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  • 1.
    Aalto, Juha
    Helsingfors universitet, matematisk-naturvetenskapliga fakulteten, institutionen för geovetenskaper och geografi.
    New perspectives on climate: Earth surface processes and thermal hydrological conditions in high latitude systems2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Climate, Earth surface processes and soil thermal hydrological conditions drive landscape development, ecosystem functioning and human activities in high latitude regions. These systems are at the focal point of concurrent global change studies as the ongoing shifts in climate regimes has already changed the dynamics of fragile and highly specialized environments across pan Arctic. This thesis aimed to 1) analyze and model extreme air temperatures, soil thermal and hydrological conditions, and the main Earth surface processes (ESP) (cryoturbation, solifluction, nivation and palsa mires) controlling the functioning of high latitude systems in current and future climate conditions; 2) identify the key environmental factors driving the spatial variation of the studied phenomena; and 3) develop methodology for producing novel high quality datasets. To accomplish these objectives, spatial analyses were conducted throughout geographical scales by utilizing multiple statistical modelling approaches, such as regression, machine learning techniques and ensemble forecasting. This thesis was based on unique datasets from the northern Fennoscandia; climate station records from Finland, Sweden and Norway, state of the art climate model simulations, fine scale field measurements collected in arctic alpine tundra and remotely sensed geospatial data. In paper I, accurate extreme air temperature maps were produced, which were notably improved after incorporating the influence of local factors such as topography and water bodies into the spatial models. In paper II, the results showed extreme variation in soil temperature and moisture over very short distances, while revealing the factors controlling the heterogeneity of ground thermal and hydrological conditions. Finally, the modelling outputs in papers III and IV provided new insights into the determination of geomorphic activity patterns across arctic alpine landscapes, while stressing the need for accurate climate data for predictive geomorphological distribution mapping. Importantly, Earth surface processes were found to be extremely climatic sensitivity, and drastic changes in geomorphic systems towards the end of 21st century can be expected. The increase of current temperature conditions by 2 ˚C was projected to cause a near complete loss of active ESPs in the high latitude study area. This thesis demonstrated the applicability of spatial modelling techniques as a useful framework in multiple key challenges of contemporary physical geography. Moreover, with the utilized model ensemble approach, the modelling uncertainty can be reduced while presenting the local trends in response variables more robustly. In future Earth system studies, it is essential to further assess the dynamics of arctic alpine landscapes under changing climatic conditions and identify potential tipping points of these sensitive systems.

  • 2. Aalto, Juha
    et al.
    le Roux, Peter C.
    Luoto, Miska
    The meso-scale drivers of temperature extremes in high-latitude Fennoscandia2014In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 42, no 1, p. 237-252Article in journal (Refereed)
    Abstract [en]

    Extreme temperatures are key drivers controlling both biotic and abiotic processes, and may be strongly modified by topography and land cover. We modelled mean and extreme temperatures in northern Fennoscandia by combining digital elevation and land cover data with climate observations from northern Finland, Norway and Sweden. Multivariate partitioning technique was utilized to investigate the relative importance of environmental variables for the variation of the three temperature parameters: mean annual absolute minima and maxima, and mean annual temperature. Generalized additive modeling showed good performance, explaining 84–95 % of the temperature variation. The inclusion of remotely sensed variables improved significantly the modelling of thermal extremes in this system. The water cover variables and topography were the most important drivers of minimum temperatures, whereas elevation was the most important factor controlling maximum temperatures. The spatial variability of mean temperatures was clearly driven by geographical location and the effects of topography. Partitioning technique gave novel insights into temperature-environment relationship at the meso-scale and thus proved to be useful tool for the study of the extreme temperatures in the high-latitude setting.

  • 3. Aartsen, M. G.
    et al.
    Abraham, K.
    Ackermann, M.
    Adams, J.
    Aguilar, J. A.
    Ahlers, M.
    Ahrens, M.
    Altmann, D.
    Andeen, K.
    Anderson, T.
    Ansseau, I.
    Anton, G.
    Archinger, M.
    Argueelles, C.
    Arlen, T. C.
    Auffenberg, J.
    Axani, S.
    Bai, X.
    Barwick, S. W.
    Baum, V.
    Bay, R.
    Beatty, J. J.
    Tjus, J. Becker
    Becker, K. -H
    BenZvi, S.
    Berghaus, P.
    Berley, D.
    Bernardini, E.
    Bernhard, A.
    Besson, D. Z.
    Binder, G.
    Bindig, D.
    Blaufuss, E.
    Blot, S.
    Boersma, D. J.
    Bohm, C.
    Boerner, M.
    Bos, F.
    Bose, D.
    Boeser, S.
    Botner, O.
    Braun, J.
    Brayeur, L.
    Bretz, H. -P
    Burgman, A.
    Casey, J.
    Casier, M.
    Cheung, E.
    Chirkin, D.
    Christov, A.
    Clark, K.
    Classen, L.
    Coenders, S.
    Collin, G. H.
    Conrad, J. M.
    Cowen, D. F.
    Silva, A. H. Cruz
    Daughhetee, J.
    Davis, J. C.
    Day, M.
    de Andre, J. P. A. M.
    De Clercq, C.
    Rosendo, E. del Pino
    Dembinski, H.
    De Ridder, S.
    Desiati, P.
    de Vries, K. D.
    de Wasseige, G.
    de With, M.
    DeYoung, T.
    Diaz-Velez, J. C.
    di Lorenzo, V.
    Dujmovic, H.
    Dumm, J. P.
    Dunkman, M.
    Eberhardt, B.
    Ehrhardt, T.
    Eichmann, B.
    Euler, S.
    Evenson, P. A.
    Fahey, S.
    Fazely, A. R.
    Feintzeig, J.
    Felde, J.
    Filimonov, K.
    Finley, C.
    Flis, S.
    Foesig, C. -C
    Fuchs, T.
    Gaisser, T. K.
    Gaior, R.
    Gallagher, J.
    Gerhardt, L.
    Ghorbani, K.
    Giang, W.
    Gladstone, L.
    Gluesenkamp, T.
    Goldschmidt, A.
    Golup, G.
    Gonzalez, J. G.
    Gora, D.
    Grant, D.
    Griffith, Z.
    Ismail, A. Haj
    Hallgren, A.
    Halzen, F.
    Hansen, E.
    Hanson, K.
    Hebecker, D.
    Heereman, D.
    Helbing, K.
    Hellauer, R.
    Hickford, S.
    Hignight, J.
    Hill, G. C.
    Hoffman, K. D.
    Hoffmann, R.
    Holzapfel, K.
    Homeier, A.
    Hoshina, K.
    Huang, F.
    Huber, M.
    Huelsnitz, W.
    Hultqvist, K.
    In, S.
    Ishihara, A.
    Jacobi, E.
    Japaridze, G. S.
    Jeong, M.
    Jero, K.
    Jones, B. J. P.
    Jurkovic, M.
    Kappes, A.
    Karg, T.
    Karle, A.
    Katz, U.
    Kauer, M.
    Keivani, A.
    Kelley, J. L.
    Kheirandish, A.
    Kim, M.
    Kintscher, T.
    Kiryluk, J.
    Kittler, T.
    Klein, S. R.
    Kohnen, G.
    Koirala, R.
    Kolanoski, H.
    Koepke, L.
    Kopper, C.
    Kopper, S.
    Koskinen, D. J.
    Kowalski, M.
    Krings, K.
    Kroll, M.
    Krueckl, G.
    Krueger, C.
    Kunnen, J.
    Kunwar, S.
    Kurahashi, N.
    Kuwabara, T.
    Labare, M.
    Lanfranchi, J. L.
    Larson, M. J.
    Lennarz, D.
    Lesiak-Bzdak, M.
    Leuermann, M.
    Lu, L.
    Luenemann, J.
    Madsen, J.
    Maggi, G.
    Mahn, K. B. M.
    Mancina, S.
    Mandelartz, M.
    Maruyama, R.
    Mase, K.
    Maunu, R.
    McNally, F.
    Meagher, K.
    Medici, M.
    Meier, M.
    Meli, A.
    Menne, T.
    Merino, G.
    Meures, T.
    Miarecki, S.
    Middell, E.
    Mohrmann, L.
    Montaruli, T.
    Moulai, M.
    Nahnhauer, R.
    Naumann, U.
    Neer, G.
    Niederhausen, H.
    Nowicki, S. C.
    Nygren, D. R.
    Pollmann, A. Obertacke
    Olivas, A.
    Omairat, A.
    O’Murchadha, A.
    Palczewski, T.
    Pandya, H.
    Pankova, D. V.
    Pepper, J. A.
    de los Heros, C. Perez
    Pfendner, C.
    Pieloth, D.
    Pinat, E.
    Posselt, J.
    Price, P. B.
    Przybylski, G. T.
    Quinnan, M.
    Raab, C.
    Rameez, M.
    Rawlins, K.
    Relich, M.
    Resconi, E.
    Rhode, W.
    Richman, M.
    Riedel, B.
    Robertson, S.
    Rott, C.
    Ruhe, T.
    Ryckbosch, D.
    Rysewyk, D.
    Sabbatini, L.
    Salvado, J.
    Herrera, S. E. Sanchez
    Sandrock, A.
    Sandroos, J.
    Sarkar, S.
    Satalecka, K.
    Schlunder, P.
    Schmidt, T.
    Schoeneberg, S.
    Schoenwald, A.
    Seckel, D.
    Seunarine, S.
    Soldin, D.
    Song, M.
    Spiczak, G. M.
    Spiering, C.
    Stamatikos, M.
    Stanev, T.
    Stasik, A.
    Steuer, A.
    Stezelberger, T.
    Stokstad, R. G.
    Stoessl, A.
    Stroem, R.
    Strotjohann, N. L.
    Sullivan, G. W.
    Sutherland, M.
    Taavola, H.
    Taboada, I.
    Tatar, J.
    Ter-Antonyan, S.
    Terliuk, A.
    Tesic, G.
    Tilav, S.
    Toale, P. A.
    Tobin, M. N.
    Toscano, S.
    Tosi, D.
    Tselengidou, M.
    Turcati, A.
    Unger, E.
    Usner, M.
    Vallecorsa, S.
    Vandenbroucke, J.
    van Eijndhoven, N.
    Vanheule, S.
    van Rossem, M.
    van Santen, J.
    Veenkamp, J.
    Voge, M.
    Vraeghe, M.
    Walck, C.
    Wallace, A.
    Wandkowsky, N.
    Weaver, Ch.
    Wendt, C.
    Westerhoff, S.
    Whelan, B. J.
    Wiebe, K.
    Wille, L.
    Williams, D. R.
    Wills, L.
    Wissing, H.
    Wolf, M.
    Wood, T. R.
    Woolsey, E.
    Woschnagg, K.
    Xu, D. L.
    Xu, X. W.
    Xu, Y.
    Yanez, J. P.
    Yodh, G.
    Yoshida, S.
    Zoll, M.
    Collaboration, IceCube
    Searches for Sterile Neutrinos with the IceCube Detector2016In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 117, no 7Article in journal (Refereed)
    Abstract [en]

    The IceCube neutrino telescope at the South Pole has measured the atmospheric muon neutrino spectrum as a function of zenith angle and energy in the approximate 320 GeV to 20 TeV range, to search for the oscillation signatures of light sterile neutrinos. No evidence for anomalous nu(mu) or (nu) over bar (mu) disappearance is observed in either of two independently developed analyses, each using one year of atmospheric neutrino data. New exclusion limits are placed on the parameter space of the 3 + 1 model, in which muon antineutrinos experience a strong Mikheyev-Smirnov-Wolfenstein-resonant oscillation. The exclusion limits extend to sin(2)2 theta(24) <= 0.02 at Delta m(2) similar to 0.3 eV(2) at the 90% confidence level. The allowed region from global analysis of appearance experiments, including LSND and MiniBooNE, is excluded at approximately the 99% confidence level for the global best-fit value of vertical bar U-e4 vertical bar(2).

  • 4. Aartsen, M. G.
    et al.
    Abraham, K.
    Ackermann, M.
    Adams, J.
    Aguilar, J. A.
    Ahlers, M.
    Ahrens, M.
    Altmann, D.
    Andeen, K.
    Anderson, T.
    Ansseau, I.
    Anton, G.
    Archinger, M.
    Arguelles, C.
    Arlen, T. C.
    Auffenberg, J.
    Axani, S.
    Bai, X.
    Barwick, S. W.
    Baum, V.
    Bay, R.
    Beatty, J. J.
    Tjus, J. Becker
    Becker, K. -H
    BenZvi, S.
    Berghaus, P.
    Berley, D.
    Bernardini, E.
    Bernhard, A.
    Besson, D. Z.
    Binder, G.
    Bindig, D.
    Bissok, M.
    Blaufuss, E.
    Blot, S.
    Boersma, D. J.
    Bohm, C.
    Boerner, M.
    Bos, F.
    Bose, D.
    Boeser, S.
    Botner, O.
    Braun, J.
    Brayeur, L.
    Bretz, H. -P
    Burgman, A.
    Casey, J.
    Casier, M.
    Cheung, E.
    Chirkin, D.
    Christov, A.
    Clark, K.
    Classen, L.
    Coenders, S.
    Collin, G. H.
    Conrad, J. M.
    Cowen, D. F.
    Silva, A. H. Cruz
    Daughhetee, J.
    Davis, J. C.
    Day, M.
    de Andre, J. P. A. M.
    De Clercq, C.
    Rosendo, E. del Pino
    Dembinski, H.
    De Ridder, S.
    Desiati, P.
    de Vries, K. D.
    de Wasseige, G.
    de With, M.
    DeYoung, T.
    Diaz-Velez, J. C.
    di Lorenzo, V.
    Dujmovic, H.
    Dumm, J. P.
    Dunkman, M.
    Eberhardt, B.
    Ehrhardt, T.
    Eichmann, B.
    Euler, S.
    Evenson, P. A.
    Fahey, S.
    Fazely, A. R.
    Feintzeig, J.
    Felde, J.
    Filimonov, K.
    Finley, C.
    Flis, S.
    Foesig, C. -C
    Franckowiak, A.
    Fuchs, T.
    Gaisser, T. K.
    Gaior, R.
    Gallagher, J.
    Gerhardt, L.
    Ghorbani, K.
    Giang, W.
    Gladstone, L.
    Glagla, M.
    Gluesenkamp, T.
    Goldschmidt, A.
    Golup, G.
    Gonzalez, J. G.
    Gora, D.
    Grant, D.
    Griffith, Z.
    Haack, C.
    Ismail, A. Haj
    Hallgren, A.
    Halzen, F.
    Hansen, E.
    Hansmann, B.
    Hansmann, T.
    Hanson, K.
    Hebecker, D.
    Heereman, D.
    Helbing, K.
    Hellauer, R.
    Hickford, S.
    Hignight, J.
    Hill, G. C.
    Hoffman, K. D.
    Hoffmann, R.
    Holzapfel, K.
    Homeier, A.
    Hoshina, K.
    Huang, F.
    Huber, M.
    Huelsnitz, W.
    Hultqvist, K.
    In, S.
    Ishihara, A.
    Jacobi, E.
    Japaridze, G. S.
    Jeong, M.
    Jero, K.
    Jones, B. J. P.
    Jurkovic, M.
    Kappes, A.
    Karg, T.
    Karle, A.
    Katz, U.
    Kauer, M.
    Keivani, A.
    Kelley, J. L.
    Kemp, J.
    Kheirandish, A.
    Kim, M.
    Kintscher, T.
    Kiryluk, J.
    Kittler, T.
    Klein, S. R.
    Kohnen, G.
    Koirala, R.
    Kolanoski, H.
    Konietz, R.
    Koepke, L.
    Kopper, C.
    Kopper, S.
    Koskinen, D. J.
    Kowalski, M.
    Krings, K.
    Kroll, M.
    Krueckl, G.
    Krueger, C.
    Kunnen, J.
    Kunwar, S.
    Kurahashi, N.
    Kuwabara, T.
    Labare, M.
    Lanfranchi, J. L.
    Larson, M. J.
    Lennarz, D.
    Lesiak-Bzdak, M.
    Leuermann, M.
    Leuner, J.
    Lu, L.
    Lunemann, J.
    Madsen, J.
    Maggi, G.
    Mahn, K. B. M.
    Mancina, S.
    Mandelartz, M.
    Maruyama, R.
    Mase, K.
    Maunu, R.
    McNally, F.
    Meagher, K.
    Medici, M.
    Meier, M.
    Meli, A.
    Menne, T.
    Merino, G.
    Meures, T.
    Miarecki, S.
    Middell, E.
    Mohrmann, L.
    Montaruli, T.
    Moulai, M.
    Nahnhauer, R.
    Naumann, U.
    Neer, G.
    Niederhausen, H.
    Nowicki, S. C.
    Nygren, D. R.
    Pollmann, A. Obertacke
    Olivas, A.
    Omairat, A.
    O’Murchadha, A.
    Palczewski, T.
    Pandya, H.
    Pankova, D. V.
    Penek, O.
    Pepper, J. A.
    de los Heros, C. Perez
    Pfendner, C.
    Pieloth, D.
    Pinat, E.
    Posselt, J.
    Price, P. B.
    Przybylski, G. T.
    Quinnan, M.
    Raab, C.
    Raedel, L.
    Rameez, M.
    Rawlins, K.
    Reimann, R.
    Relich, M.
    Resconi, E.
    Rhode, W.
    Richman, M.
    Riedel, B.
    Robertson, S.
    Rongen, M.
    Rott, C.
    Ruhe, T.
    Ryckbosch, D.
    Rysewyk, D.
    Sabbatini, L.
    Herrera, S. E. Sanchez
    Sandrock, A.
    Sandroos, J.
    Sarkar, S.
    Satalecka, K.
    Schimp, M.
    Schlunder, P.
    Schmidt, T.
    Schoenen, S.
    Schoeneberg, S.
    Schoenwald, A.
    Schumacher, L.
    Seckel, D.
    Seunarine, S.
    Soldin, D.
    Song, M.
    Spiczak, G. M.
    Spiering, C.
    Stahlberg, M.
    Stamatikos, M.
    Stanev, T.
    Stasik, A.
    Steuer, A.
    Stezelberger, T.
    Stokstad, R. G.
    Stoessl, A.
    Strom, R.
    Strotjohann, N. L.
    Sullivan, G. W.
    Sutherland, M.
    Taavola, H.
    Taboada, I.
    Tatar, J.
    Tenholt, F.
    Ter-Antonyan, S.
    Terliuk, A.
    Tesic, G.
    Tilav, S.
    Toale, P. A.
    Tobin, M. N.
    Toscano, S.
    Tosi, D.
    Tselengidou, M.
    Turcati, A.
    Unger, E.
    Usner, M.
    Vallecorsa, S.
    Vandenbroucke, J.
    van Eijndhoven, N.
    Vanheule, S.
    van Rossem, M.
    van Santen, J.
    Veenkamp, J.
    Vehring, M.
    Voge, M.
    Vraeghe, M.
    Walck, C.
    Wallace, A.
    Wallraff, M.
    Wandkowsky, N.
    Weaver, Ch.
    Wendt, C.
    Westerhoff, S.
    Whelan, B. J.
    Wickmann, S.
    Wiebe, K.
    Wiebusch, C. H.
    Wille, L.
    Williams, D. R.
    Wills, L.
    Wissing, H.
    Wolf, M.
    Wood, T. R.
    Woolsey, E.
    Woschnagg, K.
    Xu, D. L.
    Xu, X. W.
    Xu, Y.
    Yanez, J. P.
    Yodh, G.
    Yoshida, S.
    Zoll, M.
    All-flavour search for neutrinos from dark matter annihilations in the Milky Way with IceCube/DeepCore2016In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 76, no 10Article in journal (Refereed)
    Abstract [en]

    We present the first IceCube search for a signal of dark matter annihilations in the Milky Way using all-flavour neutrino-induced particle cascades. The analysis focuses on the DeepCore sub-detector of IceCube, and uses the surrounding IceCube strings as a veto region in order to select starting events in the DeepCore volume. We use 329 live-days of data from IceCube operating in its 86-string configuration during 2011-2012. No neutrino excess is found, the final result being compatible with the background-only hypothesis. From this null result, we derive upper limits on the velocity-averaged self-annihilation cross-section, , for dark matter candidate masses ranging from 30 GeV up to 10 TeV, assuming both a cuspy and a flat-cored dark matter halo profile. For dark matter masses between 200 GeV and 10 TeV, the results improve on all previous IceCube results on , reaching a level of 10 cm s, depending on the annihilation channel assumed, for a cusped NFW profile. The analysis demonstrates that all-flavour searches are competitive with muon channel searches despite the intrinsically worse angular resolution of cascades compared to muon tracks in IceCube.

  • 5. Aartsen, M. G.
    et al.
    Abraham, K.
    Ackermann, M.
    Adams, J.
    Aguilar, J. A.
    Ahlers, M.
    Ahrens, M.
    Altmann, D.
    Andeen, K.
    Anderson, T.
    Ansseau, I.
    Anton, G.
    Archinger, M.
    Arguelles, C.
    Auffenberg, J.
    Axani, S.
    Bai, X.
    Barwick, S. W.
    Baum, V.
    Bay, R.
    Beatty, J. J.
    Tjus, J. Becker
    Becker, K. -H
    BenZvi, S.
    Berghaus, P.
    Berley, D.
    Bernardini, E.
    Bernhard, A.
    Besson, D. Z.
    Binder, G.
    Bindig, D.
    Bissok, M.
    Blaufuss, E.
    Blot, S.
    Bohm, C.
    Boerner, M.
    Bos, F.
    Bose, D.
    Boeser, S.
    Botner, O.
    Braun, J.
    Brayeur, L.
    Bretz, H. -P
    Burgman, A.
    Carver, T.
    Casier, M.
    Cheung, E.
    Chirkin, D.
    Christov, A.
    Clark, K.
    Classen, L.
    Coenders, S.
    Collin, G. H.
    Conrad, J. M.
    Cowen, D. F.
    Cross, R.
    Day, M.
    de Andre, J. P. A. M.
    De Clercy, C.
    Rosendo, E. del Pino
    Dembinski, H.
    De Ridder, S.
    Desiati, P.
    de Vries, K. D.
    de Wasseige, G.
    de With, M.
    DeYoung, T.
    Diaz-Velez, J. C.
    di Lorenzo, V.
    Dujmovic, H.
    Dumm, J. P.
    Dunkman, M.
    Eberhardt, B.
    Ehrhardt, T.
    Eichmann, B.
    Eller, P.
    Euler, S.
    Evenson, P. A.
    Fahey, S.
    Fazely, A. R.
    Feintzeig, J.
    Felde, J.
    Filimonov, K.
    Finley, C.
    Flis, S.
    Foesig, C. -C
    Franckowiak, A.
    Friedman, E.
    Fuchs, T.
    Gaisser, T. K.
    Gallagher, J.
    Gerhardt, L.
    Ghorbani, K.
    Giang, W.
    Gladstone, L.
    Glagla, M.
    Gluesenkamp, T.
    Goldschmidt, A.
    Golup, G.
    Gonzalez, J. G.
    Grant, D.
    Griffith, Z.
    Haack, C.
    Ismail, A. Haj
    Hallgren, A.
    Halzen, F.
    Hansen, E.
    Hansmann, B.
    Hansmann, T.
    Hanson, K.
    Hebecker, D.
    Heereman, D.
    Helbing, K.
    Hellauer, R.
    Hickford, S.
    Hignight, J.
    Hill, G. C.
    Hoffman, K. D.
    Hoffmann, R.
    Holzapfel, K.
    Hoshina, K.
    Huang, F.
    Huber, M.
    Hultqvist, K.
    In, S.
    Ishihara, A.
    Jacobi, E.
    Japaridze, G. S.
    Jeong, M.
    Jero, K.
    Jones, B. J. P.
    Jurkovic, M.
    Kappes, A.
    Karg, T.
    Karle, A.
    Katz, U.
    Kauer, M.
    Keivani, A.
    Kelley, J. L.
    Kemp, J.
    Kheirandish, A.
    Kim, M.
    Kintscher, T.
    Kiryluk, J.
    Kittler, T.
    Klein, S. R.
    Kohnen, G.
    Koirala, R.
    Kolanoski, H.
    Konietz, R.
    Koepke, L.
    Kopper, C.
    Kopper, S.
    Koskinen, D. J.
    Kowalski, M.
    Krings, K.
    Kroll, M.
    Krueckl, G.
    Krueger, C.
    Kunnen, J.
    Kunwar, S.
    Kurahashi, N.
    Kuwabara, T.
    Labare, M.
    Lanfranchi, J. L.
    Larson, M. J.
    Lauber, F.
    Lennarz, D.
    Lesiak-Bzdak, M.
    Leuermann, M.
    Leuner, J.
    Lu, L.
    Lunemann, J.
    Madsen, J.
    Maggi, G.
    Mahn, K. B. M.
    Mancina, S.
    Mandelartz, M.
    Maruyama, R.
    Mase, K.
    Maunu, R.
    McNally, F.
    Meagher, K.
    Medici, M.
    Meier, M.
    Meli, A.
    Menne, T.
    Merino, G.
    Meures, T.
    Miarecki, S.
    Mohrmann, L.
    Montaruli, T.
    Moulai, M.
    Nahnhauer, R.
    Naumann, U.
    Neer, G.
    Niederhausen, H.
    Nowicki, S. C.
    Nygren, D. R.
    Pollmann, A. Obertacke
    Olivas, A.
    O’ Murchadha, A.
    Palczewski, T.
    Pandya, H.
    Pankova, D. V.
    Penek, O.
    Pepper, J. A.
    de los Heros, C. Perez
    Pieloth, D.
    Pinat, E.
    Price, P. B.
    Przybylski, G. T.
    Quinnan, M.
    Raab, C.
    Raedel, L.
    Rameez, M.
    Rawlins, K.
    Reimann, R.
    Relethford, B.
    Relich, M.
    Resconi, E.
    Rhode, W.
    Richman, M.
    Riedel, B.
    Robertson, S.
    Rongen, M.
    Rott, C.
    Ruhe, T.
    Ryckbosch, D.
    Rysewyk, D.
    Sabbatini, L.
    Herrera, S. E. Sanchez
    Sandrock, A.
    Sandroos, J.
    Sarkar, S.
    Satalecka, K.
    Schimp, M.
    Schlunder, P.
    Schmidt, T.
    Schoenen, S.
    Schoeneberg, S.
    Schumacher, L.
    Seckel, D.
    Seunarine, S.
    Soldin, D.
    Song, M.
    Spiczak, G. M.
    Spiering, C.
    Stahlberg, M.
    Stanev, T.
    Stasik, A.
    Steuer, A.
    Stezelberger, T.
    Stokstad, R. G.
    Stoessl, A.
    Stroem, R.
    Strotjohann, N. L.
    Sullivan, G. W.
    Sutherland, M.
    Taavola, H.
    Taboada, I.
    Tatar, J.
    Tenholt, F.
    Ter-Antonyan, S.
    Terliuk, A.
    Tesic, G.
    Tilav, S.
    Toale, P. A.
    Tobin, M. N.
    Toscano, S.
    Tosi, D.
    Tselengidou, M.
    Turcati, A.
    Unger, E.
    Usner, M.
    Vandenbroucke, J.
    van Eijndhoven, N.
    Vanheule, S.
    van Rossem, M.
    van Santen, J.
    Veenkamp, J.
    Vehring, M.
    Voge, M.
    Vraeghe, M.
    Walck, C.
    Wallace, A.
    Wallraff, M.
    Wandkowsky, N.
    Weaver, Ch.
    Weiss, M. J.
    Wendt, C.
    Westerhoff, S.
    Whelan, B. J.
    Wickmann, S.
    Wiebe, K.
    Wiebusch, C. H.
    Wille, L.
    Williams, D. R.
    Wills, L.
    Wolf, M.
    Wood, T. R.
    Woolsey, E.
    Woschnagg, K.
    Xu, D. L.
    Xu, X. W.
    Xu, Y.
    Yanez, J. P.
    Yodh, G.
    Yoshida, S.
    Zoll, M.
    Collaboration, IceCube
    Constraints on Ultrahigh-Energy Cosmic-Ray Sources from a Search for Neutrinos above 10 PeV with IceCube2016In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 117, no 24Article in journal (Refereed)
    Abstract [en]

    We report constraints on the sources of ultrahigh-energy cosmic rays (UHECRs) above 10(9) GeV, based on an analysis of seven years of IceCube data. This analysis efficiently selects very high-energy neutrino-induced events which have deposited energies from 5 x 10(5) GeV to above 10(11) GeV. Two neutrino-induced events with an estimated deposited energy of (2.6 +/- 0.3) x 10(6) GeV, the highest neutrino energy observed so far, and (7.7 +/- 2.0) x 10(5) GeV were detected. The atmospheric background-only hypothesis of detecting these events is rejected at 3.6 sigma. The hypothesis that the observed events are of cosmogenic origin is also rejected at > 99% CL because of the limited deposited energy and the nonobservation of events at higher energy, while their observation is consistent with an astrophysical origin. Our limits on cosmogenic neutrino fluxes disfavor the UHECR sources having a cosmological evolution stronger than the star formation rate, e.g., active galactic nuclei and gamma-ray bursts, assuming proton-dominated UHECRs. Constraints on UHECR sources including mixed and heavy UHECR compositions are obtained for models of neutrino production within UHECR sources. Our limit disfavors a significant part of parameter space for active galactic nuclei and new-born pulsar models. These limits on the ultrahigh-energy neutrino flux models are the most stringent to date.

  • 6. Aartsen, M. G.
    et al.
    Abraham, K.
    Ackermann, M.
    Adams, J.
    Aguilar, J. A.
    Ahlers, M.
    Ahrens, M.
    Altmann, D.
    Anderson, T.
    Ansseau, I.
    Anton, G.
    Archinger, M.
    Arguelles, C.
    Arlen, T. C.
    Auffenberg, J.
    Bai, X.
    Barwick, S. W.
    Baum, V.
    Bay, R.
    Beatty, J. J.
    Tjus, J. Becker
    Becker, K. -H
    Beiser, E.
    BenZvi, S.
    Berghaus, P.
    Berley, D.
    Bernardini, E.
    Bernhard, A.
    Besson, D. Z.
    Binder, G.
    Bindig, D.
    Bissok, M.
    Blaufuss, E.
    Blumenthal, J.
    Boersma, D. J.
    Bohm, C.
    Boerner, M.
    Bos, F.
    Bose, D.
    Boeser, S.
    Botner, O.
    Braun, J.
    Brayeur, L.
    Bretz, H. -P
    Buzinsky, N.
    Casey, J.
    Casier, M.
    Cheung, E.
    Chirkin, D.
    Christov, A.
    Clark, K.
    Classen, L.
    Coenders, S.
    Collin, G. H.
    Conrad, J. M.
    Cowen, D. F.
    Silva, A. H. Cruz
    Daughhetee, J.
    Davis, J. C.
    Day, M.
    de Andre, J. P. A. M.
    De Clercq, C.
    Rosendo, E. del Pino
    Dembinski, H.
    De Ridder, S.
    Desiati, P.
    de Vries, K. D.
    de Wasseige, G.
    de With, M.
    DeYoung, T.
    Diaz-Velez, J. C.
    di Lorenzo, V.
    Dujmovic, H.
    Dumm, J. P.
    Dunkman, M.
    Eberhardt, B.
    Ehrhardt, T.
    Eichmann, B.
    Euler, S.
    Evenson, P. A.
    Fahey, S.
    Fazely, A. R.
    Feintzeig, J.
    Felde, J.
    Filimonov, K.
    Finley, C.
    Flis, S.
    Foesig, C. -C
    Fuchs, T.
    Gaisser, T. K.
    Gaior, R.
    Gallagher, J.
    Gerhardt, L.
    Ghorbani, K.
    Gier, D.
    Gladstone, L.
    Glagla, M.
    Gluesenkamp, T.
    Goldschmidt, A.
    Golup, G.
    Gonzalez, J. G.
    Gora, D.
    Grant, D.
    Griffith, Z.
    Ha, C.
    Haack, C.
    Ismail, A. Haj
    Hallgren, A.
    Halzen, F.
    Hansen, E.
    Hansmann, B.
    Hansmann, T.
    Hanson, K.
    Hebecker, D.
    Heereman, D.
    Helbing, K.
    Hellauer, R.
    Hickford, S.
    Hignight, J.
    Hill, G. C.
    Hoffman, K. D.
    Hoffmann, R.
    Holzapfel, K.
    Homeier, A.
    Hoshina, K.
    Huang, F.
    Huber, M.
    Huelsnitz, W.
    Hulth, P. O.
    Hultqvist, K.
    In, S.
    Ishihara, A.
    Jacobi, E.
    Japaridze, G. S.
    Jeong, M.
    Jero, K.
    Jones, B. J. P.
    Jurkovic, M.
    Kappes, A.
    Karg, T.
    Karle, A.
    Katz, U.
    Kauer, M.
    Keivani, A.
    Kelley, J. L.
    Kemp, J.
    Kheirandish, A.
    Kim, M.
    Kintscher, T.
    Kiryluk, J.
    Klein, S. R.
    Kohnen, G.
    Koirala, R.
    Kolanoski, H.
    Konietz, R.
    Koepke, L.
    Kopper, C.
    Kopper, S.
    Koskinen, D. J.
    Kowalski, M.
    Krings, K.
    Kroll, G.
    Kroll, M.
    Krueckl, G.
    Kunnen, J.
    Kunwar, S.
    Kurahashi, N.
    Kuwabara, T.
    Labare, M.
    Lanfranchi, J. L.
    Larson, M. J.
    Lennarz, D.
    Lesiak-Bzdak, M.
    Leuermann, M.
    Leuner, J.
    Lu, L.
    Luenemann, J.
    Madsen, J.
    Maggi, G.
    Mahn, K. B. M.
    Mandelartz, M.
    Maruyama, R.
    Mase, K.
    Matis, H. S.
    Maunu, R.
    McNally, F.
    Meagher, K.
    Medici, M.
    Meier, M.
    Meli, A.
    Menne, T.
    Merino, G.
    Meures, T.
    Miarecki, S.
    Middell, E.
    Mohrmann, L.
    Montaruli, T.
    Morse, R.
    Nahnhauer, R.
    Naumann, U.
    Neer, G.
    Niederhausen, H.
    Nowicki, S. C.
    Nygren, D. R.
    Pollmann, A. Obertacke
    Olivas, A.
    Omairat, A.
    O’Murchadha, A.
    Palczewski, T.
    Pandya, H.
    Pankova, D. V.
    Paul, L.
    Pepper, J. A.
    Heros, C. Perez de los
    Pfendner, C.
    Pieloth, D.
    Pinat, E.
    Posselt, J.
    Price, P. B.
    Przybylski, G. T.
    Quinnan, M.
    Raab, C.
    Raedel, L.
    Rameez, M.
    Rawlins, K.
    Reimann, R.
    Relich, M.
    Resconi, E.
    Rhode, W.
    Richman, M.
    Richter, S.
    Riedel, B.
    Robertson, S.
    Rongen, M.
    Rott, C.
    Ruhe, T.
    Ryckbosch, D.
    Sabbatini, L.
    Sander, H. -G
    Sandrock, A.
    Sandroos, J.
    Sarkar, S.
    Schatto, K.
    Schimp, M.
    Schlunder, P.
    Schmidt, T.
    Schoenen, S.
    Schoeneberg, S.
    Schoenwald, A.
    Schumacher, L.
    Seckel, D.
    Seunarine, S.
    Soldin, D.
    Song, M.
    Spiczak, G. M.
    Spiering, C.
    Stahlberg, M.
    Stamatikos, M.
    Stanev, T.
    Stasik, A.
    Steuer, A.
    Stezelberger, T.
    Stokstad, R. G.
    Stoessl, A.
    Stroem, R.
    Strotjohann, N. L.
    Sullivan, G. W.
    Sutherland, M.
    Taavola, H.
    Taboada, I.
    Tatar, J.
    Ter-Antonyan, S.
    Terliuk, A.
    Tesic, G.
    Tilav, S.
    Toale, P. A.
    Tobin, M. N.
    Toscano, S.
    Tosi, D.
    Tselengidou, M.
    Turcati, A.
    Unger, E.
    Usner, M.
    Vallecorsa, S.
    Vandenbroucke, J.
    van Eijndhoven, N.
    Vanheule, S.
    van Santen, J.
    Veenkamp, J.
    Vehring, M.
    Voge, M.
    Vraeghe, M.
    Walck, C.
    Wallace, A.
    Wallraff, M.
    Wandkowsky, N.
    Weaver, Ch.
    Wendt, C.
    Westerhoff, S.
    Whelan, B. J.
    Wiebe, K.
    Wiebusch, C. H.
    Wille, L.
    Williams, D. R.
    Wills, L.
    Wissing, H.
    Wolf, M.
    Wood, T. R.
    Woschnagg, K.
    Xu, D. L.
    Xu, X. W.
    Xu, Y.
    Yanez, J. P.
    Yodh, G.
    Yoshida, S.
    Zoll, M.
    Collaboration, IceCube
    ANISOTROPY IN COSMIC-RAY ARRIVAL DIRECTIONS IN THE SOUTHERN HEMISPHERE BASED ON SIX YEARS OF DATA FROM THE ICECUBE DETECTOR2016In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 826, no 2Article in journal (Refereed)
    Abstract [en]

    The IceCube Neutrino Observatory accumulated a total of 318 billion cosmic-ray-induced muon events between 2009 May and 2015 May. This data set was used for a detailed analysis of the sidereal anisotropy in the arrival directions of cosmic rays in the TeV to PeV energy range. The observed global sidereal anisotropy features large regions of relative excess and deficit, with amplitudes of the order of 10(-3) up to about 100 TeV. A decomposition of the arrival direction distribution into spherical harmonics shows that most of the power is contained in the low-multipole (l <= 4) moments. However, higher multipole components are found to be statistically significant down to an angular scale of less than 10 degrees, approaching the angular resolution of the detector. Above 100 TeV, a change in the morphology of the arrival direction distribution is observed, and the anisotropy is characterized by a wide relative deficit whose amplitude increases with primary energy up to at least 5 PeV, the highest energies currently accessible to IceCube. No time dependence of the large-and small-scale structures is observed in the period of six years covered by this analysis. The high-statistics data set reveals more details of the properties of the anisotropy and is potentially able to shed light on the various physical processes that are responsible for the complex angular structure and energy evolution.

  • 7. Aartsen, M. G.
    et al.
    Abraham, K.
    Ackermann, M.
    Adams, J.
    Aguilar, J. A.
    Ahlers, M.
    Ahrens, M.
    Altmann, D.
    Anderson, T.
    Ansseau, I.
    Archinger, M.
    Arguelles, C.
    Arlen, T. C.
    Auffenberg, J.
    Bai, X.
    Barwick, S. W.
    Baum, V.
    Bay, R.
    Beatty, J. J.
    Tjus, J. Becker
    Becker, K. -H
    Beiser, E.
    BenZvi, S.
    Berghaus, P.
    Berley, D.
    Bernardini, E.
    Bernhard, A.
    Besson, D. Z.
    Binder, G.
    Bindig, D.
    Bissok, M.
    Blaufuss, E.
    Blumenthal, J.
    Boersma, D. J.
    Bohm, C.
    Boerner, M.
    Bos, F.
    Bose, D.
    Boeser, S.
    Botner, O.
    Braun, J.
    Brayeur, L.
    Bretz, H. -P
    Buzinsky, N.
    Casey, J.
    Casier, M.
    Cheung, E.
    Chirkin, D.
    Christov, A.
    Clark, K.
    Classen, L.
    Coenders, S.
    Cowen, D. F.
    Silva, A. H. Cruz
    Daughhetee, J.
    Davis, J. C.
    Day, M.
    de Andre, J. P. A. M.
    De Clercq, C.
    Rosendo, E. del Pino
    Dembinski, H.
    De Ridder, S.
    Desiati, P.
    de Vries, K. D.
    de Wasseige, G.
    de With, M.
    De Young, T.
    Diaz-Velez, J. C.
    di Lorenzo, V.
    Dumm, J. P.
    Dunkman, M.
    Eagan, R.
    Eberhardt, B.
    Ehrhardt, T.
    Eichmann, B.
    Euler, S.
    Evenson, P. A.
    Fadiran, O.
    Fahey, S.
    Fazely, A. R.
    Fedynitch, A.
    Feintzeig, J.
    Felde, J.
    Filimonov, K.
    Finley, C.
    Fischer-Wasels, T.
    Flis, S.
    Foesig, C. -C
    Fuchs, T.
    Gaisser, T. K.
    Gaior, R.
    Gallagher, J.
    Gerhardt, L.
    Ghorbani, K.
    Gier, D.
    Gladstone, L.
    Glagla, M.
    Gluesenkamp, T.
    Goldschmidt, A.
    Golup, G.
    Gonzalez, J. G.
    Gora, D.
    Grant, D.
    Groh, J. C.
    Gross, A.
    Ha, C.
    Haack, C.
    Ismail, A. Haj
    Hallgren, A.
    Halzen, F.
    Hansen, E.
    Hansmann, B.
    Hanson, K.
    Hebecker, D.
    Heereman, D.
    Helbing, K.
    Hellauer, R.
    Hickford, S.
    Hignight, J.
    Hill, G. C.
    Hoffman, K. D.
    Hoffmann, R.
    Holzapfel, K.
    Homeier, A.
    Hoshina, K.
    Huang, F.
    Huber, M.
    Huelsnitz, W.
    Hulth, P. O.
    Hultqvist, K.
    In, S.
    Ishihara, A.
    Jacobi, E.
    Japaridze, G. S.
    Jero, K.
    Jurkovic, M.
    Kappes, A.
    Karg, T.
    Karle, A.
    Kauer, M.
    Keivani, A.
    Kelley, J. L.
    Kemp, J.
    Kheirandish, A.
    Kiryluk, J.
    Klaes, J.
    Klein, S. R.
    Kohnen, G.
    Koirala, R.
    Kolanoski, H.
    Konietz, R.
    Koepke, L.
    Kopper, C.
    Kopper, S.
    Koskinen, D. J.
    Kowalski, M.
    Krings, K.
    Kroll, G.
    Kroll, M.
    Kunnen, J.
    Kurahashi, N.
    Kuwabara, T.
    Labare, M.
    Lanfranchi, J. L.
    Larson, M. J.
    Lesiak-Bzdak, M.
    Leuermann, M.
    Leuner, J.
    Lu, L.
    Luenemann, J.
    Madsen, J.
    Maggi, G.
    Mahn, K. B. M.
    Maruyama, R.
    Mase, K.
    Matis, H. S.
    Maunu, R.
    McNally, F.
    Meagher, K.
    Medici, M.
    Meli, A.
    Menne, T.
    Merino, G.
    Meures, T.
    Miarecki, S.
    Middell, E.
    Middlemas, E.
    Mohrmann, L.
    Montaruli, T.
    Morse, R.
    Nahnhauer, R.
    Naumann, U.
    Neer, G.
    Niederhausen, H.
    Nowicki, S. C.
    Nygren, D. R.
    Obertacke, A.
    Olivas, A.
    Omairat, A.
    O'Murchadha, A.
    Palczewski, T.
    Pandya, H.
    Pankova, D. V.
    Paul, L.
    Heros, C. Perez de Los
    Pfendner, C.
    Pieloth, D.
    Pinat, E.
    Posselt, J.
    Price, P. B.
    Przybylski, G. T.
    Puetz, J.
    Quinnan, M.
    Raab, C.
    Raedel, L.
    Rameez, M.
    Rawlins, K.
    Reimann, R.
    Relich, M.
    Resconi, E.
    Rhode, W.
    Richman, M.
    Richter, S.
    Riedel, B.
    Robertson, S.
    Rongen, M.
    Rott, C.
    Ruhe, T.
    Ryckbosch, D.
    Saba, S. M.
    Sabbatini, L.
    Sander, H. -G
    Sandrock, A.
    Sandroos, J.
    Sarkar, S.
    Schatto, K.
    Scheriau, F.
    Schimp, M.
    Schmidt, T.
    Schmitz, M.
    Schoenen, S.
    Schoeneberg, S.
    Schoenwald, A.
    Schulte, L.
    Seckel, D.
    Seunarine, S.
    Smith, M. W. E.
    Soldin, D.
    Song, M.
    Spiczak, G. M.
    Spiering, C.
    Stahlberg, M.
    Stamatikos, M.
    Stanev, T.
    Stanisha, N. A.
    Stasik, A.
    Stezelberger, T.
    Stokstad, R. G.
    Stoessl, A.
    Stroem, R.
    Strotjohann, N. L.
    Sullivan, G. W.
    Sutherland, M.
    Taavola, H.
    Taboada, I.
    Tatar, J.
    Ter-Antonyan, S.
    Terliuk, A.
    Tesic, G.
    Tilav, S.
    Toale, P. A.
    Tobin, M. N.
    Toscano, S.
    Tosi, D.
    Tselengidou, M.
    Turcati, A.
    Unger, E.
    Usner, M.
    Vallecorsa, S.
    Vandenbroucke, J.
    van Eijndhoven, N.
    Vanheule, S.
    van Santen, J.
    Veenkamp, J.
    Vehring, M.
    Voge, M.
    Vraeghe, M.
    Walck, C.
    Wallace, A.
    Wallraff, M.
    Wandkowsky, N.
    Weaver, Ch.
    Wendt, C.
    Westerhoff, S.
    Whelan, B. J.
    Whitehorn, N.
    Wiebe, K.
    Wiebusch, C. H.
    Wille, L.
    Williams, D. R.
    Wissing, H.
    Wolf, M.
    Wood, T. R.
    Woschnagg, K.
    Xu, D. L.
    Xu, X. W.
    Xu, Y.
    Yanez, J. P.
    Yodh, G.
    Yoshida, S.
    Zoll, M.
    Search for astrophysical tau neutrinos in three years of IceCube data2016In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 93, no 2Article in journal (Refereed)
    Abstract [en]

    The IceCube Neutrino Observatory has observed a diffuse flux of TeV-PeVastrophysical neutrinos at 5.7 sigma significance from an all-flavor search. The direct detection of tau neutrinos in this flux has yet to occur. Tau neutrinos become distinguishable from other flavors in IceCube at energies above a few hundred TeV, when the cascade from the tau neutrino charged current interaction becomes resolvable from the cascade from the tau lepton decay. This paper presents results from the first dedicated search for tau neutrinos with energies between 214 TeV and 72 PeV in the full IceCube detector. The analysis searches for IceCube optical sensors that observe two separate pulses in a single event-one from the tau neutrino interaction and a second from the tau decay. No candidate events were observed in three years of IceCube data. For the first time, a differential upper limit on astrophysical tau neutrinos is derived around the PeV energy region, which is nearly 3 orders of magnitude lower in energy than previous limits from dedicated tau neutrino searches.

  • 8. Aartsen, M. G.
    et al.
    Ackermann, M.
    Adams, J.
    Aguilar, J. A.
    Ahlers, M.
    Ahrens, M.
    Al Samarai, I.
    Altmann, D.
    Andeen, K.
    Anderson, T.
    Ansseau, I.
    Anton, G.
    Archinger, M.
    Argelles, C.
    Auffenberg, J.
    Axani, S.
    Bai, X.
    Barwick, S. W.
    Baum, V.
    Bay, R.
    Beatty, J. J.
    Tjus, J. Becker
    Becker, K. -H
    BenZvi, S.
    Berley, D.
    Bernardini, E.
    Besson, D. Z.
    Binder, G.
    Bindig, D.
    Blaufuss, E.
    Blot, S.
    Bohm, C.
    Boerner, M.
    Bos, F.
    Bose, D.
    Boeser, S.
    Botner, O.
    Braun, J.
    Brayeur, L.
    Bretz, H. -P
    Bron, S.
    Burgman, A.
    Carver, T.
    Casier, M.
    Cheung, E.
    Chirkin, D.
    Christov, A.
    Clark, K.
    Classen, L.
    Coenders, S.
    Collin, G. H.
    Conrad, J. M.
    Cowen, F.
    Cross, R.
    Day, M.
    de Andre, J. P. A. M.
    De Clercq, C.
    Rosendo, E. del Pino
    Dembinski, H.
    De Ridder, S.
    Desiati, P.
    de Vries, K. D.
    de Wasseige, G.
    de With, M.
    DeYoung, T.
    Diaz-Velez, J. C.
    di Lorenzo, V.
    Dujmovic, H.
    Dumm, J. P.
    Dunkman, M.
    Eberhardt, B.
    Ehrhardt, T.
    Eichmann, B.
    Eller, P.
    Euler, S.
    Evenson, A.
    Fahey, S.
    Fazely, A. R.
    Feintzeig, J.
    Felde, J.
    Filimonov, K.
    Finley, C.
    Flis, S.
    Foesig, C. -C
    Franckowiak, A.
    Friedman, E.
    Fuchs, T.
    Gaisser, T. K.
    Gallagher, J.
    Gerhardt, L.
    Ghorbani, K.
    Giang, W.
    Gladstone, L.
    Glauch, T.
    Gluesenkamp, T.
    Goldschmidt, A.
    Gonzalez, J. G.
    Grant, D.
    Griffith, Z.
    Haack, C.
    Hallgren, A.
    Halzen, F.
    Hansen, E.
    Hansmann, T.
    Hanson, K.
    Hebecker, D.
    Heereman, D.
    Helbing, K.
    Hellauer, R.
    Hickford, S.
    Hignight, J.
    Hill, G. C.
    Hoffman, K. D.
    Hoffmann, R.
    Hoshina, K.
    Huang, F.
    Huber, M.
    Hultqvist, K.
    In, S.
    Ishihara, A.
    Jacobi, E.
    Japaridze, G. S.
    Jeong, M.
    Jero, K.
    Jones, B. J. P.
    Kang, W.
    Kappes, A.
    Karg, T.
    Karle, A.
    Katz, U.
    Kauer, M.
    Keivani, A.
    Kelley, J. L.
    Kheirandish, A.
    Kim, J.
    Kim, M.
    Kintscher, T.
    Kiryluk, J.
    Kittler, T.
    Klein, S. R.
    Kohnen, G.
    Koirala, R.
    Kolanoski, H.
    Konietz, R.
    Koepke, L.
    Kopper, C.
    Kopper, S.
    Koskinen, D. J.
    Kowalski, M.
    Krings, K.
    Kroll, M.
    Krueckl, G.
    Krueger, C.
    Kunnen, J.
    Kunwar, S.
    Kurahashi, N.
    Kuwabara, T.
    Kyriacou, A.
    Labare, M.
    Lanfranchi, J. L.
    Larson, M. J.
    Lauber, F.
    Lennarz, D.
    Lesiak-Bzdak, M.
    Leuermann, M.
    Lu, L.
    Lunemann, J.
    Madsen, J.
    Maggi, G.
    Mahn, K. B. M.
    Mancina, S.
    Mandelartz, M.
    Maruyama, R.
    Mase, K.
    Maunu, R.
    McNally, F.
    Meagher, K.
    Medici, M.
    Meier, M.
    Menne, T.
    Merino, G.
    Meures, T.
    Miarecki, S.
    Micallef, J.
    Momente, G.
    Montaruli, T.
    Moulai, M.
    Nahnhauer, R.
    Naumann, U.
    Neer, G.
    Niederhausen, H.
    Nowicki, S. C.
    Nygren, D. R.
    Pollmann, A. Obertacke
    Olivas, A.
    O’Murchadha, A.
    Palczewski, T.
    Pandya, H.
    Pankova, D. V.
    Peiffer, P.
    Penek, Oe.
    Pepper, J. A.
    Heros, C. Perez de los
    Pieloth, D.
    Pinat, E.
    Price, P. B.
    Przybylski, G. T.
    Quinnan, M.
    Raab, C.
    Raedel, L.
    Rameez, M.
    Rawlins, K.
    Reimann, R.
    Relethford, B.
    Relich, M.
    Resconi, E.
    Rhode, W.
    Richman, M.
    Riedel, B.
    Robertson, S.
    Rongen, M.
    Rott, C.
    Ruhe, T.
    Ryckbosch, D.
    Rysewyk, D.
    Sabbatini, L.
    Herrera, S. E. Sanchez
    Sandrock, A.
    Sandroos, J.
    Sarkar, S.
    Satalecka, K.
    Schlunder, P.
    Schmidt, T.
    Schoenen, S.
    Schoeneberg, S.
    Schumacher, L.
    Seckel, D.
    Seunarine, S.
    Soldin, D.
    Song, M.
    Spiczak, G. M.
    Spiering, C.
    Stachurska, J.
    Stanev, T.
    Stasik, A.
    Stettner, J.
    Steuer, A.
    Stezelberger, T.
    Stokstad, R. G.
    Stossl, A.
    Stroem, R.
    Strotjohann, N. L.
    Sullivan, G. W.
    Sutherland, M.
    Taavola, H.
    Taboada, I.
    Tatar, J.
    Tenholt, F.
    Ter-Antonyan, S.
    Terliuk, A.
    Tesic, G.
    Tilav, S.
    Toale, P. A.
    Tobin, M. N.
    Toscano, S.
    Tosi, D.
    Tselengidou, M.
    Tung, C. F.
    Turcati, A.
    Unger, E.
    Usner, M.
    Vandenbroucke, J.
    van Eijndhoven, N.
    Vanheule, S.
    van Rossem, M.
    van Santen, J.
    Vehring, M.
    Voge, M.
    Vogel, E.
    Vraeghe, M.
    Walck, C.
    Wallace, A.
    Wallraff, M.
    Wandkowsky, N.
    Waza, A.
    Weaver, Ch.
    Weiss, M. J.
    Wendt, C.
    Westerhoff, S.
    Whelan, B. J.
    Wickmann, S.
    Wiebe, K.
    Wiebusch, C. H.
    Wille, L.
    Williams, D. R.
    Wills, L.
    Wolf, M.
    Wood, T. R.
    Woolsey, E.
    Woschnagg, K.
    Xu, D. L.
    Xu, X. W.
    Xu, Y.
    Yanez, J. P.
    Yodh, G.
    Yoshida, S.
    Zoll, M.
    Collaboration, IceCube
    Search for sterile neutrino mixing using three years of IceCube DeepCore data2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 95, no 11Article in journal (Refereed)
    Abstract [en]

    We present a search for a light sterile neutrino using three years of atmospheric neutrino data from the DeepCore detector in the energy range of approximately 10-60 GeV. DeepCore is the low-energy subarray of the IceCube Neutrino Observatory. The standard three-neutrino paradigm can be probed by adding an additional light (Delta m(41)(2) similar to 1 eV(2)) sterile neutrino. Sterile neutrinos do not interact through the standard weak interaction and, therefore, cannot be directly detected. However, their mixing with the three active neutrino states leaves an imprint on the standard atmospheric neutrino oscillations for energies below 100 GeV. A search for such mixing via muon neutrino disappearance is presented here. The data are found to be consistent with the standard three-neutrino hypothesis. Therefore, we derive limits on the mixing matrix elements at the level of vertical bar U mu(4)vertical bar(2) < 0.11 and vertical bar U-tau 4 vertical bar(2) < 0.15 (90% C. L.) for the sterile neutrino mass splitting Delta m(41)(2) = 1.0 eV(2).

  • 9. Abbatt, J. P. D.
    et al.
    Thomas, J. L.
    Abrahamsson, K.
    Boxe, C.
    Granfors, A.
    Jones, A. E.
    King, M. D.
    Saiz-Lopez, A.
    Shepson, P. B.
    Sodeau, J.
    Toohey, D. W.
    Toubin, C.
    von Glasow, R.
    Wren, S. N.
    Yang, X.
    Halogen activation via interactions with environmental ice and snow in the polar lower troposphere and other regions2012In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, no 14, p. 6237-6271Article in journal (Refereed)
    Abstract [en]

    The role of ice in the formation of chemically active halogens in the environment requires a full understanding because of its role in atmospheric chemistry, including controlling the regional atmospheric oxidizing capacity in specific situations. In particular, ice and snow are important for facilitating multiphase oxidative chemistry and as media upon which marine algae live. This paper reviews the nature of environmental ice substrates that participate in halogen chemistry, describes the reactions that occur on such substrates, presents the field evidence for ice-mediated halogen activation, summarizes our best understanding of ice-halogen activation mechanisms, and describes the current state of modeling these processes at different scales. Given the rapid pace of developments in the field, this paper largely addresses advances made in the past five years, with emphasis given to the polar boundary layer. The integrative nature of this field is highlighted in the presentation of work from the molecular to the regional scale, with a focus on understanding fundamental processes. This is essential for developing realistic parameterizations and descriptions of these processes for inclusion in larger scale models that are used to determine their regional and global impacts.

  • 10. Aben, Ralf C. H.
    et al.
    Barros, Nathan
    van Donk, Ellen
    Frenken, Thijs
    Hilt, Sabine
    Kazanjian, Garabet
    Lamers, Leon P. M.
    Peeters, Edwin T. H. M.
    Roelofs, Jan G. M.
    de Senerpont Domis, Lisette N.
    Stephan, Susanne
    Velthuis, Mandy
    Van de Waal, Dedmer B.
    Wik, Martin
    Thornton, Brett F.
    Wilkinson, Jeremy
    DelSontro, Tonya
    Kosten, Sarian
    Cross continental increase in methane ebullition under climate change2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, no 1Article in journal (Refereed)
    Abstract [en]

    Methane (CH4) strongly contributes to observed global warming. As natural CH4 emissions mainly originate from wet ecosystems, it is important to unravel how climate change may affect these emissions. This is especially true for ebullition (bubble flux from sediments), a pathway that has long been underestimated but generally dominates emissions. Here we show a remarkably strong relationship between CH4 ebullition and temperature across a wide range of freshwater ecosystems on different continents using multi-seasonal CH4 ebullition data from the literature. As these temperature–ebullition relationships may have been affected by seasonal variation in organic matter availability, we also conducted a controlled year-round mesocosm experiment. Here 4 °C warming led to 51% higher total annual CH4 ebullition, while diffusion was not affected. Our combined findings suggest that global warming will strongly enhance freshwater CH4 emissions through a disproportional increase in ebullition (6–20% per 1 °C increase), contributing to global warming.

  • 11. Achtert, P.
    et al.
    Brooks, I. M.
    Brooks, B. J.
    Moat, B. I.
    Prytherch, J.
    Persson, P. O. G.
    Tjernstrom, M.
    Measurement of wind profiles by motion-stabilised ship-borne Doppler lidar2015In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 8, no 11, p. 4993-5007Article in journal (Refereed)
    Abstract [en]

    Three months of Doppler lidar wind measurements were obtained during the Arctic Cloud Summer Experiment on the icebreaker Oden during the summer of 2014. Such ship-borne Doppler measurements require active stabilisation to remove the effects of ship motion. We demonstrate that the combination of a commercial Doppler lidar with a custom-made motion-stabilisation platform enables the retrieval of wind profiles in the Arctic atmospheric boundary layer during both cruising and ice-breaking with statistical uncertainties comparable to land-based measurements. This held true particularly within the atmospheric boundary layer even though the overall aerosol load was very low. Motion stabilisation was successful for high wind speeds in open water and the resulting wave conditions. It allows for the retrieval of vertical winds with a random error below 0.2 ms(-1). The comparison of lidar-measured wind and radio soundings gives a mean bias of 0.3 ms(-1) (2 degrees) and a mean standard deviation of 1.1 ms(-1) (12 degrees) for wind speed (wind direction). The agreement for wind direction degrades with height. The combination of a motion-stabilised platform with a low-maintenance autonomous Doppler lidar has the potential to enable continuous long-term high-resolution ship-based wind profile measurements over the oceans.

  • 12. Acosta Hospitaleche, Carolina
    et al.
    Hagström, Jonas
    Reguero, Marcelo
    Mörs, Thomas
    Historical perspective of Otto Nordenskjöld's Antarctic penguin fossil collection and Carl Wiman's contribution2017In: Polar Record, ISSN 0032-2474, E-ISSN 1475-3057Article in journal (Refereed)
    Abstract [en]

    The early explorer and scientist Otto Nordenskjöld, leader of the Swedish South Polar Expedition of 1901–1903, was the first to collect Antarctic penguin fossils. The site is situated in the northeastern region of Seymour Island and constitutes one of the most important localities in the study of fossilised penguins. The task of describing these specimens together with fossilised whale remains was given to Professor Carl Wiman (1867–1944) at Uppsala University, Sweden. Although the paradigm for the systematic study of penguins has changed considerably over recent years, Wiman's contributions are still remarkable. His establishment of grouping by size as a basis for classification was a novel approach that allowed them to deal with an unexpectedly high morphological diversity and limited knowledge of penguin skeletal anatomy. In the past, it was useful to provide a basic framework for the group that today could be used as ‘taxon free’ categories. First, it was important to define new species, and then to establish a classification based on size and robustness. This laid the foundation for the first attempts to use morphometric parameters for the classification of isolated penguin bones. The Nordenskjöld materials constitute an invaluable collection for comparative purposes, and every year researchers from different countries visit this collection.

  • 13. Adamčík, Slavomír
    et al.
    Slovák, Marek
    Eberhardt, Ursula
    Ronikier, Anna
    Jairus, Teele
    Hampe, Felix
    Verbeken, Annemieke
    Molecular inference, multivariate morphometrics and ecological assessment are applied in concert to delimit species in the Russula clavipes complex2016In: Mycologia, ISSN 0027-5514, E-ISSN 1557-2536, Vol. 108, no 4, p. 716-730Article in journal (Refereed)
    Abstract [en]

    Species of Russula subsect. Xerampelinae are notoriously difficult to identify and name and have not been subject to molecular study. A group of species, referred to here as the R. clavipes complex, growing in association with Salix, Betula and Populus as well as coniferous tree species from temperate to arctic and alpine habitats, were examined. Analyses of the nuc rDNA internal transcribed spacer (ITS) region and a numerical analysis of morphological characters were used. The R. clavipes complex is a monophyletic group within Russula subsect. Xerampelinae, according to molecular results. The complex includes three species: R. nuoljae is a phylogenetically and morphologically well-supported species while the other two, R. clavipes and R. pascua, are similar based on ITS data and morphology but separate based on their ecology. Russula pseudoolivascens is conspecific with R. clavipes. Several combinations of characters traditionally used in the taxonomy of R. subsect. Xerampelinae are inappropriate for species delimitation in this group and the adequacy of the ITS for species identification in this group is discussed. Detailed microscopic observations on the type collection of R. nuoljae are presented and illustrated, along with a key to the European members of R. subsect. Xerampelinae.

  • 14. Aerts, R
    The freezer defrosting: global warming and litter decomposition rates in cold biomes2006In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 94, no 4, p. 713-724Article in journal (Refereed)
    Abstract [en]

    1 Decomposition of plant litter, a key component of the global carbon budget, is hierarchically controlled by the triad: climate > litter quality > soil organisms. Given the sensitivity of decomposition to temperature, especially in cold biomes, it has been hypothesized that global warming will lead to increased litter decomposition rates, both through direct temperature effects and through indirect effects on litter quality and soil organisms. 2 A meta-analysis of experimental warming studies in cold biomes (34 site-species combinations) showed that warming resulted in slightly increased decomposition rates. However, this response was strongly dependent on the method used: open top chambers reduced decomposition rates, whereas heating lamps stimulated decomposition rates. The low responsiveness was mainly due to moisture-limited decomposition rates in the warming treatments, especially at mesic and xeric sites. This control of litter decomposition by both temperature and moisture was corroborated by natural gradient studies. 3 Interspecific differences in litter quality and decomposability are substantially larger than warming-induced phenotypic responses. Thus, the changes in the species composition and structure of plant communities that have been observed in medium-term warming studies in cold biomes will have a considerably greater impact on ecosystem litter decomposition than phenotypic responses. 4 Soil fauna communities in cold biomes are responsive to climate warming. Moreover, temperature-driven migration of the, hitherto absent, large comminuters to high-latitude sites may significantly increase decomposition rates. However, we do not know how far-reaching the consequences of changes in the species composition and structure of the soil community are for litter decomposition, as there is a lack of data on functional species redundancy and the species’ dispersal ability. 5 Global warming will lead to increased litter decomposition rates only if there is sufficient soil moisture. Hence, climate scenario and experimental studies should focus more on both factors and their interaction. As interspecific differences in potential decomposability and litter chemistry are substantially larger than phenotypic responses to warming, the focus of future research should be on the former. In addition, more light should be shed on the below-ground ‘darkness’ to evaluate the ecological significance of warming-induced soil fauna community changes for litter decomposition processes in cold biomes.

  • 15. Aerts, R
    et al.
    Cornelissen, J H C
    Dorrepaal, E
    van Logtestijn, R S P
    Callaghan, T V
    Effects of experimentally imposed climate scenarios on flowering phenology and flower production of subarctic bog species2004In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 10, no 9, p. 1599-1609Article in journal (Refereed)
    Abstract [en]

    Climate scenarios for high-latitude areas predict not only increased summer temperatures, but also larger variation in snowfall and winter temperatures. By using open-top chambers, we experimentally manipulated both summer temperatures and winter and spring snow accumulations and temperatures independently in a blanket bog in subarctic Sweden, yielding six climate scenarios. We studied the effects of these scenarios on flowering phenology and flower production of Andromeda polifolia (woody evergreen) and Rubus chamaemorus (perennial herb) during 2 years. The second year of our study (2002) was characterized by unusually high spring and early summer temperatures. Our winter manipulations led to consistent increases in winter snow cover. As a result, average and minimum air and soil temperatures in the high snow cover treatments were higher than in the winter ambient treatments, whereas temperature fluctuations were smaller. Spring warming resulted in higher average, minimum, and maximum soil temperatures. Summer warming led to higher air and soil temperatures in mid-summer (June-July), but not in late summer (August-September). The unusually high temperatures in 2002 advanced the median flowering date by 2 weeks for both species in all treatments. Superimposed on this effect, we found that for both Andromeda and Rubus, all our climate treatments (except summer warming for Rubus) advanced flowering by 1-4 days. The total flower production of both species showed a more or less similar response: flower production in the warm year 2002 exceeded that in 2001 by far. However, in both species flower production was only stimulated by the spring-warming treatments. Our results show that the reproductive ecology of both species is very responsive to climate change but this response is very dependent on specific climate events, especially those that occur in winter and spring. This suggests that high-latitude climate change experiments should focus more on winter and spring events than has been the case so far.

  • 16. Aerts, R.
    et al.
    Cornelissen, J. H. C.
    van Logtestijn, R. S. P.
    Callaghan, T. V.
    Climate change has only a minor impact on nutrient resorption parameters in a high-latitude peatland2007In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 151, no 1, p. 132-139Article in journal (Refereed)
    Abstract [en]

    Nutrient resorption from senescing plant tissues is an important determinant of the fitness of plant populations in nutrient-poor ecosystems, because it makes plants less dependent on current nutrient uptake. Moreover, it can have significant “afterlife” effects through its impact on litter chemistry and litter decomposability. Little is known about the effects of climate change on nutrient resorption. We studied the effects of climate change treatments (including winter snow addition, and spring and/or summer warming) on nutrient resorption of four dominant species in a nutrient-poor subarctic peatland. These species were Betula nana (woody deciduous), Vaccinium uliginosum (woody deciduous), Calamagrostis lapponica (graminoid) and Rubus chamaemorus (forb). After five years of treatments both mature and senesced leaf N concentrations showed a small but significant overall reduction in response to the climate treatments. However, the effects were species-specific. For example, in the controls the N concentration in senesced leaves of Calamagrostis (3.0 +/- 0.2 mg N g(-1)) was about four times lower than for Rubus (11.2 +/- 0.2 mg N g(-1)). There were no significant treatment effects on N resorption efficiency (% of the N pool in mature leaves that is resorbed during senescence). The nitrogen resorption efficiency of Calamagrostis (about 80%) was higher than in the other three species (about 60%). Thus, climate change has only a minor impact on nutrient resorption parameters. However, given the substantial interspecific differences in these parameters, substantial changes in plant-soil feedbacks may be expected as a result of the observed changes in the species composition of high-latitude vegetation. These changes are species-specific and thus difficult to predict.

  • 17. Ahlberg, P.
    et al.
    Taylor, M.E
    Ptychopariid trilobites in the Lower Cambrian of Scandinavia.1981Conference paper (Other academic)
  • 18. Akesson, S
    et al.
    Morin, J
    Muheim, R
    Ottosson, U
    Avian orientation at steep angles of inclination: experiments with migratory white-crowned sparrows at the magnetic North Pole2001In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 268, no 1479, p. 1907-1913Article in journal (Refereed)
    Abstract [en]

    The Earth’s magnetic field and celestial cues provide animals with compass information during migration. Inherited magnetic compass courses are selected based on the angle of inclination, making it difficult to orient in the near vertical fields found at high geomagnetic latitudes. Orientation cage experiments were performed at different sites in high Arctic Canada with adult and young white-crowned sparrows (Zonotrichia leucophrys gambelii) in order to investigate birds’ ability to use the Earth’s magnetic field and celestial cues for orientation in naturally,,cry steep magnetic fields at and close to the magnetic North Pole. Experiments were performed during the natural period of migration at night in the local geomagnetic field under natural clear skies and under simulated total overcast conditions. The experimental birds failed to select a meaningful magnetic compass course under overcast conditions at the magnetic North Pole, but could do so in gcomagnetic fields deviating less than 3 degrees from the vertical. Migratory orientation was successful at all sites when celestial cues were available.

  • 19. Alatalo, Juha M.
    et al.
    Jägerbrand, Annika K.
    Chen, Shengbin
    Molau, Ulf
    Responses of lichen communities to 18 years of natural and experimental warming2017In: Annals of Botany, Vol. 120, no 1, p. 159-170Article in journal (Refereed)
  • 20. Alatalo, Juha M
    et al.
    Jägerbrand, Annika K
    Juhanson, Jaanis
    Michelsen, Anders
    Ľuptáčik, Peter
    Impacts of twenty years of experimental warming on soil carbon, nitrogen, moisture and soil mites across alpine/subarctic tundra communities2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7Article in journal (Refereed)
    Abstract [en]

    High-altitude and alpine areas are predicted to experience rapid and substantial increases in future temperature, which may have serious impacts on soil carbon, nutrient and soil fauna. Here we report the impact of 20 years of experimental warming on soil properties and soil mites in three contrasting plant communities in alpine/subarctic Sweden. Long-term warming decreased juvenile oribatid mite density, but had no effect on adult oribatids density, total mite density, any major mite group or the most common species. Long-term warming also caused loss of nitrogen, carbon and moisture from the mineral soil layer in mesic meadow, but not in wet meadow or heath or from the organic soil layer. There was a significant site effect on the density of one mite species, Oppiella neerlandica, and all soil parameters. A significant plot-scale impact on mites suggests that small-scale heterogeneity may be important for buffering mites from global warming. The results indicated that juvenile mites may be more vulnerable to global warming than adult stages. Importantly, the results also indicated that global warming may cause carbon and nitrogen losses in alpine and tundra mineral soils and that its effects may differ at local scale.

  • 21. Alatalo, Juha M.
    et al.
    Jägerbrand, Annika K.
    Molau, Ulf
    Climate change and climatic events: community-, functional- and species-level responses of bryophytes and lichens to constant, stepwise, and pulse experimental warming in an alpine tundra2014In: Alpine Botany, ISSN 1664-2201, E-ISSN 1664-221X, Vol. 124, no 2, p. 81-91Article in journal (Refereed)
    Abstract [en]

    We experimentally imposed three different kinds of warming scenarios over 3 years on an alpine meadow community to identify the differential effects of climate warming and extreme climatic events on the abundance and biomass of bryophytes and lichens. Treatments consisted of (a) a constant level of warming with open top chambers (an average temperature increase of 1.87 °C), (b) a yearly stepwise increase of warming (average temperature increases of 1.0; 1.87 and 3.54 °C, consecutively), and (c) a pulse warming, i.e., a single first year pulse event of warming (average temperature increase of 3.54 °C only during the first year). To our knowledge, this is the first climate change study that attempts to distinguish between the effects of constant, stepwise and pulse warming on bryophyte and lichen communities. We hypothesised that pulse warming would have a significant short-term effect compared to the other warming treatments, and that stepwise warming would have a significant mid-term effect compared to the other warming treatments. Acrocarpous bryophytes as a group increased in abundance and biomass to the short-term effect of pulse warming. We found no significant effects of mid-term (third-year) stepwise warming. However, one pleurocarpous bryophyte species, Tomentypnum nitens, generally increased in abundance during the warm year 1997 but decreased in control plots and in response to the stepwise warming treatment. Three years of experimental warming (all treatments as a group) did have a significant impact at the community level, yet changes in abundance did not translate into significant changes in the dominance hierarchies at the functional level (for acrocarpous bryophytes, pleurocarpous bryophytes, Sphagnum or lichens), or in significant changes in other bryophyte or lichen species. The results suggest that bryophytes and lichens, both at the functional group and species level, to a large extent are resistant to the different climate change warming simulations that were applied.

  • 22. Alatalo, Juha M
    et al.
    Jägerbrand, Annika K
    Molau, Ulf
    Impacts of different climate change regimes and extreme climatic events on an alpine meadow community2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6Article in journal (Refereed)
    Abstract [en]

    Climate variability is expected to increase in future but there exist very few experimental studies that apply different warming regimes on plant communities over several years. We studied an alpine meadow community under three warming regimes over three years. Treatments consisted of (a) a constant level of warming with open-top chambers (ca. 1.9 °C above ambient), (b) yearly stepwise increases in warming (increases of ca. 1.0, 1.9 and 3.5 °C), and (c) pulse warming, a single first-year pulse event of warming (increase of ca. 3.5 °C). Pulse warming and stepwise warming was hypothesised to cause distinct first-year and third-year effects, respectively. We found support for both hypotheses; however, the responses varied among measurement levels (whole community, canopy, bottom layer, and plant functional groups), treatments, and time. Our study revealed complex responses of the alpine plant community to the different experimentally imposed climate warming regimes. Plant cover, height and biomass frequently responded distinctly to the constant level of warming, the stepwise increase in warming and the extreme pulse-warming event. Notably, we found that stepwise warming had an accumulating effect on biomass, the responses to the different warming regimes varied among functional groups, and the short-term perturbations had negative effect on species richness and diversity

  • 23. Alatalo, Juha M.
    et al.
    Jägerbrand, Annika K.
    Molau, Ulf
    Testing reliability of short-term responses to predict longer-term responses of bryophytes and lichens to environmental change2015In: Ecological Indicators, ISSN 1470-160X, E-ISSN 1872-7034, Vol. 58, no Supplement C, p. 77-85Article in journal (Refereed)
    Abstract [en]

    Abstract Environmental changes are predicted to have severe and rapid impacts on polar and alpine regions. At high latitudes/altitudes, cryptogams such as bryophytes and lichens are of great importance in terms of biomass, carbon/nutrient cycling, cover and ecosystem functioning. This seven-year factorial experiment examined the effects of fertilizing and experimental warming on bryophyte and lichen abundance in an alpine meadow and a heath community in subarctic Sweden. The aim was to determine whether short-term responses (five years) are good predictors of longer-term responses (seven years). Fertilizing and warming had significant negative effects on total and relative abundance of bryophytes and lichens, with the largest and most rapid decline caused by fertilizing and combined fertilizing and warming. Bryophytes decreased most in the alpine meadow community, which was bryophyte-dominated, and lichens decreased most in the heath community, which was lichen-dominated. This was surprising, as the most diverse group in each community was expected to be most resistant to perturbation. Warming alone had a delayed negative impact. Of the 16 species included in statistical analyses, seven were significantly negatively affected. Overall, the impacts of simulated warming on bryophytes and lichens as a whole and on individual species differed in time and magnitude between treatments and plant communities (meadow and heath). This will likely cause changes in the dominance structures over time. These results underscore the importance of longer-term studies to improve the quality of data used in climate change models, as models based on short-term data are poor predictors of long-term responses of bryophytes and lichens.

  • 24. Alatalo, Juha M
    et al.
    Jägerbrand, Annika K
    Čuchta, Peter
    Collembola at three alpine subarctic sites resistant to twenty years of experimental warming2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5Article in journal (Refereed)
    Abstract [en]

    This study examined the effects of micro-scale, site and 19 and 21 years of experimental warming on Collembola in three contrasting alpine subarctic plant communities (poor heath, rich meadow, wet meadow). Unexpectedly, experimental long-term warming had no significant effect on species richness, effective number of species, total abundance or abundance of any Collembola species. There were micro-scale effects on species richness, total abundance, and abundance of 10 of 35 species identified. Site had significant effect on effective number of species, and abundance of six species, with abundance patterns differing between sites. Site and long-term warming gave non-significant trends in species richness. The highest species richness was observed in poor heath, but mean species richness tended to be highest in rich meadow and lowest in wet meadow. Warming showed a tendency for a negative impact on species richness. This long-term warming experiment across three contrasting sites revealed that Collembola is capable of high resistance to climate change. We demonstrated that micro-scale and site effects are the main controlling factors for Collembola abundance in high alpine subarctic environments. Thus local heterogeneity is likely important for soil fauna composition and may play a crucial role in buffering Collembola against future climate change.

  • 25. Alatalo, Juha M.
    et al.
    Little, Chelsea J.
    Simulated global change: contrasting short and medium term growth and reproductive responses of a common alpine/Arctic cushion plant to experimental warming and nutrient enhancement2014In: Springer Series in Chemical Physics, ISSN 0172-6218, E-ISSN 2193-1801, Vol. 3, no 1Article in journal (Refereed)
    Abstract [en]

    Cushion plants are important components of alpine and Arctic plant communities around the world. They fulfill important roles as facilitators, nurse plants and foundation species across trophic levels for vascular plants, arthropods and soil microorganisms, the importance of these functions increasing with the relative severity of the environment. Here we report results from one of the few experimental studies simulating global change impacts on cushion plants; a factorial experiment with warming and nutrient enhancement that was applied to an alpine population of the common nurse plant, Silene acaulis, in sub-arctic Sweden. Experimental perturbations had significant short-term impacts on both stem elongation and leaf length. S. acaulis responded quickly by increasing stem elongation and (to a lesser extent) leaf length in the warming, nutrient, and the combined warming and nutrient enhancements. Cover and biomass also initially increased in response to the perturbations. However, after the initial positive short-term responses, S. acaulis cover declined in the manipulations, with the nutrient and combined warming and nutrient treatments having largest negative impact. No clear patterns were found for fruit production. Our results show that S. acaulis living in harsh environments has potential to react quickly when experiencing years with favorable conditions, and is more responsive to nutrient enhancement than to warming in terms of vegetative growth. While these conditions have an initial positive impact, populations experiencing longer-term increased nutrient levels will likely be negatively affected.

  • 26. Alatalo, Juha M.
    et al.
    Little, Chelsea J.
    Jägerbrand, Annika K.
    Molau, Ulf
    Dominance hierarchies, diversity and species richness of vascular plants in an alpine meadow: contrasting short and medium term responses to simulated global change2014In: PeerJ, ISSN 2167-8359, E-ISSN 2167-8359, Vol. 2Article in journal (Refereed)
    Abstract [en]

    We studied the impact of simulated global change on a high alpine meadow plant community. Specifically, we examined whether short-term (5 years) responses are good predictors for medium-term (7 years) changes in the system by applying a factorial warming and nutrient manipulation to 20 plots in Latnjajaure, subarctic Sweden. Seven years of experimental warming and nutrient enhancement caused dramatic shifts in dominance hierarchies in response to the nutrient and the combined warming and nutrient enhancement treatments. Dominance hierarchies in the meadow moved from a community being dominated by cushion plants, deciduous, and evergreen shrubs to a community being dominated by grasses, sedges, and forbs. Short-term responses were shown to be inconsistent in their ability to predict medium-term responses for most functional groups, however, grasses showed a consistent and very substantial increase in response to nutrient addition over the seven years. The non-linear responses over time point out the importance of longer-term studies with repeated measurements to be able to better predict future changes. Forecasted changes to temperature and nutrient availability have implications for trophic interactions, and may ultimately influence the access to and palatability of the forage for grazers. Depending on what anthropogenic change will be most pronounced in the future (increase in nutrient deposits, warming, or a combination of them both), different shifts in community dominance hierarchies may occur. Generally, this study supports the productivity–diversity relationship found across arctic habitats, with community diversity peaking in mid-productivity systems and degrading as nutrient availability increases further. This is likely due the increasing competition in plant–plant interactions and the shifting dominance structure with grasses taking over the experimental plots, suggesting that global change could have high costs to biodiversity in the Arctic.

  • 27. Alatalo, Juha M
    et al.
    Little, Chelsea J
    Jägerbrand, Annika K
    Molau, Ulf
    Vascular plant abundance and diversity in an alpine heath under observed and simulated global change2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5Article in journal (Refereed)
    Abstract [en]

    Global change is predicted to cause shifts in species distributions and biodiversity in arctic tundra. We applied factorial warming and nutrient manipulation to a nutrient and species poor alpine/arctic heath community for seven years. Vascular plant abundance in control plots increased by 31%. There were also notable changes in cover in the nutrient and combined nutrient and warming treatments, with deciduous and evergreen shrubs declining, grasses overgrowing these plots. Sedge abundance initially increased significantly with nutrient amendment and then declined, going below initial values in the combined nutrient and warming treatment. Nutrient addition resulted in a change in dominance hierarchy from deciduous shrubs to grasses. We found significant declines in vascular plant diversity and evenness in the warming treatment and a decline in diversity in the combined warming and nutrient addition treatment, while nutrient addition caused a decline in species richness. The results give some experimental support that species poor plant communities with low diversity may be more vulnerable to loss of species diversity than communities with higher initial diversity. The projected increase in nutrient deposition and warming may therefore have negative impacts on ecosystem processes, functioning and services due to loss of species diversity in an already impoverished environment.

  • 28. Aldahan, A A
    et al.
    Ning, S
    Possnert, G
    Backman, J
    Bostrom, K
    Be-10 records from sediments of the Arctic Ocean covering the past 350 ka1997In: Marine Geology, ISSN 0025-3227, E-ISSN 1872-6151, Vol. 144, no 1-3, p. 147-162Article in journal (Refereed)
    Abstract [en]

    Records of Be-10, Be-9, mineralogy and grain size were obtained from two cores collected by the Polarstern Expedition 1991 in the southern Nansen Basin (Core 2213-6) and the Yermak Plateau (Core 2208-2). The accumulation of sediments examined started from about 350 ka (BP), and includes relatively well defined trends of Be isotopes coincident with interglacial/glacial climatic cycles. Sediment accumulation rates (g/cm(2) ka) were higher during glacial periods and our estimates of 1.0 and 2.5 cm/ka sedimentation rates during the Holocene agree with other estimates for the southern Nansen Basin and the Yermak Plateau, respectively. The variations in Be-10 concentration (atoms/g) and flux (atoms/cm(2) ka) are inverse to sediment flux, where high Be-10 concentration and flux are associated with generally low sedimentation/accumulation rates during interglacial periods. We hypothesize that climate plays an important role in Be-10 records from the Arctic sediments, reflecting the intensity and distribution of the ice mass on land and the ocean. (C) 1997 Elsevier Science B.V.

  • 29. Aldahan, A.
    et al.
    Alfimov, V.
    Possnert, G.
    I-129 anthropogenic budget: Major sources and sinks2007In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 22, no 3, p. 606-618Article in journal (Refereed)
    Abstract [en]

    Data are presented here on the anthropogenic I-129 inventory in regions that have been strongly affected by releases from European reprocessing facilities which, to the authors’ knowledge, presently account for > 90% of the global isotope source in the Earth’s surface environment. The results show that > 90% of the isotope inventory occurs in marine waters with the Nordic Seas and Eurasian basin of the Arctic Ocean containing most of the I-129. Within the terrestrial environment of Europe, soils contain the largest part of the isotope inventory. However, the inventory of the terrestrial system did not provide clues on the most plausible atmospheric source of I-129 to Europe, thus supply from both gaseous and marine releases is proposed. The sum of the total inventory in both the marine and terrestrial environments did not match the estimated releases. This imbalance is likely to relate to unconstrained inventory estimates for marine basins (Irish Sea, English Channel and North Sea) close to the facilities, but also to the occurrence of I-129 in the biosphere, and possible overestimated releases from the nuclear reprocessing facilities. There is no doubt that the available data on I-129 distribution in the environment are far from representative and further research is urgently needed to construct a comprehensive picture. (c) 2006 Elsevier Ltd. All rights reserved.

  • 30. Alerstam, Thomas
    et al.
    Bäckman, Johan
    Gudmundsson, Gudmundur A.
    Hedenström, Anders
    Henningsson, Sara S.
    Karlsson, Håkan
    Rosen, Mikael
    Strandberg, Roine
    A polar system of intercontinental bird migration2007In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 274, no 1625, p. 2523-2530Article in journal (Refereed)
    Abstract [en]

    Studies of birdmigration in the Beringia region of Alaska and eastern Siberia are of special interest for revealing the importance of bird migration between Eurasia and North America, for evaluating orientation principles used by the birds at polar latitudes and for understanding the evolutionary implications of intercontinental migratory connectivity among birds as well as their parasites. We used tracking radar placed onboard the ice-breaker Oden to register bird migratory flights from 30 July to 19 August 2005 and we encountered extensive birdmigration in the whole Beringia range from latitude 64 degrees N in Bering Strait up to latitude 75 degrees N far north of Wrangel Island, with eastward flights making up 79% of all track directions. The results from Beringia were used in combination with radar studies from the Arctic Ocean north of Siberia and in the Beaufort Sea to make a reconstruction of a major Siberian-American birdmigration system in a wide Arctic sector between longitudes 1108 E and 130 degrees W, spanning one-third of the entire circumpolar circle. This system was estimated to involve more than 2 million birds, mainly shorebirds, terns and skuas, flying across the Arctic Ocean at mean altitudes exceeding 1 km (maximum altitudes 3-5 km). Great circle orientation provided a significantly better fit with observed flight directions at 20 different sites and areas than constant geographical compass orientation. The long flights over the sea spanned 40-80 degrees of longitude, corresponding to distances and durations of 1400-2600 km and 26-48 hours, respectively. The birds continued from this eastward migration system over the Arctic Ocean into several different flyway systems at the American continents and the Pacific Ocean. Minimization of distances between tundra breeding sectors and northerly stopover sites, in combination with the Beringia glacial refugium and colonization history, seemed to be important for the evolution of this major polar bird migration system.

  • 31.
    Alerstam, Thomas
    et al.
    Lund Univ, Dept Anim Ecol, SE-22362 Lund, Sweden..
    Bäckman, Johan
    Lund Univ, Dept Anim Ecol, SE-22362 Lund, Sweden..
    Strandberg, Roine
    Lund Univ, Dept Anim Ecol, SE-22362 Lund, Sweden..
    Gudmundsson, Gudmundur A.
    Iceland Inst Nat Hist, IS-125 Reykjavik, Iceland..
    Hedenström, Anders
    Lund Univ, Dept Theoret Ecol, SE-22362 Lund, Sweden..
    Henningsson, Sara S.
    Lund Univ, Dept Anim Ecol, SE-22362 Lund, Sweden..
    Karlsson, Håkan
    Lund Univ, Dept Anim Ecol, SE-22362 Lund, Sweden..
    Rosen, Mikael
    Lund Univ, Dept Anim Ecol, SE-22362 Lund, Sweden..
    Great-circle migration of arctic passerines2008In: The AUK: A Quarterly Journal of Ornithology, ISSN 0004-8038, E-ISSN 1938-4254, Vol. 125, no 4, p. 831-838Article in journal (Refereed)
    Abstract [en]

    Birds can save distance and time on their migratory journeys by following great circles rather than rhumblines, but great-circle routes require more complex orientation with changing courses. Flight directions at different places along the route and in relation to the destination can be used to test whether birds migrate along great circles or rhumblines. Such data have indicated great-circle migration among shorebirds at high latitudes, but no critical tests have been made for passerines. Using tracking radar on board the icebreaker Oden in August 2005, we recorded westerly flight directions of passerine migrants over the Chukchi Sea. The main sector of migratory directions was 237-311 degrees centered oil a mean heading direction of 274 degrees. The most likely species to participate in this westward trans-Beringia migration, mainly departing from Alaska, were Eastern Yellow Wagtail (Motacilla Ischutschensis), Arctic Warbler (Phylloscopus borealis kennicotti), Northern Wheatear (Oenanthe oenanthe), and Bluethroat (Luscinia svecica); all except the Bluethroat were recorded from the ship. Observed flight directions agreed with predicted great-circle courses but not with rhumbline courses for three of these four species with winter quarters in Southeast Asia; no definite conclusion could be drawn for the Northern Wheatear (wintering in East Africa). These results support great-circle migration among passerines traveling between Alaska and Old World winter quarters, though the long-distance precision and orientation mechanisms are Still unknown. The relative importance of different evolutionary causes-such as circumvention of geographic barriers, retracing of ancient colonization ways, or distance reduction by great-circle migration-to complex bird migration routes with changing courses remains to be understood. Received 24 August 2007, accepted 6 March 2008.

  • 32. Alerstam, Thomas
    et al.
    Rosén, Mikael
    Bäckman, Johan
    Ericson, Per G. P.
    Hellgren, Olof
    Flight speeds among bird species: allometric and phylogenetic effects2007In: PLoS biology, ISSN 1544-9173, E-ISSN 1545-7885Article in journal (Refereed)
  • 33. Alexanderson, Helena
    et al.
    Backman, Jan
    Cronin, Thomas M.
    Funder, Svend
    Ingolfsson, Olafur
    Jakobsson, Martin
    Landvik, Jon Y.
    Lowemark, Ludvig
    Mangerud, Jan
    Maerz, Christian
    Moller, Per
    O’Regan, Matt
    Spielhagen, Robert F.
    An Arctic perspective on dating Mid-Late Pleistocene environmental history2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, no SI, p. 9-31Article in journal (Refereed)
    Abstract [en]

    To better understand Pleistocene climatic changes in the Arctic, integrated palaeoenvironmental and palaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologic age control are required, not least for correlation to extra-Arctic records. In this paper we discuss, from an Arctic perspective, methods and correlation tools that are commonly used to date Arctic Pleistocene marine and terrestrial events. We review the state of the art of Arctic geochronology, with focus on factors that affect the possibility and quality of dating, and support this overview by examples of application of modern dating methods to Arctic terrestrial and marine sequences. Event stratigraphy and numerical ages are important tools used in the Arctic to correlate fragmented terrestrial records and to establish regional stratigraphic schemes. Age control is commonly provided by radiocarbon, luminescence or cosmogenic exposure ages. Arctic Ocean deep-sea sediment successions can be correlated over large distances based on geochemical and physical property proxies for sediment composition, patterns in palaeomagnetic records and, increasingly, biostratigraphic data. Many of these proxies reveal cyclical patterns that provide a basis for astronomical tuning. Recent advances in dating technology, calibration and age modelling allow for measuring smaller quantities of material and to more precisely date previously undatable material (i.e. foraminifera for C-14, and single-grain luminescence). However, for much of the Pleistocene there are still limits to the resolution of most dating methods. Consequently improving the accuracy and precision (analytical and geological uncertainty) of dating methods through technological advances and better understanding of processes are important tasks for the future. Another challenge is to better integrate marine and terrestrial records, which could be aided by targeting continental shelf and lake records, exploring proxies that occur in both settings, and by creating joint research networks that promote collaboration between marine and terrestrial geologists and modellers. (C) 2013 Elsevier Ltd. All rights reserved.

  • 34. Alfimov, V
    et al.
    Aldahan, A
    Possnert, G
    Tracing water masses with I-129 in the western Nordic Seas in early spring 20022004In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 31, no 19Article in journal (Refereed)
    Abstract [en]

    The distribution of I-129 was utilized for labeling water masses in three sections of the western Nordic Seas. An increase of the tracer in Polar Waters of the East Greenland Current was observed between the Fram Strait and 72degreesN section and attributed to either unaccounted Polar Waters and/or recirculation of cold and fresh Atlantic Waters from the West Spitzbergen Current. Recent convection homogenized I-129 in upper 1000 m of the Greenland Sea, and similar concentrations were observed in dense waters of the Denmark Strait. The densest outflow waters were not found in either the Greenland Sea or the East Greenland Current at 72degreesN.

  • 35. Alfimov, V
    et al.
    Aldahan, A
    Possnert, G
    Winsor, P
    Anthropogenic iodine-129 in seawater along a transect from the Norwegian coastal current to the North Pole2004In: Marine Pollution Bulletin, ISSN 0025-326X, E-ISSN 1879-3363, Vol. 49, no 11-12, p. 1097-1104Article in journal (Refereed)
    Abstract [en]

    Variation in the concentrations of iodine-129 (I-129, T-1/2 = 15.7 Myr), a low-level radioactive component of nuclear fuel waste, is documented in surface waters and depth profiles collected during 2001 along a transect from the Norwegian Coastal Current to the North Pole. The surface waters near the Norwegian coast are found to have 20 times higher I-129 concentration than the surface waters of the Arctic Ocean. The depth profiles of I-129 taken in the Arctic Ocean reveal a sharp decline in the concentration to a depth of about 300-500m followed by a weaker gradient extending down to the bottom. A twofold increase in the I-129 concentration is observed in the upper 1000m since 1996. Based on known estimates of marine transient time from the release sources (the nuclear reprocessing facilities at La Hague, France, and Sellafield, UK), a doubling in the I-129 inventory of the top 1000m of the Arctic Ocean is expected to occur between the years 2001 and 2006. As I-129 of polar mixed layer and Atlantic layer of the Arctic Ocean is ventilated by the East Greenland Current into the Nordic Seas and North Atlantic Ocean, further dispersal and increase of the isotope concentration in these regions will be encountered in the near future. (C) 2004 Elsevier Ltd. All rights reserved.

  • 36. Alfimov, V
    et al.
    Possnert, G
    Aldahan, A
    Anthropogenic iodine-129 in the Arctic Ocean and Nordic Seas: Numerical modeling and prognoses2006In: Marine Pollution Bulletin, ISSN 0025-326X, E-ISSN 1879-3363, Vol. 52, no 4, p. 380-385Article in journal (Refereed)
    Abstract [en]

    A numerical model simulation has been used to predict extent and variability in the anthropogenic I-129 pollution in the Arctic Ocean and Nordic Seas region over a period of 100 years. The source function of I-129 used in the model is represented by a well-known history of discharges from the Sellafield and La Hague nuclear reprocessing facilities. The simulations suggest a fast transport and large inventory of the anthropogenic I-129 in the Arctic and North Atlantic Oceans. In a fictitious case of abrupt stop of the discharges, a rapid decline of inventories is observed in all compartments except the North Atlantic Ocean, the deep Nordic Seas and the deep Arctic Ocean. Within 15 years after the stop of releases, the model prediction indicates that near-equilibrium conditions are reached in all compartments. (c) 2005 Elsevier Ltd. All rights reserved.

  • 37. Alfimov, Vasily
    et al.
    Aldahan, Ala
    Possnert, Goran
    Water masses and I-129 distribution in the Nordic Seas2013In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 294, p. 542-546Article in journal (Refereed)
    Abstract [en]

    The application of the radioactive isotope iodine-129 as a tracer of water circulation in the oceans has provided interesting information with respect to sources and mixing of different water masses. We here present results of I-129 distribution in water profiles located in the Nordic Seas and use the isotope to fingerprint water masses in the region. The samples were collected by the US research vessel Knorr in May-June 2002. I-129 signatures along the Norwegian Sea reflect a mixing of I-129-rich surface water along the Scandinavian continental slope and I-129-poor North Atlantic surface water. These two water masses become less segregated along the Fram Strait where apparent I-129 enrichment penetrates the return Arctic flow into the East Greenland Current. The I-129 data further suggest existence of a water mass that is not entirely labeled with respect to origin at the Denmark Strait bottom water. This water parcel probably originates from the Iceland Sea. I-129 data also shed light on the major deep water outflow from the Nordic Seas located at the Faeroe Bank Channel. (C) 2012 Elsevier B.V. All rights reserved.

  • 38.
    Algesten, Grete
    Umeå universitet, Ekologi och geovetenskap.
    Regulation of carbon dioxide emission from Swedish boreal lakes and the Gulf of Bothnia2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The global carbon cycle is subject to intense research, where sources and sinks for greenhouse gases, carbon dioxide in particular, are estimated for various systems and biomes. Lakes have previously been neglected in carbon balance estimations, but have recently been recognized to be significant net sources of CO2.

    This thesis estimates emission of carbon dioxide (CO2) from boreal lakes and factors regulating the CO2 saturation from field measurements of CO2 concentration along with a number of chemical, biological and physical parameters. Concentration of dissolved organic carbon (DOC) was found to be the most important factor for CO2 saturation in lake water, whereas climatic parameters such as precipitation, temperature and global radiation were less influential. All lakes were supersaturated with and, thus, sources of CO2. Sediment incubation experiments indicated that in-lake mineralization processes during summer stratification mainly occurred in the pelagial. Approximately 10% of the CO2 emitted from the lake surface was produced in epilimnetic sediments.

    The mineralization of DOC and emission of CO2 from freshwaters was calculated on a catchment basis for almost 80,000 lakes and 21 major catchments in Sweden, together with rates of sedimentation in lakes and export of organic carbon to the sea. The total export of terrestrial organic carbon to freshwaters could thereby be estimated and consequently also the importance of lakes for the withdrawal of organic carbon export from terrestrial sources to the sea. Lakes removed 30-80% of imported terrestrial organic carbon, and mineralization and CO2 emission were much more important than sedimentation of carbon. The carbon loss was closely related to water retention time, where catchments with short residence times (<1 year) had low carbon retentions, whereas in catchments with long residence times (>3 years) a majority of the imported TOC was removed in the lake systems.

    The Gulf of Bothnia was also studied in this thesis and found to be a net heterotrophic system, emitting large amounts of CO2 to the atmosphere on an annual basis. The rate of CO2 emission was depending on the balance between primary production and bacterial respiration, and the system was oscillating between being a source and a sink of CO2.

  • 39.
    Algesten, Grete
    et al.
    Umeå universitet, Ekologi och geovetenskap.
    Sobek, Sebastian
    Bergström, Ann-Kristin
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Jonsson, Anders
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Tranvik, Lars J
    Jansson, Mats
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Contribution of sediment respiration to summer CO2 emission from boreal and subarctic lakes2005In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 50, no 4, p. 529-535Article in journal (Refereed)
    Abstract [en]

    We measured sediment production of carbon dioxide (CO(2)) and methane (CH(4)) and the net flux of CO(2) across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were made in situ under ambient light conditions. The flux of CO(2) between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m(-2) day(-1) from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated to dissolved organic carbon (DOC) concentration in the water (r(2) = 0.61). The net flux of CO(2) across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed layer (r(2) = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration. Lakes with DOC concentrations <5.6 mg L(-1) had net consumption of CO(2) in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic (<2.6 mg L(-1)) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources.

  • 40. Ali, Arshad
    et al.
    Molau, Ulf
    Bai, Yang
    Jägerbrand, Annika K.
    Alatalo, Juha M.
    Diversity-productivity dependent resistance of an alpine plant community to different climate change scenarios2016In: Ecological research, ISSN 0912-3814, E-ISSN 1440-1703, Vol. 31, no 6, p. 935-945Article in journal (Refereed)
    Abstract [en]

    Here we report from a experiment imposing different warming scenarios [control with ambient temperature, constant level of moderate warming for 3 years, stepwise increase in warming for 3 years, and one season of high level warming (pulse) simulating an extreme summer event] on an alpine ecosystem to study the impact on species diversity–biomass relationship, and community resistance in terms of biomass production. Multiple linear mixed models indicate that experimental years had stronger influence on biomass than warming scenarios and species diversity. Species diversity and biomass had almost humpback relationships under different warming scenarios over different experimental years. There was generally a negative diversity–biomass relationship, implying that a positive diversity–biomass relationship was not the case. The application of different warming scenarios did not change this tendency. The change in community resistance to all warming scenarios was generally negatively correlated with increasing species diversity, the strength of the correlation varying both between treatments and between years within treatments. The strong effect of experimental years was consistent with the notion that niche complementarity effects increase over time, and hence, higher biomass productivity over experimental years. The strongest negative relationship was found in the first year of the pulse treatment, indicating that the community had weak resistance to an extreme event of one season of abnormally warm climate. Biomass production started recovering during the two subsequent years. Contrasting biomass-related resistance emerged in the different treatments, indicating that micro sites within the same plant community may differ in their resistance to different warming scenarios.

  • 41. Alling, Vanja
    et al.
    Humborg, Christoph
    Morth, Carl-Magnus
    Rahm, Lars
    Pollehne, Falk
    Tracing terrestrial organic matter by delta(34)S and delta(13)C signatures in a subarctic estuary2008In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, no 6, p. 2594-2602Article in journal (Refereed)
    Abstract [en]

    A key issue to understanding the transformations of terrestrial organic carbon in the ocean is to disentangle the latter from marine-produced organic matter. We applied a multiple stable isotope approach using delta(34)S and delta(13)C isotope signatures from estuarine dissolved organic matter (DOM), enabling us to constrain the contribution of terrestrial-derived DOM in an estuarine gradient of the northern Baltic Sea. The stable isotope signatures for dissolved organic sulfur (delta(34)S(DOS)) have twice the range between terrestrial and marine end members compared to the stable isotope signatures for dissolved organic carbon (delta(13)C(DOC)); hence, the share of terrestrial DOM in the total estuarine DOM can be calculated more precisely. DOM samples from the water column were collected using ultrafiltration on board the German RV Maria S Merian during a winter cruise, in the Bothnian Bay, Bothnian Sea, and Baltic proper. We calculated the terrestrial fraction of the estuarine DOC (DOC(ter)) from both delta(13)C(DOC) and delta(34)S(DOS) signatures and applying fixed C: S ratios for riverine and marine end members to convert S isotope signatures into DOC concentrations. The delta(34)S(DOS) signature of the riverine end member was +7.02 parts per thousand, and the mean signatures from Bothnian Bay, Bothnian Sea, and Baltic proper were +10.27, +12.51, and +13.67 parts per thousand, respectively, showing an increasing marine signal southwards (d34SDOS marine end member = 18.1 parts per thousand). These signatures indicate that 87%, 75%, and 67%, respectively, of the water column DOC is of terrestrial origin (DOC(ter)) in these basins. Comparing the fractions of DOC(ter) in each basin-that are still based on few winter values only-with the annual river input of DOC, it appears that the turnover time for DOC(ter) in the Gulf of Bothnia is much shorter than the hydraulic turnover time, suggesting that high-latitude estuaries might be efficient sinks for DOC(ter).

  • 42. Alling, Vanja
    et al.
    Sanchez-Garcia, Laura
    Porcelli, Don
    Pugach, Sveta
    Vonk, Jorien E.
    van Dongen, Bart
    Morth, Carl-Magnus
    Anderson, Leif G.
    Sokolov, Alexander
    Andersson, Per
    Humborg, Christoph
    Semiletov, Igor
    Gustafsson, Orjan
    Nonconservative behavior of dissolved organic carbon across the Laptev and East Siberian seas2010In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 24Article in journal (Refereed)
    Abstract [en]

    Climate change is expected to have a strong effect on the Eastern Siberian Arctic Shelf (ESAS) region, which includes 40% of the Arctic shelves and comprises the Laptev and East Siberian seas. The largest organic carbon pool, the dissolved organic carbon (DOC), may change significantly due to changes in both riverine inputs and transformation rates; however, the present DOC inventories and transformation patterns are poorly understood. Using samples from the International Siberian Shelf Study 2008, this study examines for the first time DOC removal in Arctic shelf waters with residence times that range from months to years. Removals of up to 10%-20% were found in the Lena River estuary, consistent with earlier studies in this area, where surface waters were shown to have a residence time of approximately 2 months. In contrast, the DOC concentrations showed a strong nonconservative pattern in areas with freshwater residence times of several years. The average losses of DOC were estimated to be 30%-50% during mixing along the shelf, corresponding to a first-order removal rate constant of 0.3 yr(-1). These data provide the first observational evidence for losses of DOC in the Arctic shelf seas, and the calculated DOC deficit reflects DOC losses that are higher than recent model estimates for the region. Overall, a large proportion of riverine DOC is removed from the surface waters across the Arctic shelves. Such significant losses must be included in models of the carbon cycle for the Arctic Ocean, especially since the breakdown of terrestrial DOC to CO2 in Arctic shelf seas may constitute a positive feedback mechanism for Arctic climate warming. These data also provide a baseline for considering the effects of future changes in carbon fluxes, as the vast northern carbon-rich permafrost areas draining into the Arctic are affected by global warming.

  • 43. Alonso-Saez, Laura
    et al.
    Andersson, Anders
    Heinrich, Friederike
    Bertilsson, Stefan
    High archaeal diversity in Antarctic circumpolar deep waters2011In: Environmental Microbiology Reports, ISSN 1758-2229, E-ISSN 1758-2229, Vol. 3, no 6, p. 689-697Article in journal (Refereed)
    Abstract [en]

    Archaea are abundant in polar oceans but important ecological aspects of this group remain enigmatic, such as patterns of diversity and biogeography. Here, we provide the first high-throughput sequencing population study of Antarctic archaea based on 198 bp fragments of the 16S rRNA gene, targeting different water masses across the Amundsen and Ross Seas. Our results suggest that archaeal community composition is strongly shaped by hydrography and significantly influenced by environmental parameters. Archaeal communities from cold continental shelf waters (SW) of the Ross Sea were similar over depth with a single thaumarchaeal phylotype dominating Antarctic surface waters (AASW) and deeper SW (contributing up to 80% of reads). However, this phylotype contributed less than 8% of reads in circumpolar deep waters (CDW). A related thaumarchaeon (98% identity) was almost absent in AASW, but contributed up to 30% of reads in CDW, suggesting ecological differentiation of closely related phylotypes. Significantly higher archaeal richness and evenness were observed in CDW, with Shannon indices (c. 2.5) twice as high as for AASW, and high contributions of Group II Euryarchaeota. Based on these results, we suggest that CDW is a hotspot of archaeal diversity and may play an important role in the dispersal of archaeal phylotypes to other oceanic water masses.

  • 44. Alonso-Saez, Laura
    et al.
    Waller, Alison S.
    Mende, Daniel R.
    Bakker, Kevin
    Farnelid, Hanna
    Yager, Patricia L.
    Lovejoy, Connie
    Tremblay, Jean-Eric
    Potvin, Marianne
    Heinrich, Friederike
    Estrada, Marta
    Riemann, Lasse
    Bork, Peer
    Pedros-Alio, Carlos
    Bertilsson, Stefan
    Role for urea in nitrification by polar marine Archaea2012In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 44, p. 17989-17994Article in journal (Refereed)
    Abstract [en]

    Despite the high abundance of Archaea in the global ocean, their metabolism and biogeochemical roles remain largely unresolved. We investigated the population dynamics and metabolic activity of Thaumarchaeota in polar environments, where these microorganisms are particularly abundant and exhibit seasonal growth. Thaumarchaeota were more abundant in deep Arctic and Antarctic waters and grew throughout the winter at surface and deeper Arctic halocline waters. However, in situ single-cell activity measurements revealed a low activity of this group in the uptake of both leucine and bicarbonate (<5% Thaumarchaeota cells active), which is inconsistent with known heterotrophic and autotrophic thaumarchaeal lifestyles. These results suggested the existence of alternative sources of carbon and energy. Our analysis of an environmental metagenome from the Arctic winter revealed that Thaumarchaeota had pathways for ammonia oxidation and, unexpectedly, an abundance of genes involved in urea transport and degradation. Quantitative PCR analysis confirmed that most polar Thaumarchaeota had the potential to oxidize ammonia, and a large fraction of them had urease genes, enabling the use of urea to fuel nitrification. Thaumarchaeota from Arctic deep waters had a higher abundance of urease genes than those near the surface suggesting genetic differences between closely related archaeal populations. In situ measurements of urea uptake and concentration in Arctic waters showed that small-sized prokaryotes incorporated the carbon from urea, and the availability of urea was often higher than that of ammonium. Therefore, the degradation of urea may be a relevant pathway for Thaumarchaeota and other microorganisms exposed to the low-energy conditions of dark polar waters.

  • 45. Alsos, I G
    et al.
    Engelskjon, T
    Gielly, L
    Taberlet, P
    Brochmann, C
    Impact of ice ages on circumpolar molecular diversity: insights from an ecological key species2005In: Molecular Ecology, ISSN 0962-1083, E-ISSN 1365-294X, Vol. 14, no 9, p. 2739-2753Article in journal (Refereed)
    Abstract [en]

    We address the impact of the ice age cycles on intraspecific cpDNA diversity, for the first time on the full circumboreal-circumarctic scale. The bird-dispersed bog bilberry (or arctic blueberry, Vaccinium uliginosum) is a key component of northern ecosystems and is here used to assess diversity in previously glaciated vs. unglaciated areas and the importance of Beringia as a refugium and source for interglacial expansion. Eighteen chloroplast DNA haplotypes were observed in and among 122 populations, grouping into three main lineages which probably diverged before, and thus were affected more or less independently by, all major glaciations. The boreal ‘Amphi-Atlantic lineage’ included one haplotype occurring throughout northern Europe and one occurring in eastern North America, suggesting expansion from at least two bottlenecked, glacial refugium populations. The boreal ‘Beringian lineage’ included seven haplotypes restricted to Beringia and the Pacific coast of USA. The ‘Arctic-Alpine lineage’ included nine haplotypes, one of them fully circumpolar. This lineage was unexpectedly diverse, also in previously glaciated areas, suggesting that it thrived on the vast tundras during the ice ages and recolonized deglaciated terrain over long distances. Its largest area of persistence during glaciations was probably situated in the north, stretching from Beringia and far into Eurasia, and it probably also survived the last glaciation in southern mountain ranges. Although Beringia apparently was important for the initial divergence and expansion of V. uliginosum as well as for continuous survival of both the Beringian and Arctic-Alpine lineages during all ice ages, this region played a minor role as a source for later interglacial expansions.

  • 46. Alsos, Inger Greve
    et al.
    Eidesen, Pernille Bronken
    Ehrich, Dorothee
    Skrede, Inger
    Westergaard, Kristine
    Jacobsen, Gro Hilde
    Landvik, Jon Y.
    Taberlet, Pierre
    Brochmann, Christian
    Frequent long-distance plant colonization in the changing Arctic2007In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 316, no 5831, p. 1606-1609Article in journal (Refereed)
    Abstract [en]

    The ability of species to track their ecological niche after climate change is a major source of uncertainty in predicting their future distribution. By analyzing DNA fingerprinting ( amplified fragment-length polymorphism) of nine plant species, we show that long-distance colonization of a remote arctic archipelago, Svalbard, has occurred repeatedly and from several source regions. Propagules are likely carried by wind and drifting sea ice. The genetic effect of restricted colonization was strongly correlated with the temperature requirements of the species, indicating that establishment limits distribution more than dispersal. Thus, it may be appropriate to assume unlimited dispersal when predicting long-term range shifts in the Arctic.

  • 47. Amon, D. J.
    et al.
    Wiklund, H.
    Dahlgren, T. G.
    Copley, J. T.
    Smith, C. R.
    Jamieson, A. J.
    Glover, A. G.
    Molecular taxonomy of Osedax (Annelida: Siboglinidae) in the Southern Ocean2014In: Zoologica Scripta, ISSN 0300-3256, E-ISSN 1463-6409, Vol. 43Article in journal (Refereed)
    Abstract [en]

    We report the discovery of three new species of Osedax in the deep Southern Ocean, expanding the diversity and geographical range of this genus of bone-eating worms. Osedax rogersi sp. n. and Osedax crouchi sp. n. were found on a whale skeleton at 1444m in the Kemp Caldera in the East Scotia Sea during the Chemosynthetic Ecosystems of the Southern Ocean (ChEsSo) project. The recently described species, Osedax antarcticus, found on whale bones implanted at a depth of 550-650m off Smith Island in the Bransfield Strait, was also found inhabiting the whale skeleton in the Kemp Caldera. Osedax crouchi as well as another new species Osedax nordenskjoeldi sp. n. have also been found on the implanted whale bones off Smith Island. These two localities are approximately 1800km apart demonstrating a wide distribution of species within the genus. We describe the three new species, O.rogersi, O.crouchi and O.nordenskjoeldi and report the second record of O.antarcticus. We also present a new phylogenetic analysis for Osedax, including data examining genetic connectivity between the Scotia Arc and the Bransfield Strait.

  • 48. Ampomah, Osei Yaw
    et al.
    Huss-Danell, Kerstin
    Nodulation of Thermopsis lupinoides by a Mesorhizobium huakuii strain with a unique nodA gene in Kamtchatka, Russia2011In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, p. 5513-5516Article in journal (Refereed)
  • 49. Ampomah, Osei Yaw
    et al.
    Mousavi, Seyed Abdollah
    Lindström, Kristina
    Huss-Danell, Kerstin
    Diverse Mesorhizobium bacteria nodulate native Astragalus and Oxytropis in arctic and subarctic areas in Eurasia2017In: Systematic and Applied Microbiology, ISSN 0723-2020, E-ISSN 1618-0984, Vol. 40, no 1, p. 51-58Article in journal (Refereed)
    Abstract [en]

    Abstract Rhizobia nodulating native Astragalus and Oxytropis spp. in Northern Europe are not well-studied. In this study, we isolated bacteria from nodules of four Astragalus spp. and two Oxytropis spp. from the arctic and subarctic regions of Sweden and Russia. The phylogenetic analyses were performed by using sequences of three housekeeping genes (16S rRNA, rpoB and recA) and two accessory genes (nodC and nifH). The results of our multilocus sequence analysis (MLSA) of the three housekeeping genes tree showed that all the 13 isolates belonged to the genus Mesorhizobium and were positioned in six clades. Our concatenated housekeeping gene tree also suggested that the isolates nodulating Astragalus inopinatus, Astragalus frigidus, Astragalus alpinus ssp. alpinus and Oxytropis revoluta might be designated as four new Mesorhizobium species. The 13 isolates were grouped in three clades in the nodC and nifH trees. 15N analysis suggested that the legumes in association with these isolates were actively fixing nitrogen.

  • 50. Amundsen, Helene
    et al.
    Anderson, Leif
    Andersson, Andreas
    Azetsu-Scott, Kumiko
    Bellerby, Richard
    Beman, Michael
    Browman, Howard I
    Carlson, Craig
    Cheung, William WL
    Chierici, Melissa
    AMAP Assessment 2013: Arctic Ocean Acidification2013Book (Other academic)
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