Artikler, rapporter og annet (geovitenskap): Recent submissions

Now showing items 341-360 of 729

    • Fast and slow components of interstadial warming in the North Atlantic during the last glacial 

      Margari, Vasiliki; Skinner, Luke C.; Menviel, Laurie; Capron, Emilie; Rhodes, Rachael H; Mleneck-Vautravers, Maryline J.; Ezat, Mohamed; Martrat, Belen; Grimalt, Joan O.; Hodell, David A; Tzedakis, Polychronis (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-08-13)
      The abrupt nature of warming events recorded in Greenland ice-cores during the last glacial has generated much debate over their underlying mechanisms. Here, we present joint marine and terrestrial analyses from the Portuguese Margin, showing a succession of cold stadials and warm interstadials over the interval 35–57 ka. Heinrich stadials 4 and 5 contain considerable structure, with a short ...

    • REE+Y uptake and diagenesis in Recent sedimentary apatites 

      Lumiste, Kaarel; Mänd, Kaarel; Bailey, Juke; Paiste, Päärn; Lang, Liisa; Lepland, Aivo; Kirsimäe, Kalle (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-30)
      Rare Earth Elements and Yttrium (REE+Y) distribution in authigenic phases are frequently used as proxies for reconstructing past seawater conditions. Sedimentary apatite precipitates near the sediment-water interface and is therefore capable of recording the REE+Y composition of the overlying water column. While the overprinting of primary REE+Y signal during late stage diagenesis is a widely known ...

    • Palaeoproterozoic oxygenated oceans following the Lomagundi–Jatuli Event 

      Mänd, Kaarel; Lalonde, Stefan V.; Robbins, Leslie J.; Thoby, Marie; Paiste, Kärt; Kreitsmann, Timmu; Paiste, Päärn; Reinhard, Christopher T.; Romashkin, Alexandr E.; Planavsky, Noah J.; Kirsimäe, Kalle; Lepland, Aivo; Konhauser, Kurt O. (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-03-16)
      The approximately 2,220–2,060 million years old Lomagundi–Jatuli Event was the longest positive carbon isotope excursion in Earth history and is traditionally interpreted to reflect an increased organic carbon burial and a transient rise in atmospheric O<sub>2</sub>. However, it is widely held that O<sub>2</sub> levels collapsed for more than a billion years after this. Here we show that black shales ...

    • Past ice sheet-seabed interactions in the northeastern Weddell Sea embayment, Antarctica 

      Arndt, Jan Erik; Larter, Robert D.; Hillenbrand, Claus-Dieter; Sørli, Simon H.; Forwick, Matthias; Smith, James A.; Wacker, Lukas (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-06-30)
      The Antarctic ice sheet extent in the Weddell Sea embayment (WSE) during the Last Glacial Maximum (LGM; ca. 19–25 calibrated kiloyears before present, ka cal BP) and its subsequent retreat from the shelf are poorly constrained, with two conflicting scenarios being discussed. Today, the modern Brunt Ice Shelf, the last remaining ice shelf in the northeastern WSE, is only pinned at a single location ...

    • Hydrothermal dedolomitisation of carbonate rocks of the Paleoproterozoic Zaonega Formation, NW Russia — Implications for the preservation of primary C isotope signals 

      Kreitsmann, Timmu; Külaviir, Marian; Lepland, Aivo; Paiste, Kärt; Paiste, Päärn; Prave, Anthony R.; Sepp, Holar; Romashkin, Alexander E; Rychanchik, Dmitry V.; Kirsimäe, Kalle (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-03-03)
      The Paleoproterozoic Zaonega Formation in Karelia, NW Russia, has played a key role in understanding the environmental conditions postdating the Great Oxidation and Lomagundi-Jatuli Events. Its carbonate- and organic-rich rocks (shungite) define the postulated Shunga Event representing an accumulation of very organic-rich sediments at c. 2 Ga and are central in ideas about changing ocean-atmosphere ...

    • The effect of an experimental decrease in salinity on the viability of the subarctic planktonic foraminifera Neogloboquadrina incompta 

      Greco, Mattia; Meilland, Julie; Zamelczyk, Kasia; Rasmussen, Tine Lander; Kucera, Michal (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-08-27)
      Chemical signatures in the calcite of shells of polar and subpolar planktonic foraminifera have been frequently used to trace and quantify past meltwater discharge events. This approach assumes that the foraminifera can tolerate low salinity under extended periods. To obtain a first experimental constraint on salinity tolerance of Subarctic foraminifera, we carried out a culturing experiment with ...

    • The tectonized central peak of the Mjølnir Impact Crater, Barents Sea 

      Corseri, Romain; Gac, Sebastien; Faleide, Jan Inge; Planke, Sverre (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-12-04)
      The Mjølnir structure, SW Barents Sea, is one of the best-preserved marine impact craters on Earth. After impact on the paleo-seafloor about 142 Ma ago, this crater experienced an atypical deformation of its central peak, which is now elevated ~435 m above the crater rims. Here, we investigate the effect of far-field tectonic stresses on the central peak uplift based on interpretation of new ...

    • Transferring grains from single-grain luminescence discs to SEM specimen stubs 

      Doverbratt, Isa; Alexanderson, Helena (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-11-21)
      The grain transfer protocol presents a step-by-step guide on how to successfully transfer positioned grains from a single-grain luminescence disc to a scanning electron microscope (SEM) specimen stub and how to transport them between laboratories. Single-grain luminescence analysis allows the determination of luminescence characteristics for individual sand-sized grains. By combining such luminescence ...

    • Adamastor – an ocean that never existed? 

      Konopasek, Jiri; Cavalcante, Carolina; Fossen, Haakon; Janoušek, Vojtěch (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-05-08)
      <p>Existing models of tectonic evolution of the Neoproterozoic orogenic system rimming the shores of the South Atlantic Ocean (the Araçuaí–Ribeira–Congo and Dom Feliciano–Kaoko–Gariep belts) interpret the belts as subduction-related orogens and emphasize the role of the “Adamastor Ocean” in their pre-collisional evolution. A critical problem in such an interpretation is the confined nature of the ...

    • Redox fluctuations, trace metal enrichment and phosphogenesis in the ~2.0 Ga Zaonega Formation 

      Kipp, Michael A.; Lepland, Aivo; Buick, Roger (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-03-24)
      The ~2.0 Ga Zaonega Formation (ZF) holds one of the oldest phosphorites in the geologic record, reaching >15% P<sub>2</sub>O<sub>5</sub>. Understanding the depositional conditions that enabled sedimentary phosphorus enrichment in this unit will thus help us to interpret the significance of the temporal distribution of phosphorites in Earth’s early history. Here we use an array of major and trace ...

    • Reduced Arctic sea ice extent during the mid-Pliocene Warm Period concurrent with increased Atlantic-climate regime 

      Rahaman, Waliur; Smik, Lukas; Köseoğlu, Denizcan; Lathika, N.; Tarique, Mohd; Thamban, Meloth; Haywood, Alan; Belt, Simon T.; Knies, Jochen (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-01)
      Quantifying the contribution of poleward oceanic heat transport to the Arctic Ocean is important for making future sea ice and climate predictions. To highlight its potential importance in a warmer world, we present a new record of water-mass exchange between the Atlantic and the Arctic Oceans using the authigenic neodymium isotopic composition of marine sediments from the Fram Strait during the ...

    • Salt-driven evolution of a gas hydrate reservoir in Green Canyon, Gulf of Mexico 

      Portnov, Aleksei D; Cook, Ann E.; Heidari, Mahdi; Sawyer, Derek E.; Nikolinakou, Maria (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09)
      The base of the gas hydrate stability zone (GHSZ) is a critical interface, providing a first-order estimate of gas hydrate distribution. Sensitivity to thermobaric conditions makes its prediction challenging particularly in the regions with dynamic pressure-temperature regime. In Green Canyon in the northern Gulf of Mexico (Block GC955), the seismically inferred base of the GHSZ is 450 meters (1476 ...

    • Elevation changes of the Fennoscandian Ice Sheet interior during the last deglaciation 

      Lane, T.P.; Paasche, Øyvind; Kvisvik, B.; Adamson, K.R.; Rodés, Á.; Patton, Henry; Gomez, N.; Gheorghiu, D.; Bakke, J.; Hubbard, Alun Lloyd (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-06-20)
      The dynamics of ice sheet interiors during the last deglaciation are poorly constrained, hindering evaluation of ice sheet models. We provide direct evidence of Fennoscandian Ice Sheet (FIS) interior behaviour during deglaciation through surface exposure dating. Our results demonstrate early thinning of the FIS, prior to the Younger Dryas (YD, 12.8‐11.7 ka). Interior thinning in central Norway was ...

    • Multi-proxy approach to unravel methane emission history of an Arctic cold seep 

      Yao, Haoyi; Niemann, Helge; Panieri, Giuliana (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-08-13)
      Arctic Ocean sediments contain large amounts of methane in the form of free gas and gas hydrate. This highly dynamic methane reservoir is susceptible to be modified by bottom water warming. The warming may lead to gas hydrate destabilization releasing elevated methane fluxes to the seafloor and seawater. Reconstructing past methane dynamics can be achieved by using specific proxies left in the ...

    • Simulated last deglaciation of the Barents Sea Ice Sheet primarily driven by oceanic conditions 

      Petrini, Michele; Colleoni, Florence; Kirchner, Nina; Hughes, Anna L.C.; Camerlenghi, Angelo; Rebesco, Michele; Lucchi, Renata Giulia; Forte, Emanuele; Colucci, Renato R.; Noormets, Riko; Mangerud, Jan (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-05-19)
      The Barents Sea Ice Sheet was part of an interconnected complex of ice sheets, collectively referred to as the Eurasian Ice Sheet, which covered north-westernmost Europe, Russia and the Barents Sea during the Last Glacial Maximum (around 21 ky BP). Due to common geological features, the Barents Sea component of this ice complex is seen as a paleo-analogue for the present-day West Antarctic Ice Sheet. ...

    • Methods for Predicting the Likelihood of Safe Fieldwork Conditions in Harsh Environments 

      Leidman, Sasha Z.; Rennermalm, Åsa K.; Broccoli, Anthony J.; van As, Dirk; van den Broeke, Michiel R.; Steffen, Konrad; Hubbard, Alun Lloyd (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-07-30)
      Every year, numerous field teams travel to remote field locations on the Greenland ice sheet to carry out polar research, geologic exploration, and other commercial, military, strategic, and recreational activities. In this region, extreme weather can lead to decreased productivity, equipment failure, increased stress, unexpected logistical challenges, and, in the worst cases, a risk of physical ...

    • Holocene precipitation seasonality in northern Svalbard: Influence of sea ice and regional ocean surface conditions 

      Kjellman, Sofia Elisabeth; Schomacker, Anders; Thomas, Elizabeth K.; Håkansson, Lena; Duboscq, Sandrine; Cluett, Allison; Farnsworth, Wesley R.; Allaart, Lis; Cowling, Owen; McKay, Nicholas P.; Brynjólfsson, Skafti; Ingólfsson, Ólafur (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-06-13)
      Arctic precipitation is predicted to increase in the coming century, due to a combination of enhanced northward atmospheric moisture transport and local surface evaporation from ice-free seas. However, large model uncertainties, limited long-term observations, and high spatiotemporal variability limit our understanding of these mechanisms, emphasizing the need for paleoclimate records of precipitation ...

    • Foreløpig helse- og miljørisikovurdering av genmodifisert soyalinje MON 87769 fra Monsanto Company (EFSA/GMO/UK/2009/76). Uttalelse fra Faggruppe for genmodifiserte organismer i Vitenskapskomiteen for mattrygghet. Innspill til EFSAs GMO Extranet 

      Nerland, Audun Helge; Andreassen, Åshild Kristine; Brandtzæg, Per; Finne, Merethe Aasmo; Holck, Askild Lorentz; Junttila, Juho; Konestabo, Heidi Sjursen; Meadow, Richard; Mikalsen, Arne; Nielsen, Kaare Magne; Sorteberg, Hilde-Gunn Opsahl; Vikse, Rose (Research report; Forskningsrapport, 2011-02-18)
      Helse- og miljørisikovurderingen av den genmodifiserte soyalinjen MON 87769 (EFSA/GMO/UK/2009/76) fra Monsanto er utført av Faggruppe for genmodifiserte organismer i Vitenskapskomiteen for mattrygghet. Mattilsynet og Direktoratet for naturforvaltning (DN) ber Vitenskapskomiteen for mattrygghet om å vurdere den genmodifiserte soyalinjen MON 87769 til bruk i næringsmidler og fôrvarer, men ikke til ...

    • Crustal processes sustain Arctic abiotic gas hydrate and fluid flow systems 

      Waghorn, Kate Alyse; Vadakkepuliyambatta, Sunil; Plaza-Faverola, Andreia; Johnson, Joel E; Bünz, Stefan; Waage, Malin (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-06-30)
      The Svyatogor Ridge and surroundings, located on the sediment-covered western flank of the Northern Knipovich Ridge, host extensive gas hydrate and related fluid flow systems. The fluid flow system here manifests in the upper sedimentary sequence as gas hydrates and free gas, indicated by bottom simulating reflections (BSRs) and amplitude anomalies. Using 2D seismic lines and bathymetric data, we ...

    • Anthropocene rockfalls travel farther than prehistoric predecessors 

      Vick, Louise Mary; Borella, Josh Walter; Quigley, Mark (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-09-02)
      Human modification of natural landscapes has influenced surface processes in many settings on Earth. Quantitative data comparing the distribution and behavior of geologic phenomena before and after human arrival are sparse but urgently required to evaluate possible anthropogenic influences on geologic hazards. We conduct field and imagery-based mapping, statistical analysis, and numerical modeling ...