases may not offset respiratory

  2. Disappearing Arctic Tundra Ponds: Assessing 60 Years of Change in the Barrow Peninsula, Alaska

    NASA Astrophysics Data System (ADS)

    Andresen, C.; Lougheed, V.

    2012-12-01

    Decadal hydrological changes of closed-basin tundra ponds in continuous permafrost fills a missing gap in arctic fresh water research. Furthermore, the lack of historic datasets and high resolution historical imagery adds to the challenge of understanding the long-term trends of these ecosystems. Given the dominance of these aquatic ecosystems in the Arctic landscape, documenting hydrological changes is important to understand carbon and energy balance, trophic energy flow, and biodiversity. We utilized historic aerial imagery from USGS archives of 1948 and modern high-resolution Quickbird imagery from 2008 to assess areal changes in arctic ponds over the past 60 years. Object-oriented classification was used to extract the areal extent of ponds and validated using a combination of ground-based measurements such as Kite Aerial Photography (KAP) and Differential Geographic Positioning System (DGPS). A total of 1120 ponds in different drained thaw lake basins (DTLB) distributed across the Barrow Peninsula were assessed. Analysis indicated a decline in total pond area and a decrease of 36% in the number of ponds, with change more pronounced in smaller ponds (<100m2). Aquatic plant cover data collected over a 40 year period (1970-2012) indicate that expansion of vegetation into the ponds may be a primary mechanism whereby ponds may experience infilling. Other mechanisms may include increased evaporation due to warmer and longer summers, transpiration from encroaching aquatic grasses and changes in precipitation patterns. However, images from additional years will be analyzed to separate out the roles of these variables on inter- versus intra-annual variability in pond surface area.

  3. Influence of BRDF on NDVI and biomass estimations of Alaska Arctic tundra

    NASA Astrophysics Data System (ADS)

    Buchhorn, Marcel; Raynolds, Martha K.; Walker, Donald A.

    2016-12-01

    Satellites provide the only practical source of data for estimating biomass of large and remote areas such as the Alaskan Arctic. Researchers have found that the normalized difference vegetation index (NDVI) correlates well with biomass sampled on the ground. However, errors in NDVI and biomass estimates due to bidirectional reflectance distribution function (BRDF) effects are not well reported in the literature. Sun-sensor-object geometries and sensor band-width affect the BRDF, and formulas relating NDVI to ground-sampled biomass vary between projects. We examined the effects of these different variables on five studies that estimated above-ground tundra biomass of two common arctic vegetation types that dominate the Alaska tundra, moist acidic tussock tundra (MAT) and moist non-acidic tundra (MNT). We found that biomass estimates were up to 33% (excluding extremes) more sensitive than NDVI to BRDF effects. Variation between the sensors resulted in differences in NDVI of under 3% over all viewing geometries, and wider bands were more stable in their biomass estimates than narrow bands. MAT was more sensitive than MNT to BRDF effects due to irregularities in surface reflectance created by the tussocks. Finally, we found that studies that sampled only a narrow range of biomass and NDVI produced equations that were more difficult to correct for BRDF effects.

  4. Analysis of state of vehicular scars on Arctic Tundra, Alaska

    NASA Technical Reports Server (NTRS)

    Lathram, E. H.

    1974-01-01

    Identification on ERTS images of severe vehicular scars in the northern Alaska tundra suggests that, if such scars are of an intensity or have spread to a dimension such that they can be resolved by ERTS sensors (20 meters), they can be identified and their state monitored by the use of ERTS images. Field review of the state of vehicular scars in the Umiat area indicates that all are revegetating at varying rates and are approaching a stable state.

  5. InSAR detects increase in surface subsidence caused by an Arctic tundra fire

    USGS Publications Warehouse

    Liu, Lin; Jafarov, Elchin E.; Schaefer, Kevin M.; Jones, Benjamin M.; Zebker, Howard A.; Williams, Christopher A.; Rogan, John; Zhang, Tingjun

    2014-01-01

    Wildfire is a major disturbance in the Arctic tundra and boreal forests, having a significant impact on soil hydrology, carbon cycling, and permafrost dynamics. This study explores the use of the microwave Interferometric Synthetic Aperture Radar (InSAR) technique to map and quantify ground surface subsidence caused by the Anaktuvuk River fire on the North Slope of Alaska. We detected an increase of up to 8 cm of thaw-season ground subsidence after the fire, which is due to a combination of thickened active layer and permafrost thaw subsidence. Our results illustrate the effectiveness and potential of using InSAR to quantify fire impacts on the Arctic tundra, especially in regions underlain by ice-rich permafrost. Our study also suggests that surface subsidence is a more comprehensive indicator of fire impacts on ice-rich permafrost terrain than changes in active layer thickness alone.

  6. Disturbance and Recovery of Arctic Alaskan Tundra Terrain. A Review of Recent Investigations.

    DTIC Science & Technology

    1987-07-01

    Engineers 1982) and the Arctic National Wildlife Refuge ( ANWR ) (U.S. * Prepared by J. Brown. Department of Interior 1983). 00 Icr. 0 0 II A wide range of...perching birds [Walker et al. 19801) were flat- ( ANWR ), which was opened to winter seismic sur- tened. Erect dead sedges were also flattened and veys in...scraping occurred. In ter operations in ANWR show that dry tundra these areas the surface albedo was higher because (Fig. 22) was the most noticeably

  7. Mapping wildfire burn severity in the Arctic Tundra from downsampled MODIS data

    USGS Publications Warehouse

    Kolden, Crystal A.; Rogan, John

    2013-01-01

    Wildfires are historically infrequent in the arctic tundra, but are projected to increase with climate warming. Fire effects on tundra ecosystems are poorly understood and difficult to quantify in a remote region where a short growing season severely limits ground data collection. Remote sensing has been widely utilized to characterize wildfire regimes, but primarily from the Landsat sensor, which has limited data acquisition in the Arctic. Here, coarse-resolution remotely sensed data are assessed as a means to quantify wildfire burn severity of the 2007 Anaktuvuk River Fire in Alaska, the largest tundra wildfire ever recorded on Alaska's North Slope. Data from Landsat Thematic Mapper (TM) and downsampled Moderate-resolution Imaging Spectroradiometer (MODIS) were processed to spectral indices and correlated to observed metrics of surface, subsurface, and comprehensive burn severity. Spectral indices were strongly correlated to surface severity (maximum R2 = 0.88) and slightly less strongly correlated to substrate severity. Downsampled MODIS data showed a decrease in severity one year post-fire, corroborating rapid vegetation regeneration observed on the burned site. These results indicate that widely-used spectral indices and downsampled coarse-resolution data provide a reasonable supplement to often-limited ground data collection for analysis and long-term monitoring of wildfire effects in arctic ecosystems.

  8. The impact of vegetation type on the shortwave radiation balance of the Arctic tundra

    NASA Astrophysics Data System (ADS)

    Juszak, Inge; Schaepman-Strub, Gabriela

    2015-04-01

    Profound changes in vegetation composition in the Arctic tundra have been observed and are predicted in a warmer future climate. Shrub expansion may positively feed back to climate warming by decreasing the shortwave albedo. On the other hand, permafrost protection through soil shading by shrubs has been discussed in literature. Several studies compared the average radiation balance across vegetation zones. However, variation within vegetation zones may be as important as differences between vegetation zones. The lowland tundra ecosystem at the Kytalyk research site (NE Siberia) is dominated by two vegetation types (dwarf shrub (Betula nana) and wet sedge (Eriophorum angustifolium)) organised in patches at a scale of about 10m. We investigated the shortwave radiation balance of both types separately and related it to the 11 year data set of the fluxtower with a mixed footprint. In addition to canopy albedo, we measured canopy transmittance below dwarf shrubs and wet sedges to quantify the often discussed effect of soil shading. Our results show that at our field site, wet sedge vegetation is shading the soil more efficiently than dwarf shrubs due to multi-year standing litter. While we measured an average transmission of 36% of the incoming shortwave radiation below dwarf shrubs, the transmission of wet sedge was 28%. Wet sedge summer albedo was on average 16% higher than dwarf shrub albedo. Additionally, the snow melted 10 days later in the sedge patches, leading to large albedo differences in the second half of May 2014. Our analysis shows, that cloud cover is the second most important control on albedo and transmittance of both vegetation types. Clouds reduced the summer albedo of both vegetation types across all zenith angles. On average, the growing season albedo was about 11% higher on clear sky days as compared to overcast days whereas the transmittance was about 23% lower. As cloud cover is expected to change with climate change, field studies of the cloud

  9. Greater shrub dominance alters breeding habitat and food resources for migratory songbirds in Alaskan arctic tundra.

    PubMed

    Boelman, Natalie T; Gough, Laura; Wingfield, John; Goetz, Scott; Asmus, Ashley; Chmura, Helen E; Krause, Jesse S; Perez, Jonathan H; Sweet, Shannan K; Guay, Kevin C

    2015-04-01

    Climate warming is affecting the Arctic in multiple ways, including via increased dominance of deciduous shrubs. Although many studies have focused on how this vegetation shift is altering nutrient cycling and energy balance, few have explicitly considered effects on tundra fauna, such as the millions of migratory songbirds that breed in northern regions every year. To understand how increasing deciduous shrub dominance may alter breeding songbird habitat, we quantified vegetation and arthropod community characteristics in both graminoid and shrub dominated tundra. We combined measurements of preferred nest site characteristics for Lapland longspurs (Calcarius lapponicus) and Gambel's White-crowned sparrows (Zonotrichia leucophrys gambelii) with modeled predictions for the distribution of plant community types in the Alaskan arctic foothills region for the year 2050. Lapland longspur nests were found in sedge-dominated tussock tundra where shrub height does not exceed 20 cm, whereas White-crowned sparrows nested only under shrubs between 20 cm and 1 m in height, with no preference for shrub species. Shrub canopies had higher canopy-dwelling arthropod availability (i.e. small flies and spiders) but lower ground-dwelling arthropod availability (i.e. large spiders and beetles). Since flies are the birds' preferred prey, increasing shrubs may result in a net enhancement in preferred prey availability. Acknowledging the coarse resolution of existing tundra vegetation models, we predict that by 2050 there will be a northward shift in current White-crowned sparrow habitat range and a 20-60% increase in their preferred habitat extent, while Lapland longspur habitat extent will be equivalently reduced. Our findings can be used to make first approximations of future habitat change for species with similar nesting requirements. However, we contend that as exemplified by this study's findings, existing tundra modeling tools cannot yet simulate the fine-scale habitat

  10. Potential Arctic tundra vegetation shifts in response to changing temperature, precipitation and permafrost thaw

    NASA Astrophysics Data System (ADS)

    van der Kolk, Henk-Jan; Heijmans, Monique M. P. D.; van Huissteden, Jacobus; Pullens, Jeroen W. M.; Berendse, Frank

    2016-11-01

    Over the past decades, vegetation and climate have changed significantly in the Arctic. Deciduous shrub cover is often assumed to expand in tundra landscapes, but more frequent abrupt permafrost thaw resulting in formation of thaw ponds could lead to vegetation shifts towards graminoid-dominated wetland. Which factors drive vegetation changes in the tundra ecosystem are still not sufficiently clear. In this study, the dynamic tundra vegetation model, NUCOM-tundra (NUtrient and COMpetition), was used to evaluate the consequences of climate change scenarios of warming and increasing precipitation for future tundra vegetation change. The model includes three plant functional types (moss, graminoids and shrubs), carbon and nitrogen cycling, water and permafrost dynamics and a simple thaw pond module. Climate scenario simulations were performed for 16 combinations of temperature and precipitation increases in five vegetation types representing a gradient from dry shrub-dominated to moist mixed and wet graminoid-dominated sites. Vegetation composition dynamics in currently mixed vegetation sites were dependent on both temperature and precipitation changes, with warming favouring shrub dominance and increased precipitation favouring graminoid abundance. Climate change simulations based on greenhouse gas emission scenarios in which temperature and precipitation increases were combined showed increases in biomass of both graminoids and shrubs, with graminoids increasing in abundance. The simulations suggest that shrub growth can be limited by very wet soil conditions and low nutrient supply, whereas graminoids have the advantage of being able to grow in a wide range of soil moisture conditions and have access to nutrients in deeper soil layers. Abrupt permafrost thaw initiating thaw pond formation led to complete domination of graminoids. However, due to increased drainage, shrubs could profit from such changes in adjacent areas. Both climate and thaw pond formation

  11. Examining vertical patterns in Arctic tundra shrub canopies: Implications for carbon cycling in a changing environment

    NASA Astrophysics Data System (ADS)

    Heskel, M.; Atkin, O.; Turnbull, M.; Rastetter, E.; Griffin, K. L.

    2012-12-01

    Climate change is facilitating the northward encroachment and expansion of woody shrub species into the Arctic tundra, which in turn is altering a number of physical and biogeochemical processes that are likely to affect how carbon is cycled in this region. Greater shrub presence also increases leaf area index and canopy complexity in the tundra, introducing the potential for vertical variation in nitrogen, photosynthesis, and respiration through the canopy. For these reasons, Arctic tundra shrub communities represent an ecologically relevant case study for investigating carbon cycling-nitrogen relationships and testing optimization models. Here, we measured photosynthesis, respiration in the dark and light, the light inhibition of respiration, stomatal conductance, leaf nitrogen, and related leaf traits at different heights representing variation in light availability in multiple Arctic Alaskan shrub communities dominated by Salix pulchra and Betula nana to examine if the relatively low-stature canopies exhibit vertical patterns. Highest rates of photosynthesis and respiration (P < 0.0001) were observed at the top of the canopy, suggesting substrate-limitation of respiration at lower, more shaded canopy levels. Leaves at the top of the canopy also exhibited the lowest inhibition of respiration by light (NS), and the highest nitrogen concentrations. (P < 0.05) implying a relationship between photosynthesis, nitrogen, and a relaxation of light-inhibition to optimize metabolic efficiency. Data from this study was also used to test leaf-level and canopy nitrogen optimization models. These data emphasize the need to include canopy complexity in tundra carbon models, as neglecting physiological differences through a canopy may lead to an underestimation of stored carbon.

  12. Potential changes in arctic seasonality and plant communities may impact tundra soil chemistry and carbon dynamics

    NASA Astrophysics Data System (ADS)

    Crow, S.; Cooper, E.; Beilman, D.; Filley, T.; Reimer, P.

    2009-04-01

    On the Svalbard archipelago, as in other high Arctic regions, tundra soil organic matter (SOM) is primarily plant detritus that is largely stabilized by cold, moist conditions and low nitrogen availability. However, the resistance of SOM to decomposition is also influenced by the quality of organic matter inputs to soil. Different plant communities are likely to give different qualities to SOM, especially where lignin-rich woody species encroach into otherwise graminoid and bryophyte-dominated regions. Arctic woody plant species are particularly sensitive to changes in temperature, snow cover, and growing season length. In a changing environment, litter chemistry may emerge as an important control on tundra SOM stabilization. In summer 2007, we collected plant material and soil from the highly-organic upper horizon (appx. 0-5 cm) and the mineral-dominated lower horizon (appx. 5-10cm) from four locations in the southwest facing valleys of Svalbard, Norway. The central goal of the ongoing experiment is to determine whether a greater abundance of woody plants could provide a negative feedback to warming impacts on the carbon (C) balance of Arctic soils. Towards this, we used a combination of plant biopolymer analyses (cupric oxide oxidation and quantification of lignin-derived phenols and cutin/suberin-derived aliphatics) and radiocarbon-based estimates of C longevity and mean residence time (MRT) to characterize potential links between plant type and soil C pools. We found that graminoid species regenerate above- and belowground tissue each year, whereas woody species (Cassiope tetragona and Dryas octopetala) regenerated only leaves yearly. In contrast, C within live branches and roots persisted for 15-18 yr on average. Leaves from woody species remained nearly intact in surface litter for up to 20 yr without being incorporated into the upper soil horizon. Leaves from both graminoid and woody species were concentrated in lignin-derived phenols relative to roots, but

  13. Soil bacterial community composition altered by increased nutrient availability in Arctic tundra soils.

    PubMed

    Koyama, Akihiro; Wallenstein, Matthew D; Simpson, Rodney T; Moore, John C

    2014-01-01

    The pool of soil organic carbon (SOC) in the Arctic is disproportionally large compared to those in other biomes. This large quantity of SOC accumulated over millennia due to slow rates of decomposition relative to net primary productivity. Decomposition is constrained by low temperatures and nutrient concentrations, which limit soil microbial activity. We investigated how nutrients limit bacterial and fungal biomass and community composition in organic and mineral soils within moist acidic tussock tundra ecosystems. We sampled two experimental arrays of moist acidic tussock tundra that included fertilized and non-fertilized control plots. One array included plots that had been fertilized annually since 1989 and the other since 2006. Fertilization significantly altered overall bacterial community composition and reduced evenness, to a greater degree in organic than mineral soils, and in the 1989 compared to the 2006 site. The relative abundance of copiotrophic α-Proteobacteria and β-Proteobacteria was higher in fertilized than control soils, and oligotrophic Acidobacteria were less abundant in fertilized than control soils at the 1989 site. Fungal community composition was less sensitive to increased nutrient availability, and fungal responses to fertilization were not consistent between soil horizons and sites. We detected two ectomycorrhizal genera, Russula and Cortinarius spp., associated with shrubs. Their relative abundance was not affected by fertilization despite increased dominance of their host plants in the fertilized plots. Our results indicate that fertilization, which has been commonly used to simulate warming in Arctic tundra, has limited applicability for investigating fungal dynamics under warming.

  14. Changes in microbial communities along redox gradients in polygonized Arctic wet tundra soils

    SciTech Connect

    Lipson, David A.; Raab, Theodore K.; Parker, Melanie; Kelley, Scott T.; Brislawn, Colin J.; Jansson, Janet K.

    2015-08-01

    Summary This study investigated how microbial community structure and diversity varied with depth and topography in ice wedge polygons of wet tundra of the Arctic Coastal Plain in northern Alaska and what soil variables explain these patterns. We observed strong changes in community structure and diversity with depth, and more subtle changes between areas of high and low topography, with the largest differences apparent near the soil surface. These patterns are most strongly correlated with redox gradients (measured using the ratio of reduced Fe to total Fe in acid extracts as a proxy): conditions grew more reducing with depth and were most oxidized in shallow regions of polygon rims. Organic matter and pH also changed with depth and topography but were less effective predictors of the microbial community structure and relative abundance of specific taxa. Of all other measured variables, lactic acid concentration was the best, in combination with redox, for describing the microbial community. We conclude that redox conditions are the dominant force in shaping microbial communities in this landscape. Oxygen and other electron acceptors allowed for the greatest diversity of microbes: at depth the community was reduced to a simpler core of anaerobes,

  15. Changes in microbial communities along redox gradients in polygonized Arctic wet tundra soils

    SciTech Connect

    Lipson, David A.; Raab, Theodore K.; Parker, Melanie; Kelley, Scott T.; Brislawn, Colin J.; Jansson, Janet K.

    2015-07-21

    This study investigated how microbial community structure and diversity varied with depth and topography in ice wedge polygons of wet tundra of the Arctic Coastal Plain in northern Alaska, and what soil variables explain these patterns. We observed strong changes in community structure and diversity with depth, and more subtle changes between areas of high and low topography, with the largest differences apparent near the soil surface. These patterns are most strongly correlated with redox gradients (measured using the ratio of reduced Fe to total Fe in acid extracts as a proxy): conditions grew more reducing with depth and were most oxidized in shallow regions of polygon rims. Organic matter and pH also changed with depth and topography, but were less effective predictors of the microbial community structure and relative abundance of specific taxa. Of all other measured variables, lactic acid concentration was the best, in combination with redox, for describing the microbial community. We conclude that redox conditions are the dominant force in shaping microbial communities in this landscape. Oxygen and other electron acceptors allowed for the greatest diversity of microbes: at depth the community was reduced to a simpler core of anaerobes, dominated by fermenters (Bacteroidetes and Firmicutes).

  16. Long-term warming restructures Arctic tundra without changing net soil carbon storage.

    PubMed

    Sistla, Seeta A; Moore, John C; Simpson, Rodney T; Gough, Laura; Shaver, Gaius R; Schimel, Joshua P

    2013-05-30

    High latitudes contain nearly half of global soil carbon, prompting interest in understanding how the Arctic terrestrial carbon balance will respond to rising temperatures. Low temperatures suppress the activity of soil biota, retarding decomposition and nitrogen release, which limits plant and microbial growth. Warming initially accelerates decomposition, increasing nitrogen availability, productivity and woody-plant dominance. However, these responses may be transitory, because coupled abiotic-biotic feedback loops that alter soil-temperature dynamics and change the structure and activity of soil communities, can develop. Here we report the results of a two-decade summer warming experiment in an Alaskan tundra ecosystem. Warming increased plant biomass and woody dominance, indirectly increased winter soil temperature, homogenized the soil trophic structure across horizons and suppressed surface-soil-decomposer activity, but did not change total soil carbon or nitrogen stocks, thereby increasing net ecosystem carbon storage. Notably, the strongest effects were in the mineral horizon, where warming increased decomposer activity and carbon stock: a 'biotic awakening' at depth.

  17. Changes in microbial communities along redox gradients in polygonized Arctic wet tundra soils.

    PubMed

    Lipson, David A; Raab, Theodore K; Parker, Melanie; Kelley, Scott T; Brislawn, Colin J; Jansson, Janet

    2015-08-01

    This study investigated how microbial community structure and diversity varied with depth and topography in ice wedge polygons of wet tundra of the Arctic Coastal Plain in northern Alaska and what soil variables explain these patterns. We observed strong changes in community structure and diversity with depth, and more subtle changes between areas of high and low topography, with the largest differences apparent near the soil surface. These patterns are most strongly correlated with redox gradients (measured using the ratio of reduced Fe to total Fe in acid extracts as a proxy): conditions grew more reducing with depth and were most oxidized in shallow regions of polygon rims. Organic matter and pH also changed with depth and topography but were less effective predictors of the microbial community structure and relative abundance of specific taxa. Of all other measured variables, lactic acid concentration was the best, in combination with redox, for describing the microbial community. We conclude that redox conditions are the dominant force in shaping microbial communities in this landscape. Oxygen and other electron acceptors allowed for the greatest diversity of microbes: at depth the community was reduced to a simpler core of anaerobes, dominated by fermenters (Bacteroidetes and Firmicutes).

  18. Light-stress avoidance mechanisms in a Sphagnum-dominated wet coastal Arctic tundra ecosystem in Alaska.

    PubMed

    Zona, D; Oechel, Walter C; Richards, James H; Hastings, Steven; Kopetz, Irene; Ikawa, Hiroki; Oberbauer, Steven

    2011-03-01

    The Arctic experiences a high-radiation environment in the summer with 24-hour daylight for more than two months. Damage to plants and ecosystem metabolism can be muted by overcast conditions common in much of the Arctic. However, with climate change, extreme dry years and clearer skies could lead to the risk of increased photoxidation and photoinhibition in Arctic primary producers. Mosses, which often exceed the NPP of vascular plants in Arctic areas, are often understudied. As a result, the effect of specific environmental factors, including light, on these growth forms is poorly understood. Here, we investigated net ecosystem exchange (NEE) at the ecosystem scale, net Sphagnum CO2 exchange (NSE), and photoinhibition to better understand the impact of light on carbon exchange from a moss-dominated coastal tundra ecosystem during the summer season 2006. Sphagnum photosynthesis showed photoinhibition early in the season coupled with low ecosystem NEE. However, later in the season, Sphagnum maintained a significant CO2 uptake, probably for the development of subsurface moss layers protected from strong radiation. We suggest that the compact canopy structure of Sphagnum reduces light penetration to the subsurface layers of the moss mat and thereby protects the active photosynthetic tissues from damage. This stress avoidance mechanism allowed Sphagnum to constitute a significant percentage (up to 60%) of the ecosystem net daytime CO2 uptake at the end of the growing season despite the high levels of radiation experienced.

  19. Bird Communities of the Arctic Shrub Tundra of Yamal: Habitat Specialists and Generalists

    PubMed Central

    Sokolov, Vasiliy; Ehrich, Dorothée; Yoccoz, Nigel G.; Sokolov, Alexander; Lecomte, Nicolas

    2012-01-01

    Background The ratio of habitat generalists to specialists in birds has been suggested as a good indicator of ecosystem changes due to e.g. climate change and other anthropogenic perturbations. Most studies focusing on this functional component of biodiversity originate, however, from temperate regions. The Eurasian Arctic tundra is currently experiencing an unprecedented combination of climate change, change in grazing pressure by domestic reindeer and growing human activity. Methodology/Principal Findings Here we monitored bird communities in a tundra landscape harbouring shrub and open habitats in order to analyse bird habitat relationships and quantify habitat specialization. We used ordination methods to analyse habitat associations and estimated the proportions of specialists in each of the main habitats. Correspondence Analysis identified three main bird communities, inhabiting upland, lowland and dense willow shrubs. We documented a stable structure of communities despite large multiannual variations of bird density (from 90 to 175 pairs/km2). Willow shrub thickets were a hotspot for bird density, but not for species richness. The thickets hosted many specialized species whose main distribution area was south of the tundra. Conclusion/Significance If current arctic changes result in a shrubification of the landscape as many studies suggested, we would expect an increase in the overall bird abundance together with an increase of local specialists, since they are associated with willow thickets. The majority of these species have a southern origin and their increase in abundance would represent a strengthening of the boreal component in the southern tundra, perhaps at the expense of species typical of the subarctic zone, which appear to be generalists within this zone. PMID:23239978

  20. Pan-Arctic ice-wedge degradation in warming permafrost and its influence on tundra hydrology

    NASA Astrophysics Data System (ADS)

    Liljedahl, Anna K.; Boike, Julia; Daanen, Ronald P.; Fedorov, Alexander N.; Frost, Gerald V.; Grosse, Guido; Hinzman, Larry D.; Iijma, Yoshihiro; Jorgenson, Janet C.; Matveyeva, Nadya; Necsoiu, Marius; Raynolds, Martha K.; Romanovsky, Vladimir E.; Schulla, Jörg; Tape, Ken D.; Walker, Donald A.; Wilson, Cathy J.; Yabuki, Hironori; Zona, Donatella

    2016-04-01

    Ice wedges are common features of the subsurface in permafrost regions. They develop by repeated frost cracking and ice vein growth over hundreds to thousands of years. Ice-wedge formation causes the archetypal polygonal patterns seen in tundra across the Arctic landscape. Here we use field and remote sensing observations to document polygon succession due to ice-wedge degradation and trough development in ten Arctic localities over sub-decadal timescales. Initial thaw drains polygon centres and forms disconnected troughs that hold isolated ponds. Continued ice-wedge melting leads to increased trough connectivity and an overall draining of the landscape. We find that melting at the tops of ice wedges over recent decades and subsequent decimetre-scale ground subsidence is a widespread Arctic phenomenon. Although permafrost temperatures have been increasing gradually, we find that ice-wedge degradation is occurring on sub-decadal timescales. Our hydrological model simulations show that advanced ice-wedge degradation can significantly alter the water balance of lowland tundra by reducing inundation and increasing runoff, in particular due to changes in snow distribution as troughs form. We predict that ice-wedge degradation and the hydrological changes associated with the resulting differential ground subsidence will expand and amplify in rapidly warming permafrost regions.

  1. Terrimonas arctica sp. nov., isolated from Arctic tundra soil.

    PubMed

    Jiang, Fan; Qiu, Xia; Chang, Xulu; Qu, Zhihao; Ren, Lvzhi; Kan, Wenjing; Guo, Youhao; Fang, Chengxiang; Peng, Fang

    2014-11-01

    A novel, Gram-stain-negative, aerobic, non-motile and rod-shaped bacterium, designated R9-86(T), was isolated from tundra soil collected near Ny-Ålesund, Svalbard Archipelago, Norway (78° N). Growth occurred at 4-28 °C (optimum, 22-25 °C) and at pH 6.0-9.0 (optimum, pH 7.0). Flexirubin-type pigments were absent. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain R9-86(T) belonged to the genus Terrimonas in the family Chitinophagaceae. 16S rRNA gene sequence similarities between strain R9-86(T) and the type strains of species of the genus Terrimonas with validly published names ranged from 93.7 to 95.0%. Strain R9-86(T) contained iso-C(15:1)-G (25.7%), iso-C(15:0) (24.5%), iso-C(17:0)-3OH (18.3%) and summed feature 3 (C(16:1)ω7c and/or C(16:1)ω6c, 8.7%) as its major cellular fatty acids; phosphatidylethanolamine and an unknown polar lipid as its main polar lipids, and MK-7 as its predominant respiratory quinone. The DNA G+C content was 48.4 mol%. On the basis of phenotypic, chemotaxonomic and phylogenetic data, strain R9-86(T) is considered to represent a novel species of the genus Terrimonas, for which the name Terrimonas arctica sp. nov. is proposed. The type strain is R9-86(T) ( =CCTCC AB 2011004(T) =NRRL B-59114(T)).

  2. Mucilaginibacter soli sp. nov., isolated from Arctic tundra soil.

    PubMed

    Jiang, Fan; Dai, Jun; Wang, Yang; Xue, Xiuqing; Xu, Mengbo; Guo, Youhao; Li, Wenxin; Fang, Chengxiang; Peng, Fang

    2012-07-01

    A novel pale-pink-coloured strain, designated R9-65(T), was isolated from a tundra soil near Ny-Ålesund, Svalbard Archipelago, Norway (78° N). The cells were facultatively anaerobic, Gram-staining-negative, non-motile and rod-shaped. Growth occurred at 4-32 °C (optimum, 25-28 °C), at pH 5.0-9.0 (optimum, pH 6.0-7.0) and with 0-1.0% (w/v) NaCl (optimum, no NaCl). Flexirubin-type pigments were absent. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain R9-65(T) belonged to the genus Mucilaginibacter in the family Sphingobacteriaceae. The 16S rRNA gene sequence similarity between strain R9-65(T) and type strains of related species ranged from 93.4 to 96.6%. Strain R9-65(T) contained summed feature 3 (C(16:1)ω7c and/or C(16:1)ω6c, 34.3%) and iso-C(15:0) (20.3%) as major cellular fatty acids, MK-7 as the major respiratory quinone, and phosphatidylethanolamine as the main polar lipid. The DNA G+C content of strain R9-65(T) was 47.2 mol%. On the basis of phylogenetic, physiological and chemotaxonomic data, strain R9-65(T) is considered to represent a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacter soli sp. nov. is proposed. The type strain is R9-65(T) (=CCTCC AB 2010331(T)=NRRL B-59458(T)).

  3. The response of Arctic vegetation and soils following an unusually severe tundra fire

    PubMed Central

    Bret-Harte, M. Syndonia; Mack, Michelle C.; Shaver, Gaius R.; Huebner, Diane C.; Johnston, Miriam; Mojica, Camilo A.; Pizano, Camila; Reiskind, Julia A.

    2013-01-01

    Fire causes dramatic short-term changes in vegetation and ecosystem function, and may promote rapid vegetation change by creating recruitment opportunities. Climate warming likely will increase the frequency of wildfire in the Arctic, where it is not common now. In 2007, the unusually severe Anaktuvuk River fire burned 1039 km2 of tundra on Alaska's North Slope. Four years later, we harvested plant biomass and soils across a gradient of burn severity, to assess recovery. In burned areas, above-ground net primary productivity of vascular plants equalled that in unburned areas, though total live biomass was less. Graminoid biomass had recovered to unburned levels, but shrubs had not. Virtually all vascular plant biomass had resprouted from surviving underground parts; no non-native species were seen. However, bryophytes were mostly disturbance-adapted species, and non-vascular biomass had recovered less than vascular plant biomass. Soil nitrogen availability did not differ between burned and unburned sites. Graminoids showed allocation changes consistent with nitrogen stress. These patterns are similar to those seen following other, smaller tundra fires. Soil nitrogen limitation and the persistence of resprouters will likely lead to recovery of mixed shrub–sedge tussock tundra, unless permafrost thaws, as climate warms, more extensively than has yet occurred. PMID:23836794

  4. The response of Arctic vegetation and soils following an unusually severe tundra fire.

    PubMed

    Bret-Harte, M Syndonia; Mack, Michelle C; Shaver, Gaius R; Huebner, Diane C; Johnston, Miriam; Mojica, Camilo A; Pizano, Camila; Reiskind, Julia A

    2013-08-19

    Fire causes dramatic short-term changes in vegetation and ecosystem function, and may promote rapid vegetation change by creating recruitment opportunities. Climate warming likely will increase the frequency of wildfire in the Arctic, where it is not common now. In 2007, the unusually severe Anaktuvuk River fire burned 1039 km(2) of tundra on Alaska's North Slope. Four years later, we harvested plant biomass and soils across a gradient of burn severity, to assess recovery. In burned areas, above-ground net primary productivity of vascular plants equalled that in unburned areas, though total live biomass was less. Graminoid biomass had recovered to unburned levels, but shrubs had not. Virtually all vascular plant biomass had resprouted from surviving underground parts; no non-native species were seen. However, bryophytes were mostly disturbance-adapted species, and non-vascular biomass had recovered less than vascular plant biomass. Soil nitrogen availability did not differ between burned and unburned sites. Graminoids showed allocation changes consistent with nitrogen stress. These patterns are similar to those seen following other, smaller tundra fires. Soil nitrogen limitation and the persistence of resprouters will likely lead to recovery of mixed shrub-sedge tussock tundra, unless permafrost thaws, as climate warms, more extensively than has yet occurred.

  5. CO2 dynamics of tundra ponds in the low-Arctic, Northwest Territories, Canada

    NASA Astrophysics Data System (ADS)

    Buell, Mary-Claire

    Extensive research has gone into measuring changes to the carbon storage capacity of Arctic terrestrial environments as well as large water bodies in order to determine a carbon budget for many regions across the Arctic. Inland Arctic waters such as small lakes and ponds are often excluded from these carbon budgets, however a handful of studies have demonstrated that they can often be significant sources of carbon to the atmosphere. This study investigated the CO2 cycling of tundra ponds in the Daring Lake area, Northwest Territories, Canada (64°52'N, 111°35'W), to determine the role ponds have in the local carbon cycle. Floating chambers, nondispersive infrared (NDIR) sensors and headspace samples were used to estimate carbon fluxes from four selected local ponds. Multiple environmental, chemical and meteorological parameters were also monitored for the duration of the study, which took place during the snow free season of 2013. Average CO2 emissions for the two-month growing season ranged from approximately -0.0035 g CO2-C m-2 d -1 to 0.12 g CO2-C m-2 d-1. The losses of CO2 from the water bodies in the Daring Lake area were approximately 2-7% of the CO2 uptake over vegetated terrestrial tundra during the same two-month period. Results from this study indicated that the production of CO2 in tundra ponds was positively influenced by both increases in air temperature, and the delivery of carbon from their catchments. The relationship found between temperature and carbon emissions suggests that warming Arctic temperatures have the potential to increase carbon emissions from ponds in the future. The findings in this study did not include ebullition gas emissions nor plant mediated transport, therefore these findings are likely underestimates of the total carbon emissions from water bodies in the Daring Lake area. This study emphasizes the need for more research on inland waters in order to improve our understanding of the total impact these waters may have on the

  6. Biomarkers as Indicators of Respiration During Laboratory Incubations of Alaskan Arctic Tundra Permafrost Soils

    NASA Astrophysics Data System (ADS)

    Hutchings, J.; Schuur, E.; Bianchi, T. S.; Bracho, R. G.

    2015-12-01

    High latitude permafrost soils are estimated to store 1,330 - 1,580 Pg C, which account for ca. 40% of global soil C and nearly twice that of atmospheric C. Disproportionate heating of high latitude regions during climate warming potentially results in permafrost thaw and degradation of surficial and previously-frozen soil C. Understanding how newly-thawed soils respond to microbial degradation is essential to predicting C emissions from this region. Laboratory incubations have been a key tool in understanding potential respiration rates from high latitude soils. A recent study found that among the common soil measurements, C:N was the best predictor of C losses. Here, we analyzed Alaskan Arctic tundra soils from before and after a nearly 3-year laboratory incubation. Bulk geochemical values as well as the following biomarkers were measured: lignin, amino acids, n-alkanes, and glycerol dialkyl glycerol tetraethers (GDGT). We found that initial C:N did not predict C losses and no significant change in C:N between initial and final samples. The lignin acid to aldehyde (Ad:Al) degradation index showed the same results with a lack of C loss prediction and no significant change during the experiment. However, we did find that C:N and Ad:Al had a significant negative correlation suggesting behavior consistent with expectations. The failure to predict C losses was likely influenced by a number of factors, including the possibility that biomarkers were tracking a smaller fraction of slower cycling components of soil C. To better interpret these results, we also used a hydroxyproline-based amino acid degradation index and n-alkanes to estimate the contribution Sphagnum mosses to soil samples - known to have slower turnover times than vascular plants. Finally, we applied a GDGT soil temperature proxy to estimate the growing season soil temperatures before each incubation, as well as investigating the effects of incubation temperature on the index's temperature estimate.

  7. Arctic biodiversity: Increasing richness accompanies shrinking refugia for a cold-associated tundra fauna

    USGS Publications Warehouse

    Hope, Andrew; Waltari, Eric; Malaney, Jason L.; Payer, David C.; Cook, J.A.; Talbot, Sandra

    2015-01-01

    As ancestral biodiversity responded dynamically to late-Quaternary climate changes, so are extant organisms responding to the warming trajectory of the Anthropocene. Ecological predictive modeling, statistical hypothesis tests, and genetic signatures of demographic change can provide a powerful integrated toolset for investigating these biodiversity responses to climate change, and relative resiliency across different communities. Within the biotic province of Beringia, we analyzed specimen localities and DNA sequences from 28 mammal species associated with boreal forest and Arctic tundra biomes to assess both historical distributional and evolutionary responses and then forecasted future changes based on statistical assessments of past and present trajectories, and quantified distributional and demographic changes in relation to major management regions within the study area. We addressed three sets of hypotheses associated with aspects of methodological, biological, and socio-political importance by asking (1) what is the consistency among implications of predicted changes based on the results of both ecological and evolutionary analyses; (2) what are the ecological and evolutionary implications of climate change considering either total regional diversity or distinct communities associated with major biomes; and (3) are there differences in management implications across regions? Our results indicate increasing Arctic richness through time that highlights a potential state shift across the Arctic landscape. However, within distinct ecological communities, we found a predicted decline in the range and effective population size of tundra species into several discrete refugial areas. Consistency in results based on a combination of both ecological and evolutionary approaches demonstrates increased statistical confidence by applying cross-discipline comparative analyses to conservation of biodiversity, particularly considering variable management regimes that seek

  8. Vegetation-associated impacts on arctic tundra bacterial and microeukaryotic communities.

    PubMed

    Shi, Yu; Xiang, Xingjia; Shen, Congcong; Chu, Haiyan; Neufeld, Josh D; Walker, Virginia K; Grogan, Paul

    2015-01-01

    The Arctic is experiencing rapid vegetation changes, such as shrub and tree line expansion, due to climate warming, as well as increased wetland variability due to hydrological changes associated with permafrost thawing. These changes are of global concern because changes in vegetation may increase tundra soil biogeochemical processes that would significantly enhance atmospheric CO2 concentrations. Predicting the latter will at least partly depend on knowing the structure, functional activities, and distributions of soil microbes among the vegetation types across Arctic landscapes. Here we investigated the bacterial and microeukaryotic community structures in soils from the four principal low Arctic tundra vegetation types: wet sedge, birch hummock, tall birch, and dry heath. Sequencing of rRNA gene fragments indicated that the wet sedge and tall birch communities differed significantly from each other and from those associated with the other two dominant vegetation types. Distinct microbial communities were associated with soil pH, ammonium concentration, carbon/nitrogen (C/N) ratio, and moisture content. In soils with similar moisture contents and pHs (excluding wet sedge), bacterial, fungal, and total eukaryotic communities were correlated with the ammonium concentration, dissolved organic nitrogen (DON) content, and C/N ratio. Operational taxonomic unit (OTU) richness, Faith's phylogenetic diversity, and the Shannon species-level index (H') were generally lower in the tall birch soil than in soil from the other vegetation types, with pH being strongly correlated with bacterial richness and Faith's phylogenetic diversity. Together, these results suggest that Arctic soil feedback responses to climate change will be vegetation specific not just because of distinctive substrates and environmental characteristics but also, potentially, because of inherent differences in microbial community structure.

  9. Ecosystem Respiration Rates of Arctic Tundra Mesocosms in Response to Cold-Season Temperatures

    NASA Astrophysics Data System (ADS)

    Oberbauer, S. F.; Moser, J. G.; Olivas, P. C.; Starr, G.; Mortazavi, B.

    2013-12-01

    The cold season in the Arctic extends over 8 to 9 mo, during which air temperatures often reach as low as -40 °C. However, as a result of the insulating layer created by snow cover, temperatures seldom fall below -15 °C, and are likely warm enough to support some metabolism. Little research has been conducted on arctic plants and tundra during the cold season, despite its length and the fact that warming is predicted to be greatest during this period. The primary focus of cold-season research has been on rates of winter ecosystem respiration (ER) for estimates of annual carbon balance. The majority of these measurements during the winter or at winter temperatures indicate that some respiration is occurring. Although rates are low, they may contribute substantially to the annual carbon balance because of the length of the cold season. However, estimates of respiration at low temperatures differ substantially, have been taken at different temperatures using different methodologies, and importantly almost none provide quantitative relationships across a range of temperatures. We measured respiration rates of intact arctic tundra monoliths from 15 to -15 °C at 5 °C steps to facilitate improved model estimates of tundra respiration. Six tundra monoliths (~900 cm2) taken from Toolik Field Station, Alaska were conditioned for the cold season in growth chambers at shortened photoperiods and low, but above-freezing temperatures. Desired temperatures were obtained with a combination of growth chambers and a modified freezer. The average of five samplings of [CO2] at each temperature step was used to estimate the ER rates. Measurements were conducted with a closed system using incubation periods of 30 to 180 min, depending on the temperature. Carbon dioxide concentrations were measured by syringe samples injected into a N2 gas stream flowing through an infrared gas analyzer. Rates of ER calculated on an area basis were close to zero at -15 °C, but increased steadily with

  10. Spectral indices for remote sensing of phytomass and deciduous shrub changes in Alaskan arctic tundra

    NASA Astrophysics Data System (ADS)

    Kushida, K.; Hobara, S.; Tsuyuzaki, S.; Watanabe, M.; Harada, K.; Kim, Y.; Shaver, G. R.; Fukuda, M.

    2010-12-01

    The relationships between spectral indices, phytomass, and plant functional types were determined by using field observations of a moist acidic tundra (MAT) and a moist non-acidic tundra (MNT) in the Toolik Lake Long Term Ecological Research (LTER) site and a sedge-shrub tundra (SS) in the Arctic National Wildlife Refuge, Alaska, USA. For the MAT and MNT observations, among aboveground phytomass, aboveground vascular phytomass, and vascular plant green phytomass, vascular plant green phytomass was the most sensitive to an exponential function of the normalized difference vegetation index (NDVI). The coefficient of determination (R2) was 0.73. Vascular plant carbon and nitrogen were estimated with exponential functions of NDVI (R2 of 0.57 and 0.53, respectively). For the MAT, MNT, and SS observations, vascular plant green phytomass was more strongly correlated with an exponential function of NDVI (ENDVI, R2 of 0.62) than any other spectral indices. On the other hand, for deciduous shrub green phytomass, the strongest correlation was with a product of an exponential function of NDVI and a spectral index (MIR - RED)/(MIR + RED) (DSSI, R2 of 0.60). Here, MIR and RED denote the bands with wavelengths 2.09-2.35 and 0.63-0.69 µm, respectively. As a result of a regression analysis, 41% of the ENDVI variance and 60% of the DSSI variance were explained by deciduous shrub green phytomass. Up to 38% of the ENDVI variance and up to 10% of the DSSI variance were explained by green phytomass of evergreen shrubs and graminoids, and phytomass of mosses/lichens. These spectral indices were applicable to evaluating tundra plant community changes.

  11. Controls over nutrient flow through plants and microbes in arctic tundra

    SciTech Connect

    Schimel, J.P.

    1990-01-01

    Plant growth in arctic tundra is generally strongly limited by nutrient availability, particularly by nitrogen. The purpose of this sub-project of the R4D program was to examine plant N-uptake and the competition for N between plants and microbes in tundra. This competition can be an important control on N-flow and plant uptake but its significance in tundra has not been studied intensively. How the factors controlling the outcome of competition are altered by disturbance has also received very limited study, yet this is important facet of the R4D program. The primary goal for this project in 1990 was to initiate studies on N-partitioning and turnover in tussock tundra and how this is affected by dust deposition. Secondary goals were to examine the effect of differential dust deposition on microbial activity and nutrient cycling processes (mineralization and nitrification), and begin studies on the control of microbial N-uptake. The N-partitioning studies used {sup 15}N injected into Eriophorum tussocks to examine both the short-term (1 day) partitioning of N and the long-term (1 month and 1 year) redistribution of N through the plant-soil system. These experiments were done in both the early season (June) and peak season (July). To examine the effect of dust on N-partitioning tussocks in the heavy dust zone and in a control site were labeled with {sup 15}N and harvested at the end of the growing season. 4 refs., 1 tab.

  12. Reconstruction and analysis of historical changes in carbon storage in arctic tundra

    SciTech Connect

    McKane, R.B.; Rastetter, E.B.; Shaver, G.R.

    1997-06-01

    Surface air temperature in arctic regions has increased since pre-industrial times, raising concerns that warmer and possibly drier conditions have increased soil decomposition rates, thereby stimulating the release to the atmosphere of the large stores of carbon (C) in arctic soils. We used a model (MBL-GEM, Marine Biological Laboratory General Ecosystem Model) of ecosystem C and nitrogen (N) dynamics to predict and analyze historical (1829-1990) changes in C storage in a N-limited, tussock-tundra ecosystem near Toolik Lake on the North Slope of Alaska. The model simulates stand-level photosynthesis and N uptake by plants, allocation of C and N to foliage, stems, and fine roots, respiration in these tissues, turnover of biomass through litterfall, and decomposition of litter and soil organic matter. We first calibrated the model by deriving a single parameter set that closely simulated the response of tussock tundra to decade-long experimental manipulations of nutrients, temperature, light, and atmospheric CO{sub 2}. 60 refs., 5 figs., 1 tab.

  13. Methane emissions from Alaska Arctic tundra - an assessment of local spatial variability

    SciTech Connect

    Morrissey, L.A.; Livingston, G.P. )

    1992-10-01

    The findings of an extensive midsummer survey of CH4 emissions measurements representing the Alaska Arctic tundra are presented. Variability in rates of emissions was similar in magnitude on local and regional scales, ranging from 0 to 286.5 mg/sq m/d overall and often varying across two orders of magnitude within 0.5 m distances. Primary control on rates of emission was determined by the substrate and position of the water table relative to the surface. Emission rates in the Arctic Foothills ranged from 0.2 mg/sq m/d for tussock tundra to 55.53 mg/sq m/d over wet meadows. Plant-mediated release of CH4 to the atmosphere was directly proportional to green leaf area and represented 92-98 percent of the total emission rates over vegetated sites. The results suggest the current published emission rates may have overestimated the contribution of boreal ecosystems to the global CH4 budget by several fold. 46 refs.

  14. Effects of long-term nutrient additions on Arctic tundra, stream, and lake ecosystems: beyond NPP.

    PubMed

    Gough, Laura; Bettez, Neil D; Slavik, Karie A; Bowden, William B; Giblin, Anne E; Kling, George W; Laundre, James A; Shaver, Gaius R

    2016-11-01

    Primary producers form the base of food webs but also affect other ecosystem characteristics, such as habitat structure, light availability, and microclimate. Here, we examine changes caused by 5-30+ years of nutrient addition and resulting increases in net primary productivity (NPP) in tundra, streams, and lakes in northern Alaska. The Arctic provides an important opportunity to examine how ecosystems characterized by low diversity and low productivity respond to release from nutrient limitation. We review how responses of algae and plants affect light availability, perennial biotic structures available for consumers, oxygen levels, and temperature. Sometimes, responses were similar across all three ecosystems; e.g., increased NPP significantly reduced light to the substrate following fertilization. Perennial biotic structures increased in tundra and streams but not in lakes, and provided important new habitat niches for consumers as well as other producers. Oxygen and temperature responses also differed. Life history traits (e.g., longevity) of the primary producers along with the fate of detritus drove the responses and recovery. As global change persists and nutrients become more available in the Arctic and elsewhere, incorporating these factors as response variables will enable better prediction of ecosystem changes and feedbacks in this biome and others.

  15. Methane emissions from Alaska Arctic tundra - An assessment of local spatial variability

    NASA Technical Reports Server (NTRS)

    Morrissey, L. A.; Livingston, G. P.

    1992-01-01

    The findings of an extensive midsummer survey of CH4 emissions measurements representing the Alaska Arctic tundra are presented. Variability in rates of emissions was similar in magnitude on local and regional scales, ranging from 0 to 286.5 mg/sq m/d overall and often varying across two orders of magnitude within 0.5 m distances. Primary control on rates of emission was determined by the substrate and position of the water table relative to the surface. Emission rates in the Arctic Foothills ranged from 0.2 mg/sq m/d for tussock tundra to 55.53 mg/sq m/d over wet meadows. Plant-mediated release of CH4 to the atmosphere was directly proportional to green leaf area and represented 92-98 percent of the total emission rates over vegetated sites. The results suggest the current published emission rates may have overestimated the contribution of boreal ecosystems to the global CH4 budget by several fold.

  16. Methane emissions from Alaska arctic tundra in response to climatic change

    SciTech Connect

    Livingston, G.P.; Morrissey, L.A.

    1992-03-01

    In situ observations of methane emissions from the Alaska North Slope in 1987 and 1989 provide insight into the environmental interactions regulating methane emissions and into the local- and regional-scale response of the arctic tundra to interannual environmental variability. Inferences regarding climate change are based on in situ measurements of methane emissions, regional landscape characterizations derived from Landsat Multispectral Scanner satellite data, and projected regional scale emissions based on observed interannual temperature differences and simulated changes in the spatial distribution of methane emissions. Results suggest that biogenic methane emissions from arctic tundra will be significantly perturbed by climatic change, leading to warmer summer soil temperatures and to vertical displacement of the regional water table. The effect of increased soil temperatures on methane emissions resulting from anaerobic decomposition in northern wetlands will be to both increase total emissions and to increase interannual and seasonal variability. The magnitude of these effects will be determined by those factors affecting the areal distribution of methane emission rates through regulation of the regional water table. At local scales, the observed 4.7 C increase in mid-summer soil temperatures between 1987 and 1989 resulted in a 3.2-fold increase in the rate of methane emissions from anaerobic soils.

  17. Radiation budget and soil heat fluxes in different Arctic tundra vegetation types

    NASA Astrophysics Data System (ADS)

    Juszak, Inge; Iturrate Garcia, Maitane; Gastellu-Etchegorry, Jean-Philippe; Schaepman, Michael E.; Schaepman-Strub, Gabriela

    2016-04-01

    While solar radiation is one of the primary energy sources for warming and thawing permafrost soil, the amount of shortwave radiation reaching the soil is reduced by vegetation shading. Climate change has led to greening, shrub expansion and encroachment in many Arctic tundra regions and further changes are anticipated. These vegetation changes feed back to the atmosphere and permafrost as they modify the surface energy budget. However, canopy transmittance of solar radiation has rarely been measured or modelled for a variety of tundra vegetation types. We assessed the radiation budget of the most common vegetation types at the Kytalyk field site in North-East Siberia (70.8°N, 147.5°E) with field measurements and 3D radiative transfer modelling and linked it to soil heat fluxes. Our results show that Arctic tundra vegetation types differ in canopy albedo and transmittance as well as in soil heat flux and active layer thickness. Tussock sedges transmitted on average 56% of the incoming light and dwarf shrubs 27%. For wet sedges we found that the litter layer was very important as it reduced the average transmittance to only 6%. Model output indicated that both, albedo and transmittance, also depend on the spatial aggregation of vegetation types. We found that permafrost thaw was more strongly related to soil properties than to canopy shading. The presented radiative transfer model allows quantifying effects of the vegetation layer on the surface radiation budget in permafrost areas. The parametrised model can account for diverse vegetation types and variation of properties within types. Our results highlight small scale radiation budget and permafrost thaw variability which are indicated and partly caused by vegetation. As changes in species composition and biomass increase can influence thaw rates, small scale patterns should be considered in assessments of climate-vegetation-permafrost feedbacks.

  18. THE HYDRAULIC CHARACTERISTICS AND GEOCHEMISTRY OF HYPORHEIC AND PARAFLUVIAL ZONES IN ARCTIC TUNDRA STREAMS, NORTH SLOPE, ALASKA

    EPA Science Inventory

    Sodium bromide and Rhodamine WT were used as conservative tracers to examine the hydrologic characteristics of seven tundra streams in Arctic Alaska, during the summers of 1994-1996. Continuous tracer additions were conducted in seven rivers ranging from 1st to 5th order with sam...

  19. Structural complexity and land-surface energy exchange along a gradient from arctic tundra to boreal forest

    USGS Publications Warehouse

    Thompson, C.; Beringer, J.; Chapin, F. S.; McGuire, A.D.

    2004-01-01

    Question: Current climate changes in the Alaskan Arctic, which are characterized by increases in temperature and length of growing season, could alter vegetation structure, especially through increases in shrub cover or the movement of treeline. These changes in vegetation structure have consequences for the climate system. What is the relationship between structural complexity and partitioning of surface energy along a gradient from tundra through shrub tundra to closed canopy forest? Location: Arctic tundra-boreal forest transition in the Alaskan Arctic. Methods: Along this gradient of increasing canopy complexity, we measured key vegetation characteristics, including community composition, biomass, cover, height, leaf area index and stem area index. We relate these vegetation characteristics to albedo and the partitioning of net radiation into ground, latent, and sensible heating fluxes. Results: Canopy complexity increased along the sequence from tundra to forest due to the addition of new plant functional types. This led to non-linear changes in biomass, cover, and height in the understory. The increased canopy complexity resulted in reduced ground heat fluxes, relatively conserved latent heat fluxes and increased sensible heat fluxes. The localized warming associated with increased sensible heating over more complex canopies may amplify regional warming, causing further vegetation change in the Alaskan Arctic.

  20. An assessment of the carbon balance of arctic tundra: comparisons among observations, process models, and atmospheric inversions

    USGS Publications Warehouse

    McGuire, A.D.; Christensen, T.R.; Hayes, D.; Heroult, A.; Euskirchen, E.; Yi, Y.; Kimball, J.S.; Koven, C.; Lafleur, P.; Miller, P.A.; Oechel, W.; Peylin, P.; Williams, M.

    2012-01-01

    Although arctic tundra has been estimated to cover only 8% of the global land surface, the large and potentially labile carbon pools currently stored in tundra soils have the potential for large emissions of carbon (C) under a warming climate. These emissions as radiatively active greenhouse gases in the form of both CO2 and CH4 could amplify global warming. Given the potential sensitivity of these ecosystems to climate change and the expectation that the Arctic will experience appreciable warming over the next century, it is important to assess whether responses of C exchange in tundra regions are likely to enhance or mitigate warming. In this study we compared analyses of C exchange of Arctic tundra between 1990–1999 and 2000–2006 among observations, regional and global applications of process-based terrestrial biosphere models, and atmospheric inversion models. Syntheses of the compilation of flux observations and of inversion model results indicate that the annual exchange of CO2 between arctic tundra and the atmosphere has large uncertainties that cannot be distinguished from neutral balance. The mean estimate from an ensemble of process-based model simulations suggests that arctic tundra acted as a sink for atmospheric CO2 in recent decades, but based on the uncertainty estimates it cannot be determined with confidence whether these ecosystems represent a weak or a strong sink. Tundra was 0.6 °C warmer in the 2000s compared to the 1990s. The central estimates of the observations, process-based models, and inversion models each identify stronger sinks in the 2000s compared with the 1990s. Similarly, the observations and the applications of regional process-based models suggest that CH4 emissions from arctic tundra have increased from the 1990s to 2000s. Based on our analyses of the estimates from observations, process-based models, and inversion models, we estimate that arctic tundra was a sink for atmospheric CO2 of 110 Tg C yr-1 (uncertainty between a

  1. Circumpolar arctic tundra biomass and productivity dynamics in response to projected climate change and herbivory.

    PubMed

    Yu, Qin; Epstein, Howard; Engstrom, Ryan; Walker, Donald

    2017-03-08

    Satellite remote sensing data have indicated a general 'greening' trend in the arctic tundra biome. However, the observed changes based on remote sensing are the result of multiple environmental drivers, and the effects of individual controls such as warming, herbivory, and other disturbances on changes in vegetation biomass, community structure, and ecosystem function remain unclear. We apply ArcVeg, an arctic tundra vegetation dynamics model, to estimate potential changes in vegetation biomass and net primary production (NPP) at the plant community and functional type levels. ArcVeg is driven by soil nitrogen output from the Terrestrial Ecosystem Model, existing densities of Rangifer populations, and projected summer temperature changes by the NCAR CCSM4.0 general circulation model across the Arctic. We quantified the changes in aboveground biomass and NPP resulting from (i) observed herbivory only; (ii) projected climate change only; and (iii) coupled effects of projected climate change and herbivory. We evaluated model outputs of the absolute and relative differences in biomass and NPP by country, bioclimate subzone, and floristic province. Estimated potential biomass increases resulting from temperature increase only are approximately 5% greater than the biomass modeled due to coupled warming and herbivory. Such potential increases are greater in areas currently occupied by large or dense Rangifer herds such as the Nenets-occupied regions in Russia (27% greater vegetation increase without herbivores). In addition, herbivory modulates shifts in plant community structure caused by warming. Plant functional types such as shrubs and mosses were affected to a greater degree than other functional types by either warming or herbivory or coupled effects of the two.

  2. Shrub line advance in Arctic and alpine tundra of the Yukon Territory

    NASA Astrophysics Data System (ADS)

    Myers-Smith, I. H.; Hik, D.

    2010-12-01

    Growing evidence indicates an expansion of canopy-forming woody shrubs up mountain slopes and northward into Arctic tundra. The correlation between warming and greening has been used to link climate change with shrub expansion; however, the exact mechanisms driving observed increases in canopy-forming shrubs are probably more complex. Shrub expansion that results in a change in canopy cover may modify the ecology of tundra ecosystems by changing understory plant composition, soil thermal dynamics, surface albedo, nutrient turnover times and carbon storage. We surveyed the abundance of all tundra willow species (Salix spp.) growing at three sites in the Yukon Territory: the mountains of the Kluane Region, the Richardson Mountains, and on Qikiqtaruk - Herschel Island in the Beaufort Sea. At the two mountainous sites, we collected sections from the largest stem of willow shrubs at shrub line (the maximum elevation at which canopy-forming shrubs grow) and below shrub line (at approximately 50% shrub cover) in a total of 16 valleys. At the coastal site we collected samples from each of the 4 vegetation types: the alluvial fan, ridges, tussock tundra and disturbed terrain. Shrub stems were thin-sectioned using a microtome, photographed with a microscope and ring widths were measured from the digital images. We compared age distributions of willow individuals at and below shrub line and found younger populations at higher elevations, particularly on warm, south-facing aspects. Younger willows at shrub line and a lack of significant mortality in the field surveys indicate that shrubs have advanced up slope at the mountainous sites. Photographic and long-term plot data indicate increases in cover and height of willow shrub patches at the coastal site. We compared growth rings to regional weather data, and found positive correlations between annual growth and summer temperatures. Our results indicate that willows grew most in years with a warm June and July. This evidence of

  3. How is climate warming altering the carbon cycle of a tundra ecosystem in the Siberian Arctic?

    NASA Astrophysics Data System (ADS)

    Belelli Marchesini, Luca; (Ko) van Huissteden, Jacobus; van der Molen, Michiel; Parmentier, Frans-Jan W.; Maximov, Trofim; Budishchev, Artem; Gallagher, Angela; (Han) Dolman, Albertus J.

    2015-04-01

    Climate has been warming over the the Arctic region with the strongest anomalies taking place in autumn and winter for the period 2000-2010, particularly in northern Eurasia. The quantification of the impact on climate warming on the degradation of permafrost and the associated potential release to the atmosphere of carbon stocked in the soil under the form of greenhouse gases, thus further increasing the radiative forcing of the atmosphere, is currently a matter of scientific debate. The positive trend in primary productivity in the last decades inferred by vegetation indexes (NDVI) and confirmed by observations on the enhanced growth of shrub vegetation represents indeed a contrasting process that, if prevalent could offset GHG emissions or even strengthen the carbon sink over the Arctic tundra. At the site of Kytalyk, in north-eastern Siberia, net fluxes of CO2 at ecosystem scale (NEE) have been monitored by eddy covariance technique since 2003. While presenting the results of the seasonal (snow free period) and inter-annual variability of NEE, conceived as the interplay between meteorological drivers and ecosystem responses, we test the role of climate as the main source of NEE variability in the last decade using a data oriented statistical approach. The impact of the timing and duration of the snow free period on the seasonal carbon budget is also considered. Finally, by including the results of continuous micrometeorological observations of methane fluxes taken during summer 2012, corroborated with seasonal CH4 budgets from two previous shorter campaigns (2008, 2009), as well as an experimentally determined estimate of dissolved organic carbon (DOC) flux, we provide an assessment of the carbon budget and its stability over time. The examined tundra ecosystem was found to sequester CO2 during the snow free season with relatively small inter-annual variability (-97.9±12.1gC m-2) during the last decade and without any evident trend despite the carbon uptake

  4. Labile carbon concentrations are strongly linked to plant production in Arctic tussock tundra soils

    NASA Astrophysics Data System (ADS)

    Darrouzet-Nardi, A.; Weintraub, M. N.; Euskirchen, E. S.; Steltzer, H.; Sullivan, P.

    2013-12-01

    The exchange of carbon and nutrients between plants and microbes is a key determinant of carbon balance in Arctic soils. Microbes rely on labile plant carbon for the energy they need to produce enzymes that can release nutrients and less energetically favorable carbon from soil organic matter. One of the main mechanisms of carbon transfer is rhizodeposition, the exudation of labile plant carbon such as sugars from roots into the rhizosphere. Despite the importance of this flow of energy and materials from plants to microbes, there have been few attempts to quantify labile carbon pools or fluxes in Arctic soils. To improve our knowledge of labile carbon dynamics in Arctic soils, we address two basic questions: (1) What are the seasonal patterns of labile carbon concentrations? and (2) How do seasonal patterns in labile carbon correlate with plant production, microbial biomass, and soil nutrients? We measured concentrations of total reducing sugars (TRS) in the soil solution of moist acidic tussock tundra on 28 dates during the 2012 growing season in 20 plots of an early snowmelt × warming experiment. We evaluated these total reducing sugar concentrations in the context of eddy flux carbon exchange data, plant NDVI, total dissolved carbon in soils, microbial biomass, and soil nutrients. Though we did not see treatment effects of the snowmelt × warming experiment, we did observe a clear seasonal pattern in TRS concentrations in which they started low at the time of thaw, then built to a maximum value around the time of peak plant physiology in July, followed by a decline as plants senesced. We observed a clear correlation between TRS and gross primary production (GPP). NDVI values also increased with TRS concentrations during the first half of the season and then leveled off as TRS began its decline. These relationships were in contrast to labile N concentrations, which remained at low concentrations all season. Our data suggest that rhizodeposition of labile carbon

  5. Geochemical characterization of Arctic tundra and implications for organic matter degradation

    NASA Astrophysics Data System (ADS)

    Gu, B.; Herndon, E.; Graham, D. E.; Phelps, T. J.; Wullschleger, S. D.; Liang, L.

    2013-12-01

    Tundra soils are uniquely cold terrestrial environments that face irrevocable change under warming climate conditions. Specifically, many tundra soils store large quantities of organic carbon that may rapidly degrade with increasing temperature, releasing C into drainage systems or to the atmosphere as greenhouse gases (CH4, CO2). In order to predict rates of C release from tundra soils, it is necessary to quantify how biogeochemical factors such as pore water chemistry, terminal electron acceptor availability, and mineral adsorption regulate rates and pathways of soil organic carbon (SOC) degradation. In this study, we examine spatial and seasonal patterns of aqueous geochemistry and SOC characteristics from across an area of tundra landscape in the Arctic. We aim to identify factors that increase or decrease rates of SOC degradation, including: 1) the composition of organic substrates, 2) abundance of terminal electron acceptors, 3) vertical transport and spatial variability of both organic and inorganic compounds, and 4) adsorption to mineral surfaces. Soil and water samples were obtained from the Barrow Environmental Observatory (BEO) in northern Alaska as part of the Next Generation Ecosystem Experiment (NGEE) Arctic project. Tundra at the BEO is characterized by permafrost below ~60 cm and polygonal features that induce topographic gradients of water saturation. Soils are organic-rich and store large amounts of slowly decomposing plant material. Chemical and physical extractions were used to obtain operationally-defined pools of SOC to evaluate their mineral associations. Water samples collected in early and late summers were analyzed for pH, electrical conductivity, and dissolved concentrations of anions, cations, organic carbon, inorganic carbon, and ferrous iron, as well as dissolved and soil gases (CH4 and CO2). We observe a steep pH gradient, with acidic pH in surface waters and near neutral pH in pore waters >20 cm below the surface. Dissolved organic

  6. Quantifying the physiology of structurally complex arctic vegetation and implications for carbon cycling in a shrubbier tundra

    NASA Astrophysics Data System (ADS)

    Formica, A. F.; Griffin, K. L.; Boelman, N.

    2013-12-01

    The arctic is undergoing a warming trend that is more extreme compared to lower latitudes. As one major consequence, repeat aerial photographs reveal that in recent decades woody deciduous shrubs have increased in dominance in valley bottoms and riparian areas of northern Alaska. Advancing shrub canopies are growing taller and more structurally complex, presumably increasing self-shading and reducing light availability with canopy depth. According to canopy optimization theory, plants will preferentially allocate nutrient resources to sun-exposed canopy leaves to enhance photosynthetic efficiency in order to take advantage of greater light availability. While canopy optimization has been studied in other, mainly forested ecosystems, this theory has yet to be tested in the arctic tundra. We made a series of measurements on canopy leaves located in high to low light environments, from three common woody deciduous shrubs on the North Slope of Alaska: dwarf birch (Betula nana), tealeaf willow (Salix pulchra), and feltleaf willow (Salix alaxensis). For each selected leaf, we measured the canopy leaf area index at its canopy position in order to quantify the amount of light intercepted by the leaf surface, and in situ chlorophyll fluorescence to evaluate its photosynthetic efficiency through calculation of leaf maximum electron transport rate. The same leaves were then removed and measured for leaf area, dry mass, and carbon to nitrogen ratio. Our data show trends that are consistent with the development of canopy optimization. Leaf nitrogen decreases significantly from the upper to lower terciles of leaf area index values (56% in Salix alaxensis, 41% in Salix pulchra, 46% in Betula nana). Similarly, there were significant reductions in the leaf maximum electron transport rate for two species (44% in Salix alaxensis, 40% Betula nana). These findings suggest that structurally complex arctic shrubs may be redistributing leaf nitrogen to more exposed parts of the canopy

  7. Long-term experimental warming alters community composition of ascomycetes in Alaskan moist and dry arctic tundra.

    PubMed

    Semenova, Tatiana A; Morgado, Luis N; Welker, Jeffrey M; Walker, Marilyn D; Smets, Erik; Geml, József

    2015-01-01

    Arctic tundra regions have been responding to global warming with visible changes in plant community composition, including expansion of shrubs and declines in lichens and bryophytes. Even though it is well known that the majority of arctic plants are associated with their symbiotic fungi, how fungal community composition will be different with climate warming remains largely unknown. In this study, we addressed the effects of long-term (18 years) experimental warming on the community composition and taxonomic richness of soil ascomycetes in dry and moist tundra types. Using deep Ion Torrent sequencing, we quantified how OTU assemblage and richness of different orders of Ascomycota changed in response to summer warming. Experimental warming significantly altered ascomycete communities with stronger responses observed in the moist tundra compared with dry tundra. The proportion of several lichenized and moss-associated fungi decreased with warming, while the proportion of several plant and insect pathogens and saprotrophic species was higher in the warming treatment. The observed alterations in both taxonomic and ecological groups of ascomycetes are discussed in relation to previously reported warming-induced shifts in arctic plant communities, including decline in lichens and bryophytes and increase in coverage and biomass of shrubs.

  8. Relationships between hyperspectral data and components of vegetation biomass in Low Arctic tundra communities at Ivotuk, Alaska

    NASA Astrophysics Data System (ADS)

    Bratsch, Sara; Epstein, Howard; Buchhorn, Marcel; Walker, Donald; Landes, Heather

    2017-02-01

    Warming in the Arctic has resulted in a lengthening of the growing season and changes to the distribution and composition of tundra vegetation including increased biomass quantities in the Low Arctic. Biomass has commonly been estimated using broad-band greenness indices such as NDVI; however, vegetation changes in the Arctic are occurring at spatial scales within a few meters. The aim of this paper is to assess the ability of hyperspectral remote sensing data to estimate biomass quantities among different plant tissue type categories at the North Slope site of Ivotuk, Alaska. Hand-held hyperspectral data and harvested biomass measurements were collected during the 1999 growing season. A subset of the data was used as a training set, and was regressed against the hyperspectral bands using LASSO. LASSO is a modification of SPLS and is a variable selection technique that is useful in studies with high collinearity among predictor variables such as hyperspectral remote sensing. The resulting equations were then used to predict biomass quantities for the remaining Ivotuk data. The majority of significant biomass-spectra relationships (65%) were for shrubs categories during all times of the growing season and bands in the blue, green, and red edge wavelength regions of the spectrum. The ability to identify unique biomass-spectra relationships per community is decreased at the height of the growing season when shrubs obscure lower-lying vegetation such as mosses. The results of this study support previous research arguing that shrubs are dominant controls over spectral reflectance in Low Arctic communities and that this dominance results in an increased ability to estimate shrub component biomass over other plant functional types.

  9. Five Years of Land Surface Phenology in a Large Scale Hydrological Manipulation Experiment in an Arctic Tundra Landscape

    NASA Astrophysics Data System (ADS)

    Goswami, S.; Gamon, J. A.; Tweedie, C. E.

    2010-12-01

    Climate change appears to be most pronounced at high northern latitudes. Many of the observed and modeled climate change responses in arctic tundra ecosystems have profound effects on surface energy budgets, land-atmosphere carbon exchange, plant phenology, and geomorphic processes. Detecting biotic responses to a changing environment is essential for understanding the consequences of global change. Plants can work as very effective indicators of changing conditions and, depending on the nature of the change, respond by increasing or decreasing amounts of green-leaf biomass, chlorophyll, and water content. Shifts in the composition and abundance of plant species have important effects on ecosystem processes such as net primary production and nutrient cycling. Vegetation is expected to be responsive to arctic warming, although there is some uncertainty as to how the interplay between geomorphic, hydrologic, climatic and other biotic will manifest over a range of spatial scales. The NSF-supported Biocomplexity project in Barrow, Alaska, involves experimental manipulation of water table (drained, flooded, and control treatments) in a vegetated arctic thaw lake basin to investigate the effects of altered hydrology on land-atmosphere carbon balance. In each experimental treatment, hyperspectral reflectance data were collected in the visible and near IR range of the spectrum using a robotic tram system that operated along a 300m tramline during the snow free growing period between June and August 2005-09. Water table depths and soil volumetric water content was also collected along these transects. The years 2005-2007 were control or unmanipulated experimental years and 2008 and 2009 were experimental years where water table was raised (+10cm) and lowered (-10cm) in flooding and draining experiments respectively. This presentation will document the change in phenology (NDVI) between years, treatments, and land cover types. Findings from this research have implications

  10. Simulating the effects of climate change and climate variability on carbon dynamics in Arctic tundra

    NASA Astrophysics Data System (ADS)

    Stieglitz, Marc; Giblin, Anne; Hobbie, John; Williams, Matthew; Kling, George

    2000-12-01

    Through a simple modeling exercise, three mechanisms have been identified, each operating at a different timescale, that may govern carbon dynamics in Arctic tundra regions and partially explain observed CO2 flux variability. At short timescales the biosphere reacts to meteorological forcing. Drier conditions are associated with aerobic soil decomposition, a large CO2efflux, and a net ecosystem loss of carbon. Cooler and moister conditions favor slower anaerobic decomposition in soils, good growing conditions, and terrestrial carbon sequestration. At intermediate timescales, periods of terrestrial carbon loss are directly linked to periods of carbon sequestration by the ability of the ecosystem to retain labile nitrogen. Labile nitrogen released to the soil during periods when the tundra is a source of carbon (soil respiration > net primary productivity) is retained within the ecosystem and accessed during periods when carbon sequestration is favored (net primary productivity > soil respiration). Finally, the ability of vegetation to respond to long-term changes in soil nutrient status via changes in leaf nitrogen and leaf area index modulates this dynamic at intermediate to long timescales.

  11. Measurements of NO(x) and NO(y) concentrations and fluxes over Arctic tundra

    NASA Technical Reports Server (NTRS)

    Bakwin, Peter S.; Wofsy, Steven C.; Fan, Song-Miao; Fitzjarrald, David R.

    1992-01-01

    Measurements of the atmospheric concentrations of NO, NO2, total NO(y), and O3 were made during the NASA Arctic Boundary Layer Expedition (ABLE 3A) at a remote location in a tundra bog ecosystem in southeastern Alaska during the growing season (July-August 1988). Concentrations of NO(x) and NO(y) were found to be very low compared to other remote continental sites, indicating that anthropogenic influences were small at this site during this time of year. The NO(y) emission rate from the soil were 0.13 +/- 0.05 x 10 exp 9 molecules/sq cm/s. Direct measurements of the flux of total NO(y) were made for the first time, indicating downward flux of NO(y) at all times of day, with maximum deposition of 2.5 +/- 0.9 x 10 exp 9 molecules/sq cm/s in the afternoon. Deposition of HNO3 appears to dominate the atmosphere/surface exchange of NO(y). The mean dry deposition rate of NO(y) to the tundra was 1.8 +/- 1.0 x 10 exp 9 molecules/sq cm/s.

  12. Measurements of NO(x) and NO(y) concentrations and fluxes over Arctic tundra

    SciTech Connect

    Bakwin, P.S.; Wofsy, S.C.; Fan, Songmiao; Fitzjarrald, D.R. New York State Univ., Albany )

    1992-10-01

    Measurements of the atmospheric concentrations of NO, NO[sub 2], total NO(y), and O[sub 3] were made during the NASA Arctic Boundary Layer Expedition (ABLE 3A) at a remote location in a tundra bog ecosystem in southeastern Alaska during the growing season (July-August 1988). Concentrations of NO(x) and NO(y) were found to be very low compared to other remote continental sites, indicating that anthropogenic influences were small at this site during this time of year. The NO(y) emission rate from the soil were 0.13 +/- 0.05 x 10 exp 9 molecules/sq cm/s. Direct measurements of the flux of total NO(y) were made for the first time, indicating downward flux of NO(y) at all times of day, with maximum deposition of 2.5 +/- 0.9 x 10 exp 9 molecules/sq cm/s in the afternoon. Deposition of HNO3 appears to dominate the atmosphere/surface exchange of NO(y). The mean dry deposition rate of NO(y) to the tundra was 1.8 +/- 1.0 x 10 exp 9 molecules/sq cm/s. 58 refs.

  13. Biogeography of bacterioplankton in lakes and streams of an Arctic tundra catchment.

    PubMed

    Crump, Ron C; Adams, Heather E; Hobbie, John E; Kling, George W

    2007-06-01

    Bacterioplankton community composition was compared across 10 lakes and 14 streams within the catchment of Toolik Lake, a tundra lake in Arctic Alaska, during seven surveys conducted over three years using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified rDNA. Bacterioplankton communities in streams draining tundra were very different than those in streams draining lakes. Communities in streams draining lakes were similar to communities in lakes. In a connected series of lakes and streams, the stream communities changed with distance from the upstream lake and with changes in water chemistry, suggesting inoculation and dilution with bacteria from soil waters or hyporheic zones. In the same system, lakes shared similar bacterioplankton communities (78% similar) that shifted gradually down the catchment. In contrast, unconnected lakes contained somewhat different communities (67% similar). We found evidence that dispersal influences bacterioplankton communities via advection and dilution (mass effects) in streams, and via inoculation and subsequent growth in lakes. The spatial pattern of bacterioplankton community composition was strongly influenced by interactions among soil water, stream, and lake environments. Our results reveal large differences in lake-specific and stream-specific bacterial community composition over restricted spatial scales (<10 km) and suggest that geographic distance and connectivity influence the distribution of bacterioplankton communities across a landscape.

  14. Carbon-Degrading Enzyme Activities Stimulated by Increased Nutrient Availability in Arctic Tundra Soils

    PubMed Central

    Koyama, Akihiro; Wallenstein, Matthew D.; Simpson, Rodney T.; Moore, John C.

    2013-01-01

    Climate-induced warming of the Arctic tundra is expected to increase nutrient availability to soil microbes, which in turn may accelerate soil organic matter (SOM) decomposition. We increased nutrient availability via fertilization to investigate the microbial response via soil enzyme activities. Specifically, we measured potential activities of seven enzymes at four temperatures in three soil profiles (organic, organic/mineral interface, and mineral) from untreated native soils and from soils which had been fertilized with nitrogen (N) and phosphorus (P) since 1989 (23 years) and 2006 (six years). Fertilized plots within the 1989 site received annual additions of 10 g N⋅m-2⋅year-1 and 5 g P⋅m-2⋅year-1. Within the 2006 site, two fertilizer regimes were established – one in which plots received 5 g N⋅m-2⋅year-1 and 2.5 g P⋅m-2⋅year-1 and one in which plots received 10 g N⋅m-2⋅year-1 and 5 g P⋅m-2⋅year-1. The fertilization treatments increased activities of enzymes hydrolyzing carbon (C)-rich compounds but decreased phosphatase activities, especially in the organic soils. Activities of two enzymes that degrade N-rich compounds were not affected by the fertilization treatments. The fertilization treatments increased ratios of enzyme activities degrading C-rich compounds to those for N-rich compounds or phosphate, which could lead to changes in SOM chemistry over the long term and to losses of soil C. Accelerated SOM decomposition caused by increased nutrient availability could significantly offset predicted increased C fixation via stimulated net primary productivity in Arctic tundra ecosystems. PMID:24204773

  15. Influence of human development and predators on nest survival of tundra birds, Arctic Coastal Plain, Alaska.

    PubMed

    Liebezeit, J R; Kendall, S J; Brown, S; Johnson, C B; Martin, P; McDonald, T L; Payer, D C; Rea, C L; Streever, B; Wildman, A M; Zack, S

    2009-09-01

    Nest predation may influence population dynamics of birds on the Arctic Coastal Plain (ACP) of Alaska, USA. Anthropogenic development on the ACP is increasing, which may attract nest predators by providing artificial sources of food, perches, den sites, and nest sites. Enhanced populations or concentrations of human-subsidized predators may reduce nest survival for tundra-nesting birds. In this study, we tested the hypothesis that nest survival decreases in proximity to human infrastructure. We monitored 1257 nests of 13 shorebird species and 619 nests of four passerine species at seven sites on the ACP from 2002 to 2005. Study sites were chosen to represent a range of distances to infrastructure from 100 m to 80 km. We used Cox proportional hazards regression models to evaluate the effects of background (i.e., natural) factors and infrastructure on nest survival. We documented high spatial and temporal variability in nest survival, and site and year were both included in the best background model. We did not detect an effect of human infrastructure on nest survival for shorebirds as a group. In contrast, we found evidence that risk of predation for passerine nests increased within 5 km of infrastructure. This finding provides quantitative evidence of a relationship between infrastructure and nest survival for breeding passerines on the ACP. A posteriori finer-scale analyses (within oil field sites and individual species) suggested that Red and Red-necked Phalaropes combined (Phalaropus fulicarius, P. lobatus) had lower productivity closer to infrastructure and in areas with higher abundance of subsidized predators. However, we did not detect such a relationship between infrastructure and nest survival for Semipalmated and Pectoral Sandpipers (Calidris pusilla, C. melanotos), the two most abundant shorebirds. High variability in environmental conditions, nest survival, and predator numbers between sites and years may have contributed to these inconsistent results

  16. Challenges in modelling isoprene and monoterpene emission dynamics of Arctic plants: a case study from a subarctic tundra heath

    NASA Astrophysics Data System (ADS)

    Tang, Jing; Schurgers, Guy; Valolahti, Hanna; Faubert, Patrick; Tiiva, Päivi; Michelsen, Anders; Rinnan, Riikka

    2016-12-01

    The Arctic is warming at twice the global average speed, and the warming-induced increases in biogenic volatile organic compounds (BVOCs) emissions from Arctic plants are expected to be drastic. The current global models' estimations of minimal BVOC emissions from the Arctic are based on very few observations and have been challenged increasingly by field data. This study applied a dynamic ecosystem model, LPJ-GUESS, as a platform to investigate short-term and long-term BVOC emission responses to Arctic climate warming. Field observations in a subarctic tundra heath with long-term (13-year) warming treatments were extensively used for parameterizing and evaluating BVOC-related processes (photosynthesis, emission responses to temperature and vegetation composition). We propose an adjusted temperature (T) response curve for Arctic plants with much stronger T sensitivity than the commonly used algorithms for large-scale modelling. The simulated emission responses to 2 °C warming between the adjusted and original T response curves were evaluated against the observed warming responses (WRs) at short-term scales. Moreover, the model responses to warming by 4 and 8 °C were also investigated as a sensitivity test. The model showed reasonable agreement to the observed vegetation CO2 fluxes in the main growing season as well as day-to-day variability of isoprene and monoterpene emissions. The observed relatively high WRs were better captured by the adjusted T response curve than by the common one. During 1999-2012, the modelled annual mean isoprene and monoterpene emissions were 20 and 8 mg C m-2 yr-1, with an increase by 55 and 57 % for 2 °C summertime warming, respectively. Warming by 4 and 8 °C for the same period further elevated isoprene emission for all years, but the impacts on monoterpene emissions levelled off during the last few years. At hour-day scale, the WRs seem to be strongly impacted by canopy air T, while at the day-year scale, the WRs are a combined

  17. Deeper winter snow reduces ecosystem C losses but increases the global warming potential of Arctic tussock tundra over the growing season.

    NASA Astrophysics Data System (ADS)

    Blanc-Betes, E.; Welker, J. M.; Gomez-Casanovas, N.; Gonzalez-Meler, M. A.

    2015-12-01

    Arctic winter precipitation is projected to increase globally over the next decades, spatial variability encompassing areas with increases and decreases in winter snow. Changes in winter precipitation strongly affect C dynamics in Arctic systems and may lead to major positive climate forcing feedbacks. However, impacts of predicted changes in snowfall and accumulation on the rate and form of C fluxes (CO2 and CH4) and associated forcing feedbacks from Arctic tundra remain uncertain. We investigated how changes in winter precipitation affect net ecosystem CO2 and CH4 fluxes and budgets of moist acidic tundra in an 18-yrs snow fence experiment over a complete growing season at Toolik Lake, AK. Arctic tundra under ambient winter precipitation (CTL) was a net source of CO2 and CH4, yielding net C losses over the growing season. Reduced snow (-15-30% snow depth; RS) switched the system to a net CO2 sink mostly by limiting SOC decomposition within colder soils. Snow additions progressively reduced net ecosystem CO2 losses compared to CTL, switching the system into a weaker net CO2 source with medium additions (+20-45% snow depth; MS) and into a small net CO2 sink with high additions (+70-100% snow depth; HS). Increasingly wetter soils with snow additions constrained the temperature sensitivity of aerobic decomposition and favored the anaerobic metabolism, buffering ecosystem CO2 losses despite substantial soil warming. Accordingly, Arctic tundra switched from a sustained CH4 sink at RS site to an increasingly stronger CH4 source with snow additions. Accounting for both CO2 and CH4, the RS site became a net C sink over the growing season, overall reducing the global warming potential (CO2 equiv.; GWP) of the system relative to CTL. Snow additions progressively reduced net C losses at the MS site compared to CTL and the system transitioned into a net C sink at HS plots, partly due to the slower metabolism of anaerobic decomposition. However, given the greater radiative

  18. Summer temperature increase has distinct effects on the ectomycorrhizal fungal communities of moist tussock and dry tundra in Arctic Alaska.

    PubMed

    Morgado, Luis N; Semenova, Tatiana A; Welker, Jeffrey M; Walker, Marilyn D; Smets, Erik; Geml, József

    2015-02-01

    Arctic regions are experiencing the greatest rates of climate warming on the planet and marked changes have already been observed in terrestrial arctic ecosystems. While most studies have focused on the effects of warming on arctic vegetation and nutrient cycling, little is known about how belowground communities, such as fungi root-associated, respond to warming. Here, we investigate how long-term summer warming affects ectomycorrhizal (ECM) fungal communities. We used Ion Torrent sequencing of the rDNA internal transcribed spacer 2 (ITS2) region to compare ECM fungal communities in plots with and without long-term experimental warming in both dry and moist tussock tundra. Cortinarius was the most OTU-rich genus in the moist tundra, while the most diverse genus in the dry tundra was Tomentella. On the diversity level, in the moist tundra we found significant differences in community composition, and a sharp decrease in the richness of ECM fungi due to warming. On the functional level, our results indicate that warming induces shifts in the extramatrical properties of the communities, where the species with medium-distance exploration type seem to be favored with potential implications for the mobilization of different nutrient pools in the soil. In the dry tundra, neither community richness nor community composition was significantly altered by warming, similar to what had been observed in ECM host plants. There was, however, a marginally significant increase in OTUs identified as ECM fungi with the medium-distance exploration type in the warmed plots. Linking our findings of decreasing richness with previous results of increasing ECM fungal biomass suggests that certain ECM species are favored by warming and may become more abundant, while many other species may go locally extinct due to direct or indirect effects of warming. Such compositional shifts in the community might affect nutrient cycling and soil organic C storage.

  19. Summer temperature increase has distinct effects on the ectomycorrhizal fungal communities of moist tussock and dry tundra in Arctic Alaska

    PubMed Central

    Morgado, Luis N; Semenova, Tatiana A; Welker, Jeffrey M; Walker, Marilyn D; Smets, Erik; Geml, József

    2015-01-01

    Arctic regions are experiencing the greatest rates of climate warming on the planet and marked changes have already been observed in terrestrial arctic ecosystems. While most studies have focused on the effects of warming on arctic vegetation and nutrient cycling, little is known about how belowground communities, such as fungi root-associated, respond to warming. Here, we investigate how long-term summer warming affects ectomycorrhizal (ECM) fungal communities. We used Ion Torrent sequencing of the rDNA internal transcribed spacer 2 (ITS2) region to compare ECM fungal communities in plots with and without long-term experimental warming in both dry and moist tussock tundra. Cortinarius was the most OTU-rich genus in the moist tundra, while the most diverse genus in the dry tundra was Tomentella. On the diversity level, in the moist tundra we found significant differences in community composition, and a sharp decrease in the richness of ECM fungi due to warming. On the functional level, our results indicate that warming induces shifts in the extramatrical properties of the communities, where the species with medium-distance exploration type seem to be favored with potential implications for the mobilization of different nutrient pools in the soil. In the dry tundra, neither community richness nor community composition was significantly altered by warming, similar to what had been observed in ECM host plants. There was, however, a marginally significant increase in OTUs identified as ECM fungi with the medium-distance exploration type in the warmed plots. Linking our findings of decreasing richness with previous results of increasing ECM fungal biomass suggests that certain ECM species are favored by warming and may become more abundant, while many other species may go locally extinct due to direct or indirect effects of warming. Such compositional shifts in the community might affect nutrient cycling and soil organic C storage. PMID:25156129

  20. Distribution and activity of ice wedges across the forest-tundra transition, western Arctic Canada

    NASA Astrophysics Data System (ADS)

    Kokelj, S. V.; Lantz, T. C.; Wolfe, S. A.; Kanigan, J. C.; Morse, P. D.; Coutts, R.; Molina-Giraldo, N.; Burn, C. R.

    2014-09-01

    Remote sensing, regional ground temperature and ground ice observations, and numerical simulation were used to investigate the size, distribution, and activity of ice wedges in fine-grained mineral and organic soils across the forest-tundra transition in uplands east of the Mackenzie Delta. In the northernmost dwarf-shrub tundra, ice wedge polygons cover up to 40% of the ground surface, with the wedges commonly exceeding 3 m in width. The largest ice wedges are in peatlands where thermal contraction cracking occurs more frequently than in nearby hummocky terrain with fine-grained soils. There are fewer ice wedges, rarely exceeding 2 m in width, in uplands to the south and none have been found in mineral soils of the tall-shrub tundra, although active ice wedges are found there throughout peatlands. In the spruce forest zone, small, relict ice wedges are restricted to peatlands. At tundra sites, winter temperatures at the top of permafrost are lower in organic than mineral soils because of the shallow permafrost table, occurrence of phase change at 0°C, and the relatively high thermal conductivity of icy peat. Due to these factors and the high coefficient of thermal contraction of frozen saturated peat, ice wedge cracking and growth is more common in peatlands than in mineral soil. However, the high latent heat content of saturated organic active layer soils may inhibit freezeback, particularly where thick snow accumulates, making the permafrost and the ice wedges in spruce forest polygonal peatlands susceptible to degradation following alteration of drainage or climate warming.

  1. Ground measurements of the hemispherical-directional reflectance of Arctic snow covered tundra for the validation of satellite remote sensing products

    NASA Astrophysics Data System (ADS)

    Ball, C. P.; Marks, A. A.; Green, P.; Mac Arthur, A.; Fox, N.; King, M. D.

    2013-12-01

    Surface albedo is the hemispherical and wavelength integrated reflectance over the visible, near infrared and shortwave infrared regions of the solar spectrum. The albedo of Arctic snow can be in excess of 0.8 and it is a critical component in the global radiation budget because it determines the proportion of solar radiation absorbed, and reflected, over a large part of the Earth's surface. We present here our first results of the angularly resolved surface reflectance of Arctic snow at high solar zenith angles (~80°) suitable for the validation of satellite remote sensing products. The hemispherical directional reflectance factor (HDRF) of Arctic snow covered tundra was measured using the GonioRAdiometric Spectrometer System (GRASS) during a three-week field campaign in Ny-Ålesund, Svalbard, in March/April 2013. The measurements provide one of few existing HDRF datasets at high solar zenith angles for wind-blown Arctic snow covered tundra (conditions typical of the Arctic region), and the first ground-based measure of HDRF at Ny-Ålesund. The HDRF was recorded under clear sky conditions with 10° intervals in view zenith, and 30° intervals in view azimuth, for several typical sites over a wavelength range of 400-1500 nm at 1 nm resolution. Satellite sensors such as MODIS, AVHRR and VIIRS offer a method to monitor the surface albedo with high spatial and temporal resolution. However, snow reflectance is anisotropic and is dependent on view and illumination angle and the wavelength of the incident light. Spaceborne sensors subtend a discrete angle to the target surface and measure radiance over a limited number of narrow spectral bands. Therefore, the derivation of the surface albedo requires accurate knowledge of the surfaces bidirectional reflectance as a function of wavelength. The ultimate accuracy to which satellite sensors are able to measure snow surface properties such as albedo is dependant on the accuracy of the BRDF model, which can only be assessed

  2. Remotely sensed vicennial changes of green phytomass, Salix cover, and leaf turnover in a sedge-shrub tundra, Arctic National Wildlife Refuge, Alaska

    NASA Astrophysics Data System (ADS)

    Kushida, K.; Kim, Y.; Tsuyuzaki, S.; Watanabe, M.; Kadosaki, G.; Sawada, Y.; Ishikawa, M.; Fukuda, M.

    2007-12-01

    We obtained the relationship between spectral indices, green phytomass, Salix - non-Salix ratio, and leaf turnover in a sedge-shrub tundra, Arctic National Wildlife Refuge (ANWR), Alaska based on the field observations of spectral reflectance and phytomass, and we used Landsat TM images acquired in July of 1986, 1994, and 2006 and the time series of NOAA AVHRR (Advanced Very High Resolution Radiometer) for evaluating the vicennial changes. 51% of Beaufort coastal plain, Alaska was occupied by lowland moist sedge-shrub tundra, lowland wet sedge tundra, riverine moist sedge-shrub tundra, and riverine wet sedge tundra, where willow shrubs and sedges dominate. We set a 50-m × 50-m plot located on the floodplain of Jago River in ANWR. Shrub (Salix lanata L.) and sedge (Carex bigelowii Torr.) dominated in the plot. Ten 0.5-m × 0.5-m quadrates (Salix} quadrates) were set on the Salix cover and ten 0.5-m × 0.5-m quadrates (non-Salix quadrates) were set on the ground that was not covered with Salix lanata. Salix lanata in each of the Salix quadrates was harvested, and the leaf area index (LAI) and the oven-dried weights of the photosynthetic (leaf) and non-photosynthetic parts were measured. After harvesting Salix, other green plants were harvested and the oven-dried weights of the plants were measured. The Salix quadrates were spectrally measured with a spectroradiometer at a wavelength of 350 - 2500 nm before and after harvesting Salix and after harvesting other green plants. Non-Salix quadrates were also spectrally measured with the spectroradiometer. The coefficients of determination (R2) of the green phytomass, Salix - non-Salix ratio, and leaf turnover estimations from the spectral indices were 0.63, 0.57, and 0.79, respectively. These estimations were used for evaluating the vicennial changes using the satellite data.

  3. Shrub biomass, net primary production, and canopy spectral imaging (NDVI) exhibit consistent correspondence across Arctic Tundra habitats.

    NASA Astrophysics Data System (ADS)

    Flower, C. E.; Welker, J. M.; Anderson-Smith, A.; Van Hoey, N.; Whelan, C.; Gonzalez-Meler, M. A.

    2014-12-01

    Climate change is contributing to rapid vegetation shifts in the ecologically sensitive arctic tundra. These tussock grass dominated systems are shifting to tussock/woody shrub communities with cascading ecological and climate feedback consequences. This shifting vegetation composition should result in concomitant changes in carbon sequestration (net ecosystem exchange, NEE) and productivity which in turn could be manifested in "Greening" and changes in normalized difference vegetation index values (NDVI). In this study, we address the need to know the relationships between NDVI, leaf area, and shrub biomass, in part so that long-term trends in NDVI can be much more accurately interpreted as true changes in ecosystem C cycling processes. These relationships will enhance our ability to predict shifts in standing carbon mass, carbon cycling, and use historic satellite products to assess change. We sampled NEE, NDVI, leaf area and shrub (Betula spp. and Salix spp.) biomass across a shrub gradient in a dry heath and moist acidic tundra. The positive relationship between NDVI and NEE highlights the potential shifts in tundra carbon sequestration associated with woody vegetation shifts. Furthermore, strong positive linear relationships found among shrub biomass, species, leaf area, and NDVI in different tundra habitats should increase the robustness of spatial scaling. Increased productivity in sites with increased NDVI can provide a mechanism through which tundra ecosystems may respond to climate change. Improvements in our ability to detect relationships between above and belowground biomass for the dominant shrubs can strengthen our ability to predict standing biomass from satellite imagery.

  4. Improving understanding of controls on spatial variability in methane fluxes in Arctic tundra

    NASA Astrophysics Data System (ADS)

    Davidson, Scott J.; Sloan, Victoria; Phoenix, Gareth; Wagner, Robert; Oechel, Walter; Zona, Donatella

    2015-04-01

    The Arctic is experiencing rapid climate change relative to the rest of the globe, and this increase in temperature has feedback effects across hydrological and thermal regimes, plant community distribution and carbon stocks within tundra soils. Arctic wetlands account for a significant amount of methane emissions from natural ecosystems to the atmosphere and with further permafrost degradation under a warming climate, these emissions are expected to increase. Methane (CH4) is an extremely important component of the global carbon cycle with a global warming potential 28.5 times greater than carbon dioxide over a 100 year time scale (IPCC, 2013). In order to validate carbon cycle models, modelling methane at broader landscape scales is needed. To date direct measurements of methane have been sporadic in time and space which, while capturing some key controls on the spatial heterogeneity, make it difficult to accurately upscale methane emissions to the landscape and regional scales. This study investigates what is controlling the spatial heterogeneity of methane fluxes across Arctic tundra. We combined over 300 portable chamber observations from 13 micro-topographic positions (with multiple vegetation types) across three locations spanning a 300km latitudinal gradient in Northern Alaska from Barrow to Ivotuk with synchronous measurements of environmental (soil temperature, soil moisture, water table, active layer thaw depth, pH) and vegetation (plant community composition, height, sedge tiller counts) variables to evaluate key controls on methane fluxes. To assess the diurnal variation in CH4 fluxes, we also performed automated chamber measurements in one study site (Barrow) location. Multiple statistical approaches (regression tree and multiple linear regression) were used to identify key controlling variables and their interactions. Methane emissions across all sites ranged from -0.08 to 15.3 mg C-CH4 m-2 hr-1. As expected, soil moisture was the main control

  5. Increasing shrub abundance and N addition in Arctic tundra affect leaf and root litter decomposition differently

    NASA Astrophysics Data System (ADS)

    McLaren, J.; van de Weg, M. J.; Shaver, G. R.; Gough, L.

    2013-12-01

    Changes in global climate have resulted in a ';greening' of the Arctic as the abundance of deciduous shrub species increases. Consequently, not only the living plant community, but also the litter composition changes, which in turn can affect carbon turnover patterns in the Arctic. We examined effects of changing litter composition (both root and leaf litter) on decomposition rates with a litter bag study, and specifically focused on the impact of deciduous shrub Betula nana litter on litter decomposition from two evergreen shrubs (Ledum palustre, and Vaccinium vitis-idaea) and one graminoid (Eriophorum vaginatum) species. Additionally, we investigated how decomposition was affected by nutrient availability by placing the litterbags in an ambient and a fertilized moist acidic tundra environment. Measurements were carried out seasonally over 2 years (after snow melt, mid-growing season, end growing season). We measured litter mass loss over time, as well as the respiration rates (standardized for temperature and moisture) and temperature sensitivity of litter respiration at the time of harvesting the litter bags. For leaves, Betula litter decomposed faster than the other three species, with Eriophorum leaves decomposing the slowest. This pattern was observed for both mass loss and litter respiration rates, although the differences in respiration became smaller over time. Surprisingly, combining Betula with any other species resulted in slower overall weight loss rates than would be predicted based on monoculture weight loss rates. This contrasted with litter respiration at the time of sampling, which showed a positive mixing effect of adding Betula leaf liter to the other species. Apparently, during the first winter months (September - May) Betula litter decomposition is negatively affected by mixing the species and this legacy can still be observed in the total mass loss results later in the year. For root litter there were fewer effects of species identity on root

  6. Feedbacks between tall shrubland development and active layer temperatures in northwest Siberian arctic tundra

    NASA Astrophysics Data System (ADS)

    Epstein, H. E.; Frost, G. V.; Walker, D. A.; Matyshak, G.

    2013-12-01

    Permafrost soils are a globally significant carbon store, but changes in permafrost thermal regime observed in recent decades across much of the Arctic suggest that permafrost carbon balance is likely to change with continued climate warming. Critical to changes in permafrost carbon balance in a warmer world, however, are feedbacks between changes in the composition and density of surface vegetation, and the thermal state of permafrost. Shrub expansion has been widely observed in the northwest Siberian Low Arctic, but the magnitude and direction of shrub-induced impacts to permafrost temperature and stability remain poorly understood. Here we evaluate changes to active layer properties and thermal regime that occur during tall shrubland development (shrubs > 1.5 m height) within a northwest Siberian landscape dominated by well-developed, small-scale patterned ground features (e.g., non-sorted circles). We measured the annual time-series of soil temperature at 5 cm and 20 cm depth, and the structural attributes of vegetation at patterned-ground microsites across four stages of tall shrubland development: low-growing tundra lacking erect shrubs, newly-developed shrublands, mature shrublands, and paludified shrublands. Mean summer soil temperatures declined with increasing shrub cover and moss thickness, but winter soil temperatures increased with shrub development. Shrubland development strongly attenuated cryoturbation, promoting the establishment of complete vegetation cover and the development of a continuous organic mat. Increased vegetation cover, in turn, led to further reduced cryoturbation and an aggrading permafrost table. These observations indicate that tall shrub expansion that is now occurring in patterned-ground landscapes of the northwest Siberian Arctic may buffer permafrost from atmospheric warming, and increase carbon storage in these systems at least in the short term.

  7. Microbial iron oxidation in the Arctic tundra and its implications for biogeochemical cycling.

    PubMed

    Emerson, David; Scott, Jarrod J; Benes, Joshua; Bowden, William B

    2015-12-01

    The role that neutrophilic iron-oxidizing bacteria play in the Arctic tundra is unknown. This study surveyed chemosynthetic iron-oxidizing communities at the North Slope of Alaska near Toolik Field Station (TFS) at Toolik Lake (lat 68.63, long -149.60). Microbial iron mats were common in submerged habitats with stationary or slowly flowing water, and their greatest areal extent is in coating plant stems and sediments in wet sedge meadows. Some Fe-oxidizing bacteria (FeOB) produce easily recognized sheath or stalk morphotypes that were present and dominant in all the mats we observed. The cool water temperatures (9 to 11°C) and reduced pH (5.0 to 6.6) at all sites kinetically favor microbial iron oxidation. A microbial survey of five sites based on 16S rRNA genes found a predominance of Proteobacteria, with Betaproteobacteria and members of the family Comamonadaceae being the most prevalent operational taxonomic units (OTUs). In relative abundance, clades of lithotrophic FeOB composed 5 to 10% of the communities. OTUs related to cyanobacteria and chloroplasts accounted for 3 to 25% of the communities. Oxygen profiles showed evidence for oxygenic photosynthesis at the surface of some mats, indicating the coexistence of photosynthetic and FeOB populations. The relative abundance of OTUs belonging to putative Fe-reducing bacteria (FeRB) averaged around 11% in the sampled iron mats. Mats incubated anaerobically with 10 mM acetate rapidly initiated Fe reduction, indicating that active iron cycling is likely. The prevalence of iron mats on the tundra might impact the carbon cycle through lithoautotrophic chemosynthesis, anaerobic respiration of organic carbon coupled to iron reduction, and the suppression of methanogenesis, and it potentially influences phosphorus dynamics through the adsorption of phosphorus to iron oxides.

  8. Microbial Iron Oxidation in the Arctic Tundra and Its Implications for Biogeochemical Cycling

    PubMed Central

    Scott, Jarrod J.; Benes, Joshua; Bowden, William B.

    2015-01-01

    The role that neutrophilic iron-oxidizing bacteria play in the Arctic tundra is unknown. This study surveyed chemosynthetic iron-oxidizing communities at the North Slope of Alaska near Toolik Field Station (TFS) at Toolik Lake (lat 68.63, long −149.60). Microbial iron mats were common in submerged habitats with stationary or slowly flowing water, and their greatest areal extent is in coating plant stems and sediments in wet sedge meadows. Some Fe-oxidizing bacteria (FeOB) produce easily recognized sheath or stalk morphotypes that were present and dominant in all the mats we observed. The cool water temperatures (9 to 11°C) and reduced pH (5.0 to 6.6) at all sites kinetically favor microbial iron oxidation. A microbial survey of five sites based on 16S rRNA genes found a predominance of Proteobacteria, with Betaproteobacteria and members of the family Comamonadaceae being the most prevalent operational taxonomic units (OTUs). In relative abundance, clades of lithotrophic FeOB composed 5 to 10% of the communities. OTUs related to cyanobacteria and chloroplasts accounted for 3 to 25% of the communities. Oxygen profiles showed evidence for oxygenic photosynthesis at the surface of some mats, indicating the coexistence of photosynthetic and FeOB populations. The relative abundance of OTUs belonging to putative Fe-reducing bacteria (FeRB) averaged around 11% in the sampled iron mats. Mats incubated anaerobically with 10 mM acetate rapidly initiated Fe reduction, indicating that active iron cycling is likely. The prevalence of iron mats on the tundra might impact the carbon cycle through lithoautotrophic chemosynthesis, anaerobic respiration of organic carbon coupled to iron reduction, and the suppression of methanogenesis, and it potentially influences phosphorus dynamics through the adsorption of phosphorus to iron oxides. PMID:26386054

  9. Exploring Relationships Between Vegetation Reflectance and Plant Physiological Parameters on Arctic Wet Sedge Tundra

    NASA Astrophysics Data System (ADS)

    Boelman, N.; Griffin, K.; Stieglitz, M.; Shaver, G. R.; Gamon, J. A.

    2001-12-01

    We explore vegetation reflectance indices, sampled with a handheld spectroradiometer, to determine the effectiveness of remotely sensed optical measurements in detecting the effects of increased N or P availability, increased temperature, and decreased light intensity on wet sedge tundra near Toolik Lake, Alaska. For the past thirteen years, nutrient availability was increased through fertilization treatments (N, P and N+P) in factorial experiments at three separate field sites. Air temperature was increased using plastic greenhouses at two sites, both with and without N+P fertilizer. Light intensity (photosynthetically active photon flux) was reduced by 50% at the same two sites. All measurements were taken during the growing season of 2001. We have employed two reflectance indices: the normalized difference vegetation index (NDVI), a proxy for chlorophyll content; and the photochemical reflectance index (PRI), a proxy for xanthophyll cycle activity, and thus of Photosystem II radiation-use efficiency. NDVI values for the N+P and P alone treatment plots are consistently higher than both the control and N alone treatment plots throughout the growing season, supporting previous findings that wet sedge tundra is a primarily P limited system. NDVI values for the shade houses are consistently lower than the control plots and all other treatment plots throughout the growing season, suggesting that a reduction in light intensity, as might be expected by increased cloud cover due to global warming, reduces the net primary productivity of wet sedge tundra. NDVI values for both warming treatments show no consistent trends. One especially interesting result is that PRI values for the N+P, warming and the P alone treatment plots are consistently lower than the control plots throughout the growing season, suggesting that these plots have higher carotenoid and zeaxanthin concentrations than the control plots. One hypothesis is that the N+P, warming and P alone treatment plots

  10. How spatial variation in areal extent and configuration of labile vegetation states affect the riparian bird community in Arctic tundra.

    PubMed

    Henden, John-André; Yoccoz, Nigel G; Ims, Rolf A; Langeland, Knut

    2013-01-01

    The Arctic tundra is currently experiencing an unprecedented combination of climate change, change in grazing pressure by large herbivores and growing human activity. Thickets of tall shrubs represent a conspicuous vegetation state in northern and temperate ecosystems, where it serves important ecological functions, including habitat for wildlife. Thickets are however labile, as tall shrubs respond rapidly to both abiotic and biotic environmental drivers. Our aim was to assess how large-scale spatial variation in willow thicket areal extent, configuration and habitat structure affected bird abundance, occupancy rates and species richness so as to provide an empirical basis for predicting the outcome of environmental change for riparian tundra bird communities. Based on a 4-year count data series, obtained through a large-scale study design in low arctic tundra in northern Norway, statistical hierarchical community models were deployed to assess relations between habitat configuration and bird species occupancy and community richness. We found that species abundance, occupancy and richness were greatly affected by willow areal extent and configuration, habitat features likely to be affected by intense ungulate browsing as well as climate warming. In sum, total species richness was maximized in large and tall willow patches of small to intermediate degree of fragmentation. These community effects were mainly driven by responses in the occupancy rates of species depending on tall willows for foraging and breeding, while species favouring other vegetation states were not affected. In light of the predicted climate driven willow shrub encroachment in riparian tundra habitats, our study predicts that many bird species would increase in abundance, and that the bird community as a whole could become enriched. Conversely, in tundra regions where overabundance of large herbivores leads to decreased areal extent, reduced height and increased fragmentation of willow thickets

  11. How Spatial Variation in Areal Extent and Configuration of Labile Vegetation States Affect the Riparian Bird Community in Arctic Tundra

    PubMed Central

    Henden, John-André; Yoccoz, Nigel G.; Ims, Rolf A.; Langeland, Knut

    2013-01-01

    The Arctic tundra is currently experiencing an unprecedented combination of climate change, change in grazing pressure by large herbivores and growing human activity. Thickets of tall shrubs represent a conspicuous vegetation state in northern and temperate ecosystems, where it serves important ecological functions, including habitat for wildlife. Thickets are however labile, as tall shrubs respond rapidly to both abiotic and biotic environmental drivers. Our aim was to assess how large-scale spatial variation in willow thicket areal extent, configuration and habitat structure affected bird abundance, occupancy rates and species richness so as to provide an empirical basis for predicting the outcome of environmental change for riparian tundra bird communities. Based on a 4-year count data series, obtained through a large-scale study design in low arctic tundra in northern Norway, statistical hierarchical community models were deployed to assess relations between habitat configuration and bird species occupancy and community richness. We found that species abundance, occupancy and richness were greatly affected by willow areal extent and configuration, habitat features likely to be affected by intense ungulate browsing as well as climate warming. In sum, total species richness was maximized in large and tall willow patches of small to intermediate degree of fragmentation. These community effects were mainly driven by responses in the occupancy rates of species depending on tall willows for foraging and breeding, while species favouring other vegetation states were not affected. In light of the predicted climate driven willow shrub encroachment in riparian tundra habitats, our study predicts that many bird species would increase in abundance, and that the bird community as a whole could become enriched. Conversely, in tundra regions where overabundance of large herbivores leads to decreased areal extent, reduced height and increased fragmentation of willow thickets

  12. Long-Term Perspectives of Shrub Expansions and Peat Initiation in Arctic Tundra on the North Slope of Alaska

    NASA Astrophysics Data System (ADS)

    Cleary, K.; Yu, Z.

    2014-12-01

    The ongoing climate warming in the Arctic has caused rapid terrestrial ecosystem changes, including shrub expansion and permafrost thaw. Here we used results from a peat-accumulating permafrost tundra in upper Imnavait Creek on the Arctic foothills of Alaska (68° 36' N, 149° 18' W) to investigate ecological responses to recent climate warming in the context of the last millennium. Six peat soil cores were collected from Sphagnum mosaics along an elevational gradient from 906 m to 950 m on a hillslope covered by Eriophorum-dominated tussock tundra. Macrofossil analysis documents a consistent development sequence among all cores from a mineral soil to a minerotrophic sedge peat and finally to an ombrotrophic Sphagnum peat. The 14C dating results show the ages of peat initiation range from about 900 to 140 cal BP, but do not follow the elevation gradient, suggesting the dominant control of local factors. The Sphagnum onset begins at 1820 AD near the ridge top, and subsequently propagates downslope to the floodplain at 2008 AD. This transition (ombrotrophication) was likely in response to Arctic warming, and subsequent permafrost thaw and active layer thickening, leading to drying initiating at the ridge top and facilitating Sphagnum colonization. Pollen analysis of the master core UIC13-3 at 916 m elevation (basal age 700 cal BP) shows that the vegetation was dominated by sedges (up to 84%) during the cool Little Ice Age until 1800 AD, followed by increases in shrubs first from dwarf birch (Betula nana) (up to 57%) and then willows (Salix spp.) up to 62% in the 1960s. These results indicate that shrub expansion of willows, due to accelerated warming in recent decades, was preceded by birch expansion over the last two centuries. Our new results provide a long-term perspective on ecological transformations in the Arctic, in particular the history of recent shrub expansions and the process of peatland initiation and expansion across Arctic tundra.

  13. Spectral determination of concentrations of functionally diverse pigments in increasingly complex arctic tundra canopies.

    PubMed

    Boelman, Natalie T; Magney, Troy S; Logan, Barry A; Griffin, Kevin L; Eitel, Jan U H; Greaves, Heather; Prager, Case M; Vierling, Lee A

    2016-09-01

    As the Arctic warms, tundra vegetation is becoming taller and more structurally complex, as tall deciduous shrubs become increasingly dominant. Emerging studies reveal that shrubs exhibit photosynthetic resource partitioning, akin to forests, that may need accounting for in the "big leaf" net ecosystem exchange models. We conducted a lab experiment on sun and shade leaves from S. pulchra shrubs to determine the influence of both constitutive (slowly changing bulk carotenoid and chlorophyll pools) and facultative (rapidly changing xanthophyll cycle) pigment pools on a suite of spectral vegetation indices, to devise a rapid means of estimating within canopy resource partitioning. We found that: (1) the PRI of dark-adapted shade leaves (PRIo) was double that of sun leaves, and that PRIo was sensitive to variation among sun and shade leaves in both xanthophyll cycle pool size (V + A + Z) (r (2) = 0.59) and Chla/b (r (2) = 0.64); (2) A corrected PRI (difference between dark and illuminated leaves, ΔPRI) was more sensitive to variation among sun and shade leaves in changes to the epoxidation state of their xanthophyll cycle pigments (dEPS) (r (2) = 0.78, RMSE = 0.007) compared to the uncorrected PRI of illuminated leaves (PRI) (r (2) = 0.34, RMSE = 0.02); and (3) the SR680 index was correlated with each of (V + A + Z), lutein, bulk carotenoids, (V + A + Z)/(Chla + b), and Chla/b (r (2) range = 0.52-0.69). We suggest that ΔPRI be employed as a proxy for facultative pigment dynamics, and the SR680 for the estimation of constitutive pigment pools. We contribute the first Arctic-specific information on disentangling PRI-pigment relationships, and offer insight into how spectral indices can assess resource partitioning within shrub tundra canopies.

  14. Contrasting radiation and soil heat fluxes in Arctic shrub and wet sedge tundra

    NASA Astrophysics Data System (ADS)

    Juszak, Inge; Eugster, Werner; Heijmans, Monique M. P. D.; Schaepman-Strub, Gabriela

    2016-07-01

    Vegetation changes, such as shrub encroachment and wetland expansion, have been observed in many Arctic tundra regions. These changes feed back to permafrost and climate. Permafrost can be protected by soil shading through vegetation as it reduces the amount of solar energy available for thawing. Regional climate can be affected by a reduction in surface albedo as more energy is available for atmospheric and soil heating. Here, we compared the shortwave radiation budget of two common Arctic tundra vegetation types dominated by dwarf shrubs (Betula nana) and wet sedges (Eriophorum angustifolium) in North-East Siberia. We measured time series of the shortwave and longwave radiation budget above the canopy and transmitted radiation below the canopy. Additionally, we quantified soil temperature and heat flux as well as active layer thickness. The mean growing season albedo of dwarf shrubs was 0.15 ± 0.01, for sedges it was higher (0.17 ± 0.02). Dwarf shrub transmittance was 0.36 ± 0.07 on average, and sedge transmittance was 0.28 ± 0.08. The standing dead leaves contributed strongly to the soil shading of wet sedges. Despite a lower albedo and less soil shading, the soil below dwarf shrubs conducted less heat resulting in a 17 cm shallower active layer as compared to sedges. This result was supported by additional, spatially distributed measurements of both vegetation types. Clouds were a major influencing factor for albedo and transmittance, particularly in sedge vegetation. Cloud cover reduced the albedo by 0.01 in dwarf shrubs and by 0.03 in sedges, while transmittance was increased by 0.08 and 0.10 in dwarf shrubs and sedges, respectively. Our results suggest that the observed deeper active layer below wet sedges is not primarily a result of the summer canopy radiation budget. Soil properties, such as soil albedo, moisture, and thermal conductivity, may be more influential, at least in our comparison between dwarf shrub vegetation on relatively dry patches and

  15. Above- and belowground responses of Arctic tundra ecosystems to altered soil nutrients and mammalian herbivory.

    PubMed

    Gough, Laura; Moore, John C; Shaver, Gauis R; Simpson, Rodney T; Johnson, David R

    2012-07-01

    Theory and observation indicate that changes in the rate of primary production can alter the balance between the bottom-up influences of plants and resources and the top-down regulation of herbivores and predators on ecosystem structure and function. The exploitation ecosystem hypothesis (EEH) posited that as aboveground net primary productivity (ANPP) increases, the additional biomass should support higher trophic levels. We developed an extension of EEH to include the impacts of increases in ANPP on belowground consumers in a similar manner as aboveground, but indirectly through changes in the allocation of photosynthate to roots. We tested our predictions for plants aboveground and for phytophagous nematodes and their predators belowground in two common arctic tundra plant communities subjected to 11 years of increased soil nutrient availability and/or exclusion of mammalian herbivores. The less productive dry heath (DH) community met the predictions of EEH aboveground, with the greatest ANPP and plant biomass in the fertilized plots protected from herbivory. A palatable grass increased in fertilized plots while dwarf evergreen shrubs and lichens declined. Belowground, phytophagous nematodes also responded as predicted, achieving greater biomass in the higher ANPP plots, whereas predator biomass tended to be lower in those same plots (although not significantly). In the higher productivity moist acidic tussock (MAT) community, aboveground responses were quite different. Herbivores stimulated ANPP and biomass in both ambient and enriched soil nutrient plots; maximum ANPP occurred in fertilized plots exposed to herbivory. Fertilized plots became dominated by dwarf birch (a deciduous shrub) and cloudberry (a perennial forb); under ambient conditions these two species coexist with sedges, evergreen dwarf shrubs, and Sphagnum mosses. Phytophagous nematodes did not respond significantly to changes in ANPP, although predator biomass was greatest in control plots. The

  16. The effect of silver nanoparticles on seasonal change in arctic tundra bacterial and fungal assemblages.

    PubMed

    Kumar, Niraj; Palmer, Gerald R; Shah, Vishal; Walker, Virginia K

    2014-01-01

    The impact of silver nanoparticles (NPs) and microparticles (MPs) on bacterial and fungal assemblages was studied in soils collected from a low arctic site. Two different concentrations (0.066% and 6.6%) of Ag NPs and Ag MPs were tested in microcosms that were exposed to temperatures mimicking a winter to summer transition. Toxicity was monitored by differential respiration, phospholipid fatty acid analysis, polymerase chain reaction-denaturing gradient gel electrophoresis and DNA sequencing. Notwithstanding the effect of Ag MPs, nanosilver had an obvious, additional impact on the microbial community, underscoring the importance of particle size in toxicity. This impact was evidenced by levels of differential respiration in 0.066% Ag NP-treated soil that were only half that of control soils, a decrease in signature bacterial fatty acids, and changes in both richness and evenness in bacterial and fungal DNA sequence assemblages. Prominent after Ag NP-treatment were Hypocreales fungi, which increased to 70%, from only 1% of fungal sequences under control conditions. Genera within this Order known for their antioxidant properties (Cordyceps/Isaria) dominated the fungal assemblage after NP addition. In contrast, sequences attributed to the nitrogen-fixing Rhizobiales bacteria appeared vulnerable to Ag NP-mediated toxicity. This combination of physiological, biochemical and molecular studies clearly demonstrate that Ag NPs can severely disrupt the natural seasonal progression of tundra assemblages.

  17. Cold- and Growing-Season Microbial Substrate Use in Arctic Tundra Soil

    NASA Astrophysics Data System (ADS)

    Schimel, J.; McMahon, S.

    2006-12-01

    Microbial communities will play a critical role in determining arctic ecosystem response to warming due to global climate change since decomposition, which is responsible for both CO2 evolution and plant nutrient availability, is a microbially-mediated process. Microorganisms living in tundra soil have access to two broad categories of carbon compounds via decomposition: complex polymers such as cellulose, lignin, protein and soil organic matter, and simple monomers such as glucose, phenolics and amino acids. Thermodynamically, labile substrates are easier to degrade because the activation energy of the reaction is lower than for more recalcitrant polymers. Thus, metabolic processes involving simple compounds are more likely under frozen conditions during the cold season. To test this theory, we incubated soils collected at Toolik Lake, Alaska before and after snowmelt and freeze-up with a variety of 13C-labelled substrates to track microbial carbon use during cold- and growing-season conditions. Surprisingly, tussock soils respired more protein-derived carbon under frozen pre-thaw conditions than late growing-season conditions. Organic shrub soils respired more glutamic acid-derived carbon under all conditions. Since nitrogen is more abundant in shrub than tussock soils, microbes in the shrub soil can afford to respire glutamic acid as an energy source rather than incorporate it into microbial biomass as a nitrogen source. This study indicates that winter substrate use may not follow predictions made strictly on a thermodynamic basis and hints at the complex nature of cold-tolerant microorganisms.

  18. The Effect of Silver Nanoparticles on Seasonal Change in Arctic Tundra Bacterial and Fungal Assemblages

    PubMed Central

    Kumar, Niraj; Palmer, Gerald R.; Shah, Vishal; Walker, Virginia K.

    2014-01-01

    The impact of silver nanoparticles (NPs) and microparticles (MPs) on bacterial and fungal assemblages was studied in soils collected from a low arctic site. Two different concentrations (0.066% and 6.6%) of Ag NPs and Ag MPs were tested in microcosms that were exposed to temperatures mimicking a winter to summer transition. Toxicity was monitored by differential respiration, phospholipid fatty acid analysis, polymerase chain reaction-denaturing gradient gel electrophoresis and DNA sequencing. Notwithstanding the effect of Ag MPs, nanosilver had an obvious, additional impact on the microbial community, underscoring the importance of particle size in toxicity. This impact was evidenced by levels of differential respiration in 0.066% Ag NP-treated soil that were only half that of control soils, a decrease in signature bacterial fatty acids, and changes in both richness and evenness in bacterial and fungal DNA sequence assemblages. Prominent after Ag NP-treatment were Hypocreales fungi, which increased to 70%, from only 1% of fungal sequences under control conditions. Genera within this Order known for their antioxidant properties (Cordyceps/Isaria) dominated the fungal assemblage after NP addition. In contrast, sequences attributed to the nitrogen-fixing Rhizobiales bacteria appeared vulnerable to Ag NP-mediated toxicity. This combination of physiological, biochemical and molecular studies clearly demonstrate that Ag NPs can severely disrupt the natural seasonal progression of tundra assemblages. PMID:24926877

  19. Where do the treeless tundra areas of northern highlands fit in the global biome system: toward an ecologically natural subdivision of the tundra biome.

    PubMed

    Virtanen, Risto; Oksanen, Lauri; Oksanen, Tarja; Cohen, Juval; Forbes, Bruce C; Johansen, Bernt; Käyhkö, Jukka; Olofsson, Johan; Pulliainen, Jouni; Tømmervik, Hans

    2016-01-01

    According to some treatises, arctic and alpine sub-biomes are ecologically similar, whereas others find them highly dissimilar. Most peculiarly, large areas of northern tundra highlands fall outside of the two recent subdivisions of the tundra biome. We seek an ecologically natural resolution to this long-standing and far-reaching problem. We studied broad-scale patterns in climate and vegetation along the gradient from Siberian tundra via northernmost Fennoscandia to the alpine habitats of European middle-latitude mountains, as well as explored those patterns within Fennoscandian tundra based on climate-vegetation patterns obtained from a fine-scale vegetation map. Our analyses reveal that ecologically meaningful January-February snow and thermal conditions differ between different types of tundra. High precipitation and mild winter temperatures prevail on middle-latitude mountains, low precipitation and usually cold winters prevail on high-latitude tundra, and Scandinavian mountains show intermediate conditions. Similarly, heath-like plant communities differ clearly between middle latitude mountains (alpine) and high-latitude tundra vegetation, including its altitudinal extension on Scandinavian mountains. Conversely, high abundance of snowbeds and large differences in the composition of dwarf shrub heaths distinguish the Scandinavian mountain tundra from its counterparts in Russia and the north Fennoscandian inland. The European tundra areas fall into three ecologically rather homogeneous categories: the arctic tundra, the oroarctic tundra of northern heights and mountains, and the genuinely alpine tundra of middle-latitude mountains. Attempts to divide the tundra into two sub-biomes have resulted in major discrepancies and confusions, as the oroarctic areas are included in the arctic tundra in some biogeographic maps and in the alpine tundra in others. Our analyses based on climate and vegetation criteria thus seem to resolve the long-standing biome

  20. Diurnal patterns of gas-exchange and metabolic pools in tundra plants during three phases of the arctic growing season

    PubMed Central

    Patankar, Rajit; Mortazavi, Behzad; Oberbauer, Steven F; Starr, Gregory

    2013-01-01

    Arctic tundra plant communities are subject to a short growing season that is the primary period in which carbon is sequestered for growth and survival. This period is often characterized by 24-h photoperiods for several months a year. To compensate for the short growing season tundra plants may extend their carbon uptake capacity on a diurnal basis, but whether this is true remains unknown. Here, we examined in situ diurnal patterns of physiological activity and foliar metabolites during the early, mid, and late growing season in seven arctic species under light-saturated conditions. We found clear diurnal patterns in photosynthesis and respiration, with midday peaks and midnight lulls indicative of circadian regulation. Diurnal patterns in foliar metabolite concentrations were less distinct between the species and across seasons, suggesting that metabolic pools are likely governed by proximate external factors. This understanding of diurnal physiology will also enhance the parameterization of process-based models, which will aid in better predicting future carbon dynamics for the tundra. This becomes even more critical considering the rapid changes that are occurring circumpolarly that are altering plant community structure, function, and ultimately regional and global carbon budgets. PMID:23467719

  1. Diurnal patterns of gas-exchange and metabolic pools in tundra plants during three phases of the arctic growing season.

    PubMed

    Patankar, Rajit; Mortazavi, Behzad; Oberbauer, Steven F; Starr, Gregory

    2013-02-01

    Arctic tundra plant communities are subject to a short growing season that is the primary period in which carbon is sequestered for growth and survival. This period is often characterized by 24-h photoperiods for several months a year. To compensate for the short growing season tundra plants may extend their carbon uptake capacity on a diurnal basis, but whether this is true remains unknown. Here, we examined in situ diurnal patterns of physiological activity and foliar metabolites during the early, mid, and late growing season in seven arctic species under light-saturated conditions. We found clear diurnal patterns in photosynthesis and respiration, with midday peaks and midnight lulls indicative of circadian regulation. Diurnal patterns in foliar metabolite concentrations were less distinct between the species and across seasons, suggesting that metabolic pools are likely governed by proximate external factors. This understanding of diurnal physiology will also enhance the parameterization of process-based models, which will aid in better predicting future carbon dynamics for the tundra. This becomes even more critical considering the rapid changes that are occurring circumpolarly that are altering plant community structure, function, and ultimately regional and global carbon budgets.

  2. Long-term experimental manipulation of winter snow regime and summer temperature in arctic and alpine tundra

    USGS Publications Warehouse

    Walker, M.D.; Walker, D.A.; Welker, J.M.; Arft, A.M.; Bardsley, T.; Brooks, P.D.; Fahnestock, J.T.; Jones, M.H.; Losleben, M.; Parsons, A.N.; Seastedt, T.R.; Turner, P.L.

    1999-01-01

    Three 60 m long, 2.8 m high snowfences have been erected to study long-term effects of changing winter snow conditions on arctic and alpine tundra. This paper describes the experimental design and short-term effects. Open-top fiberglass warming chambers are placed along the experimental snow gradients and in controls areas outside the fences; each warming plot is paired with an unwarmed plot. The purpose of the experiment is to examine short- and long-term changes to the integrated physical-biological systems under simultaneous changes of winter snow regime and summer temperature, as part of the Long-Term Ecological Research network and the International Tundra Experiment. The sites were at Niwot Ridge, Colorado, a temperate high altitude site in the Colorado Rockies, and Toolik Lake, Alaska, a high-latitude site. Initial results indicate that although experimental designs are essentially identical at the arctic and alpine sites, experimental effects are different. The drift at Niwot Ridge lasts much longer than do the Toolik Lake drifts, so that the Niwot Ridge fence affects both summer and winter conditions, whereas the Toolik Lake fence affects primarily winter conditions. The temperature experiment also differs in effect between the sites. Although the average temperature increase at the two sites is similar (daily increase 1.5oC at Toolik and 1.9oC at Niwot Ridge), at Toolik Lake there is only minor diurnal variation, whereas at Niwot Ridge the daytime increases are extreme on sunny days (as much as 7-10oC), and minimum nighttime temperatures in the chambers are often slightly cooler than ambient (by about 1oC). The experimental drifts resulted in wintertime increases in temperature and CO2 flux. Temperatures under the deep drifts were much more consistent and warmer than in control areas, and at Niwot Ridge remained very close to 0oC all winter. These increased temperatures were likely responsible for observed increases in system carbon loss. Initial changes

  3. Environmental effects on CO sub 2 efflux from water track and tussock tundra in arctic Alaska, U. S. A

    SciTech Connect

    Oberbauer, S.F. ); Tenhunen, J.D.; Reynolds, J.F. )

    1991-05-01

    CO{sub 2} efflux and variation in soil environmental characteristics were examined in two tundra vegetation communities, water track (a small drainage of intermittent water flow) and tussock tundra, in the northern foothills of the Philip Smith Mountains in arctic Alaska. Correlation analyses were performed on the observations made at six times during the growing season in order to evaluate the relationships between system CO{sub 2} loss and soil moisture, soil temperature, depth of thaw, and depth to the water table. The two sites differed significantly in terms of soil moisture, soil temperature, depth of thaw, and water table depth on several of the sampling dates. During four of the six measurement periods, the rate of CO{sub 2} efflux differed significantly between sites. Early in the season, respiration was greater in tussock tundra than at the water track, but later in the season, rates at the water track exceeded those at the tussock site. Highest rates were measured at the water track near mid-season. Efflux of CO{sub 2} at both sites was positively correlated with soil temperature. Soil surface (0-5 cm depth) environmental conditions were better predictors of CO{sub 2} efflux than were conditions measured at greater depth (5-10 cm). Soil moisture appeared to increase respiration between 100 and 700% of soil dry weight and decrease soil respiration at higher water contents. The effects of soil moisture were stronger in tussock tundra than in the water track community. These data suggest that both soil temperature and soil moisture limit CO{sub 2} efflux in water track and tussock tundra communities and that the relative importance of these factors changes throughout the growing season.

  4. Canopy Spectral Imaging (NDVI) As A Proxy For Shrub Biomass And Ecosystem Carbon Fluxes Across Arctic Tundra Habitats

    NASA Astrophysics Data System (ADS)

    Flower, C. E.; Welker, J. M.; Gonzalez-Meler, M. A.

    2015-12-01

    There is widespread consensus that climate change is contributing to rapid vegetation shifts in the ecologically sensitive Arctic tundra. These tussock grass dominated systems are shifting to tussock/woody shrub communities leading to likely alterations in carbon (C) sequestration and ecosystem productivity, which in turn can manifest in "greening" and changes in normalized difference vegetation index values (NDVI). While the expansion of woody vegetation is well established, our understanding of the ecosystem dynamics associated with this new habitat remain largely unknown. To untangle how the Arctic tundra may be impacted by these vegetation shifts we paired vegetation measurements (i.e. shrub biomass, leaf area, and shrub canopy area) and ecosystem C fluxes (e.g. net ecosystem exchange, NEE, and ecosystem respiration) with ground-level measurements of NDVI. Measurements were conducted at the Toolik Field Station in dry heath and moist acidic tundra habitats which are two primary habitat types on the North Slope of Alaska. We found strong positive relationships between shrub leaf area and biomass as well as shrub canopy area and biomass, relationships that were corroborated with NDVI measurements. This lends support for the use of NDVI as a proxy measurement of leaf area and shrub biomass. Additionally, NDVI was negatively correlated with ecosystem respiration across habitats, with respiratory fluxes consistently higher in the moist acidic relative to the dry heath tundra. Finally, we observed a significant positive nonlinear relationship between NEE and NDVI (R2~0.8; P<0.01). Shrub removal revealed that NEE was strongly controlled by woody shrubs. The positive relationship between NDVI and NEE highlights the potential shifts in the C balance of the Arctic tundra associated with woody encroachment. This increased plant productivity may offset greenhouse gas losses from permafrost degradation contributing some resilience to this system otherwise considered a

  5. Reproductive ecology of tundra swans on the Arctic National Wildlife Refuge, Alaska

    USGS Publications Warehouse

    Monda, Matthew J.; Ratti, John T.; McCabe, Thomas R.

    1994-01-01

    Management of tundra swans (Cygnus columbianus) is hampered by a lack of information on their nesting and brood-rearing ecology. We studied tundra swan nesting and brood-rearing ecology on the Arctic National Wildlife Refuge (ANWR), Alaska, 1988-90. Nest success was 58% (n = 31) in 1988, 83% (n = 36) in 1989, 84% (n = 43) in 1990, and 76% (n = 110) for the 3 years. Nests were located predominately in marshes dominated by sheathed pondweed (Potamogeton vaginatus), mare's tail (Hippuris vulgaris), and Hoppner sedge (Carex subspathacea), or by pendent grass (Arctophila fulva), water sedge (C. aquatilis), and tall cotton grass (Eriophorum angustifolium). Nests were seldom located in upland or partially vegetated habitats and were near coastal lagoons or large coastal lakes. Incubating swans were easily disturbed by ground observers and left their nests when we were 500-2,000 m from the nest. Swans did not cover eggs with nest material prior to departure; thus, eggs were vulnerable to avain predation and thermal stress. Brood-foraging sites on the Kongakut Delta (n = 41) were frequently in aquatic-marsh (59%) and saline graminoid-shrub (29%) habitats, occasionally in graminoid-marsh (7%) and partially vegetated (5%) habitats, and absent from upland, graminoid-shrub-water sedge, and graminoid-shrub-cotton grass habitats. Brood-foraging sites on the Canning Delta (n = 35) were frequently in graminoid-marsh (46%), graminoid-shrub-water sedge (26%), and aquatic-marsh (23%) habitats, occasionally in graminoid-shrub-cotton grass (3%) and upland habitats (3%), and absent from saline graminoid-shrub and partially vegetated habitats. Young cygnets grazed in terrestrial habitats more frequently than older broods on the Kongakut (P = 0.003) and Canning (P = 0.053) deltas. Wetlands with sheathed pondweed were uncommon but preferred by broods (P = 0.001). Using field experiments, we evaluated effects of swan grazing and fertilization from feces on aboveground biomass production and

  6. Recovery of arctic tundra from thermal erosion disturbance is constrained by nutrient accumulation: a modeling analysis.

    PubMed

    Pearce, A R; Rastetter, E B; Kwiatkowski, B L; Bowden, W B; Mack, M C; Jiang, Y

    2015-07-01

    Abstract. We calibrated the Multiple Element Limitation (MEL) model to Alaskan arctic tundra to simulate recovery of thermal erosion features (TEFs) caused by permafrost thaw and mass wasting. TEFs could significantly alter regional carbon (C) and nutrient budgets because permafrost soils contain large stocks of soil organic matter (SOM) and TEFs are expected to become more frequent as the climate warms. We simulated recovery following TEF stabilization and did not address initial, short-term losses of C and nutrients during TEF formation. To capture the variability among and within TEFs, we modeled a range of post-stabilization conditions by varying the initial size of SOM stocks and nutrient supply rates. Simulations indicate that nitrogen (N) losses after the TEF stabilizes are small, but phosphorus (P) losses continue. Vegetation biomass recovered 90% of its undisturbed C, N, and P stocks in 100 years using nutrients mineralized from SOM. Because of low litter inputs but continued decomposition, younger SOM continued to be lost for 10 years after the TEF began to recover, but recovered to about 84% of its undisturbed amount in 100 years. The older recalcitrant SOM in mineral soil continued to be lost throughout the 100-year simulation. Simulations suggest that biomass recovery depended on the amount of SOM remaining after disturbance. Recovery was initially limited by the photosynthetic capacity of vegetation but became co-limited by N and P once a plant canopy developed. Biomass and SOM recovery was enhanced by increasing nutrient supplies, but the magnitude, source, and controls on these supplies are poorly understood. Faster mineralization of nutrients from SOM (e.g., by warming) enhanced vegetation recovery but delayed recovery of SOM. Taken together, these results suggest that although vegetation and surface SOM on TEFs recovered quickly (25 and 100 years, respectively), the recovery of deep, mineral soil SOM took centuries and represented a major

  7. Acidobacteria dominate the active bacterial communities of Arctic tundra with widely divergent winter-time snow accumulation and soil temperatures.

    PubMed

    Männistö, Minna K; Kurhela, Emilia; Tiirola, Marja; Häggblom, Max M

    2013-04-01

    The timing and extent of snow cover is a major controller of soil temperature and hence winter-time microbial activity and plant diversity in Arctic tundra ecosystems. To understand how snow dynamics shape the bacterial communities, we analyzed the bacterial community composition of windswept and snow-accumulating shrub-dominated tundra heaths of northern Finland using DNA- and RNA-based 16S rRNA gene community fingerprinting (terminal restriction fragment polymorphism) and clone library analysis. Members of the Acidobacteria and Proteobacteria dominated the bacterial communities of both windswept and snow-accumulating habitats with the most abundant phylotypes corresponding to subdivision (SD) 1 and 2 Acidobacteria in both the DNA- and RNA-derived community profiles. However, different phylotypes within Acidobacteria were found to dominate at different sampling dates and in the DNA- vs. RNA-based community profiles. The results suggest that different species within SD1 and SD2 Acidobacteria respond to environmental conditions differently and highlight the wide functional diversity of these organisms even within the SD level. The acidic tundra soils dominated by ericoid shrubs appear to select for diverse stress-tolerant Acidobacteria that are able to compete in the nutrient poor, phenolic-rich soils. Overall, these communities seem stable and relatively insensitive to the predicted changes in the winter-time snow cover.

  8. Mercury dynamics of an arctic tundra ecosystem in northern Alaska: a mass balance

    NASA Astrophysics Data System (ADS)

    Obrist, D.; Helmig, D.; Agnan, Y.; Hedge, C.; Moore, C. W.; Paxton, D.; Hueber, J.

    2015-12-01

    To constrain the mercury (Hg) mass balance of a tundra ecosystem, we measured atmospheric mercury (Hg) concentrations and surface-atmosphere exchange at Toolik Field Station (68° 38' N) beginning September 2014. We also conducted automated measurements of gaseous Hg in soil pores and snow interstitial air to quantify gas exchange between soils, snow, and the atmosphere; and characterized wet and dry deposition and plant-derived Hg inputs. Results show that atmospheric Hg concentrations peak in winter, decrease in spring, and show summertime minima. Oxidized atmospheric Hg was below detection limits (0.05 ng m-3) indicating no significant dry deposition. Summertime minima of atmospheric Hg concentrations were associated with depositional fluxes of gaseous Hg (up to 2.8 ng m-2 hr-1; measured by a gradient method) that emerged after complete snowmelt. In contrast, gaseous Hg fluxes were below detection limits when snowpack was present; this was supported by in situ snowpack measurements and in contrast to commonly observed gaseous emissions from temperate snowpacks. The cumulative annual gaseous deposition flux of mercury was 12 µg m-2, in similar range as plant-derived inputs (17 µg m-2 yr-1) which we consider the major reason for observed gaseous Hg sink. Wet deposition was extremely low (<1 µg m-2 yr-1) compared to other sites. Hg concentrations in plants and soils are similar to levels found at temperate sites, but terrestrial pool sizes are large in comparison ranging around 400 g ha-1. The results suggest that: atmospheric Hg exposure is low at this site; that deposition is dominated by plant-derived deposition; and that significant Hg pools accumulate in tundra soils, likely driven by strong retention and low re-emissions after deposition. The high Hg soil pool sizes and key role of plant-productivity for Hg deposition may indicate a high sensitivity to climate change, in particular to permafrost soil thawing and increased growing season length.

  9. Interactions between spring temperatures and snow cover alter plant-soil nutrient feedbacks in moist acidic arctic tundra

    NASA Astrophysics Data System (ADS)

    Weintraub, M. N.; Steltzer, H.; Sullivan, P.; Darrouzet-Nardi, A.; Schimel, J.; Wallenstein, M. D.; Livensperger, C.; Segal, A. D.

    2012-12-01

    A significant spring warming trend has been observed across the arctic, resulting in higher spring temperatures and earlier snowmelt. These climate changes have the potential to alter arctic soil carbon (C) and nitrogen (N) dynamics because they can significantly influence both plant growth and decomposition during the growing season. These changes are of particular concern because arctic tundra soils contain large stores of C and may act as a significant CO2 source with warming. To determine how changes in the timing of snowmelt and higher spring temperatures affect plant growth and soil nutrient dynamics, we conducted a factorial accelerated snowmelt and warming experiment in a moist acidic tundra plant community in the Alaskan arctic. We measured changes plant phenology and growth, and soil nutrient dynamics in response to these manipulations to determine the implications of earlier snowmelt and warming. We hypothesized that accelerated snowmelt would allow plants to start growing earlier, resulting in earlier root growth and plant N uptake from these nutrient poor soils, potentially exacerbating N limitation to decomposer microorganisms and reducing their activities. Contrary to our predictions, we observed delayed and reduced root growth in response to accelerated snowmelt, without similar reductions in aboveground productivity. We also found that warming in combination with accelerated snowmelt alleviated the inhibition of root growth, suggesting that low air temperatures following snowmelt may have inhibited plant growth, as plants were unprotected from swings in air temperature without the insulating snowpack. Furthermore, we found that greater root growth was associated with elevated, not reduced, soil N availability, which was also opposite to our predictions. These results suggest that C-rich root exudates stimulate microbial N acquisition and can actually increase N availability even as roots and microbes are taking up more N. This implies that as long

  10. Effect of thaw depth on fluxes of CO₂ and CH₄ in manipulated Arctic coastal tundra of Barrow, Alaska.

    PubMed

    Kim, Yongwon

    2015-02-01

    Changes in CO₂ and CH₄ emissions represent one of the most significant consequences of drastic climate change in the Arctic, by way of thawing permafrost, a deepened active layer, and decline of thermokarst lakes in the Arctic. This study conducted flux-measurements of CO₂ and CH₄, as well as environmental factors such as temperature, moisture, and thaw depth, as part of a water table manipulation experiment in the Arctic coastal plain tundra of Barrow, Alaska during autumn. The manipulation treatment consisted of draining, controlling, and flooding treated sections by adjusting standing water. Inundation increased CH₄ emission by a factor of 4.3 compared to non-flooded sections. This may be due to the decomposition of organic matter under a limited oxygen environment by saturated standing water. On the other hand, CO₂ emission in the dry section was 3.9-fold higher than in others. CH₄ emission tends to increase with deeper thaw depth, which strongly depends on the water table; however, CO₂ emission is not related to thaw depth. Quotients of global warming potential (GWPCO₂) (dry/control) and GWPCH₄ (wet/control) increased by 464 and 148%, respectively, and GWPCH₄ (dry/control) declined by 66%. This suggests that CO₂ emission in a drained section is enhanced by soil and ecosystem respiration, and CH₄ emission in a flooded area is likely stimulated under an anoxic environment by inundated standing water. The findings of this manipulation experiment during the autumn period demonstrate the different production processes of CO₂ and CH₄, as well as different global warming potentials, coupled with change in thaw depth. Thus the outcomes imply that the expansion of tundra lakes leads the enhancement of CH₄ release, and the disappearance of the lakes causes the stimulated CO₂ production in response to the Arctic climate change.

  11. Multi-annual Turbulent Energy Fluxes in the Lena River Delta: Eddy Covariance and Remote Sensing in Siberian Arctic Tundra

    NASA Astrophysics Data System (ADS)

    Runkle, B.; Wille, C.; Langer, M.; Boike, J.; Sachs, T.; Pfeiffer, E. M.; Kutzbach, L.

    2015-12-01

    Evapotranspiration (ET) is a key component of the energy and water balances in permafrost tundra, establishing hydrological conditions for the next year and controlling several aspects of the carbon cycle. Both the energy balance and hydrological conditions of the landscape surface are important drivers of how Arctic climate change will impact landscape processes, including the carbon feedback. The accurate measurement of evapotranspiration within an energy balance context therefore provides crucial information on ecosystem functioning and raises our predictive capacity for estimating the impact of climate change. In this study we report field measurements from 13 summers (2002-14) using the eddy covariance method in a lowland ice-wedge polygon landscape within Russia's Lena River Delta. These time-series are gap-filled and extrapolated with both statistical and process-based models to generate estimates of growing season ET. We find that interannual differences - including two August periods with high ET and two with low ET - are locally driven more by changes in air temperature and vapor pressure deficit (VPD) than in land surface characteristics or radiation. Except for periods of high VPD, aerodynamic resistance was greater than canopy surface resistance. We explore predictive relationships between various land surface indicators (e.g., NDVI, LAI, LST, Growing season length) derived from remote sensing products (MODIS) to quantify local mechanisms necessary for upscaling to the Delta region. Nighttime land surface temperature (MODIS) is found to be a strong predictor of evaporative flux at weekly to monthly time scales. Contrary to expectations resulting from climate change studies, we do not see evidence of a sustained interannual trend in ET or sensible heat flux. We conclude with implications for the local energy balance and responses to changes in sea ice extent and a warming climate.

  12. Arctic tundra vegetation functional types based on photosynthetic physiology and optical properties

    NASA Astrophysics Data System (ADS)

    Huemmrich, K. F.; Gamon, J. A.; Tweedie, C. E.

    2011-12-01

    Climate change in tundra regions may alter vegetation species composition and ecosystem carbon balance, and remote sensing provides critical tools for monitoring these changes. Measurements of pure patches of key plant functional types (lichens, mosses, and vascular plants) in sedge tundra at Barrow AK, show three different values of light use efficiency (LUE). Also, discriminant analysis of patch reflectance identifies seven spectral bands that can separate each functional type and nongreen material (bare soil and dead leaves). These results were tested along a 100 m transect across the tundra. At every meter, midsummer spectral reflectance and vegetation coverage were measured. LUE estimated from coverage fractions varies widely, even over short distances. The patch-level discriminant functions successfully unmixed cover fractions of the functional types, with standard errors well within the expected measurement error of the coverage. These results demonstrate the use of hyperspectral remote sensing to provide direct estimates of tundra ecosystem LUE variability.

  13. Microclimate of Arctic Tree Line 2. Soil Microclimate of Tundra and Forest

    NASA Astrophysics Data System (ADS)

    Rouse, Wayne R.

    1984-01-01

    Forest and tundra soils display distinctive microclimates for a climatically normal year at Churchill. Forest soils are substantially warmer in the active layer than those of the tundra but the tundra active layer is deeper. Forest soils are much wetter than those of the tundra. This results from the deep winter snow pack, which provides abundant meltwater to already thawed soils. The soils remain wet throughout the year, and the large latent heat release delays the freezing of forest soils until a snow pack is established. As a result, soils stay relatively warm throughout winter and thaw rapidly and deeply before snow pack melting in the spring. The thaw period in the tree rooting zone is about 6 months, compared to 4 months at the same depth in tundra. The magnitude of soil heat storage is large, comprising 18% and 16% of net radiation in tundra and forest, respectively, during the thaw season. During freeze back it is the dominant heat exchange process. Between 80% and 90% of the total soil heat storage is involved in the latent heat exchange accompanying thawing and freezing. Soil heat flux plates strongly underestimate the ground heat exchange and are unreliable in permafrost terrain.

  14. Isotopic identification of soil and permafrost nitrate sources in an Arctic tundra ecosystem

    SciTech Connect

    Heikoop, Jeffrey M.; Throckmorton, Heather M.; Newman, Brent D.; Perkins, George B.; Iversen, Colleen M.; Chowdhury, Taniya Roy; Romanovsky, Vladimir E.; Graham, David E.; Norby, Richard J.; Wilson, Cathy J.; Wullschleger, Stan D.

    2015-06-08

    The nitrate (NO₃⁻) dual isotope approach was applied to snowmelt, tundra active layer pore waters, and underlying permafrost in Barrow, Alaska, USA, to distinguish between NO₃⁻ derived from at NO₃⁻ signal with δ¹⁵N averaging –4.8 ± 1.0‰ (standard error of the mean) and δ¹⁸O averaging 70.2 ±1.7‰. In active layer pore waters, NO₃⁻ primarily occurred at concentrations suitable for isotopic analysis in the relatively dry and oxic centers of high-centered polygons. The average δ¹⁵N and δ¹⁸O of NO₃⁻ from high-centered polygons were 0.5 ± 1.1‰ and –4.1 ± 0.6‰, respectively. When compared to the δ¹⁵N of reduced nitrogen (N) sources, and the δ¹⁸O of soil pore waters, it was evident that NO₃⁻ in high-centered polygons was primarily from microbial nitrification. Permafrost NO₃⁻ had δ¹⁵N ranging from approximately –6‰ to 10‰, similar to atmospheric and microbial NO₃⁻, and highly variable δ¹⁸O ranging from approximately –2‰ to 38‰. Permafrost ice wedges contained a significant atmospheric component of NO₃⁻, while permafrost textural ice contained a greater proportion of microbially derived NO₃⁻. Large-scale permafrost thaw in this environment would release NO₃⁻ with a δ¹⁸O signature intermediate to that of atmospheric and microbial NO₃. Consequently, while atmospheric and microbial sources can be readily distinguished by the NO₃⁻ dual isotope technique in tundra environments, attribution of NO₃⁻ from thawing permafrost will not be straightforward. The NO₃⁻ isotopic signature, however, appears useful in identifying NO₃⁻ sources in extant permafrost ice.

  15. Isotopic identification of soil and permafrost nitrate sources in an Arctic tundra ecosystem

    DOE PAGES

    Heikoop, Jeffrey M.; Throckmorton, Heather M.; Newman, Brent D.; ...

    2015-06-08

    The nitrate (NO₃⁻) dual isotope approach was applied to snowmelt, tundra active layer pore waters, and underlying permafrost in Barrow, Alaska, USA, to distinguish between NO₃⁻ derived from at NO₃⁻ signal with δ¹⁵N averaging –4.8 ± 1.0‰ (standard error of the mean) and δ¹⁸O averaging 70.2 ±1.7‰. In active layer pore waters, NO₃⁻ primarily occurred at concentrations suitable for isotopic analysis in the relatively dry and oxic centers of high-centered polygons. The average δ¹⁵N and δ¹⁸O of NO₃⁻ from high-centered polygons were 0.5 ± 1.1‰ and –4.1 ± 0.6‰, respectively. When compared to the δ¹⁵N of reduced nitrogen (N) sources,more » and the δ¹⁸O of soil pore waters, it was evident that NO₃⁻ in high-centered polygons was primarily from microbial nitrification. Permafrost NO₃⁻ had δ¹⁵N ranging from approximately –6‰ to 10‰, similar to atmospheric and microbial NO₃⁻, and highly variable δ¹⁸O ranging from approximately –2‰ to 38‰. Permafrost ice wedges contained a significant atmospheric component of NO₃⁻, while permafrost textural ice contained a greater proportion of microbially derived NO₃⁻. Large-scale permafrost thaw in this environment would release NO₃⁻ with a δ¹⁸O signature intermediate to that of atmospheric and microbial NO₃. Consequently, while atmospheric and microbial sources can be readily distinguished by the NO₃⁻ dual isotope technique in tundra environments, attribution of NO₃⁻ from thawing permafrost will not be straightforward. The NO₃⁻ isotopic signature, however, appears useful in identifying NO₃⁻ sources in extant permafrost ice.« less

  16. Annual patterns and budget of CO2 flux in an Alaskan arctic tussock tundra ecosystem at Atqasuk, Alaska

    NASA Astrophysics Data System (ADS)

    Oechel, W. C.; Kalhori, A. A.; Burba, G. G.; Gioli, B.

    2013-12-01

    Arctic ecosystem functioning is not only critically affected by climate change, but also has the potential for major positive feedbacks on climate. There is however relatively little information available on the role, patterns, and vulnerabilities of CO2 fluxes during the non-summer seasons. Presented here is a year-around study of CO2 fluxes in an Alaskan Arctic tussock tundra ecosystem. Also presented are key environmental controls on CO2 fluxes as well as possible impacts of likely changes in season timing. This is aided by a new empirical quantification of seasons in the Arctic based on net radiation, which can help describe seasonal responses to greenhouse gas fluxes under climate change. The fluxes were computed using standard FluxNet methodology and corrected using standard WPL density terms, adjusted for influences of instrument surface heating. The results showed that the non-summer season comprises a significant source of carbon to the atmosphere. The summer period was a net sink of 10.83 g C m-2 yr-1, while the non-summer seasons released more than four times the CO2 uptake observed in the summer, resulting in a net annual source of 37.6 g C m-2 yr-1 to the atmosphere. This shows a change in this region of the Arctic from a long-term annual sink of CO2 from the atmosphere to an annual source of CO2 from the terrestrial ecosystem and soils to the atmosphere. The results presented here demonstrate that nearly continuous observations may be required in order to accurately calculate the annual NEE of Arctic ecosystems, and to build predictive understanding that can be used to estimate, with confidence, Arctic fluxes under future conditions. Daily CO2 fluxes over the year, average daily net radiation, average daily PAR, average daily air temperature and average daily soil respiration (at -5 cm).

  17. Aboveground and belowground responses to nutrient additions and herbivore exclusion in Arctic tundra ecosystems in northern Alaska

    NASA Astrophysics Data System (ADS)

    Moore, J. C.; Gough, L.; Simpson, R.; Johnson, D. R.

    2011-12-01

    The Arctic has experienced significant increased regional warming over the past 30 years. Warming generally increases tundra soil nutrient availability by creating a more favorable environment for plant growth, decomposition and nutrient mineralization. Aboveground there has been a "greening" of the Arctic with increased net primary productivity (NPP), and an increase in woody vegetation. Concurrent with the changes aboveground has been an increase in root growth at lower depths and a loss of soil organic C (40 -100 g C m-2 yr-1). Given that arctic soils contain 14% of the global soil C pool, understanding the mechanisms behind shifts of this magnitude that are changing arctic soils from a net sink to a net source of atmospheric C is critical. We took an integrated multi-trophic level approach to examine how altering soil nutrients and mammalian herbivore activity affects vegetation, soil fauna, and microbial communities as well as soil physical characteristics in moist acidic (MAT) and dry heath (DH) tundra. Our work was conducted at the Arctic LTER site in northern Alaska. We sampled the nutrient (controls and annual N+P additions) and herbivore (controls and exclosures) manipulations established in 1996 after 10 years of treatment. Models that incorporated the biomass estimates from the field were used to characterize the trophic structure of the belowground food web and to estimate carbon flux among soil organisms and C-mineralization rates. Both MAT and DH exhibited significant increases in NPP and root growth and changes in vegetation structure with transitions from a mixed community to deciduous shrubs in MAT and from lichens to grasses and shrubs in DH, with nutrient additions and herbivore exclosures. Belowground responses to the treatments were dependent on ecosystem type, but exposed alterations in trophic structure that included changes in microbial biomass, the establishment of microbivorous enchytreaids, increases in root-feeding nematodes, and

  18. Net carbon exchange across the Arctic tundra-boreal forest transition in Alaska 1981-2000

    USGS Publications Warehouse

    Thompson, Catharine Copass; McGuire, A.D.; Clein, J.S.; Chapin, F. S.; Beringer, J.

    2006-01-01

    Shifts in the carbon balance of high-latitude ecosystems could result from differential responses of vegetation and soil processes to changing moisture and temperature regimes and to a lengthening of the growing season. Although shrub expansion and northward movement of treeline should increase carbon inputs, the effects of these vegetation changes on net carbon exchange have not been evaluated. We selected low shrub, tall shrub, and forest tundra sites near treeline in northwestern Alaska, representing the major structural transitions expected in response to warming. In these sites, we measured aboveground net primary production (ANPP) and vegetation and soil carbon and nitrogen pools, and used these data to parameterize the Terrestrial Ecosystem Model. We simulated the response of carbon balance components to air temperature and precipitation trends during 1981-2000. In areas experiencing warmer and dryer conditions, Net Primary Production (NPP) decreased and heterotrophic respiration (R H ) increased, leading to a decrease in Net Ecosystem Production (NEP). In warmer and wetter conditions NPP increased, but the response was exceeded by an increase in R H ; therefore, NEP also decreased. Lastly, in colder and wetter regions, the increase in NPP exceeded a small decline in R H , leading to an increase in NEP. The net effect for the region was a slight gain in ecosystem carbon storage over the 20 year period. This research highlights the potential importance of spatial variability in ecosystem responses to climate change in assessing the response of carbon storage in northern Alaska over the last two decades. ?? Springer 2005.

  19. Controls over nutrient flow through plants and microbes in Arctic tundra. Final technical report

    SciTech Connect

    Chapin, F.S. III

    1995-01-01

    We successfully developed a series of models to explore the importance of species differences in phenologies of growth and nitrogen uptake to competitive interactions in upland tussock tundra. We developed growth models for 4 major tussock tundra species, based on observed growth rates and phenologies. We found that differences in phenology and nutrient use strategy could permit coexistence of some, but not all of the tundra plants modeled. The plant that was the best competitor, because of its rapid growth rate and superior ability to retranslocate nitrogen, may be naturally limited in its competitive ability by its tussock growth form. The mechanisms behind this limitation, and the contributions of patterns of mortality to observed production, will be explored in future modeling and experimental studies. In addition, our models point out that our understanding of the dynamics of nitrogen supply is still inadequate.

  20. Estimation of surface energy fluxes in the Arctic tundra using the remote sensing thermal-based Two-Source Energy Balance model

    NASA Astrophysics Data System (ADS)

    Cristóbal, Jordi; Prakash, Anupma; Anderson, Martha C.; Kustas, William P.; Euskirchen, Eugénie S.; Kane, Douglas L.

    2017-03-01

    The Arctic has become generally a warmer place over the past decades leading to earlier snow melt, permafrost degradation and changing plant communities. Increases in precipitation and local evaporation in the Arctic, known as the acceleration components of the hydrologic cycle, coupled with land cover changes, have resulted in significant changes in the regional surface energy budget. Quantifying spatiotemporal trends in surface energy flux partitioning is key to forecasting ecological responses to changing climate conditions in the Arctic. An extensive local evaluation of the Two-Source Energy Balance model (TSEB) - a remote-sensing-based model using thermal infrared retrievals of land surface temperature - was performed using tower measurements collected over different tundra types in Alaska in all sky conditions over the full growing season from 2008 to 2012. Based on comparisons with flux tower observations, refinements in the original TSEB net radiation, soil heat flux and canopy transpiration parameterizations were identified for Arctic tundra. In particular, a revised method for estimating soil heat flux based on relationships with soil temperature was developed, resulting in significantly improved performance. These refinements result in mean turbulent flux errors generally less than 50 W m-2 at half-hourly time steps, similar to errors typically reported in surface energy balance modeling studies conducted in more temperate climatic regimes. The MODIS leaf area index (LAI) remote sensing product proved to be useful for estimating energy fluxes in Arctic tundra in the absence of field data on the local biomass amount. Model refinements found in this work at the local scale build toward a regional implementation of the TSEB model over Arctic tundra ecosystems, using thermal satellite remote sensing to assess response of surface fluxes to changing vegetation and climate conditions.

  1. Spatial variation in landscape-level CO2 and CH4 fluxes from arctic coastal tundra: influence from vegetation, wetness, and the thaw lake cycle.

    PubMed

    Sturtevant, Cove S; Oechel, Walter C

    2013-09-01

    Regional quantification of arctic CO2 and CH4 fluxes remains difficult due to high landscape heterogeneity coupled with a sparse measurement network. Most of the arctic coastal tundra near Barrow, Alaska is part of the thaw lake cycle, which includes current thaw lakes and a 5500-year chronosequence of vegetated thaw lake basins. However, spatial variability in carbon fluxes from these features remains grossly understudied. Here, we present an analysis of whole-ecosystem CO2 and CH4 fluxes from 20 thaw lake cycle features during the 2011 growing season. We found that the thaw lake cycle was largely responsible for spatial variation in CO2 flux, mostly due to its control on gross primary productivity (GPP). Current lakes were significant CO2 sources that varied little. Vegetated basins showed declining GPP and CO2 sink with age (R(2) = 67% and 57%, respectively). CH4 fluxes measured from a subset of 12 vegetated basins showed no relationship with age or CO2 flux components. Instead, higher CH4 fluxes were related to greater landscape wetness (R(2) = 57%) and thaw depth (additional R(2) = 28%). Spatial variation in CO2 and CH4 fluxes had good satellite remote sensing indicators, and we estimated the region to be a small CO2 sink of -4.9 ± 2.4 (SE) g C m(-2) between 11 June and 25 August, which was countered by a CH4 source of 2.1 ± 0.2 (SE) g C m(-2) . Results from our scaling exercise showed that developing or validating regional estimates based on single tower sites can result in significant bias, on average by a factor 4 for CO2 flux and 30% for CH4 flux. Although our results are specific to the Arctic Coastal Plain of Alaska, the degree of landscape-scale variability, large-scale controls on carbon exchange, and implications for regional estimation seen here likely have wide relevance to other arctic landscapes.

  2. Soil and Plant Mercury Concentrations and Pools in the Arctic Tundra of Northern Alaska by Hedge Christine, Obrist Daniel, Agnan Yannick, Moore Christopher, Biester Harald, Helmig Detlev

    NASA Astrophysics Data System (ADS)

    Hedge, C.; Agnan, Y.

    2015-12-01

    We present vegetation, soil and runoff mercury (Hg) concentrations and pool sizes in vegetation and soils at several arctic tundra sites, an area that represents <7 x 106 km2 of land surface globally. The primary measurement location is at Toolik Field Station (TFS, 68° 38' N) in northern Alaska, with additional samples collected along a transect from TFS to the Arctic Ocean, and in Noatak National Preserve to be collected in August 2015. Soil and vegetation samples from all sites will be analyzed for total Hg concentration, pH, soil texture, bulk density, soil moisture content, organic and total carbon (C), nitrogen, along with major and trace elements. Initial results already obtained from TFS (characterized as moist to wet tundra with Typic Aquiturbel soils) show Hg concentrations in tundra vegetation (112±15 μg kg-1) and organic soil (140±8 μg kg-1) similar to those found in temperate sites. Calculation of plant-based Hg deposition rates by litterfall of 17.3 μg kg-1 yr-1 were surprisingly high, exceeding all other Hg deposition fluxes at this site. Hg concentrations in mineral soils (95±3 μg kg-1) were 2-3 times higher than those found at temperate sites. Hg concentrations showed weak relationships to organic C concentrations contrasting patterns from temperate soils where concentrations typically decline with depth following lower organic carbon contents. In fact, vertical mass profiles of Hg showed a strong increase with depth, with mineral layers storing over 90% (200-500 g ha-1) of Hg within these soils. A principle component analysis including major and trace elements indicated that soil Hg was not of lithogenic origin but from atmospheric sources, possibly by long-range transport. Carbon-14 dating results showed over 7,000 years old organic carbon in mineral soils of the active layer where highest concentrations of soil Hg were observed, suggesting long term retention of atmospheric Hg. These patterns suggest vertical translocation of Hg from the

  3. DIFFERENTIATION IN N15 UPTAKE AND THE ORGANIZATION OF AN ARCTIC TUNDRA PLANT COMMUNITY

    EPA Science Inventory

    We used N15 soil-labeling techniques to examine how the dominant species in a N-limited, tussock tundra plant community partitioned soil N, and how such partitioning may contribute to community organization. The five most abundant species were well differentiated with respect to...

  4. Correlations between the Heterogeneity of Permafrost Thaw Depth and Vegetation in Boreal Forests and Arctic Tundra in Alaska.

    NASA Astrophysics Data System (ADS)

    Uy, K. L. Q.; Natali, S.; Kholodov, A. L.; Loranty, M. M.

    2015-12-01

    Global climate change induces rapid large scale changes in the far Northern regions of the globe, which include the thickening of the active layer of arctic and subarctic soils. Active layer depth, in turn, drives many changes to the hydrology and geochemistry of the soil, making an understanding of this layer essential to boreal forest and arctic tundra ecology. Because the structure of plant communities can affect the thermal attributes of the soil, they may drive variations in active layer depth. For instance, trees and tussocks create shade, which reduces temperatures, but also hold snow, which increases temperature through insulation; these aspects of vegetation can increase or decrease summer thaw. The goal of this project is to investigate correlations between the degree of heterogeneity of active layer depths, organic layer thickness, and aboveground vegetation to determine how these facets of Northern ecosystems interact at the ecosystem scale. Permafrost thaw and organic layer depths were measured along 20m transects in twenty-four boreal forest and tundra sites in Alaska. Aboveground vegetation along these transects was characterized by measuring tree diameter at breast height (DBH), tussock dimensions, and understory biomass. Using the coefficient of variation as a measure of heterogeneity, we found a positive correlation between thaw depth variability and tussock volume variability, but little correlation between the former and tree DBH variability. Soil organic layer depth variability was also positively correlated with thaw depth variability, but weakly correlated with tree and tussock heterogeneity. These data suggest that low vegetation and organic layer control the degree of variability in permafrost thaw at the ecosystem scale. Vegetation can thus affect the microtopography of permafrost and future changes in the plant community that affect vegetation heterogeneity will drive corresponding changes in the variability of the soil.

  5. Monitoring ecosystem dynamics in an Arctic tundra ecosystem using hyperspectral reflectance and a robotic tram system

    NASA Astrophysics Data System (ADS)

    Goswami, Santonu

    ) Is NDVI a good predictor for aboveground biomass and leaf area index (LAI) for plant species that are common in an arctic landscape? (4) How can cyberinfrastructure tools be developed to optimize ground-based remote sensing data collection, management and processing associated with a large scale experimental infrastructure? The Biocomplexity project experimentally manipulated the water table (drained, flooded, and control treatments) of a vegetated thaw lake basin to investigate the effects of altered hydrology on land-atmosphere carbon balance. In each experimental treatment, hyperspectral reflectance data were collected in the visible and near IR range of the spectrum using a robotic tram system that operated along a 300m tramline during the snow free growing period between June and August 2005-09. Water table depths (WTD) and soil volumetric water content were also collected along these transects. During 2005-2007, measurements were made without experimental treatments. Experimental treatments were run in 2008 and 2009, which involved water table being raised (+10cm) and lowered (-10cm) in flooding and draining treatments respectively. A new spectral index, the normalized difference surface water index (NDSWI) was developed and tested at multiple spatial and temporal scales. NDSWI uses the 460nm (blue) and 1000nm (IR) bands and was to capture surface hydrological dynamics in the study area using the robotic tram system. When applied to high spatial resolution satellite imagery, NDSWI was also able to capture changes in surface hydrology at the landscape scale. Interannual patterns of land-surface phenology (measured with the normalized difference vegetation index - NDVI) unexpectedly lacked marked differences under experimental conditions. Measurement of NDVI was, however, compromised when WTD was above ground level. NDVI and NDSWI were negatively correlated when WTD was above ground level, which held when scaled to MODIS imagery collected from satellite

  6. The Role of Explicitly Modeling Bryophytes in Simulating Carbon Exchange and Permafrost Dynamics of an Arctic Coastal Tundra at Barrow, Alaska

    NASA Astrophysics Data System (ADS)

    Yuan, F.; Thornton, P. E.; McGuire, A. D.; Oechel, W. C.; Yang, B.; Tweedie, C. E.; Rogers, A.; Norby, R. J.

    2013-12-01

    Bryophyte cover is greater than 50% in many Arctic tundra ecosystems. In regions of the Arctic where shrubs are expanding it is expected that bryophyte cover will be substantially reduced. Such a loss in cover could influence the hydrological, biogeochemical, and permafrost dynamics of Arctic tundra ecosystems. The explicit representation of bryophyte physiological and biophysical processes in large-scale ecological and land surface models is rare, and we hypothesize that the representation of bryophytes has consequences for estimates of the exchange of water, energy, and carbon by these models. This study explicitly represents the effects of bryophyte function and structure on the exchange of carbon (e.g., summer photosynthesis effects) and energy (e.g., summer insulation effects) with the atmosphere in the Community Land Model (CLM-CN). The modified model was evaluated for its ability to simulate C exchange, soil temperature, and soil moisture since the 1970s at Barrow, Alaska through comparison with data from AmeriFlux sites, USDA Soil Climate Networks observation sites at Barrow, and other sources. We also compare the outputs of the CLM-CN simulations with those of the recently developed Dynamical Organic Soil coupled Terrestrial Ecosystem Model (DOS-TEM). Overall, our evaluation indicates that bryophytes are important contributors to land-atmospheric C exchanges in Arctic tundra and that they play an important role to permafrost thermal and hydrological processes which are critical to permafrost stability. Our next step in this study is to examine the climate system effects of explicitly representing bryophyte dynamics in the land surface model. Key Words: Bryophytes, Arctic coastal tundra, Vegetation composition, Net Ecosystem Exchange, Permafrost, Land Surface Model, Terrestrial Ecosystem Model

  7. Controls over nutrient flow through plants and microbes in Arctic tundra

    SciTech Connect

    Chapin, F.S. III.

    1991-01-01

    During 1990, we worked primarily on two major projects. The first was a field study of {sup 15}N partitioning between plants and microbes at Imnavait Creek. {sup 15}N was absorbed faster on the tundra than in temperate climates, and release of labeled nitrogen occurs much more slowly, indicating a slow turnover. The second major project was a model of nutrient uptake by {und Eriophorum vaginatum}. The major effort for 1991 will be on continued model development to match model predictions with results of current field work. Also scheduled for 1991 is completion of field work with {und E. vaginatum} and related soils. This should provide validation of the applicability of R4D concepts to anthropogenic disturbances in tundra. 5 figs. (MHB)

  8. Intense, natural pollution affects Arctic tundra vegetation at the Smoking Hills, Canada

    SciTech Connect

    Freedman, B. ); Zobens, V.; Hutchinson, T.C.; Gizyn, W.I. )

    1990-04-01

    Long-term, natural emissions of sulfur dioxide and acidic aerosols have had an impact on remote tundra at the Smoking Hills. The emissions have caused plant damage by SO{sub 2} toxicity, and have severely acidified soil and freshwater. At the most intensively fumigated locations closest to the sources of emission, pollution stresses have devegetated the terrestrial ecosystem. The first plants that are encountered along a spatial gradient of decreasing pollution stress are Artemisia tilesii and Arctagrostis latifolia, which dominate a characteristic, pollution-tolerant community. Farther away at moderately polluted sites there are mixed communities with floristic elements of both fumigated and reference, unfumigated tundra. This pattern of ecosystem response to a concatenation of stresses caused by natural air and soil pollution is qualitatively similar to the damage that occurs in the vicinity of anthropogenic point sources of air pollution, such as smelters.

  9. Sphingoaurantiacus polygranulatus gen. nov., sp. nov., isolated from high-Arctic tundra soil, and emended descriptions of the genera Sandarakinorhabdus, Polymorphobacter and Rhizorhabdus and the species Sandarakinorhabdus limnophila, Rhizorhabdus argentea and Sphingomonas wittichii.

    PubMed

    Kim, MyongChol; Kang, OkChol; Zhang, Yumin; Ren, Lvzhi; Chang, Xulu; Jiang, Fan; Fang, Chengxiang; Zheng, Congyi; Peng, Fang

    2016-01-01

    An orange, Gram-reaction-negative and aerobic bacterium, designated MC 3718T, was isolated from a tundra soil near Ny-Ålesund, Svalbard archipelago, Norway (78° N). The cells were motile with either a polar or a subpolar flagellum and reproduced by budding or asymmetrical cell division. Growth occurred at 4-37 °C (optimum 28-30 °C) and at pH 6.0-10.0 (optimum pH 9.0). Many cells accumulated poly-β-hydroxybutyrate granules and contained a single large polyphosphate granule at a pole or in the middle of the cell. Cell walls contained meso-diaminopimelic acid as the diagnostic diamino acid, and ubiquinone 10 was the main respiratory quinone. Strain MC 3718T contained summed feature 3 (comprising C16 : 1ω7c and/or C16 : 1ω6c; 29.49 %), summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c; 29.38 %), C17 : 1ω6c (10.15 %), C14 : 0 2-OH (9.05 %) and C16 : 0 (6.84 %) as the major cellular fatty acids. The main polar lipids were two sphingoglycolipids, phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, three unknown phospholipids and two unknown polar lipids. Carotenoids were detected. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain MC 3718T belonged to the family Sphingomonadaceae. The DNA G+C content was 67.2 mol%. On the basis of phenotypic, chemotaxonomic and phylogenetic data, strain MC 3718T is considered to represent a novel genus and species in the family Sphingomonadaceae, for which the name Sphingoaurantiacus polygranulatus gen. nov., sp. nov. is proposed. The type strain of Sphingoaurantiacus polygranulatus is MC 3718T ( = CCTCC AB 2014274T = LMG 28636T). Emended descriptions of the genera Sandarakinorhabdus, Polymorphobacter and Rhizorhabdus and the species Sandarakinorhabdus limnophila, Rhizorhabdus argentea and Sphingomonas wittichii are also provided.

  10. RECONSTRUCTION AND ANALYSIS OF HISTORICAL CHANGES IN CARBON STORAGE IN ARCTIC TUNDRA

    EPA Science Inventory

    Surface air temperature in arctic regions has increased since pre-industrial times, raising concerns that warmer and possibly drier conditions have increased soil decomposition rates, thereby stimulating the release to the atmosphere of the large stores of carbon (C) in arctic so...

  11. Observed and Potential Responses of Upland Tundra Ecosystems to a Changing Climate: Results from the Arctic Long-Term Ecological Research Project, North Slope, Alaska, USA

    NASA Astrophysics Data System (ADS)

    Bowden, W. B.

    2014-12-01

    The Arctic is one of the most rapidly changing biomes on earth. Research at the Toolik Field Station by the Arctic Long-Term Ecological Research project provides a perspective on changes that are impacting the upland tussock tundra region of the North Slope of Alaska, a region that is typical of ~15% of the arctic region. The arctic is responding to a combination of long-term, gradual changes (presses) and short-term, event-driven changes (pulses). The most important press, of course, is the persistent rise in average annual air temperature observed in most places (though not at Toolik). Associated with this increase in SAT is a well-documented increase in shallow permafrost temperature (which is observed around Toolik). Our long-term research shows that this trend will favor taller and more productive shrub and grass vegetation. Higher SAT translates to earlier spring breakup and later onset of winter. This change in seasonality is affecting interactions between shrub leaf-out, insect emergence, and bird nesting. Persistent and more frequent droughts are having important impacts on the ability of Arctic grayling - the top consumer is most upland tundra streams - to survive and has the potential to block their ability to migrate to essential overwintering lakes. The interaction between temperature (which is changing) and light (which is not) creates a "seasonal asynchrony" that may be increasing the loading of nutrients - notably nitrate - to upland tundra streams late in the season, with impacts that we do not fully understand yet. The upland tundra environment is also responding to an increasing frequency of pulses, most notably wildfires and the development of thermo-erosional failures (TEFs). Wildfires transfer large quantities of carbon and nitrogen directly to the atmosphere. TEFs may deliver large quantities of sediment and nutrients to streams and lakes. Currently these pulse disturbances seem to be having only limited, local impacts. However, as shallow

  12. Photosynthetic Characterization of Plant Functional Types from Coastal Tundra to Improve Representation of the Arctic in Earth System Models

    NASA Astrophysics Data System (ADS)

    Rogers, A.; Xu, C.; McDowell, N. G.; Sloan, V. L.; Norby, R. J.

    2012-12-01

    The primary goal of Earth System Models (ESMs) is to improve understanding and projection of future global change. In order to do this they must accurately represent the carbon fluxes associated with the terrestrial carbon cycle. Photosynthetic CO2 uptake is well described by the Farquhar, von Caemmerer and Berry model of photosynthesis, and most ESMs use a derivation of this model. One of the key parameters required by the Farquhar, von Caemmerer and Berry model is an estimate of the maximum rate of carboxylation by the enzyme Rubisco (Vc,max). In ESMs the parameter Vc,max is usually fixed for a given plant functional type (PFT) and often estimated from the empirical relationship between leaf N content and Vc,max. However, uncertainty in the estimation of Vc,max has been shown to account for significant variation in model estimation of gross primary production, particularly in the Arctic. As part of a new multidisciplinary project to improve the representation of the Arctic in ESMs (Next Generation Ecosystem Experiments - Arctic) we have begun to characterize photosynthetic parameters and N acquisition in the key Arctic PFTs. We measured the response of photosynthesis (A) to internal CO2 concentration (ci) in situ in two sedges (Carex aquatilis, Eriophorum angustifolium), a grass (Dupontia fisheri) and a forb (Petasites frigidus) growing on the Barrow Environmental Observatory, Barrow, AK. The values of Vc,max (normalized to 25oC) currently used to represent Arctic PFTs in ESMs are approximately half of the values we measured in these species in July, 2012, on the coastal tundra in Barrow. We hypothesize that these plants have a greater fraction of leaf N invested in Rubisco (FLNR) than is assumed by the models. The parameter Vc,max is used directly as a driver for respiration in some ESMs, and in other ESMs Vc,max is linked to leaf N content and N acquisition through FLNR. Therefore, these results have implications for ESMs beyond photosynthesis, and suggest that

  13. Arctic Tundra Vegetation Functional Types Based on Photosynthetic Physiology and Optical Properties

    NASA Technical Reports Server (NTRS)

    Huemmrich, Karl F.; Gamon, John; Tweedie, Craig; Campbell, Petya P. K.; Landis, David; Middleton, Elizabeth

    2012-01-01

    Climate change in tundra regions may alter vegetation species composition and ecosystem carbon balance. Remote sensing provides critical tools for monitoring these changes as optical signals provide a way to scale from plot measurements to regional patterns. Gas exchange measurements of pure patches of key vegetation functional types (lichens, mosses, and vascular plants) in sedge tundra at Barrow AK, show three significantly different values of light use efficiency (LUE) with values of 0.013+/-0.001, 0.0018+/-0.0002, and 0.0012 0.0001 mol C/mol absorbed quanta for vascular plants, mosses and lichens, respectively. Further, discriminant analysis of patch reflectance identifies five spectral bands that can separate each vegetation functional type as well as nongreen material (bare soil, standing water, and dead leaves). These results were tested along a 100 m transect where midsummer spectral reflectance and vegetation coverage were measured at one meter intervals. Area-averaged canopy LUE estimated from coverage fractions of the three functional types varied widely, even over short distances. Patch-level statistical discriminant functions applied to in situ hyperspectral reflectance successfully unmixed cover fractions of the vegetation functional types. These functions, developed from the tram data, were applied to 30 m spatial resolution Earth Observing-1 Hyperion imaging spectrometer data to examine regional variability in distribution of the vegetation functional types and from those distributions, the variability of LUE. Across the landscape, there was a fivefold variation in tundra LUE that was correlated to a spectral vegetation index developed to detect vegetation chlorophyll content.

  14. Net ecosystem exchange over heterogeneous Arctic tundra: Scaling between chamber and eddy covariance measurements

    NASA Astrophysics Data System (ADS)

    Fox, Andrew M.; Huntley, Brian; Lloyd, Colin R.; Williams, Mathew; Baxter, Robert

    2008-06-01

    Net ecosystem exchange (NEE) was estimated for an area of tundra near Abisko using both eddy covariance (EC) data and chamber measurements. This area of tundra is heterogeneous with six principal elements forming a landscape mosaic. Chamber measurements in patches of the individual mosaic elements were used to model NEE as a function of irradiance and temperature. The area around the EC mast was mapped, and a footprint model was used to simulate the varying source fraction attributable to each mosaic element. Various upscaling approaches were used to estimate NEE for comparison with NEE calculated from the EC observations. The results showed that EC measurements made for such a heterogeneous site are robust to the variations in NEE between mosaic elements that also vary substantially in their source fractions. However, they also revealed a large (˜60%) bias in the absolute magnitude of the cumulative negative NEE for a 40-day study period simulated by various upscaling approaches when compared to the value calculated from the EC observations. The magnitude of this bias, if applied to estimates for the entire tundra region, is substantial in relation to other components of the global carbon budget. Various hypotheses to account for this bias are discussed and, where possible, evaluated. A need is identified for more systematic sampling strategies when performing chamber measurements in order to assess the extent to which subjectivity of chamber location may account for much of the observed bias. If this is the origin of the bias, then upscaling approaches using chamber measurements may generally overestimate CO2 uptake.

  15. Arctic Tundra Vegetation Functional Types Based on Photosynthetic Physiology and Optical Properties

    NASA Technical Reports Server (NTRS)

    Huemmrich, Karl Fred; Gamon, John A.; Tweedie, Craig E.; Campbell, Petya K. Entcheva; Landis, David R.; Middleton, Elizabeth M.

    2013-01-01

    Non-vascular plants (lichens and mosses) are significant components of tundra landscapes and may respond to climate change differently from vascular plants affecting ecosystem carbon balance. Remote sensing provides critical tools for monitoring plant cover types, as optical signals provide a way to scale from plot measurements to regional estimates of biophysical properties, for which spatial-temporal patterns may be analyzed. Gas exchange measurements were collected for pure patches of key vegetation functional types (lichens, mosses, and vascular plants) in sedge tundra at Barrow, AK. These functional types were found to have three significantly different values of light use efficiency (LUE) with values of 0.013 plus or minus 0.0002, 0.0018 plus or minus 0.0002, and 0.0012 plus or minus 0.0001 mol C mol (exp -1) absorbed quanta for vascular plants, mosses and lichens, respectively. Discriminant analysis of the spectra reflectance of these patches identified five spectral bands that separated each of these vegetation functional types as well as nongreen material (bare soil, standing water, and dead leaves). These results were tested along a 100 m transect where midsummer spectral reflectance and vegetation coverage were measured at one meter intervals. Along the transect, area-averaged canopy LUE estimated from coverage fractions of the three functional types varied widely, even over short distances. The patch-level statistical discriminant functions applied to in situ hyperspectral reflectance data collected along the transect successfully unmixed cover fractions of the vegetation functional types. The unmixing functions, developed from the transect data, were applied to 30 m spatial resolution Earth Observing-1 Hyperion imaging spectrometer data to examine variability in distribution of the vegetation functional types for an area near Barrow, AK. Spatial variability of LUE was derived from the observed functional type distributions. Across this landscape, a

  16. Arctic Tundra Vegetation Functional Types Based on Photosynthetic Physiology and Optical Properties

    NASA Technical Reports Server (NTRS)

    Huemmrich, Karl F.; Gamon, John; Tweedie, Craig; Campbell, Petya K.; Landis, David R.; Middleton, Elizabeth M.

    2013-01-01

    Non-vascular plants (lichens and mosses) are significant components of tundra landscapes and may respond to climate change differently from vascular plants affecting ecosystem carbon balance. Remote sensing provides critical tools for monitoring plant cover types, as optical signals provide a way to scale from plot measurements to regional estimates of biophysical properties, for which spatial-temporal patterns may be analyzed. Gas exchange measurements were collected for pure patches of key vegetation functional types (lichens, mosses, and vascular plants) in sedge tundra at Barrow AK. These functional types were found to have three significantly different values of light use efficiency (LUE) with values of 0.013+/-0.001, 0.0018+/-0.0002, and 0.0012+/-0.0001 mol C/mol absorbed quanta for vascular plants, mosses and lichens, respectively. Discriminant analysis of the spectra reflectance of these patches identified five spectral bands that separated each of these vegetation functional types as well as nongreen material (bare soil, standing water, and dead leaves). These results were tested along a 100 m transect where midsummer spectral reflectance and vegetation coverage were measured at one meter intervals.

  17. Importance of soil moisture and N availability to larch growth and distribution in the Arctic taiga-tundra boundary ecosystem, northeastern Siberia

    NASA Astrophysics Data System (ADS)

    Liang, Maochang; Sugimoto, Atsuko; Tei, Shunsuke; Bragin, Ivan V.; Takano, Shinya; Morozumi, Tomoki; Shingubara, Ryo; Maximov, Trofim C.; Kiyashko, Serguei I.; Velivetskaya, Tatiana A.; Ignatiev, Alexander V.

    2014-12-01

    To better understand the factors controlling the growth of larch trees in Arctic taiga-tundra boundary ecosystem, we conducted field measurements of photosynthesis, tree size, nitrogen (N) content, and isotopic ratios in larch needles and soil. In addition, we observed various environmental parameters, including topography and soil moisture at four sites in the Indigirka River Basin, near Chokurdakh, northeastern Siberia. Most living larch trees grow on mounds with relatively high elevations and dry soils, indicating intolerance of high soil moisture. We found that needle δ13C was positively correlated with needle N content and needle mass, and these parameters showed spatial patterns similar to that of tree size. These results indicate that trees with high needle N content achieved higher rates of photosynthesis, which resulted in larger amounts of C assimilation and larger C allocation to needles and led to larger tree size than trees with lower needle N content. A positive correlation was also found between needle N content and soil NH 4 + pool. Thus, soil inorganic N pool may indicate N availability, which is reflected in the needle N content of the larch trees. Microtopography plays a principal role in N availability, through a change in soil moisture. Relatively dryer soil of mounds with higher elevation and larger extent causes higher rates of soil N production, leading to increased N availability for plants, in addition to larger rooting space for trees to uptake more N.

  18. Scaling Issues Between Plot and Satellite Radiobrightness Observations of Arctic Tundra

    NASA Technical Reports Server (NTRS)

    Kim, Edward J.; England, Anthony W.; Judge, Jasmeet; Zukor, Dorothy J. (Technical Monitor)

    2000-01-01

    Data from generation of satellite microwave radiometer will allow the detection of seasonal to decadal changes in the arctic hydrology cycle as expressed in temporal and spatial patterns of moisture stored in soil and snow This nw capability will require calibrated Land Surface Process/Radiobrightness (LSP/R) model for the principal terrains found in the circumpolar Arctic. These LSP/R models can than be used in weak constraint. Dimensional Data Assimilation (DDA)of the daily satellite observation to estimate temperature and moisture profiles within the permafrost in active layer.

  19. Slow recovery of High Arctic heath communities from nitrogen enrichment.

    PubMed

    Street, Lorna E; Burns, Nancy R; Woodin, Sarah J

    2015-04-01

    Arctic ecosystems are strongly nutrient limited and exhibit dramatic responses to nitrogen (N) enrichment, the reversibility of which is unknown. This study uniquely assesses the potential for tundra heath to recover from N deposition and the influence of phosphorus (P) availability on recovery. We revisited an experiment in Svalbard, established in 1991, in which N was applied at rates representing atmospheric N deposition in Europe (10 and 50 kg N ha(-1)  yr(-1) ; 'low' and 'high', respectively) for 3-8 yr. We investigated whether significant effects on vegetation composition and ecosystem nutrient status persisted up to 18 yr post-treatment. Although the tundra heath is no longer N saturated, N treatment effects persist and are strongly P-dependent. Vegetation was more resilient to N where no P was added, although shrub cover is still reduced in low-N plots. Where P was also added (5 kg P ha(-1)  yr(-1) ), there are still effects of low N on community composition and nutrient dynamics. High N, with and without P, has many lasting impacts. Importantly, N + P has caused dramatically increased moss abundance, which influences nutrient dynamics. Our key finding is that Arctic ecosystems are slow to recover from even small N inputs, particularly where P is not limiting.

  20. Changes in Algal Trends and Nutrient Budgets in Arctic Tundra Ponds Over the Past 40 Years in Barrow, Alaska

    NASA Astrophysics Data System (ADS)

    Hernandez, C.; Lougheed, V.

    2011-12-01

    In the 1970's, Barrow, Alaska was host to a detailed ecological study, the International Biological Program (IBP), which examined physical, chemical and biological characteristics of Arctic tundra ponds. Forty years later, this area has experienced warming and potential release of nutrients from permafrost; however, there have been no follow up studies since the 1970's and biological changes in these ponds remain unknown. The 1970's IBP research suggested that algae had warmer temperature optima than ambient temperatures and that phosphorus was the limiting nutrient. The goal of this study was to understand algal growth trends during the 2010 growing season, the role of limiting nutrients, and how both these have changed through time in light of shifting climate regimes. Algae was collected and quantified weekly from periphyton (attached to sediment) and phytoplankton (free-floating algae) from several IBP ponds over the summer of 2010. Nutrient addition and release experiments with known quantities of nitrogen (N) and phosphorus (P) were utilized to determine algal nutrient limitation. Algal biomass was significantly greater in 2010 than in the 1970s. Nutrient addition experiments showed a shift from phosphorus limitation in the 1970s to nitrogen limitation of periphyton in 2010, while phytoplankton was co-limited by nitrogen and phosphorus in 2010. These preliminary results indicate substantial changes have occurred over the past 40 years. Further studies are being completed in Summer 2011 to understand inter-annual variability in these trends and to reveal the implications of these trends in algal production and nutrient budgets in the Arctic.

  1. Effects of Disturbances on Vegetation Composition and Permafrost Thaw in Boreal Forests and Tundra Ecosystems of the Siberian Arctic

    NASA Astrophysics Data System (ADS)

    Ramos, E.; Alexander, H. D.; Natali, S.

    2014-12-01

    In Arctic ecosystems, climate-driven changes to the thermal regime of permafrost soils have the potential to create surface disturbances that influence vegetation dynamics and underlying soil properties. Disturbance-mediated changes in vegetation are important because vegetation and the accumulation of soil organic matter drive ecosystem carbon (C) dynamics and contribute to the insulation of soils and protection of permafrost from thaw. We examined the effect of two disturbance types—thermokarsts and frost boils—to determine disturbance effects on the vegetation community and soil properties in northeast Siberia. In summer 2014, we measured vegetation cover, soil moisture, soil temperature, and thaw depth in two thermokarst sites within boreal forests, two frost boil sites in tundra, and in adjacent undisturbed sites within both ecosystems. Both thermokarst and frost boils resulted in decreased vegetation cover and greater exposure of mineral soils (10-40% bare soils vs. 0% in undisturbed), and consequently, 2-3 times higher soil temperature and deeper thaw depth. Compared to undisturbed areas, soil moisture was 3-4 times higher in thermokarst areas but 1.2-2 times lower in frost boil areas, which reflected differences in microtopography between these two disturbance types. In both thermokarst and frost boil disturbed areas, deciduous and evergreen shrubs covered only 5 and 10%, respectively, compared to approximately 10 and 20%, respectively, in undisturbed areas. In general, graminoids were substantially more abundant (2-20 times) in disturbed areas than in those undisturbed. These results highlight important linkages between disturbances, vegetation communities, and permafrost soils, and contribute to our understanding of how changes in arctic vegetation dynamics as direct and/or indirect consequences of climate change have the potential to impact permafrost C pools.

  2. Inclusion of Additional Plant Species and Trait Information in Dynamic Vegetation Modeling of Arctic Tundra and Boreal Forest Ecosystem

    NASA Astrophysics Data System (ADS)

    Euskirchen, E. S.; Patil, V.; Roach, J.; Griffith, B.; McGuire, A. D.

    2015-12-01

    Dynamic vegetation models (DVMs) have been developed to model the ecophysiological characteristics of plant functional types in terrestrial ecosystems. They have frequently been used to answer questions pertaining to processes such as disturbance, plant succession, and community composition under historical and future climate scenarios. While DVMs have proved useful in these types of applications, it has often been questioned if additional detail, such as including plant dynamics at the species-level and/or including species-specific traits would make these models more accurate and/or broadly applicable. A sub-question associated with this issue is, 'How many species, or what degree of functional diversity, should we incorporate to sustain ecosystem function in modeled ecosystems?' Here, we focus on how the inclusion of additional plant species and trait information may strengthen dynamic vegetation modeling in applications pertaining to: (1) forage for caribou in northern Alaska, (2) above- and belowground carbon storage in the boreal forest and lake margin wetlands of interior Alaska, and (3) arctic tundra and boreal forest leaf phenology. While the inclusion of additional information generally proved valuable in these three applications, this additional detail depends on field data that may not always be available and may also result in increased computational complexity. Therefore, it is important to assess these possible limitations against the perceived need for additional plant species and trait information in the development and application of dynamic vegetation models.

  3. What measurements are needed to capture coupled carbon and nitrogen cycles in arctic tundra?

    NASA Astrophysics Data System (ADS)

    Wright, K.; Rocha, A. V.

    2015-12-01

    Greening has been observed across the arctic, but the ecological processes that enable widespread increases in plant productivity have been difficult to understand with field measurements alone. Using the functional convergence of foliar nitrogen and leaf area index in arctic plants, we developed a simple coupled carbon and nitrogen cycling model (CCaN) to increase our understanding of warming induced vegetation changes and carbon and nitrogen coupling in the arctic. We used primary literature and data from long term ecological research sites at Toolik Field Station, Alaska to calculate prior ranges for CCaN parameters, and then we assimilated five years of eddy covariance data from a nearby field site using a batch data assimilation method based on Markov Chain Monte Carlo techniques. Variance decomposition analyses show that the majority of model variance in carbon and nitrogen stocks can be attributed to uncertainty in four parameters: proportion of nitrogen in foliage, proportion of nitrogen in roots, nitrogen uptake rate, and litter rate. These parameters associated with nitrogen cycling are widely used in biogeochemical cycling models and are difficult to constrain because they vary greatly across plant functional groups. The parameters responsible for variance in net ecosystem exchange vary seasonally; winter variance is controlled by parameters associated with the temperature sensitivity of heterotrophic respiration, and summer variance is controlled by the proportion of nitrogen in foliage. The widespread greening observed across the arctic over the last decade has been attributed to the direct effects of increased temperature, despite the inconsistency of the response of arctic plants to experimental warming indicating there must be other mechanisms at play. These mechanisms can be teased apart using models, but we must first improve model predictions by constraining widely-used processes and parameters, particularly those linked to nitrogen cycling.

  4. A Comparative Review of North American Tundra Delineations

    NASA Technical Reports Server (NTRS)

    Silver, Kirk C.; Carroll, Mark

    2013-01-01

    Recent profound changes have been observed in the Arctic environment, including record low sea ice extents and high latitude greening. Studying the Arctic and how it is changing is an important element of climate change science. The Tundra, an ecoregion of the Arctic, is directly related to climate change due to its effects on the snow ice feedback mechanism and greenhouse gas cycling. Like all ecoregions, the Tundra border is shifting, yet studies and policies require clear delineation of boundaries. There are many options for ecoregion classification systems, as well as resources for creating custom maps. To help decision makers identify the best classification system possible, we present a review of North American Tundra ecoregion delineations and further explore the methodologies, purposes, limitations, and physical properties of five common ecoregion classification systems. We quantitatively compare the corresponding maps by area using a geographic information system.

  5. Impact of elevated CO2, water table, and temperature changes on CO2 and CH4 fluxes from arctic tundra soils

    NASA Astrophysics Data System (ADS)

    Zona, Donatella; Haynes, Katherine; Deutschman, Douglas; Bryant, Emma; McEwing, Katherine; Davidson, Scott; Oechel, Walter

    2015-04-01

    Large uncertainties still exist on the response of tundra C emissions to future climate due, in part, to the lack of understanding of the interactive effects of potentially controlling variables on C emissions from Arctic ecosystems. In this study we subjected 48 soil cores (without active vegetation) from dominant arctic wetland vegetation types, to a laboratory manipulation of elevated atmospheric CO2, elevated temperature, and altered water table, representing current and future conditions in the Arctic for two growing seasons. To our knowledge this experiment comprised the most extensively replicated manipulation of intact soil cores in the Arctic. The hydrological status of the soil was the most dominant control on both soil CO2 and CH4 emissions. Despite higher soil CO2 emission occurring in the drier plots, substantial CO2 respiration occurred under flooded conditions, suggesting significant anaerobic respirations in these arctic tundra ecosystems. Importantly, a critical control on soil CO2 and CH4 fluxes was the original vascular plant cover. The dissolved organic carbon (DOC) concentration was correlated with cumulative CH4 emissions but not with cumulative CO2 suggesting C quality influenced CH4 production but not soil CO2 emissions. An interactive effect between increased temperature and elevated CO2 on soil CO2 emissions suggested a potential shift of the soils microbial community towards more efficient soil organic matter degraders with warming and elevated CO2. Methane emissions did not decrease over the course of the experiment, even with no input from vegetation. This result indicated that CH4 emissions are not carbon limited in these C rich soils. Overall CH4 emissions represented about 49% of the sum of total C (C-CO2 + C-CH4) emission in the wet treatments, and 15% in the dry treatments, representing a dominant component of the overall C balance from arctic soils.

  6. Lepidoptera Larvae as an Indicator of Multi-trophic Level Responses to Changing Seasonality in an Arctic Tundra Ecosystem

    NASA Astrophysics Data System (ADS)

    Daly, K. M.; Steltzer, H.; Boelman, N.; Weintraub, M. N.; Darrouzet-Nardi, A.; Wallenstein, M. D.; Sullivan, P.; Gough, L.; Rich, M.; Hendrix, C.; Kielland, K.; Philip, K.; Doak, P.; Ferris, C.; Sikes, D.

    2011-12-01

    Earlier snowmelt and warming temperatures in the Arctic will impact multiple trophic levels through the timing and availability of food resources. Lepidoptera are a vital link within the ecosystem; their roles include pollinator, parasitized host for other pollinating insects, and essential food source for migrating birds and their fledglings. Multiple environmental cues including temperature initiate plant growth, and in turn, trigger the emergence of Lepidoptera and the migrations of birds. If snowmelt is accelerated and temperature is increased, it is expected that the Lepidoptera larvae will respond to early plant growth by increasing their abundance within areas that have accelerated snowmelt and warmer conditions. In May of 2011 in a moist acidic tussock tundra system, we accelerated snowmelt by 15 days through the use of radiation-absorbing fabric and warmed air and soil temperatures using open-top chambers, individually and in combination. Every 1-2 days from May 27th to July 8th, 2 minute searches were performed for Lepidoptera larvae in all treatments; when an animal was found, their micro-habitat, surface temperature, behavior, food source, and time of day were noted. The length, body and head width were measured, and the animals were examined for braconid wasp and tachinid fly parasites. Lepidoptera larvae collected in pitfall traps from May 26th to July 7th were also examined and measured. Total density of parasitized larvae accounted for 54% of observed specimens and 50% of pitfall specimens, indicating that Lepidoptera larvae serve an integral role as a host for other pollinators. Total larvae density was highest within the accelerated snowmelt plots compared to the control plots; 66% of observed live specimens and 63% of pitfall specimens were found within the accelerated snowmelt plots. Ninety percent of the total observed animals were found within the open-top warming chambers. Peak density of animals occurred at Solar Noon between 14:00 -15

  7. The Contribution of Moss to Plot-Based Spectral Signals in Moist Acidic Low Arctic Tundra

    NASA Astrophysics Data System (ADS)

    May, J. L.; Beamish, A. L.

    2015-12-01

    To determine the contribution of moss to peak season normalized difference index (NDVI) field measurement of intact vegetation communities were compared to communities with individual species and litter successively removed until only the moss layer remained. Spectral measurements (n=3) were collected using a field radiometer in five upland and five lowland plots in a moist acidic tundra ecosystem at the Imnaviat Creek Watershed, North Slope Alaska. After spectral measurements were taken individual species were removed in the same order in each plot by clipping them at the moss layer. As individual species were removed NDVI values decreased. Decreases were greatest when dwarf shrub species Salix richardsonii sb. pulchra and Betula nana were removed. Notable increases in NDVI were observed once standing litter was removed. The NDVI values of the moss layer were comparable to intact vegetation communities depending on the bryophyte species composition. This suggests that the NDVI signal of moss is largely masked by vascular species but represents a significant factor missing from overall, large-scale NDVI signals. The results of this study corroborate recent data that points to the mismatch between ground based NDVI and aerial and satellite derived NDVI. This preliminary case study provides a strong basis for better characterization of the contribution of moss to NDVI for improved correction of air and space borne imagery.

  8. Carbon balance of Arctic tundra under increased snow cover mediated by a plant pathogen

    NASA Astrophysics Data System (ADS)

    Olofsson, Johan; Ericson, Lars; Torp, Mikaela; Stark, Sari; Baxter, Robert

    2011-07-01

    Climate change is affecting plant community composition and ecosystem structure, with consequences for ecosystem processes such as carbon storage. Climate can affect plants directly by altering growth rates, and indirectly by affecting predators and herbivores, which in turn influence plants. Diseases are also known to be important for the structure and function of food webs. However, the role of plant diseases in modulating ecosystem responses to a changing climate is poorly understood. This is partly because disease outbreaks are relatively rare and spatially variable, such that that their effects can only be captured in long-term experiments. Here we show that, although plant growth was favoured by the insulating effects of increased snow cover in experimental plots in Sweden, plant biomass decreased over the seven-year study. The decline in biomass was caused by an outbreak of a host-specific parasitic fungus, Arwidssonia empetri, which killed the majority of the shoots of the dominant plant species, Empetrum hermaphroditum, after six years of increased snow cover. After the outbreak of the disease, instantaneous measurements of gross photosynthesis and net ecosystem carbon exchange were significantly reduced at midday during the growing season. Our results show that plant diseases can alter and even reverse the effects of a changing climate on tundra carbon balance by altering plant composition.

  9. Luteolibacter luojiensis sp. nov., isolated from Arctic tundra soil, and emended description of the genus Luteolibacter.

    PubMed

    Jiang, Fan; Li, Wenjuan; Xiao, Mengchen; Dai, Jun; Kan, Wenjing; Chen, Lu; Li, Wenxin; Fang, Chengxiang; Peng, Fang

    2012-09-01

    A yellow-pigmented, Gram-reaction-negative, non-motile, aerobic bacterium, designated DR4-30(T), was isolated from tundra soil near Ny-Ålesund, Svalbard Archipelago, Norway (78° 58' N 12° 03' E). Growth occurred at 4-28 °C (optimum 20-25 °C) and at pH 7-8 (optimum pH 7). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain DR4-30(T) belongs to the genus Luteolibacter in the family Verrucomicrobiaceae. The 16S rRNA gene sequence of this strain showed 95.4 and 94.7 % sequence similarity to those of Luteolibacter pohnpeiensis A4T-83(T) and Luteolibacter algae A5J-41-2(T), respectively. The major respiratory quinones were MK-9 and MK-10; the predominant cellular fatty acids were summed feature 3 (C(16 : 1)ω7c and/or C(16 : 1)ω6c; 20.7 %), iso-C(14 : 0) (20.3 %), C(17 : 0) (10.7 %), C(16 : 0) (8.0 %) and C(14 : 0) (6.6 %). The DNA G+C content was 57.3 mol%. On the basis of phenotypic, chemotaxonomic and phylogenetic data, strain DR4-30(T) represents a novel species of the genus Luteolibacter, for which the name Luteolibacter luojiensis sp. nov. is proposed. The type strain is DR4-30(T) (= CCTCC AB 2010415(T) = NRRL B-59669(T)). An emended description of the genus Luteolibacter is also provided.

  10. Contrasting denitrifier communities relate to contrasting N2O emission patterns from acidic peat soils in arctic tundra.

    PubMed

    Palmer, Katharina; Biasi, Christina; Horn, Marcus A

    2012-05-01

    Cryoturbated peat circles (that is, bare surface soil mixed by frost action; pH 3-4) in the Russian discontinuous permafrost tundra are nitrate-rich 'hotspots' of nitrous oxide (N(2)O) emissions in arctic ecosystems, whereas adjacent unturbated peat areas are not. N(2)O was produced and subsequently consumed at pH 4 in unsupplemented anoxic microcosms with cryoturbated but not in those with unturbated peat soil. Nitrate, nitrite and acetylene stimulated net N(2)O production of both soils in anoxic microcosms, indicating denitrification as the source of N(2)O. Up to 500 and 10 μM nitrate stimulated denitrification in cryoturbated and unturbated peat soils, respectively. Apparent maximal reaction velocities of nitrite-dependent denitrification were 28 and 18 nmol N(2)O g(DW)(-1) h(-1), for cryoturbated and unturbated peat soils, respectively. Barcoded amplicon pyrosequencing of narG, nirK/nirS and nosZ (encoding nitrate, nitrite and N(2)O reductases, respectively) yielded ≈49 000 quality-filtered sequences with an average sequence length of 444 bp. Up to 19 species-level operational taxonomic units were detected per soil and gene, many of which were distantly related to cultured denitrifiers or environmental sequences. Denitrification-associated gene diversity in cryoturbated and in unturbated peat soils differed. Quantitative PCR (inhibition-corrected per DNA extract) revealed higher copy numbers of narG in cryoturbated than in unturbated peat soil. Copy numbers of nirS were up to 1000 × higher than those of nirK in both soils, and nirS nirK(-1) copy number ratios in cryoturbated and unturbated peat soils differed. The collective data indicate that the contrasting N(2)O emission patterns of cryoturbated and unturbated peat soils are associated with contrasting denitrifier communities.

  11. Active layer hydrology in an arctic tundra ecosystem: quantifying water sources and cycling using water stable isotopes

    SciTech Connect

    Throckmorton, Heather M.; Newman, Brent D.; Heikoop, Jeffrey M.; Perkins, George B.; Feng, Xiahong; Graham, David E.; O'Malley, Daniel; Vesselinov, Velimir V.; Young, Jessica; Wullschleger, Stan D.; Wilson, Cathy J.

    2016-04-16

    Climate change and thawing permafrost in the Arctic will significantly alter landscape hydro-geomorphology and the distribution of soil moisture, which will have cascading effects on climate feedbacks (CO2 and CH4) and plant and microbial communities. Fundamental processes critical to predicting active layer hydrology are not well understood. This study applied water stable isotope techniques (δ2H and δ18O) to infer sources and mixing of active layer waters in a polygonal tundra landscape in Barrow, Alaska (USA), in August and September of 2012. Results suggested that winter precipitation did not contribute substantially to surface waters or subsurface active layer pore waters measured in August and September. Summer rain was the main source of water to the active layer, with seasonal ice melt contributing to deeper pore waters later in the season. Surface water evaporation was evident in August from a characteristic isotopic fractionation slope (δ2H vs δ18O). Freeze-out isotopic fractionation effects in frozen active layer samples and textural permafrost were indistinguishable from evaporation fractionation, emphasizing the importance of considering the most likely processes in water isotope studies, in systems where both evaporation and freeze-out occur in close proximity. The fractionation observed in frozen active layer ice was not observed in liquid active layer pore waters. Such a discrepancy between frozen and liquid active layer samples suggests mixing of meltwater, likely due to slow melting of seasonal ice. In conclusion, this research provides insight into fundamental processes relating to sources and mixing of active layer waters, which should be considered in process-based fine-scale and intermediate-scale hydrologic models.

  12. Contrasting denitrifier communities relate to contrasting N2O emission patterns from acidic peat soils in arctic tundra

    PubMed Central

    Palmer, Katharina; Biasi, Christina; Horn, Marcus A

    2012-01-01

    Cryoturbated peat circles (that is, bare surface soil mixed by frost action; pH 3–4) in the Russian discontinuous permafrost tundra are nitrate-rich ‘hotspots' of nitrous oxide (N2O) emissions in arctic ecosystems, whereas adjacent unturbated peat areas are not. N2O was produced and subsequently consumed at pH 4 in unsupplemented anoxic microcosms with cryoturbated but not in those with unturbated peat soil. Nitrate, nitrite and acetylene stimulated net N2O production of both soils in anoxic microcosms, indicating denitrification as the source of N2O. Up to 500 and 10 μ nitrate stimulated denitrification in cryoturbated and unturbated peat soils, respectively. Apparent maximal reaction velocities of nitrite-dependent denitrification were 28 and 18 nmol N2O gDW−1 h−1, for cryoturbated and unturbated peat soils, respectively. Barcoded amplicon pyrosequencing of narG, nirK/nirS and nosZ (encoding nitrate, nitrite and N2O reductases, respectively) yielded ≈49 000 quality-filtered sequences with an average sequence length of 444 bp. Up to 19 species-level operational taxonomic units were detected per soil and gene, many of which were distantly related to cultured denitrifiers or environmental sequences. Denitrification-associated gene diversity in cryoturbated and in unturbated peat soils differed. Quantitative PCR (inhibition-corrected per DNA extract) revealed higher copy numbers of narG in cryoturbated than in unturbated peat soil. Copy numbers of nirS were up to 1000 × higher than those of nirK in both soils, and nirS nirK−1 copy number ratios in cryoturbated and unturbated peat soils differed. The collective data indicate that the contrasting N2O emission patterns of cryoturbated and unturbated peat soils are associated with contrasting denitrifier communities. PMID:22134649

  13. Active layer hydrology in an arctic tundra ecosystem: quantifying water sources and cycling using water stable isotopes

    DOE PAGES

    Throckmorton, Heather M.; Newman, Brent D.; Heikoop, Jeffrey M.; ...

    2016-04-16

    Climate change and thawing permafrost in the Arctic will significantly alter landscape hydro-geomorphology and the distribution of soil moisture, which will have cascading effects on climate feedbacks (CO2 and CH4) and plant and microbial communities. Fundamental processes critical to predicting active layer hydrology are not well understood. This study applied water stable isotope techniques (δ2H and δ18O) to infer sources and mixing of active layer waters in a polygonal tundra landscape in Barrow, Alaska (USA), in August and September of 2012. Results suggested that winter precipitation did not contribute substantially to surface waters or subsurface active layer pore waters measuredmore » in August and September. Summer rain was the main source of water to the active layer, with seasonal ice melt contributing to deeper pore waters later in the season. Surface water evaporation was evident in August from a characteristic isotopic fractionation slope (δ2H vs δ18O). Freeze-out isotopic fractionation effects in frozen active layer samples and textural permafrost were indistinguishable from evaporation fractionation, emphasizing the importance of considering the most likely processes in water isotope studies, in systems where both evaporation and freeze-out occur in close proximity. The fractionation observed in frozen active layer ice was not observed in liquid active layer pore waters. Such a discrepancy between frozen and liquid active layer samples suggests mixing of meltwater, likely due to slow melting of seasonal ice. In conclusion, this research provides insight into fundamental processes relating to sources and mixing of active layer waters, which should be considered in process-based fine-scale and intermediate-scale hydrologic models.« less

  14. Net regional methane sink in High Arctic soils of northeast Greenland

    NASA Astrophysics Data System (ADS)

    Juncher Jørgensen, Christian; Lund Johansen, Katrine Maria; Westergaard-Nielsen, Andreas; Elberling, Bo

    2015-01-01

    Arctic tundra soils serve as potentially important but poorly understood sinks of atmospheric methane (CH4), a powerful greenhouse gas. Numerical simulations project a net increase in methane consumption in soils in high northern latitudes as a consequence of warming in the past few decades. Advances have been made in quantifying hotspots of methane emissions in Arctic wetlands, but the drivers, magnitude, timing and location of methane consumption rates in High Arctic ecosystems are unclear. Here, we present measurements of rates of methane consumption in different vegetation types within the Zackenberg Valley in northeast Greenland over a full growing season. Field measurements show methane uptake in all non-water-saturated landforms studied, with seasonal averages of - 8.3 +/- 3.7 μmol CH4 m-2 h-1 in dry tundra and - 3.1 +/- 1.6 μmol CH4 m-2 h-1 in moist tundra. The fluxes were sensitive to temperature, with methane uptake increasing with increasing temperatures. We extrapolate our measurements and published measurements from wetlands with the help of remote-sensing land-cover classification using nine Landsat scenes. We conclude that the ice-free area of northeast Greenland acts as a net sink of atmospheric methane, and suggest that this sink will probably be enhanced under future warmer climatic conditions.

  15. Changes in Dissolved Carbon and Nitrogen Concentrations Along a Hill Slope Flow Path in Siberian Arctic Tundra

    NASA Astrophysics Data System (ADS)

    Theberge, J.; Schade, J. D.; Fiske, G. J.; Loranty, M. M.; Zimov, N.

    2014-12-01

    Permafrost soils contain a large pool of carbon that has accumulated for thousands of years, and remains frozen in organic form. As climate warms, permafrost thaw will lead to active cycling of old organic materials, possibly leading to release of carbon to the atmosphere or to export of organic carbon to the oceans. Organic matter breakdown may also release reactive forms of nitrogen, which may significantly impact ecosystem processes. We currently have limited understanding of where in Arctic landscapes breakdown of organic materials will occur, or whether this will influence the strength and direction of feedback loops that may occur in response to changes in C and N cycling. In this work, we studied changes in dissolved forms of C and N in water moving down a hillslope linking upland terrestrial environments to lowland floodplains within the Kolyma River watershed in the East Siberian Arctic tundra in July, 2014. The hill slope consisted of a mosaic of dry and saturated soils, generally with drier soils on the periphery and saturated soils in and around pools or short reaches of flowing surface water. We established transects at regular intervals downslope, installing wells in the center of the flow path and 5 meters laterally north and south. We analyzed pore-water from wells and surface water from pools at each transect for dissolved organic carbon (DOC) and total dissolved nitrogen (TDN). We used patterns in water chemistry to develop a conceptual model for biogeochemical changes as water moved downslope through soils, pools and runs. Pore-water analysis showed significantly higher DOC in lateral wells than in surface water and pore water in the center of the flow path, suggesting possible processing of C as water moves laterally towards the valley bottom. In contrast, DOC increased modestly down the center of the flow path, suggesting either higher hydrologic inputs or production of new DOC downslope. TDN concentration decreased downslope, suggesting

  16. Cultural Resilience of Nenets Social-Ecological Systems in Arctic Russia: A Focus on Reindeer Nomads of the Tundra

    NASA Astrophysics Data System (ADS)

    Forbes, B. C.

    2013-12-01

    Empirical data on resilience in social-ecological systems (SESs) are reviewed from local and regional scale case studies among full-time nomads in the neighbouring Nenets and Yamal-Nenets Autonomous Okrugs, Russia. The focus is on critical cultural factors contributing to SES resilience. In particular, this work presents an integrated view of people situated in specific tundra landscapes that face significantly different prospects for adaptation depending on existing or planned infrastructure associated with oil and gas development. Factors contributing to general resilience are compared to those that are adapted to certain spatial and temporal contexts. Environmental factors include ample space and an abundance of resources, such as fish and game (e.g. geese), to augment the diet of not only the migratory herders, but also residents from coastal settlements. In contrast to other regions, such as the Nenets Okrug, Yamal Nenets households consist of intact nuclear families with high retention among youth in the nomadic tundra population. Accepting attitudes toward exogenous drivers such as climate change and industrial development appear to play a significant role in how people react to both extreme weather events and piecemeal confiscation or degradation of territory. Consciousness of their role as responsible stewards of the territories they occupy has likely been a factor in maintaining viable wildlife populations over centuries. Institutions administering reindeer herding have remained flexible, especially on Yamal, and so accommodate decision-making that is sensitive to herders' needs and timetables. This affects factors such as herd demography, mobility and energetics. Resilience is further facilitated within the existing governance regimes by herders' own agency, most recently in the post-Soviet shift to smaller, privately managed herds that can better utilize available pastures in a highly dynamic environment experiencing rapid socio-economic, climate and

  17. Hydrological Controls on Ecosystem CO2 and CH4 Exchange in a MIXED Tundra and a FEN within an Arctic Landscape UNDER Current and Future Climates

    NASA Astrophysics Data System (ADS)

    Grant, R. F.; Humphreys, E.; Lafleur, P.

    2014-12-01

    Variation in CO2 and CH4 exchange in years with contrasting weather is strongly affected by hydrology in landscapes underlain by permafrost. Hypotheses for this variation were incorporated into the ecosystem model ecosys which simulated CO2 and CH4 fluxes along a topographic gradient within an arctic landscape at Daring Lake, NWT, Canada. Fluxes modelled at mixed tundra and fen sites within the gradient were compared with CO2 fluxes measured at eddy covariance towers from 2006 to 2009, and with CH4 fluxes measured with surface chambers in 2008. Slopes and correlation coefficients from regressions of modelled vs. measured CO2 fluxes were 1.0 ± 0.1 and 0.7 - 0.8 for both sites in all years. At the mixed tundra site, rises in net CO2 uptake in warmer years with earlier snowmelt were constrained by midafternoon declines in CO2 influxes when vapor pressure deficits (D) exceeded 1.5 kPa, and by rises in CO2 effluxes with greater active layer depth (ALD). Consequently annual net CO2 uptake at this site rose little with warming. At the fen site, CO2 influxes declined less with D and CO2 effluxes rose less with warming, so that rises in net CO2 uptake in warmer years were greater than those at the mixed tundra site. The greater declines in CO2 influxes with warming at the mixed tundra site were modelled from greater soil-plant-atmosphere water potential gradients that developed in drier soil, and the smaller rises in CO2 effluxes with warming at the fen site were modelled from O2 constraints to heterotrophic and below-ground autotrophic respiration that limited their responses to greater ALD. Modelled and measured CH4 exchange during July and August indicated very small influxes at the mixed tundra site, and larger emissions at the fen site. Emissions of CH4 modelled during soil freezing in October - November contributed about one-third of the annual total, and so should be included in estimates of annual emissions. These contrasting responses to warming under current

  18. Contrasting Responses of Arctic Tussock Tundra to Early Season Snow Melt: Growth Acceleration Versus Frost Damage

    NASA Astrophysics Data System (ADS)

    Oberbauer, S. F.; Starr, G.; Pop, E. W.; Ahlquist, L. E.; Parker, I. C.

    2003-12-01

    Climate warming scenarios for the Arctic include early snow melt marking the beginning of the growing season. From the perspective of the vegetation, early snow melt may have advantageous or disadvantageous effects. With warm weather following snow melt, bud break and flowering will occur early providing a longer period for growth and photosynthesis. However, if very cold weather follows snowmelt, plants will be exposed directly to freezing conditions that plants under the snow would not. Such exposed plants may suffer freeze damage and delayed bud break. We have been experimentally manipulating snow cover at Toolik Lake, Alaska, since 1995. In 9 years of early snow removal treatments, in only two years has the second scenario occurred, in 2001 and 2002. Here we document the effects of very cold conditions following snow removal on green biomass as assessed by NDVI of treatment plots relative to controls. In 2001 evergreens shrubs were killed, bud break was delayed, and NDVI was lower on treatment plots relative to controls. In contrast, in a year with warm spring temperatures following snow melt, 1999, NDVI on treatment plots was significantly greater than that of controls. Cold conditions following snow melt may lead to death of shrubs and delayed budbreak, effects that will carry over throughout the growing season and ultimately, affect community composition and ecosystem function.

  19. New York's TUNDRA.

    ERIC Educational Resources Information Center

    Kalinowski, Thomas

    1983-01-01

    Found at the summit of some of the highest peaks of New York State's Adirondack Mountains are low-growing plants similar, and in many cases, identical to plants growing in the Arctic. Describes these plants and the environment in which they are found. Includes a color plate of alpine tundra plants. (Author/JN)

  20. The Circumpolar Arctic vegetation map

    USGS Publications Warehouse

    Walker, Donald A.; Raynolds, Martha K.; Daniels, F.J.A.; Einarsson, E.; Elvebakk, A.; Gould, W.A.; Katenin, A.E.; Kholod, S.S.; Markon, C.J.; Melnikov, E.S.; Moskalenko, N.G.; Talbot, S. S.; Yurtsev, B.A.; Bliss, L.C.; Edlund, S.A.; Zoltai, S.C.; Wilhelm, M.; Bay, C.; Gudjonsson, G.; Ananjeva, G.V.; Drozdov, D.S.; Konchenko, L.A.; Korostelev, Y.V.; Ponomareva, O.E.; Matveyeva, N.V.; Safranova, I.N.; Shelkunova, R.; Polezhaev, A.N.; Johansen, B.E.; Maier, H.A.; Murray, D.F.; Fleming, Michael D.; Trahan, N.G.; Charron, T.M.; Lauritzen, S.M.; Vairin, B.A.

    2005-01-01

    Question: What are the major vegetation units in the Arctic, what is their composition, and how are they distributed among major bioclimate subzones and countries? Location: The Arctic tundra region, north of the tree line. Methods: A photo-interpretive approach was used to delineate the vegetation onto an Advanced Very High Resolution Radiometer (AVHRR) base image. Mapping experts within nine Arctic regions prepared draft maps using geographic information technology (ArcInfo) of their portion of the Arctic, and these were later synthesized to make the final map. Area analysis of the map was done according to bioclimate subzones, and country. The integrated mapping procedures resulted in other maps of vegetation, topography, soils, landscapes, lake cover, substrate pH, and above-ground biomass. Results: The final map was published at 1:7 500 000 scale map. Within the Arctic (total area = 7.11 x 106 km 2), about 5.05 ?? 106 km2 is vegetated. The remainder is ice covered. The map legend generally portrays the zonal vegetation within each map polygon. About 26% of the vegetated area is erect shrublands, 18% peaty graminoid tundras, 13% mountain complexes, 12% barrens, 11% mineral graminoid tundras, 11% prostrate-shrub tundras, and 7% wetlands. Canada has by far the most terrain in the High Arctic mostly associated with abundant barren types and prostrate dwarf-shrub tundra, whereas Russia has the largest area in the Low Arctic, predominantly low-shrub tundra. Conclusions: The CAVM is the first vegetation map of an entire global biome at a comparable resolution. The consistent treatment of the vegetation across the circumpolar Arctic, abundant ancillary material, and digital database should promote the application to numerous land-use, and climate-change applications and will make updating the map relatively easy. ?? IAVS; Opulus Press.

  1. Decadal Time Scale change in terrestrial plant communities in North American arctic and alpine tundra: A contribution to the International Polar Year Back to the Future Project (Invited)

    NASA Astrophysics Data System (ADS)

    Tweedie, C. E.; Ebert-May, D.; Hollister, R. D.; Johnson, D. R.; Lara, M. J.; Villarreal, S.; Spasojevic, M.; Webber, P.

    2010-12-01

    The International Polar Year-Back to the Future (IPY-BTF) is an endorsed International Polar Year project (IPY project #214). The overarching goal of this program is to determine how key structural and functional characteristics of high latitude/altitude terrestrial ecosystems have changed over the past 25 or more years and assess if such trajectories of change are likely to continue in the future. By rescuing data, revisiting, re-sampling historic research sites and assessing environmental change over time, we aim to provide greater understanding of how tundra is changing and what the possible drivers of these changes are. Resampling of sites established by Patrick J. Webber between 1964 and 1975 in northern Baffin Island, Northern Alaska and in the Rocky Mountains form a key contribution to the BTF project. Here we report on resampling efforts at each of these locations and initial results of a synthesis effort that finds similarities and differences in change between sites. Results suggest that although shifts in plant community composition are detectable at each location, the magnitude and direction of change differ among locations. Vegetation shifts along soil moisture gradients is apparent at most of the sites resampled. Interestingly, however, wet communities seem to have changed more than dry communities in the Arctic locations, while plant communities at the alpine site appear to be becoming more distinct regardless of soil moisture status. Ecosystem function studies performed in conjunction with plant community change suggest that there has been an increase in plant productivity at most sites resampled, especially in wet and mesic land cover types.

  2. Ecosystem CO2 and CH4 exchange in a mixed tundra and a fen within a hydrologically diverse Arctic landscape: 2. Modeled impacts of climate change

    NASA Astrophysics Data System (ADS)

    Grant, R. F.

    2015-07-01

    Climate change will have important effects on arctic productivity and greenhouse gas exchange. These changes were projected by the model ecosys under an Special Report on Emissions Scenarios (SRES) A2 scenario over the 21st century for a landscape including an upland tundra and a lowland fen at Daring Lake, NWT. Rising temperatures and precipitation caused increases in active layer depths (ALD) and eventual formation of taliks, particularly in the fen, which were attributed to heat advection from warmer and more intense precipitation and downslope flow. These changes raised net primary productivity from more rapid N mineralization and uptake, driven by more rapid heterotrophic respiration and increasing deciduous versus evergreen plant functional types. Consequently, gains in net ecosystem productivity (NEP) of 29 and 10 g C m-2 yr-1 were modeled in the tundra and fen after 90 years. However, CH4 emissions modeled from the fen rose sharply from direct effects of increasing soil temperatures and greater ALD on fermenter and methanogenic populations and from indirect effects of increasing sedge growth, which hastened transfer of CH4 through porous roots to the atmosphere. After 90 years, landscape CH4 emissions increased from 1.1 to 5.2 g C m-2 yr-1 while landscape NEP increased from 34 to 46 g C m-2 yr-1. Positive feedback to radiative forcing from increases in CH4 emissions more than offset negative feedback from increases in NEP. This feedback was largely attributed to rises in CH4 emission caused by heat advection from increasing precipitation, the impacts of which require greater attention in arctic climate change studies.

  3. Ecosystem CO2 and CH4 Exchange in a Mixed Tundra and a Fen Within an Arctic Landscape: Modeled Impacts of Climate Change

    NASA Astrophysics Data System (ADS)

    Grant, R. F.

    2015-12-01

    Climate change will have important effects on arctic productivity and greenhouse gas exchange. These changes were projected by the model ecosys under an SRES A2 scenario over the 21st century for a landscape including an upland tundra and a lowland fen at Daring Lake, NWT. Rising temperatures and precipitation caused increases in active layer depths (ALD) and eventual formation of taliks, particularly in the fen, which were attributed to heat advection from warmer and more intense precipitation and downslope flow. These changes raised net primary productivity from more rapid N mineralization and uptake, driven by more rapid heterotrophic respiration and increasing deciduous vs. evergreen plant functional types. Consequently gains in net ecosystem productivity (NEP) of 29 and 10 g C m-2 y-1 were modelled in the tundra and fen after 90 years. However CH4 emissions modelled from the fen rose sharply from direct effects of increasing soil temperatures and greater ALD on fermenter and methanogenic populations, and from indirect effects of increasing sedge growth which hastened transfer of CH4 through porous roots to the atmosphere. After 90 years, landscape CH4 emissions increased from 1.1 to 5.2 g C m-2 y-1 while landscape NEP increased from 34 to 46 g C m-2 y-1. Positive feedback to radiative forcing from increases in CH4 emissions more than offset negative feedback from increases in NEP. This feedback was largely attributed to rises in CH4 emission caused by heat advection from increasing precipitation, the impacts of which require greater attention in arctic climate change studies.

  4. Endophytic bacterial communities in three arctic plants from low arctic fell tundra are cold-adapted and host-plant specific.

    PubMed

    Nissinen, Riitta M; Männistö, Minna K; van Elsas, Jan Dirk

    2012-11-01

    Endophytic bacteria inhabit internal plant tissues, and have been isolated from a large diversity of plants, where they form nonpathogenic relationships with their hosts. This study combines molecular and culture-dependent approaches to characterize endophytic bacterial communities of three arcto-alpine plant species (Oxyria digyna, Diapensia lapponica and Juncus trifidus) sampled in the low Arctic (69°03'N). Analyses of a 325 bacterial endophyte isolates, as well as seven clone libraries, revealed a high diversity. In particular, members of the Actinobacteria, Bacteroidetes, Firmicutes, Acidobacteria, and Proteobacteria were found. The compositions of the endophytic bacterial communities were dependent on host-plant species as well as on snow cover at sampling sites. Several bacterial genera were found to be associated tightly with specific host-plant species. In particular, Sphingomonas spp. were characteristic for D. lapponica and O. digyna, and their phylogenetic grouping corresponded to the host plant. Most of the endophyte isolates grew well and retained activity at +4 °C, and isolate as well as clone library sequences were often highly similar to sequences from bacteria from cold environments. Taken together, this study shows that arctic plants harbour a diverse community of bacterial endophytes, a portion of which seems to be tightly associated with specific plant species.

  5. Methane flux time series for tundra environments

    SciTech Connect

    Whalen, S.C.; Reeburgh, W.E. )

    1988-12-01

    Seasonal measurements of net methane flux were made at permanent sites representing important components of arctic tundra. The sites include Eriophorum tussocks, intertussock depressions, moss-covered areas, and Carex stands. Methane fluxes showed high diel, seasonal, intra site, and between site variability. Eriophorum tussocks and Carex dominated methane release to the atmosphere, with mean annual net methane fluxes of 8.05 + or{minus}2.50 g CH{sub 4}/sq m and 4.88 + or{minus}0.73 g CH{sub 4}/sq m, respectively. Methane fluxes form the moss sites and intertussock depressions were much lower. Over 90% of the mean annual methane flux from the Eriophorum, intertussock depressions, and Carex sites occurred between thaw and freeze-up. Some 40% of the mean annual methane flux from the moss sites occurred during winter. Composite methane fluxes for tussock tundra and Carex-dominated wet meadow tundra environments were produced by weighting measured component fluxes according to areal coverage. Tussock and wet meadow tundra account for an estimated global methane emission of 19-33 Tg/yr. 39 refs., 7 figs., 2 tabs.

  6. Pathways and transformations of dissolved methane and dissolved inorganic carbon in Arctic tundra soils: Evidence from analysis of stable isotopes

    NASA Astrophysics Data System (ADS)

    Throckmorton, H.; Perkins, G.; Muss, J. D.; Smith, L. J.; Conrad, M. E.; Torn, M. S.; Heikoop, J. M.; Newman, B. D.; Wilson, C. J.; Wullschleger, S. D.

    2014-12-01

    Arctic soils contain a large pool of terrestrial C and are of great interest because of their potential for releasing significant amounts of carbon dioxide (CO2) and methane (CH4) to the atmosphere. Few attempts have been made, however, to derive quantitative budgets of CO2 and CH4 budgets for high-latitude ecosystems. Therefore, this study used naturally occurring geochemical and isotopic tracers to estimate production pathways and transformations of dissolved inorganic carbon (DIC = Σ (total) dissolved CO2) and dissolved CH4 in soil pore waters from 17 locations (drainages) in Barrow, Alaska (USA) in July and September, 2013; and to approximate a complete balance of belowground C cycling at our sampling locations. Results suggest that CH4 was primarily derived from biogenic acetate fermentation, with a shift at 4 locations from July to September towards CO2 reduction as the dominant methanogenic pathway. A large majority of CH4 produced at the frost table methane was transferred directly to the atmosphere via plant roots and ebullition (94.0 ± 1.4% and 96.6 ± 5.0% in July and September). A considerable fraction of the remaining CH4 was oxidized to CO2 during upward diffusion in July and September, respectively. Methane oxidization produced <1% of CO2 relative to alternative production mechanisms in deep subsurface pore waters. The majority of subsurface CO2 was produced from anaerobic respiration, likely due to reduction of Fe oxides and humics (52 ± 6 to 100 ± 13%, on average) while CO2 produced from methanogenesis accounted for the remainder (0 ± 13% to 47 ± 6%, on average) for July and September, respectively. Dissolved CH4 and dissolved CO2 concentrations correlated with thaw depth, suggesting that Arctic ecosystems will likely produce and release a greater amount of greenhouse gasses under projected warming and deepening of active layer thaw depth under future climate change scenarios.

  7. Long-term monitoring at multiple trophic levels suggests heterogeneity in responses to climate change in the Canadian Arctic tundra.

    PubMed

    Gauthier, Gilles; Bêty, Joël; Cadieux, Marie-Christine; Legagneux, Pierre; Doiron, Madeleine; Chevallier, Clément; Lai, Sandra; Tarroux, Arnaud; Berteaux, Dominique

    2013-08-19

    Arctic wildlife is often presented as being highly at risk in the face of current climate warming. We use the long-term (up to 24 years) monitoring records available on Bylot Island in the Canadian Arctic to examine temporal trends in population attributes of several terrestrial vertebrates and in primary production. Despite a warming trend (e.g. cumulative annual thawing degree-days increased by 37% and snow-melt date advanced by 4-7 days over a 23-year period), we found little evidence for changes in the phenology, abundance or productivity of several vertebrate species (snow goose, foxes, lemmings, avian predators and one passerine). Only primary production showed a response to warming (annual above-ground biomass of wetland graminoids increased by 123% during this period). We nonetheless found evidence for potential mismatches between herbivores and their food plants in response to warming as snow geese adjusted their laying date by only 3.8 days on average for a change in snow-melt of 10 days, half of the corresponding adjustment shown by the timing of plant growth (7.1 days). We discuss several reasons (duration of time series, large annual variability, amplitude of observed climate change, nonlinear dynamic or constraints imposed by various rate of warming with latitude in migrants) to explain the lack of response by herbivores and predators to climate warming at our study site. We also show how length and intensity of monitoring could affect our ability to detect temporal trends and provide recommendations for future monitoring.

  8. Contrasting effects of warming and increased snowfall on Arctic tundra plant phenology over the past two decades.

    PubMed

    Bjorkman, Anne D; Elmendorf, Sarah C; Beamish, Alison L; Vellend, Mark; Henry, Gregory H R

    2015-12-01

    Recent changes in climate have led to significant shifts in phenology, with many studies demonstrating advanced phenology in response to warming temperatures. The rate of temperature change is especially high in the Arctic, but this is also where we have relatively little data on phenological changes and the processes driving these changes. In order to understand how Arctic plant species are likely to respond to future changes in climate, we monitored flowering phenology in response to both experimental and ambient warming for four widespread species in two habitat types over 21 years. We additionally used long-term environmental records to disentangle the effects of temperature increase and changes in snowmelt date on phenological patterns. While flowering occurred earlier in response to experimental warming, plants in unmanipulated plots showed no change or a delay in flowering over the 21-year period, despite more than 1 °C of ambient warming during that time. This counterintuitive result was likely due to significantly delayed snowmelt over the study period (0.05-0.2 days/yr) due to increased winter snowfall. The timing of snowmelt was a strong driver of flowering phenology for all species - especially for early-flowering species - while spring temperature was significantly related to flowering time only for later-flowering species. Despite significantly delayed flowering phenology, the timing of seed maturation showed no significant change over time, suggesting that warmer temperatures may promote more rapid seed development. The results of this study highlight the importance of understanding the specific environmental cues that drive species' phenological responses as well as the complex interactions between temperature and precipitation when forecasting phenology over the coming decades. As demonstrated here, the effects of altered snowmelt patterns can counter the effects of warmer temperatures, even to the point of generating phenological responses

  9. Long-term monitoring at multiple trophic levels suggests heterogeneity in responses to climate change in the Canadian Arctic tundra

    PubMed Central

    Gauthier, Gilles; Bêty, Joël; Cadieux, Marie-Christine; Legagneux, Pierre; Doiron, Madeleine; Chevallier, Clément; Lai, Sandra; Tarroux, Arnaud; Berteaux, Dominique

    2013-01-01

    Arctic wildlife is often presented as being highly at risk in the face of current climate warming. We use the long-term (up to 24 years) monitoring records available on Bylot Island in the Canadian Arctic to examine temporal trends in population attributes of several terrestrial vertebrates and in primary production. Despite a warming trend (e.g. cumulative annual thawing degree-days increased by 37% and snow-melt date advanced by 4–7 days over a 23-year period), we found little evidence for changes in the phenology, abundance or productivity of several vertebrate species (snow goose, foxes, lemmings, avian predators and one passerine). Only primary production showed a response to warming (annual above-ground biomass of wetland graminoids increased by 123% during this period). We nonetheless found evidence for potential mismatches between herbivores and their food plants in response to warming as snow geese adjusted their laying date by only 3.8 days on average for a change in snow-melt of 10 days, half of the corresponding adjustment shown by the timing of plant growth (7.1 days). We discuss several reasons (duration of time series, large annual variability, amplitude of observed climate change, nonlinear dynamic or constraints imposed by various rate of warming with latitude in migrants) to explain the lack of response by herbivores and predators to climate warming at our study site. We also show how length and intensity of monitoring could affect our ability to detect temporal trends and provide recommendations for future monitoring. PMID:23836788

  10. Soil Biota and Litter Decay in High Arctic Ecosystems

    NASA Astrophysics Data System (ADS)

    González, G.; Rivera, F.; Makarova, O.; Gould, W. A.

    2006-12-01

    Frost heave action contributes to the formation of non-sorted circles in the High Arctic. Non-sorted circles tend to heave more than the surrounding tundra due to deeper thaw and the formation of ice lenses. Thus, the geomorphology, soils and vegetation on the centers of the patterned-ground feature (non-sorted circles) as compared to the surrounding soils (inter-circles) can be different. We established a decomposition experiment to look at in situ decay rates of the most dominant graminoid species on non-sorted circles and adjacent inter-circle soils along a climatic gradient in the Canadian High Arctic as a component of a larger study looking at the biocomplexity of small-featured patterned ground ecosystems. Additionally, we investigated variation in soil chemical properties and biota, including soil microarthropods and microbial composition and biomass, as they relate to climate, topographic position, and litter decay rates. Our three sites locations, from coldest to warmest, are Isachsen, Ellef Ringnes Island (ER), NU (bioclimatic subzone A); Mould Bay (MB), Prince Patrick Island, NT (bioclimatic subzone B), and Green Cabin (GC), Aulavik National Park, Thomsen River, Banks Island, NT (bioclimatic subzone C). Our sample design included the selection of 15 non-sorted circles and adjacent inter-circle areas within the zonal vegetation at each site (a total of 90 sites), and a second set of 3 non-sorted circles and adjacent inter-circle areas in dry, mesic and wet tundra at each of the sites. Soil invertebrates were sampled at each site using both pitfall traps, soil microbial biomass was determined using substrate induced respiration and bacterial populations were determined using the most probable number method. Decomposition rates were measured using litterbags and as the percent of mass remaining of Carex misandra, Luzula nivalis and Alopecuris alpinus in GC, MB and ER, respectively. Our findings indicate these graminoid species decayed significantly over

  11. Effects of temperature seasonality on tundra vegetation productivity using a daily vegetation dynamics model

    NASA Astrophysics Data System (ADS)

    Epstein, H. E.; Erler, A.; Frazier, J.; Bhatt, U. S.

    2011-12-01

    Changes in the seasonality of air temperature will elicit interacting effects on the dynamics of snow cover, nutrient availability, vegetation growth, and other ecosystem properties and processes in arctic tundra. Simulation models often do not have the fine temporal resolution necessary to develop theory and propose hypotheses for the effects of daily and weekly timescale changes on ecosystem dynamics. We therefore developed a daily version of an arctic tundra vegetation dynamics model (ArcVeg) to simulate how changes in the seasonality of air temperatures influences the dynamics of vegetation growth and carbon sequestration across regions of arctic tundra. High temporal-resolution air and soil temperature data collected from field sites across the five arctic tundra bioclimate subzones were used to develop a daily weather generator operable for sites throughout the arctic tundra. Empirical relationships between temperature and soil nitrogen were used to generate daily dynamics of soil nitrogen availability, which drive the daily uptake of nitrogen and growth among twelve tundra plant functional types. Seasonal dynamics of the remotely sensed normalized difference vegetation index (NDVI) and remotely sensed land surface temperature from the Advanced Very High Resolution Radiometer (AVHRR) GIMMS 3g dataset were used to investigate constraints on the start of the growing season, although there was no indication of any spatially consistent temperature or day-length controls on greening onset. Because of the exponential nature of the relationship between soil temperature and nitrogen mineralization, temperature changes during the peak of the growing season had greater effects on vegetation productivity than changes earlier in the growing season. However, early season changes in temperature had a greater effect on the relative productivities of different plant functional types, with potential influences on species composition.

  12. Tundra burning in 2007 - Did sea ice retreat matter?

    NASA Astrophysics Data System (ADS)

    Alexeev, Vladimir A.; Euskirchen, Eugénie S.; Cherry, Jessica E.; Busey, Robert C.

    2015-06-01

    The goal of this study was to assess the importance of the 2007 sea ice retreat for hydrologic conditions on the Alaskan North Slope, and how this may have influenced the outbreak of tundra fires in this region. This study concentrates on two years, 2007 and 1996, with different arctic sea ice conditions and tundra fire activity. The year of 2007 is characterized by a low summer sea ice extent (second lowest) and high tundra fire activity, while 1996 had high sea ice extent, and few tundra fires. Atmospheric lateral boundary forcing from the NCEP/NCAR Reanalysis drove the Weather Research and Forecast (WRF) model, along with varying sea ice surface forcing designed to delineate the role of sea ice. WRF runs successfully reproduced the differences between 1996 and 2007. Surprisingly, replacing sea ice conditions in 1996 run by those from 2007 and vice versa (2007 run with 1996 sea ice) did not change the overall picture. The atmospheric circulation in August of 1996 included a significant low-pressure system over the Beaufort and Chukchi Seas. However, in 2007, a high-pressure system dominated the circulation over the Beaufort Sea. It is argued that this difference in large-scale patterns, rather than retreat of sea ice, was responsible for anomalously dry and warm atmospheric conditions over the North Slope in summer and autumn 2007, suitable for high tundra fire activity. Circulation in 2012 is contrasted with that in 2007 to further stress its importance for local weather on the North Slope.

  13. Mycorrhizal fungi supply nitrogen to host plants in Arctic tundra and boreal forests: 15N is the key signal.

    PubMed

    Hobbie, John E; Hobbie, Erik A; Drossman, Howard; Conte, Maureen; Weber, J C; Shamhart, Julee; Weinrobe, Melissa

    2009-01-01

    Symbiotic fungi's role in providing nitrogen to host plants is well-studied in tundra at Toolik Lake, Alaska, but little-studied in the adjoining boreal forest ecosystem. Along a 570 km north-south transect from the Yukon River to the North Slope of Alaska, the 15N content was strongly reduced in ectomycorrhizal and ericoid mycorrhizal plants including Betula, Salix, Picea mariana (P. Mill.) B.S.P., Picea glauca Moench (Voss), and ericaceous plants. Compared with the 15N content of soil, the foliage of nonmycorrhizal plants (Carex and Eriophorum) was unchanged, whereas content of the ectomycorrhizal fungi was very much higher (e.g., Boletaceae, Leccinum and Cortinarius). It is hypothesized that similar processes operate in tundra and boreal forest, both nitrogen-limited ecosystems: (i) mycorrhizal fungi break down soil polymers and take up amino acids or other nitrogen compounds; (ii) mycorrhizal fungi fractionate against 15N during production of transfer compounds; (iii) host plants are accordingly depleted in 15N; and (iv) mycorrhizal fungi are enriched in 15N. Increased N availability for plant roots or decreased light availability to understory plants may have decreased N allocation to mycorrhizal partners and increased delta15N by 3-4 parts per million for southern populations of Vaccinium vitis-idaea L. and Salix. Fungal biomass, measured as ergosterol, correlated strongly with soil organic matter and attained amounts similar to those in temperate forest soils.

  14. Disappearing Arctic tundra ponds: Fine-scale analysis of surface hydrology in drained thaw lake basins over a 65 year period (1948-2013)

    NASA Astrophysics Data System (ADS)

    Andresen, Christian G.; Lougheed, Vanessa L.

    2015-03-01

    Long-term fine-scale dynamics of surface hydrology in Arctic tundra ponds (less than 1 ha) are largely unknown; however, these small water bodies may contribute substantially to carbon fluxes, energy balance, and biodiversity in the Arctic system. Change in pond area and abundance across the upper Barrow Peninsula, Alaska, was assessed by comparing historic aerial imagery (1948) and modern submeter resolution satellite imagery (2002, 2008, and 2010). This was complemented by photogrammetric analysis of low-altitude kite-borne imagery in combination with field observations (2010-2013) of pond water and thaw depth transects in seven ponds of the International Biological Program historic research site. Over 2800 ponds in 22 drained thaw lake basins (DTLB) with different geological ages were analyzed. We observed a net decrease of 30.3% in area and 17.1% in number of ponds over the 62 year period. The inclusion of field observations of pond areas in 1972 from a historic research site confirms the linear downward trend in area. Pond area and number were dependent on the age of DTLB; however, changes through time were independent of DTLB age, with potential long-term implications for the hypothesized geomorphologic landscape succession of the thaw lake cycle. These losses were coincident with increases in air temperature, active layer, and density and cover of aquatic emergent plants in ponds. Increased evaporation due to warmer and longer summers, permafrost degradation, and transpiration from encroaching aquatic emergent macrophytes are likely the factors contributing to the decline in surface area and number of ponds.

  15. Effect of warming on the degradation and production of low-molecular-weight labile organic carbon in an Arctic tundra soil

    SciTech Connect

    Yang, Ziming; Wullschleger, Stan D.; Liang, Liyuan; Graham, David E.; Gu, Baohua

    2016-01-16

    The fate of soil organic carbon (SOC) stored in the Arctic permafrost is a key concern as temperatures continue to rise in the northern hemisphere. Studies and conceptual models suggest that SOC degradation is affected by the composition of SOC, but it is unclear exactly what portions of SOC are vulnerable to rapid breakdown and what mechanisms may be controlling SOC degradation upon permafrost thaw. Here, we examine the dynamic consumption and production of labile SOC in an anoxic incubation experiment using soil samples from the active layer at the Barrow Environmental Observatory, Barrow, Alaska, USA. Free-reducing sugars, alcohols, and low-molecular-weight (LMW) organic acids were analyzed during incubation at either –2 or 8 °C for up to 240 days. Results show that simple sugar and alcohol SOC largely account for the initial rapid release of CO2 and CH4 through anaerobic fermentation, whereas the fermentation products, acetate and formate, are subsequently utilized as primary substrates for methanogenesis. Iron(III) reduction is correlated to acetate production and methanogenesis, suggesting its important role as an electron acceptor in tundra SOC respiration. These observations are further supported in a glucose addition experiment, in which rapid CO2 and CH4 production occurred concurrently with rapid production and consumption of labile organics such as acetate. However, addition of tannic acid, as a more complex organic substrate, showed little influence on the overall production of CO2 and CH4 and organic acids. Together our study shows that LMW labile organics in SOC control the initial rapid release of green-house gases upon warming. We thus present a conceptual framework for the labile SOC transformations and their relations to fermentation, iron reduction and methanogenesis, thereby providing the basis for improved model prediction of climate feedbacks in the Arctic.

  16. Effect of warming on the degradation and production of low-molecular-weight labile organic carbon in an Arctic tundra soil

    DOE PAGES

    Yang, Ziming; Wullschleger, Stan D.; Liang, Liyuan; ...

    2016-01-16

    The fate of soil organic carbon (SOC) stored in the Arctic permafrost is a key concern as temperatures continue to rise in the northern hemisphere. Studies and conceptual models suggest that SOC degradation is affected by the composition of SOC, but it is unclear exactly what portions of SOC are vulnerable to rapid breakdown and what mechanisms may be controlling SOC degradation upon permafrost thaw. Here, we examine the dynamic consumption and production of labile SOC in an anoxic incubation experiment using soil samples from the active layer at the Barrow Environmental Observatory, Barrow, Alaska, USA. Free-reducing sugars, alcohols, andmore » low-molecular-weight (LMW) organic acids were analyzed during incubation at either –2 or 8 °C for up to 240 days. Results show that simple sugar and alcohol SOC largely account for the initial rapid release of CO2 and CH4 through anaerobic fermentation, whereas the fermentation products, acetate and formate, are subsequently utilized as primary substrates for methanogenesis. Iron(III) reduction is correlated to acetate production and methanogenesis, suggesting its important role as an electron acceptor in tundra SOC respiration. These observations are further supported in a glucose addition experiment, in which rapid CO2 and CH4 production occurred concurrently with rapid production and consumption of labile organics such as acetate. However, addition of tannic acid, as a more complex organic substrate, showed little influence on the overall production of CO2 and CH4 and organic acids. Together our study shows that LMW labile organics in SOC control the initial rapid release of green-house gases upon warming. We thus present a conceptual framework for the labile SOC transformations and their relations to fermentation, iron reduction and methanogenesis, thereby providing the basis for improved model prediction of climate feedbacks in the Arctic.« less

  17. Modeling the influence of hydrological processes on spatial and temporal patterns of CO{sub 2} soil efflux from an arctic tundra catchment

    SciTech Connect

    Ostendorf, B.

    1996-08-01

    Spatial and temporal patterns of CO{sub 2} efflux from arctic tundra soils are examined with three, linked simulation models at a 2.2-km{sup 2} catchment. The model complex runs on a 20*20 m grid and a temporal resolution of 1 h over one growing season. TOPMODEL is used to predict the dynamics of the water balance and spatial pattern of water table. A canopy model (GAS-FLUX) is used to predict moss and vascular plant transpiration rates. Soil respiration is computed form an empirical regression model incorporating the effects of soil temperature and depth to the water table. Soil efflux in the riparian zones of 60 g C m{sup {minus}2} compares to 119 g C m{sup {minus}2} in the hillslopes indicating large spatial differences. An increase of air temperature and solar radiation or a decrease of precipitation increase soil respiration. The results indicate a tight connection between water and carbon cycles at the catchment scale. Keeping all other conditions constant, a seasonal increase of transpiration rates by 10% increases soil respiration by 5% or 4.6 g Cm{sup {minus}2}. Data deficiencies and suggestions for future modeling are discussed. 40 refs., 8 figs.

  18. Comparative responses of Dryas octopetala to simulated changes in climate from alpine, low- and high arctic ITEX sites

    SciTech Connect

    Welker, J.M.; Parsons, A.N.; Walker, M.D. |||

    1995-06-01

    Field manipulations of environmental conditions have been established in dry tundra sites on Niwot Ridge, CO, Toolik Lake, AK and on Svalbard, Norway as part of the International Tundra Experiment (ITEX). Dryas octopetala is the dominant species at all three sites where we have examined organismic and ecosystem responses to similar increases in temperature. Leaf and seed mass differ significantly between all sites and warmer temperatures resulted in reductions in leaf mass at both the high and low arctic sites in the initial year, but this was not observed at the alpine site. Reductions in leaf mass were accompanied by changes in leaf demography. Seed masses were inherently different between sites, being largest from plants in the alpine tundra. Plants in the alpine and in the high arctic had higher seed weights when warmed. By the end of the second year, leaf C:N ratios were higher in alpine plants which were warmed. These organismic responses may set the stage for altered colonization of bare ground while changes in C:N ratios may modify decomposition rates linking organismic and ecosystem dynamics.

  19. Alaska's Living Tundra. Alaska Wildlife Week, 25-29 April 1988. Unit 6: Primary Teacher's Guide; Upper Elementary Teacher's Guide; Junior/Senior High School Teacher's Guide; Supplement.

    ERIC Educational Resources Information Center

    Quinlan, Susan E.

    Despite its cold and barren appearance, Alaska's tundra supports a surprising variety of insects, birds, and mammals. In this document, three teacher's guides (for primary, upper elementary, and junior and senior high schools) and a supplementary resource packet present a comprehensive unit of study on Alaska's living tundra. The five lessons in…

  20. Production and Cycling of Methylmercury in High Arctic Wetland Ponds

    NASA Astrophysics Data System (ADS)

    Lehnherr, I.; St. Louis, V. L.

    2010-12-01

    Some species of freshwater fish in the Canadian high Arctic contain levels of methylmercury (MeHg) that pose health risks to the northern Inuit peoples that harvest these species as a traditional food source. In temperate regions, wetlands are known natural sites of MeHg production and hence significant MeHg sources to downstream ecosystems. However, the importance of wetlands to Hg methylation in the Arctic is unclear and the sources of MeHg to arctic freshwater ecosystems are still largely unidentified. Our research is demonstrating that some shallow and warm wetland ponds on the Arctic landscape contain high MeHg concentrations compared to nearby deep and cold lakes. We used a mass-balance approach to measure the net in-pond production of MeHg in two warm wetland ponds (Ponds 1 and 2) near Lake Hazen, Ellesmere Island, Nunavut (81° N latitude). We quantified external inputs and outputs of MeHg to and from the ponds, as well as the accumulation of MeHg in the water column during the summers of 2005 and 2008. Any changes in water column MeHg concentrations that could not be accounted for by external inputs or sinks were attributed to in-pond production. The principal external input and sink of MeHg was, respectively, wet atmospheric deposition and water-column MeHg photodemethylation. For 2005, we estimate that the net flux of MeHg from sediments into the water column was 0.015 μg m-2 d-1 in Pond 1 and 0.0016 μg m-2 d-1 in Pond 2. Compared to sediment-water MeHg fluxes measured in Alaskan tundra lakes (0.0015-0.0045 μg m-2 d-1), Pond 1 sediments are a greater source of MeHg while Pond 2 is similar to the Alaskan lakes. Furthermore, the accumulation of MeHg in the water column of Pond 1 (0.0061 μg m-2 d-1) was similar to the net yield of MeHg from temperate boreal wetlands (0.0005-0.006 μg m-2 d-1), demonstrating that these Arctic wetlands are important sites of MeHg production. In addition, we used mercury stable-isotope tracers to quantify methylation and

  1. Modelling high arctic percent vegetation cover using field digital images and high resolution satellite data

    NASA Astrophysics Data System (ADS)

    Liu, Nanfeng; Treitz, Paul

    2016-10-01

    In this study, digital images collected at a study site in the Canadian High Arctic were processed and classified to examine the spatial-temporal patterns of percent vegetation cover (PVC). To obtain the PVC of different plant functional groups (i.e., forbs, graminoids/sedges and mosses), field near infrared-green-blue (NGB) digital images were classified using an object-based image analysis (OBIA) approach. The PVC analyses comparing different vegetation types confirmed: (i) the polar semi-desert exhibited the lowest PVC with a large proportion of bare soil/rock cover; (ii) the mesic tundra cover consisted of approximately 60% mosses; and (iii) the wet sedge consisted almost exclusively of graminoids and sedges. As expected, the PVC and green normalized difference vegetation index (GNDVI; (RNIR - RGreen)/(RNIR + RGreen)), derived from field NGB digital images, increased during the summer growing season for each vegetation type: i.e., ∼5% (0.01) for polar semi-desert; ∼10% (0.04) for mesic tundra; and ∼12% (0.03) for wet sedge respectively. PVC derived from field images was found to be strongly correlated with WorldView-2 derived normalized difference spectral indices (NDSI; (Rx - Ry)/(Rx + Ry)), where Rx is the reflectance of the red edge (724.1 nm) or near infrared (832.9 nm and 949.3 nm) bands; Ry is the reflectance of the yellow (607.7 nm) or red (658.8 nm) bands with R2's ranging from 0.74 to 0.81. NDSIs that incorporated the yellow band (607.7 nm) performed slightly better than the NDSIs without, indicating that this band may be more useful for investigating Arctic vegetation that often includes large proportions of senescent vegetation throughout the growing season.

  2. Integrating Research and Education in a Study of Biocomplexity in Arctic Tundra Ecosystems: Costs, Results, and Benefits to the Research Agenda

    NASA Astrophysics Data System (ADS)

    Gould, W. A.; González, G.; Walker, D. A.

    2006-12-01

    The integration of research and education is one of the fundamental goals of our national science policy. There is strong interest to improve this integration at the graduate and undergraduate levels, with the general public, and with local and indigenous people. Efforts expended in integrating research and education can occur at the expense of research productivity and represent a cost. Results may include number of personnel involved, activities accomplished, research or other products produced. Benefits are difficult to quantify and may be short term and tangible, e.g. education-research projects enhancing research productivity with publications, or long-term and include intangibles such as personal interactions and experiences influencing career choices, the perception of research activities, enhanced communication, and direct or indirect influence on related research and educational projects. We have integrated the University field course Arctic Field Ecology with an interdisciplinary research project investigating the interactions of climate, vegetation, and permafrost in the study Biocomplexity of Arctic Tundra Ecosystems. The integration is designed to give students background in regional ecology; introduce students to the project objectives, methods, and personnel; provide for interaction with participating scientists; conduct research initiated by the class and instructors; and provide the opportunity to interact with indigenous people with interests in traditional ecological knowledge and land management. Our costs included increased logistical complexity and time-demands on the researchers and staff managing the integration. The educational component increased the size of the research group with the addition of 55 participants over the 4 field seasons of the study. Participants came from 7 countries and included 20 enrolled university students, 18 Inuit non student participants, 9 Inuit students, 3 visiting scientists, 3 staff, and 2 scientist

  3. Phenological response of tundra plants to background climate variation tested using the International Tundra Experiment.

    PubMed

    Oberbauer, S F; Elmendorf, S C; Troxler, T G; Hollister, R D; Rocha, A V; Bret-Harte, M S; Dawes, M A; Fosaa, A M; Henry, G H R; Høye, T T; Jarrad, F C; Jónsdóttir, I S; Klanderud, K; Klein, J A; Molau, U; Rixen, C; Schmidt, N M; Shaver, G R; Slider, R T; Totland, Ø; Wahren, C-H; Welker, J M

    2013-08-19

    The rapidly warming temperatures in high-latitude and alpine regions have the potential to alter the phenology of Arctic and alpine plants, affecting processes ranging from food webs to ecosystem trace gas fluxes. The International Tundra Experiment (ITEX) was initiated in 1990 to evaluate the effects of expected rapid changes in temperature on tundra plant phenology, growth and community changes using experimental warming. Here, we used the ITEX control data to test the phenological responses to background temperature variation across sites spanning latitudinal and moisture gradients. The dataset overall did not show an advance in phenology; instead, temperature variability during the years sampled and an absence of warming at some sites resulted in mixed responses. Phenological transitions of high Arctic plants clearly occurred at lower heat sum thresholds than those of low Arctic and alpine plants. However, sensitivity to temperature change was similar among plants from the different climate zones. Plants of different communities and growth forms differed for some phenological responses. Heat sums associated with flowering and greening appear to have increased over time. These results point to a complex suite of changes in plant communities and ecosystem function in high latitudes and elevations as the climate warms.

  4. The effect of snow cover on lemming population cycles in the Canadian high Arctic.

    PubMed

    Bilodeau, Frédéric; Gauthier, Gilles; Berteaux, Dominique

    2013-08-01

    Rising temperatures and changes in the precipitation regime will have a strong impact on the quality of the snow cover in the Arctic. A snow cover of good quality protecting lemmings from cold temperatures and predators is thought to be an important factor for maintaining the cyclic dynamic of their populations in the tundra. We examined if the characteristics of annual fluctuations (amplitude and shape of phases) in brown lemming (Lemmus trimucronatus) density could be determined by snow depth, snow density, sub-nivean temperature and persistence of snow. Using an 18-year time series of brown lemming abundance on Bylot Island in the Canadian Arctic, we tested if snow variables could explain the residual variation between the observed lemming density and the one predicted by models where cyclicity had been accounted for. Our analysis provides support for the hypothesis that snow cover can affect the amplitude and possibly also the periodicity of lemming population cycles in the High Arctic. Summer abundance of brown lemmings was higher following winters with a deep snow cover and a low-density snow pack near the ground but was unaffected by the date of establishment or melting and duration of the snow cover. Two snow variables showed a temporal trend; mean winter snow depth tended to increase and date of establishment of the hiemal threshold occurred earlier over time. These temporal trends, which should be favourable to lemmings, may explain why healthy population cycles have apparently been maintained at our study site contrary to other Arctic sites.

  5. Comparing carbon storage of Siberian tundra and taiga permafrost ecosystems at very high spatial resolution

    NASA Astrophysics Data System (ADS)

    Siewert, Matthias B.; Hanisch, Jessica; Weiss, Niels; Kuhry, Peter; Maximov, Trofim C.; Hugelius, Gustaf

    2015-10-01

    Permafrost-affected ecosystems are important components in the global carbon (C) cycle that, despite being vulnerable to disturbances under climate change, remain poorly understood. This study investigates ecosystem carbon storage in two contrasting continuous permafrost areas of NE and East Siberia. Detailed partitioning of soil organic carbon (SOC) and phytomass carbon (PC) is analyzed for one tundra (Kytalyk) and one taiga (Spasskaya Pad/Neleger) study area. In total, 57 individual field sites (24 and 33 in the respective areas) have been sampled for PC and SOC, including the upper permafrost. Landscape partitioning of ecosystem C storage was derived from thematic upscaling of field observations using a land cover classification from very high resolution (2 × 2 m) satellite imagery. Nonmetric multidimensional scaling was used to explore patterns in C distribution. In both environments the ecosystem C is mostly stored in the soil (≥86%). At the landscape scale C stocks are primarily controlled by the presence of thermokarst depressions (alases). In the tundra landscape, site-scale variability of C is controlled by periglacial geomorphological features, while in the taiga, local differences in catenary position, soil texture, and forest successions are more important. Very high resolution remote sensing is highly beneficial to the quantification of C storage. Detailed knowledge of ecosystem C storage and ground ice distribution is needed to predict permafrost landscape vulnerability to projected climatic changes. We argue that vegetation dynamics are unlikely to offset mineralization of thawed permafrost C and that landscape-scale reworking of SOC represents the largest potential changes to C cycling.

  6. Hypolithic microbial community of quartz pavement in the high-altitude tundra of central Tibet.

    PubMed

    Wong, Fiona K Y; Lacap, Donnabella C; Lau, Maggie C Y; Aitchison, J C; Cowan, Donald A; Pointing, Stephen B

    2010-11-01

    The hypolithic microbial community associated with quartz pavement at a high-altitude tundra location in central Tibet is described. A small-scale ecological survey indicated that 36% of quartz rocks were colonized. Community profiling using terminal restriction fragment length polymorphism revealed no significant difference in community structure among a number of colonized rocks. Real-time quantitative PCR and phylogenetic analysis of environmental phylotypes obtained from clone libraries were used to elucidate community structure across all domains. The hypolithon was dominated by cyanobacterial phylotypes (73%) with relatively low frequencies of other bacterial phylotypes, largely represented by the chloroflexi, actinobacteria, and bacteriodetes. Unidentified crenarchaeal phylotypes accounted for 4% of recoverable phylotypes, while algae, fungi, and mosses were indicated by a small fraction of recoverable phylotypes.

  7. Hypolithic Microbial Community of Quartz Pavement in the High-Altitude Tundra of Central Tibet

    PubMed Central

    Wong, Fiona K. Y.; Lacap, Donnabella C.; Lau, Maggie C. Y.; Aitchison, J. C.; Cowan, Donald A.

    2010-01-01

    The hypolithic microbial community associated with quartz pavement at a high-altitude tundra location in central Tibet is described. A small-scale ecological survey indicated that 36% of quartz rocks were colonized. Community profiling using terminal restriction fragment length polymorphism revealed no significant difference in community structure among a number of colonized rocks. Real-time quantitative PCR and phylogenetic analysis of environmental phylotypes obtained from clone libraries were used to elucidate community structure across all domains. The hypolithon was dominated by cyanobacterial phylotypes (73%) with relatively low frequencies of other bacterial phylotypes, largely represented by the chloroflexi, actinobacteria, and bacteriodetes. Unidentified crenarchaeal phylotypes accounted for 4% of recoverable phylotypes, while algae, fungi, and mosses were indicated by a small fraction of recoverable phylotypes. Electronic supplementary material The online version of this article (doi:10.1007/s00248-010-9653-2) contains supplementary material, which is available to authorized users. PMID:20336290

  8. Diverging Plant and Ecosystem Strategies in Response to Climate Change in the High Arctic

    NASA Astrophysics Data System (ADS)

    Maseyk, K. S.; Welker, J. M.; Czimczik, C. I.; Lupascu, M.; Lett, C.; Seibt, U. H.

    2014-12-01

    Increasing summer precipitation means Arctic growing seasons are becoming wetter as well as warmer, but the effect of these coupled changes on tundra ecosystem functioning remains largely unknown. We have determined how warmer and wetter summers affect coupled carbon-water cycling in a High Arctic polar semi-desert ecosystem in NW Greenland. Measurements of ecosystem CO2 and water fluxes throughout the growing season and leaf ecophysiological traits (gas exchange, morphology, leaf chemistry) were made at a long-term climate change experiment. After 9 years of exposure to warmer (+ 4°C) and / or wetter (+ 50% precipitation) treatments, we found diverging plant strategies between the responses to warming with or without an increase in summer precipitation. Warming alone resulted in an increase in leaf nitrogen, mesophyll conductance and leaf-mass per area and higher rates of leaf-level photosynthesis, but with warming and wetting combined leaf traits remain largely unchanged. However, total leaf area increased with warming plus wetting but was unchanged with warming alone. The combined effect of these leaf trait and canopy adjustments is a decrease in ecosystem water-use efficiency (the ratio of net productivity to evapotranspiration) with warming only, but a substantial increase with combined warming and wetting. We conclude that increasing summer precipitation will alter tundra ecohydrological responses to warming; that leaf-level changes in ecophysiological traits have an upward cascading consequence for ecosystem and land surface-climate interactions; and the current relative resistance of High Arctic ecosystems to warming may mask biochemical and carbon cycling changes already underway.

  9. Huanghella arctica gen. nov., sp. nov., a bacterium of the family Cytophagaceae isolated from Arctic tundra soil.

    PubMed

    Jiang, Fan; Xiao, Mengchen; Chen, Lu; Kan, Wenjing; Peng, Fang; Dai, Jun; Chang, Xulu; Li, Wenxin; Fang, Chengxiang

    2013-02-01

    A novel, strictly aerobic, red-pigmented, gram-reaction-negative bacterium, designated strain R9-9(T), was isolated from tundra soil collected near Ny-Ålesund, Svalbard Archipelago, Norway (78° N). The novel strain was subjected to a taxonomic study using a polyphasic approach. It grew optimally at 20-22 °C and at pH 7.0. Flexirubin-type pigments were absent. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain R9-9(T) represents a distinct phyletic line that reflects a novel generic status within the family Cytophagaceae. The novel strain showed relatively low 16S rRNA gene sequence similarities (<88.0 %) to members of established genera. Strain R9-9(T) contained summed feature 3 (C(16 : 1)ω7c and/or C(16 : 1)ω6c), iso-C(17 : 0) 3-OH, iso-C(15 : 0) and C(16 : 1)ω5c as its major cellular fatty acids, phosphatidylethanolamine as its main polar lipid, and MK-7 as its major respiratory quinone. The genomic DNA G+C content was 56.1 mol%. On the basis of phenotypic, chemotaxonomic and phylogenetic data, strain R9-9(T) is considered to represent a novel species in a new genus in the family Cytophagaceae, for which the name Huanghella arctica gen. nov., sp. nov. is proposed. The type strain is R9-9(T) ( = CCTCC AB 2010418(T) = NRRL B-59750(T)).

  10. Persistence of bat defence reactions in high Arctic moths (Lepidoptera).

    PubMed

    Rydell, J; Roininen, H; Philip, K W

    2000-03-22

    We investigated the bat defence reactions of three species of moths (Gynaephora groenlandica, Gynaephora rossi (Lymantriidae) and Psychophora sabini (Geometridae)) in the Canadian Arctic archipelago. Since these moths inhabit the Arctic tundra and, therefore, are most probably spatially isolated from bats, their hearing and associated defensive reactions are probably useless and would therefore be expected to disappear with ongoing adaptation to Arctic conditions. When exposed to bat-like ultrasound (26 kHz and 110 dB sound pressure level root mean square at 1 m) flying male Gynaephora spp. always reacted defensively by rapidly reversing their flight course. They could hear the sound and reacted at least 15-25 m away. Psychophora sabini walking on a surface froze at distances of at least 5-7 m from the sound source. However, two out of three individuals of this species (all males) did not respond in any way to the sound while in flight. Hence, we found evidence of degeneration of bat defence reactions, i.e. adaptation to the bat-free environment, in P. sabini but not in Gynaephora spp. Some Arctic moths (Gynaephora spp.) still possess defensive reactions against bats, possibly because the selection pressure for the loss of the trait is such that it declines only very slowly (perhaps by genetic drift; and there may not have been enough time for the trait to disappear. One possible reason may be that Arctic moths have long generation times.

  11. Biogenic volatile organic compound emissions along a high arctic soil moisture gradient.

    PubMed

    Svendsen, Sarah Hagel; Lindwall, Frida; Michelsen, Anders; Rinnan, Riikka

    2016-12-15

    Emissions of biogenic volatile organic compounds (BVOCs) from terrestrial ecosystems are important for the atmospheric chemistry and the formation of secondary organic aerosols, and may therefore influence the climate. Global warming is predicted to change patterns in precipitation and plant species compositions, especially in arctic regions where the temperature increase will be most pronounced. These changes are potentially highly important for the BVOC emissions but studies investigating the effects are lacking. The aim of this study was to investigate the quality and quantity of BVOC emissions from a high arctic soil moisture gradient extending from dry tundra to a wet fen. Ecosystem BVOC emissions were sampled five times in the July-August period using a push-pull enclosure technique, and BVOCs trapped in absorbent cartridges were analyzed using gas chromatography-mass spectrometry. Plant species compositions were estimated using the point intercept method. In order to take into account important underlying ecosystem processes, gross ecosystem production, ecosystem respiration and net ecosystem production were measured in connection with chamber-based BVOC measurements. Highest emissions of BVOCs were found from vegetation communities dominated by Salix arctica and Cassiope tetragona, which had emission profiles dominated by isoprene and monoterpenes, respectively. These results show that emissions of BVOCs are highly dependent on the plant cover supported by the varying soil moisture, suggesting that high arctic BVOC emissions may affect the climate differently if soil water content and plant cover change.

  12. Pathways and transformations of dissolved methane and dissolved inorganic carbon in Arctic tundra watersheds: Evidence from analysis of stable isotopes

    DOE PAGES

    Throckmorton, Heather M.; Heikoop, Jeffrey M.; Newman, Brent D.; ...

    2015-11-08

    Arctic soils contain a large pool of terrestrial C and are of interest due to their potential for releasing significant carbon dioxide (CO2) and methane (CH4) to the atmosphere. Due to substantial landscape heterogeneity, predicting ecosystem-scale CH4 and CO2 production is challenging. This study assessed dissolved inorganic carbon (DIC = Σ (total) dissolved CO2) and CH4 in watershed drainages in Barrow, Alaska as critical convergent zones of regional geochemistry, substrates, and nutrients. In July and September of 2013, surface waters and saturated subsurface pore waters were collected from 17 drainages. Based on simultaneous DIC and CH4 cycling, we synthesized isotopicmore » and geochemical methods to develop a subsurface CH4 and DIC balance by estimating mechanisms of CH4 and DIC production and transport pathways and oxidation of subsurface CH4. We observed a shift from acetoclastic (July) toward hydrogenotropic (September) methanogenesis at sites located toward the end of major freshwater drainages, adjacent to salty estuarine waters, suggesting an interesting landscape-scale effect on CH4 production mechanism. The majority of subsurface CH4 was transported upward by plant-mediated transport and ebullition, predominantly bypassing the potential for CH4 oxidation. Thus, surprisingly, CH4 oxidation only consumed approximately 2.51± 0.82% (July) and 0.79 ± 0.79% (September) of CH4 produced at the frost table, contributing to <0.1% of DIC production. DIC was primarily produced from respiration, with iron and organic matter serving as likely e- acceptors. Furthermore, this work highlights the importance of spatial and temporal variability of CH4 production at the watershed scale and suggests broad scale investigations are required to build better regional or pan-Arctic representations of CH4 and CO2 production.« less

  13. Science Traverses in the Canadian High Arctic

    NASA Technical Reports Server (NTRS)

    Williamson, Marie-Claude

    2012-01-01

    The presentation is divided into three parts. Part I is an overview of early expeditions to the High Arctic, and their political consequences at the time. The focus then shifts to the Geological Survey of Canada s mapping program in the North (Operation Franklin), and to the Polar Continental Shelf Project (PCSP), a unique organization that resides within the Government of Canada s Department of Natural Resources, and supports mapping projects and science investigations. PCSP is highlighted throughout the presentation so a description of mandate, budgets, and support infrastructure is warranted. In Part II, the presenter describes the planning required in advance of scientific deployments carried out in the Canadian High Arctic from the perspective of government and university investigators. Field operations and challenges encountered while leading arctic field teams in fly camps are also described in this part of the presentation, with particular emphasis on the 2008 field season. Part III is a summary of preliminary results obtained from a Polar Survey questionnaire sent out to members of the Arctic research community in anticipation of the workshop. The last part of the talk is an update on the analog program at the Canadian Space Agency, specifically, the Canadian Analog Research Network (CARN) and current activities related to Analog missions, 2009-2010.

  14. Quantitative Interpretation of Arctic Tundra Attributes Using Remote Sensing: Leveraging Field Data, Modern- and Legacy Landsat Data, and Commercial Imagery in Northern Alaska

    NASA Astrophysics Data System (ADS)

    Frost, G. V., Jr.; Macander, M. J.; Nelson, P. R.

    2014-12-01

    Integrated analysis of ground-based vegetation data and remote sensing supports vegetation mapping, landscape-change detection, wildlife habitat assessment, and tracking of phenological events such as green-up and senescence. The life-cycles of tundra plants occur within a highly compressed seasonal window, making the quantitative assessment of vegetation and landscape attributes from ≤30m resolution remotely-sensed imagery, such as above-ground biomass, % shrub cover, and % surface water, a difficult task when applied across large study domains. To support mapping of vegetation and landscape attributes across ~100,000 km2 of Alaska's North Slope, we obtained ground data for tundra vegetation using a point-intercept sampling approach across a network of 107 field plots spanning gradients of bioclimate, landscape position (upland, lowland, riverine), and geomorphic setting (foothills, coastal plain). At each plot, vegetation data were collected along three 50-m linear transects, compatible with 30-m Landsat imagery. We summarized live vegetation, litter, and non-vegetated surfaces using three terms: top cover (uppermost "hit"), percent cover (total areal cover along transect), and hit density (all "hits" at a point). We then evaluated a suite of data models (e.g., General Additive Models, classification tree, clustering) and data-mining approaches (e.g., neural networks, random forest) using midsummer Landsat TM/ETM+ acquisitions since 1985, and OLI acquisitions for 2013-2014. The large size, frequent cloudiness, and interannual variability of the study area necessitated the compositing of a multitude of Landsat scenes. A median NDVI compositing technique was used to select Landsat observations from cloud- and shadow-free pixels that met day-of-year and year constraints. This technique produced seamless, phenologically consistent composites that are largely free of artifacts and suitable for regional-scale analysis. Ground-based training data and an archive of

  15. Pathways and transformations of dissolved methane and dissolved inorganic carbon in Arctic tundra watersheds: Evidence from analysis of stable isotopes

    SciTech Connect

    Throckmorton, Heather M.; Heikoop, Jeffrey M.; Newman, Brent D.; Altmann, Garrett L.; Conrad, Mark S.; Muss, Jordan D.; Perkins, George B.; Smith, Lydia J.; Torn, Margaret S.; Wullschleger, Stan D.; Wilson, Cathy J.

    2015-11-08

    Arctic soils contain a large pool of terrestrial C and are of interest due to their potential for releasing significant carbon dioxide (CO2) and methane (CH4) to the atmosphere. Due to substantial landscape heterogeneity, predicting ecosystem-scale CH4 and CO2 production is challenging. This study assessed dissolved inorganic carbon (DIC = Σ (total) dissolved CO2) and CH4 in watershed drainages in Barrow, Alaska as critical convergent zones of regional geochemistry, substrates, and nutrients. In July and September of 2013, surface waters and saturated subsurface pore waters were collected from 17 drainages. Based on simultaneous DIC and CH4 cycling, we synthesized isotopic and geochemical methods to develop a subsurface CH4 and DIC balance by estimating mechanisms of CH4 and DIC production and transport pathways and oxidation of subsurface CH4. We observed a shift from acetoclastic (July) toward hydrogenotropic (September) methanogenesis at sites located toward the end of major freshwater drainages, adjacent to salty estuarine waters, suggesting an interesting landscape-scale effect on CH4 production mechanism. The majority of subsurface CH4 was transported upward by plant-mediated transport and ebullition, predominantly bypassing the potential for CH4 oxidation. Thus, surprisingly, CH4 oxidation only consumed approximately 2.51± 0.82% (July) and 0.79 ± 0.79% (September) of CH4 produced at the frost table, contributing to <0.1% of DIC production. DIC was primarily produced from respiration, with iron and organic matter serving as likely e- acceptors. Furthermore, this work highlights the importance of spatial and temporal variability of CH4 production at the watershed scale and suggests broad scale investigations are required to build better regional or pan-Arctic representations of CH

  16. Sources and pathways of artificial radionuclides to soils at a High Arctic site.

    PubMed

    Lokas, E; Bartmiński, P; Wachniew, P; Mietelski, J W; Kawiak, T; Srodoń, J

    2014-11-01

    Activity concentrations, inventories and activity ratios of (137)Cs, (238)Pu, (239 + 240)Pu and (241)Am in soil profiles were surveyed in the dry tundra and the adjoining proglacial zones of glaciers at a High Arctic site on Svalbard. Vertical profiles of radionuclide activities were determined in up to 14-cm-thick soil sequences. Additionally, soil properties (pH, organic matter, texture, mineral composition and sorption capacity) were analyzed. Results obtained in this study revealed a large range of activity concentrations and inventories of the fallout radionuclides from the undetectable to the uncommonly high levels (inventories of 30,900 ± 940, 47 ± 6, 886 ± 80 and 296 ± 19 Bq/m(2) for (137)Cs, (238)Pu, (239 + 240)Pu and (241)Am, respectively) found in two profiles from the proglacial zone. Concentration of these initially airborne radionuclides in the proglacial zone soils is related to their accumulation in cryoconites that have a large ability to concentrate trace metals. The cryoconites develop on the surface of glaciers, and the material they accumulate is deposited on land surface after the glaciers retreat. The radionuclide inventories in the tundra soils, which effectively retain radionuclides due to high organic matter contents, were comparable to the global fallout deposition for this region of the world. The (238)Pu/(239 + 240)Pu activity ratios for tundra soils suggested global fallout as the dominant source of Pu. The (238)Pu/(239 + 240)Pu and (239 + 240)Pu/(137)Cs activity ratios in the proglacial soils pointed to possible contributions of these radionuclides from other, unidentified sources.

  17. Bird orientation at high latitudes: flight routes between Siberia and North America across the Arctic Ocean

    PubMed

    Alerstam; Gudmundsson

    1999-12-22

    Bird migration and orientation at high latitudes are of special interest because of the difficulties associated with different compass systems in polar areas and because of the considerable differences between flight routes conforming to loxodromes (rhumblines) or orthodromes (great circle routes). Regular and widespread east-north-east migration of birds from the northern tundra of Siberia towards North America across the Arctic Ocean (without landmark influences) were recorded by ship-based tracking radar studies in July and August. Field observations indicated that waders, including species such as Phalaropusfulicarius and Calidris melanotos, dominated, but also terns and skuas may have been involved. Analysis of flight directions in relation to the wind showed that these movements are not caused by wind drift. Assuming possible orientation principles based on celestial or geomagnetic cues, different flight trajectories across the Arctic Ocean were calculated: geographical loxodromes, sun compass routes, magnetic loxodromes and magnetoclinic routes. The probabilities of these four alternatives are evaluated on the basis of both the availability of required orientation cues and the predicted flight paths. This evaluation supports orientation along sun compass routes. Because of the longitudinal time displacement sun compass routes show gradually changing compass courses in close agreement with orthodromes. It is suggested that an important migration link between Siberia and North American stopover sites 1000-2500km apart across the Arctic Ocean has evolved based on sun compass orientation along orthodrome-like routes.

  18. THE ROLE OF THERMAL REGIMEN IN TUNDRA PLANT COMMUNITY RESTORATION

    EPA Science Inventory

    Mineral extraction activities in the Arctic regions of the world produce long-lasting ecological disturbances. Assisted recovery from such disturbances may require restoration of the tundra thermal regime. We transplanted plugs of entire root zone and live tundra plants to a dist...

  19. Increased peak-growing season GPP in a Greenlandic high-Arctic fen 1992-2008

    NASA Astrophysics Data System (ADS)

    Tagesson, T.; Mastepanov, M.; Tamstorf, M. P.; Eklundh, L.; Schubert, P.; Ekberg, A.; Sigsgaard, C.; Christensen, T. R.; Strom, L.

    2010-12-01

    Arctic ecosystems play a key role in the terrestrial carbon cycle. Recent studies have shown a greening trend and indicated an increase in CO2 uptake in boreal and sub- to low-Arctic areas. Our aim was to combine satellite-based normalized difference vegetation index (NDVI) with ground-based flux measurements of CO2 to investigate possible changes in gross primary production (GPP) for the peak of the growing season between 1992 and 2008 in the high-Arctic. As study area we used a 1.4 km2 rectangle surrounding Rylekaerene, a wet tundra ecosystem situated in the Zackenberg Research Area (74o28 N 20o34 W), North Eastern Greenland. We combined the light use efficiency (LUE) model (GPP= ɛ × PAR × FAPAR, where ɛ is the light use efficiency of the vegetation, PAR is the incoming photosynthetically active radiation and FAPAR the PAR absorbed by the green vegetation) with NDVI data derived from a set of peak growing season satellite images from 1992 to 2008. The LUE-modelled results show a substantial increase in peak-growing season GPP in Rylekaerene during the period. The GPP increase was accompanied by a strong increase in CO2 concentration and air temperature. Possibly, indicating that the increase in GPP was due to the substantial increase in local air temperature, possibly in combination with CO2 fertilization. To model GPP, we first parameterized the LUE-model for the vegetation types dominating the Rylekaerene for the peak of the growing season (peak). Average noon-time PAR measured on the days with satellite images was used as incoming PAR in the model. We found a significant linear relationship between ground-based FAPARpeak and NDVI. The ɛpeak was on average 1.78 g CO2 MJ-1 for this high-Arctic wet tundra ecosystem, which is reasonable for high-Arctic ecosystems. The model was evaluated against field-measured GPP. There were large model uncertainties. This was caused by large natural variation in the field measurements which the model was based upon and

  20. Small thaw ponds: an unaccounted source of methane in the Canadian high Arctic.

    PubMed

    Negandhi, Karita; Laurion, Isabelle; Whiticar, Michael J; Galand, Pierre E; Xu, Xiaomei; Lovejoy, Connie

    2013-01-01

    Thawing permafrost in the Canadian Arctic tundra leads to peat erosion and slumping in narrow and shallow runnel ponds that surround more commonly studied polygonal ponds. Here we compared the methane production between runnel and polygonal ponds using stable isotope ratios, ¹⁴C signatures, and investigated potential methanogenic communities through high-throughput sequencing archaeal 16S rRNA genes. We found that runnel ponds had significantly higher methane and carbon dioxide emissions, produced from a slightly larger fraction of old carbon, compared to polygonal ponds. The methane stable isotopic signature indicated production through acetoclastic methanogenesis, but gene signatures from acetoclastic and hydrogenotrophic methanogenic Archaea were detected in both polygonal and runnel ponds. We conclude that runnel ponds represent a source of methane from potentially older C, and that they contain methanogenic communities able to use diverse sources of carbon, increasing the risk of augmented methane release under a warmer climate.

  1. Small Thaw Ponds: An Unaccounted Source of Methane in the Canadian High Arctic

    PubMed Central

    Negandhi, Karita; Laurion, Isabelle; Whiticar, Michael J.; Galand, Pierre E.; Xu, Xiaomei; Lovejoy, Connie

    2013-01-01

    Thawing permafrost in the Canadian Arctic tundra leads to peat erosion and slumping in narrow and shallow runnel ponds that surround more commonly studied polygonal ponds. Here we compared the methane production between runnel and polygonal ponds using stable isotope ratios, 14C signatures, and investigated potential methanogenic communities through high-throughput sequencing archaeal 16S rRNA genes. We found that runnel ponds had significantly higher methane and carbon dioxide emissions, produced from a slightly larger fraction of old carbon, compared to polygonal ponds. The methane stable isotopic signature indicated production through acetoclastic methanogenesis, but gene signatures from acetoclastic and hydrogenotrophic methanogenic Archaea were detected in both polygonal and runnel ponds. We conclude that runnel ponds represent a source of methane from potentially older C, and that they contain methanogenic communities able to use diverse sources of carbon, increasing the risk of augmented methane release under a warmer climate. PMID:24236014

  2. Coupled ecosystem carbon and nutrient cycling in a High Arctic ecosystem are altered by long-term experimental warming and higher rainfall

    NASA Astrophysics Data System (ADS)

    Schaeffer, S. M.; Schimel, J.; Welker, J. M.

    2013-12-01

    The rapid changes in temperature and precipitation in High Arctic tundra ecosystems are altering the biogeochemical cycles of nitrogen (N) and carbon (C), but in ways that are difficult to anticipate. The challenge grows from the complexity of tundra soil organic matter, the uncertainty of N cycle responses and the extent to which shifts in soil N processes are coupled with the C cycle, including leaf-level photosynthesis, gross ecosystem photosynthesis (GEP-productivity) and net CO2 exchange (NEE-C sequestration). Understanding the processes that are leading to changes in High Arctic biogeochemical processes are especially important today as soil organic C pools in the High Arctic are up to 6 times greater than previously estimated, and are sensitive to being oxidized to the atmosphere through changes in microbial decomposition associated with warmer and wetter conditions. We used a long-term (since 2003) experiment of summer warming and supplemental summer water additions to a High Arctic ecosystem in NW Greenland to determine the impact of interactions between temperature, water availability, and microbial metabolism on the cycling of C and plant-available N in High Arctic tundra soil. We have found that water availability plays a critical role in these cycles in High Arctic tundra, over and above that from temperature increases. On seasonal time scales, we observed greater net N mineralization under both global change scenarios, yet water addition also significantly increased net nitrification rates, loss of NO3--N via leaching from surface soil layers, and lowered rates of labile organic C and N production. We also expected the chronic warming and watering would lead to long-term changes in soil N-cycling that would be reflected in soil δ15N values. However, we found that soil δ15N decreased under the different climate change scenarios. Our findings indicate that warmer, wetter High Arctic tundra will be cycling N and C in ways that may transform these

  3. Trace element concentrations and gastrointestinal parasites of Arctic terns breeding in the Canadian High Arctic.

    PubMed

    Provencher, J F; Braune, B M; Gilchrist, H G; Forbes, M R; Mallory, M L

    2014-04-01

    Baseline data on trace element concentrations are lacking for many species of Arctic marine birds. We measured essential and non-essential element concentrations in Arctic tern (Sterna paradisaea) liver tissue and brain tissue (mercury only) from Canada's High Arctic, and recorded the presence/absence of gastrointestinal parasites during four different phases of the breeding season. Arctic terns from northern Canada had similar trace element concentrations to other seabird species feeding at the same trophic level in the same region. Concentrations of bismuth, selenium, lead and mercury in Arctic terns were high compared to published threshold values for birds. Selenium and mercury concentrations were also higher in Arctic terns from northern Canada than bird species sampled in other Arctic areas. Selenium, mercury and arsenic concentrations varied across the time periods examined, suggesting potential regional differences in the exposure of biota to these elements. For unknown reasons, selenium concentrations were significantly higher in birds with gastrointestinal parasites as compared to those without parasites, while bismuth concentrations were higher in Arctic terns not infected with gastrointestinal parasites.

  4. Methanotrophic diversity in high arctic wetlands on the islands of Svalbard (Norway)--denaturing gradient gel electrophoresis analysis of soil DNA and enrichment cultures.

    PubMed

    Wartiainen, Ingvild; Hestnes, Anne Grethe; Svenning, Mette M

    2003-10-01

    The methanotrophic community in arctic soil from the islands of Svalbard, Norway (78 degrees N) was analysed by combining group-specific PCR with PCR of the highly variable V3 region of the 16S rRNA gene and then by denaturing gradient gel electrophoresis (DGGE). Selected bands were sequenced for identification. The analyses were performed with DNA extracted directly from soil and from enrichment cultures at 10 and 20 degrees C. The two genera Methylobacter and Methylosinus were found in all localities studied. The DGGE band patterns were simple, and DNA fragments with single base differences were separated. The arctic tundra is a potential source of extensive methane emission due to climatic warming because of its large reservoirs of stored organic carbon. Higher temperatures due to climatic warming can cause increased methane production, and the abundance and activity of methane-oxidizing bacteria in the arctic soil may be important regulators for methane emission to the atmosphere.

  5. ArcticDEM; A Publically Available, High Resolution Elevation Model of the Arctic

    NASA Astrophysics Data System (ADS)

    Morin, Paul; Porter, Claire; Cloutier, Michael; Howat, Ian; Noh, Myoung-Jong; Willis, Michael; Bates, Brian; Willamson, Cathleen; Peterman, Kennith

    2016-04-01

    A Digital Elevation Model (DEM) of the Arctic is needed for a large number of reasons, including: measuring and understanding rapid, ongoing changes to the Arctic landscape resulting from climate change and human use and mitigation and adaptation planning for Arctic communities. The topography of the Arctic is more poorly mapped than most other regions of Earth due to logistical costs and the limits of satellite missions with low-latitude inclinations. A convergence of civilian, high-quality sub-meter stereo imagery; petascale computing and open source photogrammetry software has made it possible to produce a complete, very high resolution (2 to 8-meter posting), elevation model of the Arctic. A partnership between the US National Geospatial-intelligence Agency and a team led by the US National Science Foundation funded Polar Geospatial Center is using stereo imagery from DigitalGlobe's Worldview-1, 2 and 3 satellites and the Ohio State University's Surface Extraction with TIN-based Search-space Minimization (SETSM) software running on the University of Illinois's Blue Water supercomputer to address this challenge. The final product will be a seemless, 2-m posting digital surface model mosaic of the entire Arctic above 60 North including all of Alaska, Greenland and Kamchatka. We will also make available the more than 300,000 individual time-stamped DSM strip pairs that were used to assemble the mosaic. The Arctic DEM will have a vertical precision of better than 0.5m and can be used to examine changes in land surfaces such as those caused by permafrost degradation or the evolution of arctic rivers and floodplains. The data set can also be used to highlight changing geomorphology due to Earth surface mass transport processes occurring in active volcanic and glacial environments. When complete the ArcticDEM will catapult the Arctic from the worst to among the best mapped regions on Earth.

  6. Deposition of ozone to tundra

    SciTech Connect

    Jacob, D.J.; Fan, S.M.; Wofsy, S.C.; Spiro, P.A.; Bakwin, P.S.; Ritter, J.A.; Browell, E.V.; Gregory, G.L.; Fitzjarrald, D.R.; Moore, K.E. NASA, Langley Research Center, Hampton, VA New York State Univ., Albany )

    1992-10-01

    Eddy correlation measurements of O3 deposition fluxes to tundra during the Arctic Boundary Layer Expedition (ABLE 3A) are reported. The mean O[sub 3] deposition velocity was 0.24 cm/s in the daytime and 0.12 cm/s at night. The day-to-day difference in deposition velocity was driven by both atmospheric stability and surface reactivity. The mean surface resistance to O[sub 3] deposition was 2.6 s/cm in the daytime and 3.4 s/cm at night. The relatively low surface resistance at night is attributed to light-insensitive uptake of O[sub 3] at dry upland tundra surfaces. The small day-tonight difference in surface resistance is attributed to additional stomatal uptake by wet meadow tundra plants in the daytime. The mean O[sub 3] deposition flux to the world north of 60 deg N in July-August is estimated at 8.2 x 10 exp 10 molecules/sq cm/s. Suppression of photochemical loss by small anthropogenic inputs of nitrogen oxides could have a major effect on O[sub 3] concentrations in the summertime Arctic troposphere. 34 refs.

  7. Deposition of ozone to tundra

    NASA Technical Reports Server (NTRS)

    Jacob, D. J.; Fan, S.-M.; Wofsy, S. C.; Spiro, P. A.; Bakwin, P. S.; Ritter, J. A.; Browell, E. V.; Gregory, G. L.; Fitzjarrald, D. R.; Moore, K. E.

    1992-01-01

    Eddy correlation measurements of O3 deposition fluxes to tundra during the Arctic Boundary Layer Expedition (ABLE 3A) are reported. The mean O3 deposition velocity was 0.24 cm/s in the daytime and 0.12 cm/s at night. The day-to-day difference in deposition velocity was driven by both atmospheric stability and surface reactivity. The mean surface resistance to O3 deposition was 2.6 s/cm in the daytime and 3.4 s/cm at night. The relatively low surface resistance at night is attributed to light-insensitive uptake of O3 at dry upland tundra surfaces. The small day-tonight difference in surface resistance is attributed to additional stomatal uptake by wet meadow tundra plants in the daytime. The mean O3 deposition flux to the world north of 60 deg N in July-August is estimated at 8.2 x 10 exp 10 molecules/sq cm/s. Suppression of photochemical loss by small anthropogenic inputs of nitrogen oxides could have a major effect on O3 concentrations in the summertime Arctic troposphere.

  8. Circumpolar Arctic vegetation: a hierarchic review and roadmap toward an internationally consistent approach to survey, archive and classify tundra plot data

    NASA Astrophysics Data System (ADS)

    Walker, D. A.; Daniëls, F. J. A.; Alsos, I.; Bhatt, U. S.; Breen, A. L.; Buchhorn, M.; Bültmann, H.; Druckenmiller, L. A.; Edwards, M. E.; Ehrich, D.; Epstein, H. E.; Gould, W. A.; Ims, R. A.; Meltofte, H.; Raynolds, M. K.; Sibik, J.; Talbot, S. S.; Webber, P. J.

    2016-05-01

    Satellite-derived remote-sensing products are providing a modern circumpolar perspective of Arctic vegetation and its changes, but this new view is dependent on a long heritage of ground-based observations in the Arctic. Several products of the Conservation of Arctic Flora and Fauna are key to our current understanding. We review aspects of the PanArctic Flora, the Circumpolar Arctic Vegetation Map, the Arctic Biodiversity Assessment, and the Arctic Vegetation Archive (AVA) as they relate to efforts to describe and map the vegetation, plant biomass, and biodiversity of the Arctic at circumpolar, regional, landscape and plot scales. Cornerstones for all these tools are ground-based plant-species and plant-community surveys. The AVA is in progress and will store plot-based vegetation observations in a public-accessible database for vegetation classification, modeling, diversity studies, and other applications. We present the current status of the Alaska Arctic Vegetation Archive (AVA-AK), as a regional example for the panarctic archive, and with a roadmap for a coordinated international approach to survey, archive and classify Arctic vegetation. We note the need for more consistent standards of plot-based observations, and make several recommendations to improve the linkage between plot-based observations biodiversity studies and satellite-based observations of Arctic vegetation.

  9. Tundra photosynthesis captured by satellite-observed solar-induced chlorophyll fluorescence

    NASA Astrophysics Data System (ADS)

    Luus, K. A.; Commane, R.; Parazoo, N. C.; Benmergui, J.; Euskirchen, E. S.; Frankenberg, C.; Joiner, J.; Lindaas, J.; Miller, C. E.; Oechel, W. C.; Zona, D.; Wofsy, S.; Lin, J. C.

    2017-02-01

    Accurately quantifying the timing and magnitude of respiration and photosynthesis by high-latitude ecosystems is important for understanding how a warming climate influences global carbon cycling. Data-driven estimates of photosynthesis across Arctic regions often rely on satellite-derived enhanced vegetation index (EVI); we find that satellite observations of solar-induced chlorophyll fluorescence (SIF) provide a more direct proxy for photosynthesis. We model Alaskan tundra CO2 cycling (2012-2014) according to temperature and shortwave radiation and alternately input EVI or SIF to prescribe the annual seasonal cycle of photosynthesis. We find that EVI-based seasonality indicates spring "green-up" to occur 9 days prior to SIF-based estimates, and that SIF-based estimates agree with aircraft and tower measurements of CO2. Adopting SIF, instead of EVI, for modeling the seasonal cycle of tundra photosynthesis can result in more accurate estimates of growing season duration and net carbon uptake by arctic vegetation.

  10. Resistance and resilience of tundra plant communities to disturbance by winter seismic vehicles

    SciTech Connect

    Felix, N.A.; Raynolds, M.K.; Jorgenson, J.C.; DuBois, K.E. )

    1992-02-01

    Effects of winter seismic exploration on arctic tundra were evaluated on the coastal plain of the Arctic National Wildlife Refuge, four to five growing seasons after disturbance. Plant cover, active layer depths, and track depression were measured at plots representing major tundra plant communities and different levels of initial disturbance. Results are compared with the initial effects reported earlier. Little resilience was seen in any vegetation type, with no clearly decreasing trends in community dissimilarity. Active layer depths remained greater on plots in all nonriparian vegetation types, and most plots still had visible trails. Decreases in plant cover persisted on most plots, although a few species showed recovery or increases in cover above predisturbance level. Moist sedge-shrub tundra and dryas terraces had the largest community dissimilarities initially, showing the least resistance to high levels of winter vehicle disturbance. Community dissimilarity continued to increase for five seasons in moist sedge-shrub tundra, with species composition changing to higher sedge cover and lower shrub cover. The resilience amplitude may have been exceeded on four plots which had significant track depression.

  11. Changing Climate Sensitivity in Response to Forest-Tundra Snow Albedo Feedback during the mid to late Pliocene Cooling

    NASA Astrophysics Data System (ADS)

    Paiewonsky, P.

    2015-12-01

    The forest-tundra snow albedo feedback is an important feedback in Earth's climate system, especially due to its potential role in modulating glacial cycles. Until now, little research has been done on how the strength of this feedback might vary with the background climate state. Over the last 4 million years, I hypothesize that the feedback has been generally weaker under warm Northern Hemispheric conditions when tundra has been primarily confined to the high Arctic and forest has extended to most of the Arctic coastline than under cooler Northern Hemispheric conditions in which the forest-tundra boundary has generally lain to the south, extending across the interiors of the large continental land masses. To test the hypothesis of the weakened/strengthened feedback, I used an Earth System Model of Intermediate Complexity that consists of a dynamic terrestrial vegetation model coupled to a climate model. A set of time-slice experiments with different orbital and greenhouse gas concentrations were analyzed. In one set of experiments, the feedback gain with respect to annual average top-of-atmosphere net short wave radiation due to vegetation was 1.42 for modern conditions but only 1.14 for the mid-Pliocene. Additionally, we compared experiments with different shortwave-radiation parameterizations, which differed in the amount of shortwave energy flux reaching the surface (and subsequently affecting vegetative biomass). These techniques allowed us to isolate the mechanisms responsible for the varying strength of the forest-tundra snow albedo feedback. The results also show that many factors affect the strength of feedback. In this presentation I will concentrate on the availability of land for conversion of forest to tundra (and vice versa), cloud cover near the forest-tundra boundary, and the integrated surface insolation contrast between tundra and forest during the snow-covered season.

  12. Highly individualistic rates of plant phenological advance associated with arctic sea ice dynamics.

    PubMed

    Post, Eric; Kerby, Jeffrey; Pedersen, Christian; Steltzer, Heidi

    2016-12-01

    We analysed 12 years of species-specific emergence dates of plants at a Low-Arctic site near Kangerlussuaq, Greenland to investigate associations with sea ice dynamics, a potential contributor to local temperature variation in near-coastal tundra. Species displayed highly variable rates of phenological advance, from a maximum of -2.55 ± 0.17 and -2.93 ± 0.51 d yr(-1) among a graminoid and forb, respectively, to a minimum of -0.55 ± 0.19 d yr(-1) or no advance at all in the two deciduous shrub species. Monthly Arctic-wide sea ice extent was a significant predictor of emergence timing in 10 of 14 species. Despite variation in rates of advance among species, these rates were generally greatest in the earliest emerging species, for which monthly sea ice extent was also the primary predictor of emergence. Variation among species in rates of phenological advance reshuffled the phenological community, with deciduous shrubs leafing out progressively later relative to forbs and graminoids. Because early species advanced more rapidly than late species, and because rates of advance were greatest in species for which emergence phenology was associated with sea ice dynamics, accelerating sea ice decline may contribute to further divergence between early- and late-emerging species in this community.

  13. Turbulent transports over tundra

    NASA Technical Reports Server (NTRS)

    Fitzjarrald, David R.; Moore, Kathleen E.

    1992-01-01

    An extensive period of eddy correlation surface flux measurements was conducted at a site distant from the coast on the western Alaskan tundra. The surface exchange of heat and moisture over tundra during the summer was limited by a strong resistance to transfer from the upper soil layer through the ground cover, with canopy resistances to evaporation observed to be approximately 200 s/m. Though July 1988 was anomalously warm and dry in the region and August was close to normal temperature and rainfall, there was no appreciable difference in the canopy resistance between the periods. During the dry sunny period at the end of July, the observed evaporation rate was 2 mm/d. High canopy resistance led to an approximate equipartition of net radiation between latent and sensible heat, each accounting for 40 percent of the available energy, with heat balance apparently going into soil heat flux.

  14. Estimating Pan Arctic Net Ecosystem Exchange using Functional Relationships with Air temperature, Leaf Area Index and Photosynthetic Active Radiation

    NASA Astrophysics Data System (ADS)

    Mbufong, H.; Kusbach, A.; Lund, M.; Persson, A.; Christensen, T. R.; Tamstorf, M. P.; Connolly, J.

    2015-12-01

    The high variability in Arctic tundra net ecosystem exchange (NEE) of carbon (C) is often attributed to the high spatial heterogeneity of Arctic tundra. Current models of carbon exchange thus handle the Arctic as either a single or few ecosystems, responding to environmental change in the same manner. In this study, we developed and tested a simple NEE model using the Misterlich light response curve (LRC) function with photosynthetic photon flux density (PPFD) as the main driving variable. Model calibration was carried out with eddy covariance carbon dioxide data from 12 Arctic tundra sites. The model input parameters (fcsat, Rd and α) were estimated as a function of air temperature and leaf area index (LAI) and represent specific characteristics of the NEE-PPFD relationship. They describe the saturation flux, dark respiration and initial light use efficiency, respectively. While remotely sensed LAI is readily available as a MODIS Terra product (MCD15A3), air temperature was estimated from a direct relationship with MODIS land surface temperature (MOD11A2, LST). Therefore, no specific knowledge of the vegetation type is required. Preliminary results show the model captures the spatial heterogeneity of the Arctic tundra but so far, overestimates NEE on all 17 test sites which include heaths, bogs, fens, and tussock tundra vegetation. The final updated results and error assessment will be presented at the conference in December.

  15. Soil-plant N processes in a High Arctic ecosystem, NW Greenland are altered by long-term experimental warming and higher rainfall.

    PubMed

    Schaeffer, Sean M; Sharp, Elizabeth; Schimel, Joshua P; Welker, Jeffery M

    2013-11-01

    Rapid temperature and precipitation changes in High Arctic tundra ecosystems are altering the biogeochemical cycles of carbon (C) and nitrogen (N), but in ways that are difficult to predict. The challenge grows from the uncertainty of N cycle responses and the extent to which shifts in soil N are coupled with the C cycle and productivity of tundra systems. We used a long-term (since 2003) experiment of summer warming and supplemental summer water additions to a High Arctic ecosystem in NW Greenland, and applied a combination of discrete sampling and in situ soil core incubations to measure C and N pools and seasonal microbial processes that might control plant-available N. We hypothesized that elevated temperature and increased precipitation would stimulate microbial activity and net inorganic N mineralization, thereby increasing plant N-availability through the growing season. While we did find increased N mineralization rates under both global change scenarios, water addition also significantly increased net nitrification rates, loss of NO3 (-) -N via leaching, and lowered rates of labile organic N production. We also expected the chronic warming and watering would lead to long-term changes in soil N-cycling that would be reflected in soil δ(15) N values. We found that soil δ(15) N decreased under the different climate change scenarios. Our results suggest that temperature accelerates biological processes and existing C and N transformations, but moisture increases soil hydraulic connectivity and so alters the pathways, and changes the fate of the products of C and N transformations. In addition, our findings indicate that warmer, wetter High Arctic tundra will be cycling N and C in ways that may transform these landscapes in part leading to greater C sequestration, but simultaneously, N losses from the upper soil profile that may be transported to depth dissolved in water and or transported off site in lateral flow.

  16. Experimental Increases in Snow Alter Physical, Chemical and Feedback Processes in the High Arctic.

    NASA Astrophysics Data System (ADS)

    Rogers, M.; Welker, J.; Sullivan, P.; Sletten, R.; Arens, S.; Kristenson, H.

    2007-12-01

    Winter climate conditions are changing throughout the Arctic. In Greenland, there are observed increases in snowfall across portions of the island while the margins of the Greenland Ice Sheet are thinning. However, these changes and the consequences of altered meteorological surface dynamics on High Arctic terrestrial ecosystems and their potential feedbacks are unclear. Increases in winter snow cover may cause warmer soils in winter, greater rates of winter C losses, increases in winter N mineralization, shorter growing seasons and reduced net C gain in summer due to either reduced gross photosynthesis or increases in ecosystem respiration. In our study, we have constructed replicated snow fences in prostrate dwarf shrub tundra (polar desert and semi- desert) ecosystems in NW Greenland. Our measurements were taken at the deep (1.0 m snow depth) and intermediate (0.35 m snow depth) points along the drift to address these questions: a) how do increases in snow depth alter the surface and subsurface physical and chemical processes of these ecosystems?, and b) to what extent do increases in snow depth alter net CO2 exchange, gross ecosystem photosynthesis and ecosystem respiration? After three years of treatment we have found that in winter, deep snow results in warmer soil temperatures and in the subsequent summer, areas with deep winter snow have colder soil temperatures. This effect is most pronounced immediately following snowmelt and temperatures slowly return to ambient conditions near the end of summer. Deeper snow results in higher soil water contents in early summer, but by mid-July soil water contents have returned to ambient levels. Net ecosystem CO2 exchange rates are consistently negative (CO2 source to the atmosphere) through most of the growing season and vary in their magnitude by snow depth and ecosystem type. Areas with the deepest snow during winter consistently have the largest rates of CO2 loss to the atmosphere. The middle snow depth treatment

  17. The Contribution of Mosses to the Complex Pattern of Diurnal and Seasonal Metabolism the wet Coastal Tundra Ecosystems Near Barrow Alaska.

    NASA Astrophysics Data System (ADS)

    Zona, D.; Oechel, W.; Hastings, S.; Oberbauer, S.; Kopetz, I.; Ikawa, H.

    2006-12-01

    Despite the abundance and importance bryophytes in the Alaskan Arctic tundra there is relatively little information on the role of these plants in determining the CO2 fluxes of Arctic tundra and, in particular, the environmental controls and climate change sensitivities of current and future photosynthesis in Arctic mosses. Studies in the tundra biome during the IBP program implicated high light together with high temperature as causes of decreases in photosynthesis in arctic mosses. Several authors have reported midday depression of moss photosynthesis due to high irradiance, even under optimum temperature and fully hydrated conditions. The focus of this study is to understand the role of Sphagnum ssp. mosses of various species, the dominant moss in the Alaska coastal wet Tundra on the total ecosystem carbon exchange throughout the season and in particular soon after snowmelt when the ecosystem is a carbon source. Our hypothesis is that the ecosystem carbon source activity during this critical period may be a result of sensitivity of mosses to light and photoinhibition in the absence of the protective canopy layer of vascular plants. In this study we measured daily courses of photosynthesis and fluorescence in the moss layer and we compare it to the total ecosystem carbon fluxes determined by the eddy covariance technique. The measurements were conducted in wet coastal tundra from June 2006, right after the snow melt, to August 2006 in the Biological Experimental Observatory (BEO) in Barrow, Alaska. The photosynthesis in the moss layer was found to be strongly inhibited when the radiation exceeded 800 ìmol m-2 s-1. Mosses remained fully hydrated throughout the season, precluding drying as a cause of decreased photosynthesis. Dark-adapted fluorescence measurements (Fv/Fm) showed a relatively low value (0.6) right after the snow melt, and remained fairly stable throughout the season. This low value was previously reported as characteristic of photoinhibited

  18. Anurans in a Subarctic Tundra Landscape Near Cape Churchill, Manitoba

    USGS Publications Warehouse

    Reiter, M.E.; Boal, C.W.; Andersen, D.E.

    2008-01-01

    Distribution, abundance, and habitat relationships of anurans inhabiting subarctic regions are poorly understood, and anuran monitoring protocols developed for temperate regions may not be applicable across large roadless areas of northern landscapes. In addition, arctic and subarctic regions of North America are predicted to experience changes in climate and, in some areas, are experiencing habitat alteration due to high rates of herbivory by breeding and migrating waterfowl. To better understand subarctic anuran abundance, distribution, and habitat associations, we conducted anuran calling surveys in the Cape Churchill region of Wapusk National Park, Manitoba, Canada, in 2004 and 2005. We conducted surveys along ~l-km transects distributed across three landscape types (coastal tundra, interior sedge meadow-tundra, and boreal forest-tundra interface) to estimate densities and probabilities of detection of Boreal Chorus Frogs (Pseudacris maculata) and Wood Frogs (Lithobates sylvaticus). We detected a Wood Frog or Boreal Chorus Frog on 22 (87%) of 26 transects surveyed, but probability of detection varied between years and species and among landscape types. Estimated densities of both species increased from the coastal zone inland toward the boreal forest edge. Our results suggest anurans occur across all three landscape types in our study area, but that species-specific spatial patterns exist in their abundances. Considerations for both spatial and temporal variation in abundance and detection probability need to be incorporated into surveys and monitoring programs for subarctic anurans.

  19. Modeling the spatiotemporal variability in subsurface thermal regimes across a low-relief polygonal tundra landscape

    NASA Astrophysics Data System (ADS)

    Kumar, Jitendra; Collier, Nathan; Bisht, Gautam; Mills, Richard T.; Thornton, Peter E.; Iversen, Colleen M.; Romanovsky, Vladimir

    2016-09-01

    Vast carbon stocks stored in permafrost soils of Arctic tundra are under risk of release to the atmosphere under warming climate scenarios. Ice-wedge polygons in the low-gradient polygonal tundra create a complex mosaic of microtopographic features. This microtopography plays a critical role in regulating the fine-scale variability in thermal and hydrological regimes in the polygonal tundra landscape underlain by continuous permafrost. Modeling of thermal regimes of this sensitive ecosystem is essential for understanding the landscape behavior under the current as well as changing climate. We present here an end-to-end effort for high-resolution numerical modeling of thermal hydrology at real-world field sites, utilizing the best available data to characterize and parameterize the models. We develop approaches to model the thermal hydrology of polygonal tundra and apply them at four study sites near Barrow, Alaska, spanning across low to transitional to high-centered polygons, representing a broad polygonal tundra landscape. A multiphase subsurface thermal hydrology model (PFLOTRAN) was developed and applied to study the thermal regimes at four sites. Using a high-resolution lidar digital elevation model (DEM), microtopographic features of the landscape were characterized and represented in the high-resolution model mesh. The best available soil data from field observations and literature were utilized to represent the complex heterogeneous subsurface in the numerical model. Simulation results demonstrate the ability of the developed modeling approach to capture - without recourse to model calibration - several aspects of the complex thermal regimes across the sites, and provide insights into the critical role of polygonal tundra microtopography in regulating the thermal dynamics of the carbon-rich permafrost soils. Areas of significant disagreement between model results and observations highlight the importance of field-based observations of soil thermal and

  20. Frozen ponds: production and storage of methane during the Arctic winter in a lowland tundra landscape in northern Siberia, Lena River Delta

    NASA Astrophysics Data System (ADS)

    Langer, M.; Westermann, S.; Anthony, K. M. Walter; Wischnewski, K.; Boike, J.

    2014-07-01

    Lakes and ponds play a key role in the carbon cycle of permafrost ecosystems, where they are considered to be hotspots of carbon dioxide CO2 and methane CH4 emission. The strength of these emissions is, however, controlled by a variety of physical and biogeochemical processes whose responses to a warming climate are complex and only poorly understood. Small waterbodies have been attracting an increasing amount of attention since recent studies demonstrated that ponds can make a significant contribution to the CO2 and CH4 emissions of tundra ecosystems. Waterbodies also have a marked effect on the thermal state of the surrounding permafrost; during the freezing period they prolong the period of time during which thawed soil material is available for microbial decomposition. This study presents net CH4 production rates during the freezing period from ponds within a typical lowland tundra landscape in northern Siberia. Rate estimations were based on CH4 concentrations measured in surface lake ice from a variety of waterbody types. Vertical profiles along ice blocks showed an exponential increase in CH4 concentration with depth. These CH4 profiles were reproduced by a 1-D mass balance model and the net CH4 production rates then inferred through inverse modeling. Results revealed marked differences in early winter net CH4 production among various ponds. Initial state ponds underlain by stable permafrost with little or no signs of degradation yielded low net production rates, of the order of 10-11 to 10-10 mol m-2 s-1 (0.01 to 0.14 mgCH4 m-2 d-1). In contrast, advanced state ponds exhibiting clear signs of thermal erosion yielded net CH4 production rates of the order of 10-7 mol m-2 s-1 (140 mgCH4 m-2 d-1). The net production rate per square meter of advanced state ponds exceeded the maximum summer CH4 emission rates per square meter which was measured for the average tundra landscape at the study site. Our results therefore indicate that, once a particular threshold in

  1. Ecosystem development and carbon cycle on a glacier foreland in the high Arctic, Ny-Alesund, Svalbard.

    PubMed

    Nakatsubo, Takayuki; Bekku, Yukiko Sakata; Uchida, Masaki; Muraoka, Hiroyuki; Kume, Atsushi; Ohtsuka, Toshiyuki; Masuzawa, Takehiro; Kanda, Hiroshi; Koizumi, Hiroshi

    2005-06-01

    The Arctic terrestrial ecosystem is thought to be extremely susceptible to climate change. However, because of the diverse responses of ecosystem components to change, an overall response of the ecosystem carbon cycle to climate change is still hard to predict. In this review, we focus on several recent studies conducted to clarify the pattern of the carbon cycle on the deglaciated area of Ny-Alesund, Svalbard in the high Arctic. Vegetation cover and soil carbon pools tended to increase with the progress of succession. However, even in the latter stages of succession, the size of the soil carbon pool was much smaller than those reported for the low Arctic tundra. Cryptogams contributed the major proportion of phytomass in the later stages. However, because of water limitation, their net primary production was smaller than that of the vascular plants. The compartment model that incorporated major carbon pools and flows suggested that the ecosystem of the later stages is likely to be a net sink of carbon at least for the summer season. Based on the eco-physiological characteristics of the major ecosystem components, we suggest several possible scenarios of future changes in the ecosystem carbon cycle.

  2. Climate sensitivity of shrub growth across the tundra biome

    NASA Astrophysics Data System (ADS)

    Myers-Smith, Isla H.; Elmendorf, Sarah C.; Beck, Pieter S. A.; Wilmking, Martin; Hallinger, Martin; Blok, Daan; Tape, Ken D.; Rayback, Shelly A.; Macias-Fauria, Marc; Forbes, Bruce C.; Speed, James D. M.; Boulanger-Lapointe, Noémie; Rixen, Christian; Lévesque, Esther; Schmidt, Niels Martin; Baittinger, Claudia; Trant, Andrew J.; Hermanutz, Luise; Collier, Laura Siegwart; Dawes, Melissa A.; Lantz, Trevor C.; Weijers, Stef; Jørgensen, Rasmus Halfdan; Buchwal, Agata; Buras, Allan; Naito, Adam T.; Ravolainen, Virve; Schaepman-Strub, Gabriela; Wheeler, Julia A.; Wipf, Sonja; Guay, Kevin C.; Hik, David S.; Vellend, Mark

    2015-09-01

    Rapid climate warming in the tundra biome has been linked to increasing shrub dominance. Shrub expansion can modify climate by altering surface albedo, energy and water balance, and permafrost, yet the drivers of shrub growth remain poorly understood. Dendroecological data consisting of multi-decadal time series of annual shrub growth provide an underused resource to explore climate-growth relationships. Here, we analyse circumpolar data from 37 Arctic and alpine sites in 9 countries, including 25 species, and ~42,000 annual growth records from 1,821 individuals. Our analyses demonstrate that the sensitivity of shrub growth to climate was: (1) heterogeneous, with European sites showing greater summer temperature sensitivity than North American sites, and (2) higher at sites with greater soil moisture and for taller shrubs (for example, alders and willows) growing at their northern or upper elevational range edges. Across latitude, climate sensitivity of growth was greatest at the boundary between the Low and High Arctic, where permafrost is thawing and most of the global permafrost soil carbon pool is stored. The observed variation in climate-shrub growth relationships should be incorporated into Earth system models to improve future projections of climate change impacts across the tundra biome.

  3. High Diversity of Planctomycetes in Soils of Two Lichen-Dominated Sub-Arctic Ecosystems of Northwestern Siberia.

    PubMed

    Ivanova, Anastasia A; Kulichevskaya, Irina S; Merkel, Alexander Y; Toshchakov, Stepan V; Dedysh, Svetlana N

    2016-01-01

    A wide variety of terrestrial ecosystems in tundra have a ground vegetation cover composed of reindeer lichens (genera Cladonia and Cetraria). The microbial communities of two lichen-dominated ecosystems typical of the sub-arctic zone of northwestern Siberia, that is a forested tundra soil and a shallow acidic peatland, were examined in our study. As revealed by molecular analyses, soil and peat layers just beneath the lichen cover were abundantly colonized by bacteria from the phylum Planctomycetes. Highest abundance of planctomycetes detected by fluorescence in situ hybridization was in the range 2.2-2.7 × 10(7) cells per gram of wet weight. 16S rRNA gene fragments from the Planctomycetes comprised 8-13% of total 16S rRNA gene reads retrieved using Illumina pair-end sequencing from the soil and peat samples. Lichen-associated assemblages of planctomycetes displayed unexpectedly high diversity, with a total of 89,662 reads representing 1723 operational taxonomic units determined at 97% sequence identity. The soil of forested tundra was dominated by uncultivated members of the family Planctomycetaceae (53-71% of total Planctomycetes-like reads), while sequences affiliated with the Phycisphaera-related group WD2101 (recently assigned to the order Tepidisphaerales) were most abundant in peat (28-51% of total reads). Representatives of the Isosphaera-Singulisphaera group (14-28% of total reads) and the lineages defined by the genera Gemmata (1-4%) and Planctopirus-Rubinisphaera (1-3%) were present in both habitats. Two strains of Singulisphaera-like bacteria were isolated from studied soil and peat samples. These planctomycetes displayed good tolerance of low temperatures (4-15°C) and were capable of growth on a number of polysaccharides, including lichenan, a characteristic component of lichen-derived phytomass.

  4. High Diversity of Planctomycetes in Soils of Two Lichen-Dominated Sub-Arctic Ecosystems of Northwestern Siberia

    PubMed Central

    Ivanova, Anastasia A.; Kulichevskaya, Irina S.; Merkel, Alexander Y.; Toshchakov, Stepan V.; Dedysh, Svetlana N.

    2016-01-01

    A wide variety of terrestrial ecosystems in tundra have a ground vegetation cover composed of reindeer lichens (genera Cladonia and Cetraria). The microbial communities of two lichen-dominated ecosystems typical of the sub-arctic zone of northwestern Siberia, that is a forested tundra soil and a shallow acidic peatland, were examined in our study. As revealed by molecular analyses, soil and peat layers just beneath the lichen cover were abundantly colonized by bacteria from the phylum Planctomycetes. Highest abundance of planctomycetes detected by fluorescence in situ hybridization was in the range 2.2–2.7 × 107 cells per gram of wet weight. 16S rRNA gene fragments from the Planctomycetes comprised 8–13% of total 16S rRNA gene reads retrieved using Illumina pair-end sequencing from the soil and peat samples. Lichen-associated assemblages of planctomycetes displayed unexpectedly high diversity, with a total of 89,662 reads representing 1723 operational taxonomic units determined at 97% sequence identity. The soil of forested tundra was dominated by uncultivated members of the family Planctomycetaceae (53–71% of total Planctomycetes-like reads), while sequences affiliated with the Phycisphaera-related group WD2101 (recently assigned to the order Tepidisphaerales) were most abundant in peat (28–51% of total reads). Representatives of the Isosphaera–Singulisphaera group (14–28% of total reads) and the lineages defined by the genera Gemmata (1–4%) and Planctopirus–Rubinisphaera (1–3%) were present in both habitats. Two strains of Singulisphaera-like bacteria were isolated from studied soil and peat samples. These planctomycetes displayed good tolerance of low temperatures (4–15°C) and were capable of growth on a number of polysaccharides, including lichenan, a characteristic component of lichen-derived phytomass. PMID:28066382

  5. Evidence and Implications of Frequent Fires in Ancient Shrub Tundra

    SciTech Connect

    Higuera, P E; Brubaker, L B; Anderson, P M; Brown, T A; Kennedy, A T; Hu, F S

    2008-03-06

    Understanding feedbacks between terrestrial and atmospheric systems is vital for predicting the consequences of global change, particularly in the rapidly changing Arctic. Fire is a key process in this context, but the consequences of altered fire regimes in tundra ecosystems are rarely considered, largely because tundra fires occur infrequently on the modern landscape. We present paleoecological data that indicate frequent tundra fires in northcentral Alaska between 14,000 and 10,000 years ago. Charcoal and pollen from lake sediments reveal that ancient birchdominated shrub tundra burned as often as modern boreal forests in the region, every 144 years on average (+/- 90 s.d.; n = 44). Although paleoclimate interpretations and data from modern tundra fires suggest that increased burning was aided by low effective moisture, vegetation cover clearly played a critical role in facilitating the paleo-fires by creating an abundance of fine fuels. These records suggest that greater fire activity will likely accompany temperature-related increases in shrub-dominated tundra predicted for the 21st century and beyond. Increased tundra burning will have broad impacts on physical and biological systems as well as land-atmosphere interactions in the Arctic, including the potential to release stored organic carbon to the atmosphere.

  6. Variation in peak growing season net ecosystem production across the Canadian Arctic.

    PubMed

    Lafleur, Peter M; Humphreys, Elyn R; St Louis, Vincent L; Myklebust, May C; Papakyriakou, Tim; Poissant, Laurier; Barker, Joel D; Pilote, Martin; Swystun, Kyle A

    2012-08-07

    Tundra ecosystems store vast amounts of soil organic carbon, which may be sensitive to climatic change. Net ecosystem production, NEP, is the net exchange of carbon dioxide (CO(2)) between landscapes and the atmosphere, and represents the balance between CO(2) uptake by photosynthesis and release by decomposition and autotrophic respiration. Here we examine CO(2) exchange across seven sites in the Canadian low and high Arctic during the peak growing season (July) in summer 2008. All sites were net sinks for atmospheric CO(2) (NEP ranged from 5 to 67 g C m(-2)), with low Arctic sites being substantially larger CO(2) sinks. The spatial difference in NEP between low and high Arctic sites was determined more by CO(2) uptake via gross ecosystem production than by CO(2) release via ecosystem respiration. Maximum gross ecosystem production at the low Arctic sites (average 8.6 μmol m(-2) s(-1)) was about 4 times larger than for high Arctic sites (average 2.4 μmol m(-2) s(-1)). NEP decreased with increasing temperature at all low Arctic sites, driven largely by the ecosystem respiration response. No consistent temperature response was found for the high Arctic sites. The results of this study clearly indicate there are large differences in tundra CO(2) exchange between high and low Arctic environments and this difference should be a central consideration in studies of Arctic carbon balance and climate change.

  7. High Arctic sea ice conditions influence marine birds wintering in Low Arctic regions

    NASA Astrophysics Data System (ADS)

    McFarlane Tranquilla, Laura; Hedd, April; Burke, Chantelle; Montevecchi, William A.; Regular, Paul M.; Robertson, Gregory J.; Stapleton, Leslie Ann; Wilhelm, Sabina I.; Fifield, David A.; Buren, Alejandro D.

    2010-09-01

    Ocean climate change is having profound biological effects in polar regions. Such change can also have far-reaching downstream effects in sub-polar regions. This study documents an environmental relationship between High Arctic sea ice changes and mortality events of marine birds in Low Arctic coastal regions. During April 2007 and March 2009, hundreds of beached seabird carcasses and moribund seabirds were found along the east and northeast coasts of Newfoundland, Canada. These seabird "wrecks" (i.e. dead birds on beaches) coincided with a period of strong, persistent onshore winds and heavily-accumulated sea ice that blocked bays and trapped seabirds near beaches. Ninety-two percent of wreck seabirds were Thick-billed Murres ( Uria lomvia). Body condition and demographic patterns of wreck murres were compared to Thick-billed Murres shot in the Newfoundland murre hunt. Average body and pectoral masses of wreck carcasses were 34% and 40% lighter (respectively) than shot murres, indicating that wreck birds had starved. The acute nature of each wreck suggested that starvation and associated hypothermia occurred within 2-3 days. In 2007, first-winter murres (77%) dominated the wreck. In 2009, there were more adults (78%), mostly females (66%). These results suggest that spatial and temporal segregation in ages and sexes can play a role in differential survival when stochastic weather conditions affect discrete areas where these groups aggregate. In wreck years, southward movement of Arctic sea ice to Low Arctic latitudes was later and blocked bays longer than in most other years. These inshore conditions corresponded with recent climate-driven changes in High Arctic ice break-up and ice extent; coupled with local weather conditions, these ice conditions appeared to be the key environmental features that precipitated the ice-associated seabird wrecks in the Low Arctic region.

  8. Frozen ponds: production and storage of methane during the Arctic winter in a lowland tundra landscape in northern Siberia, Lena River delta

    NASA Astrophysics Data System (ADS)

    Langer, M.; Westermann, S.; Anthony, K. Walter; Wischnewski, K.; Boike, J.

    2015-02-01

    Lakes and ponds play a key role in the carbon cycle of permafrost ecosystems, where they are considered to be hotspots of carbon dioxide CO2 and methane CH4 emission. The strength of these emissions is, however, controlled by a variety of physical and biogeochemical processes whose responses to a warming climate are complex and only poorly understood. Small waterbodies have been attracting an increasing amount of attention since recent studies demonstrated that ponds can make a significant contribution to the CO2 and CH4emissions of tundra ecosystems. Waterbodies also have a marked effect on the thermal state of the surrounding permafrost; during the freezing period they prolong the period of time during which thawed soil material is available for microbial decomposition. This study presents net CH4 production rates during the freezing period from ponds within a typical lowland tundra landscape in northern Siberia. Rate estimations were based on CH4 concentrations measured in surface lake ice from a variety of waterbody types. Vertical profiles along ice blocks showed an exponential increase in CH4 concentration with depth. These CH4 profiles were reproduced by a 1-D mass balance model and the net CH4 production rates were then inferred through inverse modeling. Results revealed marked differences in early winter net CH4 production among various ponds. Ponds situated within intact polygonal ground structures yielded low net production rates, of the order of 10-11 to 10-10 mol m-2 s-1 (0.01 to 0.14 mgCH4 m-2 day-1). In contrast, ponds exhibiting clear signs of erosion yielded net CH4 production rates of the order of 10-7 mol m-2 s-1 (140 mg CH4 m-2 day-1). Our results therefore indicate that once a particular threshold in thermal erosion has been crossed, ponds can develop into major CH4 sources. This implies that any future warming of the climate may result in nonlinear CH4 emission behavior in tundra ecosystems.

  9. Microbial life beneath a high arctic glacier.

    PubMed

    Skidmore, M L; Foght, J M; Sharp, M J

    2000-08-01

    The debris-rich basal ice layers of a high Arctic glacier were shown to contain metabolically diverse microbes that could be cultured oligotrophically at low temperatures (0.3 to 4 degrees C). These organisms included aerobic chemoheterotrophs and anaerobic nitrate reducers, sulfate reducers, and methanogens. Colonies purified from subglacial samples at 4 degrees C appeared to be predominantly psychrophilic. Aerobic chemoheterotrophs were metabolically active in unfrozen basal sediments when they were cultured at 0.3 degrees C in the dark (to simulate nearly in situ conditions), producing (14)CO(2) from radiolabeled sodium acetate with minimal organic amendment (> or =38 microM C). In contrast, no activity was observed when samples were cultured at subfreezing temperatures (< or =-1.8 degrees C) for 66 days. Electron microscopy of thawed basal ice samples revealed various cell morphologies, including dividing cells. This suggests that the subglacial environment beneath a polythermal glacier provides a viable habitat for life and that microbes may be widespread where the basal ice is temperate and water is present at the base of the glacier and where organic carbon from glacially overridden soils is present. Our observations raise the possibility that in situ microbial production of CO(2) and CH(4) beneath ice masses (e.g., the Northern Hemisphere ice sheets) is an important factor in carbon cycling during glacial periods. Moreover, this terrestrial environment may provide a model for viable habitats for life on Mars, since similar conditions may exist or may have existed in the basal sediments beneath the Martian north polar ice cap.

  10. Nitrous oxide production and emission in high arctic soils of NW Greenland

    NASA Astrophysics Data System (ADS)

    Stills, A.; Lupascu, M.; Czimczik, C. I.; Sharp, E. D.; Welker, J. M.; Schaeffer, S. M.

    2010-12-01

    Nitrous oxide (N2O) is a potent ozone depleting greenhouse gas with a global warming potential 298 times larger than carbon dioxide (CO2 on a 100-year time scale. Recent studies identified arctic soils undergoing thawing and changes in drainage as potentially large sources of N2O to the atmosphere. More in situ2O production in and emission from arctic soils are needed to understand ecosystem feedbacks to climate change in high arctic tundra, and the role of high latitudes in the global N2O budget. We monitored the concentration of N2O in soils and emissions of N2O to the atmosphere from prostrate shrub tundra in NW Greenland under current and future climate conditions. Measurements were made monthly from June to August 2010 at a long-term climate change experiment started in 2003 consisting of +2oC warming (T1), +4oC warming (T2), +50% summer precipitation (W), +4oC × +50% summer precipitation (T2W), and control (C). In each treatment, N2O was monitored from vegetated and barren soils. In addition, we quantified nitrogen (N) mineralization rates. The concentration of N2O in soils was measured by sampling air from permanent wells ranging from 20 to 90 cm soil depth. N2O emissions were measured every 15 minutes for one hour using opaque, static chambers. Nitrous oxide samples were collected manually with syringes and stored in pre-evacuated glass vials with butyl rubber septa and aluminum crimp. The vials were sealed with silicon, shipped to UC Irvine, and analyzed by GC-ECD (Shimadzu GC-2014). To determine soil N mineralization rates, resin bags were installed under PVC cores from 8 to 10 cm in early spring in all treatments. Bags were removed at peak season. A second set was installed to capture end-of-season mineralization rates. Resin bags were extracted for future analysis of total accumulated ammonium and nitrate. Soil cores concurrently collected with resin bag installation and removal will be analyzed for % C and N, and were extracted for future analysis

  11. Identification of unrecognized tundra fire events on the north slope of Alaska

    USGS Publications Warehouse

    Jones, Benjamin M.; Breen, Amy L.; Gaglioti, Benjamin V.; Mann, Daniel H.; Rocha, Adrian V.; Grosse, Guido; Arp, Christopher D.; Kunz, Michael L.; Walker, Donald A.

    2013-01-01

    Characteristics of the natural fire regime are poorly resolved in the Arctic, even though fire may play an important role cycling carbon stored in tundra vegetation and soils to the atmosphere. In the course of studying vegetation and permafrost-terrain characteristics along a chronosequence of tundra burn sites from AD 1977, 1993, and 2007 on the North Slope of Alaska, we discovered two large, previously unrecognized tundra fires. The Meade River fire burned an estimated 500 km2 and the Ketik River fire burned an estimated 1200 km2. Based on radiocarbon dating of charred twigs, analysis of historic aerial photography, and regional climate proxy data, these fires likely occurred between AD 1880 and 1920. Together, these events double the estimated burn area on the North Slope of Alaska over the last ~100 to 130 years. Assessment of vegetation succession along the century-scale chronosequence of tundra fire disturbances demonstrates for the first time on the North Slope of Alaska that tundra fires can facilitate the invasion of tundra by shrubs. Degradation of ice-rich permafrost was also evident at the fire sites and likely aided in the presumed changes of the tundra vegetation postfire. Other previously unrecognized tundra fire events likely exist in Alaska and other Arctic regions and identification of these sites is important for better understanding disturbance regimes and carbon cycling in Arctic tundra.

  12. Historical and ecological determinants of genetic structure in arctic canids.

    PubMed

    Carmichael, L E; Krizan, J; Nagy, J A; Fuglei, E; Dumond, M; Johnson, D; Veitch, A; Berteaux, D; Strobeck, C

    2007-08-01

    Wolves (Canis lupus) and arctic foxes (Alopex lagopus) are the only canid species found throughout the mainland tundra and arctic islands of North America. Contrasting evolutionary histories, and the contemporary ecology of each species, have combined to produce their divergent population genetic characteristics. Arctic foxes are more variable than wolves, and both island and mainland fox populations possess similarly high microsatellite variation. These differences result from larger effective population sizes in arctic foxes, and the fact that, unlike wolves, foxes were not isolated in discrete refugia during the Pleistocene. Despite the large physical distances and distinct ecotypes represented, a single, panmictic population of arctic foxes was found which spans the Svalbard Archipelago and the North American range of the species. This pattern likely reflects both the absence of historical population bottlenecks and current, high levels of gene flow following frequent long-distance foraging movements. In contrast, genetic structure in wolves correlates strongly to transitions in habitat type, and is probably determined by natal habitat-biased dispersal. Nonrandom dispersal may be cued by relative levels of vegetation cover between tundra and forest habitats, but especially by wolf prey specialization on ungulate species of familiar type and behaviour (sedentary or migratory). Results presented here suggest that, through its influence on sea ice, vegetation, prey dynamics and distribution, continued arctic climate change may have effects as dramatic as those of the Pleistocene on the genetic structure of arctic canid species.

  13. Assessing the Tundra-taiga Boundary with Multi-Sensor Satellite Data

    NASA Technical Reports Server (NTRS)

    Ranson, K. J.; Sun, G.; Kharuk, V. I.; Kovacs, K.

    2004-01-01

    Monitoring the dynamics of the circumpolar boreal forest (taiga) and Arctic tundra boundary is important for understanding the causes and consequences of changes observed in these areas. This ecotone, the world's largest, stretches for over 13,400 km and marks the transition between the northern limits of forests and the southern margin of the tundra. Because of the inaccessibility and large extent of this zone, remote sensing data can play an important role for mapping the characteristics and monitoring the dynamics. Basic understanding of the capabilities of existing space borne instruments for these purposes is required. In this study we examined the use of several remote sensing techniques for identifying the existing tundra- taiga ecotone. These include Landsat-7, MISR, MODIS and RADARSAT data. Historical cover maps, recent forest stand measurements and high-resolution IKONOS images were used for local ground truth. It was found that a tundra-taiga transitional area can be characterized using multi- spectral Landsat ETM+ summer images, multi-angle MISR red band reflectance images, RADARSAT images with larger incidence angle, or multi-temporal and multi-spectral MODIS data. Because of different resolutions and spectral regions covered, the transition zone maps derived from different data types were not identical, but the general patterns were consistent.

  14. Methane Suppression: The Impacts of Fe(III) and Humic Acids on Net Methane Flux from Arctic Tundra Wetlands in Alaska and Finland (Invited)

    NASA Astrophysics Data System (ADS)

    Lipson, D.; Miller, K.; Lai, C.

    2013-12-01

    Arctic soils contain large reservoirs of carbon (C) that are vulnerable to loss from climatic warming. However the potential global impacts of this C depend on whether it is lost primarily in the form of methane (CH4) or carbon dioxide (CO2), two gases with very different greenhouse warming potentials. In anaerobic environments, the relative production of CH4 vs. CO2 may be controlled by the presence of alternative terminal electron acceptors, which allow more thermodynamically favorable anaerobic respiratory pathways to dominate over methanogenesis. This work investigated how the addition of terminal electron acceptors, ferric iron (Fe(III)) and humic acids, affected net CH4 fluxes from high-latitude wetland ecosystems. We conducted two manipulative field experiments in Barrow, Alaska (71° N) and Finnish Lapland (69° N). The ecosystem in Barrow was known from previous studies to be rich in Fe(III) and to harbor a microbial community that is dominated by Fe(III)- and humic acid-reducing microorganisms. The role of these alternative electron acceptors had not previously been studied at the Finnish site. CH4 and CO2 fluxes were measured using a portable trace gas analyzer from experimental plots, before and after amendments with Fe(III) (in the chelated form, ferric nitrilotriacetic acid), humic acids, or water as a control. Both in the ecosystem with permafrost and naturally high levels of soil Fe (Barrow, AK) and in the ecosystem with no permafrost and naturally low levels of soil Fe (Petsikko, Finland), the addition of the alternative electron acceptors Fe(III) and humic acids significantly reduced net CH4 flux. CO2 fluxes were not significantly altered by the treatments. The reduction in CH4 flux persisted for at least several weeks post-treatment. There was no significant difference between the reduction caused by humic acids versus that from Fe(III). These results show that the suppression of CH4 flux by Fe(III) and humic acids is a widespread phenomenon that

  15. Modeling the spatio-temporal variability in subsurface thermal regimes across a low-relief polygonal tundra landscape: Modeling Archive

    DOE Data Explorer

    Peter E. Thornton; Jitendra Kumar; Colleen M. Iversen; Richard T. Mills; Gautam Bisht; Nathan Collier; Vladimir Romanovsky

    2016-01-27

    This Modeling Archive is in support of an NGEE Arctic discussion paper under review and available at http://www.the-cryosphere-discuss.net/tc-2016-29/. Vast carbon stocks stored in permafrost soils of Arctic tundra are under risk of release to atmosphere under warming climate. Ice--wedge polygons in the low-gradient polygonal tundra create a complex mosaic of microtopographic features. The microtopography plays a critical role in regulating the fine scale variability in thermal and hydrological regimes in the polygonal tundra landscape underlain by continuous permafrost. Modeling of thermal regimes of this sensitive ecosystem is essential for understanding the landscape behaviour under current as well as changing climate. We present here an end-to-end effort for high resolution numerical modeling of thermal hydrology at real-world field sites, utilizing the best available data to characterize and parameterize the models. We develop approaches to model the thermal hydrology of polygonal tundra and apply them at four study sites at Barrow, Alaska spanning across low to transitional to high-centered polygon and representative of broad polygonal tundra landscape. A multi--phase subsurface thermal hydrology model (PFLOTRAN) was developed and applied to study the thermal regimes at four sites. Using high resolution LiDAR DEM, microtopographic features of the landscape were characterized and represented in the high resolution model mesh. Best available soil data from field observations and literature was utilized to represent the complex hetogeneous subsurface in the numerical model. This data collection provides the complete set of input files, forcing data sets and computational meshes for simulations using PFLOTRAN for four sites at Barrow Environmental Observatory. It also document the complete computational workflow for this modeling study to allow verification, reproducibility and follow up studies.

  16. Trends of Vegetation Greenness in the Arctic from 1982-2005

    NASA Astrophysics Data System (ADS)

    Jia, G. J.; Epstein, H. E.; Walker, D. A.

    2007-12-01

    The Arctic region has experienced a continuous trend of warming during the past 30 years. Meanwhile, many areas of the Arctic are undergoing large-scale industrial development, e.g. oil and gas exploration, at a rapid pace, indicating an increasing human pressure and land use changes even in this frontier wilderness. Major questions face arctic terrestrial ecologists are what will happen to the tundra ecosystems as the global climate warms and what will happen to the indigenous people way of life as land cover changes proceed? Here, we combine multi-scale sub-pixel analysis and remote sensing time-series analysis to investigate recent decadal changes in vegetation photosynthetic activity along spatial gradients of summer temperature and vegetation in the Arctic. The datasets used here are NASA Gimms data at 8 km pixel resolution and MODIS land cover data. Fractional vegetation cover was analyzed in order to select homogenously vegetated areas of tundra and autoregression analysis was performed on time series of those homogenous pixels. Only pixels below 70 degree north were included for 2004-2005 due to calibration errors occurred beyond 70 degree north for those years. Linear trends in Arctic tundra vegetation greenness over period 1982-2005 were positive. However, there were different magnitudes between Eurasia and North America. The rate of change was +0.64%/yr over North American Arctic compared to +0.44%/yr over Eurasian Arctic. Vegetation productivities increase from north to south along bioclimatic gradient, therefore, greenness is much higher in areas below 70 degree north compared to entire tundra biome. Higher rates of greening in High Arctic contributed to a stronger positive trend in the longer time series. The rate of greening detected here was higher than that reported in previous studies. This is likely due to two reasons: 1) we restricted our study area in tundra biome only with a phenological tundra-taiga boundary identification approach, therefore

  17. Water vapor intrusions into the High Arctic during winter

    NASA Astrophysics Data System (ADS)

    Doyle, J. G.; Lesins, G.; Thackray, C. P.; Perro, C.; Nott, G. J.; Duck, T. J.; Damoah, R.; Drummond, J. R.

    2011-06-01

    The meridional transport of water vapor into the High Arctic, accompanied by dry enthalpy and clouds, impacts the surface radiative forcing. The evolution of one such moist intrusion over 9-11 February 2010 is presented. The event is analyzed using a unique blend of measurements including a new pan-Arctic retrieval of column water vapor from the Microwave Humidity Sounders, water vapor profiles from a Raman lidar and a ground-based microwave radiometer at the Polar Environment Atmospheric Research Laboratory (PEARL), in Eureka (80°N, 86°W), on Ellesmere Island in the Canadian High Arctic. A radiation model reveals the intrusion is associated with a 17 W m-2 average increase in downwelling longwave irradiance. Optically thin clouds, as observed by the lidar, contribute a further 20 W m-2 to the downwelling longwave irradiance at their peak. Intrusion events are shown to be a regular occurrence in the Arctic winter with implications for the understanding of the mechanisms driving Arctic Amplification.

  18. Surface energy exchanges along a tundra-forest transition and feedbacks to climate

    USGS Publications Warehouse

    Beringer, J.; Chapin, F. S.; Thompson, Catharine Copass; McGuire, A.D.

    2005-01-01

    Surface energy exchanges were measured in a sequence of five sites representing the major vegetation types in the transition from arctic tundra to forest. This is the major transition in vegetation structure in northern high latitudes. We examined the influence of vegetation structure on the rates of sensible heating and evapotranspiration to assess the potential feedbacks to climate if high-latitude warming were to change the distribution of these vegetation types. Measurements were made at Council on the Seward Peninsula, Alaska, at representative tundra, low shrub, tall shrub, woodland (treeline), and boreal forest sites. Structural differences across the transition from tundra to forest included an increase in the leaf area index (LAI) from 0.52 to 2.76, an increase in canopy height from 0.1 to 6.1 m, and a general increase in canopy complexity. These changes in vegetation structure resulted in a decrease in albedo from 0.19 to 0.10 as well as changes to the partitioning of energy at the surface. Bulk surface resistance to water vapor flux remained virtually constant across sites, apparently because the combined soil and moss evaporation decreased while transpiration increased along the transect from tundra to forest. In general, sites became relatively warmer and drier along the transect with the convective fluxes being increasingly dominated by sensible heating, as evident by an increasing Bowen ratio from 0.94 to 1.22. The difference in growing season average daily sensible heating between tundra and forest was 21 W m-2. Fluxes changed non-linearly along the transition, with both shrubs and trees substantially enhancing heat transfer to the atmosphere. These changes in vegetation structure that increase sensible heating could feed back to enhance warming at local to regional scales. The magnitude of these vegetation effects on potential high-latitude warming is two to three times greater than suggested by previous modeling studies. ?? 2005 Elsevier B.V. All

  19. An active atmospheric methane sink in high Arctic mineral cryosols

    DOE PAGES

    Lau, Maggie C.Y.; Stackhouse, B.; Layton, Alice C.; ...

    2015-01-01

    The transition of Arctic carbon-rich cryosols into methane (CH₄)-emitting wetlands due to global warming is a rising concern. However, the spatially predominant mineral cryosols and their CH₄ emission potential are poorly understood. Fluxes measured in situ and estimated under laboratory conditions coupled with -omics analysis indicate (1) mineral cryosols in the Canadian high Arctic contain atmospheric CH₄-oxidizing bacteria; (2) the atmospheric CH⁺ uptake flux increases with ground temperature; and, as a result, (3) the atmospheric CH₄ sink strength will increase by a factor of 5-30 as the Arctic warms by 5-15 °C over a century. We demonstrated that acidic mineralmore » cryosols have previously unrecognized potential of negative CH₄ feedback.« less

  20. An active atmospheric methane sink in high Arctic mineral cryosols

    SciTech Connect

    Lau, Maggie C.Y.; Stackhouse, B.; Layton, Alice C.; Chauhan, Archana; Vishnivetskaya, T. A.; Chourey, Karuna; Mykytczuk, N. C.S.; Bennett, Phil C.; Lamarche-Gagnon, G.; Burton, N.; Renholm, J.; Hettich, R. L.; Pollard, W. H.; Omelon, C. R.; Medvigy, David M.; Pffifner, Susan M.; Whyte, L. G.; Onstott, T. C.

    2015-01-01

    The transition of Arctic carbon-rich cryosols into methane (CH₄)-emitting wetlands due to global warming is a rising concern. However, the spatially predominant mineral cryosols and their CH₄ emission potential are poorly understood. Fluxes measured in situ and estimated under laboratory conditions coupled with -omics analysis indicate (1) mineral cryosols in the Canadian high Arctic contain atmospheric CH₄-oxidizing bacteria; (2) the atmospheric CH⁺ uptake flux increases with ground temperature; and, as a result, (3) the atmospheric CH₄ sink strength will increase by a factor of 5-30 as the Arctic warms by 5-15 °C over a century. We demonstrated that acidic mineral cryosols have previously unrecognized potential of negative CH₄ feedback.

  1. High-Arctic butterflies become smaller with rising temperatures

    PubMed Central

    Bowden, Joseph J.; Eskildsen, Anne; Hansen, Rikke R.; Olsen, Kent; Kurle, Carolyn M.; Høye, Toke T.

    2015-01-01

    The response of body size to increasing temperature constitutes a universal response to climate change that could strongly affect terrestrial ectotherms, but the magnitude and direction of such responses remain unknown in most species. The metabolic cost of increased temperature could reduce body size but long growing seasons could also increase body size as was recently shown in an Arctic spider species. Here, we present the longest known time series on body size variation in two High-Arctic butterfly species: Boloria chariclea and Colias hecla. We measured wing length of nearly 4500 individuals collected annually between 1996 and 2013 from Zackenberg, Greenland and found that wing length significantly decreased at a similar rate in both species in response to warmer summers. Body size is strongly related to dispersal capacity and fecundity and our results suggest that these Arctic species could face severe challenges in response to ongoing rapid climate change. PMID:26445981

  2. High-Arctic butterflies become smaller with rising temperatures.

    PubMed

    Bowden, Joseph J; Eskildsen, Anne; Hansen, Rikke R; Olsen, Kent; Kurle, Carolyn M; Høye, Toke T

    2015-10-01

    The response of body size to increasing temperature constitutes a universal response to climate change that could strongly affect terrestrial ectotherms, but the magnitude and direction of such responses remain unknown in most species. The metabolic cost of increased temperature could reduce body size but long growing seasons could also increase body size as was recently shown in an Arctic spider species. Here, we present the longest known time series on body size variation in two High-Arctic butterfly species: Boloria chariclea and Colias hecla. We measured wing length of nearly 4500 individuals collected annually between 1996 and 2013 from Zackenberg, Greenland and found that wing length significantly decreased at a similar rate in both species in response to warmer summers. Body size is strongly related to dispersal capacity and fecundity and our results suggest that these Arctic species could face severe challenges in response to ongoing rapid climate change.

  3. Is climate change affecting wolf populations in the high Arctic?

    USGS Publications Warehouse

    Mech, L.D.

    2004-01-01

    Gobal climate change may affect wolves in Canada's High Arctic (80?? N) acting through three trophic levels (vegetation, herbivores, and wolves). A wolf pack dependent on muskoxen and arctic hares in the Eureka area of Ellesmere Island denned and produced pups most years from at least 1986 through 1997. However, when summer snow covered vegetation in 1997 and 2000 for the first time since records were kept, halving the herbivore nutrition-replenishment period, muskox and hare numbers dropped drastically, and the area stopped supporting denning wolves through 2003. The unusual weather triggering these events was consistent with global-climate-change phenomena. ?? 2004 Kluwer Academic Publishers.

  4. Is climate change affecting wolf populations in the high Arctic?

    USGS Publications Warehouse

    Mech, L.D.

    2004-01-01

    Global climate change may affect wolves in Canada's High Arctic (80DG N) acting through three trophic levels (vegetation, herbivores, and wolves). A wolf pack dependent on muskoxen and arctic hares in the Eureka area of Ellesmere Island denned and produced pups most years from at least 1986 through 1997. However when summer snow covered vegetation in 1997 and 2000 for the first time since records were kept, halving the herbivore nutrition-replenishment period, muskox and hare numbers dropped drastically, and the area stopped supporting denning wolves through 2003. The unusual weather triggering these events was consistent with global-climate-change phenomena.

  5. Climate Effects on Methylmercury Bioaccumulation Along a Latitudinal Gradient in the Eastern Canadian Arctic

    NASA Astrophysics Data System (ADS)

    Chetelat, J.; Richardson, M.; MacMillan, G. A.; Amyot, M.; Hintelmann, H.; Crump, D.

    2014-12-01

    Recent evidence indicates that inorganic mercury (Hg) loadings to Arctic lakes decline with latitude. However, monomethylmercury (MMHg) concentrations in fish and their prey do not decline in a similar fashion, suggesting that higher latitude lakes are more vulnerable to Hg inputs. Preliminary results will be presented from a three-year study (2012-2015) of climate effects on MMHg bioaccumulation in lakes of the eastern Canadian Arctic. We have investigated mercury transport and accumulation processes in lakes and ponds from three study regions along a latitudinal gradient in climate-controlled ecosystem types in the Canadian Arctic, specifically sub-Arctic taiga, Arctic tundra and polar desert. In each water body, we measured key aspects of MMHg bioaccumulation—MMHg bioavailability to benthic food webs and organism growth rates—as well as how watershed characteristics affect the transport of Hg and organic carbon to lakes. Novel approaches were incorporated including the use of passive samplers (Diffusive Gradient in Thin Film samplers or DGTs) to estimate sediment bioavailable MMHg concentrations and tissue RNA content to compare organism short-term growth rates. A comparison of Arctic tundra and sub-Arctic taiga lakes showed that surface water concentrations of MMHg were strongly and positively correlated to total Hg concentrations both within and among study regions, implying strong control of inorganic Hg supply. Sediment concentrations of bioavailable MMHg were highly variable among lakes, although average concentrations were similar between study regions. Local environmental conditions appear to have a strong influence on sediment potential for MMHg supply. Lake-dwelling Arctic char from tundra lakes had similar or higher total Hg concentrations compared with brook trout from sub-Arctic lakes that were exposed to higher water MMHg concentrations. Potential environmental drivers of these patterns will be discussed. This latitudinal study will provide new

  6. Future distribution of tundra refugia in northern Alaska

    USGS Publications Warehouse

    Hope, Andrew G.; Waltari, Eric; Payer, David C.; Cook, Joseph A.; Talbot, Sandra L.

    2013-01-01

    Climate change in the Arctic is a growing concern for natural resource conservation and management as a result of accelerated warming and associated shifts in the distribution and abundance of northern species. We introduce a predictive framework for assessing the future extent of Arctic tundra and boreal biomes in northern Alaska. We use geo-referenced museum specimens to predict the velocity of distributional change into the next century and compare predicted tundra refugial areas with current land-use. The reliability of predicted distributions, including differences between fundamental and realized niches, for two groups of species is strengthened by fossils and genetic signatures of demographic shifts. Evolutionary responses to environmental change through the late Quaternary are generally consistent with past distribution models. Predicted future refugia overlap managed areas and indicate potential hotspots for tundra diversity. To effectively assess future refugia, variable responses among closely related species to climate change warrants careful consideration of both evolutionary and ecological histories.

  7. Herbivore impacts to the moss layer determine tundra ecosystem response to grazing and warming.

    PubMed

    Gornall, Jemma L; Woodin, Sarah J; Jónsdóttir, Ingibjörg S; Van der Wal, Rene

    2009-10-01

    Herbivory and climate are key environmental drivers, shaping ecosystems at high latitudes. Here, we focus on how these two drivers act in concert, influencing the high arctic tundra. We aim to investigate mechanisms through which herbivory by geese influences vegetation and soil processes in tundra ecosystems under ambient and warmed conditions. To achieve this, two grazing treatments, clipping plus faecal additions and moss removal, were implemented in conjunction with passive warming. Our key finding was that, in many cases, the tundra ecosystem response was determined by treatment impacts on the moss layer. Moss removal reduced the remaining moss layer depth by 30% and increased peak grass biomass by 27%. These impacts were probably due to observed higher soil temperatures and decomposition rates associated with moss removal. The positive impact of moss removal on grass biomass was even greater with warming, further supporting this conclusion. In contrast, moss removal reduced dwarf shrub biomass possibly resulting from increased exposure to desiccating winds. An intact moss layer buffered the soil to increased air temperature and as a result there was no response of vascular plant productivity to warming over the course of this study. In fact, moss removal impacts on soil temperature were nearly double those of warming, suggesting that the moss layer is a key component in controlling soil conditions. The moss layer also absorbed nutrients from faeces, promoting moss growth. We conclude that both herbivory and warming influence this high arctic ecosystem but that herbivory is the stronger driver of the two. Disturbance to the moss layer resulted in a shift towards a more grass-dominated system with less abundant mosses and shrubs, a trend that was further enhanced by warming. Thus herbivore impacts to the moss layer are key to understanding arctic ecosystem response to grazing and warming.

  8. U.S. Tundra Biome-International Biological Program. U.S. Tundra Biome Publication List.

    DTIC Science & Technology

    1983-09-01

    Provisional checklist to the vascular, bryophyte , and lichen flora of Prudhoe Bay, Alaska. In Ecological Investigations of the Tundra Biome in the Prudhoe Bay...4040) /Bib 33-4561/ Rastorfer, J.R., H.J. Webster and D.K. Smith (1973) Floristic and ecologic studies of bryophytes of selected habitats at...57: 1025-1033. (2759) /Bib 31-1286/ Steere, W.C. (1976) Ecology , phytogeography, and floristics of arctic Alaskan bryophytes . Journal of Hattori

  9. Spatiotemporal patterns of tundra fires: late-Quaternary charcoal records from Alaska

    NASA Astrophysics Data System (ADS)

    Chipman, M. L.; Hudspith, V.; Higuera, P. E.; Duffy, P. A.; Kelly, R.; Oswald, W. W.; Hu, F. S.

    2015-07-01

    Anthropogenic climate change has altered many ecosystem processes in the Arctic tundra and may have resulted in unprecedented fire activity. Evaluating the significance of recent fires requires knowledge from the paleofire record because observational data in the Arctic span only several decades, much shorter than the natural fire rotation in Arctic tundra regions. Here we report results of charcoal analysis on lake sediments from four Alaskan lakes to infer the broad spatial and temporal patterns of tundra-fire occurrence over the past 35 000 years. Background charcoal accumulation rates are low in all records (range is 0-0.05 pieces cm-2 yr-1), suggesting minimal biomass burning across our study areas. Charcoal peak analysis reveals that the mean fire-return interval (FRI; years between consecutive fire events) ranged from ca. 1650 to 6050 years at our sites, and that the most recent fire events occurred from ca. 880 to 7030 years ago, except for the CE 2007 Anaktuvuk River Fire. These mean FRI estimates are longer than the fire rotation periods estimated for the past 63 years in the areas surrounding three of the four study lakes. This result suggests that the frequency of tundra burning was higher over the recent past compared to the late Quaternary in some tundra regions. However, the ranges of FRI estimates from our paleofire records overlap with the expected values based on fire-rotation-period estimates from the observational fire data, and the differences are statistically insignificant. Together with previous tundra-fire reconstructions, these data suggest that the rate of tundra burning was spatially variable and that fires were extremely rare in our study areas throughout the late Quaternary. Given the rarity of tundra burning over multiple millennia in our study areas and the pronounced effects of fire on tundra ecosystem processes such as carbon cycling, dramatic tundra ecosystem changes are expected if anthropogenic climate change leads to more

  10. Spatiotemporal patterns of tundra fires: late-Quaternary charcoal records from Alaska

    NASA Astrophysics Data System (ADS)

    Chipman, M. L.; Hudspith, V.; Higuera, P. E.; Duffy, P. A.; Kelly, R.; Oswald, W. W.; Hu, F. S.

    2015-02-01

    Anthropogenic climate change has altered many ecosystem processes in the Arctic tundra and may have resulted in unprecedented fire activity. Evaluating the significance of recent fires requires knowledge from the paleo-fire record because observational data in the Arctic span only several decades, much shorter than the natural fire rotation in Arctic tundra regions. Here we report results of charcoal analysis on lake sediments from four Alaskan lakes to infer the broad spatial and temporal patterns of tundra fire occurrence over the past 35 000 years. Background charcoal accumulation rates are low in all records (range = 0-0.05 pieces cm-2 year-1), suggesting minimal biomass burning across our study areas. Charcoal peak analysis reveals that the mean fire return interval (FRI; years between consecutive fire events) ranged from 1648 to 6045 years at our sites, and that the most recent fire events occurred from 882 to 7031 years ago, except for the CE 2007 Anaktuvuk River Fire. These mean FRI estimates are longer than the fire rotation periods estimated for the past 63 years in the areas surrounding three of the four study lakes. This result suggests that the frequency of tundra burning was higher over the recent past compared to the late Quaternary in some tundra regions. However, the ranges of FRI estimates from our paleo-fire records overlap with the expected values based on fire-rotation-period estimates from the observational fire data, and thus quantitative differences are not significant. Together with previous tundra-fire reconstructions, these data suggest that the rate of tundra burning was spatially variable and that fires were extremely rare in our study areas throughout the late Quaternary. Given the rarity of tundra burning over multiple millennia in our study areas and the pronounced effects of fire on tundra ecosystem processes such as carbon cycling, dramatic tundra ecosystem changes are expected if anthropogenic climate change leads to more frequent

  11. The Pleistocene ``Tundra-Steppe'' and the productivity paradox: the landscape approach

    NASA Astrophysics Data System (ADS)

    Yurtsev, Boris A.

    2001-01-01

    "Tundra-steppe" means either a certain type of plant community with codominance of both steppe and tundra species (including prostrate shrubs), or a type of landscape, codominated by both steppe and tundra (Yurtsev, Relic Steppe Complexes of Northeastern Asia. Nauka Press, Novosibirsk (in Russian) 1981; In: Hopkins, Matthews Jr., Schweger, Young, (Eds.), Paleoecology of Beringia. Academic Press, New York, 1982, pp. 157-177). A discrepancy between Pleistocene glacial climates that were much colder and drier than present in Beringia and the highly diverse herbivorous fossil fauna (the "productivity paradox") is explained in terms of much greater diversity of herbaceous vegetation (grasses, sedges and forbs) in the mosaic of Beringian 'tundra-steppe' landscapes. Analysis of the relic distribution of some predominantly herbaceous plant communities throughout Beringia (Yurtsev, 1981, 1982, Komarovskiye chteniya (Vladivostok) 33 (1986) 3-53 (in Russian); Protection of Gene- and Coenotic Pool of the Herbaceous Biogeocoenoses, Sverdlovsk, 1988, pp. 128-129 (in Russian); Bridges of Science Between North America and the Russian Far East, 45th Arctic Science Conference, Abstracts, Vol. 1. Dalnauka Press, Vladivostok, 1994, p. 268; Paleontological Journal, 6 (1996)) provides the phytogeographic and landscape — ecological grounds for the reconstruction of plant cover of these landscapes. Dry watersheds and slopes had cryophytic (cold-adapted) steppes, cryoxerophytic (cold and dry-adapted) herbaceous and prostrate shrub-herbaceous communities, dry herb-prostrate shrub tundras, and tundra-steppe communities proper. All sorts of depressions on interfluves and in valleys along with concave pediments were occupied by dry steppe-meadows and brackish-water moist meadows. In some specific habitats sparse groupings of continental halophytes (plants growing in saline soils) of "arctic takkyrs", zoochoric (plants with seeds dispersed by animals) groupings of annual-biennial "ruderals

  12. Seeing the risks of multiple Arctic amplifying feedbacks.

    NASA Astrophysics Data System (ADS)

    Carter, P.

    2014-12-01

    There are several potentially very large sources of Arctic amplifying feedbacks that have been identified. They present a great risk to the future as they could become self and inter-reinforcing with uncontrollable knock-on, or cascading risks. This has been called a domino effect risk by Carlos Duarte. Because of already committed global warming and the millennial duration of global warming, these are highly policy relevant. These Arctic feedback processes are now all operant with emissions of carbon dioxide methane and nitrous oxide detected. The extent of the risks from these feedback sources are not obvious or easy to understand by policy makers and the public. They are recorded in the IPCC AR5 as potential tipping points, as is the irreversibility of permafrost thaw. Some of them are not accounted for in the IPCC AR5 global warming projections because of quantitative uncertainty. UNEP issued a 2012 report (Policy Implications of Thawing Permafrost) advising that by omitting carbon feedback emissions from permafrost, carbon budget calculations by err on the low side. There is the other unassessed issue of a global warming safety limit for preventing uncontrollable increasing Arctic feedback emissions. Along with our paper, we provide illustrations of the Arctic feedback sources and processes from satellite imagery and flow charts that allows for their qualitative consideration. We rely on the IPCC assessments, the 2012 paper Possible role of wetlands permafrost can methane hydrates in the methane cycle under future climate change; a review, by Fiona M. O'Connor et al., and build on the WWF 2009 Arctic Climate Feedbacks: Global Implications. The potential sources of Arctic feedback processes identified include: Arctic and Far North snow albedo decline, Arctic summer sea ice albedo decline, Greenland summer ice surface melting albedo loss, albedo decline by replacement of Arctic tundra with forest, tundra fires, Boreal forest fires, Boreal forest die

  13. High Arctic Hillslope-Wetland Linkages: Types, Patterns and Importance

    NASA Astrophysics Data System (ADS)

    Young, K. L.; Abnizova, A.

    2012-12-01

    High Arctic wetlands are lush areas in an otherwise barren landscape. They help to store and replenish water and they serve as significant resting and breeding grounds for migratory birds. In addition, they provide rich grazing grounds for arctic fauna such as muskox and caribou. Arctic wetlands can be small, patchy grounds of wet vegetation or they can encompass large zones characterized by lakes, ponds, wet meadows, and, often times, they are inter-mixed with areas of dry ground. While seasonal snowmelt continues to remain the most critical source of water for recharging ponds, lakes, and meadows in these environments, less is known about the role of lateral inputs of water into low-lying wetlands, namely water flowing into these wetland ecosystems from adjacent hillslopes, which often surround them. This paper will review the different modes of hillslope runoff into both patchy and regional-scale wetlands including late-lying snowbeds, snow-filled creeks, and both small and large (>1st order) streams. It will draw upon field results from four arctic islands (Ellesmere, Cornwallis, Somerset and Bathurst Island) and a research period which spans from the mid'90s until present. Our study will evaluate seasonal and inter-seasonal patterns of snowmelt driven discharge (initiation, duration), timing, and magnitude of peak flows, in addition to stream response to rainfall and dry episodes. The impacts of these lateral water sources for a range of wetlands (ponds, wet meadows) will include an analysis of water level fluctuations (frequency, duration), shrinkage/expansion rates, and water quality. Finally, this study will surmise how these types of lateral hillslope inflows might shift in the future and suggest the impact of these changes on the sustainability of High Arctic wetland terrain.

  14. Carbon dioxide in Arctic and subarctic regions

    SciTech Connect

    Gosink, T. A.; Kelley, J. J.

    1981-03-01

    A three year research project was presented that would define the role of the Arctic ocean, sea ice, tundra, taiga, high latitude ponds and lakes and polar anthropogenic activity on the carbon dioxide content of the atmosphere. Due to the large physical and geographical differences between the two polar regions, a comparison of CO/sub 2/ source and sink strengths of the two areas was proposed. Research opportunities during the first year, particularly those aboard the Swedish icebreaker, YMER, provided additional confirmatory data about the natural source and sink strengths for carbon dioxide in the Arctic regions. As a result, the hypothesis that these natural sources and sinks are strong enough to significantly affect global atmospheric carbon dioxide levels is considerably strengthened. Based on the available data we calculate that the whole Arctic region is a net annual sink for about 1.1 x 10/sup 15/ g of CO/sub 2/, or the equivalent of about 5% of the annual anthropogenic input into the atmosphere. For the second year of this research effort, research on the seasonal sources and sinks of CO/sub 2/ in the Arctic will be continued. Particular attention will be paid to the seasonal sea ice zones during the freeze and thaw periods, and the tundra-taiga regions, also during the freeze and thaw periods.

  15. High Levels of Molecular Chlorine found in the Arctic Atmosphere

    NASA Astrophysics Data System (ADS)

    Liao, J.; Huey, L. G.; Liu, Z.; Tanner, D.; Cantrell, C. A.; Orlando, J. J.; Flocke, F. M.; Shepson, P. B.; Weinheimer, A. J.; Hall, S. R.; Beine, H.; Wang, Y.; Ingall, E. D.; Thompson, C. R.; Hornbrook, R. S.; Apel, E. C.; Fried, A.; Mauldin, L.; Smith, J. N.; Staebler, R. M.; Neuman, J. A.; Nowak, J. B.

    2014-12-01

    Chlorine radicals are a strong atmospheric oxidant, particularly in polar regions where levels of hydroxyl radicals can be quite low. In the atmosphere, chlorine radicals expedite the degradation of methane and tropospheric ozone and the oxidation of mercury to more toxic forms. Here, we present direct measurements of molecular chlorine levels in the Arctic marine boundary layer in Barrow, Alaska, collected in the spring of 2009 over a six-week period using chemical ionization mass spectrometry. We detected high levels of molecular chlorine of up to 400 pptv. Concentrations peaked in the early morning and late afternoon and fell to near-zero levels at night. Average daytime molecular chlorine levels were correlated with ozone concentrations, suggesting that sunlight and ozone are required for molecular chlorine formation. Using a time-dependent box model, we estimated that the chlorine radicals produced from the photolysis of molecular chlorine on average oxidized more methane than hydroxyl radicals and enhanced the abundance of short-lived peroxy radicals. Elevated hydroperoxyl radical levels, in turn, promoted the formation of hypobromous acid, which catalyzed mercury oxidation and the breakdown of tropospheric ozone. Therefore, we propose that molecular chlorine exerts a significant effect on the atmospheric chemistry in the Arctic. While the formation mechanisms of molecular chlorine are not yet understood, the main potential sources of chlorine include snowpack, sea salt, and sea ice. There is recent evidence of molecular halogen (Br2 and Cl2) formation in the Arctic snowpack. The coverage and composition of the snow may control halogen chemistry in the Arctic. Changes of sea ice and snow cover in the changing climate may affect air-snow-ice interaction and have a significant impact on the levels of radicals, ozone, mercury and methane in the Arctic troposphere.

  16. [CO2-exchange in tundra ecosystems of Vaygach Island during the unusually warm and dry vegetation season].

    PubMed

    Zamolodchikov, D G

    2015-01-01

    In summer of 2013, field studies of CO2-exchange in tundra ecosystems of Vaygach Island have been conducted using the chamber method. The models are developed that establish relationships between CO2 fluxes and key ecological factors such as temperature, photosynthetic active radiation, leaf mass of vascular plants, and depth of thawing. According to the model estimates, in 2013 vegetation season tundra ecosystems of Vaygach Island have been appearing to be a CO2 source to the atmosphere (31.9 ± 17.1 g C m(-2) season(-1)) with gross primary production equal to 136.6 ± 18.9 g C m(-2) season(-1) and ecosystem respiration of 168.5 ± ± 18.4 g C m(-2) season(-1). Emission of CO2 from the soil surface (soil respiration) has been equal, on the average, to 67.3% of the ecosystem respiration. The reason behind carbon losses by tundra ecosystems seems to be unusually warm and dry weather conditions in 2013 summer. The air temperature during summer months has been twice as high as the climatic norm for 1961-1990. Last decades, researches in the circumpolar Arctic revealed a growing trend to the carbon sink from the atmosphere to tundra ecosystems. This trend can be interrupted by unusually warm weather situations becoming more frequent and of larger scale.

  17. Climate feedbacks at the tundra-taiga interface.

    PubMed

    Harding, Richard; Kuhry, Peter; Christensen, Torben R; Sykes, Martin T; Dankers, Rutger; van der Linden, Sandra

    2002-08-01

    Feedbacks, or internal interactions, play a crucial role in the climate system. Negative feedback will reduce the impact of an external perturbation, a positive feedback will amplify the effect and could lead to an unstable system. Many of the feedbacks found in the climate system are positive; thus, for example, increasing CO2 levels will increase temperature, reduce the snow cover, increase the absorption of radiation and hence increase temperature further. The most obvious feedbacks, such as the snow example quoted above, are already included within our models of the climate and earth system. Others, such as the impact of increasing forest cover due to global warming, are only just being included. Others, such as, the impact of global warming on the northern peatlands and the impact of freshwater flows on the Arctic Ocean are not yet considered. The contrast in surface characteristics between low tundra vegetation to high taiga forest is considerable. The contrast is greatest in the winter, when the tundra is snow covered but the trees of the taiga protrude through the snow pack, and is probably the greatest contrast found on the land surface anywhere. This variation causes massive changes in the energy fluxes at the surface and hence the temperature conditions on the ground and within the atmosphere. There will be large resultant changes in the vegetation development, the carbon fluxes, the permafrost and the hydrology. The Arctic is already experiencing change and it is essential for us to understand the basic processes, and how these interact, to be confident of our predictions of environmental change in the future.

  18. Evidence of high-elevation amplification versus Arctic amplification

    PubMed Central

    Wang, Qixiang; Fan, Xiaohui; Wang, Mengben

    2016-01-01

    Elevation-dependent warming in high-elevation regions and Arctic amplification are of tremendous interest to many scientists who are engaged in studies in climate change. Here, using annual mean temperatures from 2781 global stations for the 1961–2010 period, we find that the warming for the world’s high-elevation stations (>500 m above sea level) is clearly stronger than their low-elevation counterparts; and the high-elevation amplification consists of not only an altitudinal amplification but also a latitudinal amplification. The warming for the high-elevation stations is linearly proportional to the temperature lapse rates along altitudinal and latitudinal gradients, as a result of the functional shape of Stefan-Boltzmann law in both vertical and latitudinal directions. In contrast, neither altitudinal amplification nor latitudinal amplification is found within the Arctic region despite its greater warming than lower latitudes. Further analysis shows that the Arctic amplification is an integrated part of the latitudinal amplification trend for the low-elevation stations (≤500 m above sea level) across the entire low- to high-latitude Northern Hemisphere, also a result of the mathematical shape of Stefan-Boltzmann law but only in latitudinal direction. PMID:26753547

  19. BRDF characteristics of tundra vegetation communities in Yamal, Western Siberia

    NASA Astrophysics Data System (ADS)

    Buchhorn, Marcel; Heim, Birgit; Walker, Donald A. Skip; Epstein, Howard; Leibman, Marina

    2013-04-01

    Satellite data from platforms with pointing capabilities (CHRIS/Proba, RapidEye) or from sensors with wide swath (AVHRR, MODIS, MERIS) is influenced by the bidirectional reflectance distribution function (BRDF). This effect can cause significant changes in the measured spectral surface reflectance depending on the solar illumination geometry and sensor viewing conditions. The Environmental Mapping and Analysis Program (EnMAP), a German hyperspectral mission with expected launch in 2016, will provide high spectral resolution observations with a ground sampling distance of 30 meters. Since the EnMAP sensor has pointing capabilities, both spectral and directional reflection characteristics need to be taken into account for the algorithms development for vegetation parameters. The 'hyperspectral method development for Arctic VEGetation biomes' (hy-Arc-VEG) project is part of the national preparation program for the EnMAP mission. Within the EnMAP projcect hy-Arc-VEG we developed a portable field spectro-goniometer, named ManTIS (Manual Transportable Instrument for Spherical BRDF observations), for the in-situ measurements of anisotropic effects of tundra surfaces (national and international patent pending - DE 102011117713.6). The goniometer was designed for field use in difficult as well as challenging terrain and climate. It is therefore of low weight, without electrical devices and weatherproof. It can be disassembled and packed into small boxes for transport. The current off-nadir viewing capacity is matched to the EnMAP sensor configuration (up to 30°). We carried out spectral field and goniometer measurements on the joint YAMAL 2011 expedition (RU-US-DE) organized by the Earth-Cryosphere Institute (ECI) in August 2011 on the Yamal Peninsula, northwestern Siberia, Russia. The field goniometer measurements (conducted under varying sun zenith angles) as well as field spectro-radiometrical measurements were carried out at the NASA Yamal Land Cover/Land Use Change

  20. Bioluminescence as an ecological factor during high Arctic polar night

    PubMed Central

    Cronin, Heather A.; Cohen, Jonathan H.; Berge, Jørgen; Johnsen, Geir; Moline, Mark A.

    2016-01-01

    Bioluminescence commonly influences pelagic trophic interactions at mesopelagic depths. Here we characterize a vertical gradient in structure of a generally low species diversity bioluminescent community at shallower epipelagic depths during the polar night period in a high Arctic fjord with in situ bathyphotometric sampling. Bioluminescence potential of the community increased with depth to a peak at 80 m. Community composition changed over this range, with an ecotone at 20–40 m where a dinoflagellate-dominated community transitioned to dominance by the copepod Metridia longa. Coincident at this depth was bioluminescence exceeding atmospheric light in the ambient pelagic photon budget, which we term the bioluminescence compensation depth. Collectively, we show a winter bioluminescent community in the high Arctic with vertical structure linked to attenuation of atmospheric light, which has the potential to influence pelagic ecology during the light-limited polar night. PMID:27805028

  1. Bioluminescence as an ecological factor during high Arctic polar night.

    PubMed

    Cronin, Heather A; Cohen, Jonathan H; Berge, Jørgen; Johnsen, Geir; Moline, Mark A

    2016-11-02

    Bioluminescence commonly influences pelagic trophic interactions at mesopelagic depths. Here we characterize a vertical gradient in structure of a generally low species diversity bioluminescent community at shallower epipelagic depths during the polar night period in a high Arctic fjord with in situ bathyphotometric sampling. Bioluminescence potential of the community increased with depth to a peak at 80 m. Community composition changed over this range, with an ecotone at 20-40 m where a dinoflagellate-dominated community transitioned to dominance by the copepod Metridia longa. Coincident at this depth was bioluminescence exceeding atmospheric light in the ambient pelagic photon budget, which we term the bioluminescence compensation depth. Collectively, we show a winter bioluminescent community in the high Arctic with vertical structure linked to attenuation of atmospheric light, which has the potential to influence pelagic ecology during the light-limited polar night.

  2. Bioluminescence as an ecological factor during high Arctic polar night

    NASA Astrophysics Data System (ADS)

    Cronin, Heather A.; Cohen, Jonathan H.; Berge, Jørgen; Johnsen, Geir; Moline, Mark A.

    2016-11-01

    Bioluminescence commonly influences pelagic trophic interactions at mesopelagic depths. Here we characterize a vertical gradient in structure of a generally low species diversity bioluminescent community at shallower epipelagic depths during the polar night period in a high Arctic fjord with in situ bathyphotometric sampling. Bioluminescence potential of the community increased with depth to a peak at 80 m. Community composition changed over this range, with an ecotone at 20–40 m where a dinoflagellate-dominated community transitioned to dominance by the copepod Metridia longa. Coincident at this depth was bioluminescence exceeding atmospheric light in the ambient pelagic photon budget, which we term the bioluminescence compensation depth. Collectively, we show a winter bioluminescent community in the high Arctic with vertical structure linked to attenuation of atmospheric light, which has the potential to influence pelagic ecology during the light-limited polar night.

  3. Cesium-137 inventories in Alaskan Tundra, lake and marine sediments: An indicator of recent organic material transport?

    SciTech Connect

    Grebmeier, J.M.; Cooper, L.W. |; Larsen, I.L.; Solis, C.; Olsen, C.R.

    1993-06-01

    Tundra sampling was accomplished in 1989--1990 at Imnavait Creek, Alaska (68{degree}37` N, 149{degree}17` W). Inventories of {sup 137}Cs (102--162 mBq/cm{sup 2}) are close to expectations, based upon measured atmospheric deposition for this latitude. Accumulated inventories of {sup 137}Cs in tundra decrease by up to 50% along a transect to Prudhoe Bay (70{degree}13` N, 148{degree}30` W). Atmospheric deposition of {sup 137}Cs decreased with latitude in the Arctic, but declines in deposition would have been relatively small over this distance (200 km). This suggests a recent loss of {sup 137}Cs and possibly associated organic matter from tundra over the northern portions of the transect between Imnavait Creek and Prudhoe Bay. Sediments from Toolik Lake (68{degree}38` N, 149{degree}38` W) showed widely varying {sup 137}Cs inventories, from a low of 22 mBq/cm{sup 2} away from the lake inlet, to a high between 140 to >200 mBq/cm{sup 2} near the main stream inflow. This was indicative of recent accumulation of cesium and possibly organic material associated with it in arctic lakes, although additional sampling is needed.

  4. High resilience in the Yamal-Nenets social-ecological system, West Siberian Arctic, Russia.

    PubMed

    Forbes, Bruce C; Stammler, Florian; Kumpula, Timo; Meschtyb, Nina; Pajunen, Anu; Kaarlejärvi, Elina

    2009-12-29

    Tundra ecosystems are vulnerable to hydrocarbon development, in part because small-scale, low-intensity disturbances can affect vegetation, permafrost soils, and wildlife out of proportion to their spatial extent. Scaling up to include human residents, tightly integrated arctic social-ecological systems (SESs) are believed similarly susceptible to industrial impacts and climate change. In contrast to northern Alaska and Canada, most terrestrial and aquatic components of West Siberian oil and gas fields are seasonally exploited by migratory herders, hunters, fishers, and domesticated reindeer (Rangifer tarandus L.). Despite anthropogenic fragmentation and transformation of a large proportion of the environment, recent socioeconomic upheaval, and pronounced climate warming, we find the Yamal-Nenets SES highly resilient according to a few key measures. We detail the remarkable extent to which the system has successfully reorganized in response to recent shocks and evaluate the limits of the system's capacity to respond. Our analytical approach combines quantitative methods with participant observation to understand the overall effects of rapid land use and climate change at the level of the entire Yamal system, detect thresholds crossed using surrogates, and identify potential traps. Institutional constraints and drivers were as important as the documented ecological changes. Particularly crucial to success is the unfettered movement of people and animals in space and time, which allows them to alternately avoid or exploit a wide range of natural and anthropogenic habitats. However, expansion of infrastructure, concomitant terrestrial and freshwater ecosystem degradation, climate change, and a massive influx of workers underway present a looming threat to future resilience.

  5. Satellite based permafrost modeling in low land tundra landscapes

    NASA Astrophysics Data System (ADS)

    Langer, M.; Westermann, S.; Heikenfeld, M.; Boike, J.

    2012-12-01

    For most of the cryosphere components such as glaciers, ice sheets, sea ice, and snow satellite monitoring and change detection is well established since several decades. For permafrost, however, which represents the largest component of the Arctic cryosphere operational satellite monitoring schemes do not exist so far. Most of the processes which control the Arctic terrestrial ecosystems are related to the thermal state of permafrost and the freeze/thaw dynamics of the active layer. Hence, satellite based permafrost monitoring would be highly beneficial for the impact assessment of climate change in the Arctic. Permafrost monitoring could also be highly beneficial for the risk assessment of infrastructure in the Arctic such as roads, pipelines, and buildings which are directly affected by the thermal stability of permafrost. Increasing thaw depths and prolonged thaw periods can damage pipelines and interrupt the access to vast regions due to road damages. Sustained warming of permafrost can result in thermal erosion and landslides which threaten buildings and other infrastructural facilities. In this study we present a possible permafrost monitoring scheme based on a numerical heat flow model which is forced by multiple satellite products and initialized by weather reanalysis data. The used forcing and initialization dataset includes the land surface temperature (LST), the snow cover fraction (SCF), and the snow water equivalent (SWE). Previous studies demonstrated that MODIS LST products can deliver reasonable surface temperature measurements in tundra landscapes (Langer et al. 2010, Westermann et al. 2011). This study is based on the ten year record of the daily MOD11A1v5 and MYD11A1v5 land surface temperature products with a spatial resolution of 1km. The snow cover evolution is obtained from the daily GlobSnow SWE product with a spatial resolution of about 25km. In addition, the MODIS snow cover products MOD10A1v5 and MYD10v5 with a resolution of 1km are used

  6. Linkage between seasonal hydrology and carbon flux dynamics in tundra ponds: Samoylov Island, Lena River Delta, Siberia

    NASA Astrophysics Data System (ADS)

    Abnizova, Anna; Bornemann, Niko; Boike, Julia

    2010-05-01

    Arctic ponds have been recently recognized as being highly sensitive to changing climate. To date, ponds and lakes are disappearing in Alaska, Siberia and Canadian High Arctic because of climate warming (Fitzgerald et al. 2003; Smith et al. 2005; and Smol et al. 2007). While numerous limnological studies have been done on arctic ponds located in the Canadian High Arctic (Douglas and Smol, 1994; Hamilton et al. 2001; Lim et al., 2001), there is a limited number of studies on tundra ponds located in other circumpolar environments (e.g. Northern Siberia). Duff et al. (1999) describes tundra lakes in northern Russia as clear, dilute, oligotrophic lakes with low nutrients and dissolved organic carbon concentration. While numerous ponds and lakes exists in the Lena River Delta averaging to 2120 lakes of all sizes for every 1000 km2, no studies have been done to understand carbon flux dynamics of these freshwater ecosystems. In this study hydrological monitoring based on water balance framework was applied to a series of ponds and lakes located on Samoylov Island, 120 km south of the Arctic Ocean in the southern central Lena River Delta (72° 22' N, 126 ° 30' E) from July to September 2008. To better understand spatial differences in pond hydrology and carbon flux dynamics, the physical and biochemical data was collected from 42 tundra ponds. The selection of the ponds was based on their size (small, medium, large) and depth values ranging from 10 to 120 cm. The estimation of the seasonal water budget in 2008 showed that losses through evapotranspiration were offset by similar precipitation inputs and resulted in the equilibrium storage values in the study ponds prior to the freeze-back. Preliminary analysis showed that more than 50% of the ponds had DOC > 6.5 mg/l which exceeds average value of other Arctic ponds reported in literature (Duff et al. 1999 and Hamilton et al. 2001). Elevated DOC concentrations (> 8 mg/l) were found in the small and medium ponds with depth

  7. Growing season and spatial variations of carbon fluxes of Arctic and boreal ecosystems in Alaska (USA).

    PubMed

    Ueyama, Masahito; Iwata, Hiroki; Harazono, Yoshinobu; Euskirchen, Eugénie S; Oechel, Walter C; Zona, Donatella

    2013-12-01

    To better understand the spatial and temporal dynamics of CO2 exchange between Arctic ecosystems and the atmosphere, we synthesized CO2 flux data, measured in eight Arctic tundra and five boreal ecosystems across Alaska (USA) and identified growing season and spatial variations of the fluxes and environmental controlling factors. For the period examined, all of the boreal and seven of the eight Arctic tundra ecosystems acted as CO2 sinks during the growing season. Seasonal patterns of the CO2 fluxes were mostly determined by air temperature, except ecosystem respiration (RE) of tundra. For the tundra ecosystems, the spatial variation of gross primary productivity (GPP) and net CO2 sink strength were explained by growing season length, whereas RE increased with growing degree days. For boreal ecosystems, the spatial variation of net CO2 sink strength was mostly determined by recovery of GPP from fire disturbance. Satellite-derived leaf area index (LAI) was a better index to explain the spatial variations of GPP and NEE of the ecosystems in Alaska than were the normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI). Multiple regression models using growing degree days, growing season length, and satellite-derived LAI explained much of the spatial variation in GPP and net CO2 exchange among the tundra and boreal ecosystems. The high sensitivity of the sink strength to growing season length indicated that the tundra ecosystem could increase CO2 sink strength under expected future warming, whereas ecosystem compositions associated with fire disturbance could play a major role in carbon release from boreal ecosystems.

  8. Congruent responses to weather variability in high arctic herbivores.

    PubMed

    Stien, Audun; Ims, Rolf A; Albon, Steve D; Fuglei, Eva; Irvine, R Justin; Ropstad, Erik; Halvorsen, Odd; Langvatn, Rolf; Loe, Leif Egil; Veiberg, Vebjørn; Yoccoz, Nigel G

    2012-12-23

    Assessing the role of weather in the dynamics of wildlife populations is a pressing task in the face of rapid environmental change. Rodents and ruminants are abundant herbivore species in most Arctic ecosystems, many of which are experiencing particularly rapid climate change. Their different life-history characteristics, with the exception of their trophic position, suggest that they should show different responses to environmental variation. Here we show that the only mammalian herbivores on the Arctic islands of Svalbard, reindeer (Rangifer tarandus) and sibling voles (Microtus levis), exhibit strong synchrony in population parameters. This synchrony is due to rain-on-snow events that cause ground ice and demonstrates that climate impacts can be similarly integrated and expressed in species with highly contrasting life histories. The finding suggests that responses of wildlife populations to climate variability and change might be more consistent in Polar regions than elsewhere owing to the strength of the climate impact and the simplicity of the ecosystem.

  9. Modeling the spatiotemporal variability in subsurface thermal regimes across a low-relief polygonal tundra landscape

    SciTech Connect

    Kumar, Jitendra; Collier, Nathan; Bisht, Gautam; Mills, Richard T.; Thornton, Peter E.; Iversen, Colleen M.; Romanovsky, Vladimir

    2016-09-27

    Vast carbon stocks stored in permafrost soils of Arctic tundra are under risk of release to the atmosphere under warming climate scenarios. Ice-wedge polygons in the low-gradient polygonal tundra create a complex mosaic of microtopographic features. This microtopography plays a critical role in regulating the fine-scale variability in thermal and hydrological regimes in the polygonal tundra landscape underlain by continuous permafrost. Modeling of thermal regimes of this sensitive ecosystem is essential for understanding the landscape behavior under the current as well as changing climate. Here, we present an end-to-end effort for high-resolution numerical modeling of thermal hydrology at real-world field sites, utilizing the best available data to characterize and parameterize the models. We also develop approaches to model the thermal hydrology of polygonal tundra and apply them at four study sites near Barrow, Alaska, spanning across low to transitional to high-centered polygons, representing a broad polygonal tundra landscape. A multiphase subsurface thermal hydrology model (PFLOTRAN) was developed and applied to study the thermal regimes at four sites. Using a high-resolution lidar digital elevation model (DEM), microtopographic features of the landscape were characterized and represented in the high-resolution model mesh. The best available soil data from field observations and literature were utilized to represent the complex heterogeneous subsurface in the numerical model. Simulation results demonstrate the ability of the developed modeling approach to capture – without recourse to model calibration – several aspects of the complex thermal regimes across the sites, and provide insights into the critical role of polygonal tundra microtopography in regulating the thermal dynamics of the carbon-rich permafrost soils. Moreover, areas of significant disagreement between model results and observations highlight the importance of field

  10. Modeling the spatiotemporal variability in subsurface thermal regimes across a low-relief polygonal tundra landscape

    DOE PAGES

    Kumar, Jitendra; Collier, Nathan; Bisht, Gautam; ...

    2016-09-27

    Vast carbon stocks stored in permafrost soils of Arctic tundra are under risk of release to the atmosphere under warming climate scenarios. Ice-wedge polygons in the low-gradient polygonal tundra create a complex mosaic of microtopographic features. This microtopography plays a critical role in regulating the fine-scale variability in thermal and hydrological regimes in the polygonal tundra landscape underlain by continuous permafrost. Modeling of thermal regimes of this sensitive ecosystem is essential for understanding the landscape behavior under the current as well as changing climate. Here, we present an end-to-end effort for high-resolution numerical modeling of thermal hydrology at real-world fieldmore » sites, utilizing the best available data to characterize and parameterize the models. We also develop approaches to model the thermal hydrology of polygonal tundra and apply them at four study sites near Barrow, Alaska, spanning across low to transitional to high-centered polygons, representing a broad polygonal tundra landscape. A multiphase subsurface thermal hydrology model (PFLOTRAN) was developed and applied to study the thermal regimes at four sites. Using a high-resolution lidar digital elevation model (DEM), microtopographic features of the landscape were characterized and represented in the high-resolution model mesh. The best available soil data from field observations and literature were utilized to represent the complex heterogeneous subsurface in the numerical model. Simulation results demonstrate the ability of the developed modeling approach to capture – without recourse to model calibration – several aspects of the complex thermal regimes across the sites, and provide insights into the critical role of polygonal tundra microtopography in regulating the thermal dynamics of the carbon-rich permafrost soils. Moreover, areas of significant disagreement between model results and observations highlight the importance of field

  11. Arctic terrestrial hydrology: A synthesis of processes, regional effects, and research challenges

    NASA Astrophysics Data System (ADS)

    Bring, A.; Fedorova, I.; Dibike, Y.; Hinzman, L.; Mârd, J.; Mernild, S. H.; Prowse, T.; Semenova, O.; Stuefer, S. L.; Woo, M.-K.

    2016-03-01

    Terrestrial hydrology is central to the Arctic system and its freshwater circulation. Water transport and water constituents vary, however, across a very diverse geography. In this paper, which is a component of the Arctic Freshwater Synthesis, we review the central freshwater processes in the terrestrial Arctic drainage and how they function and change across seven hydrophysiographical regions (Arctic tundra, boreal plains, shield, mountains, grasslands, glaciers/ice caps, and wetlands). We also highlight links between terrestrial hydrology and other components of the Arctic freshwater system. In terms of key processes, snow cover extent and duration is generally decreasing on a pan-Arctic scale, but snow depth is likely to increase in the Arctic tundra. Evapotranspiration will likely increase overall, but as it is coupled to shifts in landscape characteristics, regional changes are uncertain and may vary over time. Streamflow will generally increase with increasing precipitation, but high and low flows may decrease in some regions. Continued permafrost thaw will trigger hydrological change in multiple ways, particularly through increasing connectivity between groundwater and surface water and changing water storage in lakes and soils, which will influence exchange of moisture with the atmosphere. Other effects of hydrological change include increased risks to infrastructure and water resource planning, ecosystem shifts, and growing flows of water, nutrients, sediment, and carbon to the ocean. Coordinated efforts in monitoring, modeling, and processing studies at various scales are required to improve the understanding of change, in particular at the interfaces between hydrology, atmosphere, ecology, resources, and oceans.

  12. Arctic Climate Forcing Observations to Improve Earth System Models: Measurements at High Frequency, Fine Spatial Resolution, and Climatically Relevant Spatial Scales with the use of the Recently Deployed NGEE-Arctic Tram

    NASA Astrophysics Data System (ADS)

    Curtis, J. B.; Serbin, S.; Dafflon, B.; Raz Yaseef, N.; Torn, M. S.; Cook, P. J.; Lewin, K. F.; Wullschleger, S. D.

    2014-12-01

    In order to improve the representation of the land surface and subsurface properties and their associated feedbacks with climate forcings, climate change, and drivers in Earth System Models (ESMs), detailed observations need to be made at climatically relevant spatial and temporal scales. Pan-Arctic spatial heterogeneity and temporal variation present major challenges to the current generation of ESMs. To enable highly spatially resolved and high temporal frequency measurements for the independent validation of modeled energy and greenhouse gas surface fluxes at core to intermediate scales, we have developed, tested, and deployed an automated observational platform, the Next Generation Ecosystem Experiment (NGEE)-Arctic Tram. The NGEE-Arctic Tram, installed on the Barrow Environmental Observatory (BEO) near Barrow, AK in mid May 2014, consists of 65 meters of elevated track and a fully automated cart carrying a suite of radiation and remote sensing instrumentation. The tram transect is located within the NGEE eddy covariance tower footprint to help better understand the relative contribution of different landforms (e.g. low center vs high center polygonal tundra and associated vegetation) to the overall energy budget of the footprint. Electrical resistivity tomography (ERT), soil moisture, and soil temperature sensors are acquired autonomously and co-located with the tram to link subsurface properties with surface observations. To complement the high frequency and fine spatial resolution of the tram, during the summer field seasons of 2013 and 2014 a portable version of the NGEE-Arctic Tram (also know as the portable energy pole or PEP); was used to characterize surface albedo, NDVI, surface temperature, and photosynthetically active radiation (PAR) across two ~500 m BEO transects co-located with subsurface ERT and ground penetrating radar (GPR) measurements. In addition, a ~ 3 Km transect across three drained thaw-lake basins (DTLB) of different climate

  13. How to preserve the tundra in a warming climate?

    NASA Astrophysics Data System (ADS)

    Käyhkö, Jukka

    2014-05-01

    The warming climate of the polar regions may change much of the current arctic-alpine tundra to forest or dense scrubland. This modification requires adaptation by traditional livelihoods such as reindeer herding, which relies on diverse, seasonal pasturelands. Vegetation change may also trigger positive warming feedbacks, where more abundant forest-scrub vegetation will decrease the global albedo. NCoE Tundra team investigates the complex climate-animal-plant interaction of the tundra ecosystem and aim to unravel the capability of herbivorous mammals to control the expansion of woody vegetation. Our interdisciplinary approach involves several work packages, whose results will be summarised in the presentation. In the ecological WPs, we study the dynamics of the natural food chains involving small herbivorous and the impacts of reindeer on the vegetation and the population dynamics of those arctic-alpine plants, which are most likely to become threatened in a warmer climate. Our study demonstrates the potential of a relatively sparse reindeer stocks (2-5 heads per km2) together with natural populations of arvicoline rodents to prevent the expansion of erect woody plants at the arctic-alpine timberline. In the climatic WPs we study the impact of grazing-dependent vegetation differences on the fraction of solar energy converted to heat. In the socio-economic WPs, we study the conditions for maintaining the economic and cultural viability of reindeer herding while managing the land use so that the arctic-alpine biota would be preserved.

  14. Spatiotemporal variability in surface energy balance across tundra, snow and ice in Greenland.

    PubMed

    Lund, Magnus; Stiegler, Christian; Abermann, Jakob; Citterio, Michele; Hansen, Birger U; van As, Dirk

    2017-02-01

    The surface energy balance (SEB) is essential for understanding the coupled cryosphere-atmosphere system in the Arctic. In this study, we investigate the spatiotemporal variability in SEB across tundra, snow and ice. During the snow-free period, the main energy sink for ice sites is surface melt. For tundra, energy is used for sensible and latent heat flux and soil heat flux leading to permafrost thaw. Longer snow-free period increases melting of the Greenland Ice Sheet and glaciers and may promote tundra permafrost thaw. During winter, clouds have a warming effect across surface types whereas during summer clouds have a cooling effect over tundra and a warming effect over ice, reflecting the spatial variation in albedo. The complex interactions between factors affecting SEB across surface types remain a challenge for understanding current and future conditions. Extended monitoring activities coupled with modelling efforts are essential for assessing the impact of warming in the Arctic.

  15. Ecosystem Metabolism and Air-Water Fluxes of Greenhouse Gases in High Arctic Wetland Ponds

    NASA Astrophysics Data System (ADS)

    Lehnherr, I.; Venkiteswaran, J.; St. Louis, V. L.; Emmerton, C.; Schiff, S. L.

    2012-12-01

    Freshwater lakes and wetlands can be very productive systems on the Arctic landscape compared to terrestrial tundra ecosystems and provide valuable resources to many organisms, including waterfowl, fish and humans. Rates of ecosystem productivity dictate how much energy flows through food webs, impacting the abundance of higher-level organisms (e.g., fish), as well as the net carbon balance, which determines whether a particular ecosystem is a source or sink of carbon. Climate change is predicted to result in warmer temperatures, increased precipitation and permafrost melting in the Arctic and is already altering northern ecosystems at unprecedented rates; however, it is not known how freshwater systems are responding to these changes. To predict how freshwater systems will respond to complex environmental changes, it is necessary to understand the key processes, such as primary production and ecosystem respiration, that are driving these systems. We sampled wetland ponds (n=8) and lakes (n=2) on northern Ellesmere Island (81° N, Nunavut, Canada) during the open water season for a suite of biogeochemical parameters, including concentrations of dissolved gases (O2, CO2, CH4, N2O) as well as stable-isotope ratios of dissolved inorganic carbon (δ13C-DIC), dissolved oxygen (δ18O-DO), and water (δ18O-H2O). We will present rates of primary production and ecosystem respiration, modeled from the concentration and stable isotope ratios of DIC and DO, as well as air-water gas exchange of greenhouse gases in these high Arctic ponds and lakes. Preliminary results demonstrate that ecosystem metabolism in these ponds was high enough to result in significant deviations in the isotope ratios of DIC and DO from atmospheric equilibrium conditions. In other words ecosystem rates of primary production and respiration were faster than gas exchange even in these small, shallow, well-mixed ponds. Furthermore, primary production was elevated enough at all sites except Lake Hazen, a

  16. A Pan-Arctic Assessment of High-Latitude Lake Change ~25 Years Apart

    NASA Astrophysics Data System (ADS)

    Sheng, Y.; Smith, L. C.; Li, J.; Lyons, E. A.; Wang, J.

    2011-12-01

    The Arctic and Sub-Arctic regions are the home to the world's largest quantity of terrestrial lakes. These lakes play a preeminent role in the global water cycle and balance, are sensitive to global warming, and are vital for human and animal water supply. However, they are poorly observed, and a uniform lake inventory is unavailable at the pan-Arctic scale. Though there have been studies of Arctic lake dynamics at local scales, the general picture of Arctic lake change stays unclear. A systematic regional-scale assessment of Arctic lake change in the past ~30 years is crucial for us to address "How have Arctic lakes responded to global warming?" The presentation reports a systematic effort of high-latitude (45N and north) lake inventory using recently available high-resolution satellite imagery. Since Arctic lakes are abundant in small-size classes and their seasonality varies from region to region, pan-Arctic lake mapping requires the use of thousands of cloud-free Landsat images acquired in lake-stable seasons. Nearly eight million lakes have been mapped in various landscapes of the pan-Arctic using automated lake identification algorithms with high replicability. Lake-abundant regions are selected using a systematic sampling strategy to detect decadal lake change using the mid-1970s and circa-2000 Landsat imagery. Spatial patterns of the observed lake dynamics are analyzed at regional scales and the relationship between lake abundance and size distribution is investigated.

  17. A new high resolution tidal model in the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Cancet, Mathilde; Andersen, Ole; Lyard, Florent; Cotton, David; Benveniste, Jérôme

    2016-04-01

    The Arctic Ocean is a challenging region for tidal modeling, because of its complex and not well-documented bathymetry, together combined with the intermittent presence of sea ice and the fact that the in situ tidal observations are scarce at such high latitudes. As a consequence, the accuracy of the global tidal models decreases by several centimeters in the Polar Regions. It has a large impact on the quality of the satellite altimeter sea surface heights in these regions (ERS1/2, Envisat, CryoSat-2, SARAL/AltiKa and the future Sentinel-3 mission), but also on the end-users' applications that need accurate tidal information. Better knowledge of the tides will improve the quality of the high latitudes altimeter sea surface heights and of all derived products, such as the altimetry-derived geostrophic currents, the mean sea surface and the mean dynamic topography. In addition, accurate tidal models are highly strategic information for ever-growing maritime and industrial activities in this region. NOVELTIS and DTU Space have recently developed a regional, high-resolution tidal atlas in the Arctic Ocean, in the framework of an extension of the CryoSat Plus for Oceans (CP4O) project funded by ESA (STSE program). In particular, this atlas benefits from the assimilation of the most complete satellite altimetry dataset ever used in this region, including the Envisat data up to 82°N and the CryoSat-2 reprocessed data between 82°N and 88°N. The combination of all these satellites gives the best possible coverage of altimetry-derived tidal constituents. Tide gauge data have also been used either for assimilation or validation. This paper presents the methodology followed to develop the model and the performances of this new regional tidal model in the Arctic Ocean.

  18. Consequences of artic ground squirrels on soil carbon loss from Siberian tundra

    NASA Astrophysics Data System (ADS)

    Golden, N. A.; Natali, S.; Zimov, N.

    2014-12-01

    A large pool of organic carbon (C) has been accumulating in the Arctic for thousands of years. Much of this C has been frozen in permafrost and unavailable for microbial decomposition. As the climate warms and permafrost thaws, the fate of this large C pool will be driven not only by climatic conditions, but also by ecosystem changes brought about by arctic animal populations. In this project we studied arctic ground squirrels (Spermophilus parryii), which are widely-distributed throughout the Arctic. These social mammals create subterranean burrows that mix soil layers, increase aeration, alter soil moisture and temperature, and redistribute soil nutrients, all of which may impact microbial decomposition. We examined the effects of arctic ground squirrel activity on soil C mineralization in dry heath tundra underlain by continuous permafrost in the Kolyma River watershed in northeast Siberia, Russia. Vegetation cover was greatly reduced on the ground squirrel burrows (80% of ground un-vegetated), compared to undisturbed sites (35% of ground un-vegetated). Soils from ground squirrel burrows were also significantly dryer and warmer. To examine effects of ground squirrel activity on microbial respiration, we conducted an 8-day incubation of soil fromburrows and from adjacent undisturbed tundra. In addition, we assessed the impact of nutrient addition by including treatments with low and high levels of nitrogen addition. Microbial respiration (per gram soil) was three-fold higher in incubated soils from the undisturbed sites compared to soils collected from the burrows. The lower rates of respiration from the disturbed soils may have been a result of lower carbon quality or low soil moisture. High nitrogen addition significantly increased respiration in the undisturbed soils, but not in the disturbed burrow soils, which suggests that microbial respiration in the burrow soils was not primarily limited by nitrogen. These results demonstrate the importance of wildlife

  19. The High Arctic Large Igneous Province Mantle Plume caused uplift of Arctic Canada

    NASA Astrophysics Data System (ADS)

    Galloway, Jennifer; Ernst, Richard; Hadlari, Thomas

    2016-04-01

    The Sverdrup Basin is an east-west-trending extensional sedimentary basin underlying the northern Canadian Arctic Archipelago. The tectonic history of the basin began with Carboniferous-Early Permian rifting followed by thermal subsidence with minor tectonism. Tectonic activity rejuvenated in the Hauterivian-Aptian by renewed rifting and extension. Strata were deformed by diapiric structures that developed during episodic flow of Carboniferous evaporites during the Mesozoic and the basin contains igneous components associated with the High Arctic Large Igneous Province (HALIP). HALIP was a widespread event emplaced in multiple pulses spanning ca. 180 to 80 Ma, with igneous rocks on Svalbard, Franz Josef Island, New Siberian Islands, and also in the Sverdrup Basin on Ellef Ringnes, Axel Heiberg, and Ellesmere islands. Broadly contemporaneous igneous activity across this broad Arctic region along with a reconstructed giant radiating dyke swarm suggests that HALIP is a manifestation of large mantle plume activity probably centred near the Alpha Ridge. Significant surface uplift associated with the rise of a mantle plume is predicted to start ~10-20 my prior to the generation of flood basalt magmatism and to vary in shape and size subsequently throughout the LIP event (1,2,3) Initial uplift is due to dynamical support associated with the top of the ascending plume reaching a depth of about 1000 km, and with continued ascent the uplift topography broadens. Additional effects (erosion of the ductile lithosphere and thermal expansion caused by longer-term heating of the mechanical lithosphere) also affect the shape of the uplift. Topographic uplift can be between 1 to 4 km depending on various factors and may be followed by subsidence as the plume head decays or become permanent due to magmatic underplating. In the High Arctic, field and geochronological data from HALIP relevant to the timing of uplift, deformation, and volcanism are few. Here we present new evidence

  20. Changing Seasonality of Tundra Vegetation and Associated Climatic Variables

    NASA Astrophysics Data System (ADS)

    Bhatt, U. S.; Walker, D. A.; Raynolds, M. K.; Bieniek, P.; Epstein, H. E.; Comiso, J. C.; Pinzon, J.; Tucker, C. J.; Steele, M.; Ermold, W. S.; Zhang, J.

    2014-12-01

    This study documents changes in the seasonality of tundra vegetation productivity and its associated climate variables using long-term data sets. An overall increase of Pan-Arctic tundra greenness potential corresponds to increased land surface temperatures and declining sea ice concentrations. While sea ice has continued to decline, summer land surface temperature and vegetation productivity increases have stalled during the last decade in parts of the Arctic. To understand the processes behind these features we investigate additional climate parameters. This study employs remotely sensed weekly 25-km sea ice concentration, weekly surface temperature, and bi-weekly NDVI from 1982 to 2013. Maximum NDVI (MaxNDVI, Maximum Normalized Difference Vegetation Index), Time Integrated NDVI (TI-NDVI), Summer Warmth Index (SWI, sum of degree months above freezing during May-August), ocean heat content (PIOMAS, model incorporating ocean data assimilation), and snow water equivalent (GlobSnow, assimilated snow data set) are explored. We analyzed the data for the full period (1982-2013) and for two sub-periods (1982-1998 and 1999-2013), which were chosen based on the declining Pan-Arctic SWI since 1998. MaxNDVI has increased from 1982-2013 over most of the Arctic but has declined from 1999 to 2013 over western Eurasia, northern Canada, and southwest Alaska. TI-NDVI has trends that are similar to those for MaxNDVI for the full period but displays widespread declines over the 1999-2013 period. Therefore, as the MaxNDVI has continued to increase overall for the Arctic, TI-NDVI has been declining since 1999. SWI has large relative increases over the 1982-2013 period in eastern Canada and Greenland and strong declines in western Eurasia and southern Canadian tundra. Weekly Pan-Arctic tundra land surface temperatures warmed throughout the summer during the 1982-1998 period but display midsummer declines from 1999-2013. Weekly snow water equivalent over Arctic tundra has declined over

  1. Assessment of Fire Occurrence and Future Fire Potential in Arctic Alaska

    NASA Astrophysics Data System (ADS)

    French, N. H. F.; Jenkins, L. K.; Loboda, T. V.; Bourgeau-Chavez, L. L.; Whitley, M. A.

    2014-12-01

    An analysis of the occurrence of fire in Alaskan tundra was completed using the relatively complete historical record of fire for the region from 1950 to 2013. Spatial fire data for Alaskan tundra regions were obtained from the Alaska Large Fire Database for the region defined from vegetation and ecoregion maps. A detailed presentation of fire records available for assessing the fire regime of the tundra regions of Alaska as well as results evaluating fire size, seasonality, and general geographic and temporal trends is included. Assessment of future fire potential was determined for three future climate scenarios at four locations across the Alaskan tundra using the Canadian Forest Fire Weather Index (FWI). Canadian Earth System Model (CanESM2) weather variables were used for historical (1850-2005) and future (2006-2100) time periods. The database includes 908 fire points and 463 fire polygons within the 482,931 km2 of Alaskan tundra. Based on the polygon database 25,656 km2 (6,340,000 acres) has burned across the six tundra ecoregions since 1950. Approximately 87% of tundra fires start in June and July across all ecoregions. Combining information from the polygon and points data records, the estimated average fire size for fire in the Alaskan Arctic region is 28.1 km2 (7,070 acres), which is much smaller than in the adjacent boreal forest region, averaging 203 km2 for high fire years. The largest fire in the database is the Imuruk Basin Fire which burned 1,680 km2 in 1954 in the Seward Peninsula region (Table 1). Assessment of future fire potential shows that, in comparison with the historical fire record, fire occurrence in Alaskan tundra is expected to increase under all three climate scenarios. Occurrences of high fire weather danger (>10 FWI) are projected to increase in frequency and magnitude in all regions modeled. The changes in fire weather conditions are expected to vary from one region to another in seasonal occurrence as well as severity and frequency

  2. Polygonal tundra geomorphological change in response to warming alters future CO2 and CH4 flux on the Barrow Peninsula.

    PubMed

    Lara, Mark J; McGuire, A David; Euskirchen, Eugenie S; Tweedie, Craig E; Hinkel, Kenneth M; Skurikhin, Alexei N; Romanovsky, Vladimir E; Grosse, Guido; Bolton, W Robert; Genet, Helene

    2015-04-01

    The landscape of the Barrow Peninsula in northern Alaska is thought to have formed over centuries to millennia, and is now dominated by ice-wedge polygonal tundra that spans drained thaw-lake basins and interstitial tundra. In nearby tundra regions, studies have identified a rapid increase in thermokarst formation (i.e., pits) over recent decades in response to climate warming, facilitating changes in polygonal tundra geomorphology. We assessed the future impact of 100 years of tundra geomorphic change on peak growing season carbon exchange in response to: (i) landscape succession associated with the thaw-lake cycle; and (ii) low, moderate, and extreme scenarios of thermokarst pit formation (10%, 30%, and 50%) reported for Alaskan arctic tundra sites. We developed a 30 × 30 m resolution tundra geomorphology map (overall accuracy:75%; Kappa:0.69) for our ~1800 km² study area composed of ten classes; drained slope, high center polygon, flat-center polygon, low center polygon, coalescent low center polygon, polygon trough, meadow, ponds, rivers, and lakes, to determine their spatial distribution across the Barrow Peninsula. Land-atmosphere CO2 and CH4 flux data were collected for the summers of 2006-2010 at eighty-two sites near Barrow, across the mapped classes. The developed geomorphic map was used for the regional assessment of carbon flux. Results indicate (i) at present during peak growing season on the Barrow Peninsula, CO2 uptake occurs at -902.3 10(6) gC-CO2 day(-1) (uncertainty using 95% CI is between -438.3 and -1366 10(6) gC-CO2 day(-1)) and CH4 flux at 28.9 10(6) gC-CH4 day(-1) (uncertainty using 95% CI is between 12.9 and 44.9 10(6) gC-CH4 day(-1)), (ii) one century of future landscape change associated with the thaw-lake cycle only slightly alter CO2 and CH4 exchange, while (iii) moderate increases in thermokarst pits would strengthen both CO2 uptake (-166.9 10(6) gC-CO2 day(-1)) and CH4 flux (2.8 10(6) gC-CH4 day(-1)) with geomorphic change from low

  3. Paleoclimate records at high latitude in Arctic during the Paleogene

    NASA Astrophysics Data System (ADS)

    Salpin, Marie; Schnyder, Johann; Baudin, François; Suan, Guillaume; Labrousse, Loïc; Popescu, Speranta; Suc, Jean-Pierre

    2015-04-01

    Paleoclimate records at high latitude in Arctic during the Paleogene SALPIN Marie1,2, SCHNYDER Johann1,2, BAUDIN François1,2, SUAN Guillaume3, LABROUSSE Loïc1,2, POPESCU Speranta4, SUC Jean-Pierre1,4 1: Sorbonne Universités, UPMC Univ Paris 06, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F 75005, Paris, France 2: CNRS, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F 75005 Paris, France 3: UCB Lyon 1, UMR 5276, LGLTPE, 69622 Villeurbanne Cedex, France 4: GEOBIOSTRATDATA.CONSULTING, 385 Route du Mas Rillier 69140 Rillieux la Pape, France The Paleogene is a period of important variations of the Earth climate system either in warming or cooling. The climatic optima of the Paleogene have been recognized both in continental and marine environment. This study focus on high latitudes of the northern hemisphere, in the Arctic Basin. The basin has had an influence on the Cenozoic global climate change according to its polar position. Is there a specific behaviour of the Arctic Basin with respect to global climatic stimuli? Are there possible mechanisms of coupling/decoupling of its dynamics with respect to the global ocean? To answer these questions a unique collection of sedimentary series of Paleogene age interval has been assembled from the Laurentian margin in Northern Yukon (Canada) and from the Siberian margin (New Siberian Islands). Selected continental successions of Paleocene-Eocene age were used to study the response of the Arctic system to known global events, e.g. the climatic optima of the Paleogene (the so-called PETM, ETM2 or the Azolla events). Two sections of Paleocene-Eocene age were sampled near the Mackenzie delta, the so-called Coal Mine (CoMi) and Caribou Hills (CaH) sections. The aim of the study is to precise the climatic fluctuations and to characterise the source rock potential of the basin, eventually linked to the warming events. This study is based on data of multi-proxy analyses: mineralogy on bulk and clay

  4. Bacterial succession in a glacier foreland of the High Arctic

    PubMed Central

    Schütte, Ursel M.E.; Abdo, Zaid; Bent, Stephen J.; Williams, Christopher J.; Schneider, G. Maria; Solheim, Bjørn; Forney, Larry J.

    2009-01-01

    Succession is defined as changes in biological communities over time. It has been extensively studied in plant communities, but little is known about bacterial succession, in particular in environments such as High Arctic glacier forelands. Bacteria carry out key processes in the development of soil, biogeochemical cycling, and facilitating plant colonization. In this study we sampled two roughly parallel chronosequences in the foreland of Midre Lovén glacier on Svalbard, Norway and tested whether any of several factors were associated with changes in the structure of bacterial communities, including time after glacier retreat, horizontal variation caused by the distance between chronosequences, and vertical variation at two soil depths. The structures of soil bacterial communities at different locations were compared using terminal restriction fragment length polymorphisms (T-RFLP) of 16S rRNA genes, and the data were analyzed by sequential analysis of log-linear statistical models. While no significant differences in community structure were detected between the two chronosequences, statistically significant differences between sampling locations in the surface and mineral soils could be demonstrated even though glacier forelands are patchy and dynamic environments. These findings suggest bacterial succession occurs in High Arctic glacier forelands but may differ in different soil depths. PMID:19587774

  5. An active atmospheric methane sink in high Arctic mineral cryosols

    PubMed Central

    Lau, M C Y; Stackhouse, B T; Layton, A C; Chauhan, A; Vishnivetskaya, T A; Chourey, K; Ronholm, J; Mykytczuk, N C S; Bennett, P C; Lamarche-Gagnon, G; Burton, N; Pollard, W H; Omelon, C R; Medvigy, D M; Hettich, R L; Pfiffner, S M; Whyte, L G; Onstott, T C

    2015-01-01

    Methane (CH4) emission by carbon-rich cryosols at the high latitudes in Northern Hemisphere has been studied extensively. In contrast, data on the CH4 emission potential of carbon-poor cryosols is limited, despite their spatial predominance. This work employs CH4 flux measurements in the field and under laboratory conditions to show that the mineral cryosols at Axel Heiberg Island in the Canadian high Arctic consistently consume atmospheric CH4. Omics analyses present the first molecular evidence of active atmospheric CH4-oxidizing bacteria (atmMOB) in permafrost-affected cryosols, with the prevalent atmMOB genotype in our acidic mineral cryosols being closely related to Upland Soil Cluster α. The atmospheric (atm) CH4 uptake at the study site increases with ground temperature between 0 °C and 18 °C. Consequently, the atm CH4 sink strength is predicted to increase by a factor of 5–30 as the Arctic warms by 5–15 °C over a century. We demonstrate that acidic mineral cryosols are a previously unrecognized potential of CH4 sink that requires further investigation to determine its potential impact on larger scales. This study also calls attention to the poleward distribution of atmMOB, as well as to the potential influence of microbial atm CH4 oxidation, in the context of regional CH4 flux models and global warming. PMID:25871932

  6. An active atmospheric methane sink in high Arctic mineral cryosols.

    PubMed

    Lau, M C Y; Stackhouse, B T; Layton, A C; Chauhan, A; Vishnivetskaya, T A; Chourey, K; Ronholm, J; Mykytczuk, N C S; Bennett, P C; Lamarche-Gagnon, G; Burton, N; Pollard, W H; Omelon, C R; Medvigy, D M; Hettich, R L; Pfiffner, S M; Whyte, L G; Onstott, T C

    2015-08-01

    Methane (CH4) emission by carbon-rich cryosols at the high latitudes in Northern Hemisphere has been studied extensively. In contrast, data on the CH4 emission potential of carbon-poor cryosols is limited, despite their spatial predominance. This work employs CH4 flux measurements in the field and under laboratory conditions to show that the mineral cryosols at Axel Heiberg Island in the Canadian high Arctic consistently consume atmospheric CH4. Omics analyses present the first molecular evidence of active atmospheric CH4-oxidizing bacteria (atmMOB) in permafrost-affected cryosols, with the prevalent atmMOB genotype in our acidic mineral cryosols being closely related to Upland Soil Cluster α. The atmospheric (atm) CH4 uptake at the study site increases with ground temperature between 0 °C and 18 °C. Consequently, the atm CH4 sink strength is predicted to increase by a factor of 5-30 as the Arctic warms by 5-15 °C over a century. We demonstrate that acidic mineral cryosols are a previously unrecognized potential of CH4 sink that requires further investigation to determine its potential impact on larger scales. This study also calls attention to the poleward distribution of atmMOB, as well as to the potential influence of microbial atm CH4 oxidation, in the context of regional CH4 flux models and global warming.

  7. The 1977 tundra fire at Kokolik River, Alaska

    NASA Technical Reports Server (NTRS)

    Hall, D.; Brown, J.; Johnson, L.

    1981-01-01

    During the summer of 1977, fire totaled 44 sq km of tundra vegetation according to measurements using LANDSAT imagery. Based on the experience gained from analysis of this fire using ground observations, satellite imagery, and topographic maps, it appears that natural drainages form effective fire breaks on the subdued relief of the Arctic coastal plain and northern foothills. It is confirmed that the intensity of the fire is related to vegetation type and to the moisture content of the organic rich soils.

  8. Microbial Communities in a High Arctic Polar Desert Landscape

    PubMed Central

    McCann, Clare M.; Wade, Matthew J.; Gray, Neil D.; Roberts, Jennifer A.; Hubert, Casey R. J.; Graham, David W.

    2016-01-01

    The High Arctic is dominated by polar desert habitats whose microbial communities are poorly understood. In this study, we used next generation sequencing to describe the α- and β-diversity of microbial communities in polar desert soils from the Kongsfjorden region of Svalbard. Ten phyla dominated the soils and accounted for 95% of all sequences, with the Proteobacteria, Actinobacteria, and Chloroflexi being the major lineages. In contrast to previous investigations of Arctic soils, relative Acidobacterial abundances were found to be very low as were the Archaea throughout the Kongsfjorden polar desert landscape. Lower Acidobacterial abundances were attributed to characteristic circumneutral soil pHs in this region, which has resulted from the weathering of underlying carbonate bedrock. In addition, we compared previously measured geochemical conditions as possible controls on soil microbial communities. Phosphorus, pH, nitrogen, and calcium levels all significantly correlated with β-diversity, indicating landscape-scale lithological control of available nutrients, which in turn, significantly influenced soil community composition. In addition, soil phosphorus and pH significantly correlated with α-diversity, particularly with the Shannon diversity and Chao 1 richness indices. PMID:27065980

  9. Idiosyncratic responses of high Arctic plants to changing snow regimes.

    PubMed

    Rumpf, Sabine B; Semenchuk, Philipp R; Dullinger, Stefan; Cooper, Elisabeth J

    2014-01-01

    The Arctic is one of the ecosystems most affected by climate change; in particular, winter temperatures and precipitation are predicted to increase with consequent changes to snow cover depth and duration. Whether the snow-free period will be shortened or prolonged depends on the extent and temporal patterns of the temperature and precipitation rise; resulting changes will likely affect plant growth with cascading effects throughout the ecosystem. We experimentally manipulated snow regimes using snow fences and shoveling and assessed aboveground size of eight common high arctic plant species weekly throughout the summer. We demonstrated that plant growth responded to snow regime, and that air temperature sum during the snow free period was the best predictor for plant size. The majority of our studied species showed periodic growth; increases in plant size stopped after certain cumulative temperatures were obtained. Plants in early snow-free treatments without additional spring warming were smaller than controls. Response to deeper snow with later melt-out varied between species and categorizing responses by growth forms or habitat associations did not reveal generic trends. We therefore stress the importance of examining responses at the species level, since generalized predictions of aboveground growth responses to changing snow regimes cannot be made.

  10. Ice Mass Changes in the Russian High Arctic

    NASA Astrophysics Data System (ADS)

    Willis, M. J.; Melkonian, A. K.; Pritchard, M. E.; Golos, E. M.

    2012-12-01

    The ~2000 glaciers and icecaps on the islands of the Russian High Arctic cover a total area of about 55,600 km2. Infrequent studies have indicated that these glaciers have lost a total of ~100 km3 of ice, equivalent to about 0.3 mm of sea level, since 1960. Recent GRACE observations suggest that the Severnaya Zemlya Archipelago and Franz Josef Archipelago are approximately in balance, while the "Main Ice Sheet" of the Novaya Zemlya archipelago is losing mass at a small rate. This glacier complex, on the northern island of the archipelago is the largest ice mass in Europe (23,800 km2) and the third largest polar ice masses on the planet after the Antarctic and Greenland Ice sheets. The glaciers, ice caps and icefields of the Russian High Arctic are a major reservoir of fresh water and under climate scenarios that involve warming, a potentially increasing source of mass for sea level rise. We examine the response of the glaciers of the Russian High Arctic to recent, pronounced atmospheric warming. Digitized topographic maps, ASTER Digital Elevation Models (DEMs), cloud free ICESat returns and several DEMs calculated from recent high-resolution imagery pairs are used to provide a time-series and maps of ice surface elevation change rates between the mid-1980s' and 2012 for the "Main Ice Sheet" on Novaya Zemlya and the Franz Josef Land Archipelago. DEMs are co-registered to a common horizontal base and corrected for biases due to varying reference frames and datums. Elevation change rates are calculated on a pixel-by-pixel basis and are integrated over each ice complex to provide volume change rates. Volume rates are converted to mass rates assuming an ice density of 900 kg/m3. Glacier speeds are derived from pairs of ASTER images between 2000 and 2012 and from higher resolution imagery between 2010 and 2012. Cloudy conditions often hamper our ability to make good pairs and problems occur when there are no bedrock outcrops, which are typically used to check for

  11. The footprint of Alaskan tundra fires during the past half-century: implications for surface properties and radiative forcing

    USGS Publications Warehouse

    Rocha, Adrian V.; Loranty, Michael M.; Higuera, Phil E.; Mack, Michelle C.; Hu, Feng Sheng; Jones, Benjamin M.; Breen, Amy L.; Rastetter, Edward B.; Goetz, Scott J.; Shaver, Gus R.

    2012-01-01

    Recent large and frequent fires above the Alaskan arctic circle have forced a reassessment of the ecological and climatological importance of fire in arctic tundra ecosystems. Here we provide a general overview of the occurrence, distribution, and ecological and climate implications of Alaskan tundra fires over the past half-century using spatially explicit climate, fire, vegetation and remote sensing datasets for Alaska. Our analyses highlight the importance of vegetation biomass and environmental conditions in regulating tundra burning, and demonstrate that most tundra ecosystems are susceptible to burn, providing the environmental conditions are right. Over the past two decades, fire perimeters above the arctic circle have increased in size and importance, especially on the North Slope, indicating that future wildfire projections should account for fire regime changes in these regions. Remote sensing data and a literature review of thaw depths indicate that tundra fires have both positive and negative implications for climatic feedbacks including a decadal increase in albedo radiative forcing immediately after a fire, a stimulation of surface greenness and a persistent long-term (>10 year) increase in thaw depth. In order to address the future impact of tundra fires on climate, a better understanding of the control of tundra fire occurrence as well as the long-term impacts on ecosystem carbon cycling will be required.

  12. High Arctic Paraglacial Coastal Evolution in Northern Billefjorden, Svalbard

    NASA Astrophysics Data System (ADS)

    Strzelecki, Matt; Long, Antony; Lloyd, Jerry

    2013-04-01

    Most sediment budget studies in paraglacial, High Arctic, environments have focussed attention on quantifying sediment fluxes in glacial and fluvial catchments. In contrast, little attention has been paid to the functioning of the paraglacial coastal zone with existing models of coastal change based on relict systems developed in mid latitude settings. The pristine coasts of Spitsbergen provided a superb opportunity to quantify how High Arctic coasts are respondingto rapid climate warming and associated paraglacial landscape transformation. In this paper we reconstruct the development of the paraglacial coasts in Petuniabukta and Adolfbukta, the northernmost bays of Billefjorden, central Spitsbergen. The study area is characterized by a sheltered location, a semi-arid, sub-polar climate, limited wave fetch and tidal range, and rapid retreat of all surrounding glaciers. Using a combination of geomorphological, sedimentological, remote sensing and dating methods, we study the processes controlling the coastal zone development over annual, century and millennial timescales. Interannual changes observed between 2008-2010 show that gravel barriers in the study area are resilient to the impacts of local storms and the operation of sea-ice processes. In general, the processes controlling the short-term barrier development often operate in the opposite direction to the landforming patterns visible in the longer-term evolution. Over multi-decadal timescales, since the end of the Little Ice Age. we observe drammatic changes in sediment flux and coastal response under an interval characterised by a warming climate, retreating local ice masses, a shortened winter sea-ice season and melting permafrost. A new approach of dating juvenile mollusc found in uplifted marine barriers led to the better understating of the Late Holocene evolution of a Petuniabukta coastal zone and its reaction to deglaciation, glacioisostatic uplift and sea-level fluctuations. We propose a new

  13. Colonizing the High Arctic: Mitochondrial DNA Reveals Common Origin of Eurasian Archipelagic Reindeer (Rangifer tarandus)

    PubMed Central

    Kvie, Kjersti S.; Heggenes, Jan; Anderson, David G.; Kholodova, Marina V.; Sipko, Taras; Mizin, Ivan; Røed, Knut H.

    2016-01-01

    In light of current debates on global climate change it has become important to know more on how large, roaming species have responded to environmental change in the past. Using the highly variable mitochondrial control region, we revisit theories of Rangifer colonization and propose that the High Arctic archipelagos of Svalbard, Franz Josef Land, and Novaia Zemlia were colonized by reindeer from the Eurasian mainland after the last glacial maximum. Comparing mtDNA control region sequences from the three Arctic archipelagos showed a strong genetic connection between the populations, supporting a common origin in the past. A genetic connection between the three archipelagos and two Russian mainland populations was also found, suggesting colonization of the Eurasian high Arctic archipelagos from the Eurasian mainland. The age of the Franz Josef Land material (>2000 years before present) implies that Arctic indigenous reindeer colonized the Eurasian Arctic archipelagos through natural dispersal, before humans approached this region. PMID:27880778

  14. A Pliocene chronostratigraphy for the Canadian western and high Arctic

    NASA Astrophysics Data System (ADS)

    Gosse, John; Braschi, Lea; Rybczynski, Natalia; Lakeman, Thomas; Zimmerman, Susan; Finkel, Robert; Barendregt, Rene; Matthews, John

    2014-05-01

    The Beaufort Formation comprises an extensive (1200 km long, more than 1 km thick) clastic wedge that formed during the Pliocene along the western Canadian Arctic Archipelago (CAA). In the western Arctic, the Ballast Brook (BB) site on Banks Is. exposes more than 20 km of section through the sandy and pebble sandy braided stream deposits with detrital organic beds. Farther north, Beaufort Fm fluvial and estuarine facies have been examined on Meighen Is. In the high Arctic, high terrace gravels (450 m high surface) at the Fyles Leaf Bed (FLB) and Beaver Pond (BP) sites on Ellesmere Is. are not considered part of the Beaufort Fm but have similar paleoenvironmental records. Fossil plant and faunal material from these sediments is often very well preserved and provides evidence of a boreal-type forest and peatlands. The BP fossil site preserves the remains of fossil vertebrates including fish, frog, horse, beaver, deerlet, and black bear, consistent with a boreal type forest habitat. The FLB site has recently yielded the first fossil evidence for a High Arctic camel, identified with the help of collagen fingerprinting from a fragmentary limb bone (tibia). Paleoenvironmental reconstruction of the Ellesmere sites has yielded a Mean Annual Temperature of between 14 to 22 degrees Celsius warmer than today. Minimum cosmogenic nuclide burial ages of 3.4 and 3.8 Ma obtained for the BP and FLB sites, respectively, are consistent with vertebrate and floral biostratigraphic evidence. The paleoenvironmental records from the Beaufort Fm in the western CAA sites have revealed a similar ecosystem with noteworthy differences in MAT and perhaps seasonality. New burial ages from Meighen Is. indicate a maximum age of 6.1 Ma, consistent with yet much older than previous age estimates, but supportive of paleomagnetic and biostratigraphy at the same location. The age differences may account for some of the interpreted variations in paleoenvironments, in addition to spatial differences in

  15. Large tundra methane burst during onset of freezing.

    PubMed

    Mastepanov, Mikhail; Sigsgaard, Charlotte; Dlugokencky, Edward J; Houweling, Sander; Ström, Lena; Tamstorf, Mikkel P; Christensen, Torben R

    2008-12-04

    Terrestrial wetland emissions are the largest single source of the greenhouse gas methane. Northern high-latitude wetlands contribute significantly to the overall methane emissions from wetlands, but the relative source distribution between tropical and high-latitude wetlands remains uncertain. As a result, not all the observed spatial and seasonal patterns of atmospheric methane concentrations can be satisfactorily explained, particularly for high northern latitudes. For example, a late-autumn shoulder is consistently observed in the seasonal cycles of atmospheric methane at high-latitude sites, but the sources responsible for these increased methane concentrations remain uncertain. Here we report a data set that extends hourly methane flux measurements from a high Arctic setting into the late autumn and early winter, during the onset of soil freezing. We find that emissions fall to a low steady level after the growing season but then increase significantly during the freeze-in period. The integral of emissions during the freeze-in period is approximately equal to the amount of methane emitted during the entire summer season. Three-dimensional atmospheric chemistry and transport model simulations of global atmospheric methane concentrations indicate that the observed early winter emission burst improves the agreement between the simulated seasonal cycle and atmospheric data from latitudes north of 60 degrees N. Our findings suggest that permafrost-associated freeze-in bursts of methane emissions from tundra regions could be an important and so far unrecognized component of the seasonal distribution of methane emissions from high latitudes.

  16. Response of a tundra ecosystem to elevated atmospheric carbon dioxide and CO sub 2 -induced climate change

    SciTech Connect

    Oechel, W.C.

    1992-04-01

    This report presents the progress on the DOE funded project: Response of a Tundra Ecosystem to Elevated Atmospheric Carbon Dioxide and CO{sub 2}-Induced Climate Change.'' The current funding cycle was initiated on September 1, 1989, to run through August 31, 1992. There was an initial reduction in scope dictated by budget availabilities, primarily manipulations of CO{sub 2}, temperature and nutrients at a wet tundra located at Barrow Alaska. These experiments still need to be done over the mid- to longer term in order to accurately predict, apriori, the effects of climate change on the arctic tundra as well as possible feedbacks. Coordination and cooperation with other agencies was initiated in 1990 and formally proposed in our 1991 renewal at the national and international level and has become an important aspect of the research. To accurately and precisely scale plot and transect measurements to the circumpolar tundra is beyond the scope of the current DOE project. It is possible, however to determine the patterns and controls of CO{sub 2} flux from the current circumpolar arctic tundra with the involvement of additional agencies and governments. Results from the past two years of this project confirm that the arctic has become a source of CO{sub 2} to the atmosphere. This change coincides with recent climatic variation in the arctic, and suggest a positive feedback of arctic ecosystems on atmospheric CO{sub 2} and global change. Measurements along a latitudinal gradient across the north slope of Alaska indicate a loss of carbon from tussock tundra and wet tundra, decreasing in magnitude along a decreasing gradient of temperature but an increasing gradient in soil moisture. These data are in agreement with work done on tussock tundra in 1983{endash}85 and 1987.

  17. Response of a tundra ecosystem to elevated atmospheric carbon dioxide and CO{sub 2}-induced climate change. Progress report

    SciTech Connect

    Oechel, W.C.

    1992-04-01

    This report presents the progress on the DOE funded project: ``Response of a Tundra Ecosystem to Elevated Atmospheric Carbon Dioxide and CO{sub 2}-Induced Climate Change.`` The current funding cycle was initiated on September 1, 1989, to run through August 31, 1992. There was an initial reduction in scope dictated by budget availabilities, primarily manipulations of CO{sub 2}, temperature and nutrients at a wet tundra located at Barrow Alaska. These experiments still need to be done over the mid- to longer term in order to accurately predict, apriori, the effects of climate change on the arctic tundra as well as possible feedbacks. Coordination and cooperation with other agencies was initiated in 1990 and formally proposed in our 1991 renewal at the national and international level and has become an important aspect of the research. To accurately and precisely scale plot and transect measurements to the circumpolar tundra is beyond the scope of the current DOE project. It is possible, however to determine the patterns and controls of CO{sub 2} flux from the current circumpolar arctic tundra with the involvement of additional agencies and governments. Results from the past two years of this project confirm that the arctic has become a source of CO{sub 2} to the atmosphere. This change coincides with recent climatic variation in the arctic, and suggest a positive feedback of arctic ecosystems on atmospheric CO{sub 2} and global change. Measurements along a latitudinal gradient across the north slope of Alaska indicate a loss of carbon from tussock tundra and wet tundra, decreasing in magnitude along a decreasing gradient of temperature but an increasing gradient in soil moisture. These data are in agreement with work done on tussock tundra in 1983{endash}85 and 1987.

  18. Vegetation greening in the Canadian Arctic related to decadal warming.

    PubMed

    Jia, Gensuo J; Epstein, Howard E; Walker, Donald A

    2009-12-01

    This study is presented within the context that climate warming and sea-ice decline has been occurring throughout much of the Arctic over the past several decades, and that terrestrial ecosystems at high latitudes are sensitive to the resultant alterations in surface temperatures. Results are from analyzing interannual satellite records of vegetation greenness across a bioclimate gradient of the Canadian Arctic over the period of 1982-2006. Here, we combine multi-scale sub-pixel analysis and remote sensing time-series analysis to investigate recent decadal changes in vegetation greenness along spatial gradients of summer temperature and vegetation. Linear autoregression temporal analysis of vegetation greenness was performed with relatively "pure" vegetation pixels of Advanced Very High Resolution Radiometer (AVHRR) data, spanning Low Arctic, High Arctic and polar desert ecosystems. Vegetation greenness generally increased over tundra ecosystems in the past two decades. Peak annual greenness increased 0.49-0.79%/yr over the High Arctic where prostrate dwarf shrubs, forbs, mosses and lichens dominate and 0.46-0.67%/yr over the Low Arctic where erect dwarf shrubs and graminoids dominate. However, magnitudes of vegetation greenness differ with length of time series and periods considered, indicating a nonlinear response of terrestrial ecosystems to climate change. The decadal increases of greenness reflect increasing vegetation production during the peak of the growing season, and were likely driven by the recent warming.

  19. Decade time scale plot to landscape scale change in tundra ecosystem structure and function near Barrow, AK

    NASA Astrophysics Data System (ADS)

    Lin, D. H.; Johnson, D. R.; Lara, M. J.; Villarreal, S.; Hollister, R. D.; Webber, P. J.; Tweedie, C. E.

    2012-12-01

    Several models suggest shifts in tundra ecosystem structure and function are likely to affect the future state of the Arctic system and how these shifts may impact the global system. Validation of such predictions remains a challenge, however, due to the lack of sustained environmental observations throughout much of the Arctic. In the absence of sustained monitoring, relocating, rescuing, and retrospectively resampling historic research sites and datasets has proven to be an effective means to establish likely change scenarios and develop hypotheses of future change trajectories. This study, synthesizes several recently published works that have used this retrospective approach to explore plot to landscape change in tundra ecosystem structure and function near Barrow, Alaska over the past half Century. This study is a contribution to the International Polar Year 'Back to the Future' project IPY-BTF, IPY # 512). At the landscape level, analysis of land cover change of time series high spatial resolution aerial and satellite imagery spanning 1948-2008 show an overall increase in the extent of dry and moist land cover and open water, and a decrease in the extent of wet and aquatic, land cover types. The 'drying' trend noted for the coastal landscape of Barrow is similar to that noted for four other Alaskan tundra landscapes but in the same study, the Barrow landscape also showed the most dramatic change in wet and aquatic land cover types. Plot level studies of sites, established in 1972 during the International Biological Program, that have been resampled three times show that species richness and diversity has increased and that wet plant communities have changed more than dry plant communities. An analysis of ecosystem function coupled to this plot level study suggests the greatest functional change has occurred in aquatic and wet plant communities where methane efflux and net ecosystem production (NEP) has increased and albedo and the normalized difference

  20. Recovery of plant biomass and soil N cycling in Alaskan tundra following an unusual fire

    NASA Astrophysics Data System (ADS)

    Bret-Harte, M. S.; Mack, M. C.; Huebner, D. C.; Johnston, M.; Shaver, G. R.

    2012-12-01

    Climate warming is likely to increase the frequency of disturbances in the Arctic. The Anaktuvuk River fire of 2007 burned 1039 km2 of northern Alaskan tundra; this was unprecedented for this vegetation, which is clonal, slow-growing, and long-lived. We harvested plant biomass and soils from severely and moderately burned areas and controls in 2011 to assess recovery of plant productivity and soil N cycling four years after the fire. Biomass of vascular plants had recovered to nearly control levels in moderately burned areas, due primarily to resprouting by graminoids, particularly Eriophorum vaginatum. Graminoid biomass was actually greater in moderately burned tundra than in unburned tundra. Deciduous shrub and evergreen shrub biomass in moderately burned tundra was approximately half that seen in unburned tundra, but non-vascular plant biomass was much less, so that total aboveground biomass in moderately burned tundra had not returned to control levels. Severely burned tundra had less of all components of the community than in moderately burned tundra, except that there was higher biomass of non-vascular plants, due to colonization by fire-following liverworts and mosses. Productivity of vascular plants was similar in unburned and severely burned tundra plots, and higher in moderately burned plots, due in part to higher soil N availability. Recovery of plant biomass was largely due to resprouting of species that survived the fire, though numerous seedlings were seen. Biomass of vascular plants has recovered rapidly in the moderately burned sites, while severely burned sites and nonvascular plants are recovering more slowly, but the relative abundance of different species differs from unburned tundra. The relationship between spectral indices (NDVI, EVI-2) collected at the plot level and either biomass or NPP varied with burn category, which may complicate assessments of NPP by remote sensing following fire.

  1. The Pliocene High Arctic terrestrial palaeoenvironmental record and the development of the western Canadian Arctic coastal plain

    NASA Astrophysics Data System (ADS)

    Rybczynski, N.; Braschi, L.; Gosse, J. C.; Kennedy, C.; Fraser, D.; Lakeman, T.

    2013-12-01

    The Pliocene fossil record of the High Arctic is represented by a collection of sites that occur across the Canadian Arctic Archipelago (CAA), with deposits in the west comprising a 1200 km-long dissected clastic wedge (Beaufort Formation) and those in the east represented by high terrace gravel deposits. Fossil material from these sites is often very well preserved and provides evidence of a boreal-type forest. In the eastern Arctic our research sites includes the Fyles Leaf Bed (FLB) and the Beaver Pond (BP) sites, on west central Ellesmere Island. These are about 10 km apart and preserve evidence of forest and peatlands. The BP fossil site preserves the remains of fossil vertebrates including fish, frog, horse, beaver, deerlet, and black bear, consistent with a boreal type forest habitat. The FLB site has recently yielded the first fossil evidence for a High Arctic camel, identified with the help of collagen fingerprinting from a fragmentary limb bone (tibia). Although modern camels live in open habitats, biogeographic and comparative dental evidence, in combination, suggest that the North American Arctic camels were browsers, and therefore forest-dwelling. Paleoenvironmental reconstruction of the Ellesmere sites has yielded a Mean Annual Temperature of between 14 to 22 degrees Celsius warmer than today. Minimum cosmogenic nuclide burial ages of 3.4 and 3.8 Ma obtained for the BP and FLB sites, respectively, are consistent with vertebrate and floral biostratigraphic evidence. The Beaufort Formation, located in the Western CAA, was formed by a regional northwesterly flowing braided fluvial system. The Beaufort Formation appears to have filled at least the western portions of the 100 km-wide channels that currently separate the islands of the CAA. Intervals of Pliocene continental-shelf progradation are recorded in the lower Iperk Formation, which is situated offshore and includes complex sigmoid-oblique clinoforms indicative of high-energy, coarse

  2. A Comparison of Satellite and Aircraft-Mounted Thermal Observations of Freeze/Thaw Cycling of the Alaska Tundra and Boreal Forests during the Carbon in the Arctic Vulnerability Experiment (CARVE)

    NASA Astrophysics Data System (ADS)

    Steiner, N.; McDonald, K. C.; Miller, C. E.; Dinardo, S. J.

    2014-12-01

    Freeze/thaw (F/T) related surface processes in the Arctic are important as they bracket negative and positive modes in the flux of CO2 and CH4 between the surface and atmosphere. The Carbon in the Arctic Vulnerability Experiment (CARVE) monitors carbon gas cycling in Alaskan using aircraft-deployed gas sampling instruments along with remote sensing observations of the land surface condition. A nadir-pointed, forward looking infrared (FLIR) imager mounted on the CARVE aircraft is used to measure upwelling mid-infrared spectral radiance at 3-5 microns. The FLIR instrument was operated during the spring, summer and fall seasons of 2013 and 2014 during clear sky conditions and targeting ecosystem components affecting the carbon cycle. The instantaneous field of view (IFOV) of the FLIR instrument allows for a resolution of ~36 cm from a height of 500 m. This high resolution data allow for the discrimination of individual landscape components such as soil, vegetation and surface water features in the image footprint. We assess the effectiveness of the FLIR thermal images in monitoring thawing and inundation processes of individual ecosystem components of importance in biogeochemical cycling. We also observe how these individual components scale using coarse resolution satellite observations of land surface temperature (LST) from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Freeze/thaw state determined from the Advanced Microwave Scanning Radiometer (AMSR2) on JAXA's Shizuku (GCOM-W1) satellite. Portions of the work were carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautic and Space Administration.

  3. Fourth international circumpolar arctic vegetation mapping workshop

    USGS Publications Warehouse

    Raynolds, Martha K.; Markon, C.J.

    2002-01-01

    During the week of April 10, 2001, the Fourth International Circumpolar Arctic Vegetation Mapping Workshop was held in Moscow, Russia. The purpose of this meeting was to bring together the vegetation scientists working on the Circumpolar Arctic Vegetation Map (CAVM) to (1) review the progress of current mapping activities, (2) discuss and agree upon a standard set of arctic tundra subzones, (3) plan for the production and dissemination of a draft map, and (4) begin work on a legend for the final map.

  4. Energy and water balance studies of a snow cover during snowmelt period at a high arctic site

    NASA Astrophysics Data System (ADS)

    Bruland, O.; Maréchal, D.; Sand, K.; Killingtveit, Å.

    The predicted global warming is supposed to have an enhanced effect on the arctic regions. How this will influence the water, carbon dioxide and methane balances in the European arctic tundra is the objective of the EU-funded project ``Understanding Land Surface Physical Processes in the Arctic'' (LAPP), to which where SINTEF is one of several contributors. The snow cover is one of the limiting factors for these exchange processes and knowledge of how it behaves and will behave under a different climate is important. Data collected for water and energy balance studies in an area close to Ny-Ålesund at 79°N at Svalbard are the basis of this study. Measurements during the ablation periods since 1992 show an average air temperature for the periods of 2.1°C, an average incoming shorwave radiation of 230W/m2 and an average measured runoff intensity of 14mm/day with a maximum of 68mm/day. Three models of different complexity are tested in order to simulate the water and energy balance of a snow cover on the arctic tundra. The three models are: a complex numerical model (CROCUS), a simple energy balance model and a temperature index model. The simulations were carried out for the melt periods in 1992 and 1996 as these two periods represent very different meteorological conditions. The results of these simulations exposed weaknesses in all the models. The energy balance model lacks calculation of cold content in the snowpack. This influences both the outgoing longwave radiation and the timing of the melt. Due to the effect of compensating errors in the simulations, CROCUS performed better than the simple energy balance model but also this model has problems with the simulation of outgoing longwave radiation. The temperature index model does not perform well for snowmelt studies in regions were radiation is the main driving energy source for the melt.

  5. Impact of future Arctic shipping on high-latitude black carbon deposition (Invited)

    NASA Astrophysics Data System (ADS)

    Corbett, J. J.; Browse, J.; Carslaw, K. S.; Schmidt, A.

    2013-12-01

    The retreat of Arctic sea-ice has led to renewed calls to exploit Arctic shipping routes. The diversion of ship traffic through the Arctic will shorten shipping routes and possibly reduce global shipping emissions. However, deposition of black carbon (BC) aerosol emitted by additional Arctic ships could cause a reduction in the albedo of snow and ice, accelerating snow-melt and sea-ice loss. We use recently compiled Arctic shipping emission inventories for 2004 and 2050 together with a global aerosol microphysics model GLOMAP coupled to the chemical transport model TOMCAT to quantify the contribution of future Arctic shipping to high-latitude BC deposition. Emission rates of SOx (SO2 and SO4) and particulate matter (PM) were estimated for 2050 under both business-as-usual and high-growth scenarios. BC particles are assumed to be water-insoluble at emission but can become active in cloud drop formation through soluble material accumulation. After BC particles become cloud-active they are more efficiently wet scavenged, which accounts for 80% of modeled BC deposition. Current-day Arctic shipping contributes 0.3% to the BC mass deposited north of 60N (250 Gg). About 50% of modelled BC deposition is on open ocean, suggesting that current Arctic ship traffic may not significantly contribute to BC deposition on central Arctic sea ice. However, 6 - 8% of deposited BC on the west coast of Greenland originates from local ship traffic. Moreover, in-Arctic shipping contributes some 32% to high-latitude ship-sourced deposition despite accounting for less than 1.0% of global shipping emissions. This suggests that control of in-Arctic shipping BC emissions could yield greater decrease in high-latitude BC deposition than a similar control strategy applied only to the extra-Arctic shipping industry. Arctic shipping in 2050 will contribute less than 1% to the total BC deposition north of 60N due to the much greater relative contribution of BC transported from non-shipping sources

  6. Microbial cell retention in a melting High Arctic snowpack, Svalbard

    NASA Astrophysics Data System (ADS)

    Zarsky, Jakub; Björkman, Mats; Kühnel, Rafael; Hell, Katherina; Hodson, Andy; Sattler, Birgit; Psenner, Roland

    2014-05-01

    Introduction The melting snow pack represents a highly dynamic system not only for chemical compounds but also for bacterial cells. Microbial activity was found at subzero temperatures in ice veins when liquid water persists due to high concentration of ions on the surface of snow crystals and brine channels between large ice crystals in ice. Several observations also suggest microbial activity under subzero temperatures in seasonal snow. Even with regard to the spatial and temporal relevance of snow ecosystems, microbial activity in such an extreme habitat represents a relatively small proportion in the carbon flux of the global ecosystem and even of the glacial ecosystems specifically. On the other hand, it represents a remarkable piece of mosaic of the microbial activity in glacial ecosystems because the snow pack represents the first contact between the atmosphere and cryosphere. This topic also embodies vital crossovers to biogeochemistry and ecotoxicology, offering a quantitative view of utilization of various substrates relevant for downstream ecosystems. Here we present our study of the dynamics of both solvents and cells suspended in meltwater of the melting snowpack on a high arctic glacier to demonstrate the spatio-temporal constraint of interaction between solvent and bacterial cells in this environment. Method We used 6 lysimeters inserted into the bottom of the snowpack to collect replicated samples of melt water before it comes into contact with basal ice or slush layer at the base of the snow pack. The sampling site was chosen at Midre Lovénbreen (Svalbard, Kongsfjorden, MLB stake 6) where the snow pack showed melting on the surface but the basal ice was still dry. Sampling was conducted in June 2010 for a period of 10 days once per day and the snow profile was sampled according to distinguished layers in the profile at the beginning of the field mission and as bulk at its end. The height of snow above the lysimeters dropped from the initial 74 cm

  7. Correlated declines in Pacific arctic snow and sea ice cover

    USGS Publications Warehouse

    Stone, Robert P.; Douglas, David C.; Belchansky, Gennady I.; Drobot, Sheldon

    2005-01-01

    Simulations of future climate suggest that global warming will reduce Arctic snow and ice cover, resulting in decreased surface albedo (reflectivity). Lowering of the surface albedo leads to further warming by increasing solar absorption at the surface. This phenomenon is referred to as “temperature–albedo feedback.” Anticipation of such a feedback is one reason why scientists look to the Arctic for early indications of global warming. Much of the Arctic has warmed significantly. Northern Hemisphere snow cover has decreased, and sea ice has diminished in area and thickness. As reported in the Arctic Climate Impact Assessment in 2004, the trends are considered to be outside the range of natural variability, implicating global warming as an underlying cause. Changing climatic conditions in the high northern latitudes have influenced biogeochemical cycles on a broad scale. Warming has already affected the sea ice, the tundra, the plants, the animals, and the indigenous populations that depend on them. Changing annual cycles of snow and sea ice also affect sources and sinks of important greenhouse gases (such as carbon dioxide and methane), further complicating feedbacks involving the global budgets of these important constituents. For instance, thawing permafrost increases the extent of tundra wetlands and lakes, releasing greater amounts of methane into the atmosphere. Variable sea ice cover may affect the hemispheric carbon budget by altering the ocean–atmosphere exchange of carbon dioxide. There is growing concern that amplification of global warming in the Arctic will have far-reaching effects on lower latitude climate through these feedback mechanisms. Despite the diverse and convincing observational evidence that the Arctic environment is changing, it remains unclear whether these changes are anthropogenically forced or result from natural variations of the climate system. A better understanding of what controls the seasonal distributions of snow and ice

  8. Phenological Advances and Trophic Consequences in Low- and High-Arctic Greenland

    NASA Astrophysics Data System (ADS)

    Høye, T. T.; Schmidt, N. M.; Forchhammer, M. C.; Bøving, P. S.; Post, E.

    2009-12-01

    Seasonal timing of reproduction (phenology) is highly responsive to global warming, especially in the Arctic. Here, we present a comparative analysis of multi-annual observational data on phenological dynamics across trophic levels from Zackenberg, North-East Greenland (a High Arctic site) and Kangerlussuaq, West Greenland (a Low Arctic site). Both sites have experienced considerable warming and our analyses indicate that rates of change in plant phenological responses may differ between sites, related to different proximal drivers at the two sites. We also present parallel data on interacting organisms (pollinators and mammalian herbivores) to evaluate the risks and effects of trophic mismatch at these two sites.

  9. High Resolution CH4 Emissions and Dissolved CH4 Measurements Elucidate Surface Gas Exchange Processes in Toolik Lake, Arctic Alaska

    NASA Astrophysics Data System (ADS)

    Del Sontro, T.; Sollberger, S.; Kling, G. W.; Shaver, G. R.; Eugster, W.

    2013-12-01

    Approximately 14% of the Alaskan North Slope is covered in lakes of various sizes and depths. Diffusive carbon emissions (CH4 and CO2) from these lakes offset the tundra sink by ~20 %, but the offset would substantially increase if ebullitive CH4 emissions were also considered. Ultimately, arctic lake CH4 emissions are not insignificant in the global CH4 budget and their contribution is bound to increase due to impacts from climate change. Here we present high resolution CH4 emission data as measured via eddy covariance and a Los Gatos gas analyzer during the ice free period from Toolik Lake, a deep (20 m) Arctic lake located on the Alaskan North Slope, over the last few summers. Emissions are relatively low (< 25 mg CH4 m-2 d-1) with little variation over the summer. Diurnal variations regularly occur, however, with up to 3 times higher fluxes at night. Gas exchange is a relatively difficult process to estimate, but is normally done so as the product of the CH4 gradient across the air-water interface and the gas transfer velocity, k. Typically, k is determined based on the turbulence on the water side of the interface, which is most commonly approximated by wind speed; however, it has become increasingly apparent that this assumption does not remain valid across all water bodies. Dissolved CH4 profiles in Toolik revealed a subsurface peak in CH4 at the thermocline of up to 3 times as much CH4 as in the surface water. We hypothesize that convective mixing at night due to cooling surface waters brings the subsurface CH4 to the surface and causes the higher night fluxes. In addition to high resolution flux emission estimates, we also acquired high resolution data for dissolved CH4 in surface waters of Toolik Lake during the last two summers using a CH4 equilibrator system connected to a Los Gatos gas analyzer. Thus, having both the flux and the CH4 gradient across the air-water interface measured directly, we can calculate k and investigate the processes influencing

  10. Isoprene emissions from a tundra ecosystem

    NASA Astrophysics Data System (ADS)

    Potosnak, M. J.; Baker, B. M.; LeStourgeon, L.; Disher, S. M.; Griffin, K. L.; Bret-Harte, M. S.

    2012-10-01

    Whole-system fluxes of isoprene from a~moist acidic tundra ecosystem and leaf-level emission rates of isoprene from a common species (Salix pulchra) in that same ecosystem were measured during three separate field campaigns. The field campaigns were conducted during the summers of 2005, 2010 and 2011 and took place at the Toolik Field Station (68.6° N, 149.6° W) on the north slope of the Brooks Range in Alaska, USA. The maximum rate of whole-system isoprene flux measured was over 1.2 mg C m-2 h-1 with an air temperature of 22 ° C and a PAR level over 1500 μmol m-2 s-1. Leaf-level isoprene emission rates for S. pulchra averaged 12.4 nmol m-2 s-1 (27.4 μg C gdw-1 h-1) extrapolated to standard conditions (PAR = 1000 μmol m-2 s-1 and leaf temperature = 30° C). Leaf-level isoprene emission rates were well characterized by the Guenther algorithm for temperature, but less so for light. Chamber measurements from a nearby moist acidic tundra ecosystem with less S. pulchra emitted significant amounts of isoprene, but at lower rates (0.45 mg C m-2 h-1). Comparison of our results to predictions from a global model found broad agreement, but a detailed analysis revealed some significant discrepancies. An atmospheric chemistry box model predicts that the observed isoprene emissions have a significant impact on Arctic atmospheric chemistry, including the hydroxyl radical (OH). Our results support the prediction that isoprene emissions from Arctic ecosystems will increase with global climate change.

  11. Isoprene emissions from a tundra ecosystem

    NASA Astrophysics Data System (ADS)

    Potosnak, M. J.; Baker, B. M.; LeStourgeon, L.; Disher, S. M.; Griffin, K. L.; Bret-Harte, M. S.; Starr, G.

    2013-02-01

    Whole-system fluxes of isoprene from a moist acidic tundra ecosystem and leaf-level emission rates of isoprene from a common species (Salix pulchra) in that same ecosystem were measured during three separate field campaigns. The field campaigns were conducted during the summers of 2005, 2010 and 2011 and took place at the Toolik Field Station (68.6° N, 149.6° W) on the north slope of the Brooks Range in Alaska, USA. The maximum rate of whole-system isoprene flux measured was over 1.2 mg C m-2 h-1 with an air temperature of 22 °C and a PAR level over 1500 μmol m-2 s-1. Leaf-level isoprene emission rates for S. pulchra averaged 12.4 nmol m-2 s-1 (27.4 μg C gdw-1 h-1) extrapolated to standard conditions (PAR = 1000 μmol m-2 s-1 and leaf temperature = 30 °C). Leaf-level isoprene emission rates were well characterized by the Guenther algorithm for temperature with published coefficients, but less so for light. Chamber measurements from a nearby moist acidic tundra ecosystem with little S. pulchra emitted significant amounts of isoprene, but at lower rates (0.45 mg C m-2 h-1) suggesting other significant isoprene emitters. Comparison of our results to predictions from a global model found broad agreement, but a detailed analysis revealed some significant discrepancies. An atmospheric chemistry box model predicts that the observed isoprene emissions have a significant impact on Arctic atmospheric chemistry, including a reduction of hydroxyl radical (OH) concentrations. Our results support the prediction that isoprene emissions from Arctic ecosystems will increase with global climate change.

  12. Tall shrub and tree expansion in Siberian tundra ecotones since the 1960s.

    PubMed

    Frost, Gerald V; Epstein, Howard E

    2014-04-01

    Circumpolar expansion of tall shrubs and trees into Arctic tundra is widely thought to be occurring as a result of recent climate warming, but little quantitative evidence exists for northern Siberia, which encompasses the world's largest forest-tundra ecotonal belt. We quantified changes in tall shrub and tree canopy cover in 11, widely distributed Siberian ecotonal landscapes by comparing very high-resolution photography from the Cold War-era 'Gambit' and 'Corona' satellite surveillance systems (1965-1969) with modern imagery. We also analyzed within-landscape patterns of vegetation change to evaluate the susceptibility of different landscape components to tall shrub and tree increase. The total cover of tall shrubs and trees increased in nine of 11 ecotones. In northwest Siberia, alder (Alnus) shrubland cover increased 5.3-25.9% in five ecotones. In Taymyr and Yakutia, larch (Larix) cover increased 3.0-6.7% within three ecotones, but declined 16.8% at a fourth ecotone due to thaw of ice-rich permafrost. In Chukotka, the total cover of alder and dwarf pine (Pinus) increased 6.1% within one ecotone and was little changed at a second ecotone. Within most landscapes, shrub and tree increase was linked to specific geomorphic settings, especially those with active disturbance regimes such as permafrost patterned-ground, floodplains, and colluvial hillslopes. Mean summer temperatures increased at most ecotones since the mid-1960s, but rates of shrub and tree canopy cover expansion were not strongly correlated with temperature trends and were better correlated with mean annual precipitation. We conclude that shrub and tree cover is increasing in tundra ecotones across most of northern Siberia, but rates of increase vary widely regionally and at the landscape scale. Our results indicate that extensive changes can occur within decades in moist, shrub-dominated ecotones, as in northwest Siberia, while changes are likely to occur much more slowly in the highly continental

  13. The origin of lead in the organic horizon of tundra soils: atmospheric deposition, plant translocation from the mineral soil or soil mineral mixing?

    PubMed

    Klaminder, Jonatan; Farmer, John G; MacKenzie, Angus B

    2011-09-15

    Knowledge of the anthropogenic contribution to lead (Pb) concentrations in surface soils in high latitude ecosystems is central to our understanding of the extent of atmospheric Pb contamination. In this study, we reconstructed fallout of Pb at a remote sub-arctic region by using two ombrotrophic peat cores and assessed the extent to which this airborne Pb is able to explain the isotopic composition ((206)Pb/(207)Pb ratio) in the O-horizon of tundra soils. In the peat cores, long-range atmospheric fallout appeared to be the main source of Pb as indicated by temporal trends that followed the known European pollution history, i.e. accelerated fallout at the onset of industrialization and peak fallout around the 1960s-70s. The Pb isotopic composition of the O-horizon of podzolic tundra soil ((206)Pb/(207)Pb=1.170 ± 0.002; mean ± SD) overlapped with that of the peat ((206)Pb/(207)Pb=1.16 ± 0.01) representing a proxy for atmospheric aerosols, but was clearly different from that of the parent soil material ((206)Pb/(207)Pb=1.22-1.30). This finding indicated that long-range fallout of atmospheric Pb is the main driver of Pb accumulation in podzolic tundra soil. In O-horizons of tundra soil weakly affected by cryoturbation (cryosols) however, the input of Pb from the underlying mineral soil increased as indicated by (206)Pb/(207)Pb ratios of up to 1.20, a value closer to that of local soil minerals. Nevertheless, atmospheric Pb appeared to be the dominant source in this soil compartment. We conclude that Pb concentrations in the O-horizon of studied tundra soils - despite being much lower than in boreal soils and representative for one of the least exposed sites to atmospheric Pb contaminants in Europe - are mainly controlled by atmospheric inputs from distant anthropogenic sources.

  14. CLIMATIC EFFECTS ON TUNDRA CARBON STORAGE INFERRED FROM EXPERIMENTAL DATA AND A MODEL

    EPA Science Inventory

    We used a process-based model of ecosystem carbon (C) and nitrogen (N)dynamics, MBL-GEM (Marine Biological Laboratory General Ecosystem Model), to integrated and analyze the results of several experiments that examined the response of arctic tussock tundra to manipulations of CO2...

  15. Peopling of the high Arctic - induced by sea ice?

    NASA Astrophysics Data System (ADS)

    Funder, Svend

    2010-05-01

    'We travelled in the winter after the return of daylight and did not go into fixed camp until spring, when the ice broke up. There was good hunting on the way, seals, beluga, walrus, bear.' (From Old Merkrusârk's account of his childhood's trek from Baffin Island to Northwest Greenland, told to Knud Rasmussen on Saunders Island in 1904) Five thousand years ago people moving eastwards from Beringia spread over the barrens of the Canadian high Arctic. This was the first of three waves of prehistoric Arctic 'cultures', which eventually reached Greenland. The passage into Greenland has to go through the northernmost and most hostile part of the country with a 5 month Polar night, and to understand this extraordinary example of human behaviour and endurance, it has been customary to invoke a more favourable (warmer) climate. This presentation suggests that land-fast sea ice, i.e. stationary sea ice anchored to the coast, is among the most important environmental factors behind the spread of prehistoric polar cultures. The ice provides the road for travelling and social communion - and access to the most important source of food, the ocean. In the LongTerm Project (2006 and 2007) we attempted to establish a Holocene record for sea ice variations along oceanic coasts in northernmost Greenland. Presently the coasts north of 80° N are beleaguered by year-round sea ice - for ten months this is land-fast ice, and only for a period in the stormy autumn months are the coasts exposed to pack-ice. This presentation Land-fast ice - as opposed to pack-ice - is a product of local temperatures, but its duration over the year, and especially into the daylight season, is also conditioned by other factors, notably wind strength. In the geological record we recognize long lasting land-fast ice by two absences: absence of traces of wave action (no beach formation), which, however, can also be a result of pack-ice along the coast; - and absence of driftwood on the shore (land-fast ice

  16. Remote Sensing of Ocean Color in the High Arctic

    NASA Technical Reports Server (NTRS)

    Cota, G. F.; Platt, T.; Harrison, W. G.

    1997-01-01

    With four years of NASA SeaWiFS funding I established a completely new capability and expertise for in-water optical measurements nearly from scratch and with very little optical background. My first-year budget included only capital for a profiling spectral radiometer. Over the next 30 months we conducted six cruises and collected almost 300 optical profiles in challenging environments; many were collected from 21' launches. I also changed institutions during this period: it is very disruptive to move, set up a new lab, and hire and train new people, etc. We also did not have access to NASA funds for almost a year during the move because of difficulties in subcontracting and/or transferring funds. Nevertheless, we delivered data sets from six bio-optical cruises from three high latitude regions, although only two or three cruises from two areas were promised for our SeaWiFS research. The three Canadian Arctic field programs comprise the most comprehensive high latitude bio-optical and biogeochemical data sets in existence. Optical and pigment data from all six cruises have been submitted to NASA and are being included in the algorithm development test set. Additional data are still being submitted.

  17. Serosurvey for Toxoplasma gondii in arctic foxes and possible sources of infection in the high Arctic of Svalbard.

    PubMed

    Prestrud, Kristin Wear; Asbakk, Kjetil; Fuglei, Eva; Mørk, Torill; Stien, Audun; Ropstad, Erik; Tryland, Morten; Gabrielsen, Geir Wing; Lydersen, Christian; Kovacs, Kit M; Loonen, Maarten J J E; Sagerup, Kjetil; Oksanen, Antti

    2007-11-30

    Samples (blood or tissue fluid) from 594 arctic foxes (Alopex lagopus), 390 Svalbard reindeer (Rangifer tarandus platyrhynchus), 361 sibling voles (Microtus rossiaemeridionalis), 17 walruses (Odobenus rosmarus), 149 barnacle geese (Branta leucopsis), 58 kittiwakes (Rissa tridactyla), and 27 glaucous gulls (Larus hyperboreus) from Svalbard and nearby waters were assayed for antibodies against Toxoplasma gondii using a direct agglutination test. The proportion of seropositive animals was 43% in arctic foxes, 7% in barnacle geese, and 6% (1 of 17) in walruses. There were no seropositive Svalbard reindeer, sibling voles, glaucous gulls, or kittiwakes. The prevalence in the arctic fox was relatively high compared to previous reports from canid populations. There are no wild felids in Svalbard and domestic cats are prohibited, and the absence of antibodies against T. gondii among the herbivorous Svalbard reindeer and voles indicates that transmission of the parasite by oocysts is not likely to be an important mechanism in the Svalbard ecosystem. Our results suggest that migratory birds, such as the barnacle goose, may be the most important vectors bringing the parasite to Svalbard. In addition to transmission through infected prey and carrion, the age-seroprevalence profile in the fox population suggests that their infection levels are enhanced by vertical transmission.

  18. Nutrient Limitation of Microbial Mediated Decomposition and Arctic Soil Chronology

    NASA Astrophysics Data System (ADS)

    Melle, C. J.; Darrouzet-Nardi, A.; Wallenstein, M. D.

    2012-12-01

    effective soil age. My research is focused on addressing the questions of the extent of microbial N limitation in arctic tundra soils, the potential for co-limitation of labile C despite a high SOC environment, and the dependence, if any, nutrient limitation may have on the effective age of the soil. I have addressed these questions by conducting a laboratory soil incubation of factorial design with treatments of amended glucose, amended ammonium nitrate, and a control consisting of an addition of an equivalent volume of deionized water. Moist acid tundra soils possessing similar soil properties from two arctic sites of close proximity yet with varying deglaciation chronologies were utilized in my study. Soil properties of C-mineralization via respiration, microbial biomass, and nitrogen content in the forms of ammonium, nitrate, and total free amino acids and microbial extra-cellular enzyme production were assayed to determine the microbial response to the experimental treatments. Through the results of this work, I hope to better our understanding of biogeochemical cycling within arctic tundra ecosystems and the response to climate change by contributing to existing knowledge of nutrient limitation on microbial mediated decomposition of SOC in the arctic and how this may differ in soils of varying effective age.

  19. Ancient, highly heterogeneous mantle beneath Gakkel ridge, Arctic Ocean.

    PubMed

    Liu, Chuan-Zhou; Snow, Jonathan E; Hellebrand, Eric; Brügmann, Gerhard; von der Handt, Anette; Büchl, Anette; Hofmann, Albrecht W

    2008-03-20

    The Earth's mantle beneath ocean ridges is widely thought to be depleted by previous melt extraction, but well homogenized by convective stirring. This inference of homogeneity has been complicated by the occurrence of portions enriched in incompatible elements. Here we show that some refractory abyssal peridotites from the ultraslow-spreading Gakkel ridge (Arctic Ocean) have very depleted 187Os/188Os ratios with model ages up to 2 billion years, implying the long-term preservation of refractory domains in the asthenospheric mantle rather than their erasure by mantle convection. The refractory domains would not be sampled by mid-ocean-ridge basalts because they contribute little to the genesis of magmas. We thus suggest that the upwelling mantle beneath mid-ocean ridges is highly heterogeneous, which makes it difficult to constrain its composition by mid-ocean-ridge basalts alone. Furthermore, the existence of ancient domains in oceanic mantle suggests that using osmium model ages to constrain the evolution of continental lithosphere should be approached with caution.

  20. Measurement-based upscaling of Pan Arctic Net Ecosystem Exchange: the PANEEx project

    NASA Astrophysics Data System (ADS)

    Njuabe Mbufong, Herbert; Kusbach, Antonin; Lund, Magnus; Persson, Andreas; Christensen, Torben R.; Tamstorf, Mikkel P.; Connolly, John

    2016-04-01

    The high variability in Arctic tundra net ecosystem exchange (NEE) of carbon (C) can be attributed to the high spatial heterogeneity of Arctic tundra due to the complex topography. Current models of C exchange handle the Arctic as either a single or few ecosystems, responding to environmental change in the same manner. In this study, we developed and tested a simple pan Arctic NEE (PANEEx) model using the Misterlich light response curve (LRC) function with photosynthetic photon flux density (PPFD) as the main driving variable. Model calibration was carried out with eddy covariance carbon dioxide (CO2) data from 12 Arctic tundra sites. The model input parameters (Fcsat, Rd and α) were estimated as a function of air temperature (AirT) and leaf area index (LAI) and represent specific characteristics of the NEE-PPFD relationship, including the saturation flux, dark respiration and initial light use efficiency, respectively. LAI and air temperature were respectively estimated from empirical relationships with remotely sensed normalized difference vegetation index (NDVI) and land surface temperature (LST). These are available as MODIS Terra product MOD13Q1 and MOD11A1 respectively. Therefore, no specific knowledge of the vegetation type is required. The PANEEx model captures the spatial heterogeneity of the Arctic tundra and was effective in simulating 77% of the measured fluxes (r2 = 0.72, p < 0.001) at the 12 sites used in the calibration of the model. Further, the model effectively estimates NEE in three disparate Alaskan ecosystems (heath, tussock and fen) with an estimation ranging between 10 - 36% of the measured fluxes. We suggest that the poor agreement between the measured and modeled NEE may result from the disparity between ground-based measured LAI (used in model calibration) and remotely sensed LAI (estimated from NDVI and used in NEE estimation). Moreover, our results suggests that using simple linear regressions may be inadequate as parameters estimated

  1. Diet dichotomy between two migrant seabirds breeding near a high Arctic polynya

    PubMed Central

    Boadway, Kelly A.; Davis, Shanti E.; Maftei, Mark; Mallory, Mark L.

    2017-01-01

    High Arctic polynyas are predictable areas of open water, which offer long-distance migrant seabirds a reliable source of food during a period when they have to replenish and accumulate energy for reproduction. Investigating the interaction between species nesting sympatrically in the vicinity of polynyas should provide insights into the role that such oceanographic features play for pre-breeding seabirds. We used stable isotopes (δ13C and δ15N) to compare the diet of two ground-nesting seabirds, Sabine's gull (Xema sabini) and Arctic tern (Sterna paradisaea), nesting on an island adjacent to a recurring polynya in the Canadian high Arctic in 2008 and 2009. We show that, unlike Arctic terns, the diet of Sabine's gulls appears to include a non-negligible amount of terrestrially derived prey during early incubation, and that overall both species segregate their dietary niche during pre-laying and early incubation.

  2. Substantial contribution of northern high-latitude sources to mineral dust in the Arctic

    NASA Astrophysics Data System (ADS)

    Groot Zwaaftink, C. D.; Grythe, H.; Skov, H.; Stohl, A.

    2016-11-01

    In the Arctic, impurities in the atmosphere and cryosphere can strongly affect the atmospheric radiation and surface energy balance. While black carbon has hence received much attention, mineral dust has been in the background. Mineral dust is not only transported into the Arctic from remote regions but also, possibly increasingly, generated in the region itself. Here we study mineral dust in the Arctic based on global transport model simulations. For this, we have developed a dust mobilization scheme in combination with the Lagrangian particle dispersion model FLEXPART. A model evaluation, based on measurements of surface concentrations and annual deposition at a number of stations and aircraft vertical profiles, shows the suitability of this model to study global dust transport. Simulations indicate that about 3% of global dust emission originates from high-latitude dust sources in the Arctic. Due to limited convection and enhanced efficiency of removal, dust emitted in these source regions is mostly deposited closer to the source than dust from for instance Asia or Africa. This leads to dominant contributions of local dust sources to total surface dust concentrations ( 85%) and dust deposition ( 90%) in the Arctic region. Dust deposition from local sources peaks in autumn, while dust deposition from remote sources occurs mainly in spring in the Arctic. With increasing altitude, remote sources become more important for dust concentrations as well as deposition. Therefore, total atmospheric dust loads in the Arctic are strongly influenced by Asian ( 38%) and African ( 32%) dust, whereas local dust contributes only 27%. Dust loads are thus largest in spring when remote dust is efficiently transported into the Arctic. Overall, our study shows that contributions of local dust sources are more important in the Arctic than previously thought, particularly with respect to surface concentrations and dust deposition.

  3. Decline and recovery of a high Arctic wolf-prey system

    USGS Publications Warehouse

    Mech, L.D.

    2005-01-01

    A long-existing system of wolves (Canis lupus), muskoxen (Ovibos moschatus) and arctic hares (Lepus arcticus) in a 2600 km]2 area of Canada's High Arctic (80DG N latitude) began collapsing in 1997 because of unusual adverse summer weather but recovered to a level at which all three species were rreproducing by 2004. Recovery of wolf presence and reproduction appeared to be more dependent on muskox increase than on hare increase.

  4. Changes in tundra vascular plant biomass over thirty years at Imnavait Creek, Alaska.

    NASA Astrophysics Data System (ADS)

    Bret-Harte, M. S.; Euskirchen, E. S.; Edgar, C.; Huebner, D. C.; Okano, K.; Tucker, C.; Genet, H.; Ray, P. M.; Shaver, G. R.

    2014-12-01

    Understanding the magnitude of, and controls over, CO2 and water fluxes in arctic ecosystems is essential for accurate assessment and prediction of their responses to climate change. In 2013, we harvested vegetation and soils in the most common plant community types located in the source areas for fluxes measured by eddy covariance towers located in three representative Alaska tundra ecosystems along a toposequence (a ridge site composed of heath tundra and moist non-acidic tundra, a mid-slope site composed of moist acidic tussock tundra, and a valley bottom fen site composed of wet sedge tundra and moist acidic tundra) at Imnavait Creek, Alaska. While the purpose of this harvest was to relate biomass and production to estimates of overall net ecosystem CO2 exchange (NEE), gross primary productivity (GPP) and ecosystem respiration (ER) obtained by micrometeorological methods, it also afforded an opportunity to compare with biomass harvests done in the 1980s in moist acidic tundra at Imnavait Creek; there have been no other harvests than ours at Imnavait since then. Our data showed that plant biomass and production were greatest in the tussock tundra at the mid-slope tower, and least in the wet sedge community at the fen tower, while plant diversity was greatest in the communities at the ridge site. Aboveground biomass of vascular plants in our 2013 harvest in moist acidic tundra was nearly three times higher than that measured approximately thirty years earlier in three harvests of nearby areas at Imnavait Creek, due to an increase in the biomass of shrubs and graminoids. Comparison with other biomass harvests from the vicinity of Toolik Field Station indicate that vascular plant biomass in moist acidic tundra has increased over this time period, with the greatest increase evident by the mid-1990s, and a more gradual increase through to the present time, despite no obvious increase in air temperature as seen in data from nearby climate stations. These data will be

  5. Biogeochemical modeling of tundra recovery following thermal erosion of permafrost

    NASA Astrophysics Data System (ADS)

    Pearce, A. R.; Rastetter, E. B.; Bowden, W. B.

    2011-12-01

    We simulate the biogeochemical recovery of tundra from a thermal erosion disturbance using the Multiple Element Limitation model (MEL) and compare model results with soil organic matter and nutrient chemistry measurements collected across a chronosequence of thermal erosion features. Thermal erosion of permafrost initially depletes the tundra of much of its vegetation and shallow soil organic matter. However, several decades later, there is often little distinguishing these scars from the surrounding undisturbed tundra. As thermal erosion features become more abundant on the arctic landscape, we desire to understand how the pools of carbon and nutrients rebuild after these disturbances. MEL is a plot-scale, process-based model that optimizes the acquisition of eight resources (light, water, CO2, PO4, NH4, NO3, DON and N-fixation) by vegetation based on how much of each is required and the effort needed to acquire it. Model output includes pool sizes of carbon, nitrogen and phosphorus in vegetation, litter, young soil organic matter and old soil organic matter and the fluxes among these pools over time. This calibration of MEL, operating on a daily timestep, was created with published data collected at or near the Toolik Field Station (Toolik Lake, AK, USA) from moist acidic tussock tundra sites. We corroborate our calibration with data from plot manipulations (N and P fertilization, greenhouse, and shade house) performed as part of the NSF Arctic LTER project. The initial conditions for the recovery simulations reflect post-failure observations of some of the variation in soil organic matter, and soil and water nutrient chemistry. With sufficient nutrients from residual soil or supplied in soil water from upslope, the model indicates that vegetation can recover within several decades, but recovery of C and nutrients lost from soils may take hundreds of years.

  6. Pulsed resources at tundra breeding sites affect winter irruptions at temperate latitudes of a top predator, the snowy owl.

    PubMed

    Robillard, A; Therrien, J F; Gauthier, G; Clark, K M; Bêty, J

    2016-06-01

    Irruptive migration is mostly observed in species specialized on pulsed resources and is thought to be a response to unpredictable changes in food supply. We assessed two alternative hypotheses to explain the periodic winter irruptions of snowy owls Bubo scandiacus every 3-5 years in temperate North America: (a) the lack-of-food hypothesis, which states that a crash in small mammal abundance on the Arctic breeding grounds forces owls to move out of the tundra massively to search for food in winter; (b) the breeding-success hypothesis, which states that high abundance of tundra small mammals during the summer allows for high production of young, thus increasing the pool of migrants moving south the following winter. We modeled winter irruptions of snowy owls in relation to summer food resources and geographic location. Winter abundance of owls was obtained from citizen-based surveys from 1994 to 2011 and summer abundance of small mammals was collected in summer at two distant sites in Canada: Bylot Island, NU (eastern High Arctic) and Daring Lake, NWT (central Low Arctic). Winter owl abundance was positively related to prey abundance during the previous summer at both sites and tended to decrease from western to eastern temperate North America. Irruptive migration of snowy owls was therefore best explained by the breeding success hypothesis and was apparently caused by large-scale summer variations in food. Our results, combined with previous findings, suggest that the main determinants of irruptive migration may be species specific even in a guild of apparently similar species.

  7. Assessing seasonal backscatter variations with respect to uncertainties in soil moisture retrieval in Siberian tundra regions

    NASA Astrophysics Data System (ADS)

    Högström, Elin; Trofaier, Anna Maria; Gouttevin, Isabella; Bartsch, Annett

    2015-04-01

    Data from the Advanced Scatterometer (ASCAT) instrument provide the basis of a near real-time, coarse scale, global soil moisture product. Numerous studies have shown the applicability of this product, including recent operational use for numerical weather forecasts. Soil moisture is a key element in the global cycles of water, energy and carbon. Among many application areas, it is essential for the understanding of permafrost development in a future climate change scenario. Dramatic climate changes are expected in the Arctic, where ca 25% of the land is underlain by permafrost, and it is to a large extent remote and inaccessible. The availability and applicability of satellite derived land-surface data relevant for permafrost studies, such as surface soil moisture, is thus crucial to landscape-scale analyses of climate-induced change. However, there are challenges in the soil moisture retrieval that are specific to the Arctic. This study investigates backscatter variability unrelated to soil moisture variations in order to understand the possible impact on the soil moisture retrieval. The focus is on tundra lakes, which are a common feature in the Arctic and are expected to affect the retrieval. ENVISAT Advanced Synthetic Aperture Radar (ASAR) Wide Swath (120 m) data are used to resolve lakes and later understand and quantify their impacts on Metop ASCAT (25 km) soil moisture retrieval during the snow free period. Sites of interest are chosen according to high or low agreement between output from the land surface model ORCHIDEE and ASCAT derived SSM. The results show that in most cases low model agreement is related to high water fraction. The water fraction correlates with backscatter deviations (relative to a smooth water surface reference image) within the ASCAT footprint areas (R = 0.91-0.97). Backscatter deviations of up to 5 dB can occur in areas with less than 50% water fraction and an assumed soil moisture related range (sensitivity) of 7 dB in the ASCAT

  8. Atmospheric methane sources - Alaskan tundra bogs, an alpine fen, and a subarctic boreal marsh

    NASA Technical Reports Server (NTRS)

    Sebacher, D. I.; Harriss, R. C.; Grice, S. S.; Bartlett, K. B.; Sebacher, S. M.

    1986-01-01

    Methane (CH4) flux measurements from Alaska tundra bogs, an alpine fen, and a subarctic boreal marsh were obtained at field sites ranging from Prudhoe Bay on the coast of the Arctic Ocean to the Alaskan Range south of Fairbanks during August 1984. In the tundra, average CH4 emission rates varied from 4.9 mg CH4 per sq m per day (moist tundra) to 119 mg CH4 per sq m per day (waterlogged tundra). Fluxes averaged 40 mg CH4 per sq m per day from wet tussock meadows in the Brooks Range and 289 mg Ch4 per sq m per day from an alpine fen in the Alaskan Range. The boreal marsh had an average CH4 emission rate of 106 mg CH4 per sq m per day. Significant emissions were detected in tundra areas where peat temperatures were as low as 4 C, and permafrost was only 25 cm below the ground surface. Emission rates from the 17 sites sampled were found to be logarithmically related to water levels at the sites. Extrapolation of the data to an estimate of the total annual CH4 emission from all arctic and boreal wetlands suggests that these ecosystems are a major source of atmospheric CH4 and could account for up to 23 percent of global CH4 emissions from wetlands.

  9. Permafrost collapse after shrub removal shifts tundra ecosystem to a methane source

    NASA Astrophysics Data System (ADS)

    Nauta, Ake L.; Heijmans, Monique M. P. D.; Blok, Daan; Limpens, Juul; Elberling, Bo; Gallagher, Angela; Li, Bingxi; Petrov, Roman E.; Maximov, Trofim C.; van Huissteden, Jacobus; Berendse, Frank

    2015-01-01

    Arctic tundra ecosystems are warming almost twice as fast as the global average. Permafrost thaw and the resulting release of greenhouse gases from decomposing soil organic carbon have the potential to accelerate climate warming. In recent decades, Arctic tundra ecosystems have changed rapidly, including expansion of woody vegetation, in response to changing climate conditions. How such vegetation changes contribute to stabilization or destabilization of the permafrost is unknown. Here we present six years of field observations in a shrub removal experiment at a Siberian tundra site. Removing the shrub part of the vegetation initiated thawing of ice-rich permafrost, resulting in collapse of the originally elevated shrub patches into waterlogged depressions within five years. This thaw pond development shifted the plots from a methane sink into a methane source. The results of our field experiment demonstrate the importance of the vegetation cover for protection of the massive carbon reservoirs stored in the permafrost and illustrate the strong vulnerability of these tundra ecosystems to perturbations. If permafrost thawing can more frequently trigger such local permafrost collapse, methane-emitting wet depressions could become more abundant in the lowland tundra landscape, at the cost of permafrost-stabilizing low shrub vegetation.

  10. Distinct temperature sensitivity among taiga and tundra shrubs in Alaska

    NASA Astrophysics Data System (ADS)

    Andreu-Hayles, L.; Anchukaitis, K. J.; D'Arrigo, R.

    2014-12-01

    Shrub expansion into Arctic and alpine tundra ecosystems is well documented, mostly over the last 50 years, based on remote sensing data, aerial photography, and in-situ observations. Warming temperatures are considered the main driver of the observed change in shrub vegetation patterns. Here, we assess the relationship between temperatures and shrub growth from five populations of Salix spp. (willow) and Alnus spp. (alder) in Alaska growing within the tundra and the boreal forest (~taiga) using dendrochronological techniques. The three tundra shrub sites are located on the Dalton Highway north from Toolik Lake (~69ºN 148ºW), whereas the two taiga shrub sites are located closer to Fairbanks at the Twelve Mile Summit site (~65ºN 146ºW). Because shrub ages vary among the studied populations lead to different time spans for the ring-width chronologies generated, a common period with available satellite data spanning from 1982 to 2010 was selected for this study. All tundra shrub chronologies shared a strong positive response to summer temperatures despite growing in heterogeneous site conditions and belonging to different species. In contrast, in the taiga, summer temperatures enhance willow growth, whereas alder growth appears almost insensitive to temperature over the interval studied. Extending the analyses back in time, a very strong positive relationship was found between alder ring-width and June temperatures prior to 1970. This phenomenon, a weakening of the previously existing relationship between growth and temperatures, was also detected in white spruce (Picea glauca) growing at the same site, and it is known in the literature as the 'divergence problem'. Thus, at this taiga location, alder shrubs and trees seem to have similar growth patterns. Summer temperatures no longer seem to enhance taiga alder growth. Shrubs of different species exposed to the same climatic conditions can exhibit varied growth responses. The distinct temperature sensitivities

  11. Late snowmelt delays plant development and results in lower reproductive success in the High Arctic.

    PubMed

    Cooper, Elisabeth J; Dullinger, Stefan; Semenchuk, Philipp

    2011-01-01

    In tundra areas where the growing season is short, any delay in the start of summer may have a considerable effect on plant development, growth and reproductive success. Climate models suggest long-term changes in winter precipitation in the Arctic, which may lead to deeper snow cover and a resultant delay in date of snow melt. In this paper, we investigated the role of snow depth and melt out date on the phenological development and reproductive success of vascular plants in Adventdalen, Svalbard (78° 10'N, 16° 06'E). Effects of natural variations in snow accumulation were demonstrated using two vegetation types (snow depth: meadow 21 cm, heath 32 cm), and fences were used to experimentally increase snow depth by over 1m. Phenological delay was greatest directly after snowmelt in the earlier phenological phases, and had the largest effect on the early development of those species which normally green-up early (i.e. Dryas, Papaver, Salix, Saxifraga). Compressed growing seasons and length of the reproductive period led to a reduced reproductive success in some of the study species. There were fewer flowers, fewer plots with dispersing seeds, and lower germination rates. This can have consequences for plant establishment and community composition in the long-term.

  12. Siberian tundra ecosystem vegetation and carbon stocks four decades after wildfire

    NASA Astrophysics Data System (ADS)

    Loranty, Michael M.; Natali, Susan M.; Berner, Logan T.; Goetz, Scott J.; Holmes, Robert M.; Davydov, Sergei P.; Zimov, Nikita S.; Zimov, Sergey A.

    2014-11-01

    Tundra ecosystem fire regimes are intensifying with important implications for regional and global carbon (C) and energy dynamics. Although a substantial portion of the tundra biome is located in Russia, the vast majority of accessible studies describe North American tundra fires. Here we use field observations and high-resolution satellite remote sensing observations to describe the effects of wildfire on ecosystem C pools and vegetation communities four decades after fire for a tundra ecosystem in northeastern Siberia. Our analyses reveal no differences between soil physical properties and C pools in burned and unburned tundra, which we attribute to low combustion of organic soil associated with low-severity fire. Field and remote sensing data show no differences in aboveground C pools and vegetation communities indicating recovery to prefire conditions. These results are comparable to observations of ecosystem recovery in North American tundra. An assessment of literature data indicate that the average annual area burned in Russian tundra is an order of magnitude larger than that of Alaskan tundra, highlighting a crucial need to assess Russian tundra fire regimes in order to understand the current and future role of the biome wide fire regime in regional and global C and energy dynamics.

  13. COMPARING FIELD PERFORMANCES OF DENUDER TECHNIQUES IN THE HIGH ARCTIC

    EPA Science Inventory

    A field evaluation between two annular denuder system configurations was conducted during the spring of 2003 in the marine Arctic (Ny-Ålesund, Svalbard). The IIA annular denuder system (ADS) employs a series of five single channel annular denuders, a cyclone and a filter pack to ...

  14. Remote Sensing of Arctic Landscape Dynamics

    NASA Astrophysics Data System (ADS)

    Jones, Benjamin M.

    Amplified warming in the Arctic has likely increased the rate of landscape change and disturbances in northern high latitude regions. Remote sensing provides a valuable tool for assessing the spatial and temporal patterns associated with arctic landscape dynamics over annual, decadal, and centennial time scales. In this dissertation, I focused on remote sensing studies associated with four primary components of arctic landscape change and disturbance: (1) permafrost coastline erosion, (2) thermokarst lake dynamics, (3) tundra fires, and (4) using repeat airborne LiDAR for the measurement of vertical deformation in an arctic coastal lowland landscape. By combining observations from several high resolution satellite images for a 9 km segment of the Beaufort Sea Coast between 2008 and 2012, I demonstrated that the report of heightened erosion at the beginning of the 2000s was equaled or exceeded in every year except 2010 and that the mean annual erosion rate was tightly coupled to the number of open water days and the number of storms. By combining historical aerial photographs from the 1950s and 1980s with recent high-resolution satellite imagery from the mid-2000s, I assessed the expansion and drainage of thermokarst lakes on the northern Seward Peninsula. I found that more than half of the lakes in the study area were expanding as a result of permafrost degradation along their margins but that the rate of expansion was fairly consistent (0.35 and 0.39 m/yr) between the 1950s and 1980s and 1980s and mid-2000s, respectively. However, it appeared that in a number of instances that expansion of lakes led to the lateral drainage and that over the 55-year study period the total lake area decreased by 24%. While these studies highlight the utility of quantifying disturbance during the remotely sensed image archive period (~1950s to present) they are inherently limited temporally. Thus, I also demonstrated techniques in which field studies and remote sensing data could be

  15. Ice Mass Changes in the Russian High Arctic from Repeat High Resolution Topography.

    NASA Astrophysics Data System (ADS)

    Willis, Michael; Zheng, Whyjay; Pritchard, Matthew; Melkonian, Andrew; Morin, Paul; Porter, Claire; Howat, Ian; Noh, Myoung-Jong; Jeong, Seongsu

    2016-04-01

    We use a combination of ASTER and cartographically derived Digital Elevation Models (DEMs) supplemented with WorldView DEMs, the ArcticDEM and ICESat lidar returns to produce a time-series of ice changes occurring in the Russian High Arctic between the mid-20th century and the present. Glaciers on the western, Barents Sea coast of Novaya Zemlya are in a state of general retreat and thinning, while those on the eastern, Kara Sea coast are retreating at a slower rate. Franz Josef Land has a complicated pattern of thinning and thickening, although almost all the thinning is associated with rapid outlet glaciers feeding ice shelves. Severnaya Zemlya is also thinning in a complicated manner. A very rapid surging glacier is transferring mass into the ocean from the western periphery of the Vavilov Ice Cap on October Revolution Island, while glaciers feeding the former Matusevich Ice Shelf continue to thin at rates that are faster than those observed during the operational period of ICESat, between 2003 and 2009. Passive microwave studies indicate the total number of melt days is increasing in the Russian Arctic, although much of the melt may refreeze within the firn. It is likely that ice dynamic changes will drive mass loss for the immediate future. The sub-marine basins beneath several of the ice caps in the region suggest the pos