Origin and fate of an episodic oil seep, Gulf of St. Lawrence (Canada)

Natural oil seeps are surface indicators of hydrocarbon migration in sedimentary basins. Current understanding of oil seeps is mainly based on the study of persistent seeps, even if episodic seeps are likely to be much more widespread worldwide. We present the first evidence of an episodic oil seep in the Gulf of St. Lawrence, Canada, where the presence of oil seeps and oil resources has been disputed. High-temporal-resolution data at an unprecedented level—sub-daily satellite imaging and hourly data from an oceanographic buoy—enable the first-ever quantification of oil emission rates over time for an episodic seep. After a rapid onset without an obvious external trigger, the oil emission rate declined until emissions were no longer detectable 53 d later. About 30,000 L of oil was released over this period, with no estimate of gas emissions. We link our observations into a schematic model describing hydrocarbon migration, accumulation, and seepage in the Carboniferous Maritimes Basin. Beyond being a regionally significant discovery, this research provides a well-documented example that may serve as analog for understanding fluid migration and episodic leakage in other sedimentary basins.