Sandwaves and sand transport on the Barents Sea continental slope offshore northern Norway

摘要

We integrate morphological, geological and geophysical observations with oceanographic measurements and modelling results to interpret the processes behind the origin and evolution of sandwaves on the upper continental slope of the southwestern Barents Sea. Seven sandwave fields covering c. 130 km(2) and with a volume of c. 72 x 10(6) m(3) occur in water depths of c. 475-800 m. Individual sandwaves reach heights up to 6 m. The sandwaves are sinusoidal with asymmetric stoss-lee side relationships, and time lapse multibeam bathymetry analysis indicates that some sandwaves have migrated up to 10 m towards the NNW over a 4-year time period. This contour current parallel migration is counteracted by currents in several other directions, and the sand unit is thus not a simple contourite. Measurements show prominent diurnal period oscillations and clear spring-neap variations of current direction and speed with along-slope and cross-slope current velocities up to 75 cm s(-1) and 65 cm s(-1), respectively. Numerical ocean modelling results produce eddies travelling along the slope, positionally stable, daily recurring vortices and bottom current velocity up to 100 cm s-1 in the sandwave fields. Sandwave migration towards the SE is also observed, and the cross-slope currents are capable of transporting sand up and down the slope, as evidenced by ripples migrating normal to the sandwaves. Eroded sand accumulates in the sandwave fields along the boundary between North Atlantic Water and Norwegian Sea Arctic Intermediate Water. This is a consequence of the combined effect of the NNW directed along-slope Norwegian Atlantic Current and tidally induced topographic waves. The sandwave fields started to form 11 000-13 000 C-14 yrs BP or possibly later by current erosion of glacial sediments on the continental shelf and slope. (C) 2014 Elsevier Ltd. All rights reserved.