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Sample records for arctic vegetation amplify

  1. Changes in Arctic vegetation amplify high-latitude warming through the greenhouse effect

    OpenAIRE

    Swann, Abigail L.; Fung, Inez Y.; Levis, Samuel; BONAN, GORDON B.; Doney, Scott C.

    2010-01-01

    Arctic climate is projected to change dramatically in the next 100 years and increases in temperature will likely lead to changes in the distribution and makeup of the Arctic biosphere. A largely deciduous ecosystem has been suggested as a possible landscape for future Arctic vegetation and is seen in paleo-records of warm times in the past. Here we use a global climate model with an interactive terrestrial biosphere to investigate the effects of adding deciduous trees on bare ground at high ...

  2. Tundra shrubification and tree-line advance amplify arctic climate warming: results from an individual-based dynamic vegetation model

    International Nuclear Information System (INIS)

    One major challenge to the improvement of regional climate scenarios for the northern high latitudes is to understand land surface feedbacks associated with vegetation shifts and ecosystem biogeochemical cycling. We employed a customized, Arctic version of the individual-based dynamic vegetation model LPJ-GUESS to simulate the dynamics of upland and wetland ecosystems under a regional climate model–downscaled future climate projection for the Arctic and Subarctic. The simulated vegetation distribution (1961–1990) agreed well with a composite map of actual arctic vegetation. In the future (2051–2080), a poleward advance of the forest–tundra boundary, an expansion of tall shrub tundra, and a dominance shift from deciduous to evergreen boreal conifer forest over northern Eurasia were simulated. Ecosystems continued to sink carbon for the next few decades, although the size of these sinks diminished by the late 21st century. Hot spots of increased CH4 emission were identified in the peatlands near Hudson Bay and western Siberia. In terms of their net impact on regional climate forcing, positive feedbacks associated with the negative effects of tree-line, shrub cover and forest phenology changes on snow-season albedo, as well as the larger sources of CH4, may potentially dominate over negative feedbacks due to increased carbon sequestration and increased latent heat flux. (letter)

  3. Recent dynamics of arctic and sub-arctic vegetation

    International Nuclear Information System (INIS)

    We present a focus issue of Environmental Research Letters on the ‘Recent dynamics of arctic and sub-arctic vegetation’. The focus issue includes three perspective articles (Verbyla 2011 Environ. Res. Lett. 6 041003, Williams et al 2011 Environ. Res. Lett. 6 041004, Loranty and Goetz 2012 Environ. Res. Lett. 7 011005) and 22 research articles. The focus issue arose as a result of heightened interest in the response of high-latitude vegetation to natural and anthropogenic changes in climate and disturbance regimes, and the consequences that these vegetation changes might have for northern ecosystems. A special session at the December 2010 American Geophysical Union Meeting on the ‘Greening of the Arctic’ spurred the call for papers. Many of the resulting articles stem from intensive research efforts stimulated by International Polar Year projects and the growing acknowledgment of ongoing climate change impacts in northern terrestrial ecosystems. (synthesis and review)

  4. Seeing the risks of multiple Arctic amplifying feedbacks.

    Science.gov (United States)

    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

  5. New views on changing Arctic vegetation

    Science.gov (United States)

    Kennedy, Robert E.

    2012-03-01

    As climate changes, how will terrestrial vegetation respond? Because the fates of many biogeochemical, hydrological and economic cycles depend on vegetation, this question is fundamental to climate change science but extremely challenging to address. This is particularly true in the Arctic, where temperature change has been most acute globally (IPCC 2007) and where potential feedbacks to carbon, energy and hydrological cycles have important implications for the rest of the Earth system (Chapin et al 2000). It is well known that vegetation is tightly coupled to precipitation and temperature (Whittaker 1975), but predicting the response of vegetation to changes in climate involves much more than invoking the limitations of climate envelopes (Thuiller et al 2008). Models must also consider efficacy of dispersal, soil constraints, ecological interactions, possible CO2 fertilization impacts and the changing impact of other, more proximal anthropogenic effects such as pollution, disturbance, etc (Coops and Waring 2011, Lenihan et al 2008, Scheller and Mladenoff 2005). Given this complexity, a key test will be whether models can match empirical observations of changes that have already occurred. The challenge is finding empirical observations of change that are appropriate to test hypothesized impacts of climate change. As climate gradually changes across broad bioclimatic gradients, vegetation condition may change gradually as well. To capture these gradual trends, observations need at least three characteristics: (1) they must quantify a vegetation attribute that is expected to change, (2) they must measure that attribute in exactly the same way over long periods of time, and (3) they must sample diverse communities at geographic scales commensurate with the scale of expected climatic shifts. Observation networks meeting all three criteria are rare anywhere on the globe, but particularly so in remote areas. For this reason, satellite images have long been used as a

  6. Divergent Arctic-Boreal Vegetation Changes between North America and Eurasia over the Past 30 Years

    Directory of Open Access Journals (Sweden)

    Arindam Samanta

    2013-05-01

    Full Text Available Arctic-Boreal region—mainly consisting of tundra, shrub lands, and boreal forests—has been experiencing an amplified warming over the past 30 years. As the main driving force of vegetation growth in the north, temperature exhibits tight coupling with the Normalized Difference Vegetation Index (NDVI—a proxy to photosynthetic activity. However, the comparison between North America (NA and northern Eurasia (EA shows a weakened spatial dependency of vegetation growth on temperature changes in NA during the past decade. If this relationship holds over time, it suggests a 2/3 decrease in vegetation growth under the same rate of warming in NA, while the vegetation response in EA stays the same. This divergence accompanies a circumpolar widespread greening trend, but 20 times more browning in the Boreal NA compared to EA, and comparative greening and browning trends in the Arctic. These observed spatial patterns of NDVI are consistent with the temperature record, except in the Arctic NA, where vegetation exhibits a similar long-term trend of greening to EA under less warming. This unusual growth pattern in Arctic NA could be due to a lack of precipitation velocity compared to the temperature velocity, when taking velocity as a measure of northward migration of climatic conditions.

  7. Arctic Browning: vegetation damage and implications for carbon balance.

    Science.gov (United States)

    Treharne, Rachael; Bjerke, Jarle; Emberson, Lisa; Tømmervik, Hans; Phoenix, Gareth

    2016-04-01

    'Arctic browning' is the loss of biomass and canopy in Arctic ecosystems. This process is often driven by climatic and biological extreme events - notably extreme winter warm periods, winter frost-drought and severe outbreaks of defoliating insects. Evidence suggests that browning is becoming increasingly frequent and severe at the pan-arctic scale, a view supported by observations from more intensely observed regions, with major and unprecedented vegetation damage reported at landscape (>1000km2) and regional (Nordic Arctic Region) scales in recent years. Critically, the damage caused by these extreme events is in direct opposition to 'Arctic greening', the well-established increase in productivity and shrub abundance observed at high latitudes in response to long-term warming. This opposition creates uncertainty as to future anticipated vegetation change in the Arctic, with implications for Arctic carbon balance. As high latitude ecosystems store around twice as much carbon as the atmosphere, and vegetation impacts are key to determining rates of loss or gain of ecosystem carbon stocks, Arctic browning has the potential to influence the role of these ecosystems in global climate. There is therefore a clear need for a quantitative understanding of the impacts of browning events on key ecosystem carbon fluxes. To address this, field sites were chosen in central and northern Norway and in Svalbard, in areas known to have been affected by either climatic extremes or insect outbreak and subsequent browning in the past four years. Sites were chosen along a latitudinal gradient to capture both conditions already causing vegetation browning throughout the Norwegian Arctic, and conditions currently common at lower latitudes which are likely to become more damaging further North as climate change progresses. At each site the response of Net Ecosystem CO2 Exchange to light was measured using a LiCor LI6400 Portable Photosynthesis system and a custom vegetation chamber with

  8. Tundra vegetation effects on pan-Arctic albedo

    International Nuclear Information System (INIS)

    Recent field experiments in tundra ecosystems describe how increased shrub cover reduces winter albedo, and how subsequent changes in surface net radiation lead to altered rates of snowmelt. These findings imply that tundra vegetation change will alter regional energy budgets, but to date the effects have not been documented at regional or greater scales. Using satellite observations and a pan-Arctic vegetation map, we examined the effects of shrub vegetation on albedo across the terrestrial Arctic. We included vegetation classes dominated by low shrubs, dwarf shrubs, tussock-dominated graminoid tundra, and non-tussock graminoid tundra. Each class was further stratified by bioclimate subzones. Low-shrub tundra had higher normalized difference vegetation index values and earlier albedo decline in spring than dwarf-shrub tundra, but for tussock tundra, spring albedo declined earlier than for low-shrub tundra. Our results illustrate how relatively small changes in vegetation properties result in differences in albedo dynamics, regardless of shrub growth, that may lead to differences in net radiation upwards of 50 W m-2 at weekly time scales. Further, our findings imply that changes to the terrestrial Arctic energy budget during this important seasonal transition are under way regardless of whether recent satellite observed productivity trends are the result of shrub expansion. We conclude that a better understanding of changes in vegetation productivity and distribution in Arctic tundra is essential for accurately quantifying and predicting carbon and energy fluxes and associated climate feedbacks.

  9. Impact of Holocene climate variability on Arctic vegetation

    Science.gov (United States)

    Gajewski, K.

    2015-10-01

    This paper summarizes current knowledge about the postglacial history of the vegetation of the Canadian Arctic Archipelago (CAA) and Greenland. Available pollen data were used to understand the initial migration of taxa across the Arctic, how the plant biodiversity responded to Holocene climate variability, and how past climate variability affected primary production of the vegetation. Current evidence suggests that most of the flora arrived in the area during the Holocene from Europe or refugia south or west of the region immediately after local deglaciation, indicating rapid dispersal of propagules to the region from distant sources. There is some evidence of shrub species arriving later in Greenland, but it is not clear if this is dispersal limited or a response to past climates. Subsequent climate variability had little effect on biodiversity across the CAA, with some evidence of local extinctions in areas of Greenland in the late Holocene. The most significant impact of climate changes is on vegetation density and/or plant production.

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

    Science.gov (United States)

    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.

  11. Severity of climate change dictates the direction of biophysical feedbacks of vegetation change to Arctic climate

    Science.gov (United States)

    Zhang, Wenxin; Jansson, Christer; Miller, Paul; Smith, Ben; Samuelsson, Patrick

    2014-05-01

    Vegetation-climate feedbacks induced by vegetation dynamics under climate change alter biophysical properties of the land surface that regulate energy and water exchange with the atmosphere. Simulations with Earth System Models applied at global scale suggest that the current warming in the Arctic has been amplified, with large contributions from positive feedbacks, dominated by the effect of reduced surface albedo as an increased distribution, cover and taller stature of trees and shrubs mask underlying snow, darkening the surface. However, these models generally employ simplified representation of vegetation dynamics and structure and a coarse grid resolution, overlooking local or regional scale details determined by diverse vegetation composition and landscape heterogeneity. In this study, we perform simulations using an advanced regional coupled vegetation-climate model (RCA-GUESS) applied at high resolution (0.44×0.44° ) over the Arctic Coordinated Regional Climate Downscaling Experiment (CORDEX-Arctic) domain. The climate component (RCA4) is forced with lateral boundary conditions from EC-EARTH CMIP5 simulations for three representative concentration pathways (RCP 2.6, 4.5, 8.5). Vegetation-climate response is simulated by the individual-based dynamic vegetation model (LPJ-GUESS), accounting for phenology, physiology, demography and resource competition of individual-based vegetation, and feeding variations of leaf area index and vegetative cover fraction back to the climate component, thereby adjusting surface properties and surface energy fluxes. The simulated 2m air temperature, precipitation, vegetation distribution and carbon budget for the present period has been evaluated in another paper. The purpose of this study is to elucidate the spatial and temporal characteristics of the biophysical feedbacks arising from vegetation shifts in response to different CO2 concentration pathways and their associated climate change. Our results indicate that the

  12. Uptake of radionuclides by vegetation at a High Arctic location

    International Nuclear Information System (INIS)

    Radionuclide levels in vegetation from a High Arctic location were studied and compared to in situ soil concentrations. Levels of the anthropogenic radionuclide 137Cs and the natural radionuclides 40K, 238U, 226Ra and 232Th are discussed and transfer factor (TF) values and aggregated transfer (Tag) values are calculated for vascular plants. Levels of 137Cs in vegetation generally followed the order mosses > lichen > vascular plants. The uptake of 137Cs in vascular plants showed an inverse relationship with the uptake of 40K, with 137Cs TF and Tag values generally higher than 40K TF and Tag values. 40K activity concentrations in all vegetation showed little correlation to associated soil concentrations, while the uptake of 238U, 226Ra and 232Th by vascular and non-vascular plants was generally low. - Uptake of the anthropogenic radionuclide 137Cs is highest for moss species

  13. Simulating the effects of temperature and precipitation change on vegetation composition in Arctic tundra ecosystems

    OpenAIRE

    Van Der Kolk, H; M. M. P. D. Heijmans; Van Huissteden, J.; Pullens, J. W. M.; Berendse, F.

    2016-01-01

    Over the past decades, vegetation has changed significantly along with climatic changes 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 mechanisms drive vegetation changes in the tundra ecosystem is still not sufficiently clear. In this study, the dynamic tundra vegetation model NUCOM-tundra was used to e...

  14. Arctic Vegetation under Climate Change – Biogenic Volatile Organic Compound Emissions and Leaf Anatomy

    DEFF Research Database (Denmark)

    Schollert, Michelle

    common arctic plant species, illustrating the great importance of vegetation composition for determining ecosystem BVOC emissions. Additionally, this thesis assesses the BVOC emission responses in common arctic plant species to effects of climate change: warming, shading and snow addition. Against...... treatment effects on BVOC emissions. Furthermore, the anatomy of arctic plants seems to respond differently to warming than species at lower latitudes. The results in this thesis demonstrate the complexity of the effects of climate change on BVOC emissions and leaf anatomy of arctic plant species...... emissions from the arctic region are assumed to be low, but data from the region is lacking. BVOC emissions are furthermore expected to change drastically due to the rapidly proceeding climate change in the Arctic, which can provide a feedback to climate warming of unknown direction and magnitude. BVOC...

  15. Environment, vegetation and greenness (NDVI) along the North America and Eurasia Arctic transects

    International Nuclear Information System (INIS)

    Satellite-based measurements of the normalized difference vegetation index (NDVI; an index of vegetation greenness and photosynthetic capacity) indicate that tundra environments are generally greening and becoming more productive as climates warm in the Arctic. The greening, however, varies and is even negative in some parts of the Arctic. To help interpret the space-based observations, the International Polar Year (IPY) Greening of the Arctic project conducted ground-based surveys along two >1500 km transects that span all five Arctic bioclimate subzones. Here we summarize the climate, soil, vegetation, biomass, and spectral information collected from the North America Arctic transect (NAAT), which has a more continental climate, and the Eurasia Arctic transect (EAT), which has a more oceanic climate. The transects have broadly similar summer temperature regimes and overall vegetation physiognomy, but strong differences in precipitation, especially winter precipitation, soil texture and pH, disturbance regimes, and plant species composition and structure. The results indicate that summer warmth and NDVI increased more strongly along the more continental transect. (letter)

  16. Environment, vegetation and greenness (NDVI) along the North America and Eurasia Arctic transects

    Science.gov (United States)

    Walker, D. A.; Epstein, H. E.; Raynolds, M. K.; Kuss, P.; Kopecky, M. A.; Frost, G. V.; Daniëls, F. J. A.; Leibman, M. O.; Moskalenko, N. G.; Matyshak, G. V.; Khitun, O. V.; Khomutov, A. V.; Forbes, B. C.; Bhatt, U. S.; Kade, A. N.; Vonlanthen, C. M.; Tichý, L.

    2012-03-01

    Satellite-based measurements of the normalized difference vegetation index (NDVI; an index of vegetation greenness and photosynthetic capacity) indicate that tundra environments are generally greening and becoming more productive as climates warm in the Arctic. The greening, however, varies and is even negative in some parts of the Arctic. To help interpret the space-based observations, the International Polar Year (IPY) Greening of the Arctic project conducted ground-based surveys along two >1500 km transects that span all five Arctic bioclimate subzones. Here we summarize the climate, soil, vegetation, biomass, and spectral information collected from the North America Arctic transect (NAAT), which has a more continental climate, and the Eurasia Arctic transect (EAT), which has a more oceanic climate. The transects have broadly similar summer temperature regimes and overall vegetation physiognomy, but strong differences in precipitation, especially winter precipitation, soil texture and pH, disturbance regimes, and plant species composition and structure. The results indicate that summer warmth and NDVI increased more strongly along the more continental transect.

  17. Recent Declines in Warming and Vegetation Greening Trends over Pan-Arctic Tundra

    OpenAIRE

    Polyakov, Igor V; Tucker, Compton J.; Pinzon, Jorge E; Epstein, Howard E.; Comiso, Josefino C; Peter A. Bieniek; Walker, Donald A.; Raynolds, Martha K.; Bhatt, Uma S.

    2013-01-01

    Vegetation productivity trends for the Arctic tundra are updated for the 1982–2011 period and examined in the context of land surface temperatures and coastal sea ice. Understanding mechanistic links between vegetation and climate parameters contributes to model advancements that are necessary for improving climate projections. This study employs remote sensing data: Global Inventory Modeling and Mapping Studies (GIMMS) Maximum Normalized Difference Vegetation Index (MaxNDVI), Special Sensor ...

  18. The Drabo corymbosae-Papaveretea dahliani − a new vegetation class of the High Arctic polar deserts

    OpenAIRE

    Daniëls Fred J. A.; Elvebakk Arve; Matveyeva Nadezhda V.; Mucina Ladislav

    2016-01-01

    A new class and a new order (Drabo corymbosae-Papaveretea dahliani and Saxifrago oppositifoliae-Papaveretalia dahliani) have been described, and the Papaverion dahliani validated. This is vegetation of zonal habitats in lowlands of the High Arctic subzone A (or Arctic herb, cushion forb or polar desert subzone) and of ecologically equivalent sites at high altitudes on the mountain plateaus of the High Arctic. The new class spans three continents – North America (Canadian Arctic Archipelago an...

  19. Trends in the normalized difference vegetation index (NDVI) associated with urban development in arctic and subarctic Western Siberia

    Science.gov (United States)

    Outten, S.; Miles, V.; Ezau, I.

    2015-12-01

    Changes in normalized difference vegetation index (NDVI) in the high Arctic have been reliably documented, with widespread "greening" (increase in NDVI), specifically along the northern rim of Eurasia and Alaska. Whereas in West Siberia south of 65N, widespread "browning" (decrease in NDVI) has been noted, although the causes remain largely unclear. In this study we report results of statistical analysis of the spatial and temporal changes in NDVI around 28 major urban areas in the arctic and subarctic Western Siberia. Exploration and exploitation of oil and gas reserves has led to rapid industrialization and urban development in the region. This development has significant impact on the environment and particularly in the vegetation cover in and around the urbanized areas. The analysis is based on 15 years (2000-2014) of high-resolution (250 m) Moderate Resolution Imaging Spectroradiometer (MODIS) data acquired for summer months (June through August) over the entire arctic and subarctic Western Siberian region. The analysis shows that the NDVI background trends are generally in agreement with the trends reported in previous coarse-resolution NDVI studies. Our study reveals greening over the arctic (tundra and tundra-forest) part of the region. Simultaneously, the southern (boreal taiga forest) part is browning, with the more densely vegetation areas or areas with highest NDVI, particularly along Ob River showing strong negative trend. The unexpected and interesting finding of the study is statistically robust indication of the accelerated increase of NDVI ("greening") in the older urban areas. Many Siberian cities become greener even against the decrease in the NDVI background. Moreover, interannual variations of urban NDVI are not coherent with the NDVI background variability. We also find that in tundra zones, NDVI values are higher in a 5-10 km buffer zone around the city edge than in rural areas (40 km distance from the city edge), and in taiga in a 5-10 km

  20. Circumpolar Dynamics of Arctic Tundra Vegetation in Relation to Temperature Trends

    Science.gov (United States)

    Epstein, H. E.; Bhatt, U. S.; Raynolds, M. K.; Walker, D. A.; Reichle, L.

    2015-12-01

    Arctic tundra vegetation has generally exhibited a "greening" trend for at least the past three decades. However, these temporal trends in tundra vegetation are highly heterogeneous in space across different arctic regions, as well as showing variability over time. The factors controlling this variability are likely numerous with complex interactions, however, a first approach is to examine how vegetation dynamics relate to trends in temperature. We used a 32-year record (1982-2013) of the Normalized Difference Vegetation Index (NDVI) and Land Surface Temperatures from Advanced Very High Resolution Radiometer (AVHRR) sensors onboard NOAA satellites (GIMMS 3g dataset) to analyze observed changes in both aboveground tundra vegetation and surface temperatures. We divided the circumpolar dataset into two continental regions (North America and Eurasia), as well as by tundra subzone (A-E) sensu the Circumpolar Arctic Vegetation Map (CAVM). We 1) compared temporal trends in both MaxNDVI (peak values) and TI-NDVI (seasonally integrated values) with those of the Summer Warmth Index (SWI - sum of mean monthly temperatures > 0 °C); 2) assessed how the detrended interannual variabilities in NDVI compared to those of SWI; and 3) analyzed current and prior year SWI, as well as prior year NDVI, as controls on current year NDVI. Interannual coefficients of variation for SWI were 2.0 - 2.5 times greater than those for NDVI, and the temporal trendlines for NDVI were much "tighter" with greater r² values than those for SWI. Interannual variability in NDVI was greatest in the "Mid-Low" Arctic, whereas interannual variability in SWI was greatest in the most southern Arctic. Surprisingly, the observed relative rates of change in NDVI were greater than those of SWI for the warmer subzones for both North America and Eurasia. Finally, the change in NDVI from one year to the next was only weakly correlated with current year SWI. These results suggest that 1) there are clearly factors

  1. Pan-Arctic linkages between snow accumulation and growing season air temperature, soil moisture and vegetation

    OpenAIRE

    K. A. Luus; Gel, Y.; J. C. Lin; Kelly, R. E. J.; C. R. Duguay

    2013-01-01

    Arctic field studies have indicated that the air temperature, soil moisture and vegetation at a site influence the quantity of snow accumulated, and that snow accumulation can alter growing season soil moisture and vegetation. Climate change is predicted to bring about warmer air temperatures, greater snow accumulation and northward movements of the shrub and tree lines. Understanding the response of northern environments to changes in snow and growing season land surface characteristi...

  2. How will the greening of the Arctic affect an important prey species and disturbance agent? Vegetation effects on arctic ground squirrels.

    Science.gov (United States)

    Wheeler, H C; Chipperfield, J D; Roland, C; Svenning, J-C

    2015-07-01

    Increases in terrestrial primary productivity across the Arctic and northern alpine ecosystems are leading to altered vegetation composition and stature. Changes in vegetation stature may affect predator-prey interactions via changes in the prey's ability to detect predators, changes in predation pressure, predator identity and predator foraging strategy. Changes in productivity and vegetation composition may also affect herbivores via effects on forage availability and quality. We investigated if height-dependent effects of forage and non-forage vegetation determine burrowing extent and activity of arctic ground squirrels (Urocitellus parryii). We collected data on burrow networks and activity of arctic ground squirrels across long-term vegetation monitoring sites in Denali National Park and Preserve, Alaska. The implications of height-specific cover of potential forage and non-forage vegetation on burrowing behaviour and habitat suitability for arctic ground squirrels were investigated using hierarchical Bayesian modelling. Increased cover of forbs was associated with more burrows and burrow systems, and higher activity of systems, for all forb heights. No other potential forage functional group was related to burrow distribution and activity. In contrast, height-dependent negative effects of non-forage vegetation were observed, with cover over 50-cm height negatively affecting the number of burrows, systems and system activity. Our results demonstrate that increases in vegetation productivity have dual, potentially counteracting effects on arctic ground squirrels via changes in forage and vegetation stature. Importantly, increases in tall-growing woody vegetation (shrubs and trees) have clear negative effects, whereas increases in forb should benefit arctic ground squirrels. PMID:25666700

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

    NARCIS (Netherlands)

    Barret, K.; Rocha, A.V.; Weg, van de M.J.; Shaver, G

    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 N

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

    Science.gov (United States)

    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.

  5. Accuracy assessment of airphoto interpretation of vegetation types and disturance levels on winter seismic trails, Arctic National Wildlife Refuge, Alaska

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — An accuracy assessment was conducted to evaluate the photointerpretation of vegetation types and disturbance levels along seismic trails in the Arctic National...

  6. Accuracy assessment of airphoto interpretation of vegetation types and disturance levels on winter seismic trails, Arctic National Wildlife Refuge, Alaska

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — An accuracy assessment was conducted to evaluate the photo-interpretation of vegetation types and disturbance levels along seismic trails in the Arctic National...

  7. Understanding Pan-Arctic Tundra Vegetation Change Through Long-term Remotely Sensed Data

    Science.gov (United States)

    Bhatt, U.; Walker, D. A.; Bieniek, P.; Raynolds, M. K.; Epstein, H. E.; Comiso, J. C.; Pinzon, J. E.; Tucker, C. J.

    2012-12-01

    The goal of this paper is to present an analysis of the seasonality of tundra vegetation variability and change using long-term remotely sensed data as well as ground based measurements and reanalyses. An increase of Pan-Arctic tundra vegetation greenness has been documented using the remotely sensed Normalized Difference Vegetation Index (NDVI). Coherent variability between NDVI, springtime coastal sea ice (passive microwave) and land surface temperatures (AVHRR) has also been established. Satellite based snow and cloud cover data sets are being incorporated into this analysis. The Arctic tundra is divided into domains based on Treshnikov divisions that are modified based on floristic provinces. There is notable heterogeneity in Pan-Arctic vegetation and climate trends, which necessitates a regional analysis. This study uses remotely sensed weekly 25-km sea ice concentration, weekly surface temperature, and bi-weekly NDVI from 1982 to 2010. The GIMMS NDVI3g data has been corrected for biases during the spring and fall, with special focus on the Arctic. Trends of Maximum NDVI (MaxNDVI), Time Integrated NDVI (TI-NDVI), Summer Warmth Index (SWI, sum of degree months above freezing during May-August), and open water area are calculated for the Pan Arctic. Remotely sensed snow data trends suggest varying patterns throughout the Arctic and may in part explain the heterogeneous MaxNDVI trends. Standard climate data (station, reanalysis, and model data) and ground observations are used in the analysis to provide additional support for hypothesized mechanisms. Overall, we find that trends over the 30-year record are changing as evidenced by the following examples from recent years. The sea ice decline has increased in Eurasia and slowed in North America. The weekly AVHRR landsurface temperatures reveal that there has been summer cooling over Eurasia and that the warming over North America has slowed. The MaxNDVI rates of change have diverged between N. America and Eurasia

  8. Vegetation-Soil-Active Layer Relationships Along a Low-Arctic Bioclimate Gradient, Alaska

    Science.gov (United States)

    Walker, D. A.; Jia, G. J.; Epstein, H. E.; Shiklomanov, N.; Nelson, F.; Hinzman, L. D.; Romanovsky, V. E.

    2002-12-01

    Northern Alaska has three of five Arctic bioclimate subzones, which are representative of the circumpolar Low Arctic. This portion of the Arctic has more or less continuous tundra plant cover and well-developed moss canopies. We examined the biomass and remotely sensed spectral properties of the vegetation canopy, active-layer thickness, and the soil properties at 21 sites on the Arctic Slope and Seward Peninsula of Alaska. The sites were grouped into three bioclimate subzones according the summer warmth at the sites. The summer warmth index (SWI) is the sum of the mean monthly temperatures greater than 0 degrees C. Subzone C, the coldest subzone, occurs in a narrow strip along the northern coast of the Alaska. Subzone D covers most of the Arctic Coastal Plain and the northwest portion of the Seward Peninsula, and Subzone E covers most of the Foothills and most of the unforested portion of the Seward Peninsula. The SWIs in Subzones C, D, and E are generally less than 10-15 degrees C, 15-25 degrees C, and 25-35 degrees C respectively. The average active layer depths were 44, 55, and 47 cm respectively The shallow active layer in Subzone E is to a large degree a response to the denser vegetation canopies in Subzone E. Total plant biomass in Subzone C, D, and E averaged 421 g m-2, 503 g m-2, and 1178 g m-2 respectively. The much higher biomass in Subzone E was due primarily to woody shrubs (40 g m-2 in Subzone C, 51 g m-2 in Subzone D, and 730 g m-2 in Subzone E). The normalized difference vegetation index (NDVI) is one measure of greenness. Highest NDVI values were obtained from acidic tundra regions in Subzone E, and the lowest NDVI values were obtained in the nonacidic areas of Subzone C. In summary, the insulative properties of the vegetation play a very important role controlling the thickness of the active layer, and the amount of vegetation biomass differs according to summer warmth and soil properties. Acidic soils in the warmest parts of the Arctic (Subzone E

  9. The Drabo corymbosae-Papaveretea dahliani − a new vegetation class of the High Arctic polar deserts

    Directory of Open Access Journals (Sweden)

    Daniëls Fred J. A.

    2016-06-01

    Full Text Available A new class and a new order (Drabo corymbosae-Papaveretea dahliani and Saxifrago oppositifoliae-Papaveretalia dahliani have been described, and the Papaverion dahliani validated. This is vegetation of zonal habitats in lowlands of the High Arctic subzone A (or Arctic herb, cushion forb or polar desert subzone and of ecologically equivalent sites at high altitudes on the mountain plateaus of the High Arctic. The new class spans three continents – North America (Canadian Arctic Archipelago and Greenland, Europe (parts of Svalbard and Franz Josef Land, and Asia, including northern regions of Chelyuskin Peninsula (Taymir Peninsula, Severnaya Zemlya Archipelago and De Longa Islands.

  10. Arctic climate change with a 2C global warming. Timing, climate patterns and vegetation change

    International Nuclear Information System (INIS)

    The signatories to United Nations Framework Convention on Climate Change are charged with stabilizing the concentrations of greenhouse gases in the atmosphere at a level that prevents dangerous interference with the climate system. A number of nations, organizations and scientists have suggested that global mean temperature should not rise over 2C above preindustrial levels. However, even a relatively moderate target of 2C has serious implications for the Arctic, where temperatures are predicted to increase at least 1.5 to 2 times as fast as global temperatures. High latitude vegetation plays a significant role in the lives of humans and animals, and in the global energy balance and carbon budget. These ecosystems are expected to be among the most strongly impacted by climate change over the next century. To investigate the potential impact of stabilization of global temperature at 2C, we performed a study using data from six Global Climate Models (GCMs) forced by four greenhouse gas emissions scenarios, the BIOME4 biogeochemistry-biogeography model, and remote sensing data. GCM data were used to predict the timing and patterns of Arctic climate change under a global mean warming of 2C. A unified circumpolar classification recognizing five types of tundra and six forest biomes was used to develop a map of observed Arctic vegetation. BIOME4 was used to simulate the vegetation distributions over the Arctic at the present and for a range of 2C global warming scenarios. The GCMs simulations indicate that the earth will have warmed by 2C relative to preindustrial temperatures by between 2026 and 2060, by which stage the area-mean annual temperature over the Arctic (60-90N) will have increased by between 3.2 and 6.6C. Forest extent is predicted by BIOME4 to increase in the Arctic on the order of 3 x 106 km2 or 55% with a corresponding 42% reduction in tundra area. Tundra types generally also shift north with the largest reductions in the prostrate dwarf-shrub tundra

  11. Recent Declines in Warming and Vegetation Greening Trends over Pan-Arctic Tundra

    Directory of Open Access Journals (Sweden)

    Igor V. Polyakov

    2013-08-01

    Full Text Available Vegetation productivity trends for the Arctic tundra are updated for the 1982–2011 period and examined in the context of land surface temperatures and coastal sea ice. Understanding mechanistic links between vegetation and climate parameters contributes to model advancements that are necessary for improving climate projections. This study employs remote sensing data: Global Inventory Modeling and Mapping Studies (GIMMS Maximum Normalized Difference Vegetation Index (MaxNDVI, Special Sensor Microwave Imager (SSM/I sea-ice concentrations, and Advanced Very High Resolution Radiometer (AVHRR radiometric surface temperatures. Spring sea ice is declining everywhere except in the Bering Sea, while summer open water area is increasing throughout the Arctic. Summer Warmth Index (SWI—sum of degree months above freezing trends from 1982 to 2011 are positive around Beringia but are negative over Eurasia from the Barents to the Laptev Seas and in parts of northern Canada. Eastern North America continues to show increased summer warmth and a corresponding steady increase in MaxNDVI. Positive MaxNDVI trends from 1982 to 2011 are generally weaker compared to trends from 1982–2008. So to better understand the changing trends, break points in the time series were quantified using the Breakfit algorithm. The most notable break points identify declines in SWI since 2003 in Eurasia and 1998 in Western North America. The Time Integrated NDVI (TI-NDVI, sum of the biweekly growing season values of MaxNDVI has declined since 2005 in Eurasia, consistent with SWI declines. Summer (June–August sea level pressure (slp averages from 1999–2011 were compared to those from 1982–1998 to reveal higher slp over Greenland and the western Arctic and generally lower pressure over the continental Arctic in the recent period. This suggests that the large-scale circulation is likely a key contributor to the cooler temperatures over Eurasia through increased summer cloud

  12. Large herbivore grazing affects the vegetation structure and greenhouse gas balance in a high arctic mire

    Science.gov (United States)

    Falk, Julie Maria; Schmidt, Niels Martin; Christensen, Torben R.; Ström, Lena

    2015-04-01

    Herbivory is an important part of most ecosystems and affects the ecosystems’ carbon balance both directly and indirectly. Little is known about herbivory and its impact on the carbon balance in high arctic mire ecosystems. We hypothesized that trampling and grazing by large herbivores influences the vegetation density and composition and thereby also the carbon balance. In 2010, we established fenced exclosures in high arctic Greenland to prevent muskoxen (Ovibos moschatus) from grazing. During the growing seasons of 2011 to 2013 we measured CO2 and CH4 fluxes in these ungrazed blocks and compared them to blocks subjected to natural grazing. Additionally, we measured depth of the water table and active layer, soil temperature, and in 2011 and 2013 an inventory of the vegetation density and composition were made. In 2013 a significant decrease in total number of vascular plant (33-44%) and Eriophorum scheuchzeri (51-53%) tillers were found in ungrazed plots, the moss-layer and amount of litter had also increased substantially in these plots. This resulted in a significant decrease in net ecosystem uptake of CO2 (47%) and likewise a decrease in CH4 emission (44%) in ungrazed plots in 2013. While the future of the muskoxen in a changing arctic is unknown, this experiment points to a potentially large effect of large herbivores on the carbon balance in natural Arctic ecosystems. It thus sheds light on the importance of grazing mammals, and hence adds to our understanding of natural ecosystem greenhouse gas balance in the past and in the future.

  13. Large herbivore grazing affects the vegetation structure and greenhouse gas balance in a high arctic mire

    International Nuclear Information System (INIS)

    Herbivory is an important part of most ecosystems and affects the ecosystems’ carbon balance both directly and indirectly. Little is known about herbivory and its impact on the carbon balance in high arctic mire ecosystems. We hypothesized that trampling and grazing by large herbivores influences the vegetation density and composition and thereby also the carbon balance. In 2010, we established fenced exclosures in high arctic Greenland to prevent muskoxen (Ovibos moschatus) from grazing. During the growing seasons of 2011 to 2013 we measured CO2 and CH4 fluxes in these ungrazed blocks and compared them to blocks subjected to natural grazing. Additionally, we measured depth of the water table and active layer, soil temperature, and in 2011 and 2013 an inventory of the vegetation density and composition were made. In 2013 a significant decrease in total number of vascular plant (33–44%) and Eriophorum scheuchzeri (51–53%) tillers were found in ungrazed plots, the moss-layer and amount of litter had also increased substantially in these plots. This resulted in a significant decrease in net ecosystem uptake of CO2 (47%) and likewise a decrease in CH4 emission (44%) in ungrazed plots in 2013. While the future of the muskoxen in a changing arctic is unknown, this experiment points to a potentially large effect of large herbivores on the carbon balance in natural Arctic ecosystems. It thus sheds light on the importance of grazing mammals, and hence adds to our understanding of natural ecosystem greenhouse gas balance in the past and in the future. (letter)

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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

  16. Camera derived vegetation greenness index as proxy for gross primary production in a low Arctic wetland area

    DEFF Research Database (Denmark)

    Westergaard-Nielsen, Andreas; Lund, Magnus; Hansen, Birger;

    2013-01-01

    normalized difference vegetation index (NDVI) product derived from the WorldView-2 satellite. An object-based classification based on a bi-temporal image composite was used to classify the study area into heath, copse, fen, and bedrock. Temporal evolution of vegetation greenness was evaluated and modeled......The Arctic is experiencing disproportionate warming relative to the global average, and the Arctic ecosystems are as a result undergoing considerable changes. Continued monitoring of ecosystem productivity and phenology across temporal and spatial scales is a central part of assessing the magnitude...... of these changes. This study investigates the ability to use automatic digital camera images (DCIs) as proxy data for gross primary production (GPP) in a complex low Arctic wetland site. Vegetation greenness computed from DCIs was found to correlate significantly (R2 = 0.62, p < 0.001) with a...

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

    Science.gov (United States)

    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 (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 (in review).

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

    Science.gov (United States)

    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

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

    Directory of Open Access Journals (Sweden)

    Grzegorz Skrzypek

    Full Text Available 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.

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

    Science.gov (United States)

    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

  1. Pan-Arctic linkages between snow accumulation and growing-season air temperature, soil moisture and vegetation

    OpenAIRE

    K. A. Luus; Gel, Y.; J. C. Lin; Kelly, R. E. J.; C. R. Duguay

    2013-01-01

    Arctic field studies have indicated that the air temperature, soil moisture and vegetation at a site influence the quantity of snow accumulated, and that snow accumulation can alter growing-season soil moisture and vegetation. Climate change is predicted to bring about warmer air temperatures, greater snow accumulation and northward movements of the shrub and tree lines. Understanding the responses of northern environments to changes in s...

  2. Camera derived vegetation greenness index as proxy for gross primary production in a low Arctic wetland area

    Science.gov (United States)

    Westergaard-Nielsen, Andreas; Lund, Magnus; Hansen, Birger Ulf; Tamstorf, Mikkel Peter

    2013-12-01

    The Arctic is experiencing disproportionate warming relative to the global average, and the Arctic ecosystems are as a result undergoing considerable changes. Continued monitoring of ecosystem productivity and phenology across temporal and spatial scales is a central part of assessing the magnitude of these changes. This study investigates the ability to use automatic digital camera images (DCIs) as proxy data for gross primary production (GPP) in a complex low Arctic wetland site. Vegetation greenness computed from DCIs was found to correlate significantly (R2 = 0.62, p < 0.001) with a normalized difference vegetation index (NDVI) product derived from the WorldView-2 satellite. An object-based classification based on a bi-temporal image composite was used to classify the study area into heath, copse, fen, and bedrock. Temporal evolution of vegetation greenness was evaluated and modeled with double sigmoid functions for each plant community. GPP at light saturation modeled from eddy covariance (EC) flux measurements were found to correlate significantly with vegetation greenness for all plant communities in the studied year (i.e., 2010), and the highest correlation was found between modeled fen greenness and GPP (R2 = 0.85, p < 0.001). Finally, greenness computed within modeled EC footprints were used to evaluate the influence of individual plant communities on the flux measurements. The study concludes that digital cameras may be used as a cost-effective proxy for potential GPP in remote Arctic regions.

  3. Vegetation Feedbacks Explain Recent High-latitude Summer Warming in Alaskan Arctic and Boreal Ecosystems

    Science.gov (United States)

    Chapin, F. S.; Beringer, J.; Copass, C.; Epstein, H.; Lloyd, A.; Lynch, A.; McGuire, A. D.; Sturm, M.

    2002-12-01

    Although General Circulation Models predict the observed winter and spring warming at high latitudes, there is no obvious physical mechanism in the climate system that can account for the significant increase in summer temperatures that has occurred at high latitudes during the past 30 years. We demonstrate that vegetation-induced feedbacks in snow properties and summer energy exchange with the atmosphere explain this recent summer warming. A combination of stand-age reconstructions, repeat photography, and satellite measures of vegetation greenness demonstrate an expansion of the distribution and an infilling of shrubs in moist tundra and of trees in forest tundra. These vegetation changes increase the depth and thermal resistance of the snow pack, causing a 3oC increase in winter soil temperature and an increase in winter decomposition and nutrient mineralization, which enhance plant growth. These vegetation changes also increase summer heat transport to the atmosphere by increasing radiation absorption (lower albedo) and the proportion of absorbed energy that is transferred to the atmosphere as sensible heat. The resulting increase in atmospheric heating, on a unit-area basis, is similar to effects of a doubling of atmospheric carbon dioxide or a 2% change in solar constant, such as occurred at the last glacial-interglacial boundary. Simulations with the regional climate model ARCSyM indicate that a change from shrubless tundra to shrub-dominated tundra on the North Slope of Alaska would increase July mean temperature by 1.5 to 3.5 degrees C, with the warming effects extending south into the boreal forest of interior Alaska. If these vegetation feedbacks to regional warming are widespread, as suggested by indigenous knowledge and the satellite record, they are of sufficient magnitude to explain the summer warming that has recently been observed in northern Alaska and other regions of the circumpolar Arctic.

  4. Transitions in high-Arctic vegetation growth patterns and ecosystem productivity from 2000-2013 tracked with cameras

    DEFF Research Database (Denmark)

    Westergaard-Nielsen, Andreas; Lund, Magnus; Pedersen, Stine Højlund;

    2016-01-01

    The changes in vegetation seasonality at northern latitudes, resulting from changes in atmospheric temperatures and precipitation, are still not well understood. In this study we used 13 years of time lapse camera data and climate data from high-Arctic Northeast Greenland to assess the seasonal...... response of three vegetation types (dwarf shrub heath, grassland, and fen) to changes in snow cover, soil moisture, and air and soil temperatures. Based on the camera data, we computed a greenness index, which was subsequently used to analyze transition dates in vegetation seasonality. Snow cover...

  5. Relationships between declining summer sea ice, increasing temperatures and changing vegetation in the Siberian Arctic tundra from MODIS time series (2000–11)

    OpenAIRE

    Dutrieux, L.P.; Bartholomeus, H.; Herold, M.; Verbesselt, J.

    2012-01-01

    The concern about Arctic greening has grown recently as the phenomenon is thought to have significant influence on global climate via atmospheric carbon emissions. Earlier work on Arctic vegetation highlighted the role of summer sea ice decline in the enhanced warming and greening phenomena observed in the region, but did not contain enough details for spatially characterizing the interactions between sea ice, temperature and vegetation photosynthetic absorption. By using 1 km resolution data...

  6. Simulating the effects of soil organic nitrogen and grazing on arctic tundra vegetation dynamics on the Yamal Peninsula, Russia

    International Nuclear Information System (INIS)

    Sustainability of tundra vegetation under changing climate on the Yamal Peninsula, northwestern Siberia, home to the world's largest area of reindeer husbandry, is of crucial importance to the local native community. An integrated investigation is needed for better understanding of the effects of soils, climate change and grazing on tundra vegetation in the Yamal region. In this study we applied a nutrient-based plant community model-ArcVeg-to evaluate how two factors (soil organic nitrogen (SON) levels and grazing) interact to affect tundra responses to climate warming across a latitudinal climatic gradient on the Yamal Peninsula. Model simulations were driven by field-collected soil data and expected grazing patterns along the Yamal Arctic Transect (YAT), within bioclimate subzones C (high arctic), D (northern low arctic) and E (southern low arctic). Plant biomass and NPP (net primary productivity) were significantly increased with warmer bioclimate subzones, greater soil nutrient levels and temporal climate warming, while they declined with higher grazing frequency. Temporal climate warming of 2 deg. C caused an increase of 665 g m-2 in total biomass at the high SON site in subzone E, but only 298 g m-2 at the low SON site. When grazing frequency was also increased, total biomass increased by only 369 g m-2 at the high SON site in contrast to 184 g m-2 at the low SON site in subzone E. Our results suggest that high SON can support greater plant biomass and plant responses to climate warming, while low SON and grazing may limit plant response to climate change. In addition to the first order factors (SON, bioclimate subzones, grazing and temporal climate warming), interactions among these significantly affect plant biomass and productivity in the arctic tundra and should not be ignored in regional scale studies.

  7. The role of seasonality and large-scale climate drivers in recent Pan-Arctic tundra vegetation variability and change

    Science.gov (United States)

    Bhatt, U. S.; Walker, D. A.; Bieniek, P. A.; Raynolds, M. K.; Comiso, J. C.; Pinzon, J.; Tucker, C. J.

    2011-12-01

    An increase of Pan-Arctic tundra vegetation greenness has been documented using the remotely sensed Normalized Difference Vegetation Index (NDVI) and a coherent variability between NDVI, springtime coastal sea ice and land surface temperatures has been shown. The goal of this paper is to understand the forcing factors of this change and variability better through an analysis of the seasonality of these remotely sensed variables as well as long-term climate data sets. This study uses remotely sensed submonthly 25-km sea ice concentration, surface temperature, and NDVI from 1982 to 2010. The NDVI3g data has been corrected for biases in the spring and fall. Standard climate data (station, reanalysis, and model data) and ground observations are also examined. For overall trends, we find that summer time open water area has increased most in the Beaufort, and Siberian Seas. The seasonality of SWI trends display distinct heterogeneity across the Arctic, with maximum warming in August for most regions (Figure 1). The monthly time integrated NDVI trends display the largest positive values for most of the Arctic in July, with the exception of the E. Bering and Kara regions, which show declines during most months (Figure 2). The largest magnitude increases in Max-NDVI tend to be in subzones that are inland, particularly in the Beaufort and Chukchi regions. NDVI has increased more during spring in Eurasia and more during peak vegetation activity (July) over North America. The analysis suggests that local atmospheric circulation as well as other local factors likely plays an important role in vegetation productivity.

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

    Science.gov (United States)

    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.

  9. The response of Arctic vegetation to the summer climate: relation between shrub cover, NDVI, surface albedo and temperature

    International Nuclear Information System (INIS)

    Recently observed Arctic greening trends from normalized difference vegetation index (NDVI) data suggest that shrub growth is increasing in response to increasing summer temperature. An increase in shrub cover is expected to decrease summer albedo and thus positively feed back to climate warming. However, it is unknown how albedo and NDVI are affected by shrub cover and inter-annual variations in the summer climate. Here, we examine the relationship between deciduous shrub fractional cover, NDVI and albedo using field data collected at a tundra site in NE Siberia. Field data showed that NDVI increased and albedo decreased with increasing deciduous shrub cover. We then selected four Arctic tundra study areas and compiled annual growing season maximum NDVI and minimum albedo maps from MODIS satellite data (2000-10) and related these satellite products to tundra vegetation types (shrub, graminoid, barren and wetland tundra) and regional summer temperature. We observed that maximum NDVI was greatest in shrub tundra and that inter-annual variation was negatively related to summer minimum albedo but showed no consistent relationship with summer temperature. Shrub tundra showed higher albedo than wetland and barren tundra in all four study areas. These results suggest that a northwards shift of shrub tundra might not lead to a decrease in summer minimum albedo during the snow-free season when replacing wetland tundra. A fully integrative study is however needed to link results from satellite data with in situ observations across the Arctic to test the effect of increasing shrub cover on summer albedo in different tundra vegetation types.

  10. Relationships between declining summer sea ice, increasing temperatures and changing vegetation in the Siberian Arctic tundra from MODIS time series (2000-11)

    Science.gov (United States)

    Dutrieux, L. P.; Bartholomeus, H.; Herold, M.; Verbesselt, J.

    2012-12-01

    The concern about Arctic greening has grown recently as the phenomenon is thought to have significant influence on global climate via atmospheric carbon emissions. Earlier work on Arctic vegetation highlighted the role of summer sea ice decline in the enhanced warming and greening phenomena observed in the region, but did not contain enough details for spatially characterizing the interactions between sea ice, temperature and vegetation photosynthetic absorption. By using 1 km resolution data from the Moderate Resolution Imaging Spectrometer (MODIS) as a primary data source, this study presents detailed maps of vegetation and temperature trends for the Siberian Arctic region, using the time integrated normalized difference vegetation index (TI-NDVI) and summer warmth index (SWI) calculated for the period 2000-11 to represent vegetation greenness and temperature respectively. Spatio-temporal relationships between the two indices and summer sea ice conditions were investigated with transects at eight locations using sea ice concentration data from the Special Sensor Microwave/Imager (SSM/I). In addition, the derived vegetation and temperature trends were compared among major Arctic vegetation types and bioclimate subzones. The fine resolution trend map produced confirms the overall greening (+1% yr-1) and warming (+0.27% yr-1) of the region, reported in previous studies, but also reveals browning areas. The causes of such local decreases in vegetation, while surrounding areas are experiencing the opposite reaction to changing conditions, are still unclear. Overall correlations between sea ice concentration and SWI as well as TI-NDVI decreased in strength with increasing distance from the coast, with a particularly pronounced pattern in the case of SWI. SWI appears to be driving TI-NDVI in many cases, but not systematically, highlighting the presence of limiting factors other than temperature for plant growth in the region. Further unravelling those limiting factors

  11. Determination of Leaf Area Index, Total Foliar N, and Normalized Difference Vegetation Index for Arctic Ecosystems Dominated by Cassiope tetragona

    DEFF Research Database (Denmark)

    Campioli, M; Street, LE; Michelsen, Anders; Shaver, GR; Maere, T; Samson, R; Lemeur, R

    2009-01-01

    Leaf area index (LAI) and total foliar nitrogen (TFN) are important canopy characteristics and crucial variables needed to simulate photosynthesis and ecosystem CO2 fluxes. Although plant communities dominated by Cassiope tetragona are widespread in the Arctic, LAI and TFN for this vegetation type...... (Greenland and Svalbard). Leaves of C. tetragona are 2–6 mm long and closely appressed to their stems forming parallelepiped shoots. We determined the LAI of C. tetragona by measuring the area of the leaves while still attached to the stem, then doubling the resulting one-sided area. TFN was determined from...

  12. The regional species richness and genetic diversity of Arctic vegetation reflect both past glaciations and current climate

    DEFF Research Database (Denmark)

    Stewart, L.; Alsos, Inger G.; Bay, Christian;

    2016-01-01

    Aim The Arctic has experienced marked climatic differences between glacial and interglacial periods and is now subject to a rapidly warming climate. Knowledge of the effects of historical processes on current patterns of diversity may aid predictions of the responses of vegetation to future clima......, it will most probably also exhibit lags in response to current and future climate change. Our results also suggest that local species richness at the plot scale is more determined by local habitat factors......Aim The Arctic has experienced marked climatic differences between glacial and interglacial periods and is now subject to a rapidly warming climate. Knowledge of the effects of historical processes on current patterns of diversity may aid predictions of the responses of vegetation to future climate...... change. We aim to test whether plant species and genetic diversity patterns are correlated with time since deglaciation at regional and local scales. We also investigate whether species richness is correlated with genetic diversity in vascular plants. Location Circumarctic. Methods We investigated...

  13. CARD-FISH analysis of prokaryotic community composition and abundance along small-scale vegetation gradients in a dry arctic tundra ecosystem

    OpenAIRE

    Ushio, Masayuki; Makoto, Kobayashi; Klaminder, Jonatan; Nakano, Shin-ichi

    2013-01-01

    The size and composition of soil microbial communities have important influences on terrestrial ecosystem processes such as soil decomposition. However, compared with studies of aboveground plant communities, there are relatively few studies on belowground microbial communities and their interactions with aboveground vegetations in the arctic region. In this study, we conducted the first investigation of the abundance and composition of prokaryotic communities along small-scale vegetation gra...

  14. The distribution of arctic-alpine elements within high-altitude vegetation of the Western Carpathians in relation to environmental factors, life forms and phytogeography

    Czech Academy of Sciences Publication Activity Database

    Šibíková, I.; Šibík, J.; Hájek, Michal; Kliment, J.

    2010-01-01

    Roč. 40, 2-3 (2010), s. 189-203. ISSN 0340-269X Institutional research plan: CEZ:AV0Z60050516 Keywords : arctic-alpine species * vegetation * West Carpathians Subject RIV: EF - Botanics Impact factor: 0.618, year: 2010

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

    Science.gov (United States)

    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.

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

    Directory of Open Access Journals (Sweden)

    John-André Henden

    Full Text Available 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

  17. Relationships between declining summer sea ice, increasing temperatures and changing vegetation in the Siberian Arctic tundra from MODIS time series (2000–11)

    International Nuclear Information System (INIS)

    The concern about Arctic greening has grown recently as the phenomenon is thought to have significant influence on global climate via atmospheric carbon emissions. Earlier work on Arctic vegetation highlighted the role of summer sea ice decline in the enhanced warming and greening phenomena observed in the region, but did not contain enough details for spatially characterizing the interactions between sea ice, temperature and vegetation photosynthetic absorption. By using 1 km resolution data from the Moderate Resolution Imaging Spectrometer (MODIS) as a primary data source, this study presents detailed maps of vegetation and temperature trends for the Siberian Arctic region, using the time integrated normalized difference vegetation index (TI-NDVI) and summer warmth index (SWI) calculated for the period 2000–11 to represent vegetation greenness and temperature respectively. Spatio-temporal relationships between the two indices and summer sea ice conditions were investigated with transects at eight locations using sea ice concentration data from the Special Sensor Microwave/Imager (SSM/I). In addition, the derived vegetation and temperature trends were compared among major Arctic vegetation types and bioclimate subzones. The fine resolution trend map produced confirms the overall greening (+1% yr−1) and warming (+0.27% yr−1) of the region, reported in previous studies, but also reveals browning areas. The causes of such local decreases in vegetation, while surrounding areas are experiencing the opposite reaction to changing conditions, are still unclear. Overall correlations between sea ice concentration and SWI as well as TI-NDVI decreased in strength with increasing distance from the coast, with a particularly pronounced pattern in the case of SWI. SWI appears to be driving TI-NDVI in many cases, but not systematically, highlighting the presence of limiting factors other than temperature for plant growth in the region. Further unravelling those limiting

  18. Genetic Differentiation of Archachatina marginata Populations from Three Vegetation Zones Using Radom Amplified Polymorphic DNA Polymerase Chain Reaction

    Directory of Open Access Journals (Sweden)

    Comfort O. AFOLAYAN

    2015-09-01

    Full Text Available The genetic differentiation of Archachatina marginata populations from three different zones of Nigeria was studied with a view to delimiting them into sub-species. One hundred and nineteen (119 snail specimens were collected, comprising of forty (40 specimens from Yenagoa (Mangrove forest and from Kabba (Guinea Savanna and thirty nine (39 specimens were from Ile-Ife (Rainforest. Eight parameters of the shell specimens of A. marginata which included height of shell, width of shell, aperture height, aperture width, spire length, spire width, penultimate whorl length and first whorl length were subjected to Principal Component Analysis (PCA and Canonical Variates Analysis (CVA to delimit the populations into sub-species. DNA of the various populations was extracted from the foot muscle using CTAB (Cetyl Trimethyl Ammonium Bromide method, which was subjected to RAPD analysis. The RAPD studies employed five (5 oligonucleotide primers (OPB – 17, OPH – 12, OPH – 17, OPI – 06 and OPU – 14 to amplify DNA from 27 samples of A. marginata selected. All five primers produced different band patterns, and the number of fragments amplified per primer varied. Among them, OPB- 17 gave DNA profiles with more numerous bands than the others primers. Both PCA and CVA produced overlapped clusters of A. marginata specimens from the three vegetation zones. The height of shell was observed to be the most variable feature and preferably the most suitable parameter for population grouping. Analysis of the proportions of polymorphic loci and band sharing based on similarity indices for A. marginata samples indicated a relatively high level of genetic variation in the populations from the three areas.

  19. Estimation of the soil heat flux/net radiation ratio based on spectral vegetation indexes in high-latitude Arctic areas

    International Nuclear Information System (INIS)

    The vegetation communities in the Arctic environment are very sensitive to even minor climatic variations and therefore the estimation of surface energy fluxes from high-latitude vegetated areas is an important subject to be pursued. This study was carried out in July-August and used micro meteorological data, spectral reflectance signatures, and vegetation biomass to establish the relation between the soil heat flux/net radiation (G / Rn) ratio and spectral vegetation indices (SVIs). Continuous measurements of soil temperature and soil heat flux were used to calculate the surface ground heat flux by use of conventional methods, and the relation to surface temperature was investigated. Twenty-seven locations were established, and six samples per location, including the measurement of the surface temperature and net radiation to establish the G/Rn ratio and simultaneous spectral reflectance signatures and wet biomass estimates, were registered. To obtain regional reliability, the locations were chosen in order to represent the different Arctic vegetation communities in the study area; ranging from dry tundra vegetation communities (fell fields and dry dwarf scrubs) to moist/wet tundra vegetation communities (snowbeds, grasslands and fens). Spectral vegetation indices, including the simple ratio vegetation index (RVI) and the normalized difference vegetation index (NDVI), were calculated. A comparison of SVIs to biomass proved that RVI gave the best linear expression, and NDVI the best exponential expression. A comparison of SVIs and the surface energy flux ratio G / Rn proved that NDVI gave the best linear expression. SPOT HRV images from July 1989 and 1992 were used to map NDVI and G / Rn at a regional scale. (author)

  20. Effects of winter seismic exploration on vegetation and soil of the Coastal Plain of the Arctic National Wildlife Refuge, Alaska

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — When winter seismic exploration was conducted on the coastal plain of the Arctic National Wildlife Refuge Arctic NWR, little data were available on the longterm...

  1. Vegetation and climate history in the Laptev Sea region (Arctic Siberia) during Late Quaternary inferred from pollen records

    Science.gov (United States)

    Andreev, Andrei A.; Schirrmeister, Lutz; Tarasov, Pavel E.; Ganopolski, Andrey; Brovkin, Viktor; Siegert, Christine; Wetterich, Sebastian; Hubberten, Hans-Wolfgang

    2011-08-01

    Paleoenvironmental records from a number of permafrost sections and lacustrine cores from the Laptev Sea region dated by several methods ( 14C-AMS, TL, IRSL, OSL and 230Th/U) were analyzed for pollen and palynomorphs. The records reveal the environmental history for the last ca 200 kyr. For interglacial pollen spectra, quantitative temperature values were estimated using the best modern analogue method. Sparse grass-sedge vegetation indicating arctic desert environmental conditions existed prior to 200 kyr ago. Dense, wet grass-sedge tundra habitats dominated during an interstadial ca 200-190 kyr ago, reflecting warmer and wetter summers than before. Sparser vegetation communities point to much more severe stadial conditions ca 190-130 kyr ago. Open grass and Artemisia communities with shrub stands ( Alnus fruticosa, Salix, Betula nana) in more protected and moister places characterized the beginning of the Last Interglacial indicate climate conditions similar to present. Shrub tundra ( Alnus fruticosa and Betula nana) dominated during the middle Eemian climatic optimum, when summer temperatures were 4-5 °C higher than today. Early-Weichselian sparse grass-sedge dominated vegetation indicates climate conditions colder and dryer than in the previous interval. Middle Weichselian Interstadial records indicate moister and warmer climate conditions, for example, in the interval 40-32 kyr BP Salix was present within dense, grass-sedge dominated vegetation. Sedge-grass- Artemisia-communities indicate that climate became cooler and drier after 30 kyr BP, and cold, dry conditions characterized the Late Weichselian, ca 26-16 kyr BP, when grass-dominated communities with Caryophyllaceae, Asteraceae, Cichoriaceae, Selaginella rupestris were present. From 16 to 12 kyr BP, grass-sedge communities with Caryophyllaceae, Asteraceae, and Cichoriaceae indicate climate was significantly warmer and moister than during the previous interval. The presence of Salix and Betula reflect

  2. Plant co-existence patterns and High-Arctic vegetation composition in three common plant communities in north-east Greenland

    Directory of Open Access Journals (Sweden)

    Oriol Grau

    2014-09-01

    Full Text Available Arctic regions are expected to experience substantial changes in climate in the coming decades. In order to predict potential changes of Arctic vegetation, it is important to understand the distinct role of life forms of plants and of individual species in relation to plant co-existence patterns. Our aim is to investigate if three common Arctic plant patch types dominated by contrasting life forms (by the dwarf shrubs Salix arctica or Dryas octopetala×intermedia or by mosses are related (a to the co-existence of vascular plants and species richness at patch scale and (b to the floristic composition in three distinct plant communities (Salix snowbed, Dryas heath and fell-field associated with contrasting abiotic regimes. The study was conducted at Zackenberg, in north-east Greenland. Dryas patches showed a clear negative effect on small-scale plant richness and co-existence in the fell-field. Salix and moss patches showed a similar pattern in all the plant communities, although the number of individuals growing in Salix patches was lower than in moss patches. Salix and mosses in the fell-fields hosted a high number of species in spite of the much less vegetated aspect of this harsh, upper zone. The floristic composition varied between plant communities, but it did not change substantially between patch types within each community. This study provides novel background knowledge of plant co-existence patterns at patch scale and of the structure of contrasting Arctic plant communities, which will help to better assess the potential effects of varying abiotic stress regimes on Arctic vegetation.

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

    Science.gov (United States)

    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

  4. Relationship of cyanobacterial and algal assemblages with vegetation in the high Arctic tundra (West Spitsbergen, Svalbard Archipelago

    Directory of Open Access Journals (Sweden)

    Richter Dorota

    2015-09-01

    Full Text Available The paper presents the results of a study of cyanobacteria and green algae assemblages occurring in various tundra types determined on the basis of mosses and vascular plants and habitat conditions. The research was carried out during summer in the years 2009-2013 on the north sea-coast of Hornsund fjord (West Spitsbergen, Svalbard Archipelago. 58 sites were studied in various tundra types differing in composition of vascular plants, mosses and in trophy and humidity. 141 cyanobacteria and green algae were noted in the research area in total. Cyanobacteria and green algae flora is a significant element of many tundra types and sometimes even dominate there. Despite its importance, it has not been hitherto taken into account in the description and classification of tundra. The aim of the present study was to demonstrate the legitimacy of using phycoflora in supplementing the descriptions of hitherto described tundra and distinguishing new tundra types. Numeric hierarchical-accumulative classification (MVSP 3.1 software methods were used to analyze the cyanobacterial and algal assemblages and their co-relations with particular tundra types. The analysis determined dominant and distinctive species in the communities in concordance with ecologically diverse types of tundra. The results show the importance of these organisms in the composition of the vegetation of tundra types and their role in the ecosystems of this part of the Arctic.

  5. Late Holocene Vegetation and Climate Change From the Central and Western Canadian Arctic Inferred From Fossil Pollen Data

    Science.gov (United States)

    Peros, M.; Gajewski, K.

    2007-12-01

    Two sediment cores from the central and western Canadian Arctic were used to document landscape-scale vegetation and climate changes spanning the last ~2500 years. Both cores were dated by Pb-210 and C-14 techniques. Fossil pollen was enumerated at continuous 1 cm intervals (each centimeter representing a period of ~70 years), permitting centennial-scale changes to be placed into a long-term context. The pollen percentages are dominated by Cyperaceae and show relatively uniform values throughout the cores. Quantitative climate reconstructions, based on the percentage values, are similarly stable. However, the influx of locally- and regionally-derived pollen grains increases over the last ~150 years, suggesting that higher primary production and summer temperatures occurred over this time. The pollen results from these cores are consistent with other high-resolution (~25 year) lake sediment proxy data (BSi and LOI) from the region. Despite this, a comparison of these data with several Holocene-length pollen records from the same region indicates that the changes that characterized the last 2000 years were relatively minor compared to those of the early Holocene.

  6. Late Pliocene and Early Pleistocene vegetation history of northeastern Russian Arctic inferred from the Lake El'gygytgyn pollen record

    Science.gov (United States)

    Andreev, A. A.; Tarasov, P. E.; Wennrich, V.; Raschke, E.; Herzschuh, U.; Nowaczyk, N. R.; Brigham-Grette, J.; Melles, M.

    2014-05-01

    The 318 m thick lacustrine sediment record from Lake El'gygytgyn, northeastern Russian Arctic cored by the international El'gygytgyn Drilling Project provides unique opportunities for the time-continuous reconstruction of the regional paleoenvironmental history for the past 3.6 Myr. Pollen studies of the lower 216 m of the lacustrine sediments demonstrate their value as an excellent archive of vegetation and climate changes during the Late Pliocene and Early Pleistocene. About 3.5-3.35 Myr BP, the vegetation at Lake El'gygytgyn, now an area of tundra was dominated by spruce-larch-fir-hemlock forests. After ca. 3.35 Myr BP dark coniferous taxa gradually disappeared. A very pronounced environmental change took place ca. 3.31-3.28 Myr BP, corresponding to the Marine Isotope Stage (MIS) M2, when treeless tundra- and steppe-like habitats became dominant in the regional vegetation. Climate conditions were similar to those of Late Pleistocene cold intervals. Numerous coprophilous fungi spores identified in the pollen samples suggest the presence of grazing animals around the lake. Following the MIS M2 event, larch-pine forests with some spruce mostly dominated the area until ca. 2.6 Myr BP, interrupted by colder and drier intervals ca. 3.043-3.025, 2.935-2.912, and 2.719-2.698 Myr BP. At the beginning of the Pleistocene, ca. 2.6 Myr BP, noticeable climatic deterioration occurred. Forested habitats changed to predominantly treeless and shrubby environments, which reflect a relatively cold and dry climate. Peaks in observed green algae colonies (Botryococcus) around 2.53, 2.45, 2.32-2.305, 2.20 and 2.16-2.15 Myr BP suggest a spread of shallow water environments. A few intervals (i.e., 2.55-2.53, ca. 2.37, and 2.35-2.32 Myr BP) with a higher presence of coniferous taxa (mostly pine and larch) document some relatively short-term climate ameliorations during Early Pleistocene glacial periods.

  7. Emergent Dead Vegetation and Paired Cosmogenic Isotope Constraints on Ice Cap Activity, Baffin Island, Arctic Canada

    Science.gov (United States)

    Pendleton, S.; Miller, G. H.

    2014-12-01

    Recent summer warming has now raised the equilibrium line above almost all ice caps on Baffin Island, resulting in surface lowering and marginal recession everywhere. As cold-based ice recedes it frequently exposes in situ tundra plants that were living at the time ice expanded across the site. Radiocarbon dates for each plant records when cold summers dropped regional snowline below the site, killing the plants, and snowline remained below the site until the collection date. The kill dates also represent the last time that the climate was warm enough to expose the sampling location. Seventy-six vegetation samples collected in 2013 from the Penny Ice Cap region have been dated, with significant age populations at ~0.5, 1.8, 2.3, and 3.6 ka. The absence of ages around ~1, 2, 3, 4.5, and 5.5 ka suggest periods of either no snowline depression or stability. Sixteen vegetation samples returned ages of >45 ka (2 revisited sites from 2010, 14 new). It is postulated that these radiocarbon dead samples were last exposed during the last interglaciation (~120 ka), the last time climate was as warm as present. In addition to plant collections, bedrock exposures at the ice margins were sampled for 26Al/10Be cosmogenic nuclide dating. Seven samples from and around the Penny Ice cap have returned maximum exposure ages from ~ 0.6-0.9 ma and total histories of ~0.6-1.5 ma. In general, samples from the larger Penny Ice Cap exhibited lower amounts of exposure (~20% of total history) than those samples from smaller, localized ice caps (~55%). Radiocarbon dead sites north of the Penny Ice cap experienced significantly more exposure over their lifetimes than their counterparts east of the Penny Ice cap, suggesting significant differences in local and regional land ice fluctuations over the last 2 million years. Utilizing both the method of in situ moss and 26Al/10Be dating provides new insight into both the recent activity and long-term evolution of ice on Baffin Island. In particular

  8. Spatial and temporal patterns of greenness on the Yamal Peninsula, Russia: interactions of ecological and social factors affecting the Arctic normalized difference vegetation index

    International Nuclear Information System (INIS)

    The causes of a greening trend detected in the Arctic using the normalized difference vegetation index (NDVI) are still poorly understood. Changes in NDVI are a result of multiple ecological and social factors that affect tundra net primary productivity. Here we use a 25 year time series of AVHRR-derived NDVI data (AVHRR: advanced very high resolution radiometer), climate analysis, a global geographic information database and ground-based studies to examine the spatial and temporal patterns of vegetation greenness on the Yamal Peninsula, Russia. We assess the effects of climate change, gas-field development, reindeer grazing and permafrost degradation. In contrast to the case for Arctic North America, there has not been a significant trend in summer temperature or NDVI, and much of the pattern of NDVI in this region is due to disturbances. There has been a 37% change in early-summer coastal sea-ice concentration, a 4% increase in summer land temperatures and a 7% change in the average time-integrated NDVI over the length of the satellite observations. Gas-field infrastructure is not currently extensive enough to affect regional NDVI patterns. The effect of reindeer is difficult to quantitatively assess because of the lack of control areas where reindeer are excluded. Many of the greenest landscapes on the Yamal are associated with landslides and drainage networks that have resulted from ongoing rapid permafrost degradation. A warming climate and enhanced winter snow are likely to exacerbate positive feedbacks between climate and permafrost thawing. We present a diagram that summarizes the social and ecological factors that influence Arctic NDVI. The NDVI should be viewed as a powerful monitoring tool that integrates the cumulative effect of a multitude of factors affecting Arctic land-cover change.

  9. Vegetation

    DEFF Research Database (Denmark)

    Epstein, H.E.; Walker, D.A.; Bhatt, U.S.;

    2012-01-01

    increased 20-26%. • Increasing shrub growth and range extension throughout the Low Arctic are related to winter and early growing season temperature increases. Growth of other tundra plant types, including graminoids and forbs, is increasing, while growth of mosses and lichens is decreasing. • Increases in...

  10. Long term effects of winter seismic exploration on the vegetation of the coastal plain of the Arctic Nationa Wildlife Refuge

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — When winter seismic exploration was conducted on the coastal plain of the Arctic National Wildlife Refuge ANWR, little data was available on the longterm effects of...

  11. Intensified Arctic warming under greenhouse warming by vegetation–atmosphere–sea ice interaction

    International Nuclear Information System (INIS)

    Observations and modeling studies indicate that enhanced vegetation activities over high latitudes under an elevated CO2 concentration accelerate surface warming by reducing the surface albedo. In this study, we suggest that vegetation-atmosphere-sea ice interactions over high latitudes can induce an additional amplification of Arctic warming. Our hypothesis is tested by a series of coupled vegetation-climate model simulations under 2xCO2 environments. The increased vegetation activities over high latitudes under a 2xCO2 condition induce additional surface warming and turbulent heat fluxes to the atmosphere, which are transported to the Arctic through the atmosphere. This causes additional sea-ice melting and upper-ocean warming during the warm season. As a consequence, the Arctic and high-latitude warming is greatly amplified in the following winter and spring, which further promotes vegetation activities the following year. We conclude that the vegetation-atmosphere-sea ice interaction gives rise to additional positive feedback of the Arctic amplification. (letter)

  12. Search for latitudinal trends in the effective half-life of fallout sup(137)Cs in vegetation of the Canadian arctic

    International Nuclear Information System (INIS)

    Using published data on the integrated deposition of fallout sup(90)Sr(sup(137)Cs) until 1975 and current measurements of the sup(137)Cs activity in plant communities along the latitudinal gradient north of 50 degrees N, an estimate has been made of the sup(137)Cs effective half-life, Tsub(eff), in the composite vegetation of the Canadian arctic. The lichens Alectoria nigricans, Alectoria ochroleuca, Cladonia rangiferina, Cornicularia divergens, and Umbilicaria muhlenbergii were studied, as well as a moss, Polytrichum juniperinum, and the vascular cushion plants Dryas integrifolia, Saxifraga oppositifolia, and Silene acaulis. In all cases, the effective half-life increases with increasing latitude, the longest Tsub(eff)(10-12 years) being exhibited by dry-habitat lichens at 80 degrees N

  13. Caribou occurrence on landsat vegetation types on the coastal plain of the Arctic National Wildlife Refuge, May-June, 1980

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — Caribou Rangifer tarandus granti occurred on LANDSAT vegetation types LVT f loaded tundra, intermediate wetmoist, and sedge tundra most often during precalving. It...

  14. Satellite Remote Sensing of Pan-arctic Vegetation Productivity, Soil Respiration and net CO2 Exchange Using MODIS and AMSR-E Data

    Science.gov (United States)

    Nirala, M. L.; Heinsch, F. A.; Kimball, J. S.; Zhao, M.; Running, S.; Oechel, W.; McDonald, K.; Njoku, E.

    2005-05-01

    We have developed an approach for regional assessment and monitoring of land-atmosphere carbon dioxide (CO2) exchange, soil heterotrophic respiration (Rh) and vegetation productivity for arctic tundra using global satellite remote sensing at optical and microwave wavelengths. We use C- and X-band brightness temperatures from AMSR-E to extract surface wetness and temperature, and MODIS data to derive land cover, Leaf Area Index (LAI) and Net Primary Production (NPP) information. Calibration and validation activities involve comparisons between satellite remote sensing and tundra CO2 eddy flux tower and biophysical measurement networks and hydro-ecological process model simulations. We analyze spatial and temporal anomalies and environmental drivers of land-atmosphere net CO2 exchange at weekly and annual time steps. Surface soil moisture status and temperature as detected from satellite remote sensing observations are found to be major drivers spatial and temporal patterns of tundra net CO2 exchange and photosynthetic and respiration processes. We also find that satellite microwave measurements are capable of capturing seasonal variations and regional patterns in tundra soil heterotrophic respiration and CO2 exchange, while our ability to extract spatial patterns at the scale of surface heterogeneity is limited by the coarse spatial scale of the satellite remote sensing footprint. Our results also indicate that carbon cycle response to climate change is non-linear and strongly coupled to arctic surface hydrology. This work was performed at The University of Montana and Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

  15. Three years exclusion of large herbivores in a high arctic mire in NE Greenland resulted in changed vegetation density and greenhouse gas emission and uptake

    Science.gov (United States)

    Falk, Julie M.; Schmidt, Niels Martin; Christensen, Torben R.; Forchhammer, Mads C.; Jackowicz-Korczynski, Marcin; Ström, Lena

    2014-05-01

    Herbivory is an important part of many ecosystems and their presence effects the ecosystems carbon balance with both direct and indirect effects. Little is known about what will happen to an arctic ecosystem that is influenced by herbivory, if the animals disappear. We hypothesized that trampling and grazing by large herbivores influence the vegetation density and composition and hereby the carbon balance. Method: In 2010 an in-situ field experiment in Zackenberg, NE Greenland, were initiated to study the effects of herbivory on the vegetation and carbon balance. Exclosures were established to exclude the muskoxen (Ovibos moschatus), which are a natural part of these ecosystems. The experiment consists of five block replicates with three treatments within each block, i.e., control, exclosure and a snow fence (the treatment area is 10x10 m and the fences are 1 m high). During the growing season we have since 2011 performed weekly measurements of CO2 and CH4fluxes, the concentration of labile substrate for CH4 formation (organic acid concentration) in pore-water and additional ecosystem properties, i.e., water table depth, active layer depth and soil temperature. In 2013 a detailed analysis of the vascular plant species composition and density within each measurement plot were performed. Furthermore biomass (including mosses) samples 20x20 cm were harvested within all treatments. Results: The third year after the initiation of the experiment we observed a clear effect of excluding muskoxen grazing from the ecosystem. The exclosures had lower uptake of CO2 and lower CH4 emission. The vegetation analysis inside the plots showed a decrease in total number of vascular tillers and of Eriophorum scheuchzeri (ES) tillers. Correspondingly, the biomass samples from the exclosures had lower number of total plant tillers, ES tillers, total green leaves and green ES leaves and the height of all vascular plants and of ES plants were higher. Finally, the dry weight of the biomass

  16. Delayed responses of an Arctic ecosystem to an extreme summer: impacts on net ecosystem exchange and vegetation functioning

    Science.gov (United States)

    Zona, D.; Lipson, D. A.; Richards, J. H.; Phoenix, G. K.; Liljedahl, A. K.; Ueyama, M.; Sturtevant, C. S.; Oechel, W. C.

    2014-10-01

    The importance and consequences of extreme events on the global carbon budget are inadequately understood. This includes the differential impact of extreme events on various ecosystem components, lag effects, recovery times, and compensatory processes. In the summer of 2007 in Barrow, Arctic Alaska, there were unusually high air temperatures (the fifth warmest summer over a 65-year period) and record low precipitation (the lowest over a 65-year period). These abnormal conditions were associated with substantial desiccation of the Sphagnum layer and a reduced net Sphagnum CO2 sink but did not affect net ecosystem exchange (NEE) from this wet-sedge arctic tundra ecosystem. Microbial biomass, NH4+ availability, gross primary production (GPP), and ecosystem respiration (Reco) were generally greater during this extreme summer. The cumulative ecosystem CO2 sink in 2007 was similar to the previous summers, suggesting that vascular plants were able to compensate for Sphagnum CO2 uptake, despite the impact on other functions and structure such as desiccation of the Sphagnum layer. Surprisingly, the lowest ecosystem CO2 sink over a five summer record (2005-2009) was observed during the 2008 summer (~70% lower), directly following the unusually warm and dry summer, rather than during the extreme summer. This sink reduction cannot solely be attributed to the potential damage to mosses, which typically contribute ~40% of the entire ecosystem CO2 sink. Importantly, the return to a substantial cumulative CO2 sink occurred two summers after the extreme event, which suggests a substantial resilience of this tundra ecosystem to at least an isolated extreme event. Overall, these results show a complex response of the CO2 sink and its sub-components to atypically warm and dry conditions. The impact of multiple extreme events requires further investigation.

  17. Three-year vegetation change in the Arctic environment as observed in a permanent plot in Ny-Alesund, Svalbard

    OpenAIRE

    Satoru, Kojima

    2004-01-01

    A permanent plot was established in 1997 to monitor vegetation development in a recently abandoned coal mine in Ny-_lesund, Svalbard. A 1 mx1 m quadrat was set up and further divided into one hundred small 10 cmx10 cm cells. All the vascular plants occurring in the plot were recorded for each of the 100 cells. In 1999, the plot was revisited and examined for occurrences of vascular plants. Further, in 2002, the plot was re-surveyed and all the vascular plants were measured for their coverage....

  18. Effects of experimental spills of crude and diesel oil on arctic vegetation. A long-term study on high arctic terrestrial plant communities in Jameson Land, central East Greenland

    International Nuclear Information System (INIS)

    Biological studies were carried out in Jameson Land (70-71 deg. N) and at Mester Vig (72 deg. N), central East Greenland, in 1982 prior to oil exploration. The objective was to anticipate and take precautions for possible environmental impacts on vegetation and wildlife that might be caused by oil exploration activities. North Sea crude oil and arctic diesel oil were applied to the five major plant communities at Mester Vig in order to determine the vulnerability of plant species and to follow the recovery of plant cover in each community. The experimental spills had an intensity of 10 l m-2, and were carried out in three types of dwarf shrub heath: 1) dry Dryas-Cassiope heath, 2) dry Cassiope heath, 3) moist, mossy Vaccinium uliginosum heath, and in moist, mossy grassland and wet graminoid fen. Vegetation analyses comprising recording of species composition, frequency, and cover of vascular plants, mosses, and lichens were carried out before the spills, the following year, and six times during the period 1984-1993. The reactions of the spieces were recorded on each occasion. The spills were seen to have an immediate effect. After one year, there was a significant decline in the number of vascular species recorded, and a reduction in the total plant cover of all groups to a few percent or less in all plant communities. A delay in the reduction of moss cover was only recorded in three plots treated with diesel oil. The effects of crude oil spills seem to be more severe than the effects of diesel oil spills. Eleven years after the spills, the recovery of woody species, herbs, and graminoids was less than 1%. Mosses growing in soils with a high water content showed substantial recovery from the toxic effects of the oil. The recovery of mosses was 53% and 70% in diesel and crude oil treated fen, respectively, whereas it was c. 30% in grassland; slightly higher than in diesel oil plots. Dry habitats are more vulnerable, recovering less than 1%. (au) 17 refs

  19. Long-Term Arctic Peatland Dynamics, Vegetation and Climate History of the Pur-Taz Region, Western Siberia

    Science.gov (United States)

    Peteet, Dorothy; Andreev, Andrei; Bardeen, William; Mistretta, Francesca

    1998-01-01

    Stratigraphic analyses of peat composition, LOI, pollen, spores, macrofossils, charcoal, and AMS ages are used to reconstruct the peatland, vegetation and climatic dynamics in the Pur-Taz region of western Siberia over 5000 years (9300 - 4500 BP). Section stratigraphy shows many changes from shallow lake sediment to different combinations of forested or open sedge, moss, and Equisetum fen and peatland environments. Macrofossil and pollen data indicate that Larix sibirica and Betula pubescens trees were first to arrive, followed by Picea obovata. The dominance of Picea macrofossils 6000-5000 BP in the Pur-Taz peatland along with regional Picea pollen maxima indicate warmer conditions and movement of the spruce treeline northward at this time. The decline of pollen and macrofossils from all of these tree species in uppermost peats suggests a change in the environment less favorable for their growth, perhaps cooler temperatures and/or less moisture. Of major significance is the evidence for old ages of the uppermost peats in this area of Siberia, suggesting a real lack of peat accumulation in recent millennia or recent oxidation of uppermost peat.

  20. Biogeophysical feedbacks enhance Arctic terrestrial carbon sink in regional Earth system dynamics

    Directory of Open Access Journals (Sweden)

    W. Zhang

    2014-05-01

    Full Text Available Continued warming of the Arctic will likely accelerate terrestrial carbon (C cycling by increasing both uptake and release of C. There are still large uncertainties in modelling Arctic terrestrial ecosystems as a source or sink of C. Most modelling studies assessing or projecting the future fate of C exchange with the atmosphere are based an either stand-alone process-based models or coupled climate–C cycle general circulation models, in either case disregarding biogeophysical feedbacks of land surface changes to the atmosphere. To understand how biogeophysical feedbacks will impact on both climate and C budget over Arctic terrestrial ecosystems, we apply the regional Earth system model RCA-GUESS over the CORDEX-Arctic domain. The model is forced with lateral boundary conditions from an GCMs CMIP5 climate projection under the RCP 8.5 scenario. We perform two simulations with or without interactive vegetation dynamics respectively to assess the impacts of biogeophysical feedbacks. Both simulations indicate that Arctic terrestrial ecosystems will continue to sequester C with an increased uptake rate until 2060s–2070s, after which the C budget will return to a weak C sink as increased soil respiration and biomass burning outpaces increased net primary productivity. The additional C sinks arising from biogeophysical feedbacks are considerable, around 8.5 Gt C, accounting for 22% of the total C sinks, of which 83.5% are located in areas of Arctic tundra. Two opposing feedback mechanisms, mediated by albedo and evapotranspiration changes respectively, contribute to this response. Albedo feedback dominates over winter and spring season, amplifying the near-surface warming by up to 1.35 K in spring, while evapotranspiration feedback dominates over summer exerting the evaporative cooling by up to 0.81 K. Such feedbacks stimulate vegetation growth with an earlier onset of growing-season, leading to compositional changes in woody plants and vegetation

  1. Comparison of satellite imagery and infrared aerial photography as vegetation mapping methods in an arctic study area: Jameson Land, East Greenland

    DEFF Research Database (Denmark)

    Hansen, Birger Ulf; Mosbech, Anders

    Remote Sensing, vegetation mapping, SPOT, Landsat TM, aerial photography, Jameson Land, East Greenland......Remote Sensing, vegetation mapping, SPOT, Landsat TM, aerial photography, Jameson Land, East Greenland...

  2. Effects of winter seismic trails on visual resources, vegetation, and surface stability of the coastal plain of the Arctic National Wildlife Refuge, Alaska

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — Winter seismic exploration in 1984 and 1985 left visible trails on the coastal plain of the Arctic National Wildlife Refuge. Thirtyfour permanent intensive study...

  3. Live from the Arctic

    Science.gov (United States)

    Warnick, W. K.; Haines-Stiles, G.; Warburton, J.; Sunwood, K.

    2003-12-01

    residents speak in eloquent terms of the changes they see around them, manifested in new patterns of vegetation, the melting of permafrost and the absence of game species that used to be abundant. Meanwhile, new satellites and more sophisticated sensors on the ground and in the ice, add scientific testimony that seems to support and even extend native perceptions. Live from the Arctic will unify both perspectives, and use todays most powerful and effective communications media to connect young people and general audiences all across America to researchers and communities living and working in the Arctic. During IPY there will be a level of interest in the Polar regions unprecedented in a generation. Live from the Arctic offers unique resources to satisfy that curiosity, and encourage active participation and engagement in understanding some of Earths most significant peoples, places and rapidly changing conditions.

  4. Operational amplifiers

    CERN Document Server

    Dostal, Jiri

    1993-01-01

    This book provides the reader with the practical knowledge necessary to select and use operational amplifier devices. It presents an extensive treatment of applications and a practically oriented, unified theory of operational circuits.Provides the reader with practical knowledge necessary to select and use operational amplifier devices. Presents an extensive treatment of applications and a practically oriented, unified theory of operational circuits

  5. Arctic Newcomers

    DEFF Research Database (Denmark)

    Tonami, Aki

    2013-01-01

    Interest in the Arctic region and its economic potential in Japan, South Korea and Singapore was slow to develop but is now rapidly growing. All three countries have in recent years accelerated their engagement with Arctic states, laying the institutional frameworks needed to better understand an...

  6. Environmental and vegetation controls on the spatial variability of CH4 emission from wet-sedge and tussock tundra ecosystems in the Arctic

    OpenAIRE

    McEwing, Katherine Rose; Fisher, James Paul; Zona, Donatella

    2015-01-01

    Aims Despite multiple studies investigating the environmental controls on CH4 fluxes from arctic tundra ecosystems, the high spatial variability of CH4 emissions is not fully understood. This makes the upscaling of CH4 fluxes from plot to regional scale, particularly challenging. The goal of this study is to refine our knowledge of the spatial variability and controls on CH4 emission from tundra ecosystems. Methods CH4 fluxes were measured in four sites across a variety of wet-sedge and tusso...

  7. Arctic Climate and Terrestrial Vegetation Responses During the Middle to Late Eocene and Early Oligocene: Colder Winters Preceded Cool-Down.

    Science.gov (United States)

    Greenwood, D. R.; Eldrett, J.

    2006-12-01

    The late Eocene to early Oligocene is recognized as an interval of substantial change in the global climate, with isotopic proxies of climate indicating a significant drop in sea surface temperatures. Other studies have shown, however that at middle latitudes that terrestrial mean annual temperature did not change significantly over this interval, and that the major change was likely a shift towards a greater range of seasonal temperatures; colder winters and warmer summers. Previous analyses of high latitude (Arctic) middle Eocene climate using both leaf physiognomic analysis and qualitative analysis of identified nearest living relatives of terrestrial floras indicated upper microthermal environments (mean annual temp. or MAT ca 10°C but perhaps as high as 15°C, coldest month mean temp. or CMMT ca 0°C) for Axel Heiberg Island in the Arctic Archipelago, but did not address precipitation nor provide data on the Eocene-Oligocene transition in the Arctic. Presented here are new estimates of temperature and precipitation (annual and season amounts) for the Arctic based on NLR analysis of terrestrial plant palynomorphs (spores and pollen) from the ODP 913B and 985 cores from near Greenland. The record of climate for the Greenland cores show a similar climate in the middle Eocene to that previously estimated for Axel Heiberg Island further to the west, with MAT 10- 15°C but with CMMT >5°C. Precipitation was high (mean annual precip. or MAP >180 cm/yr), although with large uncertainties attached to the estimate. The climate proxy record for the late Eocene to early Oligocene shows a lack of change in MAT and MAP over the time interval. Consistent with other published records at middle latitudes, however, winter temperatures (as CMMT) show greater variability leading up to the E-O boundary, and consistently cooler values in the early Oligocene (CMMT 5°C). Plant groups sensitive to freezing such as palms and the floating water fern Azolla were present in the warm

  8. Letter. Late cretaceous seasonal ocean variability from the arctic

    OpenAIRE

    Davies, Andrew; Kemp, Alan E.S.; Pike, Jennifer

    2009-01-01

    The modern Arctic Ocean is regarded as barometer of global change and amplifier of global warming1 and therefore records of past Arctic change are of a premium for palaeoclimate reconstruction. Little is known of the state of the Arctic Ocean in the greenhouse period of the late Cretaceous, yet records from such times may yield important clues to its future behaviour given current global warming trends. Here we present the first seasonally resolved sedimentary record from the Cretaceous from...

  9. Arctic Watch

    Science.gov (United States)

    Orcutt, John; Baggeroer, Arthur; Mikhalevsky, Peter; Munk, Walter; Sagen, Hanne; Vernon, Frank; Worcester, Peter

    2015-04-01

    The dramatic reduction of sea ice in the Arctic Ocean will increase human activities in the coming years. This will be driven by increased demand for energy and the marine resources of an Arctic Ocean more accessible to ships. Oil and gas exploration, fisheries, mineral extraction, marine transportation, research and development, tourism and search and rescue will increase the pressure on the vulnerable Arctic environment. Synoptic in-situ year-round observational technologies are needed to monitor and forecast changes in the Arctic atmosphere-ice-ocean system at daily, seasonal, annual and decadal scales to inform and enable sustainable development and enforcement of international Arctic agreements and treaties, while protecting this critical environment. This paper will discuss multipurpose acoustic networks, including subsea cable components, in the Arctic. These networks provide communication, power, underwater and under-ice navigation, passive monitoring of ambient sound (ice, seismic, biologic and anthropogenic), and acoustic remote sensing (tomography and thermometry), supporting and complementing data collection from platforms, moorings and autonomous vehicles. This paper supports the development and implementation of regional to basin-wide acoustic networks as an integral component of a multidisciplinary, in situ Arctic Ocean Observatory.

  10. 植被和气候对阿拉斯加和加拿大北部北极苔原地区多年冻土活动层厚度的影响%Role of Vegetation and Climate in Permafrost Active Layer Depth in Arctic Tundra of Northern Alaska and Canada

    Institute of Scientific and Technical Information of China (English)

    Alexia M. Kelley; Howard E. Epstein; Donald A. Walker

    2004-01-01

    The active layer is the top layer of permafrost soils that thaws during the summer season due to increased ambient temperatures and solar radiation inputs. This layer is important because almost all biological activity takes place there luring the summer. The depth of active layer thaw is influenced by climatic conditions. Vegetation has also been found to have a strong impact on active layer thaw, because it can intercept incoming radiation, thereby insulating the soil from ambient conditions. In order to look at the role of vegetation and climate on active layer thaw, we measured thaw depth and the Normalized Difference Vegetation Index (NDVI; a proxy for aboveground plant biomass) along a latitudinal temperature gradient in arctic Alaska and Canada. At each site several measurements of thaw and NDVI were taken in areas with high amounts of vegetation and areas with little to no vegetation. Results show that the warmest regions, which had the greatest levels of NDVI, had relatively shallow thaw depths, and the coldest regions, which had the lowest levels of NDVI, also had relatively shallow thaw depths. The intermediate regions, which had moderate levels of NDVI and air temperature, had the greatest depth of thaw. These results indicate that temperature and vegetation interact to control the depth of the active layer across a range of arctic ecosystems. By developing a relationship to explain thaw depth through NDVI and temperature or latitude, the possibility exists to extrapolate thaw depth over large scales via remote sensing applications.

  11. Microsatélites amplificados al azar (RAM en estudios de diversidad genética vegetal Random amplified microsatellites (RAM´s in plant genetic diversity studies

    Directory of Open Access Journals (Sweden)

    Jaime Eduardo Muñoz Flórez

    2008-12-01

    Full Text Available Se revisó el uso e importancia, ventajas, desventajas y características de la técnica Microsatélites Amplificados al Azar (RAM en uchuva Physalis peruviana, mora Rubus spp, guayaba Psidium guajava y heliconias Heliconia spp. En mora se diferenciaron las especies R. glaucus, R. robustus y R. urticifolius, se detectaron duplicados y se encontró alta variabilidad genética en R. glaucus, la especie más importante. En uchuva se encontró alta diversidad y dos accesiones de fruto rojo que se diferenciaron genéticamente de las amarillas y una región geográfica con alta variabilidad. En guayaba los cebadores fueron altamente polimórficos y se encontró alta variabilidad en el Valle del Cauca. En heliconias y especies relacionadas se diferenciaron las familias del orden Zingiberales, algunos subgéneros y variaciones en la especie. La técnica es de bajo costo, utiliza un cebador, no requiere información previa, es altamente polimórfica y diferencia especies en los taxones evaluados.The use and importance, advantages, disadvantages and features of the Random Amplified Microsatellites RAMs technique, were reviewed in Cape gooseberry Physalis peruviana, blackberry Rubus spp, guava Psidium guajava and heliconias Heliconia spp. In blackberry, we differentiated the species R. glaucus, R. robustus y R. urticifolius, detected duplicated accessions and found high genetic diversity in R. glaucus, the most important specie. In cape gooseberry we found high diversity and two red fruit accessions genetically differentiated from the yellow fruit ones and a geographical region with high variability. In guava, primers were highly polymorphic and found high variability in Valle del Cauca region. In Heliconia and related species we differentiated families belonging to Zingiberal order, between some sub genera and variation among specie. The technique has low cost of implementation, use a single primer, do not require previous information, is highly

  12. The effect of abrupt permafrost thaw on the water table, vegetation and carbon feedback: results from a sub-arctic peatland

    Science.gov (United States)

    Malhotra, A.; Roulet, N. T.

    2015-12-01

    Uncertainty in estimating the carbon loss from thawing ice-rich permafrost is attributed, in part, to the abrupt changes in ecosystem structure and function after thaw. In a thawing peat plateau in the discontinuous permafrost zone (Stordalen, Mire, Sweden; ST), we tested for the occurrence of abrupt changes in hydrology and the effects of these changes on the water table and vegetation feedback. Using a chronosequence approach along three transects that capture several transitional thaw stages, we found abrupt hydrological changes following thaw, wherein adjacent areas (1 m apart) had unrelated water table depth (WTD) fluctuations. Despite these abrupt changes, surprisingly, the same Gaussian model of plant abundance explained by WTD could be applied to data from both ST and an undisturbed ombrotrophic peatland (Mer Bleue Bog, Canada; MB). However, the Gaussian model fit was better at MB than at ST. Furthermore, explanatory power of the model at ST decreased with increasing permafrost thaw. While water table and vegetation feedback in a thawing landscape is similar to that of a peatland without transitional land cover types, the vegetation and carbon feedback is complicated by non-linear shifts in the partitioning of gaseous effluxes between CO2 and CH4. These results will be presented along with key implications for modeling carbon loss from thawing landscapes.

  13. The Arctic

    International Nuclear Information System (INIS)

    Global climate change in the Arctic is a growing concern. Research has already documented pronounced changes, and models predict that increases in temperature from anthropogenic influences could be considerably higher than the global average. The impacts of climate change on Arctic ecosystems are complex and difficult to predict because of the many interactions within ecosystem, and between many concurrently changing environmental variables. Despite the global consequences of change in the Arctic climate the monitoring of basic abiotic as well as biotic parameters are not adequate to assess the impact of global climate change. The uneven geographical location of present monitoring stations in the Arctic limits the ability to understand the climate system. The impact of previous variations and potential future changes to ecosystems is not well understood and need to be addressed. At this point, there is no consensus of scientific opinion on how much of the current changes that are due to anthropogenic influences or to natural variation. Regardless of the cause, there is a need to investigate and assess current observations and their effects to the Arctic. In this chapter examples from both terrestrial and marine ecosystems from ongoing monitoring and research projects are given. (LN)

  14. Arctic bioremediation

    International Nuclear Information System (INIS)

    Cleanup of oil and diesel spills on gravel pads in the Arctic has typically been accomplished by utilizing a water flushing technique to remove the gross contamination or excavating the spill area and placing the material into a lined pit, or a combination of both. Enhancing the biological degradation of hydrocarbon (bioremediation) by adding nutrients to the spill area has been demonstrated to be an effective cleanup tool in more temperate locations. However, this technique has never been considered for restoration in the Arctic because the process of microbial degradation of hydrocarbon in this area is very slow. The short growing season and apparent lack of nutrients in the gravel pads were thought to be detrimental to using bioremediation to cleanup Arctic oil spills. This paper discusses the potential to utilize bioremediation as an effective method to clean up hydrocarbon spills in the northern latitudes

  15. Climate change and Arctic ecosystems: 1. Vegetation changes north of 55°N between the last glacial maximum, mid-Holocene, and present

    Science.gov (United States)

    Bigelow, N.H.; Brubaker, L.B.; Edwards, M.E.; Harrison, S.P.; Prentice, I.C.; Anderson, P.M.; Andreev, A.A.; Bartlein, P.J.; Christensen, T.R.; Cramer, W.; Kaplan, J.O.; Lozhkin, A.V.; Matveyeva, N.V.; Murray, D.F.; McGuire, A.D.; Razzhivin, V.Y.; Ritchie, J.C.; Smith, B.; Walker, D. A.; Gajewski, K.; Wolf, V.; Holmqvist, B.H.; Igarashi, Y.; Kremenetskii, K.; Paus, A.; Pisaric, M.F.J.; Volkova, V.S.

    2003-01-01

    A unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55??N at the last glacial maximum (LGM) and mid-Holocene (6000 years B.P.). The pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups. Five tundra types (cushion forb tundra, graminoid and forb tundra, prostrate dwarf-shrub tundra, erect dwarf-shrub tundra, and low- and high-shrub tundra) were distinguished and mapped on the basis of modern pollen surface samples. The tundra-forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed. During the mid-Holocene the tundra-forest boundary was north of its present position in some regions, but the pattern of this shift was strongly asymmetrical around the pole, with the largest northward shift in central Siberia (???200 km), little change in Beringia, and a southward shift in Keewatin and Labrador (???200 km). Low- and high-shrub tundra extended farther north than today. At the LGM, forests were absent from high latitudes. Graminoid and forb tundra abutted on temperate steppe in northwestern Eurasia while prostrate dwarf-shrub, erect dwarf-shrub, and graminoid and forb tundra formed a mosaic in Beringia. Graminoid and forb tundra is restricted today and does not form a large continuous biome, but the pollen data show that it was far more extensive at the LGM, while low- and high-shrub tundra were greatly reduced, illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types.

  16. River flooding as a driver of polygon dynamics: modern vegetation data and a millennial peat record from the Anabar River lowlands (Arctic Siberia

    Directory of Open Access Journals (Sweden)

    R. Zibulski

    2013-08-01

    Full Text Available The spatial and temporal variability of a low-centred polygon on the eastern floodplain area of the lower Anabar River (72.070° N, 113.921° E; northern Yakutia, Siberia has been investigated using a multi-method approach. The present-day vegetation in each square metre was analysed, revealing a community of Larix, shrubby Betula, and Salix on the polygon rim, a dominance of Carex and Andromeda polifolia in the rim-to-pond transition zone, and a predominantly monospecific Scorpidium scorpioides coverage within the pond. The total organic carbon (TOC content, TOC / TN (total nitrogen ratio, grain size, vascular plant macrofossils, moss remains, diatoms, and pollen were analysed for two vertical sections and a sediment core from a transect across the polygon. Radiocarbon dating indicates that the formation of the polygon started at least 1500 yr ago; the general positions of the pond and rim have not changed since that time. Two types of pond vegetation were identified, indicating two contrasting development stages of the polygon. The first was a well-established moss association, dominated by submerged or floating Scorpidium scorpioides and/or Drepanocladus spp. and overgrown by epiphytic diatoms such as Tabellaria flocculosa and Eunotia taxa. This stage coincides temporally with a period in which the polygon was only drained by lateral subsurface water flow, as indicated by mixed grain sizes. A different moss association occurred during times of repeated river flooding (indicated by homogeneous medium-grained sand that probably accumulated during the annual spring snowmelt, characterized by an abundance of Meesia triquetra and a dominance of benthic diatoms (e.g. Navicula vulpina, indicative of a relatively high pH and a high tolerance of disturbance. A comparison of the local polygon vegetation (inferred from moss and macrofossil spectra with the regional vegetation (inferred from pollen spectra indicated that the moss association with

  17. River flooding as a driver of polygon dynamics: modern vegetation data and a millennial peat record from the Anabar River lowlands (Arctic Siberia

    Directory of Open Access Journals (Sweden)

    R. Zibulski

    2013-03-01

    Full Text Available The spatial and temporal variability of a low-centred polygon on the eastern floodplain area of the lower Anabar River (72.070° N, 113.921° E, northern Yakutia, Siberia has been investigated using a multi-method approach. The present-day vegetation in each square metre was analysed revealing a community of Larix shrubby Betula and Salix on the polygon rim, a dominance of Carex and Andromeda polifolia in the rim-to-pond transition zone, and a predominantly monospecific Scorpidium scorpioides coverage within the pond. The TOC content, TOC/TN ratio, grain-size, vascular plant macrofossils, moss remains, diatoms, and pollen were analysed for two vertical sections and a sediment core from a transect across the polygon. Radiocarbon dating indicates that the formation of the polygon started at least 1500 yr ago; the general positions of the pond and rim have not changed since that time. Two types of pond vegetation were identified, indicating two contrasting development stages of the polygon. The first was a well-established moss association dominated by submerged or floating Scorpidium scorpioides and/or Drepanocladus spp. and overgrown by epiphytic diatoms such as Tabellaria flocculosa and Eunotia taxa. This stage coincides temporally with a period in which the polygon was only drained by lateral subsurface water flow, as indicated by mixed grain sizes. A different moss association occurred during times of repeated river flooding (indicated by homogeneous medium-grained sand that probably accumulated during the annual spring snow melt, characterized by an abundance of Meesia triquetra and a dominance of benthic diatoms (e.g. Navicula vulpina, indicative of a relatively high pH and a high tolerance of disturbance. A comparison of the local polygon vegetation (inferred from moss and macrofossil spectra with the regional vegetation (inferred from pollen spectra indicated that the moss association with Scorpidium scorpioides became established during

  18. Arctic bioremediation

    International Nuclear Information System (INIS)

    Cleanup of oil and diesel spills on gravel pads in the Arctic has typically been accomplished by utilizing a water flushing technique to remove the gross contamination or excavating the spill area and placing the material into a lined pit, or a combination of both. This paper discusses the potential to utilize bioremediation as an effective method to clean up hydrocarbon spills in the northern latitudes. Discussed are the results of a laboratory bioremediation study which simulated microbial degradation of hydrocarbon under arctic conditions

  19. Methan Dynamics in an Arctic Wetland

    DEFF Research Database (Denmark)

    Nielsen, Cecilie Skov

    Rising temperatures in the Arctic have the potential to increase methane (CH4) emissions from arctic wetlands due to increased decomposition, changes in vegetation cover, and increased substrate input from vegetation and thawing permafrost. The effects of warming and changes in vegetation cover on...... be used to oxidize CH4. The over all effect of the presence of sedges on the CH4 budget is unknown for most arctic species. Here the effects of warming and changes in plant cover on CH4 dynamics and emissions in a wetland in Blæsedalen, Disko Island, W. Greenland were investigated. The importance of...... CH4 oxidation in the rhizosphere of Carex aquatilis ssp. stans and Eriophorum angustifolium was quantified using a 13CH4 tracer. The results showed that rhizospheric CH4 oxidation mediated less than 2% of ecosystem CH4 emissions. No significant effects of warming or shrub removal on ecosystem CH4...

  20. Species interactions and response time to climate change: ice-cover and terrestrial run-off shaping Arctic char and brown trout competitive asymmetries

    Science.gov (United States)

    Finstad, A. G.; Palm Helland, I.; Jonsson, B.; Forseth, T.; Foldvik, A.; Hessen, D. O.; Hendrichsen, D. K.; Berg, O. K.; Ulvan, E.; Ugedal, O.

    2011-12-01

    There has been a growing recognition that single species responses to climate change often mainly are driven by interaction with other organisms and single species studies therefore not are sufficient to recognize and project ecological climate change impacts. Here, we study how performance, relative abundance and the distribution of two common Arctic and sub-Arctic freshwater fishes (brown trout and Arctic char) are driven by competitive interactions. The interactions are modified both by direct climatic effects on temperature and ice-cover, and indirectly through climate forcing of terrestrial vegetation pattern and associated carbon and nutrient run-off. We first use laboratory studies to show that Arctic char, which is the world's most northernmost distributed freshwater fish, outperform trout under low light levels and also have comparable higher growth efficiency. Corresponding to this, a combination of time series and time-for-space analyses show that ice-cover duration and carbon and nutrient load mediated by catchment vegetation properties strongly affected the outcome of the competition and likely drive the species distribution pattern through competitive exclusion. In brief, while shorter ice-cover period and decreased carbon load favored brown trout, increased ice-cover period and increased carbon load favored Arctic char. Length of ice-covered period and export of allochthonous material from catchments are major, but contrasting, climatic drivers of competitive interaction between these two freshwater lake top-predators. While projected climate change lead to decreased ice-cover, corresponding increase in forest and shrub cover amplify carbon and nutrient run-off. Although a likely outcome of future Arctic and sub-arctic climate scenarios are retractions of the Arctic char distribution area caused by competitive exclusion, the main drivers will act on different time scales. While ice-cover will change instantaneously with increasing temperature

  1. Low cost instrumentation amplifier

    Science.gov (United States)

    Sturman, J. C.

    1974-01-01

    Amplifier can be used for many applications requiring high input impedance and common mode rejection, low drift, and gain accuracy on order of one percent. Performance of inexpensive amplifier approaches that of some commercial instrumentation amplifiers in many specifications.

  2. Arctic Wears - Perspectives on Arctic Clothing

    OpenAIRE

    Konola, Sanna; Kähkönen, Päivi

    2015-01-01

    Arctic issues are rising around us on every field at the point of view of environment, sustainability, climate change, indigenous peoples’ rights, design and society, snow and ice building knowledge, challenges and possibilities in Arctic areas. The Arctic is written in Finland’s future strategies, and in 2017 Finland assumes the chairmanship of Arctic Council. In the northernmost university of European Union, University of Lapland, the northern issues have always been written in the DNA ...

  3. Global warming triggers the loss of a key Arctic refugium

    OpenAIRE

    K. M. Rühland; Paterson, A. M.; Keller, W; Michelutti, N.; Smol, J.P.

    2013-01-01

    We document the rapid transformation of one of the Earth's last remaining Arctic refugia, a change that is being driven by global warming. In stark contrast to the amplified warming observed throughout much of the Arctic, the Hudson Bay Lowlands (HBL) of subarctic Canada has maintained cool temperatures, largely due to the counteracting effects of persistent sea ice. However, since the mid-1990s, climate of the HBL has passed a tipping point, the pace and magnitude of which is exceptional eve...

  4. Gain ranging amplifier

    International Nuclear Information System (INIS)

    A gain ranging amplifier system is provided for use in the acquisition of data. Voltage offset compensation is utilized to correct errors in the gain ranging amplifier system caused by thermal drift and temperature dependent voltage offsets, both of which are associated with amplifiers in the gain ranging amplifier system

  5. Arctic studies

    International Nuclear Information System (INIS)

    Idaho National Engineering Laboratory (INEL) conducted a study of contamination of the Arctic Ocean and surrounding areas in order to better understand the severity of the problem and identify possible parallels in the United States. The findings were published in a quarterly report as a part of this technical task plan (TTP). While many radioactive and hazardous material contamination sites in this region have been identified, official Russian statements indicate that contaminant concentrations are within normal limits and are currently confined to specific areas

  6. Amplified Quantum Transforms

    OpenAIRE

    Cornwell, David

    2014-01-01

    In this thesis we investigate two new Amplified Quantum Transforms. In particular we create and analyze the Amplified Quantum Fourier Transform (Amplified-QFT) and the Amplified-Haar Wavelet Transform. First, we provide a brief history of quantum mechanics and quantum computing. Second, we examine the Amplified-QFT in detail and compare it against the Quantum Fourier Transform (QFT) and Quantum Hidden Subgroup (QHS) algorithms for solving the Local Period Problem. We calculate the probabiliti...

  7. Boundary layer stability and Arctic climate change: a feedback study using EC-Earth

    NARCIS (Netherlands)

    Bintanja, R.; Linden, van der E.C.; Hazeleger, W.

    2012-01-01

    Amplified Arctic warming is one of the key features of climate change. It is evident in observations as well as in climate model simulations. Usually referred to as Arctic amplification, it is generally recognized that the surface albedo feedback governs the response. However, a number of feedback m

  8. Unmanned Platforms Monitor the Arctic Atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    de Boer, Gijs; Ivey, Mark D.; Schmid, Beat; McFarlane, Sally A.; Petty, Rickey C.

    2016-02-22

    In the Arctic, drones and tethered balloons can make crucial atmospheric measurement to provide a unique perspective on an environment particularly vulnerable to climate change. Climate is rapidly changing all over the globe, but nowhere is that change faster than in the Arctic. The evidence from recent years is clear: Reductions in sea ice (Kwok and Unstersteiner, 2011) and permafrost (Romanovsky et al., 2002), in addition to modification of the terriestrial ecosystem through melting permafrost and shifting vegetation zones (burek et al., 2008; Sturm, et al., 2001), all point to a rapidly evolving.

  9. Portable musical instrument amplifier

    Energy Technology Data Exchange (ETDEWEB)

    Christian, David E. (Danbury, CT)

    1990-07-24

    The present invention relates to a musical instrument amplifier which is particularly useful for electric guitars. The amplifier has a rigid body for housing both the electronic system for amplifying and processing signals from the guitar and the system's power supply. An input plug connected to and projecting from the body is electrically coupled to the signal amplifying and processing system. When the plug is inserted into an output jack for an electric guitar, the body is rigidly carried by the guitar, and the guitar is operatively connected to the electrical amplifying and signal processing system without use of a loose interconnection cable. The amplifier is provided with an output jack, into which headphones are plugged to receive amplified signals from the guitar. By eliminating the conventional interconnection cable, the amplifier of the present invention can be used by musicians with increased flexibility and greater freedom of movement.

  10. Amplifier for nuclear spectrometry

    International Nuclear Information System (INIS)

    The spectroscopy amplifier model AE-020 is designed to adjust suitable the pulses coming from nuclear radiation detectors. Due to is capacity and specifications, the amplifier can be used together with high and medium resolution spectroscopy system

  11. High voltage distributed amplifier

    Science.gov (United States)

    Willems, D.; Bahl, I.; Wirsing, K.

    1991-12-01

    A high-voltage distributed amplifier implemented in GaAs MMIC technology has demonstrated good circuit performance over at least two octave bandwidth. This technique allows for very broadband amplifier operation with good efficiency in satellite, active-aperture radar, and battery-powered systems. Also, by increasing the number of FETs, the amplifier can be designed to match different voltage rails. The circuit does require a small amount of additional chip size over conventional distributed amplifiers but does not require power dividers or additional matching networks. This circuit configuration should find great use in broadband power amplifier design.

  12. Nonlinear controls on evapotranspiration in Arctic coastal wetlands

    OpenAIRE

    A. K. Liljedahl; Hinzman, L. D.; Harazono, Y.; Zona, D.; C. E. Tweedie; Hollister, R. D.; R. Engstrom; Oechel, W.C. (ed.)

    2011-01-01

    Projected increases in air temperature and precipitation due to climate change in Arctic wetlands could dramatically affect ecosystem functioning. As a consequence, it is important to define the controls on evapotranspiration, which is the major pathway of water loss from these systems. We quantified the multi-year controls on midday arctic coastal wetland evapotranspiration measured with the eddy covariance method at two vegetated drained thaw lake basins near Barrow, Alaska. Variations in n...

  13. Nonlinear controls on evapotranspiration in arctic coastal wetlands

    OpenAIRE

    A. K. Liljedahl; Hinzman, L. D.; Harazono, Y.; Zona, D.; C. E. Tweedie; Hollister, R. D.; R. Engstrom; Oechel, W.C. (ed.)

    2011-01-01

    Projected increases in air temperature and precipitation due to climate change in Arctic wetlands could dramatically affect ecosystem function. As a consequence, it is important to define controls on evapotranspiration, the major pathway of water loss from these systems. We quantified the multi-year controls on midday Arctic coastal wetland evapotranspiration, measured with the eddy covariance method at two vegetated, drained thaw lake basins near Barrow, Alaska. Variations ...

  14. Nonlinear controls on evapotranspiration in arctic coastal wetlands

    OpenAIRE

    A. K. Liljedahl; Hinzman, L. D.; Harazono, Y.; Zona, D.; C. E. Tweedie; Hollister, R. D.; R. Engstrom; Oechel, W.C. (ed.)

    2011-01-01

    Projected increases in air temperature and precipitation due to climate change in Arctic wetlands could dramatically affect ecosystem function. As a consequence, it is important to define controls on evapotranspiration, the major pathway of water loss from these systems. We quantified the multi-year controls on midday Arctic coastal wetland evapotranspiration, measured with the eddy covariance method at two vegetated, drained thaw lake basins near Barrow, Alaska. Variations in near-surface so...

  15. Observations on the vegetation and vascular plants of Hopen

    OpenAIRE

    Skye, Erik

    1986-01-01

    The vascular plant flora of the small arctic island of Hopen, located in the Barents Sea. was inventoried during a visit in the summer of 1982. Eighteen vascular plant species were observed and mapped. and the vegetation described.

  16. Distribution and drivers of ectomycorrhizal fungal communities across the North American Arctic

    OpenAIRE

    Timling, Ina; Dahlberg, Anders; Walker, D. A.; Gardes, M; Charcosset, J.Y.; Welker, J.; Taylor, D. L.

    2012-01-01

    Ectomycorrhizal fungi (EMF) form symbioses with a few plant species that comprise a large fraction of the arctic vegetation. Despite their importance, the identity, abundance and distribution of EMF in the Arctic, as well as the key drivers controlling their community composition are poorly understood. In this study, we investigated the diversity and structure of EMF communities across a bioclimatic gradient spanning much of the North American Arctic. We collected roots from two principal arc...

  17. The Greening of the Arctic IPY Project

    Science.gov (United States)

    Walker, D. A.; Bhatt, U. S.; Epstein, H. E.

    2008-12-01

    In 2007, Arctic sea ice extent declined to the lowest level in recorded history, 24 percent lower than the previous record in 2005. If the Arctic continues to warm over the next few decades as predicted by most arctic scientists, large changes in vegetation biomass will occur and will have important consequences to many components of the Arctic system including status of the permafrost, hydrological cycles, wildlife, and human occupation. There will also be important feedbacks to climate through changes in albedo and carbon fluxes. Changes in biomass are already happening. In Arctic Alaska from 1981 to 2001, the greenness of the landscapes as measured by satellite-derived values of the normalized difference vegetation index (NDVI) increased by 17 percent. It is uncertain what this remarkable change in greenness means with respect to plant biomass, but current NDVI-biomass relationships suggest that an average of over 100 g m-2 have been added to the tundra of northern Alaska within the past twenty years. Other studies have shown a major increase of shrub cover across northern Alaska during the past 50 years. If the Arctic Ocean becomes ice- free during the summer, some of the largest percentage increases could occur in the coldest parts of the Arctic. The three major objectives of this project are: (1) establish baseline ground observations along two transects in North American and Eurasia that traverse the entire Arctic bioclimate gradient; (2) use remote sensing and climate change analysis to determine how changes in sea ice concentrations affect land-surface temperature and the NDVI, (3) use vegetation-change models to predict how vegetation will change in the future. Strong correlations exist between sea-ice concentrations, land-surface temperatures, and the maximum and integrated NDVI). The changes in greening have been strongest in the Beaufort Sea region. Between 1982 and 2007, sea ice in the 50-km coastal strip of Beaufort Sea area during the period 18 June

  18. Is climate change affecting wolf populations in the high Arctic?

    Science.gov (United States)

    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.

  19. Is climate change affecting wolf populations in the high arctic?

    Energy Technology Data Exchange (ETDEWEB)

    Mech, L.D. [Northern Prairie Wildlife Research Center, Biological Resources Division, U.S. Geological Survey, 8711-37th St., SE, 58401-7317 Jamestown, North Dakota (United States)

    2004-11-01

    Global climate change may affect wolves in Canadas High Arctic (80{sup o} 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.

  20. Sensitivity of Coastal Environments and Wildlife to Spilled Oil: Northwest Arctic, Alaska: HABITATS (Habitat Polygons)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This data set contains sensitive biological resource data for submerged aquatic vegetation (SAV) in Northwest Arctic, Alaska. Vector polygons in this data set...

  1. Satellite observations of high northern latitude vegetation productivity changes between 1982 and 2008: ecological variability and regional differences

    International Nuclear Information System (INIS)

    To assess ongoing changes in high latitude vegetation productivity we compared spatiotemporal patterns in remotely sensed vegetation productivity in the tundra and boreal zones of North America and Eurasia. We compared the long-term GIMMS (Global Inventory Modeling and Mapping Studies) NDVI (Normalized Difference Vegetation Index) to the more recent and advanced MODIS (Moderate Resolution Imaging Spectroradiometer) NDVI data set, and mapped circumpolar trends in a gross productivity metric derived from the former. We then analyzed how temporal changes in productivity differed along an evergreen-deciduous gradient in boreal Alaska, along a shrub cover gradient in Arctic Alaska, and during succession after fire in boreal North America and northern Eurasia. We find that the earlier reported contrast between trends of increasing tundra and decreasing boreal forest productivity has amplified in recent years, particularly in North America. Decreases in boreal forest productivity are most prominent in areas of denser tree cover and, particularly in Alaska, evergreen forest stands. On the North Slope of Alaska, however, increases in tundra productivity do not appear restricted to areas of higher shrub cover, which suggests enhanced productivity across functional vegetation types. Differences in the recovery of post-disturbance vegetation productivity between North America and Eurasia are described using burn chronosequences, and the potential factors driving regional differences are discussed.

  2. Satellite observations of high northern latitude vegetation productivity changes between 1982 and 2008: ecological variability and regional differences

    Energy Technology Data Exchange (ETDEWEB)

    Beck, Pieter S A; Goetz, Scott J, E-mail: pbeck@whrc.org [Woods Hole Research Center, 149 Woods Hole Road, Falmouth, MA 02540 (United States)

    2011-10-15

    To assess ongoing changes in high latitude vegetation productivity we compared spatiotemporal patterns in remotely sensed vegetation productivity in the tundra and boreal zones of North America and Eurasia. We compared the long-term GIMMS (Global Inventory Modeling and Mapping Studies) NDVI (Normalized Difference Vegetation Index) to the more recent and advanced MODIS (Moderate Resolution Imaging Spectroradiometer) NDVI data set, and mapped circumpolar trends in a gross productivity metric derived from the former. We then analyzed how temporal changes in productivity differed along an evergreen-deciduous gradient in boreal Alaska, along a shrub cover gradient in Arctic Alaska, and during succession after fire in boreal North America and northern Eurasia. We find that the earlier reported contrast between trends of increasing tundra and decreasing boreal forest productivity has amplified in recent years, particularly in North America. Decreases in boreal forest productivity are most prominent in areas of denser tree cover and, particularly in Alaska, evergreen forest stands. On the North Slope of Alaska, however, increases in tundra productivity do not appear restricted to areas of higher shrub cover, which suggests enhanced productivity across functional vegetation types. Differences in the recovery of post-disturbance vegetation productivity between North America and Eurasia are described using burn chronosequences, and the potential factors driving regional differences are discussed.

  3. RF Power Amplifier Analysis

    OpenAIRE

    M. Lokay; K. Pelikan

    1993-01-01

    The special program is presented for the demonstration of RF power transistor amplifiers for the purposes of the high-school education in courses of radio transmitters. The program is written in Turbo Pascal 6. 0 and enables to study the waveforms in selected points of the amplifier and to draw the trajectories of the working point in a plot of output transistor characteristics.

  4. Amplifier improvement circuit

    Science.gov (United States)

    Sturman, J.

    1968-01-01

    Stable input stage was designed for the use with a integrated circuit operational amplifier to provide improved performance as an instrumentation-type amplifier. The circuit provides high input impedance, stable gain, good common mode rejection, very low drift, and low output impedance.

  5. Boundary layer stability and Arctic climate change: a feedback study using EC-Earth

    Energy Technology Data Exchange (ETDEWEB)

    Bintanja, R.; Linden, E.C. van der; Hazeleger, W. [Royal Netherlands Meteorological Institute (KNMI), De Bilt (Netherlands)

    2012-12-15

    Amplified Arctic warming is one of the key features of climate change. It is evident in observations as well as in climate model simulations. Usually referred to as Arctic amplification, it is generally recognized that the surface albedo feedback governs the response. However, a number of feedback mechanisms play a role in AA, of which those related to the prevalent near-surface inversion have received relatively little attention. Here we investigate the role of the near-surface thermal inversion, which is caused by radiative surface cooling in autumn and winter, on Arctic warming. We employ idealized climate change experiments using the climate model EC-Earth together with ERA-Interim reanalysis data to show that boundary-layer mixing governs the efficiency by which the surface warming signal is 'diluted' to higher levels. Reduced vertical mixing, as in the stably stratified inversion layer in Arctic winter, thus amplifies surface warming. Modelling results suggest that both shortwave - through the (seasonal) interaction with the sea ice feedback - and longwave feedbacks are affected by boundary-layer mixing, both in the Arctic and globally, with the effect on the shortwave feedback dominating. The amplifying effect will decrease, however, with climate warming because the surface inversion becomes progressively weaker. We estimate that the reduced Arctic inversion has slowed down global warming by about 5% over the past 2 decades, and we anticipate that it will continue to do so with ongoing Arctic warming. (orig.)

  6. Arctic Climate Tipping Points

    OpenAIRE

    Lenton, Timothy M.

    2012-01-01

    There is widespread concern that anthropogenic global warming will trigger Arctic climate tipping points. The Arctic has a long history of natural, abrupt climate changes, which together with current observations and model projections, can help us to identify which parts of the Arctic climate system might pass future tipping points. Here the climate tipping points are defined, noting that not all of them involve bifurcations leading to irreversible change. Past abrupt climate changes in the A...

  7. Amplified Arctic warming by phytoplankton under greenhouse warming

    OpenAIRE

    Park, Jong-Yeon; Kug, Jong-Seong; Bader, Jürgen; Rolph, Rebecca; Kwon, Minho

    2015-01-01

    One of the important impacts of marine phytoplankton on climate systems is the geophysical feedback by which chlorophyll and the related pigments in phytoplankton absorb solar radiation and then change sea surface temperature. Yet such biogeophysical impact is still not considered in many climate projections by state-of-the-art climate models, nor is its impact on the future climate quantified. This study shows that, by conducting global warming simulations with and without an active marine e...

  8. Arctic wind energy

    Energy Technology Data Exchange (ETDEWEB)

    Peltola, E. [Kemijoki Oy (Finland); Holttinen, H.; Marjaniemi, M. [VTT Energy, Espoo (Finland); Tammelin, B. [Finnish Meteorological Institute, Helsinki (Finland)

    1998-12-31

    Arctic wind energy research was aimed at adapting existing wind technologies to suit the arctic climatic conditions in Lapland. Project research work included meteorological measurements, instrument development, development of a blade heating system for wind turbines, load measurements and modelling of ice induced loads on wind turbines, together with the development of operation and maintenance practices in arctic conditions. As a result the basis now exists for technically feasible and economically viable wind energy production in Lapland. New and marketable products, such as blade heating systems for wind turbines and meteorological sensors for arctic conditions, with substantial export potential, have also been developed. (orig.)

  9. Arctic wind energy

    International Nuclear Information System (INIS)

    Arctic wind energy research was aimed at adapting existing wind technologies to suit the arctic climatic conditions in Lapland. Project research work included meteorological measurements, instrument development, development of a blade heating system for wind turbines, load measurements and modelling of ice induced loads on wind turbines, together with the development of operation and maintenance practices in arctic conditions. As a result the basis now exists for technically feasible and economically viable wind energy production in Lapland. New and marketable products, such as blade heating systems for wind turbines and meteorological sensors for arctic conditions, with substantial export potential, have also been developed. (orig.)

  10. White Arctic vs. Blue Arctic: Making Choices

    Science.gov (United States)

    Pfirman, S. L.; Newton, R.; Schlosser, P.; Pomerance, R.; Tremblay, B.; Murray, M. S.; Gerrard, M.

    2015-12-01

    As the Arctic warms and shifts from icy white to watery blue and resource-rich, tension is arising between the desire to restore and sustain an ice-covered Arctic and stakeholder communities that hope to benefit from an open Arctic Ocean. If emissions of greenhouse gases to the atmosphere continue on their present trend, most of the summer sea ice cover is projected to be gone by mid-century, i.e., by the time that few if any interventions could be in place to restore it. There are many local as well as global reasons for ice restoration, including for example, preserving the Arctic's reflectivity, sustaining critical habitat, and maintaining cultural traditions. However, due to challenges in implementing interventions, it may take decades before summer sea ice would begin to return. This means that future generations would be faced with bringing sea ice back into regions where they have not experienced it before. While there is likely to be interest in taking action to restore ice for the local, regional, and global services it provides, there is also interest in the economic advancement that open access brings. Dealing with these emerging issues and new combinations of stakeholders needs new approaches - yet environmental change in the Arctic is proceeding quickly and will force the issues sooner rather than later. In this contribution we examine challenges, opportunities, and responsibilities related to exploring options for restoring Arctic sea ice and potential pathways for their implementation. Negotiating responses involves international strategic considerations including security and governance, meaning that along with local communities, state decision-makers, and commercial interests, national governments will have to play central roles. While these issues are currently playing out in the Arctic, similar tensions are also emerging in other regions.

  11. Semiconductor optical amplifiers

    CERN Document Server

    Dutta, Niloy K

    2013-01-01

    This invaluable look provides a comprehensive treatment of design and applications of semiconductor optical amplifiers (SOA). SOA is an important component for optical communication systems. It has applications as in-line amplifiers and as functional devices in evolving optical networks. The functional applications of SOAs were first studied in the early 1990's, since then the diversity and scope of such applications have been steadily growing. This is the second edition of a book on Semiconductor Optical Amplifiers first published in 2006 by the same authors. Several chapters and sections rep

  12. RF Power Amplifier Analysis

    Directory of Open Access Journals (Sweden)

    M. Lokay

    1993-04-01

    Full Text Available The special program is presented for the demonstration of RF power transistor amplifiers for the purposes of the high-school education in courses of radio transmitters. The program is written in Turbo Pascal 6. 0 and enables to study the waveforms in selected points of the amplifier and to draw the trajectories of the working point in a plot of output transistor characteristics.

  13. Noise in Optical Amplifiers

    DEFF Research Database (Denmark)

    Jeppesen, Palle

    1997-01-01

    Noise in optical amplifiers is discussed on the basis of photons and electromagntic fields. Formulas for quantum noise from spontaneous emission, signal-spontaneous beat noise and spontaneous-spontaneous beat noise are derived.......Noise in optical amplifiers is discussed on the basis of photons and electromagntic fields. Formulas for quantum noise from spontaneous emission, signal-spontaneous beat noise and spontaneous-spontaneous beat noise are derived....

  14. Charge-sensitive amplifier

    OpenAIRE

    Startsev V. I.; Yampolsky Ju. S.

    2008-01-01

    The authors consider design and circuit design techniques of reduction of the influence of the pyroelectric effect on operation of the charge sensitive amplifiers. The presented experimental results confirm the validity of the measures taken to reduce the impact of pyroelectric currents. Pyroelectric currents are caused by the influence of the temperature gradient on the piezoelectric sensor and on the output voltage of charge sensitive amplifiers.

  15. E-537 MWPC amplifier

    International Nuclear Information System (INIS)

    The design of a fast MWPC amplifier for the beam chambers and the absorber chamber is completed and all parts are on order. A prototype 16 channel board has been built and satisfactorily tested. Artwork is completed for the board and out to be photographed. The board fabrication contract has been let. Listed below is a summary of the amplifier characteristics as well as test results obtained with the prototype

  16. Electrospun Amplified Fiber Optics

    OpenAIRE

    Morello, Giovanni; Camposeo, Andrea; Moffa, Maria; Pisignano, Dario

    2015-01-01

    A lot of research is focused on all-optical signal processing, aiming to obtain effective alternatives to existing data transmission platforms. Amplification of light in fiber optics, such as in Erbium-doped fiber amplifiers, is especially important for an efficient signal transmission. However, the complex fabrication methods, involving high-temperature processes performed in highly pure environment, slow down the fabrication and make amplified components expensive with respect to an ideal, ...

  17. Arctic Environmental Data Directory

    International Nuclear Information System (INIS)

    The Arctic Environmental Data Directory (AEDD) is being developed in cooperation with the US Global Change Research Plan. The AEDD Working Group, with members from US and Canadian agencies and academia, have described more than 300 Arctic data sets in a subset of an online data directory maintained by the US Geological Survey (USGS), ESDD (the Earth Science Data Directory). Through various links known as the Inter-operable Directory, the contents of AEDD are made available to scientists who use the NASA, NOAA, NSF and USGS data directories. Thus, scientists studying global change have access to Arctic data, and scientists studying the Arctic have access to global change data. The AEDD Working Group has sponsored development of a prototype Compact Disc Read Only Memory (CDROM) containing the indexed contents of the AEDD. Named Arctic Data Interactive (ADI), the disc was developed for use on Apple Macintosh and IBM PC-compatible computers, and uses a graphical and intuitive hypermedia user interface. The disc also contains portions of an Arctic Bibliography prepared in concert with the Polar Library Colloquy, sample full-text articles with illustrations, and selected data sets, including tabular data, text, and imagery. The ADI prototype is prepared as a model for organizing, presenting and distributing large quantities of Arctic and global change data and information to the science community. It is intended to be the first series of CDROMs with a consistent graphic design and user interface to place Arctic data and information on the desktop. The data are packaged with a powerful set of intuitive tools to navigate through and preview data sets from many disciplines and institutions. AEDD and ADI are sponsored by the Inter-agency Arctic Research Policy Committee and the Inter-agency Working Group on Data Management for Global Change, with guidance from the US Arctic Research Commission

  18. Molecular and isotopic characterization of terrestrial organic carbon released to (sub-)Arctic coastal waters

    OpenAIRE

    Vonk, Jorien Elisabeth

    2010-01-01

    Arctic soils store half of the global soil organic carbon (OC) pool and twice as much C as is currently present in the atmosphere. A considerable part of these carbon pools are stored in permafrost. Amplified climate warming in the Arctic will thaw permafrost and remobilize some of these substantial carbon stocks into the active carbon cycle, potentially causing positive feedback to global warming. Despite the global importance of this mechanism, our understanding of the fate of these thawing...

  19. Arctic Climate Systems Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Ivey, Mark D. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Robinson, David G. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Boslough, Mark B. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Backus, George A. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Peterson, Kara J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); van Bloemen Waanders, Bart G. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Swiler, Laura Painton [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Desilets, Darin Maurice [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Reinert, Rhonda Karen [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-03-01

    This study began with a challenge from program area managers at Sandia National Laboratories to technical staff in the energy, climate, and infrastructure security areas: apply a systems-level perspective to existing science and technology program areas in order to determine technology gaps, identify new technical capabilities at Sandia that could be applied to these areas, and identify opportunities for innovation. The Arctic was selected as one of these areas for systems level analyses, and this report documents the results. In this study, an emphasis was placed on the arctic atmosphere since Sandia has been active in atmospheric research in the Arctic since 1997. This study begins with a discussion of the challenges and benefits of analyzing the Arctic as a system. It goes on to discuss current and future needs of the defense, scientific, energy, and intelligence communities for more comprehensive data products related to the Arctic; assess the current state of atmospheric measurement resources available for the Arctic; and explain how the capabilities at Sandia National Laboratories can be used to address the identified technological, data, and modeling needs of the defense, scientific, energy, and intelligence communities for Arctic support.

  20. Plant-derived compounds stimulate the decomposition of organic matter in arctic permafrost soils.

    Science.gov (United States)

    Wild, Birgit; Gentsch, Norman; Čapek, Petr; Diáková, Kateřina; Alves, Ricardo J Eloy; Bárta, Jiři; Gittel, Antje; Hugelius, Gustaf; Knoltsch, Anna; Kuhry, Peter; Lashchinskiy, Nikolay; Mikutta, Robert; Palmtag, Juri; Schleper, Christa; Schnecker, Jörg; Shibistova, Olga; Takriti, Mounir; Torsvik, Vigdis L; Urich, Tim; Watzka, Margarete; Šantrůčková, Hana; Guggenberger, Georg; Richter, Andreas

    2016-01-01

    Arctic ecosystems are warming rapidly, which is expected to promote soil organic matter (SOM) decomposition. In addition to the direct warming effect, decomposition can also be indirectly stimulated via increased plant productivity and plant-soil C allocation, and this so called "priming effect" might significantly alter the ecosystem C balance. In this study, we provide first mechanistic insights into the susceptibility of SOM decomposition in arctic permafrost soils to priming. By comparing 119 soils from four locations across the Siberian Arctic that cover all horizons of active layer and upper permafrost, we found that an increased availability of plant-derived organic C particularly stimulated decomposition in subsoil horizons where most of the arctic soil carbon is located. Considering the 1,035 Pg of arctic soil carbon, such an additional stimulation of decomposition beyond the direct temperature effect can accelerate net ecosystem C losses, and amplify the positive feedback to global warming. PMID:27157964

  1. Plant-derived compounds stimulate the decomposition of organic matter in arctic permafrost soils

    Science.gov (United States)

    Wild, Birgit; Gentsch, Norman; Čapek, Petr; Diáková, Kateřina; Alves, Ricardo J. Eloy; Bárta, Jiři; Gittel, Antje; Hugelius, Gustaf; Knoltsch, Anna; Kuhry, Peter; Lashchinskiy, Nikolay; Mikutta, Robert; Palmtag, Juri; Schleper, Christa; Schnecker, Jörg; Shibistova, Olga; Takriti, Mounir; Torsvik, Vigdis L.; Urich, Tim; Watzka, Margarete; Šantrůčková, Hana; Guggenberger, Georg; Richter, Andreas

    2016-05-01

    Arctic ecosystems are warming rapidly, which is expected to promote soil organic matter (SOM) decomposition. In addition to the direct warming effect, decomposition can also be indirectly stimulated via increased plant productivity and plant-soil C allocation, and this so called “priming effect” might significantly alter the ecosystem C balance. In this study, we provide first mechanistic insights into the susceptibility of SOM decomposition in arctic permafrost soils to priming. By comparing 119 soils from four locations across the Siberian Arctic that cover all horizons of active layer and upper permafrost, we found that an increased availability of plant-derived organic C particularly stimulated decomposition in subsoil horizons where most of the arctic soil carbon is located. Considering the 1,035 Pg of arctic soil carbon, such an additional stimulation of decomposition beyond the direct temperature effect can accelerate net ecosystem C losses, and amplify the positive feedback to global warming.

  2. Plant-derived compounds stimulate the decomposition of organic matter in arctic permafrost soils

    DEFF Research Database (Denmark)

    Wild, Birgit; Gentsch, Norman; Čapek, Petr;

    2016-01-01

    Arctic ecosystems are warming rapidly, which is expected to promote soil organic matter (SOM) decomposition. In addition to the direct warming effect, decomposition can also be indirectly stimulated via increased plant productivity and plant-soil C allocation, and this so called "priming effect......" might significantly alter the ecosystem C balance. In this study, we provide first mechanistic insights into the susceptibility of SOM decomposition in arctic permafrost soils to priming. By comparing 119 soils from four locations across the Siberian Arctic that cover all horizons of active layer and...... direct temperature effect can accelerate net ecosystem C losses, and amplify the positive feedback to global warming....

  3. A micropower electrocardiogram amplifier.

    Science.gov (United States)

    Fay, L; Misra, V; Sarpeshkar, R

    2009-10-01

    We introduce an electrocardiogram (EKG) preamplifier with a power consumption of 2.8 muW, 8.1 muVrms input-referred noise, and a common-mode rejection ratio of 90 dB. Compared to previously reported work, this amplifier represents a significant reduction in power with little compromise in signal quality. The improvement in performance may be attributed to many optimizations throughout the design including the use of subthreshold transistor operation to improve noise efficiency, gain-setting capacitors versus resistors, half-rail operation wherever possible, optimal power allocations among amplifier blocks, and the sizing of devices to improve matching and reduce noise. We envision that the micropower amplifier can be used as part of a wireless EKG monitoring system powered by rectified radio-frequency energy or other forms of energy harvesting like body vibration and body heat. PMID:23853270

  4. A vircator amplifier

    International Nuclear Information System (INIS)

    A cavity vircator has demonstrated that formation of a virtual cathode in a cavity can improve microwave production efficiency and narrow the radiation bandwidth. When the virtual cathode radiates the microwave fields grow from noise. For each cavity, there is only one or a limited number of allowable modes for a given frequency. In this paper, a novel device - a vircator amplifier is described. The device consists of a relativistic magnetron and a cavity vircator with both devices powered by a 1 MeV, 3 Ω, 65 ns FWHM pulser. The idea is to inject a signal from the magnetron before and during virtual cathode formation in a cavity. The injected signal should lock the frequency and enhance electron bunching and therefore improve efficiency further. Experiments underway to evaluate the amplifier operating characteristics are discussed. The applicability of vircator amplifiers to the next generation of high-power microwave devices are addressed

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

    NARCIS (Netherlands)

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

    2016-01-01

    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.

  6. Pan-arctic land cover mapping and fire assessment for the ESA Data User Element Permafrost

    NARCIS (Netherlands)

    Urban, M.; Hese, S.; Herold, M.; Pöcking, S.; Schmullius, C.

    2010-01-01

    The paper presents first results of a pan-boreal scale land cover harmonization and classification. A methodology is presented that combines global and regional vegetation datasets to extract percentage cover information for different vegetation physiognomy and barren for the pan-arctic region withi

  7. Arctic Shipping Emissions in the Changing Climate

    OpenAIRE

    Vihanninjoki, Vesa

    2014-01-01

    Due to the Arctic climate change and the related diminishing of Arctic sea ice cover, the general conditions for Arctic shipping are changing. The retreat of Arctic sea ice opens up new routes for maritime transportation, both trans-Arctic passages and new alternatives within the Arctic region. Hence the amount of Arctic shipping is presumed to increase. Despite the observed development, the sailing conditions in the Arctic waters will remain challenging. Thus particular attention will be ...

  8. Arctic Bathymetry (batharcst)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — The digitally compiled map includes geology, oil and gas field centerpoints, and geologic provinces of the Arctic (North Pole area encircled by 640 N Latitude). The...

  9. Arctic_Bathymetry

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Models project the Arctic Ocean will become undersaturated with respect to carbonate minerals in the next decade. Recent field results indicate parts may already be...

  10. Arctic survey, 1957

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report summarizes a survey and game patrol conducted to twelve villages in the Arctic from April 24 to May 2 1957. The report covers animals take for income...

  11. Arctic Geology (geoarcst)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — The digitally compiled map includes geology, oil and gas field centerpoints, and geologic provinces of the Arctic (North Pole area encircled by 640 N Latitude). The...

  12. Ground-Based Hyperspectral Characterization of Alaska Tundra Vegetation along Environmental Gradients

    OpenAIRE

    Marcel Schwieder; Epstein, Howard E.; Raynolds, Martha K.; Marcel Buchhorn; Walker, Donald A.; Birgit Heim

    2013-01-01

    Remote sensing has become a valuable tool in monitoring arctic environments. The aim of this paper is ground-based hyperspectral characterization of Low Arctic Alaskan tundra communities along four environmental gradients (regional climate, soil pH, toposequence, and soil moisture) that all vary in ground cover, biomass, and dominating plant communities. Field spectroscopy in connection with vegetation analysis was carried out in summer 2012, along the North American Arctic Transect (NAAT). S...

  13. Investigating the effects of arctic dietary intake on lung health

    DEFF Research Database (Denmark)

    Baines, K J; Backer, V; Gibson, P G;

    2015-01-01

    assessed using multiple linear regression models. RESULTS: The dietary composition differed significantly in the two regions, with higher whale, seal and wild meat intake and lower fruit and vegetable intake in the Arctic regions compared with Denmark. Consumption of vegetables (P=0.004) and whale and....../or seal (P<0.0001) was significantly and positively associated with FEV1, as well as with FVC (vegetables: P=0.001, whale and/or seal: P=0.002). Regular fruit intake was included in the statistical models; however, it did not reach statistical significance (FEV1: P=0.053; FVC: P=0.055). CONCLUSIONS: High...

  14. Arctic Tourism: Realities & Possibilities

    OpenAIRE

    Pashkevich, Albina

    2014-01-01

    This paper addresses human capital in the Arctic in relation to tourism. More specifically, with an ever-increasing number oftourists recognizing the attractiveness of the Arctic, tour companies are increasingly recognizing the opportunities. The media(typically southern media) sells the image, either before or after the tourists arrive, and communities are often left to deal with therepercussions – whether those are social, economic, environmental, or the like. Many of the repercussions are ...

  15. Arctic freshwater synthesis: Introduction

    Science.gov (United States)

    Prowse, T.; Bring, A.; Mârd, J.; Carmack, E.

    2015-11-01

    In response to a joint request from the World Climate Research Program's Climate and Cryosphere Project, the International Arctic Science Committee, and the Arctic Council's Arctic Monitoring and Assessment Program, an updated scientific assessment has been conducted of the Arctic Freshwater System (AFS), entitled the Arctic Freshwater Synthesis (AFSΣ). The major reason for joint request was an increasing concern that changes to the AFS have produced, and could produce even greater, changes to biogeophysical and socioeconomic systems of special importance to northern residents and also produce extra-Arctic climatic effects that will have global consequences. Hence, the key objective of the AFSΣ was to produce an updated, comprehensive, and integrated review of the structure and function of the entire AFS. The AFSΣ was organized around six key thematic areas: atmosphere, oceans, terrestrial hydrology, terrestrial ecology, resources and modeling, and the review of each coauthored by an international group of scientists and published as separate manuscripts in this special issue of Journal of Geophysical Research-Biogeosciences. This AFSΣ—Introduction reviews the motivations for, and foci of, previous studies of the AFS, discusses criteria used to define the domain of the AFS, and details key characteristics of the definition adopted for the AFSΣ.

  16. Enabling Use of Unmanned Aircraft Systems for Arctic Environmental Monitoring

    DEFF Research Database (Denmark)

    Storvold, Rune; la Cour-Harbo, Anders; Mulac, Brenda;

    , satellites and manned aircraft are the traditional platforms on which scientists gather data of the atmosphere, sea ice, glaciers, fauna and vegetation. However, significant data gaps still exist over much of the Arctic because there are few research stations, satellites are often hindered by cloud cover......, poor resolution, and the complicated surface of snow and ice. Measurements made from manned aircraft are also limited because of range and endurance, as well as the danger and costs presented by operating manned aircraft in harsh and remote environments like the Arctic. Unmanned aircraft systems (UAS...

  17. The Arctic Visiting Speakers Program

    Science.gov (United States)

    Wiggins, H. V.; Fahnestock, J.

    2013-12-01

    The Arctic Visiting Speakers Program (AVS) is a program of the Arctic Research Consortium of the U.S. (ARCUS) and funded by the National Science Foundation. AVS provides small grants to researchers and other Arctic experts to travel and share their knowledge in communities where they might not otherwise connect. The program aims to: initiate and encourage arctic science education in communities with little exposure to arctic research; increase collaboration among the arctic research community; nurture communication between arctic researchers and community residents; and foster arctic science education at the local level. Individuals, community organizations, and academic organizations can apply to host a speaker. Speakers cover a wide range of arctic topics and can address a variety of audiences including K-12 students, graduate and undergraduate students, and the general public. Preference is given to tours that reach broad and varied audiences, especially those targeted to underserved populations. Between October 2000 and July 2013, AVS supported 114 tours spanning 9 different countries, including tours in 23 U.S. states. Tours over the past three and a half years have connected Arctic experts with over 6,600 audience members. Post-tour evaluations show that AVS consistently rates high for broadening interest and understanding of arctic issues. AVS provides a case study for how face-to-face interactions between arctic scientists and general audiences can produce high-impact results. Further information can be found at: http://www.arcus.org/arctic-visiting-speakers.

  18. Arctic Rabies – A Review

    Directory of Open Access Journals (Sweden)

    Prestrud Pål

    2004-03-01

    Full Text Available Rabies seems to persist throughout most arctic regions, and the northern parts of Norway, Sweden and Finland, is the only part of the Arctic where rabies has not been diagnosed in recent time. The arctic fox is the main host, and the same arctic virus variant seems to infect the arctic fox throughout the range of this species. The epidemiology of rabies seems to have certain common characteristics in arctic regions, but main questions such as the maintenance and spread of the disease remains largely unknown. The virus has spread and initiated new epidemics also in other species such as the red fox and the racoon dog. Large land areas and cold climate complicate the control of the disease, but experimental oral vaccination of arctic foxes has been successful. This article summarises the current knowledge and the typical characteristics of arctic rabies including its distribution and epidemiology.

  19. Observational determination of albedo decrease caused by vanishing Arctic sea ice.

    Science.gov (United States)

    Pistone, Kristina; Eisenman, Ian; Ramanathan, V

    2014-03-01

    The decline of Arctic sea ice has been documented in over 30 y of satellite passive microwave observations. The resulting darkening of the Arctic and its amplification of global warming was hypothesized almost 50 y ago but has yet to be verified with direct observations. This study uses satellite radiation budget measurements along with satellite microwave sea ice data to document the Arctic-wide decrease in planetary albedo and its amplifying effect on the warming. The analysis reveals a striking relationship between planetary albedo and sea ice cover, quantities inferred from two independent satellite instruments. We find that the Arctic planetary albedo has decreased from 0.52 to 0.48 between 1979 and 2011, corresponding to an additional 6.4 ± 0.9 W/m(2) of solar energy input into the Arctic Ocean region since 1979. Averaged over the globe, this albedo decrease corresponds to a forcing that is 25% as large as that due to the change in CO2 during this period, considerably larger than expectations from models and other less direct recent estimates. Changes in cloudiness appear to play a negligible role in observed Arctic darkening, thus reducing the possibility of Arctic cloud albedo feedbacks mitigating future Arctic warming. PMID:24550469

  20. STABILIZED TRANSISTOR AMPLIFIER

    Science.gov (United States)

    Noe, J.B.

    1963-05-01

    A temperature stabilized transistor amplifier having a pair of transistors coupled in cascade relation that are capable of providing amplification through a temperature range of - 100 un. Concent 85% F to 400 un. Concent 85% F described. The stabilization of the amplifier is attained by coupling a feedback signal taken from the emitter of second transistor at a junction between two serially arranged biasing resistances in the circuit of the emitter of the second transistor to the base of the first transistor. Thus, a change in the emitter current of the second transistor is automatically corrected by the feedback adjustment of the base-emitter potential of the first transistor and by a corresponding change in the base-emitter potential of the second transistor. (AEC)

  1. The biome reconstruction approach as a tool for interpretation of past vegetation and climate changes: application to modern and fossil pollen data from Lake El'gygytgyn, Far East Russian Arctic

    Directory of Open Access Journals (Sweden)

    P. E. Tarasov

    2013-06-01

    Full Text Available The modern and fossil pollen data obtained under the framework of the multi-disciplinary international "El'gygytgyn Drilling Project" represent a unique archive that allows the testing of a range of pollen-based reconstruction approaches and the deciphering of changes in the regional vegetation and climate since ~3.58 Ma. In the current study we provide details of the biome reconstruction method applied to the late Pliocene and Quaternary pollen records from Lake El'gygytgyn. All terrestrial pollen taxa identified in the spectra from Lake El'gygytgyn were assigned to major vegetation types (biomes, which today occur near the lake and in the broader region of eastern and northern Asia and, thus, could potentially have been present in this region during the past. When applied to the modern surface pollen spectra from the lake, the method shows a dominance of the tundra biome that currently characterizes the Lake El'gygytgyn area. When applied to the pollen spectra from the middle Pleistocene to present, the method suggests (1 a predominance of tundra during the Holocene, (2 a short interval during the marine isotope stage (MIS 5.5 interglacial distinguished by cold deciduous forest, and (3 a long phase of taiga dominance during MIS 31 and, particularly, MIS 11.3. These two latter interglacials seem to be some of the longest and warmest intervals within the past million years. During the late Pliocene–early Pleistocene interval (i.e., ~3.562–2.200 Ma, there is good correspondence between the millennial-scale vegetation changes documented in the Lake El'gygytgyn record and the alternation of cold and warm marine isotope stages, which reflect changes in the global ice volume and sea level. The biome reconstruction demonstrates changes in the regional vegetation which suggest a step-like transition from generally warmer/wetter environments of the earlier (i.e., Pliocene interval towards colder/drier environments of the Pleistocene. The

  2. Principal modes in fiber amplifiers

    CERN Document Server

    Fridman, Moti; Dubinskii, Mark; Friesem, Asher A; Davidson, Nir

    2010-01-01

    The dynamics of the state of polarization in single mode and multimode fiber amplifiers are presented. The experimental results reveal that although the state of polarizations at the output can vary over a large range when changing the temperatures of the fiber amplifiers, the variations are significantly reduced when resorting to the principal states of polarization in single mode fiber amplifiers and principal modes in multimode fiber amplifiers.

  3. Helical Fiber Amplifier

    Science.gov (United States)

    Koplow, Jeffrey P.; Kliner, Dahy; Goldberg, Lew

    2002-12-17

    A multi-mode gain fiber is provided which affords substantial improvements in the maximum pulse energy, peak power handling capabilities, average output power, and/or pumping efficiency of fiber amplifier and laser sources while maintaining good beam quality (comparable to that of a conventional single-mode fiber source). These benefits are realized by coiling the multimode gain fiber to induce significant bend loss for all but the lowest-order mode(s).

  4. Radio Frequency Solid State Amplifiers

    CERN Document Server

    Jacob, J

    2015-01-01

    Solid state amplifiers are being increasingly used instead of electronic vacuum tubes to feed accelerating cavities with radio frequency power in the 100 kW range. Power is obtained from the combination of hundreds of transistor amplifier modules. This paper summarizes a one hour lecture on solid state amplifiers for accelerator applications.

  5. Presettlement Vegetation

    Data.gov (United States)

    Minnesota Department of Natural Resources — Presettlement vegetation of Minnesota based on Marschner's original analysis of Public Land Survey notes and landscape patterns. Marschner compiled his results in...

  6. Tundra Rehabilitation in Alaska's Arctic

    Science.gov (United States)

    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

  7. Electronic amplifiers for automatic compensators

    CERN Document Server

    Polonnikov, D Ye

    1965-01-01

    Electronic Amplifiers for Automatic Compensators presents the design and operation of electronic amplifiers for use in automatic control and measuring systems. This book is composed of eight chapters that consider the problems of constructing input and output circuits of amplifiers, suppression of interference and ensuring high sensitivity.This work begins with a survey of the operating principles of electronic amplifiers in automatic compensator systems. The succeeding chapters deal with circuit selection and the calculation and determination of the principal characteristics of amplifiers, as

  8. Simplified design of IC amplifiers

    CERN Document Server

    Lenk, John

    1996-01-01

    Simplified Design of IC Amplifiers has something for everyone involved in electronics. No matter what skill level, this book shows how to design and experiment with IC amplifiers. For experimenters, students, and serious hobbyists, this book provides sufficient information to design and build IC amplifier circuits from 'scratch'. For working engineers who design amplifier circuits or select IC amplifiers, the book provides a variety of circuit configurations to make designing easier.Provides basics for all phases of practical design.Covers the most popular forms for amplif

  9. Improved Sampling Strategy for Arctic Snow Distribution

    Science.gov (United States)

    Homan, J. W.; Kane, D. L.

    2012-12-01

    Watershed scale hydrologic models require good estimates of the spatially distributed snow water equivalent (SWE) at winter's end. Snow on the ground in treeless Arctic environments is susceptible to significant wind redistribution, which results in very heterogeneous snowpacks, with greater quantities of snow collection in depressions, valley bottoms and leeward sides of ridges. In the Arctic, precipitation and snow gauges are very poor indicators of the actual spatial snowpack distribution, particularly at winter's end when ablation occurs. Snow distribution patterns are similar from year to year because they are largely controlled by the interaction of topography, vegetation, and consistent weather patterns. From one year to the next, none of these controls radically change. Consequently, shallow and deep areas of snow tend to be spatially predetermined, resulting in depth (or SWE) differences that may vary as a whole, but not relative to each other, from year to year. This work attempts to identify snowpack distribution patterns at a watershed scale in the Arctic. Snow patterns are intended to be established by numerous field survey points from past end-of-winter field campaigns. All measured SWE values represent a certain percentage of a given watershed. Some may represent small-scale anomalies (local scale), while others might represent a large-scale area (regional scale). Since we are interested in identifying snowpack distribution patterns at a watershed scale, we aim to develop an improved point-source sampling strategy that only surveys regional representative areas. This will only be possible if the extreme high and low SWE measurements that represent local-scale snow conditions are removed in the sampled data set. The integration of these pattern identification methods will produce a hybrid approach to identifying snowpack distribution patterns. Improvement in our estimates of the snowpack distribution will aid in the forecasting of snowmelt runoff

  10. Dynamics of aboveground phytomass of the circumpolar Arctic tundra during the past three decades

    International Nuclear Information System (INIS)

    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. (letter)

  11. Building valve amplifiers

    CERN Document Server

    Jones, Morgan

    2013-01-01

    Building Valve Amplifiers is a unique hands-on guide for anyone working with tube audio equipment--as an electronics hobbyist, audiophile or audio engineer. This 2nd Edition builds on the success of the first with technology and technique revisions throughout and, significantly, a major new self-build project, worked through step-by-step, which puts into practice the principles and techniques introduced throughout the book. Particular attention has been paid to answering questions commonly asked by newcomers to the world of the valve, whether audio enthusiasts tackling their first build or

  12. Wideband amplifier design

    CERN Document Server

    Hollister, Allen L

    2007-01-01

    In this book, the theory needed to understand wideband amplifier design using the simplest models possible will be developed. This theory will be used to develop algebraic equations that describe particular circuits used in high frequency design so that the reader develops a ""gut level"" understanding of the process and circuit. SPICE and Genesys simulations will be performed to show the accuracy of the algebraic models. By looking at differences between the algebraic equations and the simulations, new algebraic models will be developed that include parameters originally left out of the model

  13. REGENERATIVE TRANSISTOR AMPLIFIER

    Science.gov (United States)

    Kabell, L.J.

    1958-11-25

    Electrical circults for use in computers and the like are described. particularly a regenerative bistable transistor amplifler which is iurned on by a clock signal when an information signal permits and is turned off by the clock signal. The amplifier porforms the above function with reduced power requirements for the clock signal and circuit operation. The power requirements are reduced in one way by employing transformer coupling which increases the collector circuit efficiency by eliminating the loss of power in the collector load resistor.

  14. Quantum entanglement degrees amplifier

    CERN Document Server

    Wu, Xiang-Yao; Liu, Xiao-Jing; Liang, Yu; Meng, Xiang-Dong; Li, Hong; Zhang, Si-Qi

    2015-01-01

    The quantum entangled degrees of entangled states become smaller with the transmission distance increasing, how to keep the purity of quantum entangled states is the puzzle in quantum communication. In the paper, we have designed a new type entanglement degrees amplifier by one-dimensional photonic crystal, which is similar as the relay station of classical electromagnetic communication. We find when the entangled states of two-photon and three-photon pass through photonic crystal, their entanglement degrees can be magnified, which make the entanglement states can be long range propagation and the quantum communication can be really realized.

  15. Feedback from plant species change amplifies CO2 enhancement of grassland productivity

    Science.gov (United States)

    Dynamic global vegetation models simulate feedbacks of vegetation change on ecosystem processes, but direct, experimental evidence for feedbacks that result from atmospheric CO2 enrichment is rare. We hypothesized that feedbacks from species change would amplify the initial CO2 stimulation of above...

  16. Communicating Arctic Change (Invited)

    Science.gov (United States)

    Serreze, M.

    2009-12-01

    Nowhere on the planet are emerging signals of climate change more visible than in the Arctic. Rapid warming, a quickly shrinking summer sea ice cover, and thawing permafrost, will have impacts that extend beyond the Arctic and may reverberate around the globe. The National Snow and Ice Data Center (NSIDC) of the University of Colorado has taken a leading role in trying to effectively communicate the science and importance of Arctic change. Our popular “Sea Ice News and Analysis” web site tracks the Arctic’s shrinking ice cover and provides scientific analysis with language that is accurate yet accessible to a wide audience. Our Education Center provides accessible information on all components of the Earth’s cryosphere, the changes being seen, and how scientists conduct research. A challenge faced by NSIDC is countering the increasing level of confusion and misinformation regarding Arctic and global change, a complex problem that reflects the low level of scientific literacy by much of the public, the difficulties many scientists face in communicating their findings in accurate but understandable terms, and efforts by some groups to deliberately misrepresent and distort climate change science. This talk will outline through examples ways in which NSIDC has been successful in science communication and education, as well as lessons learned from failures.

  17. Contest for Arctic

    International Nuclear Information System (INIS)

    Warming of Earth surface access the defrosting north extensiveness of economic activities. The Russian Federation (RF) has delegated two bathyscaphs in order to put capsule with Russian flag on the bottom under North Pole. In this paper the territorial pretensions of the RF on the Arctic region are discussed

  18. DIAMOND AMPLIFIED PHOTOCATHODES.

    Energy Technology Data Exchange (ETDEWEB)

    SMEDLEY,J.; BEN-ZVI, I.; BOHON, J.; CHANG, X.; GROVER, R.; ISAKOVIC, A.; RAO, T.; WU, Q.

    2007-11-26

    High-average-current linear electron accelerators require photoinjectors capable of delivering tens to hundreds of mA average current, with peak currents of hundreds of amps. Standard photocathodes face significant challenges in meeting these requirements, and often have short operational lifetimes in an accelerator environment. We report on recent progress toward development of secondary emission amplifiers for photocathodes, which are intended to increase the achievable average current while protecting the cathode from the accelerator. The amplifier is a thin diamond wafer which converts energetic (few keV) primary electrons into hundreds of electron-hole pairs via secondary electron emission. The electrons drift through the diamond under an external bias and are emitted into vacuum via a hydrogen-terminated surface with negative electron affinity (NEA). Secondary emission gain of over 200 has been achieved. Two methods of patterning diamond, laser ablation and reactive-ion etching (RIE), are being developed to produce the required geometry. A variety of diagnostic techniques, including FTIR, SEM and AFM, have been used to characterize the diamonds.

  19. Universal Signal Conditioning Amplifier

    Science.gov (United States)

    Kinney, Frank

    1997-01-01

    The Technological Research and Development Authority (TRDA) and NASA-KSC entered into a cooperative agreement in March of 1994 to achieve the utilization and commercialization of a technology development for benefiting both the Space Program and U.S. industry on a "dual-use basis". The technology involved in this transfer is a new, unique Universal Conditioning Amplifier (USCA) used in connection with various types of transducers. The project was initiated in partnership with I-Net Corporation, Lockheed Martin Telemetry & Instrumentation (formerly Loral Test and Information Systems) and Brevard Community College. The project consists of designing, miniaturizing, manufacturing, and testing an existing prototype of USCA that was developed for NASA-KSC by the I-Net Corporation. The USCA is a rugged and field-installable self (or remotely)- programmable amplifier that works in combination with a tag random access memory (RAM) attached to various types of transducers. This summary report comprises performance evaluations, TRDA partnership tasks, a project summary, project milestones and results.

  20. Evidence and Implications of Recent Climate Change in Terrestrial Regions of the Arctic

    Science.gov (United States)

    Hinzman, L. D.; Bettez, N.; Chapin, F. S.; Dyurgerov, M.; Fastie, C.; Griffith, D. B.; Hope, A.; Huntington, H. P.; Jensen, A.; Kane, D. L.; Kofinas, G.; Lynch, A.; Lloyd, A.; McGuire, A. D.; Nelson, F. E.; Osterkamp, T.; Oechel, W. C.; Racine, C.; Romanovsky, V. E.; Schimel, J.; Stow, D.; Sturm, M.; Tweedie, C. E.; Vourlitis, G.; Walker, M.; Webber, P. J.; Welker, J.; Winker, K.; Yoshikawa, K.

    2002-12-01

    Are changes occurring in the polar terrestrial regime? Is the distribution of permafrost and Arctic region freeze and thaw changing? Is the hydrology of Arctic terrestrial regions changing? Are significant changes occurring in the distribution and productivity of high-latitude vegetation? If one examines any individual scientific discipline, evidence of climate change in arctic regions offers only pieces of the puzzle. Here we present a broad array of evidence to provide a convincing case of change in the arctic climate and a system-wide response of terrestrial processes. The thermal regime of the Arctic holds unique characteristics and consequently will display marked changes in response to climate warming. In many cases, threshold changes will occur in physical systems proceeding from permanently frozen to periodically thawed. Dramatic changes also accompany biological systems adapting to an evolving environment. In the last 25 to 400 years a wide range of changes in the Arctic have been detected. In many cases, these changes started, or accelerated, in the mid-1970s. Some of the changes, like later freeze-up and earlier break-up of arctic rivers and lakes, mirror arctic-wide and even global increases in air temperature. Others document more subtle or complex responses of the arctic system as it adapts to current and longer-term trends in climate. Since the arctic system is particularly sensitive to changes in rain- and snowfall, timing of freeze-up and break-up, and the intensity of storm activity, it is likely that much of what has been documented to date, and will be observed in the future, arises from changes in these forcing fields. Unfortunately, compared with temperature, they are poorly known. Regardless of the driving forces, however, the combined observations and documentation offer diffuse but substantial evidence that the arctic system may be entering a state not seen before in recent history.

  1. The Arctic Circle

    Science.gov (United States)

    McDonald, Siobhan

    2016-04-01

    My name is Siobhan McDonald. I am a visual artist living and working in Dublin. My studio is based in The School of Science at University College Dublin where I was Artist in Residence 2013-2015. A fascination with time and the changeable nature of landmass has led to ongoing conversations with scientists and research institutions across the interweaving disciplines of botany, biology and geology. I am developing a body of work following a recent research trip to the North Pole where I studied the disappearing landscape of the Arctic. Prompted by my experience of the Arctic shelf receding, this new work addresses issues of the instability of the earth's materiality. The work is grounded in an investigation of material processes, exploring the dynamic forces that transform matter and energy. This project combines art and science in a fascinating exploration of one of the Earth's last relatively untouched wilderness areas - the High Arctic to bring audiences on journeys to both real and artistically re-imagined Arctic spaces. CRYSTALLINE'S pivotal process is collaboration: with The European Space Agency; curator Helen Carey; palaeontologist Prof. Jenny McElwain, UCD; and with composer Irene Buckley. CRYSTALLINE explores our desire to make corporeal contact with geological phenomena in Polar Regions. From January 2016, in my collaboration with Jenny McElwain, I will focus on the study of plants and atmospheres from the Arctic regions as far back as 400 million years ago, to explore the essential 'nature' that, invisible to the eye, acts as imaginary portholes into other times. This work will be informed by my arctic tracings of sounds and images recorded in the glaciers of this disappearing frozen landscape. In doing so, the urgencies around the tipping of natural balances in this fragile region will be revealed. The final work will emerge from my forthcoming residency at the ESA in spring 2016. Here I will conduct a series of workshops in ESA Madrid to work with

  2. Amplification of Arctic warming by past air pollution reductions in Europe

    Science.gov (United States)

    Acosta Navarro, J. C.; Varma, V.; Riipinen, I.; Seland, Ø.; Kirkevåg, A.; Struthers, H.; Iversen, T.; Hansson, H.-C.; Ekman, A. M. L.

    2016-04-01

    The Arctic region is warming considerably faster than the rest of the globe, with important consequences for the ecosystems and human exploration of the region. However, the reasons behind this Arctic amplification are not entirely clear. As a result of measures to enhance air quality, anthropogenic emissions of particulate matter and its precursors have drastically decreased in parts of the Northern Hemisphere over the past three decades. Here we present simulations with an Earth system model with comprehensive aerosol physics and chemistry that show that the sulfate aerosol reductions in Europe since 1980 can potentially explain a significant fraction of Arctic warming over that period. Specifically, the Arctic region receives an additional 0.3 W m-2 of energy, and warms by 0.5 °C on annual average in simulations with declining European sulfur emissions in line with historical observations, compared with a model simulation with fixed European emissions at 1980 levels. Arctic warming is amplified mainly in fall and winter, but the warming is initiated in summer by an increase in incoming solar radiation as well as an enhanced poleward oceanic and atmospheric heat transport. The simulated summertime energy surplus reduces sea-ice cover, which leads to a transfer of heat from the Arctic Ocean to the atmosphere. We conclude that air quality regulations in the Northern Hemisphere, the ocean and atmospheric circulation, and Arctic climate are inherently linked.

  3. Wieslander Vegetation

    Data.gov (United States)

    California Department of Resources — Digital version of the 1945 California Vegetation Type Maps by A. E. Wieslander of the U.S. Forest Service. Source scale of maps are 1:100,000. These compiled maps...

  4. Kuchler Vegetation

    Data.gov (United States)

    California Department of Resources — Digital version of potential natural plant communites as compiled and published on 'Map of the Natural Vegetation of California' by A. W. Kuchler, 1976. Source map...

  5. Characterisation Of Low Noise Amplifier

    OpenAIRE

    MAULIK B.PATEL; ABHISEK CHOBEY; SUNIL B.PATEL

    2012-01-01

    Amplification is one of the most basic and prevalent microwave circuit functions inmodern RF and microwave systems. Early microwave amplifiers relied on tubes, such asklystrons and traveling-wave tubes, or solid-state reflection amplifiers based on thenegative resistance characteristics of tunnel or varactor diodes. But due to the dramaticimprovements and innovations in solid-state technology that have occurred since the1970s, most RF and microwave amplifiers today use transistor devices such...

  6. Modeling of semiconductor optical amplifiers

    DEFF Research Database (Denmark)

    Mørk, Jesper; Bischoff, Svend; Berg, Tommy Winther;

    We discuss the modelling of semiconductor optical amplifiers with emphasis on their high-speed properties. Applications in linear amplification as well as ultrafast optical signal processing are reviewed. Finally, the possible role of quantum-dot based optical amplifiers is discussed.......We discuss the modelling of semiconductor optical amplifiers with emphasis on their high-speed properties. Applications in linear amplification as well as ultrafast optical signal processing are reviewed. Finally, the possible role of quantum-dot based optical amplifiers is discussed....

  7. Amplified leak detection

    Energy Technology Data Exchange (ETDEWEB)

    Mahony, James

    2011-12-15

    Leaks are one of the major concerns for oil and gas producers. But recently, a Calgary-based company developed a tool that can find natural gas leaks in wellbores. This has relieved the oil and gas producers because the optics of finding downhole leaks just got a little brighter. Since then, there have been continuous efforts to broaden and refine fiber optics based methods. This paper presents amplified leak detection using fiber optics to identify even the smallest liquid leaks downhole. At high volumes, detection of downhole leaks in liquids is not a problem but at lower flow rates, the leaks become harder to detect, and at very low flow rates, they might not be detected at all. Hifi Engineering Inc. has developed the LeakSonar fiber optic acoustic sensor array that is specifically designed to detect and locate fluid migration in wellbores, even through multiple strings of casing.

  8. Metatronic transistor amplifier

    Science.gov (United States)

    Chettiar, Uday K.; Engheta, Nader

    2015-10-01

    Utilizing the notion of metamaterials, in recent years the concept of a circuit and lumped circuit elements have been extended to the optical domains, providing the paradigm of optical metatronics, i.e., metamaterial-inspired optical nanocircuitry, as a powerful tool for design and study of more complex systems at the nanoscale. In this paper we present a design for a new metatronic element, namely, a metatronic transistor that functions as an amplifier. As shown by our analytical and numerical paper here, this metatronic transistor provides gain as well as isolation between the input and output ports of such two-port device. The cascadability and fan-out aspects of this element are also explored.

  9. Acquatorialities of the Arctic Region

    DEFF Research Database (Denmark)

    Harste, Gorm

    2013-01-01

    In order to describe the Arctic system I propose using a concept functionally equivalent to territoriality, namely aquatoriality. Whether communicating about territoriality or aquatoriality, concepts and delimitations are both contingent to forms of communication systems. I will distinguish between...... six communications systems that differentiated from each other could become involved in the new deals emerging around the Arctic. Apart of an economic communication code about the Arctic, a legal code, ecological communication codes, and tourist communication codes, I will cope with the military...

  10. Disparities in Arctic Health

    Centers for Disease Control (CDC) Podcasts

    2008-02-04

    Life at the top of the globe is drastically different. Harsh climate devoid of sunlight part of the year, pockets of extreme poverty, and lack of physical infrastructure interfere with healthcare and public health services. Learn about the challenges of people in the Arctic and how research and the International Polar Year address them.  Created: 2/4/2008 by Emerging Infectious Diseases.   Date Released: 2/20/2008.

  11. Summer Arctic sea fog

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Synchronous or quasi-synchronous sea-land-air observations were conducted using advanced sea ice, atmospheric and marine instruments during China' s First Arctic Expedition. Based on the Precious data from the expedition, it was found that in the Arctic Ocean, most part of which is covered with ice or is mixed with ice, various kinds of sea fog formed such as advection fog, radiation fog and vapor fog. Each kind has its own characteristic and mechanics of creation. In the southern part of the Arctic Ocean, due to the sufficient warm and wet flow there, it is favorable for advection fog to form,which is dense and lasts a long time. On ice cap or vast floating ice, due to the strong radiation cooling effect, stable radiating fog is likely to form. In floating ice area there forms vapor fog with the appearance of masses of vapor from a boiling pot, which is different from short-lasting land fog. The study indicates that the reason why there are many kinds of sea fog form in the Arctic Ocean is because of the complicated cushion and the consequent sea-air interaction caused by the sea ice distribution and its unique physical characteristics. Sea fog is the atmospheric phenomenon of sea-air heat exchange. Especially, due to the high albedo of ice and snow surface, it is diffcult to absorb great amount of solar radiation during the polar days. Besides, ice is a poor conductor of heat; it blocks the sea-air heat exchange.The sea-air exchange is active in floating ice area where the ice is broken. The sea sends heat to the atmosphere in form of latent heat; vapor fog is a way of sea-air heat exchange influencing the climate and an indicator of the extent of the exchange. The study also indicates that the sea also transports heat to the atmosphere in form of sensible heat when vapor fog occurs.

  12. Semiconductor DC amplifier AEP 1487

    International Nuclear Information System (INIS)

    A semiconductor dc amplifier has been designed with the object of achieving low drift without component selection or special temperature-balancing adjustments. Modulator and ac-amplifier techniques have been adopted in order to avoid the drifts that occur when transistors are directly coupled. The diode-ring modulator described in CREL-902 has been used as the input chopper. (author)

  13. Surface air temperature variability and trends in the Arctic: new amplification assessment and regionalisation

    Directory of Open Access Journals (Sweden)

    Ola M. Johannessen

    2016-05-01

    Full Text Available Arctic amplification of temperature change is theorised to be an important feature of the Earth's climate system. For observational assessment and understanding of mechanisms of this amplification, which remain uncertain, thorough and detailed analyses of surface air temperature (SAT variability and trends in the Arctic are needed. Here we present an analysis of Arctic SAT variability in comparison with mid-latitudes and the Northern Hemisphere (NH, based on an advanced SAT dataset – NansenSAT. We define an index for the Arctic amplification as the ratio between absolute values of the Arctic (65–90°N and NH 30-yr running linear SAT trends. It is demonstrated that the temperature amplification in the Arctic is characteristic not only for the recent warming but also the early 20th century warming (ETCW and subsequent cooling. The amplification appears to be weaker during the recent warming than in the ETCW, simply because the index values reflect the more pervasive nature of the recent warming that reflects the background of anthropogenic global warming. We also produced a new Arctic regionalisation created from hierarchical cluster analysis, which identifies six major natural regions in the Arctic that reflect SAT variability. Statistical comparison with several climate indices shows that the Atlantic Multidecadal Oscillation (AMO is the mode of variability that is most significantly associated with the amplified warming–cooling in the Arctic, with a stronger correlation during the ETCW and recent warming than during the intermediate period. Regionally, differences are identified in terms of annual and seasonal rates of change and in their correlations with modes of variability.

  14. VEGETATION MAPPING IN WETLANDS

    Directory of Open Access Journals (Sweden)

    F. PEDROTTI

    2004-01-01

    Full Text Available The current work examines the main aspects of wetland vegetation mapping, which can be summarized as analysis of the ecological-vegetational (ecotone gradients; vegetation complexes; relationships between vegetation distribution and geomorphology; vegetation of the hydrographic basin lo which the wetland in question belongs; vegetation monitoring with help of four vegetation maps: phytosociological map of the real and potential vegetation, map of vegetation dynamical tendencies, map of vegetation series.

  15. Observed and model simulated 20th century Arctic temperature variability: Canadian Earth System Model CanESM2

    OpenAIRE

    Chylek, P.; Li, J.; Dubey, M. K.; Wang, M.; Lesins, G.

    2011-01-01

    We present simulations of the 20th century Arctic temperature anomaly from the second generation Canadian Earth System Model (CanESM2). The new model couples together an atmosphere-ocean general circulation model, a land-vegetation model and terrestrial and oceanic interactive carbon cycle. It simulates well the observed 20th century Arctic temperature variability that includes the early and late 20th century warming periods and the intervening 1940–1970 period of substantial cooling. The add...

  16. Observed and model simulated 20th century Arctic temperature variability: Canadian Earth System Model CanESM2

    OpenAIRE

    Chylek, P.; Li, J.; Dubey, M. K.; Wang, M.; Lesins, G.

    2011-01-01

    We present simulations of the 20th century Arctic temperature anomaly from the second generation Canadian Earth System Model (CanESM2). The new model couples together an atmosphere-ocean general circulation model, a land-vegetation model and terrestrial and oceanic interactive carbon cycle. It simulates well the observed 20th century Arctic temperature variability that includes the early and late 20th century warming periods and the intervening 1940–1970 period of substantia...

  17. Small signal microwave amplifier design

    CERN Document Server

    Grosch, Theodore

    2000-01-01

    This book explains techniques and examples for designing stable amplifiers for high-frequency applications in which the signal is small and the amplifier circuit is linear. An in-depth discussion of linear network theory provides the foundation needed to develop actual designs. Examples throughout the book will show you how to apply the knowledge gained in each chapter leading to the complex design of low noise amplifiers. Many exercises at the end of each chapter will help students to practice their skills. The solutions to these design problems are available in an accompanying solutions book

  18. International Standardization Activities for Optical Amplifiers

    Institute of Scientific and Technical Information of China (English)

    Haruo Okamura

    2003-01-01

    International standardization activities for Optical Amplifiers at IECTC86 and ITU-T SG15 are reviewed. Current discussions include Optical Amplifier safety guideline, Reliability standard, Rest methods of Noise and PMD, Definitions of Raman amplifier parameters and OA classification.

  19. AMAP Assessment 2013: Arctic Ocean acidification

    Science.gov (United States)

    2013-01-01

    This assessment report presents the results of the 2013 AMAP Assessment of Arctic Ocean Acidification (AOA). This is the first such assessment dealing with AOA from an Arctic-wide perspective, and complements several assessments that AMAP has delivered over the past ten years concerning the effects of climate change on Arctic ecosystems and people. The Arctic Monitoring and Assessment Programme (AMAP) is a group working under the Arctic Council. The Arctic Council Ministers have requested AMAP to: - produce integrated assessment reports on the status and trends of the conditions of the Arctic ecosystems;

  20. Arctic Submarine Slope Stability

    Science.gov (United States)

    Winkelmann, D.; Geissler, W.

    2010-12-01

    Submarine landsliding represents aside submarine earthquakes major natural hazard to coastal and sea-floor infrastructure as well as to coastal communities due to their ability to generate large-scale tsunamis with their socio-economic consequences. The investigation of submarine landslides, their conditions and trigger mechanisms, recurrence rates and potential impact remains an important task for the evaluation of risks in coastal management and offshore industrial activities. In the light of a changing globe with warming oceans and rising sea-level accompanied by increasing human population along coasts and enhanced near- and offshore activities, slope stability issues gain more importance than ever before. The Arctic exhibits the most rapid and drastic changes and is predicted to change even faster. Aside rising air temperatures, enhanced inflow of less cooled Atlantic water into the Arctic Ocean reduces sea-ice cover and warms the surroundings. Slope stability is challenged considering large areas of permafrost and hydrates. The Hinlopen/Yermak Megaslide (HYM) north of Svalbard is the first and so far only reported large-scale submarine landslide in the Arctic Ocean. The HYM exhibits the highest headwalls that have been found on siliciclastic margins. With more than 10.000 square kilometer areal extent and app. 2.400 cubic kilometer of involved sedimentary material, it is one of the largest exposed submarine slides worldwide. Geometry and age put this slide in a special position in discussing submarine slope stability on glaciated continental margins. The HYM occurred 30 ka ago, when the global sea-level dropped by app. 50 m within less than one millennium due to rapid onset of global glaciation. It probably caused a tsunami with circum-Arctic impact and wave heights exceeding 130 meters. The HYM affected the slope stability field in its neighbourhood by removal of support. Post-megaslide slope instability as expressed in creeping and smaller-scaled slides are

  1. a New Japanese Project for Arctic Climate Change Research - Grene Arctic - (Invited)

    Science.gov (United States)

    Enomoto, H.

    2013-12-01

    A new Arctic Climate Change Research Project 'Rapid Change of the Arctic Climate System and its Global Influences' has started in 2011 for a five years project. GRENE-Arctic project is an initiative of Arctic study by more than 30 Japanese universities and institutes as the flame work of GRENE (Green Network of Excellence) of MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan). The GRENE-Arctic project set four strategic research targets: 1. Understanding the mechanism of warming amplification in the Arctic 2. Understanding the Arctic system for global climate and future change 3. Evaluation of the effects of Arctic change on weather in Japan, marine ecosystems and fisheries 4. Prediction of sea Ice distribution and Arctic sea routes This project aims to realize the strategic research targets by executing following studies: -Improvement of coupled general circulation models based on validations of the Arctic climate reproducibility and on mechanism analyses of the Arctic climate change and variability -The role of Arctic cryosphere in the global change -Change in terrestrial ecosystem of pan-Arctic and its effect on climate -Studies on greenhouse gas cycles in the Arctic and their responses to climate change -Atmospheric studies on Arctic change and its global impacts -Ecosystem studies of the Arctic ocean declining Sea ice -Projection of Arctic Sea ice responding to availability of Arctic sea route (* ** ***) *Changes in the Arctic ocean and mechanisms on catastrophic reduction of Arctic sea ice cover **Coordinated observational and modeling studies on the basic structure and variability of the Arctic sea ice-ocean system ***Sea ice prediction and construction of ice navigation support system for the Arctic sea route. Although GRENE Arctic project aims to product scientific contribution in a concentrated program during 2011-2016, Japanese Arctic research community established Japan Consortium for Arctic Environmental Research (JCAR) in May

  2. Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes

    Science.gov (United States)

    Bartlein, P. J.; Edwards, M. E.; Hostetler, S. W.; Shafer, S. L.; Anderson, P. M.; Brubaker, L. B.; Lozhkin, A. V.

    2015-09-01

    Arctic land-cover changes induced by recent global climate change (e.g., expansion of woody vegetation into tundra and effects of permafrost degradation) are expected to generate further feedbacks to the climate system. Past changes can be used to assess our understanding of feedback mechanisms through a combination of process modeling and paleo-observations. The subcontinental region of Beringia (northeastern Siberia, Alaska, and northwestern Canada) was largely ice-free at the peak of deglacial warming and experienced both major vegetation change and loss of permafrost when many arctic regions were still ice covered. The evolution of Beringian climate at this time was largely driven by global features, such as the amplified seasonal cycle of Northern Hemisphere insolation and changes in global ice volume and atmospheric composition, but changes in regional land-surface controls, such as the widespread development of thaw lakes, the replacement of tundra by deciduous forest or woodland, and the flooding of the Bering-Chukchi land bridge, were probably also important. We examined the sensitivity of Beringia's early Holocene climate to these regional-scale controls using a regional climate model (RegCM). Lateral and oceanic boundary conditions were provided by global climate simulations conducted using the GENESIS V2.01 atmospheric general circulation model (AGCM) with a mixed-layer ocean. We carried out two present-day simulations of regional climate - one with modern and one with 11 ka geography - plus another simulation for 6 ka. In addition, we performed five ~ 11 ka climate simulations, each driven by the same global AGCM boundary conditions: (i) 11 ka Control, which represents conditions just prior to the major transitions (exposed land bridge, no thaw lakes or wetlands, widespread tundra vegetation), (ii) sea-level rise, which employed present-day continental outlines, (iii) vegetation change, with deciduous needleleaf and deciduous broadleaf boreal

  3. Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes

    Directory of Open Access Journals (Sweden)

    P. J. Bartlein

    2015-03-01

    Full Text Available Arctic land-cover changes (e.g., expansion of woody vegetation into tundra and effects of permafrost degradation that have been induced by recent global climate change are expected to generate further feedbacks to the climate system. Past changes can be used to assess our understanding of feedback mechanisms through a combination of process modelling and paleo-observations. The sub-continental region of Beringia (Northeast Siberia, Alaska, and northwestern Canada was largely ice-free at the peak of deglacial warming and experienced both major vegetation change and loss of permafrost when many arctic regions were still ice covered. The evolution of Beringian climate at this time was largely driven by global features, such as the amplified seasonal cycle of Northern Hemisphere insolation and changes in global ice volume and atmospheric composition, but changes in regional land-surface controls, such as the widespread development of thaw lakes, the replacement of tundra by deciduous forest or woodland, and the flooding of the Bering–Chukchi land bridge, were probably also important. We examined the sensitivity of Beringia's early Holocene climate to these regional-scale controls using a regional climate model (RegCM. Lateral and oceanic boundary conditions were provided by global climate simulations conducted using the GENESIS V2.01 atmospheric general circulation model (AGCM with a mixed-layer ocean. We carried out two present day simulations of regional climate, one with modern and one with 11 ka geography, plus another simulation for 6 ka. In addition, we performed five ∼11 ka climate simulations, each driven by the same global AGCM boundary conditions: (i 11 ka "Control", which represents conditions just prior to the major transitions (exposed land bridge, no thaw lakes or wetlands, widespread tundra vegetation, (ii sea-level rise, which employed present day continental outlines, (iii vegetation change, with deciduous needleleaf and

  4. Arctic charr farming

    OpenAIRE

    Brännäs, Eva; Larsson, Stefan; Saether, Björn Steinar; Siikavuopio, Sten Ivar; Thorarensen, Helgi; Sigurgeirsson, Ólafur; Jeuthe, Henrik

    2011-01-01

    The Arctic charr (Salvelinus alpinus L.) is a holarctic salmonid fish species with both landlocked and anadromous populations. In Scandinavia it is mainly found in the mountain area, but it also appears in deep and large lake further south, i.e. in the Alps. It is the northernmost freshwater fish and A. charr is generally regarded as the most cold-adapted freshwater fish. A. charr has been commercially farmed since the early 90ths and today, the total production is 3000, 2300 and 700 tonnes/y...

  5. Research with Arctic peoples

    DEFF Research Database (Denmark)

    Smith, H Sally; Bjerregaard, Peter; Chan, Hing Man;

    2006-01-01

    entitled "Research with Arctic Peoples: Unique Research Opportunities in Heart, Lung, Blood and Sleep Disorders". The meeting was international in scope with investigators from Greenland, Iceland and Russia, as well as Canada and the United States. Multiple health agencies from Canada and the United States...... sent representatives. Also attending were representatives from the International Union for Circumpolar Health (IUCH) and the National Indian Health Board. The working group developed a set of ten recommendations related to research opportunities in heart, lung, blood and sleep disorders; obstacles and...

  6. Arctic species resilience

    DEFF Research Database (Denmark)

    Mortensen, Lars O.; Forchhammer, Mads C.; Jeppesen, Erik

    , an extensive monitoring program has been conducted in the North Eastern Greenland National Park, the Zackenberg Basic. The objective of the program is to provide long time series of data on the natural innate oscillations and plasticity of a High Arctic ecosystem. With offset in the data provided through...... and precipitation. Concurrently, phenological change has been recorded in a wide range of plants and animals, with climate change seemingly being the primary driver of these changes. A major concern is whether species and biological systems embrace the plasticity in their phenological responses needed for tracking...

  7. Long-range transport of air pollution into the Arctic

    Science.gov (United States)

    Stohl, A.; Berg, T.; Breivik, K.; Burkhart, J. F.; Eckhardt, S.; Fjæraa, A.; Forster, C.; Herber, A.; Lunder, C.; McMillan, W. W.; None, N.; Manø, S.; Oltmans, S.; Shiobara, M.; Stebel, K.; Hirdman, D.; Stroem, J.; Tørseth, K.; Treffeisen, R.; Virkkunen, K.; Yttri, K. E.; Andrews, E.; Kowal, D.; Mefford, T.; Ogren, J. A.; Sharma, S.; Spichtinger, N.; Stone, R.; Hoch, S.; Wehrli, C.

    2007-12-01

    This paper presents an overview of air pollution transport into the Arctic. The major transport processes will be highlighted, as well as their seasonal, interannual, and spatial variability. The source regions of Arctic air pollution will be discussed, with a focus on black carbon (BC) sources, as BC can produce significant radiative forcing in the Arctic. It is found that Europe is the main source region for BC in winter, whereas boreal forest fires are the strongest source in summer, especially in years of strong burning. Two case studies of recent extreme Arctic air pollution events will be presented. In summer 2004, boreal forest fires in Alaska and Canada caused pan-Arctic enhancements of black carbon. The BC concentrations measured at Barrow (Alaska), Alert (Canada), Summit (Greenland) and Zeppelin (Spitsbergen) were all episodically elevated, as a result of the long-range transport of the biomass burning emissions. Aerosol optical depth was also episodically elevated at these stations, with an almost continuous elevation over more than a month at Summit. During the second episode in spring 2006, new records were set for all measured air pollutant species at the Zeppelin station (Spitsbergen) as well as for ozone in Iceland. At Zeppelin, BC, AOD, aerosol mass, ozone, carbon monoxide and other compounds all reached new record levels, compared to the long-term monitoring record. The episode was caused by transport of polluted air masses from Eastern Europe deep into the Arctic, a consequence of the unusual warmth in the European Arctic during the episode. While fossil fuel combustion sources certainly contributed to this episode, smoke from agricultural fires in Eastern Europe was the dominant pollution component. We also suggest a new revolatilization mechanism for persistent organic pollutants (POPs) stored in soils and vegetation by fires, as POPs were strongly elevated during both episodes. All this suggests a considerable influence of biomass burning on

  8. A Transformer Class E Amplifier

    Directory of Open Access Journals (Sweden)

    Mikolajewski Miroslaw

    2014-12-01

    Full Text Available In a high-efficiency Class E ZVS resonant amplifier a matching and isolation transformer can replace some or even all inductive components of the amplifier thus simplifying the circuit and reducing its cost. In the paper a theoretical analysis, a design example and its experimental verification for a transformer Class E amplifier are presented. In the experimental amplifier with a transformer as the only inductive component in the circuit high efficiency ηMAX = 0.95 was achieved for supply voltage VI = 36 V, maximum output power POMAX = 100 W and the switching frequency f = 300 kHz. Measured parameters and waveforms showed a good agreement with theoretical predictions. Moreover, the relative bandwidth of the switching frequency was only 19% to obtain output power control from 4.8 W to POMAX with efficiency not less than 0.9 in the regulation range.

  9. TARC: Carlo Rubbia's Energy Amplifier

    CERN Multimedia

    Laurent Guiraud

    1997-01-01

    Transmutation by Adiabatic Resonance Crossing (TARC) is Carlo Rubbia's energy amplifier. This CERN experiment demonstrated that long-lived fission fragments, such as 99-TC, can be efficiently destroyed.

  10. New Packaging for Amplifier Slabs

    Energy Technology Data Exchange (ETDEWEB)

    Riley, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Thorsness, C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Suratwala, T. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Steele, R. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Rogowski, G. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-03-18

    The following memo provides a discussion and detailed procedure for a new finished amplifier slab shipping and storage container. The new package is designed to maintain an environment of <5% RH to minimize weathering.

  11. Transistor oscillator and amplifier grids

    OpenAIRE

    Weikle, Robert M., II; Kim, Moonil; Hacker, Jonathan B.; De Lisio, Michael P.; Popvić, Zoya B.; Rutledge, David B.

    1992-01-01

    Although quasi-optical techniques are applicable to a large variety of solid-state devices, special attention is given to transistors, which are attractive because they can be used as either amplifiers or oscillators. Experimental results for MESFET bar-grid and planar grid oscillators are presented. A MESFET grid amplifier that receives only vertically polarized waves at the input and radiates horizontally polarized waves at the output is discussed. These planar grids can be scaled for opera...

  12. A KIND OF NEW AMPLIFIER

    Institute of Scientific and Technical Information of China (English)

    YIN XUN-HE; FENG RU-PENG; REN YONG

    2000-01-01

    Chaotic characteristics in the iteration of logistic map (one-dimensional discrete dynamic system) are simulatedand analyzed. The circuit implementation of a kind of chaotic amplifier model is based on the chaotic characteristicsthat chaos is sensitively dependent on its initial conditions, and the circuit simulation result is given using simulationprogram with integrated circuit emphasis for personal computer (PSPICE), and is compared with linear amplifier.Advantages and disadvantages of such a model are indicated.

  13. Casimir force on amplifying bodies

    OpenAIRE

    Sambale, Agnes; Welsch, Dirk-Gunnar; Buhmann, Stefan Yoshi; Dung, Ho Trung

    2009-01-01

    Based on a unified approach to macroscopic QED that allows for the inclusion of amplification in a limited space and frequency range, we study the Casimir force as a Lorentz force on an arbitrary partially amplifying system of linearly locally responding (isotropic) magnetoelectric bodies. We demonstrate that the force on a weakly polarisable/magnetisable amplifying object in the presence of a purely absorbing environment can be expressed as a sum over the Casimir--Polder forces on the excite...

  14. State of the Arctic Environment

    International Nuclear Information System (INIS)

    The Arctic environment, covering about 21 million km2, is in this connection regarded as the area north of the Arctic Circle. General biological and physical features of the terrestrial and freshwater environments of the Arctic are briefly described, but most effort is put into a description of the marine part which constitutes about two-thirds of the total Arctic environment. General oceanography and morphological characteristics are included; e.g. that the continental shelf surrounding the Arctic deep water basins covers approximately 36% of the surface areas of Arctic waters, but contains only 2% of the total water masses. Blowout accident may release thousands of tons of oil per day and last for months. They occur statistically very seldom, but the magnitude underlines the necessity of an efficient oil spill contingency as well as sound safety and quality assurance procedures. Contingency plans should be coordinated and regularly evaluated through simulated and practical tests of performance. Arctic conditions demand alternative measures compared to those otherwise used for oil spill prevention and clean-up. New concepts or optimization of existing mechanical equipment is necessary. Chemical and thermal methods should be evaluated for efficiency and possible environmental effects. Both due to regular discharges of oil contaminated drilled cuttings and the possibility of a blowout or other spills, drilling operations in biological sensitive areas may be regulated to take place only during the less sensitive parts of the year. 122 refs., 8 figs., 8 tabs

  15. Nuanced Perceptions and Arctic Disputes

    DEFF Research Database (Denmark)

    Burke, Danita Catherine

    -depth consideration and analysis. As such, this thesis explores the complexities and evolution of the Canadian-Arctic relationship through two central research questions: how have the dominant cultural attitudes about the Canadian Arctic emerged and evolved within Canadian society and how have these cultural ideas...... interests and disputes in the Canadian Arctic region at the regional and international levels are affects by domestic cultural and political factors. The thesis was submitted in May 2015 and successfully defended in September 2015. The external examiner was Professor Philip Steinberg (Professor in the...

  16. Arctic warming, atmospheric blocking and cold European winters in CMIP5 models

    International Nuclear Information System (INIS)

    Amplified Arctic warming is expected to have a significant long-term influence on the midlatitude atmospheric circulation by the latter half of the 21st century. Potential influences of recent and near future Arctic changes on shorter timescales are much less clear, despite having received much recent attention in the literature. In this letter, climate models from the recent CMIP5 experiment are analysed for evidence of an influence of Arctic temperatures on midlatitude blocking and cold European winters in particular. The focus is on the variability of these features in detrended data and, in contrast to other studies, limited evidence of an influence is found. The occurrence of cold European winters is found to be largely independent of the temperature variability in the key Barents–Kara Sea region. Positive correlations of the Barents–Kara temperatures with Eurasian blocking are found in some models, but significant correlations are limited. (paper)

  17. Does ocean coupling matter for the northern extratropical response to projected Arctic sea ice loss?

    Science.gov (United States)

    Deser, Clara; Sun, Lantao; Tomas, Robert A.; Screen, James

    2016-03-01

    The question of whether ocean coupling matters for the extratropical Northern Hemisphere atmospheric response to projected late 21st century Arctic sea ice loss is addressed using a series of experiments with Community Climate System Model version 4 at 1° spatial resolution under different configurations of the ocean model component: no interactive ocean, thermodynamic slab ocean, and full-depth (dynamic plus thermodynamic) ocean. Ocean-atmosphere coupling magnifies the response to Arctic sea ice loss but does not change its overall structure; however, a slab ocean is inadequate for inferring the role of oceanic feedbacks. The westerly winds along the poleward flank of the eddy-driven jet weaken in response to Arctic sea ice loss, accompanied by a smaller-magnitude strengthening on the equatorward side, with largest amplitudes in winter. Dynamical and thermodynamic oceanic feedbacks amplify this response by approximately 50%. Air temperature, precipitation, and sea level pressure responses also show sensitivity to the degree of ocean coupling.

  18. The atmospheric role in the Arctic water cycle: A review on processes, past and future changes, and their impacts

    Science.gov (United States)

    Vihma, Timo; Screen, James; Tjernström, Michael; Newton, Brandi; Zhang, Xiangdong; Popova, Valeria; Deser, Clara; Holland, Marika; Prowse, Terry

    2016-03-01

    Atmospheric humidity, clouds, precipitation, and evapotranspiration are essential components of the Arctic climate system. During recent decades, specific humidity and precipitation have generally increased in the Arctic, but changes in evapotranspiration are poorly known. Trends in clouds vary depending on the region and season. Climate model experiments suggest that increases in precipitation are related to global warming. In turn, feedbacks associated with the increase in atmospheric moisture and decrease in sea ice and snow cover have contributed to the Arctic amplification of global warming. Climate models have captured the overall wetting trend but have limited success in reproducing regional details. For the rest of the 21st century, climate models project strong warming and increasing precipitation, but different models yield different results for changes in cloud cover. The model differences are largest in months of minimum sea ice cover. Evapotranspiration is projected to increase in winter but in summer to decrease over the oceans and increase over land. Increasing net precipitation increases river discharge to the Arctic Ocean. Over sea ice in summer, projected increase in rain and decrease in snowfall decrease the surface albedo and, hence, further amplify snow/ice surface melt. With reducing sea ice, wind forcing on the Arctic Ocean increases with impacts on ocean currents and freshwater transport out of the Arctic. Improvements in observations, process understanding, and modeling capabilities are needed to better quantify the atmospheric role in the Arctic water cycle and its changes.

  19. Impacts of a Warming Arctic. Arctic Climate Impact Assessment

    International Nuclear Information System (INIS)

    The Arctic is warming much more rapidly than previously known, at nearly twice the rate as the rest of the globe, and increasing greenhouse gases from human activities are projected to make it warmer still, according to an unprecedented four-year scientific study of the region conducted by an international team of 300 scientists. At least half the summer sea ice in the Arctic is projected to melt by the end of this century, along with a significant portion of the Greenland Ice Sheet, as the region is projected to warm an additional 4-7C by the year 2100. These changes will have major global impacts, such as contributing to global sea-level rise and intensifying global warming, according to the final report of the Arctic Climate Impact Assessment (ACIA). The assessment was commissioned by the Arctic Council (a ministerial intergovernmental forum comprised of the eight Arctic countries and six Indigenous Peoples organizations) and the International Arctic Science Committee (an international scientific organization appointed by 18 national academies of science). The assessment's projections are based on a moderate estimate of future emissions of carbon dioxide and other greenhouse gases, and incorporate results from five major global climate models used by the Intergovernmental Panel on Climate Change (IPCC)

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

    Science.gov (United States)

    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.

  1. Low-Noise Band-Pass Amplifier

    Science.gov (United States)

    Kleinberg, L.

    1982-01-01

    Circuit uses standard components to overcome common limitation of JFET amplifiers. Low-noise band-pass amplifier employs JFET and operational amplifier. High gain and band-pass characteristics are achieved with suitable choice of resistances and capacitances. Circuit should find use as low-noise amplifier, for example as first stage instrumentation systems.

  2. EMI-resilient amplifier circuits

    CERN Document Server

    van der Horst, Marcel J; Linnenbank, André C

    2014-01-01

    This book enables circuit designers to reduce the errors introduced by the fundamental limitations and electromagnetic interference (EMI) in negative-feedback amplifiers.  The authors describe a systematic design approach for application specific negative-feedback amplifiers, with specified signal-to-error ratio (SER).  This approach enables designers to calculate noise, bandwidth, EMI, and the required bias parameters of the transistors used in  application specific amplifiers in order to meet the SER requirements.   ·         Describes design methods that incorporate electromagnetic interference (EMI) in the design of application specific negative-feedback amplifiers; ·         Provides designers with a structured methodology to avoid the use of trial and error in meeting signal-to-error ratio (SER) requirements; ·         Equips designers to increase EMI immunity of the amplifier itself, thus avoiding filtering at the input, reducing the number of components and avoiding detr...

  3. Spectroscopic amplifier for pin diode

    International Nuclear Information System (INIS)

    The photodiode remains the basic choice for the photo-detection and is widely used in optical communications, medical diagnostics and field of corpuscular radiation. In detecting radiation it has been used for monitoring radon and its progeny and inexpensive spectrometric systems. The development of a spectroscopic amplifier for Pin diode is presented which has the following characteristics: canceler Pole-Zero (P/Z) with a time constant of 8 μs; constant gain of 57, suitable for the acquisition system; 4th integrator Gaussian order to waveform change of exponential input to semi-Gaussian output and finally a stage of baseline restorer which prevents Dc signal contribution to the next stage. The operational amplifier used is the TLE2074 of BiFET technology of Texas Instruments with 10 MHz bandwidth, 25 V/μs of slew rate and a noise floor of 17 nv/(Hz)1/2. The integrated circuit has 4 operational amplifiers and in is contained the total of spectroscopic amplifier that is the goal of electronic design. The results show like the exponential input signal is converted to semi-Gaussian, modifying only the amplitude according to the specifications in the design. The total system is formed by the detector, which is the Pin diode, a sensitive preamplifier to the load, the spectroscopic amplifier that is what is presented and finally a pulse height analyzer (Mca) which is where the spectrum is shown. (Author)

  4. SCICEX: Submarine Arctic Science Program

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Submarine Arctic Science Program, SCICEX, is a federal interagency collaboration among the operational Navy, research agencies, and the marine research...

  5. Arctic Terrestrial Biodiversity Monitoring Plan

    DEFF Research Database (Denmark)

    Christensen, Tom; Payne, J.; Doyle, M.;

    -Terrestrial Plan/the Plan) as the framework for coordinated, long-term Arctic terrestrial biodiversity monitoring. The goal of the CBMP-Terrestrial Plan is to improve the collective ability of Arctic traditional knowledge (TK) holders, northern communities, and scientists to detect, understand and report on long......-term change in Arctic terrestrial ecosystems and biodiversity. The CBMP-Terrestrial Plan aims to address these priority management questions: 1. What are the status, distribution, and conditions of terrestrial focal species, populations, communities, and landscapes/ecosystems and key processes...... network of scientists, conservation organizations, government agencies, Permanent Participants Arctic community experts and leaders. Using an ecosystem-based monitoring approach which includes species, ecological functions, ecosystems, their interactions, and potential drivers, the CBMP focuses on...

  6. Development of arctic wind technology

    Energy Technology Data Exchange (ETDEWEB)

    Holttinen, H.; Marjaniemi, M.; Antikainen, P. [VTT Energy, Espoo (Finland)

    1998-10-01

    The climatic conditions of Lapland set special technical requirements for wind power production. The most difficult problem regarding wind power production in arctic regions is the build-up of hard and rime ice on structures of the machine

  7. Identification of Forest Vegetation Using Vegetation Indices

    Institute of Scientific and Technical Information of China (English)

    Yuan Jinguo; Wang Wei

    2004-01-01

    Spectral feature of forest vegetation with remote sensing techniques is the research topic all over the world, because forest plays an important role in human beings' living environment. Research on vegetation classification with vegetation index is still very little recently. This paper proposes a method of identifying forest types based on vegetation indices,because the contrast of absorbing red waveband with reflecting near-infrared waveband strongly for different vegetation types is recognized as the theoretic basis of vegetation analysis with remote sensing. Vegetation index is highly related to leaf area index, absorbed photosynthetically active radiation and vegetation cover. Vegetation index reflects photosynthesis intensity of plants and manifests different forest types. According to reflectance data of forest canopy and soil line equation NIR=1.506R+0.0076 in Jingyuetan, Changchun of China, many vegetation indices are calculated and analyzed. The result shows that the relationships between vegetation indices and forest types are that perpendicular vegetation index (PVI) identifies broadleaf forest and coniferous forest the most easily;the next is transformed soil-adjusted vegetation index(TSVI) and modified soil-adjusted vegetation index(MSVI), but their calculation is complex. Ratio vegetation index (RVT) values of different coniferous forest vary obviously, so RVI can classify conifers.Therefore, the combination of PVI and RVI is evaluated to classify different vegetation types.

  8. Vegetation development on extensive vegetated green roofs

    OpenAIRE

    Emilsson, Tobias

    2008-01-01

    Technology for establishment of vegetated roofs (green roofs) has developed rapidly over recent years but knowledge about how these systems will develop over time is still limited. This study investigates vegetation development on unfertilised thin extensive vegetated roofs during a 3-year period. The vegetation systems investigated were designed to be low maintenance and had a saturated weight of 50 kg/m2, a thickness of 4 cm and drought-resistant succulent and bryophyte vegetation. Vegetati...

  9. Carbon dioxide and methane fluxes from arctic mudboils

    International Nuclear Information System (INIS)

    Carbon-rich ecosystems in the Arctic have large stores of soil carbon. However, small changes in climate have the potential to change the carbon (C) balance. This study examined how changes in ecosystem structure relate to differences in the exchange of greenhouse gases, notably carbon dioxide (CO2) and methane (CH4), between the atmosphere and soil. In particular, it examined low-center mudboils to determine the influence that this distinct form of patterned ground in the Arctic may have on the overall C balance of Tundra ecosystems. The net ecosystem exchange of carbon dioxide (NEE) was measured along with methane efflux along a 35-m transect intersecting two mudboils in a wet sedge fen in Canada's Southern Arctic during the summer of 2008. Mudboil features revealed significant variations in vegetation, soil temperature and thaw depth, and soil organic matter content along this transect. Variations in NEE were attributed to changes in the amount of vascular vegetation, but CO2 and CH4 effluxes were similar among the two mudboil and the sedge fen sampling areas. The study showed that vegetation played a key role in limiting temporal variations in CH4 effluxes through plant mediated transport in both mudboil and sedge fen sampling areas. The negligible vascular plant colonization in one of the mudboils was likely due to more active frost heave processes. Growth and decomposition of cryptogamic organisms along with inflow of dissolved organic C and warmer soil temperatures may have been the cause of the rather high CO2 and CH4 efflux in this mudboil area.

  10. Gaussian amplifier for nuclear spectrometry

    International Nuclear Information System (INIS)

    One of the major goals of nuclear spectrometry is the determination of the energy spectrum of a radioactive source. To measure this spectrum with electronic instrumentation one need to use a nuclear spectrometry chain of which the amplifier is part of, and whose filter shaping considerably influences the final energy resolution achieved. The amplifier released accomplishes a 7th order Gaussian filter shape with Taylor series approximation synthesized by the Shifted Companion Form and mounted using only electronic components availablein Brazil. The final version has been tested and the results showed a very good performance and the energy resolution achieved was equivalent to the imported models. (Author)

  11. Circumpolar Arctic greening: Relationships to summer sea-ice concentrations, land temperatures and disturbance regimes

    Science.gov (United States)

    Walker, D. A.; Bhatt, U. S.; Epstein, H. E.; Raynolds, M. K.; Frost, G. V.; Leibman, M. O.; Khomutov, A.; Jia, G.; Comiso, J. C.; Pinzon, J. E.; Tucker, C. J.; Webber, P. J.; Tweedie, C. E.

    2009-12-01

    The global distribution of Arctic tundra vegetation is closely tied to the presence of summer sea ice. Models predict that the reduction of sea ice will cause large changes to summer land-surface temperatures. Warming combined with increased natural and anthropogenic disturbance are expected to greatly increase arctic tundra productivity. To examine where tundra productivity is changing most rapidly, we studied 1982-2008 trends of sea-ice concentrations, summer warmth index (SWI) and the annual Maximum Normalized Difference Vegetation Index (MaxNDVI). We summarize the results according to the tundra adjacent to 14 Arctic seas. Sea-ice concentrations have declined and summer land temperatures have increased in all parts of the Arctic coast. The overall percentage increase in Arctic MaxNDVI was +7%. The trend was much greater in North America (+11%) than in Eurasia (+4%). Large percentage increases of MaxNDVI occurred inland from Davis Straight (+20%), Baffin Bay (+18%), Canadian Archipelago (+14%), Beaufort Sea (+12%), and Laptev Sea (+8%). Declines occurred in the W. Chukchi (-6%) and E. Bering (-5%) seas. The changes in NDVI are strongly correlated to changes in summer ground temperatures. Two examples from a 900-km north-south Arctic transect in Russia and long-term observations at a High Arctic site in Canada provide insights to where the changes in productivity are occurring most rapidly. At tree line near Kharp in northwest Siberia, alder shrubs are expanding vigorously in fire-disturbed areas; seedling establishment is occurring primarily in areas with disturbed mineral soils, particularly nonsorted circles. In the Low Arctic tundra areas of the central Yamal Peninsula greening is concentrated in riparian areas and upland landslides associated with degrading massive ground ice, where low-willow shrublands replace the zonal sedge, dwarf-shrub tundra growing on nutrient-poor sands. In polar desert landscapes near the Barnes Ice Cap, Baffin Island, Canada

  12. 77 FR 31677 - Request for Public Comment on Interagency Arctic Research Policy Committee (IARPC) Arctic...

    Science.gov (United States)

    2012-05-29

    ... TECHNOLOGY POLICY Request for Public Comment on Interagency Arctic Research Policy Committee (IARPC) Arctic Research Plan: FY2013-2017 May 22, 2012. ACTION: Request for public comment. SUMMARY: The Arctic Research and Policy Act of 1984 (ARPA), Public Law 98-373, established the Interagency Arctic Research...

  13. A characterization of Arctic aerosols on the basis of aerosol optical depth and black carbon measurements

    Directory of Open Access Journals (Sweden)

    R. S. Stone

    2014-06-01

    Full Text Available Abstract Aerosols, transported from distant source regions, influence the Arctic surface radiation budget. When deposited on snow and ice, carbonaceous particles can reduce the surface albedo, which accelerates melting, leading to a temperature-albedo feedback that amplifies Arctic warming. Black carbon (BC, in particular, has been implicated as a major warming agent at high latitudes. BC and co-emitted aerosols in the atmosphere, however, attenuate sunlight and radiatively cool the surface. Warming by soot deposition and cooling by atmospheric aerosols are referred to as “darkening” and “dimming” effects, respectively. In this study, climatologies of spectral aerosol optical depth AOD (2001–2011 and Equivalent BC (EBC (1989–2011 from three Arctic observatories and from a number of aircraft campaigns are used to characterize Arctic aerosols. Since the 1980s, concentrations of BC in the Arctic have decreased by more than 50% at ground stations where in situ observations are made. AOD has increased slightly during the past decade, with variations attributed to changing emission inventories and source strengths of natural aerosols, including biomass smoke and volcanic aerosol, further influenced by deposition rates and airflow patterns.

  14. A wideband dc-coupled amplifier

    International Nuclear Information System (INIS)

    A method is described whereby an ac-coupled high-frequency amplifier and a dc-coupled low-frequency amplifier are connected in parallel in order to obtain a dc-coupled wideband amplifier. By using an operational amplifier which compares the output voltage with the input voltage, the low-frequency amplifier contributes to the overall gain only when the gain of the ac-coupled amplifier droops at low frequencies. Thus, no frequency splitting networks are necessary and the excellent low-frequency features of an operational amplifier are added to those of the ac-coupled wideband amplifier. As an example, a low noise amplifier is described which exhibits a hundredfold gain, a bandwidth from dc to 550 MHz, an input bias current of less than 1 nA, and an output voltage range of ±1 V

  15. Arctic cities and climate change: climate-induced changes in stability of Russian urban infrastructure built on permafrost

    Science.gov (United States)

    Shiklomanov, Nikolay; Streletskiy, Dmitry; Swales, Timothy

    2014-05-01

    Planned socio-economic development during the Soviet period promoted migration into the Arctic and work force consolidation in urbanized settlements to support mineral resources extraction and transportation industries. These policies have resulted in very high level of urbanization in the Soviet Arctic. Despite the mass migration from the northern regions during the 1990s following the collapse of the Soviet Union and the diminishing government support, the Russian Arctic population remains predominantly urban. In five Russian Administrative regions underlined by permafrost and bordering the Arctic Ocean 66 to 82% (depending on region) of the total population is living in Soviet-era urban communities. The political, economic and demographic changes in the Russian Arctic over the last 20 years are further complicated by climate change which is greatly amplified in the Arctic region. One of the most significant impacts of climate change on arctic urban landscapes is the warming and degradation of permafrost which negatively affects the structural integrity of infrastructure. The majority of structures in the Russian Arctic are built according to the passive principle, which promotes equilibrium between the permafrost thermal regime and infrastructure foundations. This presentation is focused on quantitative assessment of potential changes in stability of Russian urban infrastructure built on permafrost in response to ongoing and future climatic changes using permafrost - geotechnical model forced by GCM-projected climate. To address the uncertainties in GCM projections we have utilized results from 6 models participated in most recent IPCC model inter-comparison project. The analysis was conducted for entire extent of Russian permafrost-affected area and on several representative urban communities. Our results demonstrate that significant observed reduction in urban infrastructure stability throughout the Russian Arctic can be attributed to climatic changes and that

  16. Characterisation Of Low Noise Amplifier

    Directory of Open Access Journals (Sweden)

    MAULIK B.PATEL

    2012-08-01

    Full Text Available Amplification is one of the most basic and prevalent microwave circuit functions inmodern RF and microwave systems. Early microwave amplifiers relied on tubes, such asklystrons and traveling-wave tubes, or solid-state reflection amplifiers based on thenegative resistance characteristics of tunnel or varactor diodes. But due to the dramaticimprovements and innovations in solid-state technology that have occurred since the1970s, most RF and microwave amplifiers today use transistor devices such as Si or SiGeBJTs, GaAs HBTs, GaAs or InP FETs, or GaAs HEMTs. Microwave transistor amplifiersare rugged, low-cost, reliable, and can be easily integrated in both hybrid andmonolithic integrated circuitry. Transistor amplifiers can be used at frequencies inexcess of 100 GHz in a wide range of applications requiring small size, low-noise figure,broad bandwidth, and low to medium power capacity. Although microwave tubes are stillrequired for very high power and/or very high frequency applications, continuingimprovement in the performance of microwave transistors is steadily reducing the needfor microwave tubes

  17. Dielectric waveguide amplifiers and lasers

    NARCIS (Netherlands)

    Pollnau, M.

    2014-01-01

    The performance of semiconductor amplifiers and lasers has made them the preferred choice for optical gain on a micro-chip. In the past few years, we have demonstrated that also rare-earth-ion-doped dielectric waveguides show remarkable performance, ranging from a small-signal gain per unit length o

  18. The Arctic policy of China and Japan

    DEFF Research Database (Denmark)

    Tonami, Aki

    2014-01-01

    At the May 2013 Arctic Council Ministerial Meeting, five Asian states, namely China, Japan, India, Singapore and South Korea, were accepted to become new Permanent Observers at the Arctic Council. Nonetheless, little attention has been paid to the Asian states and their interest in the Arctic. Most...... discussions have focused on China and the assessment of China’s interest in the Arctic is divided. This paper attempts to fill this gap by presenting and comparing the various components of the Arctic policies of China and Japan. Referring to Putnam’s model of the “two-level game” and Young’s categorization...... of Arctic stakeholders’ interests, data from policy documents and interviews with relevant stakeholders were analysed. This analysis shows the Chinese and Japanese governments are in the gradual process of consolidating their Arctic policies, but both China and Japan see the Arctic less as a...

  19. Low Cost RF Amplifier for Community TV

    Science.gov (United States)

    Ch, Syafaruddin; Sasongko, Sudi Mariyanto Al; Made Budi Suksmadana, I.; Mustiko Okta Muvianto, Cahyo; Ariessaputra, Suthami

    2016-01-01

    he capability of television to deliver audio video makes this media become the most effective method to spread information. This paper presents an experiment of RF amplifier design having low-cost design and providing sufficient RF power particularly for community television. The RF amplifier consists of two stages of amplifier. The first stage amplifier was used to leverage output of TV modulator from 11dBm to enable to drive next stage amplifier. CAD simulation and fabrication were run to reach optimum RF amplifier design circuit. The associated circuit was made by determining stability circle, stability gain, and matching impedance. Hence, the average power of first stage RF amplifier was 24.68dBm achieved. The second stage used RF modules which was ready match to 50 ohm for both input and output port. The experiment results show that the RF amplifier may operate at frequency ranging from 174 to 230MHz. The average output power of the 2nd stage amplifier was 33.38 Watt with the overall gain of 20.54dB. The proposed RF amplifier is a cheap way to have a stable RF amplifier for community TV. The total budget for the designed RF amplifier is only a 1/5 compared to local design of final TV amplifier.

  20. Arctic Landscape Within Reach

    Science.gov (United States)

    2008-01-01

    This image, one of the first captured by NASA's Phoenix Mars Lander, shows flat ground strewn with tiny pebbles and marked by small-scale polygonal cracking, a pattern seen widely in Martian high latitudes and also observed in permafrost terrains on Earth. The polygonal cracking is believed to have resulted from seasonal contraction and expansion of surface ice. Phoenix touched down on the Red Planet at 4:53 p.m. Pacific Time (7:53 p.m. Eastern Time), May 25, 2008, in an arctic region called Vastitas Borealis, at 68 degrees north latitude, 234 degrees east longitude. This image was acquired at the Phoenix landing site by the Surface Stereo Imager on day 1 of the mission on the surface of Mars, or Sol 0, after the May 25, 2008, landing. The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  1. Audubon vegetation monitoring

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This document is the summary and the analysis of vegetative data for the Audubon Refuge from NPWRC. The data included measurements of vegetation density, vegetation...

  2. Rich and cold: diversity, distribution and drivers of fungal communities in patterned-ground ecosystems of the North American Arctic.

    Science.gov (United States)

    Timling, I; Walker, D A; Nusbaum, C; Lennon, N J; Taylor, D L

    2014-07-01

    Fungi are abundant and functionally important in the Arctic, yet comprehensive studies of their diversity in relation to geography and environment are not available. We sampled soils in paired plots along the North American Arctic Transect (NAAT), which spans all five bioclimatic subzones of the Arctic. Each pair of plots contrasted relatively bare, cryoturbated patterned-ground features (PGFs) and adjacent vegetated between patterned-ground features (bPGFs). Fungal communities were analysed via sequencing of 7834 ITS-LSU clones. We recorded 1834 OTUs - nearly half the fungal richness previously reported for the entire Arctic. These OTUs spanned eight phyla, 24 classes, 75 orders and 120 families, but were dominated by Ascomycota, with one-fifth belonging to lichens. Species richness did not decline with increasing latitude, although there was a decline in mycorrhizal taxa that was offset by an increase in lichen taxa. The dominant OTUs were widespread even beyond the Arctic, demonstrating no dispersal limitation. Yet fungal communities were distinct in each subzone and were correlated with soil pH, climate and vegetation. Communities in subzone E were distinct from the other subzones, but similar to those of the boreal forest. Fungal communities on disturbed PGFs differed significantly from those of paired stable areas in bPGFs. Indicator species for PGFs included lichens and saprotrophic fungi, while bPGFs were characterized by ectomycorrhizal and pathogenic fungi. Our results suggest that the Arctic does not host a unique mycoflora, while Arctic fungi are highly sensitive to climate and vegetation, with potential to migrate rapidly as global change unfolds. PMID:24689939

  3. Arctic char - friend or foe?: Climate driven seasonal variation in competitive impact of Arcticchar (Salvelinus alpinus L) on brown trout (Salmo truttaence L)

    OpenAIRE

    Ulvan, Eva Marita

    2010-01-01

    Here I test for climate driven seasonal effects on competition in lakes using brown trout (Salmo trutta L.) and Arctic char (Salvelinus alpinus L.) as model organisms. Winter and summer brown trout consumption rates were estimated by 1374 Cs tracer methodology using brown trout sampled in  allopatric (brown trout) and 10 sympatric (brown trout/Arctic char) lakes, located along an altitudinal gradient in central Scandinavia. Lake catchment area  vegetation properties ranged from southern borea...

  4. Modeling the Arctic freshwater system and its integration in the global system: Lessons learned and future challenges

    Science.gov (United States)

    Lique, Camille; Holland, Marika M.; Dibike, Yonas B.; Lawrence, David M.; Screen, James A.

    2016-03-01

    Numerous components of the Arctic freshwater system (atmosphere, ocean, cryosphere, and terrestrial hydrology) have experienced large changes over the past few decades, and these changes are projected to amplify further in the future. Observations are particularly sparse, in both time and space, in the polar regions. Hence, modeling systems have been widely used and are a powerful tool to gain understanding on the functioning of the Arctic freshwater system and its integration within the global Earth system and climate. Here we present a review of modeling studies addressing some aspect of the Arctic freshwater system. Through illustrative examples, we point out the value of using a hierarchy of models with increasing complexity and component interactions, in order to dismantle the important processes at play for the variability and changes of the different components of the Arctic freshwater system and the interplay between them. We discuss past and projected changes for the Arctic freshwater system and explore the sources of uncertainty associated with these model results. We further elaborate on some missing processes that should be included in future generations of Earth system models and highlight the importance of better quantification and understanding of natural variability, among other factors, for improved predictions of Arctic freshwater system change.

  5. Environmental radioactivity in the Arctic

    International Nuclear Information System (INIS)

    The conference considered several broad themes: (1) assessment of releases from landbased sources and river transport, (2) assessment of dumping of nuclear waste, (3) arctic radioecology, (4) assessment of impacts of nuclear explosions and accidents, (5) nuclear safety and consequences of nuclear accidents in the arctic, and (6) waste management. The presentations demonstrated that current levels of radioactivity in the Arctic are generally low. The two most important sources are global fallout from the nuclear weapons tests of the 1950's and 1960's, and discharges to the sea from reprocessing plants in Western Europe which are transported northward by prevailing currents. The conference was attended by scientists from 17 countries and served as a forum for collection and dissemination of information on the range of themes and described above. It is hoped that this will serve to increase awareness of areas of uncertainty and act as a stimulus to further research

  6. Amplifying the evanescent field of free electrons

    OpenAIRE

    So, J.-K.; Ou, J.-Y.; Adamo, G.; García de Abajo, F. J.; MacDonald, K. F.; Zheludev, N.I.

    2013-01-01

    We provide the first experimental demonstration that the evanescent field of free electrons can be amplified by a plasmonic nanolayer in much that same way as optical evanescent fields are amplified in the ‘poor-man’s superlens’.

  7. Amplifying free-electron evanescent fields

    OpenAIRE

    So, J.-K.; Ou, J.-Y.; Adamo, G.; García de Abajo, F. J.; MacDonald, K. F.; Zheludev, N.I.

    2013-01-01

    We show experimentally for the first time that free-electron evanescent fields can be amplified by a plasmonic nanolayer in a manner analogous to the way in which optical fields are amplified in the poor-man's superlens.

  8. Analog circuit design designing high performance amplifiers

    CERN Document Server

    Feucht, Dennis

    2010-01-01

    The third volume Designing High Performance Amplifiers applies the concepts from the first two volumes. It is an advanced treatment of amplifier design/analysis emphasizing both wideband and precision amplification.

  9. Compact dual channel spectroscopy amplifier cum discriminator

    International Nuclear Information System (INIS)

    A single width NIM module having two channels of spectroscopy amplifier cum discriminator has been developed for Nuclear Physics experiments at IUAC. Each channel contains a shaping amplifier along with logic circuits to generate the energy and timing information respectively

  10. Lake Bathymetric Aquatic Vegetation

    Data.gov (United States)

    Minnesota Department of Natural Resources — Aquatic vegetation represented as polygon features, coded with vegetation type (emergent, submergent, etc.) and field survey date. Polygons were digitized from...

  11. Single conversion stage amplifier - SICAM

    Energy Technology Data Exchange (ETDEWEB)

    Ljusev, P.

    2005-12-15

    This Ph.D. thesis presents a thorough analysis of the so called SICAM - SIngle Converter stage AMplifier approach to building direct energy conversion audio power amplifiers. The mainstream approach for building isolated audio power amplifiers today consists of isolated DC power supply and Class D amplifier, which essentially represents a two stage solution, where each of the components can be viewed as separate and independent part. The proposed SICAM solution strives for direct energy conversion from the mains to the audio output, by dedicating the operation of the components one to another and integrating their functions, so that the final audio power amplifier represents a single-stage topology with higher efficiency, lower volume, less board space, lower component count and subsequently lower cost. The SICAM approach is both applicable to non-isolated and isolated audio power amplifiers, but the problems encountered in these two cases are different. Non-isolated SICAM solutions are intended for both AC mains-connected and battery-powered devices. In non-isolated mains-connected SICAMs the main idea is to simplify the power supply or even provide integrated power factor correction (PFC) functions, while still maintaining low component stress and good audio performance by generally decreasing the input voltage level to the Class D audio power amplifier. On the other hand, non-isolated battery-powered SICAMs have to cope with the ever changing battery voltage and provide output voltage levels which are both lower and higher than the battery voltage, while still being simple and single-stage energy conversion solutions. In isolated SICAMs the isolation transformer adjusts the voltage level on the secondary side to the desired level, so the main challenges here are decreasing the size of the magnetic core and reducing the number and size of bulky reactive components as much as possible. The main focus of this thesis is directed towards the isolated SICAMs and

  12. Arctic Energy Resources: Energy Research

    Science.gov (United States)

    Gryc, George

    1984-04-01

    Arctic Energy Resources is a volume of 26 papers recording the proceedings of the Comite' Arctique International Conference, held at the Veritas Centre, Oslo, Norway, September 22-24, 1982. This was the fourth of a series of meetings on the Arctic organized by the Comite', an organization established in the Principality of Monaco with the active support of H.S.H. Prince Rainer III. The fourth Conference was opened by H.R.H. Crown Prins Harald of Norway, a noble beginning for a noble objective.The North Polar Region has drawn world attention recently because of several large hydrocarbon and other mineral discoveries and because of major political and environmental actions in the North American Arctic. Since 1923 when Naval Petroleum Reserve number 4 (NPR-4) was established, northern Alaska has been considered a major petroleum province. It was first explored systematically with modern techniques from 1943 to 1953. In 1958, Alaska became a state, and both federal and state lands in northern Alaska were available for private exploration. Building on the knowledge base provided by the Pet-4 program and its spinoff research laboratory at Barrow, industry explored the area east of NPR-4 and discovered the largest hydrocarbon accumulation (9.6 bbl crude oil and 26 Tcf (trillion cubic feet) gas) in North America at Prudhoe Bay. Concerns for environmental impacts, including oil spills, led to the passing of the National Environmental Policy Act in 1969. In 1970, over 9 million acres were set aside, now known as the Arctic National Wildlife Range, and in 1971 the Alaska Native Claims Settlement Act was passed by the U.S. Congress. The Arab oil embargo of 1973 heightened the energy crisis and changed the economic basis for further exploration in the Arctic. The convergence of these events dramatically changed the balance of power and the pace of activity in the North American Arctic.

  13. European Research on THz Vacuum Amplifiers

    DEFF Research Database (Denmark)

    Brunetti, F.; Cojocarua, C.-S.; de Rossi, A.; Di Carlo, A.; Dispenza, M.; Dolfi, D.; Durand, A.; Fiorello, A.; Gohier, A.; Guiset, P.; Korantia, M.; Krozer, V.; Legagneux, P.; Marchesin, R.; Megtert, S.; Bouamrane, F.; Mineo, M.; Paoloni, C.; Pham, K.; Schnell, J.P.; Secchi, A.; Tamburri, E.; Terranova, M.L.; Ulisse, G.; Zhurbenko, Vitaliy

    The OPTHER (OPtically Driven TeraHertz AmplifiERs) project represents a considerable advancement in the field of high frequency amplification. The design and realization of a THz amplifier within this project is a consolidation of efforts at the international level from the main players of the Eu...... European research, academy and industry in vacuum electronics. This paper describes the status of the project and progress towards the THz amplifier realization....

  14. Improved charge amplifier using hybrid hysteresis compensation

    Science.gov (United States)

    Amin-Shahidi, Darya; Trumper, David L.

    2013-08-01

    We present a novel charge amplifier, with a robust feedback circuit and a method for compensating piezoelectric actuator's hysteresis at low frequencies. The amplifier uses a modified feedback circuit which improves robustness to the addition of series load impedance such as in cabling. We also describe a hybrid hysteresis compensation method for enabling the charge amplifier to reduce hysteresis at low frequencies. Experimental results demonstrate the utility of the new amplifier design.

  15. Quantum Theory of Laser Amplifiers.

    Science.gov (United States)

    Mander, Gillian Linda

    Available from UMI in association with The British Library. Requires signed TDF. We calculate the input-output characteristics of a below threshold laser amplifier. Expressions are derived for the output second- and fourth-order spectral and temporal correlation functions in terms of the corresponding input quantities, and for the photocount first and second factorial moments for both homodyne and direct detection. The general results are applied to several cases of practical interest, including specific non-classical input states. We show that a maximum of twofold amplification is permitted if squeezing in the input is to survive at the output. Similarly, for preservation of photon antibunching in amplification we show that only very small gains are allowed. The model treated here provides a detailed example of the amplifier noise limitations imposed by quantum mechanics. In particular, we show that minimum noise occurs in a cavity that is asymmetric with respect to the mirror reflectivities. The latter part of this work treats the above threshold laser amplifier. The laser output is back-scattered from a moving target to provide a weak Doppler-shifted signal which re-enters the laser cavity and is amplified. We show that the three-level atomic lasing medium is equivalent to a two-level medium pumped by an inverted bath. We use the methods of quantum statistical analysis to obtain time -evolution equations for the c-number amplitudes of the laser and signal fields. We show that the results may be applied to the below threshold regime for appropriate values of the pump parameter. By considering the amplitude differential gain we show explicitly that the behaviour of the laser around threshold is characteristic of a second -order phase transition. We calculate the output intensity gain appropriate to a heterodyne detection process, and find good agreement between the predicted gain profiles and measured data for both carbon dioxide and argon-ion lasers.

  16. Compact, harmonic multiplying gyrotron amplifiers

    Energy Technology Data Exchange (ETDEWEB)

    Guo, H.Z.; Granatstein, V.L.; Antonsen, T.M. Jr.; Levush, B.; Tate, J.; Chen, S.H. [Univ. of Maryland, College Park, MD (United States). Inst. for Plasma Research

    1995-12-31

    A compact, harmonic multiplying gyrotron traveling wave amplifier is being developed. The device is a three-stage tube with the output section running as a fourth harmonic gyro-TWT, the input section running as a fundamental gyro-TWT, and the middle operating at the second harmonic of the cyclotron frequency. Radiation is suppressed by servers between the sections. The operating beam of the tube is produced by a magnetron injection gun (MIG). A TE{sub 0n} mode selective interaction circuit consisting of mode converters and a filter waveguide is employed for both input and output sections to solve the mode competition problem, which is pervasive in gyro-TWT operation. The input section has an input coupler designed as a TE{sub 0n} mode launcher. It excites a signal at the fundamental cyclotron frequency (17.5 GHz), which is amplified in the first TWT interaction region. So far the device is similar to a two-stage harmonic gyro-TWT. The distinction is that in the three-stage device the second section will be optimized not for output power but for fourth harmonic bunching of the beam. A gyroklystron amplifier has also been designed. The configuration is similar to the gyro-TWT but with the traveling wave interaction structures replaced by mode selective special complex cavities. Cold test results of the wideband input coupler and the TE{sub 0n} mode selective interaction circuit have been obtained.

  17. SPS RF System Amplifier plant

    CERN Multimedia

    1977-01-01

    The picture shows a 2 MW, 200 MHz amplifier plant with feeder lines. The main RF-system of the SPS comprises four cavities: two of 20 m length and two of 16.5 m length. They are all installed in one long straight section (LSS 3). These cavities are of the travelling-wave type operating at a centre frequency of 200.2 MHz. They are wideband, filling time about 700 ns and untuned. The power amplifiers, using tetrodes are installed in a surface building 200 m from the cavities. Initially only two cavities were installed, a third cavity was installed in 1978 and a forth one in 1979. The number of power amplifiers was also increased: to the first 2 MW plant a second 2 MW plant was added and by end 1979 there were 8 500 kW units combined in pairs to feed each of the 4 cavities with up to about 1 MW RF power, resulting in a total accelerating voltage of about 8 MV. See also 7412016X, 7412017X, 7411048X.

  18. European Research on THz Vacuum Amplifiers

    DEFF Research Database (Denmark)

    Brunetti, F.; Cojocarua, C.-S.; de Rossi, A.;

    2010-01-01

    The OPTHER (OPtically Driven TeraHertz AmplifiERs) project represents a considerable advancement in the field of high frequency amplification. The design and realization of a THz amplifier within this project is a consolidation of efforts at the international level from the main players of the Eu...

  19. NASA developments in solid state power amplifiers

    Science.gov (United States)

    Leonard, Regis F.

    1990-01-01

    Over the last ten years, NASA has undertaken an extensive program aimed at development of solid state power amplifiers for space applications. Historically, the program may be divided into three phases. The first efforts were carried out in support of the advanced communications technology satellite (ACTS) program, which is developing an experimental version of a Ka-band commercial communications system. These first amplifiers attempted to use hybrid technology. The second phase was still targeted at ACTS frequencies, but concentrated on monolithic implementations, while the current, third phase, is a monolithic effort that focusses on frequencies appropriate for other NASA programs and stresses amplifier efficiency. The topics covered include: (1) 20 GHz hybrid amplifiers; (2) 20 GHz monolithic MESFET power amplifiers; (3) Texas Instruments' (TI) 20 GHz variable power amplifier; (4) TI 20 GHz high power amplifier; (5) high efficiency monolithic power amplifiers; (6) GHz high efficiency variable power amplifier; (7) TI 32 GHz monolithic power amplifier performance; (8) design goals for Hughes' 32 GHz variable power amplifier; and (9) performance goals for Hughes' pseudomorphic 60 GHz power amplifier.

  20. Solid state, S-band, power amplifier

    Science.gov (United States)

    Digrindakis, M.

    1973-01-01

    The final design and specifications for a solid state, S-band, power amplifier is reported. Modifications from a previously proposed design were incorporated to improve efficiency and meet input overdrive and noise floor requirements. Reports on the system design, driver amplifier, power amplifier, and voltage and current limiter are included along with a discussion of the testing program.

  1. Solid state ku-band power amplifier

    Science.gov (United States)

    Bowers, H. C.; Lockyear, W. H.

    1972-01-01

    The design, fabrication, and testing of two types of IMPATT diode reflection amplifiers and a transmission amplifier are given. The Ku-band IMPATT diode development is discussed. Circuitry and electrical performance of the final version of the Ku-band amplifier is described. Construction details and an outline and mounting drawing are presented.

  2. low pump power photonic crystal fibre amplifiers

    DEFF Research Database (Denmark)

    Hougaard, Kristian G.; Broeng, Jes; Bjarklev, Anders Overgaard

    2003-01-01

    Designs of low pump power optical amplifiers, based on photonic crystal fibres are presented. The potential of these fibre amplifiers is investigated, and it is demonstrated that such amplifiers may deliver gains of more than 15 dB at 1550 nm with less than 1 mW of optical pump power....

  3. U.S. Arctic Research Commission

    Science.gov (United States)

    “North to the Future” is a well-known slogan in Alaska. This slogan also expresses the spirit with which the U.S. Arctic Research Commission (ARC) has begun its work.The commission was established as a result of Sen. Murkowski's (R-Alaska) Arctic Research and Policy Act of 1984, and its members were appointed by President Reagan last February (Eos, February 26, 1985, p. 91). The ARC has been directed to develop and recommend an integrated Arctic research policy and to work with the concomitantly established Interagency Arctic Research Policy Committee in the formulation of a comprehensive 5-year Arctic research plan (see Figure 1). The Arctic Research and Policy Act designates the National Science Foundation as the lead agency responsible for implementing the policy with other federal agencies; it further requires the preparation of a single, integrated multiagency budget request for Arctic research.

  4. Changing Seasonality of Tundra Vegetation and Associated Climatic Variables

    Science.gov (United States)

    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

  5. Arctic Glass: Innovative Consumer Technology in Support of Arctic Research

    Science.gov (United States)

    Ruthkoski, T.

    2015-12-01

    The advancement of cyberinfrastructure on the North Slope of Alaska is drastically limited by location-specific conditions, including: unique geophysical features, remoteness of location, and harsh climate. The associated cost of maintaining this unique cyberinfrastructure also becomes a limiting factor. As a result, field experiments conducted in this region have historically been at a technological disadvantage. The Arctic Glass project explored a variety of scenarios where innovative consumer-grade technology was leveraged as a lightweight, rapidly deployable, sustainable, alternatives to traditional large-scale Arctic cyberinfrastructure installations. Google Glass, cloud computing services, Internet of Things (IoT) microcontrollers, miniature LIDAR, co2 sensors designed for HVAC systems, and portable network kits are several of the components field-tested at the Toolik Field Station as part of this project. Region-specific software was also developed, including a multi featured, voice controlled Google Glass application named "Arctic Glass". Additionally, real-time sensor monitoring and remote control capability was evaluated through the deployment of a small cluster of microcontroller devices. Network robustness was analyzed as the devices delivered streams of abiotic data to a web-based dashboard monitoring service in near real time. The same data was also uploaded synchronously by the devices to Amazon Web Services. A detailed overview of solutions deployed during the 2015 field season, results from experiments utilizing consumer sensors, and potential roles consumer technology could play in support of Arctic science will be discussed.

  6. Greenland soil bacteria & biogeochemistry: a vegetation cover proxy for climate warming effects

    Science.gov (United States)

    Dowdy, K. L.; Sistla, S.; Buckeridge, K. M.; Schimel, J.; Schaeffer, S. M.

    2013-12-01

    Climate warming in the high Arctic is expected to increase plant biomass, deepen thaw, and stimulate decomposition of soil organic matter. However, it remains unclear how warming, plant growth, and microbial processing will interact to drive Arctic carbon and nutrient cycling. For example, greater plant growth should increase carbon storage in the ecosystem; however, increasing plant C inputs and thawing permafrost carbon should stimulate microbial biomass, potentially causing soil respiration to outpace storage. Alternatively, greater plant cover may lower soil temperature through shading, potentially curtailing the predicted increase in microbial activity. To evaluate microbial responses to climate warming in the high Arctic, we characterized the soil bacterial community and related soil biogeochemical properties, including pH, temperature, moisture, bulk density, extractable nutrient pools, extractable organic carbon and nitrogen, and total microbial biomass along a vegetation cover gradient in northwest Greenland. Vegetation cover was classified using the Normalized Difference Vegetation Index (NDVI), and vegetation cover classes were used as a proxy for changes associated with warming. We found that soil moisture increased and soil temperature decreased significantly with vegetation cover; moisture and temperature were higher in organic than in mineral horizons. Extractable nutrients (NO3-, NH4+, PO43-) and extractable organic C and N generally increased with vegetation cover and are higher in organic than in mineral horizons within a given vegetation class, with the exception of NO3-, which was comparable between horizons. Despite increases in available carbon and nutrients, microbial biomass carbon in both horizons ultimately decreased with vegetation cover, as did microbial biomass nitrogen in the mineral horizon. Moreover, the relative proportion of microbial biomass carbon to extractable organic carbon decreased with vegetation cover, indicating that

  7. NIF/LMJ prototype amplifier mechanical design

    International Nuclear Information System (INIS)

    Amplifier prototypes for the National Ignition Facility and the Laser Megajoule will be tested at Lawrence Livermore National Laboratory. The prototype amplifier, which is an ensemble of modules from LLNL and Centre d'Etudes de Limeil-Valenton, is cassette-based with bottom access for maintenance. A sealed maintenance transfer vehicle which moves optical cassettes between the amplifier and the assembly cleanroom, and a vacuum gripper which holds laser slabs during cassette assembly will also be tested. The prototype amplifier will be used to verify amplifier optical performance, thermal recovery time, and cleanliness of mechanical operations

  8. An Implantable CMOS Amplifier for Nerve Signals

    DEFF Research Database (Denmark)

    Nielsen, Jannik Hammel; Lehmann, Torsten

    In this paper, a low noise high gain CMOS amplifier for minute nerve signals is presented. The amplifier is constructed in a fully differential topology to maximize noise rejection. By using a mixture of weak- and strong inversion transistors, optimal noise suppression in the amplifier is achieved....... A continuous-time current-steering offset-compensation technique is utilized in order to minimize the noise contribution and to minimize dynamic impact on the amplifier input nodes. The method for signal recovery from noisy nerve signals is presented. A prototype amplifier is realized in a standard...

  9. HIGH AVERAGE POWER OPTICAL FEL AMPLIFIERS

    International Nuclear Information System (INIS)

    Historically, the first demonstration of the optical FEL was in an amplifier configuration at Stanford University [l]. There were other notable instances of amplifying a seed laser, such as the LLNL PALADIN amplifier [2] and the BNL ATF High-Gain Harmonic Generation FEL [3]. However, for the most part FELs are operated as oscillators or self amplified spontaneous emission devices. Yet, in wavelength regimes where a conventional laser seed can be used, the FEL can be used as an amplifier. One promising application is for very high average power generation, for instance FEL's with average power of 100 kW or more. The high electron beam power, high brightness and high efficiency that can be achieved with photoinjectors and superconducting Energy Recovery Linacs (ERL) combine well with the high-gain FEL amplifier to produce unprecedented average power FELs. This combination has a number of advantages. In particular, we show that for a given FEL power, an FEL amplifier can introduce lower energy spread in the beam as compared to a traditional oscillator. This properly gives the ERL based FEL amplifier a great wall-plug to optical power efficiency advantage. The optics for an amplifier is simple and compact. In addition to the general features of the high average power FEL amplifier, we will look at a 100 kW class FEL amplifier is being designed to operate on the 0.5 ampere Energy Recovery Linac which is under construction at Brookhaven National Laboratory's Collider-Accelerator Department

  10. High temperature charge amplifier for geothermal applications

    Science.gov (United States)

    Lindblom, Scott C.; Maldonado, Frank J.; Henfling, Joseph A.

    2015-12-08

    An amplifier circuit in a multi-chip module includes a charge to voltage converter circuit, a voltage amplifier a low pass filter and a voltage to current converter. The charge to voltage converter receives a signal representing an electrical charge and generates a voltage signal proportional to the input signal. The voltage amplifier receives the voltage signal from the charge to voltage converter, then amplifies the voltage signal by the gain factor to output an amplified voltage signal. The lowpass filter passes low frequency components of the amplified voltage signal and attenuates frequency components greater than a cutoff frequency. The voltage to current converter receives the output signal of the lowpass filter and converts the output signal to a current output signal; wherein an amplifier circuit output is selectable between the output signal of the lowpass filter and the current output signal.

  11. The scavenging processes controlling the seasonal cycle in Arctic sulphate and black carbon aerosol

    Science.gov (United States)

    Pringle, K.; Browse, J.; Carslaw, K. S.; Arnold, S.; Boucher, O.

    2013-12-01

    The seasonal cycle in Arctic aerosol is typified by high concentrations of large aged anthropogenic particles transported from lower latitudes in the late Arctic winter and early spring followed by a sharp transition to low concentrations of locally sourced smaller particles in the summer. However, multi-model assessments show that many models fail to simulate a realistic cycle. Here, we use a global aerosol microphysics model (GLOMAP) and surface-level aerosol observations to understand how wet scavenging processes control the seasonal variation in Arctic black carbon (BC) and sulphate aerosol. We show that the transition from high wintertime concentrations to low concentrations in the summer is controlled by the transition from ice-phase cloud scavenging to the much more efficient warm cloud scavenging in the late spring troposphere. This seasonal cycle is amplified further by the appearance of warm drizzling cloud in the late spring and summer boundary layer. Implementing these processes in GLOMAP greatly improves the agreement between the model and observations at the three Arctic ground-stations Alert, Barrow and Zeppelin Mountain on Svalbard. The SO4 model-observation correlation coefficient (R) increases from: -0.33 to 0.71 at Alert (82.5N), from -0.16 to 0.70 at Point Barrow (71.0N) and from -0.42 to 0.40 at Zeppelin Mountain (78N). The BC model-observation correlation coefficient increases from -0.68 to 0.72 at Alert and from -0.42 to 0.44 at Barrow. Observations at three marginal Arctic sites (Janiskoski, Oulanka and Karasjok) indicate a far weaker aerosol seasonal cycle, which we show is consistent with the much smaller seasonal change in the frequency of ice clouds compared to higher latitude sites. Our results suggest that the seasonal cycle in Arctic aerosol is driven by temperature-dependent scavenging processes that may be susceptible to modification in a future climate.

  12. Landscape Level Analyses of Vegetation Cover in Northern Alaska

    Science.gov (United States)

    Botting, T.; Hollister, R. D.

    2013-12-01

    Many International Tundra Experiment (ITEX) studies have been conducted to identify vegetation changes due to warming. However, knowledge gaps remain. For example, most of these studies are conducted at the plot level, not the landscape level, potentially masking larger scale impacts of climate change. An Arctic Systems Science (ARCSS) grid was established in Atqasuk, Alaska and Barrow, Alaska in the mid 1990's. In 2010, approximately 100 untreated vegetation plots were implemented at each grid site. These vegetation plots are 1 meter squared, spaced 100 meters apart, and span 1 kilometer squared. Each vegetation plot represents 100 square meters along the grid. This project will focus on how vegetation cover has changed at the landscape level, using the point frame method, from 2010 to 2013. Preliminary data analysis indicates that in Atqasuk, graminoids, deciduous shrubs, and evergreen shrubs show increased cover, while little change has occurred with bryophytes, forbs and lichens. In Barrow, graminoids, lichens and forbs have shown an increase in cover, while little change has occurred with bryophytes and deciduous shrubs. At both sites, graminoids represent the greatest increase in cover of all growth forms analyzed. This study will be the foundation for later work, with the purpose of predicting what ARCSS grid vegetation community compositions will be in the future. These expectations will be based on anticipated warming data from ITEX passively warmed vegetation plots. This will be the first time that ITEX vegetation warming research is applied to landscape level research in Barrow and Atqasuk.

  13. Interact - Access to the Arctic

    Science.gov (United States)

    Johansson, M.; Callaghan, T. V.

    2013-12-01

    INTERACT is currently a network of 50 terrestrial research stations from all Arctic countries, but is still growing. The network was inaugurated in January 2011 when it received an EU 7th Framework award. INTERACT's main objective is to build capacity for identifying, understanding, predicting and responding to diverse environmental changes throughout the wide environmental and land-use envelopes of the Arctic. Implicit in this objective is the task to build capacity for monitoring, research, education and outreach. INTERACT is increasing access to the Arctic: 20 INTERACT research stations in Europe and Russia are offering Transnational Access and so far, 5600 person-days of access have been granted from the total of 10,000 offered. An INTERACT Station Managers' Forum facilitates a dialogue among station managers on subjects such as best practice in station management and standardised monitoring. The Station Managers' Forum has produced a unique 'one-stop-shop' for information from 45 research stations in an informative and attractive Station Catalogue that is available in hard copy and on the INTERACT web site (www.eu-interact.org). INTERACT also includes three joint research activities that are improving monitoring in remote, harsh environments and are making data capture and dissemination more efficient. Already, new equipment for measuring feedbacks from the land surface to the climate system has been installed at several locations, while best practices for sensor networking have been established. INTERACT networks with most of the high-level Arctic organisations: it includes AMAP and WWF as partners, is endorsed by IASC and CBMP, has signed MoUs with ISAC and the University of the Arctic, is a task within SAON, and contributes to the Cold Region community within GEO/GEOSS. INTERACT welcomes other interactions.

  14. Shrubs in the cold : interactions between vegetation, permafrost and climate in Siberian tundra

    NARCIS (Netherlands)

    Blok, D.

    2011-01-01

    The Arctic is experiencing strong increases in air temperature during the last decades. High-latitude tundra regions are very responsive to changes in temperature and may cause a shift in tundra vegetation composition towards greater dominance of deciduous shrubs. With increasing deciduous shrub cov

  15. Audio power amplifier design handbook

    CERN Document Server

    Self, Douglas

    2013-01-01

    This book is essential for audio power amplifier designers and engineers for one simple reason...it enables you as a professional to develop reliable, high-performance circuits. The Author Douglas Self covers the major issues of distortion and linearity, power supplies, overload, DC-protection and reactive loading. He also tackles unusual forms of compensation and distortion produced by capacitors and fuses. This completely updated fifth edition includes four NEW chapters including one on The XD Principle, invented by the author, and used by Cambridge Audio. Cro

  16. Cathode-follower power amplifier

    International Nuclear Information System (INIS)

    In circular accelerators and particularly in storage rings it is essential that the total impedance, as seen by the beam, be kept below some critical value. A model of the accelerating system was built using a single-ended cathode-follower amplifier driving a ferrite-loaded cavity. The system operated at 234.5 kHz with a peak output voltage of +-10 kV on the gap. The dynamic output impedance, as measured on the gap, was < 15 ohms

  17. Arctic Climate during Eocene Hyperthermals: Wet Summers on Ellesmere Island?

    Science.gov (United States)

    Greenwood, D. R.; West, C. K.; Basinger, J. F.

    2012-12-01

    Previous work has shown that during the late Paleocene to middle Eocene, mesothermal conditions (i.e., MAT ~12-15° C) and high precipitation (MAP > 150cm/yr) characterized Arctic climates - an Arctic rain forest. Recent analyses of Arctic Eocene wood stable isotope chemistry are consistent with the annual and seasonal temperature estimates from leaf physiognomy and nearest living relative analogy from fossil plants, including the lack of freezing winters, but is interpreted as showing that there was a summer peak in precipitation - modern analogs are best sought on the summer-wet east coasts (e.g., China, Japan, South Korea) not the winter-wet west coasts of present-day northern temperate continents (e.g., Pacific northwest of North America). Highly seasonal 'monsoon-type' summer-wet precipitation regimes (i.e., summer precip./winter precip. > 3.0) seem to characterize Eocene hyperthermal conditions in several regions of the earth, including the Arctic and Antarctic, based on both climate model sensitivity experiments and the paleoclimate proxy evidence. The leaf physiognomy proxy previously applied to estimate Arctic Paleogene precipitation was leaf area analysis (LAA), a correlation between mean leaf size in woody dicot vegetation and annual precipitation. New data from modern monsoonal sites, however demonstrates that for deciduous-dicot dominated vegetation, summer precipitation determines mean leaf size, not annual totals, and therefore that under markedly seasonal precipitation and/or light regimes that summer precipitation is being estimated using LAA. Presented here is a new analysis of a leaf macrofloras from 3 separate florules of the Margaret Formation (Split Lake, Stenkul Fiord and Strathcona Fiord) from Ellesmere Island that are placed stratigraphically as early Eocene, and likely fall within Eocene thermal maximum 1 (ETM1; = the 'PETM') or ETM2. These floras are each characterized by a mix of large-leafed and small-leafed dicot taxa, with overall

  18. Projected regime shift in Arctic cloud and water vapor feedbacks

    International Nuclear Information System (INIS)

    The Arctic climate is changing faster than any other large-scale region on Earth. A variety of positive feedback mechanisms are responsible for the amplification, most of which are linked with changes in snow and ice cover, surface temperature (Ts), atmospheric water vapor (WV), and cloud properties. As greenhouse gases continue to accumulate in the atmosphere, air temperature and water vapor content also increase, leading to a warmer surface and ice loss, which further enhance evaporation and WV. Many details of these interrelated feedbacks are poorly understood, yet are essential for understanding the pace and regional variations in future Arctic change. We use a global climate model (Goddard Institute for Space Studies, Atmosphere–Ocean Model) to examine several components of these feedbacks, how they vary by season, and how they are projected to change through the 21st century. One positive feedback begins with an increase in Ts that produces an increase in WV, which in turn increases the downward longwave flux (DLF) and Ts, leading to further evaporation. Another associates the expected increases in cloud cover and optical thickness with increasing DLF and Ts. We examine the sensitivities between DLF and other climate variables in these feedbacks and find that they are strongest in the non-summer seasons, leading to the largest amplification in Ts during these months. Later in the 21st century, however, DLF becomes less sensitive to changes in WV and cloud optical thickness, as they cause the atmosphere to emit longwave radiation more nearly as a black body. This regime shift in sensitivity implies that the amplified pace of Arctic change relative to the northern hemisphere could relax in the future.

  19. Projected Regime Shift in Arctic Cloud and Water Vapor Feedbacks

    Science.gov (United States)

    Chen, Yonghua; Miller, James R.; Francis, Jennifer; Russel, Gary L.

    2011-01-01

    The Arctic climate is changing faster than any other large-scale region on Earth. A variety of positive feedback mechanisms are responsible for the amplification, most of which are linked with changes in snow and ice cover, surface temperature (T(sub s)), atmospheric water vapor (WV), and cloud properties. As greenhouse gases continue to accumulate in the atmosphere, air temperature and water vapor content also increase, leading to a warmer surface and ice loss, which further enhance evaporation and WV. Many details of these interrelated feedbacks are poorly understood, yet are essential for understanding the pace and regional variations in future Arctic change. We use a global climate model (Goddard Institute for Space Studies, Atmosphere-Ocean Model) to examine several components of these feedbacks, how they vary by season, and how they are projected to change through the 21st century. One positive feedback begins with an increase in T(sub s) that produces an increase in WV, which in turn increases the downward longwave flux (DLF) and T(sub s), leading to further evaporation. Another associates the expected increases in cloud cover and optical thickness with increasing DLF and T(sub s). We examine the sensitivities between DLF and other climate variables in these feedbacks and find that they are strongest in the non-summer seasons, leading to the largest amplification in Ts during these months. Later in the 21st century, however, DLF becomes less sensitive to changes in WV and cloud optical thickness, as they cause the atmosphere to emit longwave radiation more nearly as a black body. This regime shift in sensitivity implies that the amplified pace of Arctic change relative to the northern hemisphere could relax in the future.

  20. High power RF solid state power amplifier system

    Science.gov (United States)

    Sims, III, William Herbert (Inventor); Chavers, Donald Gregory (Inventor); Richeson, James J. (Inventor)

    2011-01-01

    A high power, high frequency, solid state power amplifier system includes a plurality of input multiple port splitters for receiving a high-frequency input and for dividing the input into a plurality of outputs and a plurality of solid state amplifier units. Each amplifier unit includes a plurality of amplifiers, and each amplifier is individually connected to one of the outputs of multiport splitters and produces a corresponding amplified output. A plurality of multiport combiners combine the amplified outputs of the amplifiers of each of the amplifier units to a combined output. Automatic level control protection circuitry protects the amplifiers and maintains a substantial constant amplifier power output.

  1. Geologic Provinces of the Circum-Arctic, 2008 (north of the Arctic Circle)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This shapefile includes arcs and polygons that describe U.S. Geological Survey defined 33 geologic provinces of the Circum-Arctic (north of the Arctic Circle). Each...

  2. Potential of C and X Band SAR for Shrub Growth Monitoring in Sub-Arctic Environments

    Directory of Open Access Journals (Sweden)

    Yannick Duguay

    2015-07-01

    Full Text Available The Arctic and sub-Arctic environments have seen a rapid growth of shrub vegetation at the expense of the Arctic tundra in recent decades. In order to develop better tools to assess and understand this phenomenon, the sensitivity of multi-polarized SAR backscattering at C and X band to shrub density and height is studied under various conditions. RADARSAT-2 and TerraSAR-X images were acquired from November 2011 to March 2012 over the Umiujaq community in northern Quebec (56.55°N, 76.55°W and compared to in situ measurements of shrub vegetation density and height collected during the summer of 2009. The results show that σ0 is sensitive to changes in shrub coverage up to 20% and is sensitive to changes in shrub height up to around 1 m. The cross-polarized backscattering (σ0 HV displays the best sensitivity to both shrub height and density, and RADARSAT-2 is more sensitive to shrub height, as TerraSAR-X tends to saturate more rapidly with increasing volume scattering from the shrub branches. These results demonstrate that SAR data could provide essential information, not only on Remote Sens. 2015, 7 9411 the spatial expansion of shrub vegetation, but also on its vertical growth, especially at early stages of colonization.

  3. The Arctic Voice at the UN Climate Negotiations: Interplay Between Arctic & Climate Governance

    OpenAIRE

    Duyck, Sébastien, 1983-

    2015-01-01

    During the past decade, the Arctic has progressively gained the status of a “global barometer” of the implications of climate change. As governments finalize in 2015 the negotiations towards a new climate change agreement and as the priorities of the Arctic Council are shifting towards a stronger focus on climate change, the current year offers a timely opportunity to review the interplay between Arctic policies and the international climate change regime. Indeed, several of the Arctic st...

  4. The effect of misleading surface temperature estimations on the sensible heat fluxes at a high Arctic site – the Arctic Turbulence Experiment 2006 on Svalbard (ARCTEX-2006

    Directory of Open Access Journals (Sweden)

    J. Lüers

    2010-01-01

    Full Text Available The observed rapid climate warming in the Arctic requires improvements in permafrost and carbon cycle monitoring, accomplished by setting up long-term observation sites with high-quality in-situ measurements of turbulent heat, water and carbon fluxes as well as soil physical parameters in Arctic landscapes. But accurate quantification and well adapted parameterizations of turbulent fluxes in polar environments presents fundamental problems in soil-snow-ice-vegetation-atmosphere interaction studies. One of these problems is the accurate estimation of the surface or aerodynamic temperature T(0 required to force most of the bulk aerodynamic formulae currently used. Results from the Arctic-Turbulence-Experiment (ARCTEX-2006 performed on Svalbard during the winter/spring transition 2006 helped to better understand the physical exchange and transport processes of energy. The existence of an atypical temperature profile close to the surface in the Arctic spring at Svalbard could be proven to be one of the major issues hindering estimation of the appropriate surface temperature. Thus, it is essential to adjust the set-up of measurement systems carefully when applying flux-gradient methods that are commonly used to force atmosphere-ocean/land-ice models. The results of a comparison of different sensible heat-flux parameterizations with direct measurements indicate that the use of a hydrodynamic three-layer temperature-profile model achieves the best fit and reproduces the temporal variability of the surface temperature better than other approaches.

  5. Arctic tipping points: governance in turbulent times.

    Science.gov (United States)

    Young, Oran R

    2012-02-01

    Interacting forces of climate change and globalization are transforming the Arctic. Triggered by a non-linear shift in sea ice, this transformation has unleashed mounting interest in opportunities to exploit the region's natural resources as well as growing concern about environmental, economic, and political issues associated with such efforts. This article addresses the implications of this transformation for governance, identifies limitations of existing arrangements, and explores changes needed to meet new demands. It advocates the development of an Arctic regime complex featuring flexibility across issues and adaptability over time along with an enhanced role for the Arctic Council both in conducting policy-relevant assessments and in promoting synergy in interactions among the elements of the emerging Arctic regime complex. The emphasis throughout is on maximizing the fit between the socioecological features of the Arctic and the character of the governance arrangements needed to steer the Arctic toward a sustainable future. PMID:22270707

  6. Strategic metal deposits of the Arctic Zone

    Science.gov (United States)

    Bortnikov, N. S.; Lobanov, K. V.; Volkov, A. V.; Galyamov, A. L.; Vikent'ev, I. V.; Tarasov, N. N.; Distler, V. V.; Lalomov, A. V.; Aristov, V. V.; Murashov, K. Yu.; Chizhova, I. A.; Chefranov, R. M.

    2015-11-01

    Mineral commodities rank high in the economies of Arctic countries, and the status of mineral resources and the dynamics of their development are of great importance. The growing tendency to develop strategic metal resources in the Circumarctic Zone is outlined in a global perspective. The Russian Arctic Zone is the leading purveyor of these metals to domestic and foreign markets. The comparative analysis of tendencies in development of strategic metal resources of the Arctic Zone in Russia and other countries is crucial for the elaboration of trends of geological exploration and research engineering. This paper provides insight into the development of Arctic strategic metal resources in global perspective. It is shown that the mineral resource potential of the Arctic circumpolar metallogenic belt is primarily controlled by large and unique deposits of nonferrous, noble, and rare metals. The prospective types of economic strategic metal deposits in the Russian Arctic Zone are shown.

  7. Latitudinal distribution of the recent Arctic warming

    Energy Technology Data Exchange (ETDEWEB)

    Chylek, Petr [Los Alamos National Laboratory; Lesins, Glen K [DALLHOUSIE UNIV.; Wang, Muyin [UNIV OF WASHINGTON

    2010-12-08

    Increasing Arctic temperature, disappearance of Arctic sea ice, melting of the Greenland ice sheet, sea level rise, increasing strength of Atlantic hurricanes are these impending climate catastrophes supported by observations? Are the recent data really unprecedented during the observational records? Our analysis of Arctic temperature records shows that the Arctic and temperatures in the 1930s and 1940s were almost as high as they are today. We argue that the current warming of the Arctic region is affected more by the multi-decadal climate variability than by an increasing concentration of carbon dioxide. Unfortunately, none of the existing coupled Atmosphere-Ocean General Circulation Models used in the IPCC 2007 cIimate change assessment is able to reproduce neither the observed 20th century Arctic cIimate variability nor the latitudinal distribution of the warming.

  8. Underestimation of mid-Holocene Arctic warming in PMIP simulations

    Science.gov (United States)

    Zhang, Qiong; Muschitiello, Francesco

    2016-04-01

    Due to the orbital forcing, Arctic is warmer during mid-Holocene (~ 6 kyr BP) in summer because the region received more insolation and also warmer in winter because of strong feedbacks, leads to an annual mean temperature warming. Existing proxy reconstructions show that the Arctic can be two degrees warmer than pre-industrial. However, not all the climate models can capture the warming, and the amplitude is about 0.5 degree less than that seen from proxy data. One possible reason is that these simulations did not take into account a fact of 'Green Sahara', where the large area of Sahara region is covered by vegetation instead of desert as it is today. By using a fully coupled climate model EC-Earth with about 100 km resolution, we have run a series of sensitivity experiments by changing the surface type, as well as accompanied change in dust emission over the northern Sahara. The results show that a green sahara not only results in local climate response such as the northward extension and strengthening of African monsoon, but also affect the large scale circulation and corresponding meridional heat transport. The combination of green sahara and reduced dust entails a general strengthening of the mid-latitude Westerlies, results in a change to more positive North Atlantic Oscillation-like conditions, and more heat transport from lower latitudes to high latitudes both in atmosphere and ocean, eventually leads to a shift towards warmer conditions over the North Atlantic and Arctic regions. This mechanism would explain the sign of rapid hydro-climatic perturbations recorded in several reconstructions from high northern latitudes after the termination of the African Humid Period around 5.5 - 5.0 kyr BP, suggesting that these regions are sensitive to changes in Saharan land cover during the present interglacial. This is central in the debate surrounding Arctic climate amplification and future projections for subtropical precipitation changes and related surface type

  9. Evolution of the Arctic Calanus complex: an Arctic marine avocado?

    OpenAIRE

    Berge, Jørgen; Gabrielsen, Tove M.; Mark A Moline; Renaud, Paul

    2012-01-01

    Before man hunted the large baleen whales to near extinction by the end of the nineteenth century, Arctic ecosystems were strongly influenced by these large predators. Their main prey were zooplankton, among which the calanoid copepod species of the genus Calanus, long considered key elements of polar marine ecosystems, are particularly abundant. These herbivorous zooplankters display a range of adaptations to the highly seasonal environments of the polar oceans, most notably extensive energy...

  10. Arctic whaling : proceedings of the International Symposium Arctic Whaling February 1983

    NARCIS (Netherlands)

    Jacob, H.K. s'; Snoeijing, K

    1984-01-01

    Contents: D.M. Hopkins and Louie Marincovich Jr. Whale Biogeography and the history of the Arctic Basin P.M. Kellt, J.H.W. Karas and L.D. Williams Arctic Climate: Past, Present and Future Torgny E. Vinje On the present state and the future fate of the Arctic sea ice cover P.J.H. van Bree On the biol

  11. Arctic shipping emissions inventories and future scenarios

    OpenAIRE

    J. J. Corbett; D. A. Lack; J. J. Winebrake; Harder, S; J. A. Silberman; Gold, M.

    2010-01-01

    The Arctic is a sensitive region in terms of climate change and a rich natural resource for global economic activity. Arctic shipping is an important contributor to the region's anthropogenic air emissions, including black carbon – a short-lived climate forcing pollutant especially effective in accelerating the melting of ice and snow. These emissions are projected to increase as declining sea ice coverage due to climate change allows for increased shipping activity in the Arctic. To understa...

  12. Identifying uncertainties in Arctic climate change projections

    OpenAIRE

    Hodson, Daniel L. R.; Keeley, Sarah P. E.; West, Alex; Ridley, Jeff; Hawkins, Ed; Hewitt, Helene T.

    2013-01-01

    Wide ranging climate changes are expected in the Arctic by the end of the 21st century, but projections of the size of these changes vary widely across current global climate models. This variation represents a large source of uncertainty in our understanding of the evolution of Arctic climate. Here we systematically quantify and assess the model uncertainty in Arctic climate changes in two CO2 doubling experiments: a multimodel ensemble (CMIP3) and an ensemble constructed using a single mode...

  13. Arctic cephalopod distributions and their associated predators

    OpenAIRE

    Gardiner, Kathleen; Terry A Dick

    2010-01-01

    Cephalopods are key species of the eastern Arctic marine food web, both as prey and predator. Their presence in the diets of Arctic fish, birds and mammals illustrates their trophic importance. There has been considerable research on cephalopods (primarily Gonatus fabricii) from the north Atlantic and the west side of Greenland, where they are considered a potential fishery and are taken as a by-catch. By contrast, data on the biogeography of Arctic cephalopods are still incomplete. This stud...

  14. Shaping a Sustainability Strategy for the Arctic

    OpenAIRE

    Azcarate, Juan; Balfors, Berit; Destouni, Georgia; Bring, Arvid

    2011-01-01

    The development of the Arctic is shaped by the opportunities and constraints brought by climate change and technological advances. In the Arctic, warmer climate is expected to affect ecosystems, local communities and infrastructure due to a combination of effects like reduced sea ice and glaciers, thawing permafrost and increased frequency of floods. Less ice and new technologies mean openings to exploit natural resources in the Arctic. Fishing, mining, hydrocarbon extraction and vessel trans...

  15. High-efficiency solid state power amplifier

    Science.gov (United States)

    Wallis, Robert E. (Inventor); Cheng, Sheng (Inventor)

    2005-01-01

    A high-efficiency solid state power amplifier (SSPA) for specific use in a spacecraft is provided. The SSPA has a mass of less than 850 g and includes two different X-band power amplifier sections, i.e., a lumped power amplifier with a single 11-W output and a distributed power amplifier with eight 2.75-W outputs. These two amplifier sections provide output power that is scalable from 11 to 15 watts without major design changes. Five different hybrid microcircuits, including high-efficiency Heterostructure Field Effect Transistor (HFET) amplifiers and Monolithic Microwave Integrated Circuit (MMIC) phase shifters have been developed for use within the SSPA. A highly efficient packaging approach enables the integration of a large number of hybrid circuits into the SSPA.

  16. YANG-MILLS FIELD AMPLIFIER

    Directory of Open Access Journals (Sweden)

    Trunev A. P.

    2015-09-01

    Full Text Available The article presents a project of the Yang-Mills amplifier. Amplifier model is a multilayer spherical shell with increasing density towards the center. In the center of the amplifier is the core of high-density material. It is shown that in such a system, the amplitude of the Yang-Mills waves rises from the periphery to the center of several orders of magnitude. The role of the Yang-Mills field in the processes occurring in the nuclei of galaxies, stars and planets is discussed. The data modeling to strengthen the Yang-Mills field in the bowels of the planet, with an atomic explosion, and in some special devices such as the voltaic pile. To describe the mechanism of amplification chromodynamics field used as accurate results in Yang-Mills theory and numerical models developed based on an average and the exact equations as well. Among the exact solutions of the special role played by the centralsymmetric metric describing the contribution of the Yang-Mills field in the speed of recession of galaxies. Among the approximate numerical models can be noted the eight-scalar model we have developed for the simulation of non-linear color oscillations and chaos in the Yang-Mills theory. Earlier models were investigated spatio-temporal oscillations of the YangMills theory in the case of three and eight colors. The results of numerical simulation show that the nonlinear interaction does not lead to a spatial mixing of colors as it might be in the case of turbulent diffusion. Depending on the system parameters there is a suppression of the amplitude of the oscillations the first three by five colors or vice versa. The kinetic energy fluctuations or shared equally between the color components, or dominated by the kinetic energy of repressed groups of colors. In the present study, we found that amplification chromodynamic field leads to a sharp increase in the amplitude of the suppressed color, which can lead to an increase in entropy, excitation of nuclear

  17. Plate tectonic history of the Arctic

    Science.gov (United States)

    Burke, K.

    1984-01-01

    Tectonic development of the Arctic Ocean is outlined, and geological maps are provided for the Arctic during the mid-Cenozoic, later Cretaceous, late Jurassic, early Cretaceous, early Jurassic and late Devonian. It is concluded that Arctic basin history is moulded by the events of the following intervals: (1) continental collision and immediately subsequent rifting and ocean formation in the Devonian, and continental rifting ocean formation, rapid rotation of microcontinents, and another episode of collision in the latest Jurassic and Cretaceous. It is noted that Cenozoic Arctic basin formation is a smaller scale event superimposed on the late Mesozoic ocean basin.

  18. Arctic tides from GPS on sea ice

    DEFF Research Database (Denmark)

    Kildegaard Rose, Stine; Skourup, Henriette; Forsberg, René

    The presence of sea-ice in the Arctic Ocean plays a significant role in the Arctic climate. Sea ice dampens the ocean tide amplitude with the result that global tidal models which use only astronomical data perform less accurately in the polar regions. This study presents a kinematic processing of...... Global Positioning System (GPS) buoys placed on sea-ice at five different sites north of Greenland for the study of sea level height and tidal analysis to improve tidal models in the Central Arctic. The GPS measurements are compared with the Arctic tidal model AOTIM-5, which assimilates tide-gauges and...

  19. Enhanced Gain in Photonic Crystal Amplifiers

    DEFF Research Database (Denmark)

    Ek, Sara; Semenova, Elizaveta; Hansen, Per Lunnemann;

    2012-01-01

    study of a 1 QW photonic crystal amplifier. Net gain is achieved which enables laser oscillation in photonic crystal micro cavities. The ability to freely tailor the dispersion in a semiconductor optical amplifier makes it possible to raise the optical gain considerably over a certain bandwidth. These...... results are promising for short and efficient semiconductor optical amplifiers. This effect will also benefit other devices, such as mode locked lasers....

  20. Aerosols indirectly warm the Arctic

    Directory of Open Access Journals (Sweden)

    T. Mauritsen

    2010-07-01

    Full Text Available On average, airborne aerosol particles cool the Earth's surface directly by absorbing and scattering sunlight and indirectly by influencing cloud reflectivity, life time, thickness or extent. Here we show that over the central Arctic Ocean, where there is frequently a lack of aerosol particles upon which clouds may form, a small increase in aerosol loading may enhance cloudiness thereby likely causing a climatologically significant warming at the ice-covered Arctic surface. Under these low concentration conditions cloud droplets grow to drizzle sizes and fall, even in the absence of collisions and coalescence, thereby diminishing cloud water. Evidence from a case study suggests that interactions between aerosol, clouds and precipitation could be responsible for attaining the observed low aerosol concentrations.

  1. Arctic Basemaps In Google Maps

    DEFF Research Database (Denmark)

    Muggah, J.; Mioc, Darka

    2010-01-01

    the advantages of the use of Google Maps, to display the OMG's Arctic data. The map should should load the large Artic dataset in a reasonable time. The bathymetric images were created using software in Linux written by the OMG, and a step-by-step process was used to create images from the multibeam data...... collected by the OMG in the Arctic. The website was also created using Linux operating system. The projection needed to be changed from Lambert Conformal Conic (useful at higher Latitudes) to Mercator (used by Google Maps) and the data needed to have a common colour scheme. After creating and testing...... a prototype website using Google Ground overlay and Tile overlay, it was determined that the high resolution images (10m) were loading very slowly and the ground overlay method would not be useful for displaying the entire dataset. Therefore the Tile overlays were selected to be used within Google Maps. Tile...

  2. Reflection amplifiers in self-regulated learning

    OpenAIRE

    Verpoorten, Dominique

    2012-01-01

    Verpoorten, D. (2012). Reflection amplifiers in self-regulated learning. Doctoral thesis. November, 9, 2012, Heerlen, The Netherlands: Open Universiteit (CELSTEC). Datawyse / Universitaire Pers Maastricht.

  3. Dynamics of Soliton Cascades in Fiber Amplifiers

    CERN Document Server

    Arteaga-Sierra, F R; Agrawal, Govind P

    2016-01-01

    We study numerically the formation of cascading solitons when femtosecond optical pulses are launched into a fiber amplifier with less energy than required to form a soliton of equal duration. As the pulse is amplified, cascaded fundamental solitons are created at different distances, without soliton fission, as each fundamental soliton moves outside the gain bandwidth through the Raman-induced spectral shifts. As a result, each input pulse creates multiple, temporally separated, ultrashort pulses of different wavelengths at the amplifier output. The number of pulses depends not only on the total gain of the amplifier but also on the width of input pulses.

  4. The Arctic Research Consortium of the United States (ARCUS): Connecting Arctic Research

    Science.gov (United States)

    Rich, R. H.; Wiggins, H. V.; Creek, K. R.; Sheffield Guy, L.

    2015-12-01

    This presentation will highlight the recent activities of the Arctic Research Consortium of the United States (ARCUS) to connect Arctic research. ARCUS is a nonprofit membership organization of universities and institutions that have a substantial commitment to research in the Arctic. ARCUS was formed in 1988 to serve as a forum for planning, facilitating, coordinating, and implementing interdisciplinary studies of the Arctic; to act as a synthesizer and disseminator of scientific information on arctic research; and to educate scientists and the general public about the needs and opportunities for research in the Arctic. ARCUS, in collaboration with the broader science community, relevant agencies and organizations, and other stakeholders, coordinates science planning and educational activities across disciplinary and organizational boundaries. Examples of ARCUS projects include: Arctic Sea Ice Outlook - an international effort that provides monthly summer reports synthesizing community estimates of the expected sea ice minimum. Sea Ice for Walrus Outlook - a resource for Alaska Native subsistence hunters, coastal communities, and others that provides weekly reports with information on sea ice conditions relevant to walrus in Alaska waters. PolarTREC (Teachers and Researchers Exploring and Collaborating) - a program whereby K-12 educators and researchers work together in hands-on field experiences in the Arctic and Antarctic to advance polar science education. ArcticInfo mailing list, Witness the Arctic newsletter, and the Arctic Calendar - communication tools for the arctic science community to keep apprised of relevant news, meetings, and announcements. Coordination for the Study of Environmental Arctic Change (SEARCH) program, which aims to provide scientific understanding of arctic environmental change to help society understand and respond to a rapidly changing Arctic. More information about these and other ARCUS activities can be found at the ARCUS website at

  5. Sea surface salinity of the Eocene Arctic Azolla event using innovative isotope modeling

    Science.gov (United States)

    Speelman, E. N.; Sewall, J. O.; Noone, D.; Huber, M.; Sinninghe Damste, J. S.; Reichart, G. J.

    2009-04-01

    With the realization that the Eocene Arctic Ocean was covered with enormous quantities of the free floating freshwater fern Azolla, new questions regarding Eocene conditions facilitating these blooms arose. Our present research focuses on constraining the actual salinity of, and water sources for, the Eocene Arctic basin through the application of stable water isotope tracers. Precipitation pathways potentially strongly affect the final isotopic composition of water entering the Arctic Basin. Therefore we use the Community Atmosphere Model (CAM3), developed by NCAR, combined with a recently developed integrated isotope tracer code to reconstruct the isotopic composition of global Eocene precipitation and run-off patterns. We further addressed the sensitivity of the modeled hydrological cycle to changes in boundary conditions, such as pCO2, sea surface temperatures (SSTs) and sea ice formation. In this way it is possible to assess the effect of uncertainties in proxy estimates of these parameters. Overall, results of all runs with Eocene boundary conditions, including Eocene topography, bathymetry, vegetation patterns, TEX86 derived SSTs and pCO2 estimates, show the presence of an intensified hydrological cycle with precipitation exceeding evaporation in the Arctic region. Enriched, precipitation weighted, isotopic values of around -120‰ are reported for the Arctic region. Combining new results obtained from compound specific isotope analyses (δD) on terrestrially derived n-alkanes extracted from Eocene sediments, and model outcomes make it possible to verify climate reconstructions for the middle Eocene Arctic. Furthermore, recently, characteristic long-chain mid-chain ω20 hydroxy wax constituents of Azolla were found in ACEX sediments. δD values of these C32 - C36 diols provide insight into the isotopic composition of the Eocene Arctic surface water. As the isotopic signature of the runoff entering the Arctic is modelled, and the final isotopic composition of

  6. Ping-pong auto-zero amplifier with glitch reduction

    Science.gov (United States)

    Larson, Mark R.

    2008-01-22

    A ping-pong amplifier with reduced glitching is described. The ping-pong amplifier includes a nulling amplifier coupled to a switching network. The switching network is used to auto-zero a ping amplifier within a ping-pong amplifier. The nulling amplifier drives the output of a ping amplifier to a proper output voltage level during auto-zeroing of the ping amplifier. By being at a proper output voltage level, glitches associated with transitioning between a ping amplifier and a pong amplifier are reduced or eliminated.

  7. Linearisation of RF Power Amplifiers

    DEFF Research Database (Denmark)

    Nielsen, Per Asbeck

    2001-01-01

    linearisation systems with focus on polar modulation feedback, and a chip oriented part focusing on integrating of separate building blocks of the system on a chip. The system oriented part of this thesis deals with analog feedback linearisation systems. The Polar modulation feedback system is compared with the...... more traditional Cartesian modulation feedback system in terms of loop settlement and dependencies between the feedback signals. A method to calculate the distortion functions of the linearisation system (AM/AM and AM/PM)based on the distortion functions of the power amplifier is presented. Also the...... polar loop architecture and it’s suitability to modern digital transmitters is discussed. A proposal of an architecture that is suitable for digital transmitters, which means that it has an interface to the digital back-end, defined by low-pass signals in polar form, is presented. Simulation guidelines...

  8. Transverse pumped laser amplifier architecture

    Science.gov (United States)

    Bayramian, Andrew James; Manes, Kenneth; Deri, Robert; Erlandson, Al; Caird, John; Spaeth, Mary

    2013-07-09

    An optical gain architecture includes a pump source and a pump aperture. The architecture also includes a gain region including a gain element operable to amplify light at a laser wavelength. The gain region is characterized by a first side intersecting an optical path, a second side opposing the first side, a third side adjacent the first and second sides, and a fourth side opposing the third side. The architecture further includes a dichroic section disposed between the pump aperture and the first side of the gain region. The dichroic section is characterized by low reflectance at a pump wavelength and high reflectance at the laser wavelength. The architecture additionally includes a first cladding section proximate to the third side of the gain region and a second cladding section proximate to the fourth side of the gain region.

  9. Towards an ice free Arctic

    International Nuclear Information System (INIS)

    The article surveys the rate of ice melting in Arctic and forecasts that the region will be free of ice during this century. Observations of the atmospheric and sea climate, total ice areas for the period 1978 to 1998 and predictions for the areas from 1990 to 2040 by using two different models are presented. Possible reasons for the changes are discussed and some views on the consequences for the Norwegian climate presented

  10. Building Materials in Arctic Climate

    DEFF Research Database (Denmark)

    Jensen, Ole Mejlhede

    2005-01-01

    Building in the artic requires special attention on the appropriateness of building materials. The harsh climate makes execution difficult and sets unusual requirements for the pure material properties. In addition, there is a lack of choice of good, natural building materials in the arctic. This...... results in high transport costs. The building materials situation in Greenland may potentially be improved by intensifying the reuse of building materials or by promoting the local production of building materials....

  11. Extrapolating future Arctic ozone losses

    OpenAIRE

    Knudsen, B. M.; Harris, N. R. P.; S. B. Andersen; Christiansen, B.; N. Larsen; Rex, M.; B. Naujokat

    2004-01-01

    Future increases in the concentration of greenhouse gases and water vapour may cool the stratosphere further and increase the amount of polar stratospheric clouds (PSCs). Future Arctic PSC areas have been extrapolated from the highly significant trends 1958-2001. Using a tight correlation between PSC area and the total vortex ozone depletion and taking the decreasing amounts of ozone depleting substances into account we make empirical estimates of future ozone. The result...

  12. Arctic adaptation and climate change

    International Nuclear Information System (INIS)

    The amplification of climatic warming in the Arctic and the sensitivity of physical, biological, and human systems to changes in climate make the Arctic particularly vulnerable to climate changes. Large areas of the Arctic permafrost and sea ice are expected to disappear under climate warming and these changes will have considerable impacts on the natural and built environment of the north. A review is presented of some recent studies on what these impacts could be for the permafrost and sea ice environment and to identify linkages with socioeconomic activities. Terrestrial adaptation to climate change will include increases in ground temperature; melting of permafrost with consequences such as frost heave, mudslides, and substantial settlement; rotting of peat contained in permafrost areas, with subsequent emission of CO2; increased risk of forest fire; and flooding of low-lying areas. With regard to the manmade environment, structures that will be affected include buildings, pipelines, highways, airports, mines, and railways. In marine areas, climate change will increase the ice-free period for marine transport operations and thus provide some benefit to the offshore petroleum industry. This benefit will be offset by increased wave height and period, and increased coastal erosion. The offshore industry needs to be particularly concerned with these impacts since the expected design life of industry facilities (30-60 y) is of the same order as the time frame for possible climatic changes. 18 refs., 5 figs

  13. Procedures for Sampling Vegetation

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This report outlines vegetation sampling procedures used on various refuges in Region 3. The importance of sampling the response of marsh vegetation to management...

  14. The Weird Vegetable Price

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The Chinese Government faces the task of stabilizing vegetable prices to avoid steep increases and dips Fluctuations of vegetable prices in China have recently caused near panic in the domestic market.Purchase prices for farm produce are decreasing dramatically

  15. Arctic whaling: proceedings of the International Symposium Arctic Whaling February 1983

    OpenAIRE

    H.K. 's Jacob; Snoeijing, K

    1984-01-01

    Contents: D.M. Hopkins and Louie Marincovich Jr. Whale Biogeography and the history of the Arctic Basin P.M. Kellt, J.H.W. Karas and L.D. Williams Arctic Climate: Past, Present and Future Torgny E. Vinje On the present state and the future fate of the Arctic sea ice cover P.J.H. van Bree On the biology of whales Edward Mitchell Ecology of North Atlantic Boreal and Arctic Monodontid and Mysticete Whales Allen P. McCartney History of native whaling in the Arctic and Subarctic Albert A. Dekin Jr...

  16. Experimental icing affects growth, mortality, and flowering in a high Arctic dwarf shrub.

    Science.gov (United States)

    Milner, Jos M; Varpe, Øystein; van der Wal, René; Hansen, Brage Bremset

    2016-04-01

    Effects of climate change are predicted to be greatest at high latitudes, with more pronounced warming in winter than summer. Extreme mid-winter warm spells and heavy rain-on-snow events are already increasing in frequency in the Arctic, with implications for snow-pack and ground-ice formation. These may in turn affect key components of Arctic ecosystems. However, the fitness consequences of extreme winter weather events for tundra plants are not well understood, especially in the high Arctic. We simulated an extreme mid-winter rain-on-snow event at a field site in high Arctic Svalbard (78°N) by experimentally encasing tundra vegetation in ice. After the subsequent growing season, we measured the effects of icing on growth and fitness indices in the common tundra plant, Arctic bell-heather (Cassiope tetragona). The suitability of this species for retrospective growth analysis enabled us to compare shoot growth in pre and postmanipulation years in icing treatment and control plants, as well as shoot survival and flowering. Plants from icing treatment plots had higher shoot mortality and lower flowering success than controls. At the individual sample level, heavily flowering plants invested less in shoot growth than nonflowering plants, while shoot growth was positively related to the degree of shoot mortality. Therefore, contrary to expectation, undamaged shoots showed enhanced growth in ice treatment plants. This suggests that following damage, aboveground resources were allocated to the few remaining undamaged meristems. The enhanced shoot growth measured in our icing treatment plants has implications for climate studies based on retrospective analyses of Cassiope. As shoot growth in this species responds positively to summer warming, it also highlights a potentially complex interaction between summer and winter conditions. By documenting strong effects of icing on growth and reproduction of a widespread tundra plant, our study contributes to an understanding of

  17. Biomarkers of Canadian High Arctic Litoral Sediments for Assessment of Organic Matter Sources and Degradation

    Science.gov (United States)

    Pautler, B. G.; Austin, J.; Otto, A.; Stewart, K.; Lamoureux, S. F.; Simpson, M. J.

    2009-05-01

    Carbon stocks in the High Arctic are particularly sensitive to global climate change, and investigation of variations in organic matter (OM) composition is beneficial for the understanding of the alteration of organic carbon under anticipated future elevated temperatures. Molecular-level characterization of solvent extractable compounds and CuO oxidation products of litoral sedimentary OM at the Cape Bounty Arctic Watershed Observatory in the Canadian Arctic Archipelago was conducted to determine the OM sources and decomposition patterns. The solvent extracts contained a series of aliphatic lipids, steroids and one triterpenoid primarily of higher plant origin and new biomarkers, iso- and anteiso-alkanes originating from cerastium arcticum (Arctic mouse-ear chickweed, a native angiosperm) were discovered. Carbon preference index (CPI) values for the n-alkanes, n-alkanols and n-alkanoic acids suggests that the OM biomarkers result from fresh material input in early stage of degradation. The CuO oxidation products were comprised of benzyls, lignin phenols and short-chain diacids and hydroxyacids. High abundance of terrestrial OM biomarkers observed at sites close to the river inlet suggests fluvial inputs as an important pathway to deliver OM into the lake. The lignin phenol vegetation index (LPVI) also suggests that the OM origin is mostly from non-woody angiosperms. A relatively high degree of lignin alteration in the litoral sediments is evident from the abundant ratio of acids and aldehydes of the vanillyl and syringyl monomers. This suggests that the lignin contents have been diagenetically altered as the result of a long residence time in this ecosystem. The molecular-level characterization of litoral sedimentary OM in Canadian High Arctic region provides insight into current OM composition,potential responses to future disturbances and the biogeochemical cycling of carbon in the Arctic.

  18. Natural vegetation inventory

    Science.gov (United States)

    Schrumpf, B. J.

    1973-01-01

    Unique characteristics of ERTS imagery can be used to inventory natural vegetation. While satellite images can seldom be interpreted and identified directly in terms of vegetation types, such types can be inferred by interpretation of physical terrain features and through an understanding of the ecology of the vegetation.

  19. Amplified spontaneous emission and its restraint in a terawatt Ti:sapphire amplifier

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Amplified spontaneous emission (ASE) and its restraint in a femtosecond Ti: sapphire chirped_pulse amplifier were investigated. The noises arising from ASE were effectively filtered out in the spatial, temporal and spectral domain. Pulses as short as 38 fs were amplified to peak power of 1.4 TW. The power ratio between the amplified femtosecond pulse and the ASE was higher than 106:1.

  20. Distributed feedback laser amplifiers combining the functions of amplifiers and channel filters

    DEFF Research Database (Denmark)

    Wang, Z.; Durhuus, T.; Mikkelsen, Benny;

    1994-01-01

    A dynamic model for distributed feedback amplifiers, including the mode coupled equations and the carrier rate equation, is established. The presented mode coupled equations have taken into account the interaction between fast changing optical signal and the waveguide with corrugations. By showin...... the possibility of amplifying 100 ps pulses without pulse broadening, we anticipate that a distributed feedback amplifier can be used as a combined amplifier and channel filter in high bit rate transmission systems....

  1. Arctic Black Carbon Initiative: Reducing Emissions of Black Carbon from Power & Industry in Russia

    Science.gov (United States)

    Cresko, J.; Hodson, E. L.; Cheng, M.; Fu, J. S.; Huang, K.; Storey, J.

    2012-12-01

    Deposition of black carbon (BC) on snow and ice is widely considered to have a climate warming effect by reducing the surface albedo and promoting snowmelt. Such positive climate feedbacks in the Arctic are especially problematic because rising surface temperatures may trigger the release of large Arctic stores of terrestrial carbon, further amplifying current warming trends. Recognizing the Arctic as a vulnerable region, the U.S. government committed funds in Copenhagen in 2009 for international cooperation targeting Arctic BC emissions reductions. As a result, the U.S. Department of State has funded three research and demonstration projects with the goal to better understand and mitigate BC deposition in the Russian Arctic from a range of sources. The U.S. Department of Energy's (DOE) Arctic BC initiative presented here is focused on mitigating BC emissions resulting from heat and power generation as well as industrial applications. A detailed understanding of BC sources and its transport and fate is required to prioritize efforts to reduce BC emissions from sources that deposit in the Russian Arctic. Sources of BC include the combustion of fossil fuels (e.g. coal, fuel oil, diesel) and the combustion of biomass (e.g. wildfires, agricultural burning, residential heating and cooking). Information on fuel use and associated emissions from the industrial and heat & power sectors in Russia is scarce and difficult to obtain from the open literature. Hence, our project includes a research component designed to locate Arctic BC emissions sources in Russia and determine associated BC transport patterns. We use results from the research phase to inform a subsequent assessment/demonstration phase. We use a back-trajectory modeling method (potential source contribution function - PSCF), which combines multi-year, high-frequency measurements with knowledge about atmospheric transport patterns. The PSCF modeling allows us to map the probability (by season and year) at course

  2. A general-purpose pulse amplifier

    International Nuclear Information System (INIS)

    In the paper proposals are made for using the technique, known from analogue computation, for transforming nuclear pulses to the shape and size desired by the means of ''operational amplifiers''. By using this technique it is possible, by means of one fundamental amplifier but with different feedback networks, to have pre-amplifiers and head-amplifiers with different pulse-handling performances and optimized with respect to the parameter of greatest interest, such as linearity, stability or overloading characteristics. As this technique involves the use of parallel-feedback it is specially suited for pre-amplifiers since most detectors are current-generators. An amplifier fulfilling the requirements necessary for use as an operational amplifier is described. The most important specifications are: 90 db gain from DC-10 kHz, then falling approximately 20 db/decade until 15 MHz (30 db gain). Four tubes are used in the amplifier. For most pulse-handling applications a stabilized power-supply is unnecessary and the stability will depend solely on the stability of the feedback network used. (author)

  3. Self-pulsation in Raman fiber amplifiers

    DEFF Research Database (Denmark)

    Pedersen, Martin Erland Vestergaard; Ott, Johan Raunkjær; Rottwitt, Karsten

    2009-01-01

    Dynamic behavior caused by Brillouin scattering in Raman fiber amplifiers is studied. Modes of self-pulsation steady state oscillations are found. Their dependence on amplification scheme is demonstrated.......Dynamic behavior caused by Brillouin scattering in Raman fiber amplifiers is studied. Modes of self-pulsation steady state oscillations are found. Their dependence on amplification scheme is demonstrated....

  4. High efficiency, low magnetic field gyroklystron amplifiers

    International Nuclear Information System (INIS)

    The possibility of operating a gyroklystron amplifier at high efficiency and low magnetic field is considered. Two devices are discussed: A two cavity second harmonic TE02 gyroklystron amplifier operating at 19.7 GHz with subharmonic bunching, and a fundamental mode TE01 gyrotwistron at 16 GHz. The nonlinear efficiency is given for both devices

  5. BROADBAND TRAVELLING WAVE SEMICONDUCTOR OPTICAL AMPLIFIER

    DEFF Research Database (Denmark)

    2010-01-01

    Broadband travelling wave semiconductor optical amplifier (100, 200, 300, 400, 800) for amplification of light, wherein the amplifier (100, 200, 300, 400, 800) comprises a waveguide region (101, 201, 301, 401, 801) for providing confinement of the light in transverse directions and adapted for...

  6. Waveguide optical amplifier for telecom applications

    OpenAIRE

    Taccheo, Stefano; Zannin, Marcelo; Ennser, Karin; Careglio, Davide; Solé Pareta, Josep; Aracil Rico, Javier

    2009-01-01

    In this paper we review progress in optical gain clamped waveguide amplifiers for applications to optical communications. We demonstrate that compact waveguide devices may offer advantages compared to standard fiber amplifiers. In particular we focus on the application of gain clamping and optical burst switching networks where physical impairments may occur due to variation of the input power. Peer Reviewed

  7. An atmosphere-ocean GCM modelling study of the climate response to changing Arctic seaways in the early Cenozoic.

    Science.gov (United States)

    Roberts, C. D.; Legrande, A. N.; Tripati, A. K.

    2008-12-01

    The report of fossil Azolla (a freshwater aquatic fern) in sediments from the Lomonosov Ridge suggests low salinity conditions occurred in the Arctic Ocean in the early Eocene. Restricted passages between the Arctic Ocean and the surrounding oceans are hypothesized to have caused this Arctic freshening. We investigate this scenario using a water-isotope enabled atmosphere-ocean general circulation model with Eocene boundary conditions including 4xCO2, 7xCH4, altered bathymetry and topography, and an estimated distribution of Eocene vegetational types. In one experiment, oceanic exchange between the Arctic Ocean and other ocean basins was restricted to two shallow (~250 m) seaways, one in the North Atlantic, the Greenland-Norwegian seaway, and the second connecting the Arctic Ocean with the Tethys Ocean, the Turgai Straits. In the restricted configuration, the Greenland-Norwegian seaway was closed and exchange through the Turgai Straits was limited to a depth of ~60 m. The simulations suggest that the severe restriction of Arctic seaways in the early Eocene may have been sufficient to freshen Arctic Ocean surface waters, conducive to Azolla blooms. When exchange with the Arctic Ocean is limited, salinities in the upper several hundred meters of the water column decrease by ~10 psu. In some regions, surface salinity is within 2-3 psu of the reported maximum modern conditions tolerated by Azolla (~5 psu). In the restricted scenario, salt is stored preferentially in the North Atlantic and Tethys oceans, resulting in enhanced meridional overturning, increased poleward heat transport in the North Atlantic western boundary current, and warming of surface and intermediate waters in the North Atlantic by several degrees. Increased sensible and latent heat fluxes from the North Atlantic Ocean, combined with a reduction in cloud albedo, also lead to an increase in surface air temperature of over much of North America, Greenland and Eurasia. Our work is consistent with

  8. Evaporative cooling over the Tibetan Plateau induced by vegetation growth.

    Science.gov (United States)

    Shen, Miaogen; Piao, Shilong; Jeong, Su-Jong; Zhou, Liming; Zeng, Zhenzhong; Ciais, Philippe; Chen, Deliang; Huang, Mengtian; Jin, Chun-Sil; Li, Laurent Z X; Li, Yue; Myneni, Ranga B; Yang, Kun; Zhang, Gengxin; Zhang, Yangjian; Yao, Tandong

    2015-07-28

    In the Arctic, climate warming enhances vegetation activity by extending the length of the growing season and intensifying maximum rates of productivity. In turn, increased vegetation productivity reduces albedo, which causes a positive feedback on temperature. Over the Tibetan Plateau (TP), regional vegetation greening has also been observed in response to recent warming. Here, we show that in contrast to arctic regions, increased growing season vegetation activity over the TP may have attenuated surface warming. This negative feedback on growing season vegetation temperature is attributed to enhanced evapotranspiration (ET). The extra energy available at the surface, which results from lower albedo, is efficiently dissipated by evaporative cooling. The net effect is a decrease in daily maximum temperature and the diurnal temperature range, which is supported by statistical analyses of in situ observations and by decomposition of the surface energy budget. A daytime cooling effect from increased vegetation activity is also modeled from a set of regional weather research and forecasting (WRF) mesoscale model simulations, but with a magnitude smaller than observed, likely because the WRF model simulates a weaker ET enhancement. Our results suggest that actions to restore native grasslands in degraded areas, roughly one-third of the plateau, will both facilitate a sustainable ecological development in this region and have local climate cobenefits. More accurate simulations of the biophysical coupling between the land surface and the atmosphere are needed to help understand regional climate change over the TP, and possible larger scale feedbacks between climate in the TP and the Asian monsoon system. PMID:26170316

  9. Health in the Arctic and climate change

    OpenAIRE

    Sloth Pedersen, Henning

    2007-01-01

    The Arctic environment is like a magnifying glass. Many of the hazards stemming from industrial activity in the South tend to concentrate in the North. This is true for DDT, PCB, heavy metals and many other substances that may endanger human health. Climate change is yet another example of how the negative impact of industrial activity may be magnified in the Arctic region.

  10. Arctic freshwater export: Status, mechanisms, and prospects

    NARCIS (Netherlands)

    Haine, T.W.N.; Curry, B.; Gerdes, R.; Hansen, E.; Karcher, M.; Lee, C.; Rudels, B.; Spreen, G.; de Steur, L.; Stewart, K.D.; Woodgate, R.

    2015-01-01

    Large freshwater anomalies clearly exist in the Arctic Ocean. For example, liquid freshwater has accumulated in the Beaufort Gyre in the decade of the 2000s compared to 1980–2000, with an extra ˜ 5000 km3 — about 25% — being stored. The sources of freshwater to the Arctic from precipitation and runo

  11. Pacific Northwest Laboratory Alaska (ARCTIC) research program

    International Nuclear Information System (INIS)

    The current program continues studies of arctic ecosystems begun in 1959 as part of the Cape Thompson Program. Specific ecosystem aspects include studies of the ecology of arctic and red foxes, small mammel and bird population studies, lichen studies, and radiation ecology studies

  12. Pleistocene graminoid-dominated ecosystems in the Arctic

    Science.gov (United States)

    Blinnikov, Mikhail S.; Gaglioti, Benjamin V.; Walker, Donald A.; Wooller, Matthew J.; Zazula, Grant D.

    2011-10-01

    We review evidence obtained from analyses of multiple proxies (floristics, mammal remains, paleoinsects, pollen, macrofossils, plant cuticles, phytoliths, stable isotopes, and modeling) that elucidate the composition and character of the graminoid-dominated ecosystems of the Pleistocene Arctic. The past thirty years have seen a renewed interest in this now-extinct biome, sometimes referred to as "tundra-steppe" (steppe-tundra in North American sources). While many questions remain, converging evidence from many new terrestrial records and proxies coupled with better understanding of paleoclimate dynamics point to the predominance of xeric and cold adapted grassland as the key former vegetation type in the Arctic confirming earlier conjectures completed in the 1960s-1980s. A variety of still existing species of grasses and forbs played key roles in the species assemblages of the time, but their mixtures were not analogous to the tundras of today. Local mosaics based on topography, proximity to the ice sheets and coasts, soil heterogeneity, animal disturbance, and fire regimes were undoubtedly present. However, inadequate coverage of terrestrial proxies exist to resolve this spatial heterogeneity. These past ecosystems were maintained by a combination of dry and cold climate and grazing pressure/disturbance by large (e.g., mammoth and horse) and small (e.g., ground squirrels) mammals. Some recent studies from Eastern Beringia (Alaska) suggest that more progress will be possible when analyses of many proxies are combined at local scales.

  13. mm-wave solid state amplifiers

    Science.gov (United States)

    Wolfert, P. H.; Crowley, J. D.; Fank, F. B.

    The development of mm-wave amplifiers using InP Gunn diodes is reviewed including a low-noise eight-stage amplifier for replacement of a Ka-band TWTA and a three-stage amplifier for the 42.5 to 44.5 range with an output power of 100 mW and 20 dB associated gain. A detailed description of a three-stage amplifier for the 54 to 58 GHz range is given with 100 mW output power and 15 dB associated gain, a small signal gain of 30 dB and an N.F. of 15.5 to 16.5 dB. The design of a broad band, low-loss V-band circulator, which was used in the amplifier, is described.

  14. Detection of Non-Amplified Genomic DNA

    CERN Document Server

    Corradini, Roberto

    2012-01-01

    This book offers a state-of-the-art overview on non amplified DNA detection methods and provides chemists, biochemists, biotechnologists and material scientists with an introduction to these methods. In fact all these fields have dedicated resources to the problem of nucleic acid detection, each contributing with their own specific methods and concepts. This book will explain the basic principles of the different non amplified DNA detection methods available, highlighting their respective advantages and limitations. The importance of non-amplified DNA sequencing technologies will be also discussed. Non-amplified DNA detection can be achieved by adopting different techniques. Such techniques have allowed the commercialization of innovative platforms for DNA detection that are expected to break into the DNA diagnostics market. The enhanced sensitivity required for the detection of non amplified genomic DNA has prompted new strategies that can achieve ultrasensitivity by combining specific materials with specifi...

  15. Semiconductor quantum-dot lasers and amplifiers

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Borri, Paola; Ledentsov, N. N.;

    2002-01-01

    We have produced GaAs-based quantum-dot edge-emitting lasers operating at 1.16 mu m with record-low transparency current, high output power, and high internal quantum efficiencies. We have also realized GaAs-based quantum-dot lasers emitting at 1.3 mu m, both high-power edge emitters and low-power...... biased to positive net gain. We have further measured gain recovery times in quantum dot amplifiers that are significantly lower than in bulk and quantum-well semiconductor optical amplifiers. This is promising for future demonstration of quantum dot devices with high modulation bandwidth...... surface emitting VCSELs. We investigated the ultrafast dynamics of quantum-dot semiconductor optical amplifiers. The dephasing time at room temperature of the ground-state transition in semiconductor quantum dots is around 250 fs in an unbiased amplifier, decreasing to below 50 fs when the amplifier is...

  16. Radiation tolerant isolation amplifiers for temperature measurement

    International Nuclear Information System (INIS)

    This paper concentrates on the selection of radiation tolerant isolation amplifiers, which are suitable for the signal conditioners for cryogenic system in the Large Hadron Collider (LHC). The evolution and the results of different commercial isolation amplifiers' parameters under neutron and gamma radiation are presented. In most cases, the tested isolation amplifiers' input offset voltage, bias currents and output offset voltage hardly changed during the radiation. The DC gain in input stage was only affected for some isolation amplifiers with a small open loop gain. Transmission coefficient showed decrease for all the tested isolation amplifiers. Also, the DC output voltage increased and the ripple voltage decreased for all the build-in isolated regulators. In addition, results on 1B41 signal conditioner showed that it was tolerant to 7-8x1012 n/cm2, which was 50% higher than the expected dose in the LHC

  17. An Implantable CMOS Amplifier for Nerve Signals

    DEFF Research Database (Denmark)

    Nielsen, Jannik Hammel; Lehmann, Torsten

    2001-01-01

    In this paper, a low noise high gain CMOS amplifier for minute nerve signals is presented. By using a mixture of weak- and strong inversion transistors, optimal noise suppression in the amplifier is achieved. A continuous-time offset-compensation technique is utilized in order to minimize impact on...... the amplifier input nodes. The method for signal recovery from noisy nerve signals is presented. A prototype amplifier is realized in a standard digital 0.5 μm CMOS single poly, n-well process. The prototype amplifier features a gain of 80 dB over a 3.6 kHz bandwidth, a CMRR of more than 87 dB and a...

  18. Design and performance of the beamlet amplifiers

    Energy Technology Data Exchange (ETDEWEB)

    Erlandson, A.C.; Rotter, M.D.; Frank, M.D.; McCracken, R.W.

    1996-06-01

    In future laser systems, such as the National Ignition Facility (NIF), multi-segment amplifiers (MSAs) will be used to amplify the laser beam to the required levels. As a prototype of such a laser architecture, the authors have designed, built, and tested flash-lamp-pumped, Nd:Glass, Brewster-angle slab MSAs for the Beamlet project. In this article, they review the fundamentals of Nd:Glass amplifiers, describe the MSA geometry, discuss parameters that are important in amplifier design, and present our results on the characterization of the Beamlet MSAs. In particular, gain and beam steering measurements show that the Beamlet amplifiers meet all optical performance specifications and perform close to model predictions.

  19. Qubit readout with a directional parametric amplifier

    Science.gov (United States)

    Sliwa, K. M.; Abdo, B.; Narla, A.; Shankar, S.; Hatridge, M.; Frunzio, L.; Schoelkopf, R. J.; Devoret, M. H.

    2014-03-01

    Josephson junction based quantum limited parametric amplifiers play an essential role in superconducting qubit measurements. These measurements necessitate circulators and isolators between the amplifier and qubit to add directionality and/or isolation. Unfortunately, this extra hardware limits both quantum measurement efficiency and experimental scalability. Here we present a quantum-limited Josephson-junction-based directional amplifier (JDA) based on a novel coupling between two nominally identical Josephson parametric converters (JPCs). The device achieves a forward gain of 11 dB with a 15 MHz dynamical bandwidth, but higher gains are possible at the expense of bandwidth. We also present measurements of a transmon qubit made with the JDA, and show minimal measurement back-action despite the absence of any isolator or circulator before the amplifier. These results provide a first step toward realizing on-chip integration of qubits and parametric amplifiers. Work supported by: IARPA, ARO, and NSF.

  20. Design of an 1800nm Raman amplifier

    DEFF Research Database (Denmark)

    Svane, Ask Sebastian; Rottwitt, Karsten

    2013-01-01

    We present the experimental results for a Raman amplifier that operates at 1810 nm and is pumped by a Raman fiber laser at 1680 nm. Both the pump laser and the Raman amplifier is polarization maintaining. A challenge when scaling Raman amplifiers to longer wavelengths is the increase in...... transmission loss, but also the reduction in the Raman gain coefficient as the amplifier wavelength is increased. Both polarization components of the Raman gain is characterized, initially for linearly co-polarized signal and pump, subsequently linearly polarized orthogonal signal and pump. The noise...... performance of the amplifier is also investigated for both configurations. Our results show an on/off gain exceeding 20 dB at 1810 nm for which the obtained effective noise figure is below 3 dB....

  1. On the Flow of Atlantic Water Towards the Arctic Ocean; a Synergy Between Altimetry and Hydrography.

    Science.gov (United States)

    Chafik, L.; Nilsson, J.; Skagseth, O.; Lundberg, P.

    2015-12-01

    The Arctic climate is strongly influenced by the inflow of warm Atlantic water conveyed by the Norwegian Atlantic Slope Current (NwASC); the main heat conveyor into the Arctic Ocean. Based on sea surface height (SSH) data from altimetry, we develop a dynamical measure of the NwASC transport to diagnose its spatio-temporal variability. This supports a dynamical division of the NwASC into two flow regimes; the Svinøy Branch (SvB) in the Norwegian Sea, and the Fram Strait Branch (FSB) west of Spitsbergen. The SvB transport is well correlated with the SSH and atmospheric variability within the Nordic Seas, factors that also affect the inflow to the Barents Sea. In contrast, the FSB is regulated by regional atmospheric patterns around Svalbard and northern Barents Sea. We further relate anomalous flow events to temperature fluctuations of Atlantic water. A warm anomaly is found to propagate northwards, with a tendency to amplify enroute, after events of strong flow in the Norwegian Sea. A roughly 12-months delayed temperature signal is identified in the FSB. This suggests that hydrographic anomalies both upstream from the North Atlantic, and locally generated in the Norwegian Sea, are important for the oceanic heat and salt transport that eventually enters into the Arctic. We believe that the combination of the flow from altimetry and temperature fluctuations in the Nordic Seas can be used to qualitatively predict warm anomalies towards the Arctic Ocean, which could be a valuable addition to the forecast skill of the statistical Arctic sea-ice models.

  2. Measurement-based upscaling of Pan Arctic Net Ecosystem Exchange: the PANEEx project

    Science.gov (United States)

    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

  3. CHARACTERISTICS OF HYDROCARBON EXPLOITATION IN ARCTIC CIRCLE

    Directory of Open Access Journals (Sweden)

    Vanja Lež

    2013-12-01

    Full Text Available The existence of large quantities of hydrocarbons is supposed within the Arctic Circle. Assumed quantities are 25% of the total undiscovered hydrocarbon reserves on Earth, mostly natural gas. Over 500 major and minor gas accumulations within the Arctic Circle were discovered so far, but apart from Snøhvit gas field, there is no commercial exploitation of natural gas from these fields. Arctic gas projects are complicated, technically hard to accomplish, and pose a great threat to the return of investment, safety of people and equipment and for the ecosystem. Russia is a country that is closest to the realization of the Arctic gas projects that are based on the giant gas fields. The most extreme weather conditions in the seas around Greenland are the reason why this Arctic region is the least explored and furthest from the realization of any gas project (the paper is published in Croatian .

  4. Ecological factors regulating growth of seaweeds in Arctic communities

    Directory of Open Access Journals (Sweden)

    Shoshina E. V.

    2016-03-01

    Full Text Available Features of seaweeds in the Arctic communities in connection with periodic and unperiodic influences of ecological factors have been analyzed. It has been shown that the existence of benthic algae biocenosis of the northern seas is mainly controlled by the primary periodic environmental factors acting as triggers that determine the direction of vegetative and generative processes, as well as contribute to the emergence of adaptive devices to extreme environmental conditions. Therefore, periodic exposure to environmental factors cause only structural changes in plant communities due to the elastic stability of fucus algae populations acquired as a result of the long process of adaptation to the northern seas conditions. Unperiodic primary factors also violate the ratio of the number by elimination and inhibit growth of certain algae age stages. However thanks to the stability of resistant the algae community can eventually restore its structural and functional organization

  5. Marine Transportation Implications of the Last Arctic Sea Ice Refuge

    Science.gov (United States)

    Brigham, L. W.

    2010-12-01

    Marine access is increasing throughout the Arctic Ocean and the 'Last Arctic Sea Ice Refuge' may have implications for governance and marine use in the region. Arctic marine transportation is increasing due to natural resource developemnt, increasing Arctic marine tourism, expanded Arctic marine research, and a general linkage of the Arctic to the gloabl economy. The Arctic Council recognized these changes with the release of the Arctic Marine Shipping Assessment of 2009. This key study (AMSA)can be viewed as a baseline assessment (using the 2004 AMSA database), a strategic guide for a host of stakeholders and actors, and as a policy document of the Arctic Council. The outcomes of AMSA of direct relevance to the Ice Refuge are within AMSA's 17 recommendations provided under three themes: Enhancing Arctic Marine Safety, Protecting Arctic People and the Environment, and Building the Arctic Marine Infrastructure. Selected recommendations of importance to the Ice Refuge include: a mandatory polar navigation code; identifying areas of heightened ecological and cultural significance; potential designation of special Arctic marine areas; enhancing the tracking and monitoring of Arctic marine traffic; improving circumpolar environmental response capacity; developing an Arctic search and rescue agreement; and, assessing the effects of marine transportation on marine mammals. A review will be made of the AMSA outcomes and how they can influence the governance, marine use, and future protection of this unique Arctic marine environment.

  6. Microbial Biomass and Population Densities of Non-Sorted Circles in High Arctic Ecosystems

    Science.gov (United States)

    Rivera-Figueroa, F.; González, G.; Gould, W. A.; Cantrell, S.; Pérez, J.

    2006-12-01

    Non-sorted circles are small patterned-ground features that occur in arctic soils as a result of intensive frost heave action. This tundra feature has been extensively described. However, little is known about the ecological relationships between this pattern and above- and belowground organisms. In this study, we compare the biomass and populaton densities of microbes in non-sorted circles and the vegetated surrounding soils (inter-circles) in the High Arctic. We collected soil samples during the summer of 2004 and 2005 on Banks and Prince Patrick and Ellef Ringnes Islands, Canada. Soil samples (0-10 cm) were gathered from non- sorted circles and inter-circles along a topographic sequence: dry (ridge), mesic (mid slope) and wet (valley) and along three transects in zonal (mesic) sites on each island. We estimated total microbial biomass and bacterial population densities using substrate induce respiration (SIR) and the most probable number method (MPN), respectively. We also isolated soil fungi using Rose Bengal and Saboraud Dextrose culture media. We are in the process of analyzing the catena samples using a terminal restriction fragment length polymorphism (TRFLP) technique of PCR-amplified 16S rRNA. Based on the SIR trials, the average microbial biomass at the mid slope position in the Banks site (Green Cabin) was 0.49 mg C g-1 dry soil in the non- sorted circles and 0.95 mg C g-1 dry soil in the inter-circles. At Prince Patrick Island (Mould Bay) the microbial biomass was 0.54 mg C g-1 dry soil in the non-sorted circles and 0.74 mg C g-1 dry soil in the inter-circles. In Ellef Ringnes (Isachsen) the microbial biomass was 0.09 mg C g-1 dry soil in the non- sorted circles and 0.14 mg C g-1 dry soil in the inter-circles. At the mesic site at Green Cabin, bacteria vary from 2.92 x 106 cell g-1 dry soil in the non-sorted circles to 6.74 x 106 cell g-1 dry soil in the inter-circles. At Mould Bay the range was 7.67 x 105 cells g-1 dry soil in the non-sorted circles

  7. Arctic Shrub Growth Response to Climate Variation and Infrastructure Development on the North Slope of Alaska

    Science.gov (United States)

    Ackerman, D.; Finlay, J. C.; Griffin, D.

    2015-12-01

    Woody shrub growth in the arctic tundra is increasing on a circumpolar scale. Shrub expansion alters land-atmosphere carbon fluxes, nutrient cycling, and habitat structure. Despite these ecosystem effects, the drivers of shrub expansion have not been precisely established at the landscape scale. This project examined two proposed anthropogenic drivers: global climate change and local infrastructure development, a press disturbance that generates high levels of dust deposition. Effects of global change were studied using dendrochronology to establish a relationship between climate and annual growth in Betula and Salix shrubs growing in the Alaskan low Arctic. To understand the spatial heterogeneity of shrub expansion, this analysis was replicated in shrub populations across levels of landscape properties including soil moisture and substrate age. Effects of dust deposition on normalized difference vegetation index (NDVI) and photosynthetic rate were measured on transects up to 625 meters from the Dalton Highway. Dust deposition rates decreased exponentially with distance from road, matching previous models of road dust deposition. NDVI tracked deposition rates closely, but photosynthetic rates were not strongly affected by deposition. These results suggest that dust deposition may locally bias remote sensing measurements such as NDVI, without altering internal physiological processes such as photosynthesis in arctic shrubs. Distinguishing between the effects of landscape properties, climate, and disturbance will improve our predictions of the biogeochemical feedbacks of arctic shrub expansion, with potential application in climate change modeling.

  8. Arctic climate response to the termination of the African Humid Period

    Science.gov (United States)

    Muschitiello, Francesco; Zhang, Qiong; Sundqvist, Hanna S.; Davies, Frazer J.; Renssen, Hans

    2015-10-01

    The Earth's climate response to the rapid vegetation collapse at the termination of the African Humid Period (AHP) (5.5-5.0 kyr BP) is still lacking a comprehensive investigation. Here we discuss the sensitivity of mid-Holocene Arctic climate to changes in albedo brought by a rapid desertification of the Sahara. By comparing a network of surface temperature reconstructions with output from a coupled global climate model, we find that, through a system of land-atmosphere feedbacks, the end of the AHP reduced the atmospheric and oceanic poleward heat transport from tropical to high northern latitudes. This entails a general weakening of the mid-latitude Westerlies, which results in a shift towards cooling over the Arctic and North Atlantic regions, and a change from positive to negative Arctic Oscillation-like conditions. This mechanism would explain the sign of rapid hydro-climatic perturbations recorded in several reconstructions from high northern latitudes at 5.5-5.0 kyr BP, suggesting that these regions are sensitive to changes in Saharan land cover during the present interglacial. This is central in the debate surrounding Arctic climate amplification and future projections for subtropical precipitation changes.

  9. Local variability in growth and reproduction of Salix arctica in the High Arctic

    Directory of Open Access Journals (Sweden)

    Noémie Boulanger-Lapointe

    2016-06-01

    Full Text Available Arctic terrestrial ecosystems are heterogeneous because of the strong influences of microtopography, soil moisture and snow accumulation on vegetation distribution. The interaction between local biotic and abiotic factors and global climate patterns will influence species responses to climate change. Salix arctica (Arctic willow is a structuring species, ubiquitous and widespread, and as such is one of the most important shrub species in the High Arctic. In this study, we measured S. arctica reproductive effort, early establishment, survival and growth in the Zackenberg valley, north-east Greenland. We sampled four plant communities that varied with respect to snow conditions, soil moisture, nutrient content and plant composition. We found large variability in reproductive effort and success with total catkin density ranging from 0.6 to 66 catkins/m2 and seedling density from <1 to 101 seedlings/m2. There were also major differences in crown area increment (4–23 cm2/year and stem radial growth (40–74 µm/year. The snowbed community, which experienced a recent reduction in snow cover, supported young populations with high reproductive effort, establishment and growth. Soil nutrient content and herbivore activity apparently did not strongly constrain plant reproduction and growth, but competition by Cassiope tetragona and low soil moisture may inhibit performance. Our results show that local environmental factors, such as snow accumulation, have a significant impact on tundra plant response to climate change and will affect the understanding of regional vegetation response to climate change.

  10. Large increases in Arctic biogenic volatile emissions are a direct effect of warming

    Science.gov (United States)

    Kramshøj, Magnus; Vedel-Petersen, Ida; Schollert, Michelle; Rinnan, Åsmund; Nymand, Josephine; Ro-Poulsen, Helge; Rinnan, Riikka

    2016-05-01

    Biogenic volatile organic compounds are reactive gases that can contribute to atmospheric aerosol formation. Their emission from vegetation is dependent on temperature and light availability. Increasing temperature, changing cloud cover and shifting composition of vegetation communities can be expected to affect emissions in the Arctic, where the ongoing climate changes are particularly severe. Here we present biogenic volatile organic compound emission data from Arctic tundra exposed to six years of experimental warming or reduced sunlight treatment in a randomized block design. By separately assessing the emission response of the whole ecosystem, plant shoots and soil in four measurements covering the growing season, we have identified that warming increased the emissions directly rather than via a change in the plant biomass and species composition. Warming caused a 260% increase in total emission rate for the ecosystem and a 90% increase in emission rates for plants, while having no effect on soil emissions. Compared to the control, reduced sunlight decreased emissions by 69% for the ecosystem, 61-65% for plants and 78% for soil. The detected strong emission response is considerably higher than observed at more southern latitudes, emphasizing the high temperature sensitivity of ecosystem processes in the changing Arctic.

  11. Vegetation composition and shrub extent on the Yukon coast, Canada, are strongly linked to ice-wedge polygon degradation

    OpenAIRE

    Wolter, Juliane; Lantuit, Hugues; Fritz, Michael; Macias-Fauria, Marc; Myers-Smith, Isla; Herzschuh, Ulrike

    2016-01-01

    Changing environmental and geomorphological conditions are resulting in vegetation change in ice-wedge polygons in Arctic tundra. However, we do not yet know how microscale vegetation patterns relate to individual environmental and geomorphological parameters. This work aims at examining these relations in polygonal terrain. We analysed composition and cover of vascular plant taxa and surface height, active layer depth, soil temperature, carbon and nitrogen content, pH and electrical conducti...

  12. Vegetation Fuel Mapping

    Directory of Open Access Journals (Sweden)

    A. V. Volokitina

    2014-12-01

    Full Text Available All vegetation sites as objects of burning are structural complexes of various fuels. Especially complex are forest biogeoceonoses. For practical use, pyrological characteristics of vegetation are reflected on plans and maps showing both general one-sided estimations with site descriptions (for example, their fire hazard and detailed multi-sided characteristics of all compounds in the vegetation fuel complexes. The latter become basic maps for obtaining various pyrological estimations and are called vegetation fuel maps. Vegetation fuel (VF mapping can be made using two methodological approaches: first, by distinguishing pyrological vegetation categories as standard complexes; second, by individually characterizing each vegetation site in terms of VF. Obviously, the standard VF characteristic of sites can be only approximate and rough, since the possible number of studied site categories is limited. For large-scale mapping, the detailed individual characteristic of vegetation sites in terms of VF is more preferable and precise but more expensive. Therefore, historically, the first approach to VF mapping got its development, i. e. distinguishing and mapping of certain vegetation categories with standard characteristics. Foreign and Russian methodical approaches to vegetation fuel (VF classification and mapping are considered. Examples of VF mapping at different scales and guidelines for their use are given.

  13. Arctic Visiting Speakers Series (AVS)

    Science.gov (United States)

    Fox, S. E.; Griswold, J.

    2011-12-01

    The Arctic Visiting Speakers (AVS) Series funds researchers and other arctic experts to travel and share their knowledge in communities where they might not otherwise connect. Speakers cover a wide range of arctic research topics and can address a variety of audiences including K-12 students, graduate and undergraduate students, and the general public. Host applications are accepted on an on-going basis, depending on funding availability. Applications need to be submitted at least 1 month prior to the expected tour dates. Interested hosts can choose speakers from an online Speakers Bureau or invite a speaker of their choice. Preference is given to individuals and organizations to host speakers that reach a broad audience and the general public. AVS tours are encouraged to span several days, allowing ample time for interactions with faculty, students, local media, and community members. Applications for both domestic and international visits will be considered. Applications for international visits should involve participation of more than one host organization and must include either a US-based speaker or a US-based organization. This is a small but important program that educates the public about Arctic issues. There have been 27 tours since 2007 that have impacted communities across the globe including: Gatineau, Quebec Canada; St. Petersburg, Russia; Piscataway, New Jersey; Cordova, Alaska; Nuuk, Greenland; Elizabethtown, Pennsylvania; Oslo, Norway; Inari, Finland; Borgarnes, Iceland; San Francisco, California and Wolcott, Vermont to name a few. Tours have included lectures to K-12 schools, college and university students, tribal organizations, Boy Scout troops, science center and museum patrons, and the general public. There are approximately 300 attendees enjoying each AVS tour, roughly 4100 people have been reached since 2007. The expectations for each tour are extremely manageable. Hosts must submit a schedule of events and a tour summary to be posted online

  14. Phytomass patterns across a temperature gradient of the North American arctic tundra

    Science.gov (United States)

    Epstein, Howard E.; Walker, Donald A.; Raynolds, Martha K.; Jia, Gensuo J.; Kelley, Alexia M.

    2008-09-01

    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. An additional complicating factor for studying vegetation of arctic tundra is the high spatial variability associated with small patterned-ground features, 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°C of mean July temperatures. Vegetation biomass was analyzed as functions of the summer warmth index (SWI-sum of mean monthly temperatures > 0°C). The total absolute biomass (g m-2) and biomass of shrubs increased monotonically with SWI, however, biomass of nonvascular species (mosses and lichens), were a parabolic function of SWI, with greatest values at the ends of the gradient. The components of plant biomass on patterned-ground features (i.e., on nonsorted circles or within small polygons) were constrained to a greater degree with colder climate than undisturbed tundra, likely due to the effect of frost heave disturbances on the vegetation. There were also clear differences in the relative abundances of vascular versus nonvascular plants on and off patterned-ground features along the SWI gradient. The spatial patterns of biomass differ among plant functional groups and suggest that plant community responses to temperature, and land-surface processes that produce patterned-ground features, are quite complex.

  15. Arctic sea ice and Eurasian climate: A review

    OpenAIRE

    Gao, Yongqi; Sun, Jianqi; Li, Fei; HE Shengping; Sandven, Stein; Yan, Qing; Zhang, Zhongshi; Lohmann, Katja; Keenlyside, Noel; Furevik, Tore; Suo, Lingling

    2014-01-01

    The Arctic plays a fundamental role in the climate system and has shown significant climate change in recent decades, including the Arctic warming and decline of Arctic sea-ice extent and thickness. In contrast to the Arctic warming and reduction of Arctic sea ice, Europe, East Asia and North America have experienced anomalously cold conditions, with record snowfall during recent years. In this paper, we review current understanding of the sea-ice impacts on the Eurasian climate. Paleo, obser...

  16. THE ARCTIC: AN INDICATOR OF THE PLANET"S HEALTH

    OpenAIRE

    Callaghan, Terry

    2012-01-01

    The Arctic is a critically important component of the earth system and the Arctic is subject to dramatic change due to global warming in particular. To build capacity for better environmental monitoring and research in the Arctic, the EU has funded the SCANNET-INTERACT Consortium, which consists of partners from all the Arctic countries and 33 research infrastructures located throughout the large environmental envelope of the Arctic and a further 8 research facilities have joined as "observer...

  17. Radioactivity assessment in the Arctic Monitoring and Assessment Programme

    International Nuclear Information System (INIS)

    In 1991 ministers from eight Arctic countries committed themselves to the establishment of the Arctic Monitoring and Assessment Programme (AMAP). AMAP was asked to prepare regular State of the Arctic Environment Reports. This paper describes the background, methods and table of contents of the radioactivity section of the State of the Arctic Environment Report, being prepared for presentation to the ministers from the eight Arctic countries in 1996. 2 refs

  18. Estimating carbon and energy fluxes in arctic tundra

    Science.gov (United States)

    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

  19. The scavenging processes controlling the seasonal cycle in Arctic sulphate and black carbon aerosol

    Directory of Open Access Journals (Sweden)

    J. Browse

    2012-01-01

    Full Text Available The seasonal cycle in Arctic aerosol is typified by high concentrations of large aged anthropogenic particles transported from lower latitudes in the late Arctic winter and early spring followed by a sharp transition to low concentrations of locally sourced smaller particles in the summer. However, multi-model assessments show that many models fail to simulate a realistic cycle. Here, we use a global aerosol microphysics model and surface-level aerosol observations to understand how wet scavenging processes control the seasonal variation in Arctic black carbon (BC and sulphate aerosol concentrations. We show that the transition from high wintertime to low summertime Arctic aerosol concentrations is caused by the change from inefficient scavenging in ice clouds to the much more efficient scavenging in warm liquid clouds. This seasonal cycle is amplified further by the appearance of warm drizzling cloud in late spring and summer at a time when aerosol transport shifts mainly to low levels. Implementing these processes in a model greatly improves the agreement between the model and observations at the three Arctic ground-stations Alert, Barrow and Zeppelin Mountain on Svalbard. The SO4 model-observation correlation coefficient (R increases from: −0.33 to 0.71 at Alert (82.5° N, from −0.16 to 0.70 at Point Barrow (71.0° N and from −0.42 to 0.40 at Zeppelin Mountain (78° N while, the BC model-observation correlation coefficient increases from −0.68 to 0.72 at Alert and from −0.42 to 0.44 at Barrow. Observations at three marginal Arctic sites (Janiskoski, Oulanka and Karasjok indicate a far weaker aerosol seasonal cycle, which we show is consistent with the much smaller seasonal changes in ice clouds compared to the higher latitude sites. Our results suggest that the seasonal cycle in Arctic aerosol is driven by temperature-dependent scavenging processes that may be susceptible to modification in a future climate.

  20. Deeper snow alters soil nutrient availability and leaf nutrient status in high Arctic tundra

    DEFF Research Database (Denmark)

    Semenchuk, Philipp R.; Elberling, Bo; Amtorp, Cecilie;

    2015-01-01

    Svalbard in two vegetation types spanning three moisture regimes. We measured growing-season availability of ammonium (NH4 (+)), nitrate (NO3 (-)), total dissolved organic carbon (DOC) and nitrogen (TON) in soil; C, N, delta N-15 and chlorophyll content in Salix polaris leaves; and leaf sizes of Salix...... season. Changing nutrient availability may be reflected in plant N and chlorophyll content and lead to increased photosynthetic capacity, plant growth, and ultimately carbon (C) assimilation by plants. In this study, we increased snow depth and thereby cold-season soil temperatures in high Arctic...... some species. Responses to cold-season soil warming are vegetation type- and species-specific, with potentially stronger responses in moister vegetation types. This study therefore highlights the contrasting effect of snow in a tundra landscape and has important implications for projections of whole...

  1. The 60 GHz solid state power amplifier

    Science.gov (United States)

    Mcclymonds, J.

    1991-01-01

    A new amplifier architecture was developed during this contract that is superior to any other solid state approach. The amplifier produced 6 watts with 4 percent efficiency over a 2 GHz band at 61.5 GHz. The unit was 7 x 9 x 3 inches in size, 5.5 pounds in weight, and the conduction cooling through the baseplate is suitable for use in space. The amplifier used high efficiency GaAs IMPATT diodes which were mounted in 1-diode circuits, called modules. Eighteen modules were used in the design, and power combining was accomplished with a proprietary passive component called a combiner plate.

  2. Laser Cooled High-Power Fiber Amplifier

    OpenAIRE

    Nemova, Galina

    2009-01-01

    A theoretical model for laser cooled continuous-wave fiber amplifier is presented. The amplification process takes place in the Tm3+-doped core of the fluoride ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) glass fiber. The cooling process takes place in the Yb3+:ZBLAN fiber cladding. It is shown that for each value of the pump power and the amplified signal there is a distribution of the concentration of the Tm3+ along the length of the fiber amplifier, which provides its athermal operation. The influence ...

  3. Effect of Soliton Propagation in Fiber Amplifiers

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The propagation of optical solitons in fiber amplifiers is discussed by considering a model that includes linear high order dispersion, two-photon absorption, nonlinear high-order dispersion, self-induced Ramam and five-order nonlinear effects. Based on travelling wave method, the solutions of the nonlinear Schrdinger equations, and the influence on soliton propagation as well as high-order effect in the fiber amplifier are discussed in detail. It is found that because of existing five-order nonlinear effect, the solution is not of secant hyperbola type, but shows high gain state of the fiber amplifier which is very favourable to the propagation of solitons.

  4. Noise reduction in AC-coupled amplifiers

    OpenAIRE

    Serrano Finetti, Roberto Ernesto; Pallàs Areny, Ramon

    2014-01-01

    AC-coupled amplifiers are noisier than dc-coupled amplifiers because of the thermal noise of the resistor(s) in the ac-coupling network and the increased contribution of the amplifier input noise current i(n). Both contributions, however, diminish if the corner frequency f(c) of the high-pass filter observed by the signal is lowered, the cost being a longer transient response. At the same time, the presence of large resistors in the ac-coupling network suggests that the use of FET-input ampli...

  5. Fundamentals of RF and microwave transistor amplifiers

    CERN Document Server

    Bahl, Inder J

    2009-01-01

    A Comprehensive and Up-to-Date Treatment of RF and Microwave Transistor Amplifiers This book provides state-of-the-art coverage of RF and microwave transistor amplifiers, including low-noise, narrowband, broadband, linear, high-power, high-efficiency, and high-voltage. Topics covered include modeling, analysis, design, packaging, and thermal and fabrication considerations. Through a unique integration of theory and practice, readers will learn to solve amplifier-related design problems ranging from matching networks to biasing and stability. More than 240 problems are included to help read

  6. Observed and model simulated 20th century Arctic temperature variability: Canadian Earth System Model CanESM2

    Science.gov (United States)

    Chylek, P.; Li, J.; Dubey, M. K.; Wang, M.; Lesins, G.

    2011-08-01

    We present simulations of the 20th century Arctic temperature anomaly from the second generation Canadian Earth System Model (CanESM2). The new model couples together an atmosphere-ocean general circulation model, a land-vegetation model and terrestrial and oceanic interactive carbon cycle. It simulates well the observed 20th century Arctic temperature variability that includes the early and late 20th century warming periods and the intervening 1940-1970 period of substantial cooling. The addition of the land-vegetation model and the terrestrial and oceanic interactive carbon cycle to the coupled atmosphere-ocean model improves the agreement with observations from 1900-1970, however, it increases the overestimate of the post 1970 warming. In contrast the older generation coupled atmosphere-ocean general circulation models Canadian CanCM3 and NCAR/LANL CCSM3, used in the IPCC 2007 climate change assessment report, overestimate the rate of the 20th century Arctic warming by factor of two to three and they are unable to reproduce the observed 20th century Arctic climate variability.

  7. Observed and model simulated 20th century Arctic temperature variability: Canadian Earth System Model CanESM2

    Directory of Open Access Journals (Sweden)

    P. Chylek

    2011-08-01

    Full Text Available We present simulations of the 20th century Arctic temperature anomaly from the second generation Canadian Earth System Model (CanESM2. The new model couples together an atmosphere-ocean general circulation model, a land-vegetation model and terrestrial and oceanic interactive carbon cycle. It simulates well the observed 20th century Arctic temperature variability that includes the early and late 20th century warming periods and the intervening 1940–1970 period of substantial cooling. The addition of the land-vegetation model and the terrestrial and oceanic interactive carbon cycle to the coupled atmosphere-ocean model improves the agreement with observations from 1900–1970, however, it increases the overestimate of the post 1970 warming. In contrast the older generation coupled atmosphere-ocean general circulation models Canadian CanCM3 and NCAR/LANL CCSM3, used in the IPCC 2007 climate change assessment report, overestimate the rate of the 20th century Arctic warming by factor of two to three and they are unable to reproduce the observed 20th century Arctic climate variability.

  8. Vegetative pyoderma gangrenosum

    OpenAIRE

    Kim, Randie H.; Lewin, Jesse; Hale, Christopher S; Meehan, Shane A.; Stein, Jennifer; Ramachandran, Sarika

    2015-01-01

    Vegetative pyoderma gangrenosum is a rare, superficial variant of pyoderma gangrenosum that is more commonly found on the trunk as single or multiple, non-painful lesions. There is typically no associated underlying systemic disease. Compared to classic pyoderma gangrenosum, vegetative lesions are more likely to heal without the use of systemic glucocorticoids, although up to 39% of patients required a short course of prednisone in a review of 46 cases. Treatments for vegetative pyoderma gang...

  9. Facility engineering for Arctic conditions

    Energy Technology Data Exchange (ETDEWEB)

    Hunt, D.M.; McClusky, K.R.; Shirley, R.; Spitzenberger, R. [Mustang Engineering Inc., Houston, TX (United States)

    2001-07-01

    The Northstar Development Project is located on Seal Island in the Beaufort Sea, north of Prudhoe Bay. The design and engineering of the facilities for the Northstar Development Project was fraught with challenges. Mustang Engineering Incorporated was involved in the design and engineering of the pipe rack, pump house, process and compressor modules. All the characteristics of an offshore facility are present, even though the project is land-based on a man-made island. A number of the strategies developed for offshore platforms of the Gulf of Mexico were adapted to the fabrication, logistics and installation of the modules. To reduce yard fabrication time, a modularized design concept was adopted. Cost savings and onsite fabrication efficiencies were realized through open communication with the operator, early discussions with vendors, regulatory agencies, and local fabrication and installation contractors. Some improvisation and deviations were required to meet the stringent requirements for operation under Arctic conditions. The lessons learned on this project will be of use in future Arctic projects. 1 tab., 6 figs.

  10. Environmental marine geology of the Arctic Ocean

    International Nuclear Information System (INIS)

    The Arctic Ocean and its ice cover are major regulators of Northern Hemisphere climate, ocean circulation and marine productivity. The Arctic is also very sensitive to changes in the global environment because sea ice magnifies small changes in temperature, and because polar regions are sinks for air pollutants. Marine geology studies are being carried out to determine the nature and rate of these environmental changes by study of modern ice and sea bed environments, and by interpretation of geological records imprinted in the sea floor sediments. Sea ice camps, an ice island, and polar icebreakers have been used to study both western and eastern Arctic Ocean basins. Possible early warning signals of environmental changes in the Canadian Arctic are die-back in Arctic sponge reefs, outbreaks of toxic dinoflagellates, and pesticides in the marine food chain. Eastern Arctic ice and surface waters are contaminated by freon and radioactive fallout from Chernobyl. At present, different sedimentary processes operate in the pack ice-covered Canadian polar margin than in summer open waters off Alaska and Eurasia. The geological records, however, suggest that a temperature increase of 1-4C would result in summer open water throughout the Arctic, with major changes in ocean circulation and productivity of waters off Eastern North America, and more widespread transport of pollutants from eastern to western Arctic basins. More studies of longer sediment cores are needed to confirm these interpretations, but it is now clear that the Arctic Ocean has been the pacemaker of climate change during the past 1 million years

  11. Environmental marine geology of the Arctic Ocean

    International Nuclear Information System (INIS)

    The Arctic Ocean and its ice cover are major regulators of Northern Hemisphere climate, ocean circulation and marine productivity. The Arctic is also very sensitive to changes in the global environment because sea ice magnifies small changes in temperature, and because polar regions are sinks for air pollutants. Marine geology studies are being carried out to determine the nature and rate of these environmental changes by study of modem ice and sea-bed environments, and by interpretation of geological records imprinted in the sea-floor sediments. Sea ice camps, an ice island, and polar icebreakers have been used to study both western and eastern Arctic Ocean basins. Possible early warning signals of environmental changes in the Canadian Arctic are die-back in Arctic sponge reefs, outbreaks of toxic dinoflagellates, and pesticides in the marine food chain. Eastern Arctic ice and surface waters are contaminated by freon and radioactive fallout from Chernobyl. At present, different sedimentary processes operate in the pack ice-covered Canadian polar margin than in summer open waters off Alaska and Eurasia. The geological records, however, suggest that a temperature increase of 1-4 degree C would result in summer open water throughout the Arctic, with major changes in ocean circulation and productivity of waters off Eastern North America, and more widespread transport of pollutants from eastern to western Arctic basins. More studies of longer sediment cores are needed to confirm these interpretations, but is is now clear that the Arctic Ocean has been the pacemaker of climate change during the past 1 million years

  12. Irradiation of dehydrated vegetables

    International Nuclear Information System (INIS)

    The reason for radurization was to decreased the microbial count of dehydrated vegetables. The average absorbed irradiation dose range between 2kGy and 15kGy. The product catagories include a) Green vegetables b) White vegetables c) Powders of a) and b). The microbiological aspects were: Declining curves for the different products of T.P.C., Coliforms, E. Coli, Stap. areus, Yeast + Mold at different doses. The organoleptical aspects were: change in taste, flavour, texture, colour and moisture. The aim is the marketing of irradiated dehydrated vegetables national and international basis

  13. Shared Knowledge for Decision-making on Environment and Health Issues in the Arctic

    Science.gov (United States)

    Maynard, Nancy G.

    2003-01-01

    This paper will describe a remote sensing and GIs-based system to bring indigenous traditional knowledge together with contemporary scientific knowledge to address impacts resulting from changes in climate, environment, weather and pollution in the Arctic. As scientists and policy-makers from both indigenous and non-indigenous communities continue to build closer partnerships to address common sustainability issues such as the health impacts of climate change and anthropogenic activities, it becomes increasingly important to create shared information management systems which integrate all relevant factors for optimal information sharing and decision-making. This system is being designed to bring together remotely sensed, indigenous and other data and observations for analysis, measuring, and monitoring parameters of interest (e.g., snow cover, rainfall, temperature, ice conditions, vegetation, infrastructure, fires). A description of the system and its components as well as a preliminary application of the system in the Arctic will be presented.

  14. Ambient UV-B radiation reduces PSII performance and net photosynthesis in high Arctic Salix arctica

    DEFF Research Database (Denmark)

    Albert, Kristian Rost; Mikkelsen, Teis Nørgaard; Ro-Poulsen, Helge;

    2011-01-01

    Ambient ultraviolet-B (UV-B) radiation potentially impacts the photosynthetic performance of high Arctic plants. We conducted an UV-B exclusion experiment in a dwarf shrub heath in NE Greenland (74°N), with open control, filter control, UV-B filtering and UV-AB filtering, all in combination with......, nitrogen and UV-B absorbing compounds. Compared to a 60% reduced UV-B irradiance, the ambient solar UV-B reduced net photosynthesis in Salix arctica leaves fixed in the 45° position which exposed leaves to maximum natural irradiance. Also a reduced Calvin Cycle capacity was found, i.e. the maximum rate of...... across position in the vegetation. These findings add to the evidence that the ambient solar UV-B currently is a significant stress factor for plants in high Arctic Greenland....

  15. Investigating vegetation-climate feedbacks during the early Eocene

    Directory of Open Access Journals (Sweden)

    C. A. Loptson

    2013-08-01

    Full Text Available Evidence suggests that the early Eocene was a time of extreme global warmth, extending to the high latitudes. However, there are discrepancies between the results of many previous modelling studies and the proxy data at high latitudes, with models struggling to simulate the shallow temperature gradients of this time period to the same extent as the proxies indicate. Vegetation-climate feedbacks play an important role in the present day, but are often neglected in paleoclimate modelling studies and this may be a contributing factor to resolving the model-data discrepancy. Here we investigate these vegetation-climate feedbacks by carrying out simulations of the early Eocene climate at 2 × and 4 × pre-industrial atmospheric CO2 with fixed vegetation (homogeneous shrubs everywhere and dynamic vegetation. The results show that the simulations with dynamic vegetation are warmer in the global annual mean than the simulations with fixed shrubs by 0.9 °C at 2 × and 1.8 °C at 4 ×. In addition, the warming when CO2 is doubled from 2 × to 4 × is 1 °C higher (in the global annual mean with dynamic vegetation than with fixed shrubs. This corresponds to an increase in climate sensitivity of 26%. This difference in warming is enhanced at high latitudes, with temperatures increasing by over 50% in some regions of Antarctica. In the Arctic, ice-albedo feedbacks are responsible for the majority of this warming. On a global scale, energy balance analysis shows that the enhanced warming with dynamic vegetation is mainly associated with an increase in atmospheric water vapour but changes in clouds also contribute to the temperature increase. It is likely that changes in surface albedo due to changes in vegetation cover resulted in an initial warming which triggered these water vapour feedbacks. In conclusion, dynamic vegetation goes some way to resolving the discrepancy, but our modelled temperatures cannot reach the same warmth as the data suggests in the

  16. Spatial distribution of thermokarst landforms across Arctic Alaska

    Science.gov (United States)

    Farquharson, L. M.; Grosse, G.; Romanovsky, V. E.; Jones, B. M.; Arp, C. D.; McGuire, A. D.

    2013-12-01

    Arctic Alaska is characterized by widespread past and present thaw of ice rich permafrost and subsequent thermokarst development. Variations in ice content and distribution, and topography across Arctic Alaska result in thermokarst landform diversity. Thermokarst causes a number of biogeochemical and ecological shifts that include changes in soil carbon dynamics, nutrient cycling, vegetation composition, wildlife habitat, and fresh water availability. Ongoing climate change may lead to an increase in thermokarst landscape features. Thus, a better understanding of the current temporal and spatial dynamics of thermokarst is needed in order to project its future dynamics. Understanding how vulnerable Arctic Alaska is to future thermokarst development is critical for resource management, industry development, and subsistence hunting. We focused on the distribution of thermokarst landforms among ten study sites aligned with the NSF CALON (Towards a Circum-Arctic Lakes Observation Network) project in Arctic Alaska. Sites represent diverse substrates including eolian silt, eolian sand, marine sand, deltaic, and marine silt. We conducted thermokarst landform mapping and spatial and morphometric analyses using high-resolution aerial photography, an interferometric synthetic aperture radar derived digital elevation model (IfSAR DEM), and hydrographic layers from the National Land Cover Database derived from Landsat-7. Non-lake thermokarst landforms were visually mapped and hand digitized using aerial photographs and the IfSAR DEM. Initial results show thermokarst forms are most prevalent in marine silt areas with up to 99% of study areas affected by thermokarst activity. Eolian sand areas are the least thermokarst affected (mean of 57%). Drained thermokarst lake basins, thermokarst lakes, and areas affected by thermokarst pit formation were the dominant thermokarst landforms, covering up to 70%, 54%, and 8% of the landscape. The number of overlapping lake and basin

  17. Atmospheric DMS in the High Arctic

    OpenAIRE

    Lundén, Jenny

    2010-01-01

    During the Arctic summer when the anthropogenic influence is limited, the natural marine source of sulfur in the form of gas-phase dimethyl sulfide viz. DMS(g), is of great importance for cloud formation. The harsh environment of the Arctic makes it difficult to perform in situ measurements of DMS(g) and hence regional model simulations can serve as a complement to increase our understanding of DMS related processes in the Arctic. In this thesis a regional scale meteorological forecast model,...

  18. The adaptation challenge in the Arctic

    Science.gov (United States)

    Ford, James D.; McDowell, Graham; Pearce, Tristan

    2015-12-01

    It is commonly asserted that human communities in the Arctic are highly vulnerable to climate change, with the magnitude of projected impacts limiting their ability to adapt. At the same time, an increasing number of field studies demonstrate significant adaptive capacity. Given this paradox, we review climate change adaptation, resilience and vulnerability research to identify and characterize the nature and magnitude of the adaptation challenge facing the Arctic. We find that the challenge of adaptation in the Arctic is formidable, but suggest that drivers of vulnerability and barriers to adaptation can be overcome, avoided or reduced by individual and collective efforts across scales for many, if not all, climate change risks.

  19. Politics of sustainability in the Arctic (POSUSA)

    DEFF Research Database (Denmark)

    Gad, Ulrik Pram; Jakobsen, Uffe; Strandsbjerg, Jeppe

    The concept of sustainability is of central importance in Arctic politics. However, for different actors (governments, indigenious peoples, NGOs) the concept implies different sets of precautions and opportunities. Sustainability, therefore, is much more a fundamental concept to be further...... elaborated than a definable term with a specific meaning. This is the core hypothesis in a collective research project, the POSUSA project (Politics of Sustainability in the Arctic) that aims to map and analyse the role of sustainability in various political and economic strategies in the Arctic....

  20. Introduction: World Routes in the Arctic

    Directory of Open Access Journals (Sweden)

    Art Leete

    2011-12-01

    Full Text Available The Arctic is associated in popular perception with a vast frozen snow covered empty place. Everybody who has been in the Arctic, whether in the Eurasian or North American part, knows that this stereotype is correct. Indeed, the Arctic is a place with lots of space that determines the lifestyle of the people in this area. All human activities – whether livelihood or mastering of the territory– are and always have been connected with substantial movement. Hunting, fishing, trading, the establishment of settlements and keeping them alive, all this needs the movement of goods and human resources.

  1. On the role of temperature feedbacks for Arctic amplification

    Science.gov (United States)

    Pithan, Felix; Mauritsen, Thorsten

    2013-04-01

    The amplification of global climate changes at the poles is a well-known feature of the climate system mentioned already by Arrhenius (1896). It has been linked to the surface-albedo feedback, changes in atmospheric and oceanic heat convergence, water vapour and cloud feedbacks and the albedo effect of black carbon on snow (Serreze and Barry, 2011). We here focus on the role of temperature feedbacks, which have received rather little attention in recent debates. The basic temperature feedback is the Planck feedback or the increase in the Earth's blackbody radiation due to a uniform temperature increase. Since the blackbody radiation scales with the fourth power of temperature, stronger warming is necessary in cold regions to balance a globally uniform radiative forcing. The second temperature feedback is caused by changes in the vertical atmospheric temperature structure: In the Tropics, deep convection leads to warming aloft being larger than at the surface, which causes a greater increase in outgoing longwave radiation compared a vertically uniform forcing and thus constitutes a negative feedback mechanism. In the Arctic, where warming is amplified at the surface, the lapse-rate feedback is positive (Wetherald and Manabe, 1975). We use CMIP5 model output and radiative Kernels to investigate the zonal distribution of temperature feedbacks. Arrhenius, S. (1896). On the influence of carbonic acid in the air upon the temperature of the ground Philos. Mag. J. Sci., 5, pp. 237-276 Serreze, M.C. and Barry, R.G. (2011) . Processes and impacts of Arctic amplification: A research synthesis, Global and Planetary Change, 77(1-2), pp. 85-96 Wetherald, R. and Manabe, S. (1975). The effects of changing the solar constant on the climate of a general circulation model. J. Atmos. Sci., 23 pp 2044-2059

  2. High Energy Single Frequency Resonant Amplifier Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This SBIR phase I project proposes a single frequency high energy resonant amplifier for remote sensing. Current state-of-art technologies can not provide all...

  3. Noise in phase-preserving linear amplifiers

    Energy Technology Data Exchange (ETDEWEB)

    Pandey, Shashank; Jiang, Zhang; Combes, Joshua [Center for Quantum Information and Control, University of New Mexico, Albuquerque, NM 87131-0001 (United States); Caves, Carlton M. [Center for Quantum Information and Control, University of New Mexico, Albuquerque, NM 87131-0001, USA and Centre for Engineered Quantum Systems, School of Mathematics and Physics, University of Queensland, Brisbane, QLD 4072 (Australia)

    2014-12-04

    The purpose of a phase-preserving linear amplifier is to make a small signal larger, so that it can be perceived by instruments incapable of resolving the original signal, while sacrificing as little as possible in signal-to-noise. Quantum mechanics limits how well this can be done: the noise added by the amplifier, referred to the input, must be at least half a quantum at the operating frequency. This well-known quantum limit only constrains the second moments of the added noise. Here we provide the quantum constraints on the entire distribution of added noise: any phasepreserving linear amplifier is equivalent to a parametric amplifier with a physical state σ for the ancillary mode; σ determines the properties of the added noise.

  4. Noise in phase-preserving linear amplifiers

    Science.gov (United States)

    Pandey, Shashank; Jiang, Zhang; Combes, Joshua; Caves, Carlton M.

    2014-12-01

    The purpose of a phase-preserving linear amplifier is to make a small signal larger, so that it can be perceived by instruments incapable of resolving the original signal, while sacrificing as little as possible in signal-to-noise. Quantum mechanics limits how well this can be done: the noise added by the amplifier, referred to the input, must be at least half a quantum at the operating frequency. This well-known quantum limit only constrains the second moments of the added noise. Here we provide the quantum constraints on the entire distribution of added noise: any phasepreserving linear amplifier is equivalent to a parametric amplifier with a physical state σ for the ancillary mode; σ determines the properties of the added noise.

  5. Cryogenic Amplifier Based Receivers at Submillimeter Wavelengths

    Science.gov (United States)

    Chattopadhyay, Goutam; Reck, Theodore and; Schlecht, Erich; Lin, Robert; Deal, William

    2012-01-01

    The operating frequency of InP high electron mobility transistor (HEMT) based amplifiers has moved well in the submillimeter-wave frequencies over the last couple of years. Working amplifiers with usable gain in waveguide packages has been reported beyond 700 GHz. When cooled cryogenically, they have shown substantial improvement in their noise temperature. This has opened up the real possibility of cryogenic amplifier based heterodyne receivers at submillimeter wavelengths for ground-based, air-borne, and space-based instruments for astrophysics, planetary, and Earth science applications. This paper provides an overview of the science applications at submillimeter wavelengths that will benefit from this technology. It also describes the current state of the InP HEMT based cryogenic amplifier receivers at submillimeter wavelengths.

  6. Application of a Real-time Reverse Transcription Loop Mediated Amplification Method to the Detection of Rabies Virus in Arctic Foxes in Greenland

    DEFF Research Database (Denmark)

    Wakeley, Philip; Johnson, Nicholas; Rasmussen, Thomas Bruun

    Reverse transcription loop mediated amplification (RT-LAMP) offers a rapid, isothermal method for amplification of virus RNA. In this study a panel of positive rabies virus samples originally prepared from arctic fox brain tissue was assessed for the presence of rabies viral RNA using a real time...... RT-LAMP. The method had previously been shown to work with samples from Ghana which clustered with cosmopolitan lineage rabies viruses but the assay had not been assessed using samples from animals infected with rabies from the arctic region. The assay is designed to amplify both cosmopolitan strains...... and arctic-like strains of classical rabies virus due to the primer design and is therefore expected to be universally applicable independent of region of the world where the virus is isolated. Of the samples tested all were found to be positive after incubation for 25 to 30 minutes. The method made...

  7. Quantum cloning with an optical fiber amplifier

    OpenAIRE

    Fasel, Sylvain; Gisin, Nicolas; Ribordy, Grégoire; Scarani, Valerio; Zbinden, Hugo

    2002-01-01

    It has been shown theoretically that a light amplifier working on the physical principle of stimulated emission should achieve optimal quantum cloning of the polarization state of light. We demonstrate close-to-optimal universal quantum cloning of polarization in a standard fiber amplifier for telecom wavelengths. For cloning 1 --> 2 we find a fidelity of 0.82, the optimal value being 5/6 = 0.83.

  8. Permafrost dynamics structure species compositions of oribatid mite (Acari: Oribatida) communities in sub-Arctic palsa mires

    OpenAIRE

    Markkula, Inkeri

    2014-01-01

    Palsa mires are sub-Arctic peatland complexes, vulnerable ecosystems with patches of permafrost. Permafrost thawing in palsa mires occurs throughout Fennoscandia, probably due to local climatic warming. In palsa mires, permafrost thaw alters hydrological conditions, vegetation structure and microhabitat composition with unknown consequences for invertebrate fauna. This study's objectives were to examine the role of microhabitat heterogeneity and the effects of permafrost dynamics and thaw on ...

  9. The Unexpected Re-Growth of Ice-Entombed Bryophytes in the Canadian High Arctic

    Science.gov (United States)

    La Farge, C.

    2014-12-01

    The rapid retreat of glaciers and ice caps throughout the Canadian Arctic is exposing pristine vegetation preserved beneath cold-based ice. For the past half century this vegetation has been consistently reported as dead. This interpretation has been overturned by the successful re-growth of Little Ice Age (1550-1850 AD) bryophytes emerging from the Teardrop Glacier, Sverdrup Pass, Ellesmere Island (79° N) collected in 2009. Some populations showed regeneration in the field and lab experiments confirmed their capacity to regrow. The species richness of these subglacial populations is exceptional, comprising >62 species that represent 44% of the extant bryophyte flora of Sverdrup Pass. Cold-based glaciers are known to provide critical habitats for a variety of microbiota (i.e., fungi, algae, cyanobacteria, bacteria and viruses) in high latitude ecosystems. The regeneration of Little Ice Age bryophytes fundamentally expands the concept of biological refugia to land plants that was previously restricted to survival above and beyond glacial margins. Given this novel understanding of subglacial ecosystems, fieldwork is now being extended southward to plateau ice caps on Baffin Island, Nunavut, where ice retreat is exposing subglacial populations of greater antiquity (thousands to tens of thousands of radiocarbon years before present). Bryophytes by nature are totipotent (stem cell equivalency) and poikilohydric (desiccation tolerance), which facilitate their unique adaptation to extreme environments. Continuity of the Arctic bryophyte flora extends back through the Holocene to the late Tertiary [Beaufort Fm, 2-5 Ma], when the majority of taxa were the same, based on records spanning the archipelago from Ellesmere to Banks Island. This record contrasts with that of vascular plants, which have had a number of extinctions, necessitating recolonization of arctic populations from outside the region. The biological significance of a stable bryophyte element highlights their

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

    Science.gov (United States)

    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.

  11. Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum

    Science.gov (United States)

    Sluijs, A.; Schouten, S.; Pagani, M.; Woltering, M.; Brinkhuis, H.; Damste, J.S.S.; Dickens, G.R.; Huber, M.; Reichart, G.-J.; Stein, R.; Matthiessen, J.; Lourens, L.J.; Pedentchouk, N.; Backman, J.; Moran, K.; Clemens, S.; Cronin, T.; Eynaud, F.; Gattacceca, J.; Jakobsson, M.; Jordan, R.; Kaminski, M.; King, J.; Koc, N.; Martinez, N.C.; McInroy, D.; Moore, T.C., Jr.; O'Regan, M.; Onodera, J.; Palike, H.; Rea, B.; Rio, D.; Sakamoto, T.; Smith, D.C.; St John, K.E.K.; Suto, I.; Suzuki, N.; Takahashi, K.; Watanabe, M. E.; Yamamoto, M.

    2006-01-01

    The Palaeocene/Eocene thermal maximum, ???55 million years ago, was a brief period of widespread, extreme climatic warming, that was associated with massive atmospheric greenhouse gas input. Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition. We show that sea surface temperatures near the North Pole increased from ???18??C to over 23??C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations, but the absolute polar temperatures that we derive before, during and after the event are more than 10??C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms-perhaps polar stratospheric clouds or hurricane-induced ocean mixing-to amplify early Palaeogene polar temperatures. ?? 2006 Nature Publishing Group.

  12. V-band IMPATT power amplifier

    Science.gov (United States)

    Schell, S. W.

    1985-09-01

    This program is the result of the continuing demand and future requirement for a high data rate 60-GHz communications link. A reliable solid-state transmitter which delivers the necessary power over a wide bandwidth using the present IMPATT diode technology required the development of combining techniques. The development of a 60-GHz IMPATT power combiner amplifier is detailed. The results form a basis from which future wideband, high-power IMPATT amplifiers may be developed. As a result, several state-of-the-art advancements in millimeter-wave components technology were achieved. Specific achievements for the amplifier integration were: development of a nonresonant divider/combiner circuit; reproducible multiple junction circulator assemblies; and reliable high power 60-GHz IMPATT diodes. The various design approaches and tradeoffs which lead to the final amplifier configuration are discussed. A detailed circuit design is presented for the various amplifier components, and the conical line combiner, radial line combiner, and circulator development are discussed. The performance of the amplifier, the overall achievement of the program, the implications of the results, and an assessment of future development needs and recommendations are examined.

  13. Multiple excitation regenerative amplifier inertial confinement system

    International Nuclear Information System (INIS)

    The invention relates to apparatus and methods for producing high intensity laser radiation generation which is achieved through an optical amplifier-storage ring design. One or two synchronized, counterpropagating laser pulses are injected into a regenerative amplifier cavity and amplified by gain media which are pumped repetitively by electrical or optical means. The gain media excitation pulses are tailored to efficiently amplify the laser pulses during each transit. After the laser pulses have been amplified to the desired intensity level, they are either switched out of the cavity by some switch means, as for example an electro-optical device, for any well known laser end uses, or a target means may be injected into the regenerative amplifier cavity in such a way as to intercept simultaneously the counterpropagating laser pulses. One such well known end uses to which this invention is intended is for production of high density and temperature plasmas suitable for generating neutrons, ions and x-rays and for studying matter heated by high intensity laser radiation

  14. An improved AC-amplifier for electrophysiology

    Directory of Open Access Journals (Sweden)

    Jorgovanović Nikola

    2009-01-01

    Full Text Available We present the design, simulation and test results of a new AC amplifier for electrophysiological measurements based on a three op-amp instrumentation amplifier (IA. The design target was to increase the common mode rejection ratio (CMRR, thereby improving the quality of the recorded physiological signals in a noisy environment. The new amplifier actively suppresses the DC component of the differential signal and actively reduces the common mode signal in the first stage of the IA. These functions increase the dynamic range of the amplifier's first stage of the differential signal. The next step was the realization of the amplifier in a single chip technology. The design and tests of the new AC amplifier with a differential gain of 79.2 dB, a CMRR of 130 dB at 50 Hz, a high-pass cutoff frequency at 0.01 Hz and common mode reduction in the first stage of the 49.8 dB are presented in this paper.

  15. Spatial and Temporal Variation in Primary Productivity (NDVI) of Coastal Alaskan Tundra: Decreased Vegetation Growth Following Earlier Snowmelt

    Science.gov (United States)

    Gamon, John A.; Huemmrich, K. Fred; Stone, Robert S.; Tweedie, Craig E.

    2015-01-01

    In the Arctic, earlier snowmelt and longer growing seasons due to warming have been hypothesized to increase vegetation productivity. Using the Normalized Difference Vegetation Index (NDVI) from both field and satellite measurements as an indicator of vegetation phenology and productivity, we monitored spatial and temporal patterns of vegetation growth for a coastal wet sedge tundra site near Barrow, Alaska over three growing seasons (2000-2002). Contrary to expectation, earlier snowmelt did not lead to increased productivity. Instead, productivity was associated primarily with precipitation and soil moisture, and secondarily with growing degree days, which, during this period, led to reduced growth in years with earlier snowmelt. Additional moisture effects on productivity and species distribution, operating over a longer time scale, were evident in spatial NDVI patterns associated with microtopography. Lower, wetter regions dominated by graminoids were more productive than higher, drier locations having a higher percentage of lichens and mosses, despite the earlier snowmelt at the more elevated sites. These results call into question the oft-stated hypothesis that earlier arctic growing seasons will lead to greater vegetation productivity. Rather, they agree with an emerging body of evidence from recent field studies indicating that early-season, local environmental conditions, notably moisture and temperature, are primary factors determining arctic vegetation productivity. For this coastal arctic site, early growing season conditions are strongly influenced by microtopography, hydrology, and regional sea ice dynamics, and may not be easily predicted from snowmelt date or seasonal average air temperatures alone. Our comparison of field to satellite NDVI also highlights the value of in-situ monitoring of actual vegetation responses using field optical sampling to obtain detailed information on surface conditions not possible from satellite observations alone.

  16. Climatically sensitive 'Arctic': Another scientific frontier for India

    Energy Technology Data Exchange (ETDEWEB)

    Khare, N. [Ministry of Earth Sciences, Goa (India). National Centre for Antarctic and Ocean Research

    2008-01-15

    According to the recent Intergovernmental Panel on Climate Change report, climate change is set to impact every continent and threaten nearly a third of the world's species with extinction. Effects on the earth's weather systems from increasing greenhouse gases will change rainfall pattern, punch-up the power of storms and boost the risk of droughts, flooding and stress on water supplies. Therefore, economic planners are in the quest of predictive models of such climatic change. It has now become a global responsibility to understand the climate change, on both short and long timescales as a global phenomenon, with different parts of the earth responding to the climatic change with a time lead-lag and by different orders of magnitude. Though the exact cause of climatic change on earth is still unknown, the time lead-lag in climatic change in different parts of the earth helps in understanding the role of various regions in triggering (?) or enhancing the climatic change. Deciphering and inter-comparing the climatic history of different geographic regions can help to better understand the possible role of different geographic regions in global climatic variations. The Arctic region is critical for studying global change because it impacts the entire earth system through powerful feedback processes involving the atmosphere, cryosphere, land surface and ocean. The Arctic region will experience the effects of global warming first and will amplify its effects within the earth system. Rapid changes are being observed in the Arctic region, which may be considered as the barometer of global climatic change. The Arctic region and its ecosystem serve an area of active research because it is particularly sensitive to climate change and also because climatically induced environmental changes can induce further changes of global consequence. The Arctic system is not only an amplifier of variability in the global climate, but also of the effects of greenhouse forcings

  17. Landscape-precipitation feedback mediated by ice nuclei: an example from the Arctic

    Science.gov (United States)

    Stopelli, Emiliano; Conen, Franz; Zimmermann, Lukas; Morris, Cindy; Alewell, Christine

    2016-04-01

    The Arctic is one of the regions on Earth which are particularly sensitive to the effects of climate change. One of the largest uncertainties in describing climate and climate change is constituted by the characterisation of the behaviour of clouds. Specifically in the Arctic region there is a low abundance of cloud condensation nuclei (CCN) resulting in low droplet concentrations in clouds. Ice nucleating particles (INPs) in the atmosphere promote the aggregation of water molecules into ice, increasing the chance for precipitation. Therefore, a change in the absolute abundance of INPs and their relative presence compared to CCN is expected to have strong impacts on climate in the Arctic in terms of the radiative budget and of precipitation. In July 2015 we sampled particles from air at Haldde Observatory, Norway (69° 55'45" N, 22° 48'30" E, 905 m a.s.l.) on PM10 filters. We determined the number of INPs active at moderate supercooling temperatures (≥ -15 ° C, INPs‑15) by immersion freezing. To identify potential sources of airborne INPs we also collected samples of soil from a highland and decaying leaf litter. Air masses passing over the land were enriched in INPs‑15, with concentrations twice to three times larger than those found in air masses directly coming from the Barents Sea. Ice nucleation spectra suggest that it is mainly litter which accounts for this enrichment in INPs‑15. This example helps elucidating the feedback linking landscapes and atmosphere mediated by INPs in the frame of climate change. While the snow coverage is progressively reducing in the Arctic, areas with decaying leaf litter and vegetation that are exposed to wind and grazing are expected to increase, resulting into a larger abundance of INPs in the local atmosphere. This increase in airborne INPs can promote a change in the freezing of clouds, with impact on the lifetime and on the radiative properties of clouds, and ultimately on the occurrence of precipitation in the

  18. Surface water inundation in the boreal-Arctic: potential impacts on regional methane emissions

    International Nuclear Information System (INIS)

    Northern wetlands may be vulnerable to increased carbon losses from methane (CH4), a potent greenhouse gas, under current warming trends. However, the dynamic nature of open water inundation and wetting/drying patterns may constrain regional emissions, offsetting the potential magnitude of methane release. Here we conduct a satellite data driven model investigation of the combined effects of surface warming and moisture variability on high northern latitude (⩾45° N) wetland CH4 emissions, by considering (1) sub-grid scale changes in fractional water inundation (Fw) at 15 day, monthly and annual intervals using 25 km resolution satellite microwave retrievals, and (2) the impact of recent (2003–11) wetting/drying on northern CH4 emissions. The model simulations indicate mean summer contributions of 53 Tg CH4 yr−1 from boreal-Arctic wetlands. Approximately 10% and 16% of the emissions originate from open water and landscapes with emergent vegetation, as determined from respective 15 day Fw means or maximums, and significant increases in regional CH4 efflux were observed when incorporating satellite observed inundated land fractions into the model simulations at monthly or annual time scales. The satellite Fw record reveals widespread wetting across the Arctic continuous permafrost zone, contrasting with surface drying in boreal Canada, Alaska and western Eurasia. Arctic wetting and summer warming increased wetland emissions by 0.56 Tg CH4 yr−1 compared to the 2003–11 mean, but this was mainly offset by decreasing emissions (−0.38 Tg CH4 yr−1) in sub-Arctic areas experiencing surface drying or cooling. These findings underscore the importance of monitoring changes in surface moisture and temperature when assessing the vulnerability of boreal-Arctic wetlands to enhanced greenhouse gas emissions under a shifting climate. (letter)

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

    Science.gov (United States)

    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.

  20. Radioactive contamination in the Arctic - Present situation and future challenges

    International Nuclear Information System (INIS)

    There is currently a focus on radioactivity and the Arctic region. The reason for this is the high number of nuclear sources in parts of the Arctic and the vulnerability of Arctic systems to radioactive contamination. The Arctic environment is also perceived as a wilderness and the need for the protection of this wilderness against contamination is great. In 1991, the International Arctic Environmental Protection Strategy (IAEPS) was launched and the Arctic Monitoring and Assessment Programme (AMAP) established. AMAP is undertaking an assessment of the radioactive contamination of the Arctic and its radiological consequences. This paper summarises some of current knowledge about sources of radioactive contamination, vulnerability, exposure of man, and potential sources for radioactive contamination within Arctic and some views on the future needs for work concerning radioactivity in Arctic. (author)

  1. Seasonality of Air-sea-ice-land Variables for Arctic Tundra in Northern Eurasia and North America

    Science.gov (United States)

    Bhatt, U. S.; Walker, D. A.; Raynolds, M. K.; Steele, M.; Epstein, H.; Jia, G.; Comiso, J. C.; Pinzon, J. E.; Tucker, C. J.

    2009-12-01

    The strength of tundra productivity trends as measured by the annual maximum Normalized Difference Vegetation Index (MaxNDVI) and time integrated NDVI (TI-NDVI) vary around the Arctic over the 1982-2008 period. Our analysis suggests that the timing of terrestrial vegetation growth is connected to seasonal patterns of sea-ice concentrations, ocean temperatures and land surface temperatures. This study used SSMI estimates of sea ice concentration, based on a bootstrap algorithm and AVHRR radiometric surface temperature. Summer Warmth Index (SWI) was calculated as the sum from May to August of the degree months above freezing of surface temperature at each pixel and is an accepted measure of plant growth potential. The Normalized Difference Vegetation Index (NDVI) represents vegetation greenness and has been used extensively to monitor changes in the Arctic. The albedo of green plants varies with solar radiation wavelength, which is the basis for the NDVI index. The analysis was conducted within 50 km of the Arctic coastline to focus on the region of maximum maritime influence. Time series of regional sea-ice concentration, SWI and NDVI were constructed for the 50-km width domains for the Pan-Arctic, North America, Eurasia and Arctic subregions. Standard climate analysis techniques were applied to the regional time series to investigate the seasonality of sea ice, NDVI and SWI. MaxNDVI has increased in the 50-km land domain contiguous to the Beaufort Sea by 17% since 1982, whereas it has only increased by 3% in the coastal Kara Sea region. Analysis of semimonthly MaxNDVI indicates that the vegetation greens up more rapidly in the spring in the Beaufort than the W. Kara and the Kara has slightly higher NDVI in the fall. The climatological weekly sea ice concentrations in 50-km coastal domain displays an earlier breakup in the Beaufort and a later freeze-up in the Kara Sea area. Regional differences in the seasonal cycle can in part explain the spatially varied trends

  2. Towards a process-based understanding of Holocene polar climate change. Using glacier-fed lake sediments from Arctic Svalbard and Antarctic South Georgia

    OpenAIRE

    Bilt, Willem van der

    2016-01-01

    Earth`s polar regions are undergoing dramatic changes due to ongoing climate change as demonstrated by increasing temperatures, collapsing ice shelves, Arctic sea ice loss and rapid glacier retreat. Driving an accelerating rise in global sea level, this amplified regional response may have devastating global socio-economic consequences in the foreseeable future. Yet the causes and range of polar climate variability remain poorly understood as observational records are short and fragmentary, w...

  3. Soil and vegetation surveillance

    Energy Technology Data Exchange (ETDEWEB)

    Antonio, E.J.

    1995-06-01

    Soil sampling and analysis evaluates long-term contamination trends and monitors environmental radionuclide inventories. This section of the 1994 Hanford Site Environmental Report summarizes the soil and vegetation surveillance programs which were conducted during 1994. Vegetation surveillance is conducted offsite to monitor atmospheric deposition of radioactive materials in areas not under cultivation and onsite at locations adjacent to potential sources of radioactivity.

  4. Arctic and Southern Ocean Sea Ice Concentrations

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Monthly sea ice concentration for Arctic (1901 to 1995) and Southern oceans (1973 to 1990) were digitized on a standard 1-degree grid (cylindrical projection) to...

  5. Acoustic Resonance Reaction Control Thruster (ARCTIC) Project

    Data.gov (United States)

    National Aeronautics and Space Administration — ORBITEC proposes to develop and demonstrate the innovative Acoustic Resonance Reaction Control Thruster (ARCTIC) to provide rapid and reliable in-space impulse...

  6. Arctic Landfast Sea Ice 1953-1998

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The files in this data set contain landfast sea ice data (monthly means) gathered from both Russian Arctic and Antarctic Research Institute (AARI) and Canadian Ice...

  7. Arctic climate change: Greenhouse warming unleashed

    Science.gov (United States)

    Mauritsen, Thorsten

    2016-04-01

    Human activity alters the atmospheric composition, which leads to global warming. Model simulations suggest that reductions in emission of sulfur dioxide from Europe since the 1970s could have unveiled rapid Arctic greenhouse gas warming.

  8. Arctic and Aleutian terns, Amchitka Island, Alaska

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — Baird 1980 has recently reported on the ecology of Arctic terns Sterna paradisaea and Aleutian terns Sterna aleutica from 4 areas of mainland Alaska. However, prior...

  9. Arctic Marine Transportation Program 1979-1986

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The purpose of this program was to collect data relevant to developing year-round transportation capabilities in the Arctic Ocean. The US Maritime Administration...

  10. Geologic Provinces of the Arctic, 2000 (prvarcst)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This coverage includes arcs, polygons and polygon labels that describe Arctic portion of the U.S. Geological Survey defined geologic provinces of the World in 2000.

  11. Nutrient Limitations Constrain the Feedback Capacity of Landscapes in the High Arctic: Nonlinearities and Synergism

    Science.gov (United States)

    Arens, S. J.; Sullivan, P. F.; Welker, J. M.; Rogers, M. C.; Holland, K.; Schimel, J.; Persson, K.

    2006-12-01

    Nutrient availability appears to be a controlling factor in the structure and function of High Arctic terrestrial systems as depicted by biological hot spots such as bird cliffs which are found throughout the arctic. Understanding the processes by which nutrients control plant production, canopy structure, and ecosystem carbon cycling have been well studied in the Low Arctic, where fertilization experiments have been employed for decades. Few studies have examined how the amount and type of nutrient augmentations (fertilization) affects the magnitude and pattern of CO2 exchange, species composition and optical properties of prostrate dwarf-shrub, herb tundra, the largest ecosystem in the High Arctic. In this study, amendments of three levels of nitrogen (N) (0.5 g/m2, 1.0 g/m2 and 5.0 g/m2) phosphorus (P) (2.5 g/m2) were initiated in prostrate dwarf- shrub, herb tundra near Pituffik (Thule), Greenland (76¢ªN, 68¢ªW). Species composition, net ecosystem CO2 exchange (NEE), gross primary photosynthesis (GPP), ecosystem respiration (ER) and plot-level normalized difference vegetation index (NDVI) were used to quantify changes in ecosystem structure and function. Non- linear responses to the addition of different levels of N were observed. CO2 gas exchange and NDVI showed indicated the strongest response at middle levels of N addition (1.0 g/m2). Strong and synergystic responses to the combined addition of nitrogen and phosphorus were observed. Increases in vegetation density and a shift in species composition were observed when N and P were added to these systems, partially explaining the near doubling of NDVI values from 0.3 to 0.6. Rates of NEE, GPP and ER were significantly higher when N and P were combined compared to independent additions of each or when compared to non-fertilized areas. Our results indicate that feedback processes such as CO2 exchange, optical properties and vegetation composition and structure are co-limited by N and P and that the addition

  12. Reconstruction of Centennial and Millennial-scale Climate and Environmental Variability during the Holocene in the Central Canadian Arctic

    Science.gov (United States)

    Rolland, N.; Porinchu, D.; MacDonald, G.; Moser, K.

    2007-12-01

    The Arctic and sub-Arctic regions are experiencing dramatic changes in surface temperature, sea-ice extent, glacial melt, river discharge, soil carbon storage and snow cover. According to the IPCC high latitude regions are expected to warm between 4°C and 7°C over the next 100 years. The magnitude of warming and the rate at which it occurs will dwarf any previous warming episodes experienced by latitude regions over the last 11,000 years. It is critical that we improve our understanding of how the Arctic and sub-Arctic regions responded to past periods of warming, especially in light of the changes these regions will be experiencing over the next 100 years. One of the lines of evidence increasingly utilized in multi-proxy paleolimnological research is the Chironomidae (Insecta: Diptera). Also known as non-biting midge flies, chironomids are ubiquitous, frequently the most abundant insects found in freshwater ecosystems and very sensitive to environmental conditions. This research uses Chironomidae to quantitatively characterize climate and environmental conditions of the continental interior of Arctic Canada during the Holocene. Spanning four major vegetation zones (boreal forest, forest-tundra, birch tundra and herb tundra), the surface samples of 80 lakes recovered from the central Canadian Arctic were used to assess the relationship of 22 environmental variables with the chironomid distribution. Redundancy analysis (RDA) identified four variables, total Kjeldahl nitrogen (TKN), pH, summer surface water temperature (SSWT) and depth, which best explain the variance in the distribution of chironomids within these ecoregions. In order to provide new quantitative estimates of SSWT, a 1-component weighted average partial least square (WA-PLS) model was developed (r2jack = 0.76, RMSEP = 1.42°C) and applied downcore in two low arctic continental Nunavut lakes located approximately 50 km and 200 km north of modern treeline. This robust midge-inferred temperature

  13. Arctic shipping emissions inventories and future scenarios

    OpenAIRE

    J. J. Corbett; D. A. Lack; J. J. Winebrake; Harder, S; J. A. Silberman; Gold, M.

    2010-01-01

    This paper presents 5 km×5 km Arctic emissions inventories of important greenhouse gases, black carbon and other pollutants under existing and future (2050) scenarios that account for growth of shipping in the region, potential diversion traffic through emerging routes, and possible emissions control measures. These high-resolution, geospatial emissions inventories for shipping can be used to evaluate Arctic climate sensitivity to black carbon (a short-lived climate forcing pollutant especial...

  14. Isotopes in the Arctic atmospheric water cycle

    OpenAIRE

    Bonne, Jean-Louis; Werner, Martin; Meyer, Hanno; Kipfstuhl, Sepp; Rabe, Benjamin; Behrens, Melanie; Schönicke, Lutz; Steen-Larsen, Hans Christian; Masson-Delmotte, Valérie

    2016-01-01

    The ISO-ARC project aims at documenting the Arctic atmospheric hydrological cycle, by assessing the imprint of the marine boundary conditions (e.g. temperature variations, circulation changes, or meltwater input) to the isotopic composition of the atmospheric water cycle (H218O and HDO) with a focus on North Atlantic and Arctic oceans. For this purpose, two continuous monitoring water vapour stable isotopes cavity ring-down spectrometers have been installed in July 2015: on-boar...

  15. The Anatomy of an Arctic Knowledge Debate

    DEFF Research Database (Denmark)

    Sejersen, Frank

    2005-01-01

    Within the last decades, the Arctic research community and the Inuit communities have focused on the question of knowledge to such an extent that we may in fact speak of a knowledge cult.......Within the last decades, the Arctic research community and the Inuit communities have focused on the question of knowledge to such an extent that we may in fact speak of a knowledge cult....

  16. Arctic cushion plants as fallout 'monitors'

    International Nuclear Information System (INIS)

    The internal distribution of fallout 137Cs was determined for arctic cushion plants Dryas integrifolia, Silene acaulis and the bryophytes Rhacomitrium lanuginosum and Polytrichum juniperinum collected at various latitudes in Canadian Arctic. The results indicate that these plants have functioned as biological monitors of radioactive fallout and it is suggested that analysis of the internal distribution of 137Cs could serve as a model for other airborne contaminants. (author)

  17. Arctic ecosystem responses to a warming climate

    DEFF Research Database (Denmark)

    Mortensen, Lars O.

    is frozen solid for the main part of the year. However, in recent decades, arctic temperatures have in-creased between two and three times that of the global averages, which have had a substantial impact on the physical environment of the arctic ecosystem, such as deglaciation of the Greenland inland ice......’ of ecosystem re-sponses to the future global climate change....

  18. Studying ocean acidification in the Arctic Ocean

    Science.gov (United States)

    Robbins, Lisa

    2012-01-01

    The U.S. Geological Survey (USGS) partnership with the U.S. Coast Guard Ice Breaker Healey and its United Nations Convention Law of the Sea (UNCLOS) cruises has produced new synoptic data from samples collected in the Arctic Ocean and insights into the patterns and extent of ocean acidification. This framework of foundational geochemical information will help inform our understanding of potential risks to Arctic resources due to ocean acidification.

  19. Land-Based Marine Pollution in Arctic

    OpenAIRE

    Haile, Fitsum Gebreselassie

    2014-01-01

    Land-based pollution represents the single most important cause of marine pollution. The threat of land-based pollution to the marine environment is a serious one since it mainly affects coastal waters, which are sites of high biological productivity. The occurrence of high concentrations of pollutants in the Arctic environment has been a concern for many years.. Regional and international actions over the past two decades attempting to manage pollutants in the Arctic environment from land- b...

  20. Zooplankton in the Arctic outflow

    Science.gov (United States)

    Soloviev, K. A.; Dritz, A. V.; Nikishina, A. B.

    2009-04-01

    Climate changes in the Arctic cause the changes in the current system that may have cascading effect on the structure of plankton community and consequently on the interlinked and delicately balanced food web. Zooplankton species are by definition incapable to perform horizontal moving. Their transport is connected with flowing water. There are zooplankton species specific for the definite water masses and they can be used as markers for the different currents. That allows us to consider zooplankton community composition as a result of water mixing in the studied area. Little is known however about the mechanisms by which spatial and temporal variability in advection affect dynamics of local populations. Ice conditions are also very important in the function of pelagic communities. Melting time is the trigger to all "plankton blooming" processes, and the duration of ice-free conditions determines the food web development in the future. Fram Strait is one of the key regions for the Arctic: the cold water outflow comes through it with the East Greenland Current and meets warm Atlantic water, the West Spitsbergen Current, producing complicated hydrological situation. During 2007 and 2008 we investigated the structure functional characteristics of zooplankton community in the Fram Strait region onboard KV "Svalbard" (April 2007, April and May 2008) and RV "Jan Mayen" (May 2007, August 2008). This study was conducted in frame of iAOOS Norway project "Closing the loop", which, in turn, was a part of IPY. During this cruises multidisciplinary investigations were performed, including sea-ice observations, CTD and ADCP profiling, carbon flux, nutrients and primary production measurements, phytoplankton sampling. Zooplankton was collected with the Hydro-Bios WP2 net and MultiNet Zooplankton Sampler, (mouth area 0.25 m2, mesh size 180 um).Samples were taken from the depth strata of 2000-1500, 1500-1000, 1000-500,500-200, 200-100, 100-60, 60-30, 30-0 m. Gut fluorescence

  1. The great challenges in Arctic Ocean paleoceanography

    International Nuclear Information System (INIS)

    Despite the importance of the Arctic in the climate system, the data base we have from this area is still very weak, and large parts of the climate history have not been recovered at all in sedimentary sections. In order to fill this gap in knowledge, international, multidisciplinary expeditions and projects for scientific drilling/coring in the Arctic Ocean are needed. Key areas and approaches for drilling and recovering undisturbed and complete sedimentary sequences are depth transects across the major ocean ridge systems, i.e., the Lomonosov Ridge, the Alpha-Mendeleev Ridge, and the Chukchi Plateau/Northwind Ridge, the Beaufort, Kara and Laptev sea continental margins, as well as the major Arctic gateways towards the Atlantic and Pacific oceans. The new detailed climate records from the Arctic Ocean spanning time intervals from the Late Cretaceous/Paleogene Greenhouse world to the Neogene-Quaternary Icehouse world and representing short- and long-term climate variability on scales from 10 to 106 years, will give new insights into our understanding of the Arctic Ocean within the global climate system and provide an opportunity to test the performance of climate models used to predict future climate change. With this, studying the Arctic Ocean is certainly one of the major challenges in climate research for the coming decades.

  2. Influence of sea ice on Arctic precipitation.

    Science.gov (United States)

    Kopec, Ben G; Feng, Xiahong; Michel, Fred A; Posmentier, Eric S

    2016-01-01

    Global climate is influenced by the Arctic hydrologic cycle, which is, in part, regulated by sea ice through its control on evaporation and precipitation. However, the quantitative link between precipitation and sea ice extent is poorly constrained. Here we present observational evidence for the response of precipitation to sea ice reduction and assess the sensitivity of the response. Changes in the proportion of moisture sourced from the Arctic with sea ice change in the Canadian Arctic and Greenland Sea regions over the past two decades are inferred from annually averaged deuterium excess (d-excess) measurements from six sites. Other influences on the Arctic hydrologic cycle, such as the strength of meridional transport, are assessed using the North Atlantic Oscillation index. We find that the independent, direct effect of sea ice on the increase of the percentage of Arctic sourced moisture (or Arctic moisture proportion, AMP) is 18.2 ± 4.6% and 10.8 ± 3.6%/100,000 km(2) sea ice lost for each region, respectively, corresponding to increases of 10.9 ± 2.8% and 2.7 ± 1.1%/1 °C of warming in the vapor source regions. The moisture source changes likely result in increases of precipitation and changes in energy balance, creating significant uncertainty for climate predictions. PMID:26699509

  3. Arctic response strategy: Canadian Coast Guard

    International Nuclear Information System (INIS)

    The revision of the Canadian Coast Guard's Arctic response strategy was described with particular focus on the consultative method used to ensure that all perspectives were taken into consideration. Some tankers used to re-supply fuel to remote Arctic communities carry more than 30,000 tonnes of product, putting them at risk for major spills. The Arctic response strategy was revised to emphasize recommendations for prevention, preparedness and response. Prevention was recognized as the most effective solution to oil spills in the Arctic. The leadership and coordination roles of the Canadian Coast Guard were demonstrated in relation to ship-source oil pollution. The new strategy also outlined the equipment requirements needed to respond to a large spill in the Arctic. Categorization of spill sizes as tier 1 to 4 was determined by examining southern regimes as was the characterization of corresponding equipment. Implementation of the new recommendations of the revised Arctic response strategy will take place over the next 2 years. The prevention aspect will include some legislative changes or stricter guidelines

  4. Arctic response strategy: Canadian Coast Guard

    Energy Technology Data Exchange (ETDEWEB)

    Goodman, J.C. [Canadian Coast Guard, Sarnia, ON (Canada)

    2000-07-01

    The revision of the Canadian Coast Guard's Arctic response strategy was described with particular focus on the consultative method used to ensure that all perspectives were taken into consideration. Some tankers used to re-supply fuel to remote Arctic communities carry more than 30,000 tonnes of product, putting them at risk for major spills. The Arctic response strategy was revised to emphasize recommendations for prevention, preparedness and response. Prevention was recognized as the most effective solution to oil spills in the Arctic. The leadership and coordination roles of the Canadian Coast Guard were demonstrated in relation to ship-source oil pollution. The new strategy also outlined the equipment requirements needed to respond to a large spill in the Arctic. Categorization of spill sizes as tier 1 to 4 was determined by examining southern regimes as was the characterization of corresponding equipment. Implementation of the new recommendations of the revised Arctic response strategy will take place over the next 2 years. The prevention aspect will include some legislative changes or stricter guidelines.

  5. The OPTHER Project: Progress toward the THz Amplifier

    DEFF Research Database (Denmark)

    Paoloni, C; Brunetti, F; Di Carlo, A;

    2011-01-01

    This paper describes the status of the OPTHER (OPtically driven TeraHertz AmplifiERs) project and progress toward the THz amplifier realization. This project represents a considerable advancement in the field of high frequency amplification. The design and realization of a THz amplifier within th...

  6. DNA barcoding of Arctic Ocean holozooplankton for species identification and recognition

    Science.gov (United States)

    Bucklin, Ann; Hopcroft, Russell R.; Kosobokova, Ksenia N.; Nigro, Lisa M.; Ortman, Brian D.; Jennings, Robert M.; Sweetman, Christopher J.

    2010-01-01

    Zooplankton species diversity and distribution are important measures of environmental change in the Arctic Ocean, and may serve as 'rapid-responders' of climate-induced changes in this fragile ecosystem. The scarcity of taxonomists hampers detailed and up-to-date monitoring of these patterns for the rarer and more problematic species. DNA barcodes (short DNA sequences for species recognition and discovery) provide an alternative approach to accurate identification of known species, and can speed routine analysis of zooplankton samples. During 2004-2008, zooplankton samples were collected during cruises to the central Arctic Ocean and Chukchi Sea. A ˜700 base-pair region of the mitochondrial cytochrome oxidase I (mtCOI) gene was amplified and sequenced for 82 identified specimens of 41 species, including cnidarians (six hydrozoans, one scyphozoan), arthropod crustaceans (five amphipods, 24 copepods, one decapod, and one euphausiid); two chaetognaths; and one nemertean. Phylogenetic analysis used the Neighbor-Joining algorithm with Kimura-2-Parameter (K-2-P) distances, with 1000-fold bootstrapping. K-2-P genetic distances between individuals of the same species ranged from 0.0 to 0.2; genetic distances between species ranged widely from 0.1 to 0.7. The mtCOI gene tree showed monophyly (at 100% bootstrap value) for each of the 26 species for which more than one individual was analyzed. Of seven genera for which more than one species was analyzed, four were shown to be monophyletic; three genera were not resolved. At higher taxonomic levels, only the crustacean order Copepoda was resolved, with bootstrap value of 83%. The mtCOI barcodes accurately discriminated and identified known species of 10 taxonomic groups of Arctic Ocean holozooplankton. A comprehensive DNA barcode database for the estimated 300 described species of Arctic holozooplankton will allow rapid assessment of species diversity and distribution in this climate-vulnerable ocean ecosystem.

  7. Pulsed ti: sapphire laser power amplifier

    International Nuclear Information System (INIS)

    We have demonstrated an all solid state Ti:Sapphire laser system consisting of a power oscillator and single pass amplifier. The electrical-to-optical efficiency far exceeds that of the current CW systems. The pump lasers have lower capital and operating costs than the Argon-ion laser. In the future, we plan to scale the output power to higher levels by adding a fourth pump laser and improving the output power of the current pump lasers. Modeling results suggest that a large increase in efficiency can be realized by improving the beam quality of the pump lasers, even at the cost of reduced output power. We will explore this option by adding apertures to the cavity and/or reducing the rod diameter along with optimizing the resonator design. Other improvements in efficiency which will be investigated include double passing the amplifier for better extraction. To complete this work, the laser system will be converted into a two-stage amplifier. A narrow band, lower power oscillator currently under development will be injected in to the amplifier to study the extraction and efficiency characteristics of the amplifier throughout the tuning range of Ti:Sapphire. Detailed beam quality measurements will also be made. Other work will include doubling the narrow band output for materials processing applications

  8. The scavenging processes controlling the seasonal cycle in Arctic sulphate and black carbon aerosol

    Directory of Open Access Journals (Sweden)

    J. Browse

    2012-08-01

    Full Text Available The seasonal cycle in Arctic aerosol is typified by high concentrations of large aged anthropogenic particles transported from lower latitudes in the late Arctic winter and early spring followed by a sharp transition to low concentrations of locally sourced smaller particles in the summer. However, multi-model assessments show that many models fail to simulate a realistic cycle. Here, we use a global aerosol microphysics model (GLOMAP and surface-level aerosol observations to understand how wet scavenging processes control the seasonal variation in Arctic black carbon (BC and sulphate aerosol. We show that the transition from high wintertime concentrations to low concentrations in the summer is controlled by the transition from ice-phase cloud scavenging to the much more efficient warm cloud scavenging in the late spring troposphere. This seasonal cycle is amplified further by the appearance of warm drizzling cloud in the late spring and summer boundary layer. Implementing these processes in GLOMAP greatly improves the agreement between the model and observations at the three Arctic ground-stations Alert, Barrow and Zeppelin Mountain on Svalbard. The SO4 model-observation correlation coefficient (R increases from: −0.33 to 0.71 at Alert (82.5° N, from −0.16 to 0.70 at Point Barrow (71.0° N and from −0.42 to 0.40 at Zeppelin Mountain (78° N. The BC model-observation correlation coefficient increases from −0.68 to 0.72 at Alert and from −0.42 to 0.44 at Barrow. Observations at three marginal Arctic sites (Janiskoski, Oulanka and Karasjok indicate a far weaker aerosol seasonal cycle, which we show is consistent with the much smaller seasonal change in the frequency of ice clouds compared to higher latitude sites. Our results suggest that the seasonal cycle in Arctic aerosol is driven by temperature-dependent scavenging processes that may be susceptible to modification in a future climate.

  9. Vegetable Production System (Veggie)

    Science.gov (United States)

    Levine, Howard G.; Smith, Trent M.

    2016-01-01

    The Vegetable Production System (Veggie) was developed by Orbital Technologies Corp. to be a simple, easily stowed, and high growth volume yet low resource facility capable of producing fresh vegetables on the International Space Station (ISS). In addition to growing vegetables in space, Veggie can support a variety of experiments designed to determine how plants respond to microgravity, provide real-time psychological benefits for the crew, and conduct outreach activities. Currently, Veggie provides the largest volume available for plant growth on the ISS.

  10. Long-term trends of the Polar and Arctic cells influencing the Arctic climate since 1989

    Science.gov (United States)

    Qian, Weihong; Wu, Kaijun; Leung, Jeremy Cheuk-Hin; Shi, Jian

    2016-03-01

    The strengthening and broadening trends of the Hadley cell have been revealed, while the existence of the Arctic cell has also been confirmed in previous studies. This study extends previous strengthening trend analyses of the Hadley cell to the Polar and Arctic cells in the Northern Hemisphere and explores their climate influences. Results show that the Polar cell experienced an abrupt change from a slow to a rapid strengthening trend in 1989, while the Arctic cell showed an insignificant strengthening trend and a significant weakening trend successively. The strengthening subsidence flow associated with the Polar and Arctic cells can partly explain the warming surface air temperature and declining sea ice concentration through the increasing tropospheric height and temperature trends. These results provide new insights for understanding the interdecadal relationship between atmospheric circulation and climate change in the Arctic region.

  11. Inter-annual carbon dioxide uptake of a wet sedge tundra ecosystem in the Arctic

    OpenAIRE

    Harazono, Yoshinobu; Mano, Masayoshi; Miyata, Akira; Zulueta, Rommel C.; Oechel, Walter C.

    2011-01-01

    The CO2 flux of a wet sedge tundra ecosystem in the Arctic, at Barrow, Alaska, has been measured by the eddy correlation method since spring 1999, and the CO2 uptake by the vegetation during the spring and growing periods was examined between 1999 and 2000. CO2 flux changed to a sink immediately after the spring thaw in 1999 and the photosynthetic activity was high in the first half of the growing period. At this time the air temperature was low and solar radiation was high. In the 2000 seaso...

  12. The Content of Fat and Polyenoic Acids in the Major Food Sources of the Arctic Diet

    DEFF Research Database (Denmark)

    Shukla, V. K. S.; Clausen, Jytte Lene; Egsgaard, Helge;

    1980-01-01

    in western countries. The triglyceride content of muscle samples was also estimated. A gas chromatography-mass spectrometry system was used for localizing the position of double bonds in the unsaturated acids, by means of their pyrrolidides. The fat tissue from the seal was the main source of...... polyenoic acids, tri- and pentaenoic acids in the diet of the Arctic hunter. Those acids were derived metabolically from linolenic acid. In contrast polyenoic acids, linoleic acid and its derivatives in the nonarctic diet, were mainly supplied from muscle of nonruminant animals and from sources of vegetable...

  13. Enhanced seasonal CO2 exchange caused by amplified plant productivity in northern ecosystems

    Science.gov (United States)

    Forkel, Matthias; Carvalhais, Nuno; Rödenbeck, Christian; Keeling, Ralph; Heimann, Martin; Thonicke, Kirsten; Zaehle, Sönke; Reichstein, Markus

    2016-04-01

    Atmospheric monitoring has shown an increase in the seasonal cycle of carbon dioxide (CO2) in high northern latitudes (> 40°N) since the 1960s. The much stronger increase of the seasonal CO2 amplitude in high latitudes compared to low latitudes suggests that northern ecosystems are experiencing large changes in carbon cycle dynamics. However the underlying mechanisms are not yet fully understood and current climate/carbon cycle models under-estimate observed changes in the seasonal CO2 amplitude. Here we aim to explain the observed latitudinal gradient of seasonal CO2 amplitude trends by contrasting observations from long-term monitoring sites of atmospheric CO2 concentration, satellite observation of vegetation greenness, and global observation-based datasets of gross primary production and net biome productivity, with results from the LPJmL dynamic global vegetation model coupled to the TM3 atmospheric transport model. Our results demonstrate that the latitudinal gradient of the enhanced seasonal CO2 amplitude is mainly driven by positive trends in photosynthetic carbon uptake caused by recent climate change and mediated by changing vegetation cover in boreal and arctic ecosystems. Climate change affects processes such as plant physiology, phenology, water availability, and vegetation dynamics, ultimately leading to increased plant productivity and vegetation cover in northern ecosystems in the last decades. Thereby photosynthetic carbon uptake has reacted much more strongly to warming than respiratory carbon release processes. Continued long-term observation of atmospheric CO2 together with ground and satellite observations of land surface and vegetation dynamics will be the key to detect, model, and better predict changes in high-latitude land/carbon cycle dynamics.

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

    Science.gov (United States)

    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.

  15. The Arctic Grand Challenge: Abrupt Climate Change

    Science.gov (United States)

    Wilkniss, P. E.

    2003-12-01

    Trouble in polar paradise (Science, 08/30/02), significant changes in the Arctic environment are scientifically documented (R.E. Moritz et al. ibid.). More trouble, lots more, "abrupt climate change," (R. B. Alley, et al. Science 03/28/03). R. Corell, Arctic Climate Impact Assessment team (ACIA), "If you want to see what will happen in the rest of the world 25 years from now just look what's happening in the Arctic," (Arctic Council meeting, Iceland, 08/03). What to do? Make abrupt Arctic climate change a grand challenge for the IPY-4 and beyond! Scientifically:Describe the "state" of the Arctic climate system as succinctly as possible and accept it as the point of departure.Develop a hypothesis and criteria what constitutes "abrupt climate change," in the Arctic that can be tested with observations. Observations: Bring to bear existing observations and coordinate new investments in observations through an IPY-4 scientific management committee. Make the new Barrow, Alaska, Global Climate Change Research Facility a major U.S. contribution and focal point for the IPY-4 in the U.S Arctic. Arctic populations, Native peoples: The people of the North are living already, daily, with wrenching change, encroaching on their habitats and cultures. For them "the earth is faster now," (I. Krupnik and D. Jolly, ARCUS, 2002). From a political, economic, social and entirely realistic perspective, an Arctic grand challenge without the total integration of the Native peoples in this effort cannot succeed. Therefore: Communications must be established, and the respective Native entities must be approached with the determination to create well founded, well functioning, enduring partnerships. In the U.S. Arctic, Barrow with its long history of involvement and active support of science and with the new global climate change research facility should be the focal point of choice Private industry: Resource extraction in the Arctic followed by oil and gas consumption, return the combustion

  16. Single mode terahertz quantum cascade amplifier

    Energy Technology Data Exchange (ETDEWEB)

    Ren, Y., E-mail: yr235@cam.ac.uk; Wallis, R.; Shah, Y. D.; Jessop, D. S.; Degl' Innocenti, R.; Klimont, A.; Kamboj, V.; Beere, H. E.; Ritchie, D. A. [Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, CB3 0HE Cambridge (United Kingdom)

    2014-10-06

    A terahertz (THz) optical amplifier based on a 2.9 THz quantum cascade laser (QCL) structure has been demonstrated. By depositing an antireflective coating on the QCL facet, the laser mirror losses are enhanced to fully suppress the lasing action, creating a THz quantum cascade (QC) amplifier. Terahertz radiation amplification has been obtained, by coupling a separate multi-mode THz QCL of the same active region design to the QC amplifier. A bare cavity gain is achieved and shows excellent agreement with the lasing spectrum from the original QCL without the antireflective coating. Furthermore, a maximum optical gain of ∼30 dB with single-mode radiation output is demonstrated.

  17. Ultrashort pulse amplification in cryogenically cooled amplifiers

    Energy Technology Data Exchange (ETDEWEB)

    Backus, Sterling J.; Kapteyn, Henry C.; Murnane, Margaret Mary

    2004-10-12

    A laser amplifier system amplifies pulses in a single "stage" from .about.10.sup.-9 joules to more than 10.sup.-3 joules, with average power of 1-10 watts, and beam quality M.sup.2 <2. The laser medium is cooled substantially below room temperature, as a means to improve the optical and thermal characteristics of the medium. This is done with the medium inside a sealed, evacuated or purged cell to avoid moisture or other materials condensing on the surface. A "seed" pulse from a separate laser is passed through the laser medium, one or more times, in any of a variety of configurations including single-pass, multiple-pass, and regenerative amplifier configurations.

  18. Transistorized pulse amplifiers (A.I.T.)

    International Nuclear Information System (INIS)

    The two amplifiers whose design and operation are described in this report have been studied for neutron detection units used in piles. They are designed to allow an important reduction of the volume and of the weight of the detector and its amplifier, and to simplify the operation of the detection assembly. To these characteristics can be added the mechanical and electrical robustness and the very reduced micro-phony. The first transistorized amplifier (AIT.1) is simple, very robust, and can be used for radioprotection installations. The second (AIT.4) has a better performance and makes it possible to replace the APT.2 in most of its applications (it has even been used satisfactorily in an apparatus where the micro-phony and the sensitivity to interference of the APT.2 made this latter unusable). (author)

  19. An automated test facility for neutronic amplifiers

    International Nuclear Information System (INIS)

    Neutronic amplifiers are used at the Chalk River Laboratory in applications such as neutron flux monitoring and reactor control systems. Routine preventive maintenance of control and safety systems included annual calibration and characterization of the neutronic amplifiers. An investigation into the traditional methods of annual routine maintenance of amplifiers concluded that frequency and phase response measurements in particular were labour intensive and subject to non-repeatable errors. A decision was made to upgrade testing methods and facilities by using programmable test equipment under the control of a computer. In order to verify the results of the routine measurements, expressions for the transfer functions were derived from the circuit diagrams. Frequency and phase responses were then calculated and plotted thus providing a bench-mark to which the test results can be compared. (author)

  20. Coma / Vegetative State

    Science.gov (United States)

    ... Employment & Training Physical Symptoms of Brain Injury Thinking / Cognitive Symptoms Brain Injury Symptoms Family Concerns Policy Vision ... vegetative state include: Return of a sleep-wake cycle with periods of eye opening and eye closing ...

  1. Description of vegetation types

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This document provides descriptions of five vegetation types found in Iowa- oak savannah, mature hardwoods, floodplain woods, scrub woods, and riparian woods. Oak...

  2. Vegetation survey of Sengwa

    Directory of Open Access Journals (Sweden)

    G. C. Craig

    1983-12-01

    Full Text Available The approach and initial results of a vegetation survey of the Sengwa Wildlife Area are outlined. The objectives were to produce a vegetation classification and map sufficiently detailed to serve as a base for the management of the natural vegetation. The methods adopted consist of (a stratification of the area into homogeneous units using 1:10 000 colour aerial photographs; (b plotless random sampling of each stratum by recording cover abundance on the Braun-Blaunquet scale for all woody species; and (c analysis of the data by indicator species analysis using the computer programme 'Twinspan’. The classification produced is successful in achieving recognizable vegetation types which tie in well with known environmental features.

  3. Changing geo-political realities in the Arctic region

    DEFF Research Database (Denmark)

    Sørensen, Camilla T. N.

    2014-01-01

    This article analyzes and discusses how Denmark seeks to manage the changing geopolitical realities in the Arctic region specifically focusing on how Denmark seeks to manage its relations with China in the Arctic region....

  4. Hydrochemical Atlas of the Arctic Ocean (NODC Accession 0044630)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The present Hydrochemical Atlas of the Arctic Ocean is a description of hydrochemical conditions in the Arctic Ocean on the basis of a greater body of hydrochemical...

  5. A quantitative assessment of Arctic shipping in 2010–2014

    KAUST Repository

    Eguíluz, Victor M.

    2016-08-01

    Rapid loss of sea ice is opening up the Arctic Ocean to shipping, a practice that is forecasted to increase rapidly by 2050 when many models predict that the Arctic Ocean will largely be free of ice toward the end of summer. These forecasts carry considerable uncertainty because Arctic shipping was previously considered too sparse to allow for adequate validation. Here, we provide quantitative evidence that the extent of Arctic shipping in the period 2011–2014 is already significant and that it is concentrated (i) in the Norwegian and Barents Seas, and (ii) predominantly accessed via the Northeast and Northwest Passages. Thick ice along the forecasted direct trans-Arctic route was still present in 2014, preventing transit. Although Arctic shipping remains constrained by the extent of ice coverage, during every September, this coverage is at a minimum, allowing the highest levels of shipping activity. Access to Arctic resources, particularly fisheries, is the most important driver of Arctic shipping thus far.

  6. Arctic shipping emissions inventories and future scenarios

    Directory of Open Access Journals (Sweden)

    J. J. Corbett

    2010-04-01

    Full Text Available The Arctic is a sensitive region in terms of climate change and a rich natural resource for global economic activity. Arctic shipping is an important contributor to the region's anthropogenic air emissions, including black carbon – a short-lived climate forcing pollutant especially effective in accelerating the melting of ice and snow. These emissions are projected to increase as declining sea ice coverage due to climate change allows for increased shipping activity in the Arctic. To understand the impacts of these increased emissions, scientists and modelers require high-resolution, geospatial emissions inventories that can be used for regional assessment modeling. This paper presents 5 km×5 km Arctic emissions inventories of important greenhouse gases, black carbon and other pollutants under existing and future (2050 scenarios that account for growth of shipping in the region, potential diversion traffic through emerging routes, and possible emissions control measures. Short-lived forcing of ~4.5 gigagrams of black carbon from Arctic shipping may increase climate forcing; a first-order calculation of global warming potential due to 2030 emissions in the high-growth scenario suggests that short-lived forcing of ~4.5 gigagrams of black carbon from Arctic shipping may increase climate forcing due to Arctic ships by at least 17% compared to warming from these vessels' CO2 emissions (~42 000 gigagrams. The paper also presents maximum feasible reduction scenarios for black carbon in particular. These emissions reduction scenarios will enable scientists and policymakers to evaluate the efficacy and benefits of technological controls for black carbon, and other pollutants from ships.

  7. Satellite Monitoring of Disturbances in Arctic Ecosystems

    Science.gov (United States)

    Prieto-Blanco, A.; Disney, M.; Lewis, P.

    2008-12-01

    We explored the capability of satellite remote sensing to detect temporal changes in northern Fennoscandian regions through the application of a temporal model of surface bidirectional reflectance. Remote sensing offers the potential to monitor changes over large areas and at hard to access locations. Specifically in remote Arctic locations, where ground surveys and aircraft observations are constrained by weather conditions and logistics, remote sensing provides a unique capability for repetitive and frequent sampling. A major disturbance in mountain birch forests typical of northern Sweden and Finland is caused by outbreaks of defoliating insects such as the autumn moth (Epirrita autumnata) and the winter moth (Operophtera brumata). These outbreaks occur more or less cyclically every 9-10 years and attack mainly birch (Betula spp.) leaving a mosaic of open woodland within the forest. It is expected that global warming will affect the incidence and the intensity of this outbreaks. The ecological and economical consequences can be severe hence the importance of close monitoring of shifts in the distribution of events. Defoliated areas of up to 6000 to 7000 ha of birch forest have been reported. Severely affected areas could potentially be detected by satellite providing valuable data to understand the behavior, estimate the damage and predict the development of forest pests. Quantification of the impact of such outbreaks will also permit far more accurate estimation of the terrestrial carbon budget of such regions. Here we applied a generic algorithm to detect sudden changes on land surface cover to daily 500m MODIS surface reflectance data over the Fennoscandian area. Moderate Resolution Imaging Spectraradiometer (MODIS) sensors on board the polar orbiting satellites Terra and Aqua provide an overpass at least once a day over the area of interest. Unfortunately, frequent cloud cover limits the acquisition of satellite imagery and persistent cloud cover may

  8. Dissolved organic carbon (DOC in Arctic ground ice

    Directory of Open Access Journals (Sweden)

    M. Fritz

    2015-01-01

    Full Text Available Thermal permafrost degradation and coastal erosion in the Arctic remobilize substantial amounts of organic carbon (OC and nutrients which have been accumulated in late Pleistocene and Holocene unconsolidated deposits. Their vulnerability to thaw subsidence, collapsing coastlines and irreversible landscape change is largely due to the presence of large amounts of massive ground ice such as ice wedges. However, ground ice has not, until now, been considered to be a source of dissolved organic carbon (DOC, dissolved inorganic carbon (DIC and other elements, which are important for ecosystems and carbon cycling. Here we show, using geochemical data from a large number of different ice bodies throughout the Arctic, that ice wedges have the greatest potential for DOC storage with a maximum of 28.6 mg L−1 (mean: 9.6 mg L−1. Variation in DOC concentration is positively correlated with and explained by the concentrations and relative amounts of typically terrestrial cations such as Mg2+ and K+. DOC sequestration into ground ice was more effective during the late Pleistocene than during the Holocene, which can be explained by rapid sediment and OC accumulation, the prevalence of more easily degradable vegetation and immediate incorporation into permafrost. We assume that pristine snowmelt is able to leach considerable amounts of well-preserved and highly bioavailable DOC as well as other elements from surface sediments, which are rapidly stored in ground ice, especially in ice wedges, even before further degradation. In the Yedoma region ice wedges represent a significant DOC (45.2 Tg and DIC (33.6 Tg pool in permafrost areas and a fresh-water reservoir of 4172 km3. This study underlines the need to discriminate between particulate OC and DOC to assess the availability and vulnerability of the permafrost carbon pool for ecosystems and climate feedback upon mobilization.

  9. Nonlinear controls on evapotranspiration in arctic coastal wetlands

    Directory of Open Access Journals (Sweden)

    A. K. Liljedahl

    2011-11-01

    Full Text Available Projected increases in air temperature and precipitation due to climate change in Arctic wetlands could dramatically affect ecosystem function. As a consequence, it is important to define controls on evapotranspiration, the major pathway of water loss from these systems. We quantified the multi-year controls on midday Arctic coastal wetland evapotranspiration, measured with the eddy covariance method at two vegetated, drained thaw lake basins near Barrow, Alaska. Variations in near-surface soil moisture and atmospheric vapor pressure deficits were found to have nonlinear effects on midday evapotranspiration rates. Vapor pressure deficits (VPD near 0.3 kPa appeared to be an important hydrological threshold, allowing latent heat flux to persistently exceed sensible heat flux. Dry (compared to wet soils increased bulk surface resistance (water-limited. Wet soils favored ground heat flux and therefore limited the energy available to sensible and latent heat flux (energy-limited. Thus, midday evapotranspiration was suppressed from both dry and wet soils but through different mechanisms. We also found that wet soils (ponding excluded combined with large VPD, resulted in an increased bulk surface resistance and therefore suppressing evapotranspiration below its potential rate (Priestley-Taylor α < 1.26. This was likely caused by the limited ability of mosses to transfer moisture during large atmospheric demands. Ultimately, in addition to net radiation, the various controlling factors on midday evapotranspiration (i.e., near-surface soil moisture, atmospheric vapor pressure, and the limited ability of saturated mosses to transfer water during high VPD resulted in an average evapotranspiration rate of up to 75% of the potential evapotranspiration rate. These multiple limitations on midday evapotranspiration rates have the potential to moderate interannual variation of total evapotranspiration and reduce excessive water loss in a warmer climate

  10. Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

    Science.gov (United States)

    Mann, Daniel H.; Groves, Pamela; Kunz, Michael L.; Reanier, Richard E.; Gaglioti, Benjamin V.

    2013-06-01

    Radical restructuring of the terrestrial, large mammal fauna living in arctic Alaska occurred between 14,000 and 10,000 years ago at the end of the last ice age. Steppe bison, horse, and woolly mammoth became extinct, moose and humans invaded, while muskox and caribou persisted. The ice age megafauna was more diverse in species and possibly contained 6× more individual animals than live in the region today. Megafaunal biomass during the last ice age may have been 30× greater than present. Horse was the dominant species in terms of number of individuals. Lions, short-faced bears, wolves, and possibly grizzly bears comprised the predator/scavenger guild. The youngest mammoth so far discovered lived ca 13,800 years ago, while horses and bison persisted on the North Slope until at least 12,500 years ago during the Younger Dryas cold interval. The first people arrived on the North Slope ca 13,500 years ago. Bone-isotope measurements and foot-loading characteristics suggest megafaunal niches were segregated along a moisture gradient, with the surviving species (muskox and caribou) utilizing the warmer and moister portions of the vegetation mosaic. As the ice age ended, the moisture gradient shifted and eliminated habitats utilized by the dryland, grazing species (bison, horse, mammoth). The proximate cause for this change was regional paludification, the spread of organic soil horizons and peat. End-Pleistocene extinctions in arctic Alaska represent local, not global extinctions since the megafaunal species lost there persisted to later times elsewhere. Hunting seems unlikely as the cause of these extinctions, but it cannot be ruled out as the final blow to megafaunal populations that were already functionally extinct by the time humans arrived in the region.

  11. Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

    Science.gov (United States)

    Mann, Daniel H.; Groves, Pamela; Kunz, Michael L.; Reanier, Richard E.; Gaglioti, Benjamin V.

    2013-01-01

    Radical restructuring of the terrestrial, large mammal fauna living in arctic Alaska occurred between 14,000 and 10,000 years ago at the end of the last ice age. Steppe bison, horse, and woolly mammoth became extinct, moose and humans invaded, while muskox and caribou persisted. The ice age megafauna was more diverse in species and possibly contained 6× more individual animals than live in the region today. Megafaunal biomass during the last ice age may have been 30× greater than present. Horse was the dominant species in terms of number of individuals. Lions, short-faced bears, wolves, and possibly grizzly bears comprised the predator/scavenger guild. The youngest mammoth so far discovered lived ca 13,800 years ago, while horses and bison persisted on the North Slope until at least 12,500 years ago during the Younger Dryas cold interval. The first people arrived on the North Slope ca 13,500 years ago. Bone-isotope measurements and foot-loading characteristics suggest megafaunal niches were segregated along a moisture gradient, with the surviving species (muskox and caribou) utilizing the warmer and moister portions of the vegetation mosaic. As the ice age ended, the moisture gradient shifted and eliminated habitats utilized by the dryland, grazing species (bison, horse, mammoth). The proximate cause for this change was regional paludification, the spread of organic soil horizons and peat. End-Pleistocene extinctions in arctic Alaska represent local, not global extinctions since the megafaunal species lost there persisted to later times elsewhere. Hunting seems unlikely as the cause of these extinctions, but it cannot be ruled out as the final blow to megafaunal populations that were already functionally extinct by the time humans arrived in the region.

  12. Remote sensing af vegetation

    OpenAIRE

    Nielsen, Kristine Bak

    2011-01-01

    This report concerns the correlation between the two vegetation indices NDVI and EVI obtained from satellite measurements and observed data for the gross primary production in Lille Bøgeskov near Sorø, Zealand, Denmark. The vegetation indices are based on the ratio between reflection of visible and near-infrared light. Plants will absorbe visible light in the process of photosynthesis and reflect near-infrared light. Because of this indices based on these wavelengths will be...

  13. Cryogenic cooling for high power laser amplifiers

    OpenAIRE

    Perin J.P.; Millet F.; Divoky M.; Rus B.

    2013-01-01

    Using DPSSL (Diode Pumped Solid State Lasers) as pumping technology, PW-class lasers with enhanced repetition rates are developed. Each of the Yb YAG amplifiers will be diode-pumped at a wavelength of 940 nm. This is a prerequisite for achieving high repetition rates (light amplification duration 1 millisecond and repetition rate 10 Hz). The efficiency of DPSSL is inversely proportional to the temperature, for this reason the slab amplifier have to be cooled at a temperature in the range of 1...

  14. Transportable setup for amplifier phase fidelity measurements

    Science.gov (United States)

    Tröbs, M.; Bogan, C.; Barke, S.; Kühn, G.; Reiche, J.; Heinzel, G.; Danzmann, K.

    2015-05-01

    One possible laser source for the Laser Interferometer Space Antenna (LISA) consists of an Ytterbium-doped fiber amplifier originally developed for inter-satellite communication, seeded by the laser used for the technology demonstrator mission LISA Pathfinder. LISA needs to transmit clock information between its three spacecraft to correct for phase noise between the clocks on the individual spacecraft. For this purpose phase modulation sidebands at GHz frequencies will be imprinted on the laser beams between spacecraft. Differential phase noise between the carrier and a sideband introduced within the optical chain must be very low. We report on a transportable setup to measure the phase fidelity of optical amplifiers.

  15. Optimization of Pr3+:ZBLAN fiber amplifiers

    DEFF Research Database (Denmark)

    Pedersen, B.; Miniscalco, J. W.; Quimby, R. S.

    1992-01-01

    Experimental parameters have been measured and used in a quantitative model of Pr3+-doped fluorozirconate fiber amplifiers. The optimum cutoff wavelength was determined to be 800 nm and the gain for 400 mW of pump was found to increase from 12 to 34 dB if the NA was increased from 0.15 to 0.......25. Lengthening the metastable state lifetime from 110 to 300 μs would significantly improve amplifier performance while concentration quenching can appreciably degrade it...

  16. Beyond nonlinear saturation of backward Raman amplifiers

    Science.gov (United States)

    Barth, Ido; Toroker, Zeev; Balakin, Alexey A.; Fisch, Nathaniel J.

    2016-06-01

    Backward Raman amplification is limited by relativistic nonlinear dephasing resulting in saturation of the leading spike of the amplified pulse. Pump detuning is employed to mitigate the relativistic phase mismatch and to overcome the associated saturation. The amplified pulse can then be reshaped into a monospike pulse with little precursory power ahead of it, with the maximum intensity increasing by a factor of two. This detuning can be employed advantageously both in regimes where the group velocity dispersion is unimportant and where the dispersion is important but small.

  17. Operational amplifier circuits analysis and design

    CERN Document Server

    Nelson, J C C

    1995-01-01

    This book, a revised and updated version of the author's Basic Operational Amplifiers (Butterworths 1986), enables the non-specialist to make effective use of readily available integrated circuit operational amplifiers for a range of applications, including instrumentation, signal generation and processing.It is assumed the reader has a background in the basic techniques of circuit analysis, particularly the use of j notation for reactive circuits, with a corresponding level of mathematical ability. The underlying theory is explained with sufficient but not excessive, detail. A range of compu

  18. Arctic shipping and China : Governance structure and future developments

    OpenAIRE

    Hjalti Þór Hreinsson 1984

    2014-01-01

    The goal of this thesis is to study China’s shipping ambitions in the Arctic and the pertinent governing instruments. Arctic shipping poses significant challenges for Arctic governance with increased access to its oceans for shipping companies. Arctic transit is driven by demanding world markets in the West and the rising economic powers of the East, looking for the most cost-efficient routes. Rapid ice melt leads to better access for vessels, but other obstacles await those interested in Arc...

  19. Vegetation dynamics using AVHRR/NDVI: Regional climate, carbon dioxide fertilization and crop yield relations

    Science.gov (United States)

    Lim, Chai Kyung

    Vegetation development is closely related to climate factors, and, therefore, it is important to understand how it responds to global climate changes. For the last two decades it has been possible to monitor vegetation development at continental or global scales utilizing remote sensing Normalized Difference Vegetation Index (NDVI) data. We have developed a frequency analysis method to investigate land's vegetation greenness change and its response to the El Nino Southern Oscillation (ENSO). We found an ENSO influence on a tropical forest, southern semi-deciduous forest and a northeastern mixed forest. Our analysis shows the annual trends in vegetation greenness respond more sensitively than averaging methods. Atmospheric CO2 increase is another concern for climate change, for which fertilization effect on land vegetation has been suggested. Atmospheric CO2 and NDVI have a seasonal pattern of negative correlation, which makes it difficult to discern any positive influence of CO2 on vegetation. We adopted the concept of the rate of change in atmospheric CO2 concentration and NDVI to overcome this set pattern, and to reveal undergoing fluctuations. We found evidence that suggests a CO2 fertilization effect in some arctic and sub arctic regions and northern and inland parts of the eastern humid temperate zones in North America. Although NDVI reveals the vegetation greenness only at a fixed time and location, we have transformed NDVI effectively to describe the vegetation growth dynamics in the form of a new index, Normalized Growth Index (NGI). Utilizing NGI, we found the vegetation growth during the growing season is highly negatively correlated with the initial minimum vegetation greenness. One needs to be careful when comparing Net Primary Production (NPP) using NDVI between different types of vegetation, because the same NDVI value can imply the existence of different biomass due to different Leaf Area Index (LAI). To overcome this difficulty we have developed

  20. Arctic River Mobility: A Baseline Assessment

    Science.gov (United States)

    Rowland, J. C.; Wilson, C. J.; Brumby, S. P.; Pope, P. A.

    2009-12-01

    In many arctic river systems, permafrost and the presence of frozen floodplain materials provides a significant source of bank cohesion. Due to this cohesion, permafrost may play an important control of arctic river mobility and meandering dynamics. Whether changes in the rates of permafrost thawing has had or will have as significant a geomorphic impact on arctic river meandering as has already been observed for arctic coastline retreat, lake size and distribution, and hillslope stability is at present an unanswered question. The potential impact of climate driven changes in arctic river meandering has important implications for river planform morphology, floodplain dynamics, river ecology, and the export of carbon and nutrients to coastal oceans. We present results of remote sensing analysis of river mobility for the Yukon River in Alaska and sections of the Siberian Rivers including the Lena, the Kolyma and the Indigirka Rivers. Comparisons of river location at successive intervals in time were conducted using Landsat imagery archives and higher resolution aerial photographs and satellite imagery. Extraction of river channel locations was accomplished using the GeniePro automated feature extraction software. Over the period of Landsat coverage (mid-1980s to present) arctic rivers show limited to no movement at the resolution of the Landsat data (30 m per pixel). On the Yukon Flats regions of the Yukon River, the most mobile sections of the river have migration rates comparable to reach-average values reported for temperate rivers; given that large portions of the Yukon display no detectable movement, reach-averaged values are far less than observed in temperate systems. Field inspection of areas of high erosion along the Yukon River indicate that erosional processes associated with the thermal degradation of permafrost play a dominant role in many of these areas. Thermal niching and large scale bank collapse due to undercutting play a large role in bank erosion

  1. Arctic Ocean freshwater: How robust are model simulations?

    NARCIS (Netherlands)

    Jahn, A.; Aksenov, Y.; de Cuevas, B.A.; de Steur, L.; Häkkinen, S.; Hansen, E.; Herbaut, C.; Houssais, M.N.; Karcher, M.; Kauker, F.; Lique, C.; Nguyen, A.; Pemberton, P.; Worthen, D.; Zhang, J.

    2012-01-01

    The Arctic freshwater (FW) has been the focus of many modeling studies, due to the potential impact of Arctic FW on the deep water formation in the North Atlantic. A comparison of the hindcasts from ten ocean-sea ice models shows that the simulation of the Arctic FW budget is quite different in the

  2. Establishing Shared Knowledge about Globalization in Asia and the Arctic

    DEFF Research Database (Denmark)

    Bertelsen, Rasmus Gjedssø; Graczyk, Piotr

    2016-01-01

    We discuss the role of knowledge in relations between Arctic communities and Asia (the Arctic Council observer states: China, India, Japan, Singapore, South Korea). We argue that mutual and shared knowledge between Arctic communities and Asia is necessary for local benefits and comprehensively...

  3. Exploring Arctic Transpolar Drift During Dramatic Sea Ice Retreat

    DEFF Research Database (Denmark)

    Gascard, J.C.; Festy, J.; le Goff, H.;

    2008-01-01

    The Arctic is undergoing significant environmental changes due to climate warming. The most evident signal of this warming is the shrinking and thinning of the ice cover of the Arctic Ocean. If the warming continues, as global climate models predict, the Arctic Ocean will change from a perennially...

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

    Science.gov (United States)

    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. Arctic Spring Transition in Warming Climate: A Study Using Reanalysis Dataset

    Science.gov (United States)

    De, B.; Zhang, X.

    2014-12-01

    An increased warming trend over the Arctic in recent years has been documented using observations, and is expected to continue by climate model projections. This increase may shift the springtime transition time, resulting in a longer sea-ice melt and vegetation growing period over the Arctic. In this study, we investigated variability of and changes in the spring transition in a warming climate and examined attributions of various dynamic and thermodynamic processes. The results demonstrate a dramatic increase in springtime surface air temperature (SAT) over the Arctic since 1979. Physical analysis reveals the importance of large-scale poleward moisture and energy advection accompanied by an enhancement in net downward radiation flux, which result in the surface warming. The cloudiness could impact the surface radiation budget and retreat of sea ice cover reduces surface albedo, making an additional contribution to the surface warming. In addition to the overall evaluation of these physical processes, composite analysis suggests that relative contributions from these processes to the increased springtime SAT vary across different geographic sub-regions.

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

    Science.gov (United States)

    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.

  7. Arctic shipping emissions inventories and future scenarios

    Directory of Open Access Journals (Sweden)

    J. J. Corbett

    2010-10-01

    Full Text Available This paper presents 5 km×5 km Arctic emissions inventories of important greenhouse gases, black carbon and other pollutants under existing and future (2050 scenarios that account for growth of shipping in the region, potential diversion traffic through emerging routes, and possible emissions control measures. These high-resolution, geospatial emissions inventories for shipping can be used to evaluate Arctic climate sensitivity to black carbon (a short-lived climate forcing pollutant especially effective in accelerating the melting of ice and snow, aerosols, and gaseous emissions including carbon dioxide. We quantify ship emissions scenarios which are expected to increase as declining sea ice coverage due to climate change allows for increased shipping activity in the Arctic. A first-order calculation of global warming potential due to 2030 emissions in the high-growth scenario suggests that short-lived forcing of ~4.5 gigagrams of black carbon from Arctic shipping may increase global warming potential due to Arctic ships' CO2 emissions (~42 000 gigagrams by some 17% to 78%. The paper also presents maximum feasible reduction scenarios for black carbon in particular. These emissions reduction scenarios will enable scientists and policymakers to evaluate the efficacy and benefits of technological controls for black carbon, and other pollutants from ships.

  8. Arctic Ocean Scientific Drilling: The Next Frontier

    Directory of Open Access Journals (Sweden)

    Ruediger Stein

    2010-04-01

    Full Text Available The modern Arctic Ocean appears to be changing faster than any other region on Earth. To understand the potential extent of high latitude climate change, it is necessary to sample the history stored in the sediments filling the basins and covering the ridges of the Arctic Ocean. These sediments have been imaged with seismic reflection data, but except for the superficial record, which has been piston cored, they have been sampled only on the Lomonosov Ridge in 2004 during the Arctic Coring Expedition (ACEX-IODP Leg 302; Backman et al., 2006 and in 1993 in the ice-free waters in the Fram Strait/Yermak Plateau area (ODP Leg 151; Thiede et al., 1996.Although major progress in Arctic Ocean research has been made during the last few decades, the short- and long-term paleoceanographic and paleoclimatic history as well as its plate-tectonic evolution are poorly known compared to the other oceans. Despite the importance of the Arctic in the climate system, the database we have from this area is still very weak. Large segments of geologic time have not been sampled in sedimentary sections. The question of regional variations cannot be addressed.

  9. 2nd International Arctic Ungulate Conference

    Directory of Open Access Journals (Sweden)

    A. Anonymous

    1996-01-01

    Full Text Available The 2nd International Arctic Ungulate Conference was held 13-17 August 1995 on the University of Alaska Fairbanks campus. The Institute of Arctic Biology and the Alaska Cooperative Fish and Wildlife Research Unit were responsible for organizing the conference with assistance from biologists with state and federal agencies and commercial organizations. David R. Klein was chair of the conference organizing committee. Over 200 people attended the conference, coming from 10 different countries. The United States, Canada, and Norway had the largest representation. The conference included invited lectures; panel discussions, and about 125 contributed papers. There were five technical sessions on Physiology and Body Condition; Habitat Relationships; Population Dynamics and Management; Behavior, Genetics and Evolution; and Reindeer and Muskox Husbandry. Three panel sessions discussed Comparative caribou management strategies; Management of introduced, reestablished, and expanding muskox populations; and Health risks in translocation of arctic ungulates. Invited lectures focused on the physiology and population dynamics of arctic ungulates; contaminants in food chains of arctic ungulates and lessons learned from the Chernobyl accident; and ecosystem level relationships of the Porcupine Caribou Herd.

  10. VLF propagation measurements in the Canadian Arctic

    Science.gov (United States)

    Lauber, Wilfred R.; Bertrand, Jean M.

    1993-05-01

    For the past three years, during a period of high sun spot numbers, propagation measurements were made on the reception of VLF signals in the Canadian Arctic. Between Aug. and Dec. 1989, the received signal strengths were measured on the Canadian Coast Guard icebreaker, John A. MacDonald in the Eastern Canadian Arctic. Between Jul. 1991 and Jun. 1992, the received signal strengths were measured at Nanisivik, Baffin Island. The purposes of this work were to check the accuracy and estimate variances of the Naval Ocean Systems Center's (NOSC) Long Wave Propagation Capability (LWPC) predictions in the Canadian Arctic and to gather ionospheric storm data. In addition, the NOSC data taken at Fort Smith and our data at Nanisivik were used to test the newly developed Longwave Noise Prediction (LNP) program and the CCIR noise predictions, at 21.4 and 24.0 kHz. The results of the work presented and discussed in this paper show that in general the LWPC predicts accurate values of received signal strength in the Canadian Arctic with standard deviations of 1 to 2 dB over several months. Ionospheric storms can gauge the received signal strengths to decrease some 10 dB for a period of several hours or days. However, the effects of these storms are highly dependent on the propagation path. Finally the new LNP atmospheric noise model predicts lower values of noise in the Arctic than the CCIR model and our limited measurements tend to support these lower values.

  11. THE MEDITERRANEAN WEEDY VEGETATION AND ITS ORIGIN

    Directory of Open Access Journals (Sweden)

    R: GUARINO

    2007-01-01

    Full Text Available An overview on the origin and evolutionary trends in the Mediterranean weedy vegetation is presented, with reference to the phytosociological units to which they are ascribed: Stellarietea mediae, Papaveretea rhoeadis, Oryzetea sativae. It is postulated that the “Neolithic revolution” was more likely a “Neolithic evolution”, i.e. the result of a process of selection and demographic growth that lasted for at least 10000 yrs, before leading to the domestication of plants and animals. During this very long time, wild crop relatives were simply growing together with the wild weed relatives, in their original milieu. At the beginning of agriculture, fields were obtained to the detriment of oak-woods and maquis-vegetation; the deforestation had probably a patchy pattern, resulting from the burn-beating practice, and the annual plants from the vegetation around the fields were probably quite abundant also within the fields, at least those having the most prolific seed set, the most durable seeds and the most effective dispersal strategies, together with a diachronic, life-long, flowering and seed-dispersal. These features, apparently in contrast with the achievement of a within-population- organizational hierarchy, are in reality an extreme expression of the attitude of weedy plant species in “amplifying adaptation”, or, in other words, of its “adaptation to adapt”, which is the cornerstone of the opportunistic life strategy. The Mediterranean weedy vegetation is therefore a flexible system, able to cope with changes and disturbances: species frequency and composition may undergo great variations, but the functional role of any weedy community keeps.

  12. The JRC and the Arctic - How JRC science can underpin the successful implementation of an EU Arctic Policy

    OpenAIRE

    WILSON Julian; Vignati, Elisabetta; DOBRICIC SRDAN; STILIANAKIS Nikolaos; Dowell, Mark; WESTRA VAN HOLTHE MARION; ZAMPIERI Alessandra; Martinsohn, Jann; VESPE MICHELE

    2015-01-01

    The Arctic is experiencing unprecedented and disproportionately high rates of environmental change due to effects of climate change. These changing conditions are making it easier to exploit the natural wealth of the Arctic (mineral, fisheries, land) while putting the existence of Arctic ecosystems and the indigenous population that rely on them under threat. EU institutions have recognised these opportunities for, and threats to, the Arctic. The EU Commission and the EEAS (European External ...

  13. Ultra-low Voltage CMOS Cascode Amplifier

    DEFF Research Database (Denmark)

    Lehmann, Torsten; Cassia, Marco

    In this paper, we design a folded cascode operational transconductance amplifier in a standard CMOS process, which has a measured 69 dB DC gain, a 2 MHz bandwidth and compatible input- and output voltage levels at a 1 V power supply. This is done by a novel Current Driven Bulk (CDB) technique...

  14. Compensation techniques for operational amplifier bias current

    International Nuclear Information System (INIS)

    Two techniques are proposed for the compensation of the input current on operational amplifiers that can be used on inverting and non-inverting configurations. A qualitative analysis of temperature drift problems is made, and as a practical application, the construction of a voltage follower for high impedance measurements is presented. (Author)

  15. Stereoscopy Amplifies Emotions Elicited by Facial Expressions.

    Science.gov (United States)

    Hakala, Jussi; Kätsyri, Jari; Häkkinen, Jukka

    2015-12-01

    Mediated facial expressions do not elicit emotions as strongly as real-life facial expressions, possibly due to the low fidelity of pictorial presentations in typical mediation technologies. In the present study, we investigated the extent to which stereoscopy amplifies emotions elicited by images of neutral, angry, and happy facial expressions. The emotional self-reports of positive and negative valence (which were evaluated separately) and arousal of 40 participants were recorded. The magnitude of perceived depth in the stereoscopic images was manipulated by varying the camera base at 15, 40, 65, 90, and 115 mm. The analyses controlled for participants' gender, gender match, emotional empathy, and trait alexithymia. The results indicated that stereoscopy significantly amplified the negative valence and arousal elicited by angry expressions at the most natural (65 mm) camera base, whereas stereoscopy amplified the positive valence elicited by happy expressions in both the narrowed and most natural (15-65 mm) base conditions. Overall, the results indicate that stereoscopy amplifies the emotions elicited by mediated emotional facial expressions when the depth geometry is close to natural. The findings highlight the sensitivity of the visual system to depth and its effect on emotions. PMID:27551358

  16. Predistortion of a Bidirectional Cuk Audio Amplifier

    DEFF Research Database (Denmark)

    Birch, Thomas Hagen; Nielsen, Dennis; Knott, Arnold;

    2014-01-01

    using predistortion. This paper suggests linearizing a nonlinear bidirectional Cuk audio amplifier using an analog predistortion approach. A prototype power stage was built and results show that a voltage gain of up to 9 dB and reduction in THD from 6% down to 3% was obtainable using this approach....

  17. Imminent ocean acidification in the Arctic projected with the NCAR global coupled carbon cycle-climate model

    Directory of Open Access Journals (Sweden)

    M. Steinacher

    2009-04-01

    Full Text Available Ocean acidification from the uptake of anthropogenic carbon is simulated for the industrial period and IPCC SRES emission scenarios A2 and B1 with a global coupled carbon cycle-climate model. Earlier studies identified seawater saturation state with respect to aragonite, a mineral phase of calcium carbonate, as a key variable governing impacts on corals and other shell-forming organisms. Globally in the A2 scenario, water saturated by more than 300%, considered suitable for coral growth, vanishes by 2070 AD (CO2≈630 ppm, and the ocean volume fraction occupied by saturated water decreases from 42% to 25% over this century. The largest simulated pH changes worldwide occur in Arctic surface waters, where hydrogen ion concentration increases by up to 185% (ΔpH=−0.45. Projected climate change amplifies the decrease in Arctic surface mean saturation and pH by more than 20%, mainly due to freshening and increased carbon uptake in response to sea ice retreat. Modeled saturation compares well with observation-based estimates along an Arctic transect and simulated changes have been corrected for remaining model-data differences in this region. Aragonite undersaturation in Arctic surface waters is projected to occur locally within a decade and to become more widespread as atmospheric CO2 continues to grow. The results imply that surface waters in the Arctic Ocean will become corrosive to aragonite, with potentially large implications for the marine ecosystem, if anthropogenic carbon emissions are not reduced and atmospheric CO2 not kept below 450 ppm.

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

    Science.gov (United States)

    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

  19. Carbon dioxide exchange in the High Arctic - examples from terrestrial ecosystems

    DEFF Research Database (Denmark)

    Grøndahl, L.

    and temperature in the growing season strongly control the interannual variability in ecosystem CO2 uptake rates. The area has during the past years experienced a warming during the summer season, which was shown to increase the uptake of CO2 by the vegetation. The increasing earlier snowmelt prolonged the length......The thesis provides an analysis of the exchange of CO2 between the atmosphere and the vegetation communities in the High Arctic at different temporal and spatial scales. Using a time series of data from a dry heath ecosystem in Zackenberg NE Greenland, it was shown that timing of snowmelt...... to increased warming in the region. A cross scale analysis of eddy covariance and chamber data showed a good agreement between the two methods, which lead to an estimate of CO2 exchange based on NDVI. A timeseries of satellite imagery for the 2004 growing season provided the opportunity to upscale fluxes from...

  20. Record-low primary productivity and high plant damage in the Nordic Arctic Region in 2012 caused by multiple weather events and pest outbreaks

    Science.gov (United States)

    Bjerke, Jarle W.; Rune Karlsen, Stein; Arild Høgda, Kjell; Malnes, Eirik; Jepsen, Jane U.; Lovibond, Sarah; Vikhamar-Schuler, Dagrun; Tømmervik, Hans

    2014-08-01

    The release of cold temperature constraints on photosynthesis has led to increased productivity (greening) in significant parts (32-39%) of the Arctic, but much of the Arctic shows stable (57-64%) or reduced productivity (browning, insect and fungal pests also contributed to low greenness. Vegetation greenness in 2012 was 6.8% lower than the 2000-11 average and 58% lower in the worst affected areas that were under multiple stressors. These results indicate the importance of events (some being mostly neglected in climate change effect studies and monitoring) for primary productivity in a high-latitude maritime region, and highlight the importance of monitoring plant damage in the field and including frequencies of stress events in models of carbon economy and ecosystem change in the Arctic. Fourteen weather events and anomalies and 32 hypothesized impacts on plant productivity are summarized as an aid for directing future research.

  1. Holocene glaciation and climate evolution of Baffin Island, Arctic Canada

    Science.gov (United States)

    Miller, Gifford H.; Wolfe, Alexander P.; Briner, Jason P.; Sauer, Peter E.; Nesje, Atle

    2005-08-01

    Lake sediment cores and cosmogenic exposure (CE) dates constrain the pattern of deglaciation and evolution of climate across Baffin Island since the last glacial maximum (LGM). CE dating of erratics demonstrates that the northeastern coastal lowlands became ice-free ca.14 ka as the Laurentide Ice Sheet (LIS) receded from its LGM margin on the continental shelf. Coastal lakes in southeastern Baffin Island started to accumulate sediment at this time, whereas initial lacustrine sedimentation was delayed by two millennia in the north. Reduced organic matter in lake sediment deposited during the Younger Dryas chron, and the lack of a glacial readvance at that time suggest cold summers and reduced snowfall. Ice retreated rapidly after 11 ka but was interrupted by a widespread readvance of both the LIS and local mountain glaciers ˜9.6 ka (Cockburn Substage). A second readvance occurred just before 8 ka during a period of unusually cold summers, corresponding to the 8.2 ka cold event in the Greenland Ice Sheet. Most local glaciers were behind their present margins before 7 ka, and in some instances much earlier, although the Foxe Dome of the LIS continued to slowly retract toward the present day Barnes Ice Cap throughout the Holocene. Pollen in lake sediments is rare and dominated by exotic sources prior to 12 ka. Subsequently, grass tundra became established, followed by modern tundra vegetation ca. 8 ka, with subtle changes in pollen assemblages in the late Holocene. Lake primary productivity peaked in the early Holocene, before terrestrial vegetation or marine surface waters reached their apparent thermal maxima. Lacustrine, marine, and glacial proxies all reflect significant late Holocene cooling. The onset of Neoglaciation is well dated in lacustrine records at ca. 6 ka, with intensification after 2.5 ka. The expansion of local glaciers during the Little Ice Age represents the most extensive advance since 7 ka. We suggest that the replacement of Atlantic surface

  2. Soil Biota and Litter Decay in High Arctic Ecosystems

    Science.gov (United States)

    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

  3. AROME-Arctic: New operational NWP model for the Arctic region

    Science.gov (United States)

    Süld, Jakob; Dale, Knut S.; Myrland, Espen; Batrak, Yurii; Homleid, Mariken; Valkonen, Teresa; Seierstad, Ivar A.; Randriamampianina, Roger

    2016-04-01

    In the frame of the EU-funded project ACCESS (Arctic Climate Change, Economy and Society), MET Norway aimed 1) to describe the present monitoring and forecasting capabilities in the Arctic; and 2) to identify the key factors limiting the forecasting capabilities and to give recommendations on key areas to improve the forecasting capabilities in the Arctic. We have observed that the NWP forecast quality is lower in the Arctic than in the regions further south. Earlier research indicated that one of the factors behind this is the composition of the observing system in the Arctic, in particular the scarceness of conventional observations. To further assess possible strategies for alleviating the situation and propose scenarios for a future Arctic observing system, we have performed a set of experiments to gain a more detailed insight in the contribution of the components of the present observing system in a regional state-of-the-art non-hydrostatic NWP model using the AROME physics (Seity et al, 2011) at 2.5 km horizontal resolution - AROME-Arctic. Our observing system experiment studies showed that conventional observations (Synop, Buoys) can play an important role in correcting the surface state of the model, but prove that the present upper-air conventional (Radiosondes, Aircraft) observations in the area are too scarce to have a significant effect on forecasts. We demonstrate that satellite sounding data play an important role in improving forecast quality. This is the case with satellite temperature sounding data (AMSU-A, IASI), as well as with the satellite moisture sounding data (AMSU-B/MHS, IASI). With these sets of observations, the AROME-Arctic clearly performs better in forecasting extreme events, like for example polar lows. For more details see presentation by Randriamampianina et al. in this session. The encouraging performance of AROME-Arctic lead us to implement it with more observations and improved settings into daily runs with the objective to

  4. Chytrids dominate arctic marine fungal communities.

    Science.gov (United States)

    Hassett, B T; Gradinger, R

    2016-06-01

    Climate change is altering Arctic ecosystem structure by changing weather patterns and reducing sea ice coverage. These changes are increasing light penetration into the Arctic Ocean that are forecasted to increase primary production; however, increased light can also induce photoinhibition and cause physiological stress in algae and phytoplankton that can favour disease development. Fungi are voracious parasites in many ecosystems that can modulate the flow of carbon through food webs, yet are poorly characterized in the marine environment. We provide the first data from any marine ecosystem in which fungi in the Chytridiomycota dominate fungal communities and are linked in their occurrence to light intensities and algal stress. Increased light penetration stresses ice algae and elevates disease incidence under reduced snow cover. Our results show that chytrids dominate Arctic marine fungal communities and have the potential to rapidly change primary production patterns with increased light penetration. PMID:26754171

  5. Predictability of the Arctic sea ice edge

    Science.gov (United States)

    Goessling, H. F.; Tietsche, S.; Day, J. J.; Hawkins, E.; Jung, T.

    2016-02-01

    Skillful sea ice forecasts from days to years ahead are becoming increasingly important for the operation and planning of human activities in the Arctic. Here we analyze the potential predictability of the Arctic sea ice edge in six climate models. We introduce the integrated ice-edge error (IIEE), a user-relevant verification metric defined as the area where the forecast and the "truth" disagree on the ice concentration being above or below 15%. The IIEE lends itself to decomposition into an absolute extent error, corresponding to the common sea ice extent error, and a misplacement error. We find that the often-neglected misplacement error makes up more than half of the climatological IIEE. In idealized forecast ensembles initialized on 1 July, the IIEE grows faster than the absolute extent error. This means that the Arctic sea ice edge is less predictable than sea ice extent, particularly in September, with implications for the potential skill of end-user relevant forecasts.

  6. Fate of mercury in the Arctic (FOMA)

    DEFF Research Database (Denmark)

    Skov, H.; Christensen, J.; Asmund, G.;

    This report is the final reporting of the project FONA, funded by the Danish Environmental Protection Agency with means from the MIKA/DANCEA funds for Environmental Support to the Arctic Region. The aim of the project is to study the intercompartment mercury transport chain in the arctic area. From...... atmospheric deposition of mercury on sea surfaces to uptake in marine organisms, bio-accumulation, and finally mercury levels in mammals. The studies in the project are focused on the behaviour of mercury during the spring period where special phenomena lead to an enhanced deposition of mercury in the Arctic...... environment, at a time where the marine ecosystem is particularly active. The studies also include a comprehensive time trend study of mercury in top carnivore species. Each of these studies contributes towards establishing the knowledge necessary to develop a general model for transport and uptake of mercury...

  7. Mean Dynamic Topography of the Arctic Ocean

    Science.gov (United States)

    Farrell, Sinead Louise; Mcadoo, David C.; Laxon, Seymour W.; Zwally, H. Jay; Yi, Donghui; Ridout, Andy; Giles, Katherine

    2012-01-01

    ICESat and Envisat altimetry data provide measurements of the instantaneous sea surface height (SSH) across the Arctic Ocean, using lead and open water elevation within the sea ice pack. First, these data were used to derive two independent mean sea surface (MSS) models by stacking and averaging along-track SSH profiles gathered between 2003 and 2009. The ICESat and Envisat MSS data were combined to construct the high-resolution ICEn MSS. Second, we estimate the 5.5-year mean dynamic topography (MDT) of the Arctic Ocean by differencing the ICEn MSS with the new GOCO02S geoid model, derived from GRACE and GOCE gravity. Using these satellite-only data we map the major features of Arctic Ocean dynamical height that are consistent with in situ observations, including the topographical highs and lows of the Beaufort and Greenland Gyres, respectively. Smaller-scale MDT structures remain largely unresolved due to uncertainties in the geoid at short wavelengths.

  8. Arctic Ozone Depletion from UARS MLS Measurements

    Science.gov (United States)

    Manney, G. L.

    1995-01-01

    Microwave Limb Sounder (MLS) measurements of ozone during four Arctic winters are compared. The evolution of ozone in the lower stratosphere is related to temperature, chlorine monoxide (also measured by MLS), and the evolution of the polar vortex. Lagrangian transport calculations using winds from the United Kingdom Meteorological Office's Stratosphere-Troposphere Data Assimilation system are used to estimate to what extent the evolution of lower stratospheric ozone is controlled by dynamics. Observations, along with calculations of the expected dynamical behavior, show evidence for chemical ozone depletion throughout most of the Arctic lower stratospheric vortex during the 1992-93 middle and late winter, and during all of the 1994-95 winter that was observed by MLS. Both of these winters were unusually cold and had unusually cold and had unusually strong Arctic polar vortices compared to meteorological data over the past 17 years.

  9. Pathways of PFOA to the Arctic: variabilities and contributions of oceanic currents and atmospheric transport and chemistry sources

    Directory of Open Access Journals (Sweden)

    I. Stemmler

    2010-05-01

    Full Text Available Perfluorooctanoic acid (PFOA and other perfluorinated compounds are industrial chemicals in use since decades which resist degradation in the environment and seem to accumulate in polar regions. Transport of PFOA was modeled using a spatially resolved global multicompartment model including fully coupled three-dimensional ocean and atmosphere general circulation models, and two-dimensional top soil, vegetation surfaces, and sea ice compartments. In addition to primary emissions, the formation of PFOA in the atmosphere from degradation of 8:2 fluorotelomer alcohol was included as a PFOA source. Oceanic transport, delivered 14.8±5.0 (8–23 t a−1 to the Arctic, strongly influenced by changes in water transport, which determined its interannual variability. This pathway constituted the dominant source of PFOA to the Arctic. Formation of PFOA in the atmosphere lead to episodic transport events (timescale of days into the Arctic with small spatial extent. Deposition in the polar region was found to be dominated by wet deposition over land, and shows maxima in boreal winter. The total atmospheric deposition of PFOA in the Arctic in the 1990s was ≈1 t a−1, much higher than previously estimated, and is dominated by primary emissions rather than secondarily formed.

  10. Pathways of PFOA to the Arctic: variabilities and contributions of oceanic currents and atmospheric transport and chemistry sources

    Science.gov (United States)

    Stemmler, I.; Lammel, G.

    2010-10-01

    Perfluorooctanoic acid (PFOA) and other perfluorinated compounds are industrial chemicals in use for decades which resist degradation in the environment and seem to accumulate in polar regions. Transport of PFOA was modeled using a spatially resolved global multicompartment model including fully coupled three-dimensional ocean and atmosphere general circulation models, and two-dimensional top soil, vegetation surfaces, and sea ice compartments. In addition to primary emissions, the formation of PFOA in the atmosphere from degradation of 8:2 fluorotelomer alcohol was included as a PFOA source. Oceanic transport, delivered 14.8±5.0 (8-23) t a-1 to the Arctic, strongly influenced by changes in water transport, which determined its interannual variability. This pathway constituted the dominant source of PFOA to the Arctic. Formation of PFOA in the atmosphere led to episodic transport events (timescale of days) into the Arctic with small spatial extent. Deposition in the polar region was found to be dominated by wet deposition over land, and shows maxima in boreal winter. The total atmospheric deposition of PFOA in the Arctic in the 1990s was ≈1 t a-1, much higher than previously estimated, and is dominated by primary emissions rather than secondary formation.

  11. Pathways of PFOA to the Arctic: variabilities and contributions of oceanic currents and atmospheric transport and chemistry sources

    Directory of Open Access Journals (Sweden)

    I. Stemmler

    2010-10-01

    Full Text Available Perfluorooctanoic acid (PFOA and other perfluorinated compounds are industrial chemicals in use for decades which resist degradation in the environment and seem to accumulate in polar regions. Transport of PFOA was modeled using a spatially resolved global multicompartment model including fully coupled three-dimensional ocean and atmosphere general circulation models, and two-dimensional top soil, vegetation surfaces, and sea ice compartments. In addition to primary emissions, the formation of PFOA in the atmosphere from degradation of 8:2 fluorotelomer alcohol was included as a PFOA source. Oceanic transport, delivered 14.8±5.0 (8–23 t a−1 to the Arctic, strongly influenced by changes in water transport, which determined its interannual variability. This pathway constituted the dominant source of PFOA to the Arctic. Formation of PFOA in the atmosphere led to episodic transport events (timescale of days into the Arctic with small spatial extent. Deposition in the polar region was found to be dominated by wet deposition over land, and shows maxima in boreal winter. The total atmospheric deposition of PFOA in the Arctic in the 1990s was ≈1 t a−1, much higher than previously estimated, and is dominated by primary emissions rather than secondary formation.

  12. Ground-Based Hyperspectral Characterization of Alaska Tundra Vegetation along Environmental Gradients

    Directory of Open Access Journals (Sweden)

    Marcel Schwieder

    2013-08-01

    Full Text Available Remote sensing has become a valuable tool in monitoring arctic environments. The aim of this paper is ground-based hyperspectral characterization of Low Arctic Alaskan tundra communities along four environmental gradients (regional climate, soil pH, toposequence, and soil moisture that all vary in ground cover, biomass, and dominating plant communities. Field spectroscopy in connection with vegetation analysis was carried out in summer 2012, along the North American Arctic Transect (NAAT. Spectral metrics were extracted, including the averaged reflectance and absorption-related metrics such as absorption depths and area of continuum removal. The spectral metrics were investigated with respect to “greenness”, biomass, vegetation height, and soil moisture regimes. The results show that the surface reflectances of all sites are similar in shape with a reduced near-infrared (NIR reflectance that is specific for low-growing biomes. The main spectro-radiometric findings are: (i Southern sites along the climate gradient have taller shrubs and greater overall vegetation biomass, which leads to higher reflectance in the NIR. (ii Vegetation height and surface wetness are two antagonists that balance each other out with respect to the NIR reflectance along the toposequence and soil moisture gradients. (iii Moist acidic tundra (MAT sites have “greener” species, more leaf biomass, and green-colored moss species that lead to higher pigment absorption compared to moist non-acidic tundra (MNT sites. (iv MAT and MNT plant community separation via narrowband Normalized Difference Vegetation Index (NDVI shows the potential of hyperspectral remote sensing applications in the tundra.

  13. Arctic Hydrology and the role of feedbacks in the climate system (Invited)

    Science.gov (United States)

    Hinzman, L. D.

    2009-12-01

    The effects of a warming climate on the terrestrial regions of the Arctic are already quite apparent and impacts to the hydrologic system are also quite evident. The broadest impacts to the terrestrial arctic regions will result through consequent effects of changing permafrost structure and extent. As the climate differentially warms in summer and winter, the permafrost will become warmer, the active layer (the layer of soil above the permafrost that annually experiences freeze and thaw) will become thicker, the lower boundary of permafrost will become shallower and permafrost extent will decrease in area. These simple structural changes will affect every aspect of the surface water and energy balances and local ecology. Surface moisture and surface temperature are the main driving variables in local terrestrial and atmospheric linkages. Surface temperature is the linchpin in energy fluxes since it links atmospheric thermal gradients, forcing convective heat transfer, with the subsurface thermal gradients, driving conductive heat transfer. Soil moisture exerts a strong influence upon energy fluxes through controls on evaporative heat flux, phase change in thawing of permafrost, and indirect effects on thermal conductivity. In order to understand and predict ecosystem responses to a changing climate and the resultant feedbacks, it is critical to quantify the dynamic interactions of soil moisture and temperature with changes in permafrost as a function of climatic processes, landscape type, and vegetation. In future climate scenarios, the Arctic is expected to be warmer, and experience greater precipitation. With the lengthening of the summer season, however, more of this precipitation will occur as rain. The periods of potential evaporation, and transpiration will also increase. Oddly enough, even now, the Arctic may be considered a desert. The vast wetlands that cover large portions of Alaska, Canada and Siberia exist because permafrost prevents soil moisture and

  14. Arctic Warming as News - Perils and Possibilities

    Science.gov (United States)

    Revkin, A. C.

    2015-12-01

    A science journalist in his 30th year covering human-driven climate change, including on three Arctic reporting trips, reflects on successes and setbacks as news media, environmentalists and Arctic communities have tried to convey the significance of polar change to a public for which the ends of the Earth will always largely be a place of the imagination.Novel challenges are arising in the 24/7 online media environment, as when a paper by a veteran climate scientist proposing a mechanism for abrupt sea-level rise became a big news story before it was accepted by the open-review journal to which it had been submitted. New science is digging in on possible connections between changing Arctic sea ice and snow conditions and disruptive winter weather in more temperate northern latitudes, offering a potential link between this distant region and the lives of ordinary citizens. As cutting-edge research, such work gets substantial media attention. But, as with all new areas of inquiry, uncertainty dominates - creating the potential for distracting the public and policymakers from the many aspects of anthropogenic climate change that are firmly established - but, in a way, boring because of that.With the challenges, there are unprecedented opportunities for conveying Arctic science. In some cases, researchers on expeditions are partnering with media, offering both scientists and news outlets fresh ways to convey the story of Arctic change in an era of resource constraints.Innovative uses of crittercams, webcams, and satellite observations offer educators and interested citizens a way to track and appreciate Arctic change. But more can be done to engage the public directly without the news media as an intermediary, particularly if polar scientists or their institutions test some of the established practices honed by more experienced communicators at NASA.

  15. Arctic sea ice balance and climate

    International Nuclear Information System (INIS)

    Proxy data and local historical records show that sea ice extent has undergone large secular variations over past millennia and centuries, for reasons that are only qualitatively understood. Since the onset of systematic observations in situ and satellites, the record shows a remarkable constancy of the annual cycle of the arctic sea ice cover. This cycle is described by a continuity equation that is used to discuss the mechanisms relating ice extent and thickness to climate, and to illustrate how ice formation, transport, and melting combine to produce the seasonal cycle of sea ice cover. The heat balances and stresses at the surface and bottom of the sea ice are external forcing functions with small-scale and large-scale feedbacks. Examples are the stable stratification of the ocean boundary layer caused by bottom melting and surface drainage which suppress the vertical ocean heat flux, and the arctic summer stratus which forms over ice-covered ocean regions and limits surface melting. Recent efforts to model the seasonal cycle of sea ice in the Arctic are discussed in light of the observational record. A promising new development is the incorporation of satellite data as explicit variables carried in dynamic-thermodynamic ice models. Of special interest in the context of climate is the fresh water budget of the Arctic Basin. Its largest components, the runoff generated by mid-latitude precipitation over the Eurasian continent, and the ice export driven by the wind field over the Arctic Basin, have no immediately apparent connection. Taking into account all other components of the fresh water balance, Aagaard and Carmack estimate that the contemporary influx and outflux of fresh water at the perimeter of the Arctic Basin are equal. The unraveling of the mechanisms responsible for this equality, and the consequence of a possible imbalance remain challenging questions

  16. Bioaccumulation of radiocaesium in Arctic seals.

    Science.gov (United States)

    Carroll, Jolynn; Wolkers, Hans; Andersen, Magnus; Rissanen, Kristina

    2002-12-01

    Seals are high trophic level feeders that bioaccumulate many contaminants to a greater degree than most lower trophic level organisms. Their trophic status in the marine food web and wide-spread distribution make seals useful sentinels of arctic environmental change. The purpose of this investigation is to document the levels and bioaccumulation potential of radiocaesium in high latitude seal species for which data have not previously been available. The study was carried out on harp, ringed, and bearded seals caught north of the island archipelago of Svalbard (82 degrees N) in 1999. The results are then compared with previous studies in order to elucidate factors responsible for bioaccumulation in Arctic seals. Concentrations of 137Cs were determined in muscle, liver and kidney samples from a total of 10 juvenile and one adult seal. The mean concentration in muscle samples for all animals was 0.23 +/- 0.045 Bq/kg f.w. 137Cs concentrations in both liver and kidney samples were near detection limits (approximately 0.2 Bq/kg f.w.). The results are consistent with previous studies indicating low levels of radiocaesium in Arctic seals in response to a long term trend of decreasing levels of 137Cs in the Barents Sea region. Bioconcentration factors (BCFs) estimated for seals from NE Svalbard are low, ranging from 34 to 130. Comparing these values with reported BCFs for Greenland seals from other sectors of the European Arctic, we suggest that the combination of physiological and ecological factors on radiocaesium bioaccumulation is comparable among different Arctic seal populations. The application of this work to Arctic monitoring and assessment programs is discussed. PMID:12523541

  17. Bioaccumulation of radiocaesium in Arctic seals

    International Nuclear Information System (INIS)

    Seals are high trophic level feeders that bioaccumulate many contaminants to a greater degree than most lower trophic level organisms. Their trophic status in the marine food web and wide-spread distribution make seals useful sentinels of arctic environmental change. The purpose of this investigation is to document the levels and bioaccumulation potential of radiocaesium in high latitude seal species for which data have not previously been available. The study was carried out on harp, ringed, and bearded seals caught north of the island archipelago of Svalbard (82 deg. N) in 1999. The results are then compared with previous studies in order to elucidate factors responsible for bioaccumulation in Arctic seals. Concentrations of 137Cs were determined in muscle, liver and kidney samples from a total of 10 juvenile and one adult seal. The mean concentration in muscle samples for all animals was 0.23±0.045 Bq/kg f.w. 137Cs concentrations in both liver and kidney samples were near detection limits (∼0.2 Bq/kg f.w.). The results are consistent with previous studies indicating low levels of radiocaesium in Arctic seals in response to a long term trend of decreasing levels of 137Cs in the Barents Sea region. Bioconcentration factors (BCFs) estimated for seals from NE Svalbard are low, ranging from 34 to 130. Comparing these values with reported BCFs for Greenland seals from other sectors of the European Arctic, we suggest that the combination of physiological and ecological factors on radiocaesium bioaccumulation is comparable among different Arctic seal populations. The application of this work to Arctic monitoring and assessment programs is discussed

  18. Bioaccumulation of radiocaesium in Arctic seals

    Energy Technology Data Exchange (ETDEWEB)

    Carroll, JoLynn; Wolkers, Hans; Andersen, Magnus; Rissanen, Kristina

    2002-12-01

    Seals are high trophic level feeders that bioaccumulate many contaminants to a greater degree than most lower trophic level organisms. Their trophic status in the marine food web and wide-spread distribution make seals useful sentinels of arctic environmental change. The purpose of this investigation is to document the levels and bioaccumulation potential of radiocaesium in high latitude seal species for which data have not previously been available. The study was carried out on harp, ringed, and bearded seals caught north of the island archipelago of Svalbard (82 deg. N) in 1999. The results are then compared with previous studies in order to elucidate factors responsible for bioaccumulation in Arctic seals. Concentrations of {sup 137}Cs were determined in muscle, liver and kidney samples from a total of 10 juvenile and one adult seal. The mean concentration in muscle samples for all animals was 0.23{+-}0.045 Bq/kg f.w. {sup 137}Cs concentrations in both liver and kidney samples were near detection limits ({approx}0.2 Bq/kg f.w.). The results are consistent with previous studies indicating low levels of radiocaesium in Arctic seals in response to a long term trend of decreasing levels of {sup 137}Cs in the Barents Sea region. Bioconcentration factors (BCFs) estimated for seals from NE Svalbard are low, ranging from 34 to 130. Comparing these values with reported BCFs for Greenland seals from other sectors of the European Arctic, we suggest that the combination of physiological and ecological factors on radiocaesium bioaccumulation is comparable among different Arctic seal populations. The application of this work to Arctic monitoring and assessment programs is discussed.

  19. Export of nutrients from the Arctic Ocean

    Science.gov (United States)

    Torres-Valdés, Sinhué; Tsubouchi, Takamasa; Bacon, Sheldon; Naveira-Garabato, Alberto C.; Sanders, Richards; McLaughlin, Fiona A.; Petrie, Brian; Kattner, Gerhard; Azetsu-Scott, Kumiko; Whitledge, Terry E.

    2013-04-01

    study provides the first physically based mass-balanced transport estimates of dissolved inorganic nutrients (nitrate, phosphate, and silicate) for the Arctic Ocean. Using an inverse model-generated velocity field in combination with a quasi-synoptic assemblage of hydrographic and hydrochemical data, we quantify nutrient transports across the main Arctic Ocean gateways: Davis Strait, Fram Strait, the Barents Sea Opening (BSO), and Bering Strait. We found that the major exports of all three nutrients occur via Davis Strait. Transports associated with the East Greenland Current are almost balanced by transports associated with the West Spitsbergen Current. The most important imports of nitrate and phosphate to the Arctic occur via the BSO, and the most important import of silicate occurs via Bering Strait. Oceanic budgets show that statistically robust net silicate and phosphate exports exist, while the net nitrate flux is zero, within the uncertainty limits. The Arctic Ocean is a net exporter of silicate (-15.7 ± 3.2 kmol s-1) and phosphate (-1.0 ± 0.3 kmol s-1; net ± 1 standard error) to the North Atlantic. The export of excess phosphate (relative to nitrate) from the Arctic, calculated at -1.1 ± 0.3 kmol s-1, is almost twice as large as previously estimated. Net transports of silicate and phosphate from the Arctic Ocean provide 12% and 90%, respectively, of the net southward fluxes estimated at 47°N in the North Atlantic. Additional sources of nutrients that may offset nutrient imbalances are explored, and the relevance and the pathway of nutrient transports to the North Atlantic are discussed.

  20. Role of Greenland meltwater in the changing Arctic

    Science.gov (United States)

    Dukhovskoy, Dmitry; Proshutinsky, Andrey; Timmermans, Mary-Louise; Myers, Paul; Platov, Gennady; Bamber, Jonathan; Curry, Beth; Somavilla, Raquel

    2016-04-01

    Observational data show that the Arctic ocean-ice-atmosphere system has been changing over the last two decades. Arctic change is manifest in the atypical behavior of the climate indices in the 21st century. Before the 2000s, these indices characterized the quasi-decadal variability of the Arctic climate related to different circulation regimes. Between 1948 and 1996, the Arctic atmospheric circulation alternated between anticyclonic circulation regimes and cyclonic circulation regimes with a period of 10-15 years. Since 1997, however, the Arctic has been dominated by an anticyclonic regime. Previous studies indicate that in the 20th century, freshwater and heat exchange between the Arctic Ocean and the sub-Arctic seas were self-regulated and their interactions were realized via quasi-decadal climate oscillations. What physical processes in the Arctic Ocean - sub-Arctic ocean-ice-atmosphere system are responsible for the observed changes in Arctic climate variability? The presented work is motivated by our hypothesis that in the 21st century, these quasi-decadal oscillations have been interrupted as a result of an additional freshwater source associated with Greenland Ice Sheet melt. Accelerating since the early 1990s, the Greenland Ice Sheet mass loss exerts a significant impact on thermohaline processes in the sub-Arctic seas. Surplus Greenland freshwater, the amount of which is about a third of the freshwater volume fluxed into the region during the 1970s Great Salinity Anomaly event, can spread and accumulate in the sub-Arctic seas influencing convective processes there. It is not clear, however, whether Greenland freshwater can propagate into the interior convective regions in the Labrador Sea and the Nordic Seas. In order to investigate the fate and pathways of Greenland freshwater in the sub-Arctic seas and to determine how and at what rate Greenland freshwater propagates into the convective regions, several numerical experiments using a passive tracer to