Palaeo-ice streams

Morphological interpretation of regional and detailed bathymetric data sets on the 2500-km-long Norwegian shelf from the North Sea (57°N) to Svalbard (80°N) has revealed a dynamic ice-flow pattern along the western marginof the Scandinavian and Barents/Svalbard ice sheets. About 20 cross-shelf troughs with megascale glacial lineations (MSGL; elongate ridges and grooves oriented parallel to trough long axes) are interpreted as former pathways for fast-flowing ice streams. Studies of large-scale margin morphology and seismic profiles have identified large submarine fans at the mouths of several major cross-shelf troughs. Less dynamic ice probably existed on shallower banks. The two largest paleo-ice streams were the Norwegian Channel Ice Stream and Bear Island Trough Ice Stream, each 150-200 km wide at the mouth. The lengths of individual MSGL vary from hundreds of meters to several tens of kilometers, and the distance between ridges varies from 0.1 to 3 km. MSGL amplitudes reach 15 m, but are commonly <10 m. The onset of MSGL and, hence, fast ice flow is generally close to the outer coast, at the border zone between crystalline rocks and softer sedimentary rocks. Transverse submarine ridges on various scales, commonly parallel to the shelf edge, reflect either the maximum ice-sheet position or the recessional pattern of the ice sheet. Lateral ice-stream moraines several tens of kilometers long have also been mapped along the sides of several cross-shelf troughs, identifying the border zone between fast ice flow and stagnant or slow-flowing ice on intervening banks.

Submarine landforms and the reconstruction of fast-flowing ice streams within a large Quaternary ice sheet: The 2500-km-long Norwegian-Svalbard margin (57°–80°N)

http://www.ig.uit.no/geo3128/Canals_etal_2004_utdrag.pdf

Slope failure dynamics and impacts from seafloor and shallow sub-seafloor geophysical data: case studies from the COSTA project

The Storegga Slide: architecture, geometry and slide development

Glacio-seismotectonics: ice sheets, crustal deformation and seismicity

The norwegian–greenland sea continental margins: morphology and late quaternary sedimentary processes and environment

In the present paper a hydrostatic “reduced gravity” model, generally used to simulate transient bottom-arrested gravity plumes, was coupled with a sediment transport model. The coupled model considers the respective contribution of suspended sediment particles on the buoyancy of a plume and allows one to simulate autosuspension and size-differential deposition of sediments based on the local turbulence and settling velocities. Simulations using the coupled model reveal that sediment-enriched plumes are able to inject both entrained and original shelf water masses into intermediate and bottom layers of an adjacent ocean basin in an ageostrophic dynamical balance. Hence the mechanism described here is more rapid than classic, “seawater” plumes, which are solely driven by surplus density of the water masses. Results suggest that “turbidity” plumes may constitute an important process in the formation and renewal of deep waters in the Arctic Ocean. In case a turbidity plume reaches its level of equilibrium density, deposition of suspended particles causes the density of the interstitial fluid to be lower than the density of the ambient fluid. This initiates upward convection within the water column.

The substantial difference between TS- and turbidity plumes is described by model experiments that utilize idealized slope and sediment distributions. A realistic simulation of a turbidity plume cascading down the continental slope of the western Barents Sea is presented. The computed distribution of deposited sediments agrees well with observations in an area of high accumulation of shelf-derived sediments. The frequency of occurrence of sediment-enriched gravity plumes originating from the Barents Sea shelf is estimated from the various geological variables (thickness of sediments at the bottom, grain size composition) measured from bottom sediments samples.

/pdf/sediments-in-bottom-arrested-gravity-plumes-numerical-case-2itosuvwvz.pdf

Sediments in Bottom-Arrested Gravity Plumes: Numerical Case Studies*

Acoustic mapping and sampling of Holocene and Late Weichselian deglacial sediments combined with oceanographic measurements in the sediment source and accumulation areas on the eastern continental margin of the Norwegian-Greenland Sea provide evidence that episodic transport towards high-accumulation areas is primarily downslope and gravity driven Triggered by various hydrographic conditions, the runoff repeatedly followed the local gullies and channels of the seafloor

Records and Processes of Near-Bottom Sediment Transport along the Norwegian-Greenland Sea Margins during Holocene and Late Weichselian (Termination I) Times

Sediment transport processes in the northern North Atlantic have been investigated on the basis of various numerical models. A general circulation model has been used to investigate large-scale particle transport, a reduced gravity plume model has been used to investigate particle transport by cascading from the shelves into the deep basins, an ocean slice model has been used to investigate particle exchange processes between a bottom current and the ambient water mass, and a Bottom Boundary Layer model has been used to investigate particle interactions influencing the settling behavior of suspended particles. In this paper, the various processes investigated in these models are described (i) schematically, (ii) on the basis of field data, if available, and (iii) by employing results from numerical simulations. In a first attempt the northern North Atlantic will be divided into separate process defined areas, which can be used in carbon budgeting, for example.

Frank Blaume

Papers

The norwegian–greenland sea continental margins: morphology and late quaternary sedimentary processes and environment

Sediments in Bottom-Arrested Gravity Plumes: Numerical Case Studies*

Records and Processes of Near-Bottom Sediment Transport along the Norwegian-Greenland Sea Margins during Holocene and Late Weichselian (Termination I) Times

Modern Ocean Current-Controlled Sediment Transport in the Greenland-Iceland-Norwegian (GIN) Seas