Long-term near-bed observations of velocity and hydrographic properties in the northwest Barents Sea with implications for sediment transport

Abstract

Combined results from time-series observations of currents and water properties from two moorings and a benthic tripod measuring near-bed velocity profiles are used to evaluate the potential for sediment transport in the Storfjord, east of Hopen Island, and in Olgastretet in the Barents Sea near the southeast Svalbard Archipelago. Current observations include a 15-month time series from each mooring with the lowermost current meter on each mooring positioned at 6 mab and a 5-month time series from the tripod with four current meters located within 1.2 mab. Threshold of grain motion was estimated from seabed sediment characteristics sampled at each site, bed roughness length was calculated from the benthic tripod velocity profiles. Results from the Storfjord and east of Hopen Island suggest that near-bed currents and bottom stresses cannot resuspend sediment in the summer months. Currents exceed the threshold of grain motion during the fall and winter months in response to strong flows forced by surface cooling and winds. Threshold of grain motion occurs for approximately 10 days per year in both the Storfjord and east of Hopen Island. In Olgastretet, measured bottom currents had distinct reversals from north to south over periods of 3–8 days throughout the record. The highest currents (and largest bottom stresses) were directed southward and were high enough to resuspend bottom sediment about 19 days during the deployment period. Near-bottom flows are dominantly southward at all stations during times that sediment threshold velocities are exceeded, thus strong flows exiting the fjords in southern Svalbard during winter may also transport significant quantities of sediment into the deep northern Norwegian Sea.