Blar i forfatter "Johnsen, Geir"

Viser treff 21-26 av 26

    • Phytoplankton community succession and dynamics using optical approaches 

      Fragoso, Glaucia Moreira; Johnsen, Geir; Chauton, Matilde Skogen; Cottier, Finlo Robert; Ellingsen, Ingrid H. (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-04)
      The phytoplankton in coastal regions are responding to constant environmental changes, thus the use of proxies derived from in situ frequent time-series observations and validated from traditional microscopic or pigment methods can be a solution for detecting rapid responses of community dynamics and succession. In this study, we combined in situ high-frequency (every 30 min from May to September ...

    • Seabirds during Arctic Polar Night: underwater observations from Svalbard archipelago, Norway 

      Ostaszewska, Kaja; Balazy, Piotr; Berge, Jørgen; Johnsen, Geir; Staven, Robert (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-09)
      Visually-oriented predators, such as seabirds, are highly light dependent, and thus their presence and activity under continuously dark conditions of Arctic polar night pose a number of questions about the strategies and mechanisms they use to find prey. Here, opportunistic observations of the behaviors of Thick-billed Murres (Uria lomvia; n = 4) and juvenile Black Guillemots (Cepphus grylle; n ...

    • Spectral and RGB analysis of the light climate and its ecological impacts using an all-sky camera system in the Arctic 

      Grant, Stephen Denis; Johnsen, Geir; McKee, David; Zolich, Artur Piotr; Cohen, Jonathan H. (Journal article; Tidsskriftartikkel, 2023-06-21)
      The ArcLight observatory provides an hourly continuous time series of all-sky images providing light climate data (intensity, spectral composition, and photoperiod) from the Arctic (Svalbard at 79°N). Until recently, no complete annual time series of light climate relevant for biological processes has been provided from the high Arctic because of insufficient sensitivity of commercial light sensors ...

    • Still Arctic? — The changing Barents Sea 

      Gerland, Sebastian; Ingvaldsen, Randi Brunvær; Reigstad, Marit; Sundfjord, Arild; Bogstad, Bjarte; Chierici, Melissa; Hop, Haakon; Renaud, Paul Eric; Smedsrud, Lars Henrik; Stige, Leif Christian; Årthun, Marius; Berge, Jørgen; Bluhm, Bodil Annikki Ulla Barbro; Borgå, Katrine; Bratbak, Gunnar; Divine, Dmitry V; Eldevik, Tor; Eriksen, Elena; Fer, Ilker; Fransson, Agneta; Gradinger, Rolf Rudolf; Granskog, Mats A.; Haug, Tore; Husum, Katrine; Johnsen, Geir; Jonassen, Marius Opsanger; Jørgensen, Lis Lindal; Kristiansen, Svein; Larsen, Aud; Lien, Vidar Surén; Lind, Sigrid; Lindstrøm, Ulf Ove; Mauritzen, Cecilie; Melsom, Arne; Mernild, Sebastian H.; Müller, Malte; Nilsen, Frank; Primicerio, Raul; Søreide, Janne; van der Meeren, Gro Ingleid; Wassmann, Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-11-13)
      The Barents Sea is one of the Polar regions where current climate and ecosystem change is most pronounced. Here we review the current state of knowledge of the physical, chemical and biological systems in the Barents Sea. Physical conditions in this area are characterized by large seasonal contrasts between partial sea-ice cover in winter and spring versus predominantly open water in summer and ...

    • Underwater Hyperspectral Imaging of Arctic Macroalgal Habitats during the Polar Night Using a Novel Mini-ROV-UHI Portable System 

      Summers, Natalie; Johnsen, Geir; Mogstad, Aksel Alstad; Løvås, Håvard; Fragoso, Glaucia Moreira; Berge, Jørgen (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-09)
      We describe an Underwater Hyperspectral Imager (UHI) deployed on an instrumentcarrying platform consisting of two interconnected mini-ROVs (Remotely Operated Vehicle) for the mapping and monitoring of Arctic macroalgal habitats in Kongsfjorden (Svalbard) during the Polar Night. The mini-ROV-UHI system is easy to transport, assemble and deploy from shore, even under the dark, icy and cold conditions ...

    • Use of an Autonomous Surface Vehicle reveals small-scale diel vertical migrations of zooplankton and susceptibility to light pollution under low solar irradiance 

      Ludvigsen, Martin; Berge, Jørgen; Geoffroy, Maxime; Cohen, Jonathan H.; De La Torre, Pedro R.; Nornes, Stein Melvær; Singh, Hanumant; Sørensen, Asgeir Johan; Daase, Malin; Johnsen, Geir (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-10)
      Light is a major cue for nearly all life on Earth. However, most of our knowledge concerning the importance of light is based on organisms’ response to light during daytime, including the dusk and dawn phase. When it is dark, light is most often considered as pollution, with increasing appreciation of its negative ecological effects. Using an Autonomous Surface Vehicle fitted with a hyperspectral ...