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  • Online Resource  (9)
  • Wiley  (9)
  • Iversen, Morten H.  (9)
  • 1
    Online Resource
    Online Resource
    Microbial communities in the nepheloid layers and hypoxic zones of the Canary Current upwelling system
    Wiley ; 2019
    In:  MicrobiologyOpen Vol. 8, No. 5 ( 2019-05)
    Details
    In: MicrobiologyOpen, Wiley, Vol. 8, No. 5 ( 2019-05)
    Abstract: Eastern boundary upwelling systems ( EBUS s) are among the most productive marine environments in the world. The Canary Current upwelling system off the coast of Mauritania and Morocco is the second most productive of the four EBUS , where nutrient‐rich waters fuel perennial phytoplankton blooms, evident by high chlorophyll a concentrations off Cape Blanc, Mauritania. High primary production leads to eutrophic waters in the surface layers, whereas sinking phytoplankton debris and horizontally dispersed particles form nepheloid layers ( NL s) and hypoxic waters at depth. We used Catalyzed Reporter Deposition Fluorescence In Situ Hybridization ( CARD ‐ FISH ) in combination with fatty acid (measured as methyl ester; FAME ) profiles to investigate the bacterial and archaeal community composition along transects from neritic to pelagic waters within the “giant Cape Blanc filament” in two consecutive years (2010 and 2011), and to evaluate the usage of FAME data for microbial community studies. We also report the first fatty acid profile of Pelagibacterales strain HTCC 7211 which was used as a reference profile for the SAR 11 clade. Unexpectedly, the reference profile contained low concentrations of long chain fatty acids 18:1 cis 11, 18:1 cis 11 11methyl, and 19:0 cyclo11–12 fatty acids, the main compounds in other Alphaproteobacteria . Members of the free‐living SAR 11 clade were found at increased relative abundance in the hypoxic waters in both years. In contrast, the depth profiles of Gammaproteobacteria (including Alteromonas and Pseudoalteromonas ), Bacteroidetes , Roseobacter , and Synechococcus showed high abundances of these groups in layers where particle abundance was high, suggesting that particle attachment or association is an important mechanisms of dispersal for these groups. Collectively, our results highlight the influence of NL s, horizontal particle transport, and low oxygen on the structure and dispersal of microbial communities in upwelling systems.
    Type of Medium: Online Resource
    ISSN: 2045-8827 , 2045-8827
    URL: Issue
    URL: Article
    DOI: 10.1002/mbo3.2019.8.issue-5
    DOI: 10.1002/mbo3.705
    Language: English
    Publisher: Wiley
    Publication Date: 2019
    detail.hit.zdb_id: 2661368-2
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  • 2
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    Effects of Atlantification and changing sea‐ice dynamics on zooplankton community structure and carbon flux between 2000 and 2016 in the eastern Fram Strait
    Wiley ; 2023
    In:  Limnology and Oceanography Vol. 68, No. S1 ( 2023-06)
    Details
    In: Limnology and Oceanography, Wiley, Vol. 68, No. S1 ( 2023-06)
    Abstract: The collection of zooplankton swimmers and sinkers in time‐series sediment traps provides unique insight into year‐round and interannual trends in zooplankton population dynamics. These samples are particularly valuable in remote and difficult to access areas such as the Arctic Ocean, where samples from the ice‐covered season are rare. In the present study, we investigated zooplankton composition based on swimmers and sinkers collected by sediment traps at water depths of 180–280, 800–1320, and 2320–2550 m, over a period of 16 yr (2000–2016) at the Long‐Term Ecological Research observatory HAUSGARTEN located in the eastern Fram Strait (79°N, 4°E). The time‐series data showed seasonal and interannual trends within the dominant zooplankton groups including copepoda, foraminifera, ostracoda, amphipoda, pteropoda, and chaetognatha. Amphipoda and copepoda dominated the abundance of swimmers while pteropoda and foraminifera were the most important sinkers. Although the seasonal occurrence of these groups was relatively consistent between years, there were notable interannual variations in abundance, suggesting the influence of various environmental conditions such as sea‐ice dynamic and lateral advection of water masses, for example, meltwater and Atlantic water. Statistical analyses revealed a correlation between the Arctic dipole climatic index and sea‐ice dynamics (i.e., ice coverage and concentration), as well as the importance of the distance from the ice edge on swimmer composition patterns and carbon export.
    Type of Medium: Online Resource
    ISSN: 0024-3590 , 1939-5590
    URL: Issue
    URL: Article
    DOI: 10.1002/lno.v68.S1
    DOI: 10.1002/lno.12192
    Language: English
    Publisher: Wiley
    Publication Date: 2023
    detail.hit.zdb_id: 2033191-5
    detail.hit.zdb_id: 412737-7
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  • 3
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    Flow and diffusion around and within diatom aggregates: Effects of aggregate composition and shape
    Wiley ; 2020
    In:  Limnology and Oceanography Vol. 65, No. 8 ( 2020-08), p. 1818-1833
    Details
    In: Limnology and Oceanography, Wiley, Vol. 65, No. 8 ( 2020-08), p. 1818-1833
    Abstract: Diatom aggregates constitute a significant fraction of the particle flux from the euphotic zone into the mesopelagic ocean as part of the ocean's biological carbon pump. Modeling studies of their exchange processes with the surrounding water usually assume spherical shape and that aggregates are impermeable to flow. Using particle image velocimetry, we examined flow distributions around individual aggregates of various irregular shapes formed from two different diatom species: (1) Skeletonema marinoi , known for its cell–cell stickiness, and (2) Chaetoceros affinis , exhibiting cell‐TEP (transparent exopolymeric particles) stickiness. Chaetoceros aggregates formed porous, highly irregularly shaped aggregates as compared to the more compact and near‐spherical Skeletonema aggregates, yet flow distributions around both types of aggregates were relatively similar at a millimeter scale. At a micrometer scale, the irregular shape of diatom aggregates caused velocity gradients and vorticity close to the surface to locally vary more than for spherical model aggregates (agar‐yeast spheres). Water was deflected from the surface of all aggregate types and we found no direct evidence that flow occurred within aggregates. Digital holographic imaging and Alcian blue staining revealed a substantial presence of TEP likely clogging the interstitial pore spaces in Chaetoceros aggregates. Radial oxygen concentration distributions measured by O 2 microsensors within the aggregates were similar to those modeled for aggregates and spheres impermeable to flow. Thus, transport of gases, nutrients, and solutes likely occurs by diffusion, even within large, irregularly shaped diatom aggregates during sinking.
    Type of Medium: Online Resource
    ISSN: 0024-3590 , 1939-5590
    URL: Issue
    URL: Article
    DOI: 10.1002/lno.v65.8
    DOI: 10.1002/lno.11420
    Language: English
    Publisher: Wiley
    Publication Date: 2020
    detail.hit.zdb_id: 2033191-5
    detail.hit.zdb_id: 412737-7
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  • 4
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    Featured L&O E‐Lecture: The Ocean's Biological Carbon Pump as Part of the Global Carbon Cycle
    Wiley ; 2016
    In:  Limnology and Oceanography Bulletin Vol. 25, No. 1 ( 2016-02), p. 22-23
    Details
    In: Limnology and Oceanography Bulletin, Wiley, Vol. 25, No. 1 ( 2016-02), p. 22-23
    Type of Medium: Online Resource
    ISSN: 1539-607X , 1539-6088
    URL: Issue
    URL: Article
    DOI: 10.1002/lob.v25.1
    DOI: 10.1002/lob.10083
    Language: English
    Publisher: Wiley
    Publication Date: 2016
    detail.hit.zdb_id: 2241831-3
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  • 5
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    Online Resource
    Embedding and slicing of intact in situ collected marine snow
    Wiley ; 2018
    In:  Limnology and Oceanography: Methods Vol. 16, No. 6 ( 2018-06), p. 339-355
    Details
    In: Limnology and Oceanography: Methods, Wiley, Vol. 16, No. 6 ( 2018-06), p. 339-355
    Abstract: The biological carbon pump is largely driven by the formation and sinking of marine snow. Because of their high organic matter content, marine snow aggregates are hotspots for microbial activity, and microbial organic matter degradation plays an important role in the attenuation of carbon fluxes to the deep sea. Our inability to examine and characterize microscale distributions of compounds making up the aggregate matrix, and of possible niches inside marine snow, has hindered our understanding of the basic processes governing marine carbon export and sequestration. To address this issue, we have adapted soft‐embedding and sectioning to study the spatial structure and components of marine aggregates at high resolution. Soft‐embedding enables rapid quantitative sampling of undisturbed marine aggregates from the water column and from sediment traps, followed by spatially resolved staining and characterization of substrates of the aggregate matrix and the microorganisms attached to it. Particular strengths of the method include in situ embedding in sediment traps and successful fluorescence in situ hybridization (FISH)‐probe labeling, supporting studies of microbial diversity and ecology. The high spatial resolution achieved by thin‐sectioning of soft‐embedded aggregates offers the possibility for improved understanding of the composition and structure of marine snow, which directly influence settling velocity, microbial colonization and diversity, degradation rates, and carbon content. Our method will help to elucidate the small‐scale processes underlying large‐scale carbon cycling in the marine environment, which is especially relevant in the context of rising anthropogenic CO 2 emissions and global change.
    Type of Medium: Online Resource
    ISSN: 1541-5856 , 1541-5856
    URL: Issue
    URL: Article
    DOI: 10.1002/lom3.v16.6
    DOI: 10.1002/lom3.10251
    Language: English
    Publisher: Wiley
    Publication Date: 2018
    detail.hit.zdb_id: 2161715-6
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  • 6
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    New guidelines for the application of Stokes' models to the sinking velocity of marine aggregates
    Wiley ; 2020
    In:  Limnology and Oceanography Vol. 65, No. 6 ( 2020-06), p. 1264-1285
    Details
    In: Limnology and Oceanography, Wiley, Vol. 65, No. 6 ( 2020-06), p. 1264-1285
    Abstract: Numerical simulations of ocean biogeochemical cycles need to adequately represent particle sinking velocities (SV). For decades, Stokes' Law estimating particle SV from density and size has been widely used. But while Stokes' Law holds for small, smooth, and rigid spheres settling at low Reynolds number, it fails when applied to marine aggregates complex in shape, structure, and composition. Minerals and zooplankton can alter phytoplankton aggregates in ways that change their SV, potentially improving the applicability of Stokes' models. Using rolling cylinders, we experimentally produced diatom aggregates in the presence and absence of minerals and/or microzooplankton. Minerals and to a lesser extent microzooplankton decreased aggregate size and roughness and increased their sphericity and compactness. Stokes' Law parameterized with a fractal porosity modeled adequately size‐SV relationships for mineral‐loaded aggregates. Phytoplankton‐only aggregates and those exposed to microzooplankton followed the general Navier‐Stokes drag equation suggesting an indiscernible effect of microzooplankton and a drag coefficient too complex to be calculated with a Stokes' assumption. We compared our results with a larger data set of ballasted and nonballasted marine aggregates. This confirmed that the size‐SV relationships for ballasted aggregates can be simulated by Stokes' models with an adequate fractal porosity parameterization. Given the importance of mineral ballasting in the ocean, our findings could ease biogeochemical model parameterization for a significant pool of particles in the ocean and especially in the mesopelagic zone where the particulate organic matter : mineral ratio decreases. Our results also reinforce the importance of accounting for porosity as a decisive predictor of marine aggregate SV.
    Type of Medium: Online Resource
    ISSN: 0024-3590 , 1939-5590
    URL: Issue
    URL: Article
    DOI: 10.1002/lno.v65.6
    DOI: 10.1002/lno.11388
    Language: English
    Publisher: Wiley
    Publication Date: 2020
    detail.hit.zdb_id: 2033191-5
    detail.hit.zdb_id: 412737-7
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  • 7
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    Hard and soft plastic resin embedding for single‐cell element uptake investigations of marine‐snow‐associated microorganisms using nano‐scale secondary ion mass spectrometry
    Wiley ; 2018
    In:  Limnology and Oceanography: Methods Vol. 16, No. 8 ( 2018-08), p. 484-503
    Details
    In: Limnology and Oceanography: Methods, Wiley, Vol. 16, No. 8 ( 2018-08), p. 484-503
    Abstract: Marine snow aggregates are microhabitats for diverse microbial communities with various active metabolic pathways. Rapid recycling and symbiotic transfer of nutrients within aggregates poses a significant challenge for accurately assessing aggregate‐associated turnover rates. Although single‐cell uptake measurements are well‐established for free‐living microorganisms, suitable methods for cells embedded in marine snow are currently lacking. Comparable cell‐specific measurements within sinking pelagic aggregates would have the potential to address core questions regarding aggregate‐associated fluxes. However, the capacity to perform microscale studies is limited by the difficulty of sampling and preserving the fragile aggregate structure. Furthermore, the application of nano‐scale secondary ion mass spectrometry (NanoSIMS) to aggregates is complicated by technical requirements related to vacuum and ablation resistance. Here, we present a NanoSIMS‐optimized method for fixation, embedding, and sectioning of marine snow. Stable isotope labeling of laboratory‐generated aggregates enabled visualization of label incorporation into prokaryotic and eukaryotic cells embedded in the aggregate structure. The current method is also amenable to various staining procedures, including transparent exopolymer particles, Coomassie stainable particles, nucleic acids, and eukaryotic cytoplasm. We demonstrate the potential for using structural stains to generate three‐dimensional (3D) models of marine snow and present a simplified calculation of porosity and fractal dimension. This multipurpose method enables combined investigations of 3D aggregate structure, spatial microbial distribution, and single‐cell activity within individual aggregates and provides new possibilities for future studies on microbial interactions and elemental uptake within marine snow.
    Type of Medium: Online Resource
    ISSN: 1541-5856 , 1541-5856
    URL: Issue
    URL: Article
    DOI: 10.1002/lom3.v16.8
    DOI: 10.1002/lom3.10261
    Language: English
    Publisher: Wiley
    Publication Date: 2018
    detail.hit.zdb_id: 2161715-6
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  • 8
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    Submesoscale physicochemical dynamics directly shape bacterioplankton community structure in space and time
    Wiley ; 2021
    In:  Limnology and Oceanography Vol. 66, No. 7 ( 2021-07), p. 2901-2913
    Details
    In: Limnology and Oceanography, Wiley, Vol. 66, No. 7 ( 2021-07), p. 2901-2913
    Abstract: Submesoscale eddies and fronts are important components of oceanic mixing and energy fluxes. These phenomena occur in the surface ocean for a period of several days, on scales between a few hundred meters and few tens of kilometers. Remote sensing and modeling suggest that eddies and fronts may influence marine ecosystem dynamics, but their limited temporal and spatial scales make them challenging for observation and in situ sampling. Here, the study of a submesoscale filament in summerly Arctic waters (depth 0–400 m) revealed enhanced mixing of Polar and Atlantic water masses, resulting in a ca. 4 km wide and ca. 50 km long filament with distinct physical and biogeochemical characteristics. Compared to the surrounding waters, the filament was characterized by a distinct phytoplankton bloom, associated with depleted inorganic nutrients, elevated chlorophyll a concentrations, as well as twofold higher phyto‐ and bacterioplankton cell abundances. High‐throughput 16S rRNA gene sequencing of bacterioplankton communities revealed enrichment of typical phytoplankton bloom‐associated taxonomic groups (e.g., Flavobacteriales ) inside the filament. Furthermore, linked to the strong water subduction, the vertical export of organic matter to 400 m depth inside the filament was twofold higher compared to the surrounding waters. Altogether, our results show that physical submesoscale mixing can shape distinct biogeochemical conditions and microbial communities within a few kilometers of the ocean. Hence, the role of submesoscale features in polar waters for surface ocean biodiversity and biogeochemical processes need further investigation, especially with regard to the fate of sea ice in the warming Arctic Ocean.
    Type of Medium: Online Resource
    ISSN: 0024-3590 , 1939-5590
    URL: Issue
    URL: Article
    DOI: 10.1002/lno.v66.7
    DOI: 10.1002/lno.11799
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 2033191-5
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  • 9
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    The ballasting effect of Saharan dust deposition on aggregate dynamics and carbon export: Aggregation, settling, and scavenging potential of marine snow
    Wiley ; 2018
    In:  Limnology and Oceanography Vol. 63, No. 3 ( 2018-05), p. 1386-1394
    Details
    In: Limnology and Oceanography, Wiley, Vol. 63, No. 3 ( 2018-05), p. 1386-1394
    Abstract: Lithogenic material such as Saharan dust can be incorporated into organic aggregates and act as ballast, potentially enhancing the marine carbon export via increased sinking velocities of aggregates. We studied the ballasting effects of Saharan dust on the aggregate dynamics in the upwelling region off Cape Blanc (Mauritania). Aggregate formation from a natural plankton community exposed to Saharan dust deposition resulted in higher abundance of aggregates with higher sinking velocities compared to aggregate formation with low dust. This higher aggregate abundance and sinking velocities potentially increased the carbon export 10‐fold when the aggregates were ballasted by Saharan dust. After aggregate formation in the surface waters, subsequent sinking through suspended Saharan dust minerals had no influence on aggregate sizes, abundance, and sinking velocities. We found that aggregates formed in the surface ocean off Mauritania were already heavily ballasted with lithogenic material and could therefore not scavenge any additional minerals during their descent. This suggests that carbon export to the deep ocean in regions with high dust deposition is strongly controlled by dust input to the surface ocean while suspended dust particles in deeper water layers do not significantly interact with sinking aggregates.
    Type of Medium: Online Resource
    ISSN: 0024-3590 , 1939-5590
    URL: Issue
    URL: Article
    DOI: 10.1002/lno.v63.3
    DOI: 10.1002/lno.10779
    Language: English
    Publisher: Wiley
    Publication Date: 2018
    detail.hit.zdb_id: 2033191-5
    detail.hit.zdb_id: 412737-7
    SSG: 12
    SSG: 14
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