Contour current driven continental slope-situated sandwaves with effects from secondary current processes on the Barents Sea margin offshore Norway

摘要

Seabed data acquired from the southern Barents Sea continental margin offshore Norway reveal detailed morphology of large sandwave fields. Multibeam echosounder bathymetry and backscatter, shallow seismic, sediment samples and seabed video data collected by the MAREANO program have been used to describe and interpret the morphology, distribution and transport of the sandwaves. The bedforms lie on a slope dominated by relict glacial forms and muddy/sandy/gravelly sediments. Sandwave migration across small gravity mass failures of the glacial mud constrains the field initiation as earlypost glacial or later. The contour-parallel nature of the fields and crestlines normal to the bathymetry contours and the geostrophic Norwegian Atlantic Current (NwAC) demonstrate that the NNW-flowing oceanographic circulation is the primary driving current. The fields coincide with the depth range at which a transition between warm, saline and underlying cooler, less saline waters fluctuate across the seabed. Statistically rigorous measurements of height, width and various parameters of slope and symmetry confirm a tendency to downstream (NNW) sandwave migration but with significant exceptions. Anomalous bedform symmetry domains within the fields are tuned to meso-scale topography along (relict) glacial debris flow chutes, indicating current focusing. Upstream and upper slope-derived winnowed sand transport eroded from the glacial sediments is the supposed source. Sandwave flank slope values are comparable to the regional slope such that the gravitational vector would have a cumulative downslope migration affect unless balanced by upslope drivers. Perpendicular cross-cutting of stoss face 3-D ripples by linear (2-D) ripples in the sandwave troughs and lee faces is evidence for non-synchronous, episodic current variations. Though deep Ekman transport and internal wave action are unproven here, these could explain chute-related tuning of bedform symmetry through funneling in the debris flow chutes and favor sand recycling, thus contributing to long-term maintenance of the sandwave field.