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  • 4151. Zhu, Q.
    et al.
    Liu, J.
    Peng, C.
    Chen, H.
    Fang, X.
    Jiang, H.
    Yang, G.
    Zhu, D.
    Wang, W.
    Zhou, X.
    Modelling methane emissions from natural wetlands by development and application of the TRIPLEX-GHG model2014Ingår i: Geoscientific Model Development, Vol. 7, nr 3, s. 981-999Artikel i tidskrift (Refereegranskat)
  • 4152. Zimmermann, Bettina
    et al.
    Porcelli, Don
    Frank, Martin
    Andersson, Per S.
    Baskaran, M.
    Lee, Der-Chuen
    Halliday, Alex N.
    Hafnium isotopes in Arctic Ocean water2009Ingår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 73, nr 11, s. 3218-3233Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The first isotopic compositions of dissolved hafnium in seawater from across the Arctic Ocean are reported. Most samples from the four sub-basins of the Arctic Ocean have values within error of an average of epsilon(Hf) = +0.8. Combined Hf-Nd isotope compositions do not fall on the well-established positive correlation for mantle and crustal rocks. Instead, Arctic waters have Hf that is more radiogenic than that typically found in rocks with similar Nd isotope compositions, a feature previously found in ferromanganese crusts and waters from the Pacific Ocean. Arctic seawater samples generally fall on the lower part of the ferromanganese crust array, reflecting influences of inputs from Arctic rivers and interactions of shelf waters with underlying sediments. Arctic rivers have much higher Hf concentrations (7-30 pM) than Arctic seawater (0.36-4.2 pM). Water from the Mackenzie River has the least radiogenic Hf, with epsilon(Hf) = -7.1 +/- 1.7, and plots furthest away from the ferromanganese crust array, while waters from the Ob, Yenisey, and Lena Rivers have values that are indistinguishable from most Arctic waters. In the Amundsen, Makarov, and Canada basins, Hf concentrations are highest at the surface and lowest in the deeper waters, reflecting the influences of riverine inputs and of waters that have flowed over the extensive Siberian continental shelves and have Nd and Hf characteristics that reflect water-sediment interactions. This is in contrast to the relatively low near surface Hf concentrations reported for locations elsewhere. The Pacific water layer in the Canada Basin exhibits the highest value of epsilon(Hf) = +6.8 +/- 1.8, reflecting the Hf isotopic composition of waters entering the Arctic from the Pacific Ocean. Mixing relationships indicate that a substantial fraction of the Hf in the Mackenzie River is lost during estuarine mixing; the behaviour of Hf from other rivers is less constrained. (C) 2009 Elsevier Ltd. All rights reserved.

  • 4153.
    Zipprich, L.
    Geol. Inst..
    Geologie, Struktur und Metamorphose der Region südlich des Lullihatjårro am Nordufer des Torneträsk (Schwedisch - Lappland).1988Studentuppsats (Examensarbete)
  • 4154. Ziska, F.
    et al.
    Quack, B.
    Abrahamsson, K.
    Archer, S. D.
    Atlas, E.
    Bell, T.
    Butler, J. H.
    Carpenter, L. J.
    Jones, C. E.
    Harris, N. R. P.
    Hepach, H.
    Heumann, K. G.
    Hughes, C.
    Kuss, J.
    Krueger, K.
    Liss, P.
    Moore, R. M.
    Orlikowska, A.
    Raimund, S.
    Reeves, C. E.
    Reifenhaeuser, W.
    Robinson, A. D.
    Schall, C.
    Tanhua, T.
    Tegtmeier, S.
    Turner, S.
    Wang, L.
    Wallace, D.
    Williams, J.
    Yamamoto, H.
    Yvon-Lewis, S.
    Yokouchi, Y.
    Global sea-to-air flux climatology for bromoform, dibromomethane and methyl iodide2013Ingår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, nr 17, s. 8915-8934Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Volatile halogenated organic compounds containing bromine and iodine, which are naturally produced in the ocean, are involved in ozone depletion in both the troposphere and stratosphere. Three prominent compounds transporting large amounts of marine halogens into the atmosphere are bromoform (CHBr3), dibromomethane (CH2Br2) and methyl iodide (CH3I). The input of marine halogens to the stratosphere has been estimated from observations and modelling studies using low-resolution oceanic emission scenarios derived from top-down approaches. In order to improve emission inventory estimates, we calculate data-based high resolution global sea-to-air flux estimates of these compounds from surface observations within the HalOcAt (Halocarbons in the Ocean and Atmosphere) database (https://halocat.geomar.de/). Global maps of marine and atmospheric surface concentrations are derived from the data which are divided into coastal, shelf and open ocean regions. Considering physical and biogeochemical characteristics of ocean and atmosphere, the open ocean water and atmosphere data are classified into 21 regions. The available data are interpolated onto a 1 degrees x 1 degrees grid while missing grid values are interpolated with latitudinal and longitudinal dependent regression techniques reflecting the compounds’ distributions. With the generated surface concentration climatologies for the ocean and atmosphere, global sea-to-air concentration gradients and sea-to-air fluxes are calculated. Based on these calculations we estimate a total global flux of 1.5/2.5 Gmol Br yr(-1) for CHBr3, 0.78/0.98 Gmol Br yr(-1) for CH2Br2 and 1.24/1.45 Gmol Br yr(-1) for CH3I (robust fit/ordinary least squares regression techniques). Contrary to recent studies, negative fluxes occur in each sea-to-air flux climatology, mainly in the Arctic and Antarctic regions. “Hot spots” for global polybromomethane emissions are located in the equatorial region, whereas methyl iodide emissions are enhanced in the subtropical gyre regions. Inter-annual and seasonal variation is contained within our flux calculations for all three compounds. Compared to earlier studies, our global fluxes are at the lower end of estimates, especially for bromoform. An under-representation of coastal emissions and of extreme events in our estimate might explain the mismatch between our bottom-up emission estimate and top-down approaches.

  • 4155. Zolotukhina, N.
    et al.
    Polekh, N.
    Kurkin, V.
    Rogov, D.
    Romanova, E.
    Chelpanov, M.
    Ionospheric effects of St. Patrick’s storm over Asian Russia: 17–19 March 20152017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 2, s. 2484-2504Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have carried out a comprehensive analysis of data from the high-frequency coherent radar located near Yekaterinburg, ground-based ionospheric, riometric, and magnetic stations, situated within the radar field of view and in the vicinity of it, as well as from eight radio paths crossing the Asian region of Russia. Using these data, we studied dynamics of ionospheric disturbances over wide longitudinal sector during the first 3 days of the St. Patrick’s two-step severe geomagnetic storm and determined the main mechanisms of their development. We showed that on 17 March during the main and early recovery storm phases, the major contribution to the generation of the ionospheric disturbances had been made by impact ionization by precipitating magnetospheric particles. This had lead to appearance of intense sporadic layers, alternating with intervals of total absorption. The main features of the storm were the large latitude width of the auroral precipitation zone and an expansion of this zone to corrected geomagnetic latitude   45°. We suppose that these peculiarities were due to high variability of interplanetary magnetic field and solar wind impacted on the magnetosphere. The most probable cause of the negative ionospheric disturbance on 18 March might have been a change in the neutral atmosphere composition. Significant differences between measured and simulated values of maximal electron concentration in F2 layer point to the need to improve the existing empirical models of thermosphere, auroral precipitations, and magnetospheric convection in order to use them for modeling of ionospheric parameters during severe geomagnetic storms.

  • 4156.
    Åberg, Jan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Production and emission of CO2 in two unproductive lakes in northern Sweden2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Unproductive lakes are one of few natural landscape compartments with net release of carbon to the atmosphere. Lakes also generally decrease the net terrestrial carbon uptake, since most of the CO2 production in unproductive lakes are derived from organic carbon produced on land (e.g. in forests). High latitude lakes are predicted to be particularly affected by the global climate change. The carbon cycling in these lakes and their role in the landscape are therefore important to study.

    In this thesis, carbon turnover processes were studied in two lakes above the arctic circle (Lake Diktar-Erik and Lake Merasjärvi) in year 2004 and 2005. Both lakes were net heterotrophic, with large variations in CO2 concentrations both on shorter (30min) and longer (24h) time-scales. The pelagic habitat supported a major part of the net production of CO2, with larger dynamics in the CO2 production than the sediments. The CO2 variations of the surface water were related to respiration of allochthonous organic carbon, and were affected by the concentration and quality of the DOC, as well as the whole lake water temperatures, and vertical water movements.

    The emission of CO2 from Lake Merasjärvi was measured with the eddy covariance tech­nique. The results showed that the gas transfer rate during moderate winds were higher than expected, causing the two most commonly used models to underestimate the long term fluxes of CO2 from the lake.

    Taken together, the results of the thesis show that the studied lakes contributed to bring terrestrial organic carbon back into the atmosphere, driven by a substantial internal CO2 production based on mineralization of allochthonous organic carbon. Major results are that the eddy covariance technique indicated that commonly used models tend to underestimate the net release rate of CO2 from lakes to the atmosphere, and that the lake CO2 dynamics can be the results of interactions between biogeochemical and physical processes in the lake water.

  • 4157.
    Åberg, Jan
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Jansson, Mats
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Jonsson, Anders
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Importance of water temperature and thermal stratification dynamics for temporal variation of surface water CO2 in a boreal lake2010Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, nr G02024, s. 10PP-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Variation of the surface water CO2 concentration is likely to be the result of biological activity and physical processes as water mixing and gas exchange with the atmosphere. Here we have studied the variations in surface water CO2 during the ice-free period in the humic Lake Merasjärvi in northern Sweden. Meteorological, hydrological and limnological data were collected using data logging equipment permitting high time-resolution. The surface water of the lake was supersaturated with respect to CO2 throughout the study period. There were, however, considerable diurnal and longer-term temporal variations of the surface water CO2 concentrations. Partial least squares (PLS) models were used to link the logged CO2 data to the multivariate dataset. On the longer-term time scale (analyzed with 24h means of the logged data) high concentrations of surface water CO2 were best related to the depth and temperature of the upper warmer layer (epilimnion), and to erosion of the underlying colder layer (hypolimnion). The diurnal variation (analyzed with 30 minute means of the logged data) was best related to the thermal dynamics within the epilimnion, which regulated the surface water access to CO2 stores within this layer. Variables related to CO2 emission and photosynthesis (wind and PAR), showed only weak correlations to variations of the surface water CO2 concentration. Accordingly, the CO2 flux, measured with the eddy-covariance technique, was not correlated to the surface water CO2 concentration.

  • 4158.
    Åberg, Jan
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Jansson, Mats
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Nääs, Klockar-Jenny
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Jonsson, Anders
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Pelagic and benthic net production of dissolved inorganic carbon in an unproductive subarctic lake2007Ingår i: Freshwater Biology, Vol. 52, nr 3, s. 549-560Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    1. Both the pelagic and benthic net dissolved inorganic carbon (DIC) productions were measured in situ on four occasions from June to September 2004, in the unproductive Lake Diktar-Erik in subarctic Sweden. The stable isotopic signal (δ13C) of respired organic material was estimated from hypolimnion water data and data from a laboratory incubation using epilimnion water.

    2. Both pelagic and benthic habitats were net heterotrophic during the study period, with a total net DIC production of 416 mg C m-2 day-1, of which the pelagic habitat contributed approximately 85%. The net DIC production decreased with depth both in the pelagic water and in the sediments, and most of the net DIC production occurred in the upper water column.

    3. Temporal variations in both pelagic and benthic DIC production were small, although we observed a significant decrease in pelagic net DIC production after the autumn turnover. Water temperature was the single most important factor explaining temporal and vertical variations in pelagic DIC production. No single factor explained more than 10% of the benthic net DIC production, which probably was regulated by several interacting factors.

    4. Pelagic DIC production, and thus most of the whole-lake net production of DIC, was mainly due to the respiration of allochthonous organic carbon. Stable isotope data inferred that nearly 100% of accumulated DIC in the hypolimnion water had an allochthonous carbon source. Similarly, in the laboratory incubation using epilimnion water, c. 85% of accumulated DIC was indicated to have an allochthonous organic carbon source.

  • 4159. Åkerman, H. Jonas
    et al.
    Johansson, Margareta
    Thawing permafrost and thicker active layers in sub-arctic Sweden2008Ingår i: Permafrost and Periglacial Processes, ISSN 1045-6740, E-ISSN 1099-1530, Vol. 19, nr 3, s. 279-292Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Observations of active‐layer thickness from nine sites with up to 29 years of gridded measurements located in the Torneträsk region, northernmost Sweden, were examined in relation to climatic trends. Mean annual air temperatures in this area have warmed and recently rose above 0°C. Active layers at all sites have become thicker, at rates ranging from 0.7 to 1.3 cm per year. This trend has accelerated in the past decade, especially in the westernmost site where rates have reached 2 cm per year and permafrost has disappeared at 81 per cent of the sampling points. Increased active‐layer thicknesses are correlated with increases in mean summer air temperature, thawing degree‐days and, in five of the nine sites, with increases in snow depth.

  • 4160. Åkerman, H.J. (Ed.)
    High alpine environmental fluctuations and slope processes in the Holocene. Report from an International field symposium in Abisko, August 1991.1992Rapport (Övrigt vetenskapligt)
  • 4161. Åkerman, H.J.
    et al.
    Malmström, B.
    Permafrost mounds in the Abisko area, northern Sweden.1986Ingår i: Geografiska Annaler, Vol. 68A, nr 3, s. 155-165Artikel i tidskrift (Övrigt vetenskapligt)
  • 4162. Åkerman, J.
    Aspects on the significance of climatic changes for the periglacial environment in northern Sweden.1991Ingår i: Svensk Geografisk Årsbok, Vol. 67, s. 176-187Artikel i tidskrift (Övrigt vetenskapligt)
  • 4163. Åkerman, J.
    et al.
    Rapp, A. (Eds)
    Nivation och lokalglaciation - geomorfologiska och klimatologiska tillämpningar. Rapport från ett minisymposium, Abisko sept. 1983.1985Rapport (Övrigt vetenskapligt)
  • 4164. Åkesson, O.A
    Några bilder från Sveriges naturforskarestation vid Vassijaure.1907Ingår i: Betlehem Kristlig Kalender 21: 105-111, Vol. 21, s. 105-111Artikel i tidskrift (Övrigt vetenskapligt)
  • 4165. Åkesson, O.A.
    et al.
    Bergstrand, E.
    Vassijaure Nat. Vet. Station, Observations Météorologiques a Vassijaure, II. 1 Aout 1906-31 Juillet 1907.1910Rapport (Övrigt vetenskapligt)
  • 4166. Åkesson, Susanne
    et al.
    Morin, Jens
    Muheim, Rachel
    Ottosson, Ulf
    Dramatic orientation shift of white-crowned sparrows displaced across longitudes in the high Arctic2005Ingår i: Current Biology, Vol. 15, nr 17, s. 1591-1597Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Advanced spatial-learning adaptations have been shown for migratory songbirds (1], but it is not well known how the simple genetic program encoding migratory distance and direction in young birds [2-4] translates to a navigation mechanism used by adults [2, 4-6]. A number of convenient cues are available to define latitude on the basis of geomagnetic and celestial information [7-15], but very few are useful to defining longitude [12-15]. To investigate the effects of displacements across longitudes on orientation, we recorded orientation of adult and juvenile migratory white-crowned sparrows, Zonotrichia leucophrys gambelii, after passive longitudinal displacements, by ship, of 266-2862 km across high-arctic North America. After eastward displacement to the magnetic North Pole and then across the 0 degrees declination line, adults and juveniles abruptly shifted their orientation from the migratory direction to a direction that would lead back to the breeding area or to the normal migratory route, suggesting that the birds began compensating for the displacement by using geomagnetic cues alone or together with solar cues. In contrast to predictions by a simple genetic migration program, our experiments suggest that both adults and juveniles possess a navigation system based on a combination of celestial and geomagnetic information, possibly declination, to correct for eastward longitudinal displacements.

  • 4167. Ångström, A.
    On the radiation and temperature of snow and the convection of the air at its surface.1918Rapport (Övrigt vetenskapligt)
  • 4168. Ångström, A.
    et al.
    Tryselius, O.
    Total radiation from sun and sky at Abisko.1934Ingår i: Geografiska Annaler, Vol. 1, s. 53-69Artikel i tidskrift (Övrigt vetenskapligt)
  • 4169. Åsbrink, G.
    Övre Norrland, 2. Riksgränsbanan.: Statens Järnvägars resehandböcker, ed. 31931Bok (Övrig (populärvetenskap, debatt, mm))
  • 4170. Åsbrink, G.
    Övre Norrland. Resehandbok.: Statens Järnvägars resehandböcker, ed. 21920Bok (Övrig (populärvetenskap, debatt, mm))
  • 4171.
    Öberg, Lisa
    Mittuniversitetet, Avdelningen för naturvetenskap.
    Treeline dynamics in short and long term perspectives: observational and historical evidence from the southern Swedish Scandes2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Avhandlingen belyser förskjutningar i olika tidsskalor av den alpina trädgränsens läge i de svenska Skanderna. Trädgränsen definieras som den högsta nivån (m ö.h.) för minst 2 m höga individer av en viss art i en definierad del av en fjällsluttning. Avhandlingen består av fyra separata uppsatser, publicerade i olika välrenommerade vetenskapliga tidskrifter. 

    I Paper I analyseras förändringar av trädgränserna för fjällens vanligaste trädarter, fjällbjörk, gran och tall (Betula pubescens ssp. czerepanovii, Picea abies och Pinus sylvestris) mellan 1915 och 2007. Undersökningen omfattar ett 8000 km2 stort, naturgeografiskt heterogent område, med mer än 100 lokaler. De maximala trädgränsförskjutningarna för samtliga trädarter uppgår till omkring 200 m. Resultaten motsvarar de trädgränsförskjutningar som teoretiskt kan förutsägas utifrån den temperaturhöjning med cirka 1,4 °C som skett under samma tidsperiod, förutsatt ideala förhållanden. För större delen av området råder emellertid andra, icke-ideala förhållanden, varför trädgränsernas uppflyttning i allmänhet blivit avsevärt mindre än 200 m. Den främsta anledningen till detta är lokala topoklimatiska begränsningar, d.v.s. kombinerade effekter av geomorfologi, vind, snöfördelning, jorddjup, etc., som i stora delar av det starkt brutna fjällandskapet mer eller mindre effektivt hindrar träden från att nå sina potentiellt högst belägna växtplatser betingade av temperaturen. Efter 1975 har björken förlorat sin roll som arten med den snabbast expanderande trädgränsen. I stället har tall och gran avancerat med större hastighet. Det innebär att även om klimatets uppvärmning fortsätter, så kommer det subalpina björkbältet att expandera i avsevärt mindre omfattning än vad som ofta förebådats. Möjligtvis kommer det att ersättas av tall.

    Paper II behandlar björkens trädgränsdynamik under perioden 2005/2007-2010/2011 längs en regional klimatgradient med avseende på maritimitet/kontientalitet. Trädgränsen har under den aktuella perioden avancerat 3,0 m/år i den maritimt präglade delen av gradienten, vilket kontrasterar signifikant mot en sänkning med 0,4 m/år i området med mer kontinentalt klimat. Skillnaderna diskuteras i termer av klimatförändringens varierande effekter på snötäckets utbredning och varaktighet och dess inverkan på markfuktigheten. En allt tidigare total utsmältning av snölegorna i de kontinentala områdena har av allt att döma resulterat i vattenbrist under sommaren. Torka medför reducerad vitalitet för existerande björkar och förhindrar både sexuell förökning och uppflyttning av trädgränsen. I de maritima delarna kvarligger alltjämt mycket snö under en stor del av sommaren. Trädgränsens position har därför kunnat bibehållas eller flyttas upp. Vissa omständigheter tyder på att trädgränsens stigning i högre grad har varit baserad på fröföryngring efter 1975, jämfört med perioden 1915-1975.

    Utgångspunkten för Paper III är erfarenheter från Paper I, som visar att trädgränsens uppflyttning för gran och björk huvudsakligen är resultatet av ökad höjdtillväxt av äldre, i vissa fall flertusenåriga, mer eller mindre buskformiga individer (krummholz), som vuxit på nivåer långt ovanför trädgränsen. Som ett svar på de senaste hundra årens varmare klimat har dessa antagit trädform, varigenom trädgränsen höjts. För en fördjupad förståelse av den här mekanismen har megafossil, d.v.s. grova vedrester bevarade i marken under gamla grankloner i trädgränsekotonen, 14C-daterats. Resultaten tyder på att granar i exponerad fjällmiljö kan uppnå i det närmaste ”evigt” liv genom sin förmåga till vegetativ förökning och möjligheten att växla mellan busk- och trädform i takt med klimatets växlingar. Vissa nu levande kloner existerade av allt att döma redan för 9500 år sedan. Den nu dokumenterat tidiga förekomsten av gran, bekräftar den på senare tid allt tydligare bilden av granen som en tidig invandrare till fjällkedjan. Möjligtvis har granen ”övervintrat” den senaste istiden närmare Skandinavien än vad som till helt nyligen varit den gängse uppfattningen.

    Paper IV behandlar en för Skandinavien ny metod för historisk trädgränsrekonstruktion. I uppsatsen analyseras 14C-dateringar av totalt 78 större veddelar (megafossil) som nyligen exponerats i anslutning till smältande glaciäris och ”perenna” snölegor i tre huvudområden, Helags-Sylarna, Tärna och Abisko, högt ovanför dagens trädgräns. Det framkommer att tall (Pinus sylvestris) koloniserade tidigt framsmälta nunatakker redan under senglacial tid. För omkring 9600-9500 år sedan inträffade en första massiv våg av björk- och talletablering i isfria glaciärnischer. Båda arterna växte 400-600 m ovanför sina nuvarande trädgränspositioner, i ett klimat som kan ha varit 3,5 °C varmare än idag.

    Under intervallet 9600 till 4400 BP uppträdde björken i ett 100-150 m brett bälte ovanför de översta tallarna. Som ett svar på klimatets successiva avkylning under senare delen av Holocen sänktes både björkens och tallens trädgränser i de aktuella miljöerna, till dess de för 4400 respektive 5900 år sedan helt försvann från lokaler där glaciärer och perenna snöfält började bildas. De analyserade trädresterna, som länge bevarats av glaciäris och perenn snö representerar en period med ett klimat långt varmare än under det senaste århundradet. Med denna analogi från det förflutna kan det därför antas att i en framtid där sommartemperaturerna rent hypotetiskt är 3,5 °C högre än i nutiden, skulle trädgränserna lokalt kunna flyttas upp med ungefär 600 m.

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  • 4172.
    Öberg, Lisa
    et al.
    Mittuniversitetet, Institutionen för tillämpad naturvetenskap och design.
    Kullman, Leif
    Umeå University, Department of Ecology and Environmental Science, SE 90187 Umeå.
    Recent Glacier Recession – a New Source of Postglacial Treeline and Climate History in the Swedish Scandes2012Ingår i: Landscape Online, ISSN 1865-1542, E-ISSN 1865-1542, Vol. 26, s. 1-38Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate warming during the past century has imposed recession of glaciers and perennial snow/ice patches along the entire Swedish Scandes. On the newly exposed forefields, subfossil wood remnants are being outwashed from beneath ice and snow bodies. In Scandinavia, this kind of detrital wood is a previously unused source of postglacial vegetation and climate history. The present study reports radiocarbon dates of a set of 78 wood samples, retrieved from three main sites, high above modern treelines and stretching along the Swedish Scandes. In accord with previous studies, pine (Pinus sylvestris) colonized early emerging nunataks already during the Late Glacial. Around 9600-9500 cal. yr BP a first massive wave of tree establishment, birch and pine, took place in "empty" glacier cirques. Both species grew 400-600 m above their present-ay treeline position and the summer temperatures may have been 3.5 °C warmer than present. In respons to Neoglacial cooling, treelines of both birch and pine descended until their final disappearance from the record 4400 and 5900 cal. yr BP, respectively. During the entire interval 9600 to 4400 cal. yr BP, birch prospered in a 100-150 broad belt above the uppermost pines. The recent emergence of tree remnants in the current habitats relates to the contemporary episode of climate warming, possibly unprecedented for several past millennia. It is inferred, by an anology with the past, that in a future scenario with summers 3.5 ° warmer than present, the birch treeline may rise by 600 m or so.

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    FULLTEXT01
  • 4173. Ödman, O.H.
    Beskrivning till berggrundskarta över urberget i Norrbottens län.1957Rapport (Övrigt vetenskapligt)
  • 4174.
    Ögren, Amanda
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Is above- and belowground phenology of Eriophorum vaginatum in sync in a peatland underlain by permafrost?2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The phenology of plants in northern ecosystems is currently changing. Roots have a key role in these ecosystems, though the phenology of roots is still poorly understood. The aim of this report was to investigate if above- and belowground phenology of the circumpolar sedge Eriophorum vaginatum was synchronized in a subarctic peatland underlain by permafrost, and to investigate which abiotic factors are limiting root growth. Additionally, the length of the belowground growing season was examined. The study was performed with a non-destructive in situ method (minirhizotrons and NDVI measurements) in the northernmost part of Sweden. Both above- and belowground phenology was measured biweekly during the whole growing season in 2016. The depth of the active layer, air temperature, soil temperature and soil moisture were measured to investigate the determinants of root growth. Root growth and aboveground activity was asynchronous, as peak in root growth occurred on average 21 days before maximum NDVI was reached. Soil temperature and thaw depth seem to be important factors regulating root growth in this peatland. The result highlight that solely studying the aboveground parts of plants can give a misleading interpretation about the phenology of the entire plant and thus during which time periods important ecosystem processes take place. Hence, to more accurate forecast ecosystem responses to global warming, both aboveground and belowground phenology should be considered.

  • 4175.
    Öhmark, Sara
    Mittuniversitetet, Avdelningen för naturvetenskap.
    Winter browsing by moose and hares in subarctic birch forest: Scale dependency and responses to food addition2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Despite their difference in body size and morphology, the moose (Alces alces) andthe mountain hare (Lepus timidus) sustain themselves during winter on similar plantspecies and plant parts in in subarctic environments, namely apical twigs ofmountain birch (Betula pubescens ssp. czerepanovii). Herbivores must select areas anditems of food that provide sufficient intake rates and food nutritional quality whilebalancing this against their intake of dietary fiber and potentially detrimental plantsecondary metabolites. This selection takes place simultaneously at multiple spatialscales, from individual plants and plant parts to patches of food and parts of the wider landscape. While the herbivores must consider their need for food to sustaindaily activities, for body growth and reproduction it is also necessary to avoid predators and harsh environmental conditions. For managers, an understanding of key factors for animal foraging distributions is pivotal to reach intended goals ofmanagement and conservation plans. Knowledge in this area is also important formodels to make accurate predictions of foraging responses of herbivores to resource distributions. The mountain birch forest displays a naturally heterogeneous distribution of trees and shrubs which presents herbivores with a challenge to findgood feeding areas. In an investigation of the spatial distribution of moose browsing on birch and willows (Salix spp.) in two winter seasons separated in time by 14 years,it was found that moose browsing patterns in 1996 were correlated to those observed in 2010. It was also found that moose browsing was spatially clustered within the same distances (1000-2500 m) as densities of willow and birch, but at other spatial scales, browsing was mostly randomly distributed. It was concluded that foragedensity is a cue for moose but only at certain spatial scales. Similarly, a comparison of foraging distribution by hare and moose showed that high birch density was a key factor for both species. In spite of this, hares and moose used different parts ofthe same environment because they respond to food resource distribution at different spatial scales. Hares fed from smaller plants, and focused their foraging activity on smaller spatial scales than moose. These results emphasize the importance of taking into account the distribution of food resources at spatial scales relevant for each species in plans for conservation and management. In an experimental study it was found that intensified browsing on natural forage by mountain hares can be induced locally through placement of food. The induced browsing varied with the amount and quality of the added food, but also with thedensity of natural food plants and natural foraging distribution by hares. Finally, ina last experiment habitat preference of mountain hares across edges between open and forested areas was studied. The results were not consistent; hares utilized baitto a greater extent within forested areas than bait placed on a nearby lake ice, butbait on mires and heaths was either preferred over bait in nearby forest, or utilizedto a similar extent. A possible explanation is that hares have knowledge of their environment such that both forested areas and subarctic mires and heaths are partof its natural home range, whilst the extreme environment on the lake ice is not. During recent decades arctic areas have had an increase in vegetation density andwill be affected by future climate warming and therefore, factors that determineforaging ecology of key herbivores need to be identified. This thesis sheds some light on these factors in relation to spatial scale and forage distribution for two high profile herbivores in the subarctic.

  • 4176.
    Öhmark, Sara
    et al.
    Mittuniversitetet, Avdelningen för naturvetenskap.
    Palo, Thomas
    Swedish Univ Agr Sci, Dept Wildlife Fish & Environm Studies, S-90183 Umea, Sweden.
    Iason, Glenn
    James Hutton Inst, Aberdeen AB15 8QH, Scotland, UK.
    Spatially segregated foraging patterns of moose (Alces alces) and mountain hare (Lepus timidus) in a subarctic landscape: different tables in the same restaurant?2015Ingår i: Canadian Journal of Zoology, ISSN 0008-4301, E-ISSN 1480-3283, Vol. 93, nr 5, s. 391-396Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Differences in body sizes of mountain hares (Lepus timidus L., 1758) and moose (Alces alces (L., 1758)) affect their abilityto perceive and respond to environmental heterogeneity and plant density. Therefore, we expect these species to show nicheseparation at different scales in the same environment. Results showed that the numbers of mountain birches (Betula pubescenssubsp. czerepanovii L.) browsed by moose per unit area was inversely related to hare browsing. Moose browsed larger birchescompared with hares, and while hares targeted areas with high birch densities regardless of tree sizes, moose preferentiallybrowsed areas with high densities of large birches. Moose browsing was clustered at spatial intervals of 1000–1500 m, while harebrowsing was clustered at intervals of less than 500 m. Willows (genus Salix L.) in the study area were heavily browsed by moose,while few observations of hare browsing on willow were made. Regarding both hare and moose, numbers of birch stems withnew browsing per sample plot were positively correlated with the numbers of birch stems with old browsing, indicating thathare and moose preferred the same foraging sites from year to year. These findings have implications for management of thespecies because they show the importance of scale and landscape perspectives in planning and actions.

  • 4177. Öquist, M.
    Northern Peatland Carbon Biogeochemistry. The influence of vascular plants and edaphic factors on carbon dioxide and methane exchange.2001Rapport (Övrigt vetenskapligt)
  • 4178. Östergren, O.
    Antennaria glabrata (J. Vahl) Pors.1921Ingår i: Svensk Botanisk Tidskrift, Vol. 15, nr 2-4, s. 271-Artikel i tidskrift (Övrigt vetenskapligt)
  • 4179. Östman, C.J.
    Snöstormvarningar på Riksgränsbanan.1930Ingår i: Teknisk Tidskrift, Vol. 60, s. 7-11Artikel i tidskrift (Övrigt vetenskapligt)
  • 4180. Östman, C.J.
    Vinden i Sveriges högre luftlager. Resultat av pilotballongobservationer utförda under åren 1919-1929.1933Rapport (Övrigt vetenskapligt)
  • 4181. Østrem, G.
    et al.
    Nyberg, R. (Eds)
    Glacial and periglacial environments1986Ingår i: Geografiska Annaler, Vol. 68A, nr 3Artikel i tidskrift (Övrigt vetenskapligt)
  • 4182. Škaloud, Pavel
    et al.
    Škaloudová, Magda
    Procházková, Anna
    Němcová, Yvonne
    Morphological delineation and distribution patterns of four newly described species within the Synura petersenii species complex (Chrysophyceae, Stramenopiles)2014Ingår i: European journal of phycology, ISSN 0967-0262, E-ISSN 1469-4433, Vol. 49, nr 2, s. 213-229Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Synura petersenii species complex represents a common, cosmopolitan and highly diverse taxon of autotrophic freshwater flagellates. In this paper, we describe and characterize four new species (S. borealis, S. heteropora, S. hibernica and S. laticarina) that have been identified during our extensive sampling of freshwater habitats in 15 European countries. Morphometric analyses of siliceous scales led to the significant phenotypic differentiation of all four newly described species, and their separation from other related species of the S. petersenii complex. Two of these newly described species (S. hibernica and S. borealis) can be clearly distinguished by characteristic large colonies consisting of elongated, lanceolate-shaped cells. Development of strongly elongated, narrow cells in S. hibernica could be explained by the adaptation of this species to oligotrophic conditions. Though morphologically distinct, S. borealis possesses an exceptionally high degree of genetic diversity, possibly indicating recent speciation and evolutionary diversification within this taxon. Three of the four newly described species exhibit restricted biogeographic distribution. The evolutionarily related S. borealis and S. laticarina occur only in Northern Europe, and seem to be adapted to colder areas. The most remarkable distribution pattern was observed for S. hibernica, which has a geographic distribution that is restricted to western Ireland.

  • 4183.
    Alajaureområdet. Översiktlig naturinventering.1979Artikel i tidskrift (Övrigt vetenskapligt)
  • 4184.
    Arctic and alpine ecology and environmental impacts.1993Konferensbidrag (Övrigt vetenskapligt)
  • 4185.
    Bihang 2 till meteorologiska iakttagelser i Sverige.1917Rapport (Övrigt vetenskapligt)
  • 4186.
    Bör Torneträsk regleras?1960Ingår i: Kungliga Svenska Vetenskapsakademiens Skrifter i naturskyddsärenden, Vol. 50Artikel i tidskrift (Övrigt vetenskapligt)
  • 4187.
    Cambridge expedition to Swedish Lappland.1965Ingår i: Cambridge Expeditions Journal, Vol. 1965, s. 48-49Artikel i tidskrift (Övrigt vetenskapligt)
  • 4188.
    Einwanderung und Verbreitung der Süsswasserfische in Norwegen mit einem Anhang über den Krebs1924Ingår i: Archiv für Hydrobiologie, Vol. 14, s. 223-314Artikel i tidskrift (Övrigt vetenskapligt)
  • 4189.
    Fjällen. Samebyarnas redovisning av renskötselns markanvändning 1974.1975Ingår i: Rapport, Vol. 20, nr 3, s. 31-Artikel i tidskrift (Övrigt vetenskapligt)
  • 4190.
    Lavin! Lavin! (Skildring av sex personer, som 1950 upplevde och delvis begravdes under en lavin på Vassitjåkko).1952Ingår i: På Skidor, Vol. 1952, s. 141-152Artikel i tidskrift (Övrigt vetenskapligt)
  • 4191.
    Lavin vid Katterjaurestugan. (Sven Hörnell: Photograph of a snow avalanche at Katterjaure).1946Ingår i: Till Fjälls, Vol. 18, s. 88-Artikel i tidskrift (Övrigt vetenskapligt)
  • 4192.
    Meteorologiska iakttagelser i Riksgränsen 1930-37.: SMHA ÅrsbokBok (Övrig (populärvetenskap, debatt, mm))
  • 4193.
    Ornitologkongress. 10. Internationale Ornithologkongres i Sverige juni 1950.1951Ingår i: Dansk Ornithologisk Forening Tidsskrift, Vol. 45, s. 51-56Artikel i tidskrift (Övrigt vetenskapligt)
  • 4194.
    Regulierung des Torne Älv in Schweden. (Mitgeteilt vom Limnologischen Institut der Hydrobiologischen Anstalt der Max-Planck-Gesellschaft, Schlitz-Hessen).1961Ingår i: Naturwissenschaftliche Rundschau, Vol. 14, nr 7, s. 2-Artikel i tidskrift (Övrigt vetenskapligt)
  • 4195.
    Svenska Turistföreningen.1928Ingår i: Sveriges Natur, Vol. 1928, s. 183-185Artikel i tidskrift (Övrigt vetenskapligt)
  • 4196. Gårdfeldt, Katarina (Redaktör)
    Lindgren, Åsa (Redaktör)
    SWEDARCTIC Arctic Ocean 2016: Expedition Report2017Rapport (Övrigt vetenskapligt)
    Ladda ner fulltext (pdf)
    fulltext
  • 4197.
    Torneträsk.1972Konferensbidrag (Övrigt vetenskapligt)
  • 4198.
    Vetenskapen mellan Turisten och Östra.1974Rapport (Övrigt vetenskapligt)
81828384 4151 - 4198 av 4198
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