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Sökning: L773:0967 0637 OR L773:1879 0119

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  • Belkin, Igor, et al. (författare)
  • On the discovery of ferromanganese nodules in the world ocean
  • 2021
  • Ingår i: Deep Sea Research Part I. - : Elsevier. - 0967-0637 .- 1879-0119. ; 175
  • Tidskriftsartikel (refereegranskat)abstract
    • For a century, the discovery of ferromanganese (Fe–Mn) nodules in the World Ocean was universally and indisputably credited to the Challenger circum-global oceanographic expedition of 1872–1876, during which the first manganese nodules and crusts were dredged up from the sea floor in February–March 1873. A century later, a counterclaim appeared in the literature, crediting Nordenskiold ¨ ’s expedition on Sofia in 1868, five years before the Challenger findings, for the discovery of Fe–Mn nodules in the ocean. This counterclaim, widely accepted without scrutiny, was based on the Gustaf Lindstrom ¨ (1884) chemical analysis of a single bottom sediment sample among 14 samples from two Arctic expeditions led by Nordenskiold: ¨ Sofia 1868 and Vega 1878–1880. The Lindstrom ¨ (1884) report published as an eight-page brochure in Swedish remained almost unknown to the research community until now. A close examination of this report and other historical evidence revealed that the counterclaim of discovery by the Sofia 1868 expedition to the Kara Sea is invalid based on three notable facts: (1) Sofia never sailed in the Kara Sea; (2) the single bottom sediment sample with an extremely high content of Mn (24%), was collected in the Kara Sea during the Vega Expedition across the Northeast Passage; (3) the Vega sampling was in 1878, not in 1868. Meanwhile, five and a half years prior to the Vega sampling, the first Fe–Mn nodules and crusts were dredged up from the sea floor on 18 February and March 7, 1873 during the Challenger expedition. These findings have been promptly reported and published in May 1873. Thus, the credit for the discovery of ferromanganese nodules in the World Ocean firmly belongs to the Challenger expedition.
  • Björk, Göran, 1956, et al. (författare)
  • Flow of Canadian Basin Deep Water in the Western Eurasian Basin of the Arctic Ocean
  • 2010
  • Ingår i: Deep Sea Research. - 0967-0637 .- 1879-0119. ; 57:4, s. 577-586
  • Tidskriftsartikel (refereegranskat)abstract
    • The LOMROG 2007 expedition targeted the previously unexplored southern part of the Lomonosov Ridge north of Greenland together with a section from the Morris Jesup Rise to Gakkel Ridge. The oceanographic data shows that Canadian Basin Deep Water (CBDW) passes the Lomonosov Ridge in the area of the Intra Basin close to the North Pole and then continues along the ridge towards Greenland and further along its northernmost continental slope. The CBDW is clearly evident as a salinity maximum and oxygen minimum at a depth of about 2000 m. The cross slope sections at the Amundsen Basin side of the Lomonosov Ridge and further south at the Morris Jesup Rise show a sharp frontal structure higher up in the water column between Makarov Basin water and Amundsen Basin water. The frontal structure continues upward into the Atlantic Water up to a depth of about 300 m. The observed water mass division at levels well above the ridge crest indicates a strong topographic steering of the flow and that different water masses tend to pass the ridge guided by ridge-crossing isobaths at local topographic heights and depressions. A rough scaling analysis shows that the extremely steep and sharply turning bathymetry of the Morris Jesup Rise may force the boundary current to separate and generate deep eddies.
  • Chambault, Philippine, et al. (författare)
  • The Gulf Stream frontal system : A key oceanographic feature in the habitat selection of the leatherback turtle?
  • 2017
  • Ingår i: Deep Sea Research Part I. - 0967-0637 .- 1879-0119. ; 123, s. 35-47
  • Tidskriftsartikel (refereegranskat)abstract
    • Although some associations between the leatherback turtle Dermochelys coriacea and the Gulf Stream current have been previously suggested, no study has to date demonstrated strong affinities between leatherback movements and this particular frontal system using thorough oceanographic data in both the horizontal and vertical dimensions. The importance of the Gulf Stream frontal system in the selection of high residence time (HRT) areas by the North Atlantic leatherback turtle is assessed here for the first time using state-of-the-art ocean reanalysis products. Ten adult females from the Eastern French Guianese rookery were satellite tracked during post-nesting migration to relate (1) their horizontal movements to physical gradients (Sea Surface Temperature (SST), Sea Surface Height (SSH) and filaments) and biological variables (micronekton and chlorophyll a), and (2) their diving behaviour to vertical structures within the water column (mixed layer, thermocline, halocline and nutricline). All the turtles migrated northward towards the Gulf Stream north wall. Although their HRT areas were geographically remote (spread between 80-30 degrees W and 28-45 degrees N), all the turtles targeted similar habitats in terms of physical structures, i.e. strong gradients of SST, SSH and a deep mixed layer. This close association with the Gulf Stream frontal system highlights the first substantial synchronization ever observed in this species, as the HRTs were observed in close match with the autumn phytoplankton bloom. Turtles remained within the enriched mixed layer at depths of 38.5 +/- 7.9 m when diving in HRT areas, likely to have an easier access to their prey and maximize therefore the energy gain. These depths were shallow in comparison to those attained within the thermocline (82.4 +/- 5.6 m) while crossing the nutrient-poor subtropical gyre, probably to reach cooler temperatures and save energy during the transit. In a context of climate change, anticipating the evolution of such frontal structure under the influence of global warming is crucial to ensure the conservation of this vulnerable species.
  • Cranston, Alex, et al. (författare)
  • A population specific mitochondrial intron from the sponge Phakellia robusta in the North-East Atlantic
  • 2021
  • Ingår i: Deep Sea Research Part I. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0967-0637 .- 1879-0119. ; 172
  • Tidskriftsartikel (refereegranskat)abstract
    • Self-splicing mitochondrial introns are a rarely reported phenomenon in animals, with a sparse and uneven distribution confined to some species of sponges, corals, placozoans, and a single species of annelid. Here, we describe a mitochondrial intron present only in some populations of Phakellia robusta, a sponge distributed across the North-east Atlantic deep-sea. The mitochondrial intron of P. robusta was detected in the position 387 of the COI gene and classified as a Group I intron of class IB. Interestingly, this intron was only detected in the shallower populations of P. robusta from Ireland to Norway, spanning 1000 km and was absent in deeper samples of the species. Such deeper populations have recently been proposed to be the result of hybridization between P. robusta and its congeneric Phakellia hirondellei. We propose that this past hybridization might be behind the absence of the intron in the specimens of P. robusta occurring at deep waters. Our analyses indicate that the intron detected in P. robusta might have a double origin (most likely fungi and other organism), as it has previously suggested for the sponge Stupenda singularis. BLAST searches produced matches with the homing endonuclease gene (HEG) nested within the S. singularis intron and this HEG belongs to the family of LAGLIDADG homing endonucleases (LHEs). The evolutionary relevance of the presence/absence of this intron for this species needs to be determined and potential adaptive advantages should not be ruled out.
  • Darelius, E., et al. (författare)
  • Downward flow of dense water leaning on a submarine ridge
  • 2007
  • Ingår i: deep sea research part I. ; 54:7, s. 1173-1188
  • Tidskriftsartikel (refereegranskat)abstract
    • Large-scale dense bottom currents are geostrophic to leading order, with the main flow direction along the continental slope. Bottom friction makes the water descend to greater depths, but only at a small angle to the horizontal. Here the effect of a submarine ridge that intersects the slope is considered. It is shown that the presence of a submarine ridge greatly enhances the downward transport. By leaning against the ridge it is possible for the dense water to flow downhill, perpendicular to the depth contours, even though the first-order dynamics are geostrophic. The requirement for downward flow next to the ridge is that the frictional transport that it induces is sufficiently large to counteract geostrophic advection along the isobaths and out of the ridge region. The dynamics are similar to those of downward flow in submarine canyons, but ridges appear to be more effective in channeling the dense water downhill, in particular for narrow ridges/canyons with small seaward slope of the ridge/canyon axis. The downward flow is analyzed using a simplified analytical model and the results are compared to data from the Filchner Overflow, which agree qualitatively with the model.
  • Eerkes-Medrano, Dafne, et al. (författare)
  • A community assessment of the demersal fish and benthic invertebrates of the Rosemary Bank Seamount marine protected area (NE Atlantic)
  • 2020
  • Ingår i: Deep Sea Research Part I. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0967-0637 .- 1879-0119. ; 156
  • Tidskriftsartikel (refereegranskat)abstract
    • The Rosemary Bank Seamount in the NE Atlantic was designated a Marine Protected Area in 2014 by the Scottish Government. Visual and trawl surveys of the seamount have been undertaken since 2007. Here these data are compiled and analysed to provide an assessment of the communities of demersal fish and benthic invertebrates found there. The fish and benthic invertebrate communities changed markedly with depth. Cluster analysis revealed at least four distinct communities of fish: those on the summit, the mid slope, the lower slope and the deep moat at the base of the seamount. The invertebrate community changed at a depth of 1100 m, where mixed-species sponge aggregations dominated to depths of 1500 m. The seamount is an important site for vulnerable marine ecosystems, most notably the extensive and unusually diverse deep-sea sponge grounds on the lower slope. Other prioritised conservation species and habitats recorded included cold water corals, orange roughy, blue ling, leafscale gulper shark and the Portuguese dogfish. Due to sampling constraints some areas of the seamount still remain unknown. A precautionary approach to protecting the entire seamount would achieve multiple conservation objectives. The data presented here serve as a base-line to assess the impact of management intervention in the future.
  • Giongo, Adriana, et al. (författare)
  • Discovery of a chemosynthesis-based community in the western South Atlantic Ocean
  • 2016
  • Ingår i: Deep Sea Research Part I. - : Elsevier. - 0967-0637 .- 1879-0119. ; 112, s. 45-56
  • Tidskriftsartikel (refereegranskat)abstract
    • Chemosynthetic communities have been described from a variety of deep-sea environments across the world's oceans. They constitute very interesting biological systems in terms of their ecology, evolution and biogeography, and also given their potential as indicators of the presence and abundance of consistent hydrocarbon-based nutritional sources. Up to now such peculiar biotic assemblages have not been reported for the western South Atlantic Ocean, leaving this large region undocumented with respect to the presence, composition and history of such communities. Here we report on the presence of a chemosynthetic community off the coast of southern Brazil, in an area where high-levels of methane and the presence of gas hydrates have been detected. We performed metagenomic analyses of the microbial community present at this site, and also employed molecular approaches to identify components of its benthic fauna. We conducted phylogenetic analyses comparing the components of this assemblage to those found elsewhere in the world, which allowed a historical assessment of the structure and dynamics of these systems. Our results revealed that the microbial community at this site is quite diverse, and contains many components that are very closely related to lineages previously sampled in ecologically similar environments across the globe. Anaerobic methanotrophic (ANME) archaeal groups were found to be very abundant at this site, suggesting that methane is indeed an important source of nutrition for this community. In addition, we document the presence at this site of a vestimentiferan siboglinid polychaete and the bivalve Acharax sp., both of which are typical components of deep-sea chemosynthetic communities. The remarkable similarity in biotic composition between this area and other deep-sea communities across the world supports the interpretation that these assemblages are historically connected across the global oceans, undergoing colonization from distant sites and influenced by local ecological features that select a stereotyped suite of specifically adapted organisms. (C) 2015 Elsevier Ltd. All rights reserved.
  • Graham, Robert M., et al. (författare)
  • Identifying sources and transport pathways of iron in the Southern Ocean
  • Ingår i: Deep Sea Research Part I. - 0967-0637 .- 1879-0119.
  • Tidskriftsartikel (refereegranskat)abstract
    • Over large regions of the global ocean primary productivity is limited by the availability of dissolved iron. Changes in the supply of iron to these regions could have major impacts on primary productivity and the carbon cycle. One of the largest sources of dissolved iron to the ocean is thought to be from shelf sediments, and this source is often parameterized in biogeochemical models as a depth dependent iron flux through the seafloor. Using the knowledge that Southern Ocean surface waters are iron limited, we infer source regions of iron to the Southern Ocean by identifying where the most intense chlorophyll blooms develop. We further derive surface current patterns from satellite sea surface height fields to assess the role of the ocean circulation in transporting iron away from these source regions. We find a tight relationship between satellite chlorophyll concentrations and sea surface height. Large chlorophyll blooms develop on the shelf and where the western boundary currents detach from the continental shelves and turn eastward into the Southern Ocean. This is likely due to shelf supplied iron becoming entrained into western boundary currents and advected into the Southern Ocean along the Dynamical Subtropical Front. The most intense chlorophyll blooms are located along coastal margins of islands and continents. Blooms do not develop over submerged seamounts or plateaus in the open ocean. This suggests that shelf sediments in coastal regions act as large bioavailable iron sources to the Southern Ocean. We recommend that a more accurate method of parameterizing the shelf sediment iron flux could be to prescribe this flux only through grid cells neighboring coastlines. Finally, we hypothesize how changes in sea level during glacial-interglacial cycles may have altered the distribution of shelf sediment iron sources in the Southern Ocean and helped to drive export production anomalies in the Sub-Antarctic Zone.
  • Graham, Robert M., et al. (författare)
  • Inferring source regions and supply mechanisms of iron in the Southern Ocean from satellite chlorophyll data
  • 2015
  • Ingår i: Deep Sea Research Part I. - 0967-0637 .- 1879-0119. ; 104, s. 9-25
  • Tidskriftsartikel (refereegranskat)abstract
    • Primary productivity is limited by the availability of iron over large areas of the global ocean. Changes in the supply of iron to these regions could have major impacts on primary productivity and the carbon cycle. However, source regions and supply mechanisms of iron to the global oceans remain poorly constrained. Shelf sediments are considered one of the largest sources of dissolved iron to the global ocean, and a large shelf sediment iron flux is prescribed in many biogeochemical models over all areas of bathymetry shallower than 1000 m. Here, we infer the likely location of shelf sediment iron sources in the Southern Ocean, by identifying where satellite chlorophyll concentrations are enhanced over shallow bathymetry (< 1000 m). We further compare chlorophyll concentrations with the position of ocean fronts, to assess the relative role of horizontal advection and upwelling for supplying iron to the ocean surface. We show that mean annual chlorophyll concentrations are not visibly enhanced over areas of shallow bathymetry that are located more than 500 km from a coastline. Mean annual chlorophyll concentrations > 2 mg m(-3) are only found within 50 km of a continental or island coastline. These results suggest that sedimentary iron sources only exist on continental and island shelves. Large sedimentary iron fluxes do not seem present on seamounts and submerged plateaus. Large chlorophyll blooms develop where the western boundary currents detach from the continental shelves, and turn eastward into the Sub-Antarctic Zone. Chlorophyll concentrations are enhanced along contours of sea surface height extending off the continental shelves, as shown by the trajectories of virtual water parcels in satellite altimetry data. These analyses support the hypothesis that bioavailable iron from continental shelves is entrained into western boundary currents, and advected into the Sub-Antarctic Zone along the Dynamical Subtropical Front. Our results indicate that upwelling at fronts in the open ocean is unlikely to deliver iron to the ocean surface from deep sources. Finally, we hypothesise how a reduction in sea level may have altered the distribution of shelf sediment iron sources in the Southern Ocean and increased export production over the Sub-Antarctic Zone during glacial intervals.
  • Gustafsson, Örjan, et al. (författare)
  • Th-234-derived surface export fluxes of POC from the Northern Barents Sea and the Eurasian sector of the Central Arctic Ocean
  • 2012
  • Ingår i: Deep Sea Research Part I. - 0967-0637 .- 1879-0119. ; 68, s. 1-11
  • Tidskriftsartikel (refereegranskat)abstract
    • Settling-based surface ocean export of particulate organic carbon (POC) in the western Eurasian sector of the Arctic Ocean was investigated from the marginal ice zone (MIZ) of the northern Barents Sea to the North Pole area. Upper ocean profiles of POC were combined with corresponding dissolved and particulate Th-234 activities measured with a low-volume at-sea direct beta counting protocol to constrain the Th-234-derived POC export in July and August of 2001 to 6-32 mmol m(-2) d(-1) for the Barents Sea MIZ dropping to 2-6 mmol m(-2) d(-1) for multi-year-ice (MYI) covered central Arctic stations in Nansen, Amundsen and Makarov basins. Secular equilibrium between Th-234 and U-238 activities in intermediate to deep waters in the Amundsen Basin (n=10) demonstrated that the at-sea measurement protocol was functioning satisfactorily. There was no distinction in POC export efficiency between the MIZ and the MYI-covered interior basins with an average ratio between Th-234-derived POC export and primary production (so-called ThE ratio) of 44%. A projected increase in primary production with retreat in areal extent of sea ice is thus likely to yield increased POC sequestration in the Arctic Ocean interior.
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