Sediment dynamics and distribution on the Norwegian continental shelf between the Lofoten Islands and the southern Barents Sea
|Location||International Geological Congress,oslo 2008|
|Author||Bellec, Valérie۱; Dolan, Margaret۱; Boe, Reidulv۱; Rise, Leif۱; Ottesen, Dag۱; Thorsnes, Terje۱; Buhl-Mortensen, Lene۲; Buhl-Mortensen, Pal۲|
|Holding Date||08 October 2008|
A large seabed mapping programme (MAREANO) has been initiated in the Lofoten - Southern Barents Sea area to investigate the physical, biological and environmental status of the seabed. Three institutions (Institute of Marine Research, Geological Survey of Norway, Norwegian Hydrographic Service) cooperate closely with several other institutions to perform the mapping. The results are available on the internet (www.mareano.no). Multibeam bathymetry and backscatter data together with samples and video have been acquired on the Norwegian continental shelf between the Lofoten Islands and the southern Barents Sea (Nordland VII, Troms II and Tromsøflaket). The Norwegian shelf is composed of shallow banks alternating with deep glacial troughs that have been strongly eroded by ice during the last glaciations.
A sediment grain-size map together with an erosion-deposition map have been produced in the Troms II and Tromsøflaket areas. Shallow banks of Troms II show very coarse deposits (mainly sandy gravel to boulders) due to strong currents which eroded most of the shallow banks. Deposition of finer sediments (fine sand and sandy mud) occur in shallow depressions on the banks and in the glacial troughs. The shallow areas of Tromsøflaket (150-200 m depth) are also characterised by coarse deposits (mainly gravelly sand to sandy gravel). Nevertheless, sand and sandy mud occur in depressions, pits and iceberg ploughmarks. The sediments become finer with depth and the finest sediments (mud) have been found in the Ingøydjupet glacial trough at 400 m depth. By contrast, the Sørøydjupet trough at 300 m depth displays coarse sediments, caused by the strong currents present in this area.
Detailed investigations have shown bedforms linked to different glacial processes (iceberg ploughmarks, glacial lineations, depressions, moraines) or to currents (lineations, dunes, sandy ribbons, giant comet marks). Iceberg ploughmarks cover most of Tromsøflaket whereas they occur only on the sides of glacial troughs or in the deeper banks of Nordland VII and Troms II. Glacial lineations are mainly present in the glacial troughs.
The main current-related bedforms are erosive structures and are mostly found in the Nordland VII and Troms II areas. Elongated lineations occur both on banks and in glacial troughs. Some of these lineations were formed during the ice melting and have been preserved during the last transgression due to their very coarse grain-size. They are covered by sandy ribbons on the banks, indicating active processes. Small dunes detected by video are present in sandy environments, as well as furrows and comet marks. Giant comet marks occur in the Nordland VII area.