In August 2010, a 253 km2 ice island calved from the floating glacial tongue of Petermann Glacier in Northwest Greenland. Petermann Ice Island (PII)-B, a large fragment of this original ice island, is the most intensively observed ice island in recent decades. We chronicle PII-B’s deterioration over four years while it drifted more than 2,400 km south along Canada’s eastern Arctic coast, investigate the ice island’s interactions with surrounding ocean waters, and report on its substantial seafloor scour. Three-dimensional sidewall scans of PII-B taken while it was grounded 130 km southeast of Clyde River, Nunavut, show that prolonged wave erosion at the waterline during sea ice-free conditions created a large underwater protrusion. The resulting buoyancy forces caused a 100 m × 1 km calving event, which was recorded by two GPS units. A field team observed surface waters to be warmer and fresher on the side of PII-B where the calving occurred, which perhaps led to the accelerated growth of the protrusion. PII-B produced up to 3.8 gigatonnes (3.8 × 1012 kg) of ice fragments, known hazards to the shipping and resource extraction industries, monitored over 22 months. Ice island seafloor scour, such as a 850 m long, 3 m deep trench at PII-B’s grounding location, also puts subseafloor installations (e.g., pipelines) at risk. This long-term and interdisciplinary assessment of PII-B is the first such study in the eastern Canadian Arctic and captures the multiple implications and risks that ice islands impose on the natural environment and offshore industries.Publisher PDFPeer reviewe

The Port of Saint John is a highly stratified, hyper-tidal estuary that requires frequent hydrographic surveys to ensure that minimum underkeel clearances are maintained and to monitor dredge operations. The potential achievable accuracy and efficiency of a multibeam sonar survey correlates to the knowledge of the physical oceanographic conditions of the harbour. A high-resolution baroclinic hydrodynamic model of the Port of Saint John was constructed to understand the dynamic physical oceanographic environment over four periods representing the limits in river flow conditions. The model provides time-varying outputs of temperature and salinity at predefined depth intervals over the domain. Sound speed is derived from the model output and is used for ray tracing multibeam sonar data and survey planning to minimize refraction errors. Ray-tracing depth error statistics are calculated from Moving Vessel Profiler (MVP) temperature and salinity casts and used to evaluate the model skill. Results demonstrate that the model can be used to replace observed sound speed profiles and stay within depth accuracy specifications within a swath width of 60 degrees, or more, for most of the year throughout the harbour. Uncertainty increases for swath widths of more than 55 degrees during the most severe stratification of the spring freshet.