Seafloor pockmarks offshore Vancouver Island

Pockmarks are crater-like depressions of erosive nature in marine or lacustrine sediments. They are often interpreted as the surface manifestation of hydrocarbon venting but may also result from freshwater flow in coastal regions, compaction induced sediment dewatering, or bottom scouring around natural or anthropogenic objects. Hence, they can be of relevance for the global carbon cycle, offshore infrastructure, benthic life, and slope stability. New bathymetric data from offshore Vancouver Island, Canada, indicate the presence of a huge pockmark field that had escaped attention in previous studies. The pockmarks are located between 100 and 200 mt depth around the head of Barkley Canyon. Owing to the presence of a large cabled underwater observatory related to the canyon, a wealth of multi-resolution and multi-disciplinary seafloor data is available from the pockmark field. Available data include multibeam surveys, seafloor video footage, seismic and EK60 echo-sounder profiles, and multibeam water-column information. First results from seafloor mapping indicate that the pockmark field consists of several thousands of pockmarks. By applying workflows that automatically map the pockmarks in digital elevation models, we are able to quantitatively investigate their morphology and spatial distribution. The pockmarks range in size between 100 - 500 m², with some exceptions as large as 900 m². Their mean depth varies between 0.5 - 2 m. Seepage of gas from the seafloor is well known from the area but could not yet been directly associated with the pockmark depressions. Instead, limited video footage from the seafloor indicate that at least some depressions host meter-sized boulders within their craters. We will next investigate possible temporal changes in pockmark morphology and seep activity by individual analysis of datasets that have been repeatedly collected between 2010-2020. By resolving pockmark morphologies and seep activities on an annual time-scale over a decade, the results will hopefully add a level of detail to our understanding of pockmark formation and seep activity within one of North Americas largest pockmark fields.