Assessing Exploratory Drilling Impacts on an Arctic Deepwater Sea-Pen Habitat Offshore Norway

Abstract Drilling in Norwegian Arctic waters provokes concern regarding potential impacts on commercial fisheries and the marine environment. Of particular concern are deep-water sponge and sea-pen habitats. Drilling permits require environmental surveys to be carried out before and after drilling, to document drill cutting impacts. Lack of data on bottom currents in deep, northern waters may introduce errors in deposition models. This study aimed to provide data for environmental waste management in the Norwegian Arctic, at a drilling location at approximately 1400 m depth, inhabited by the deep-water seapen tentatively identified as Umbellula enchrinus, which occurs along the continental slope across the entire European Arctic. More than 70 Umbellula colonies were mapped using underwater video within approximately 1 km2 around the drilling location. Four surveys were carried out between 2010 and 2013, covering pre- and post-drilling conditions. Sediment core samples were taken before and after drilling to quantify the thickness and spatial extent of deposited drill cuttings. An Acoustic Doppler Current Profiler (ADCP) was deployed to measure water currents in the lower 450 m of the water column, at high resolution, during the entire drilling period. The upper water masses comprised northward-flowing Atlantic water, with cold Norwegian Sea Deep Water in the lowest 200 m overlying the seabed. Visible deposition of drill cuttings was restricted to within 100 m from the drilling location in most directions, and extending to around 150 m to the south-west, in accordance with bottom water movements. Exposure to cuttings deposition was not lethal, but organisms immediately near the well were mechanically destroyed. This likely is the most detailed investigation of live Umbellula organisms world-wide, and contributes to biological research on drilling impacts. Innovative water column measurements and drill cuttings impact assessments provide data for planning environmentally-sound drilling waste management strategies for offshore operations in Arctic Norway.