Subtidal circulation in a deep‐silled fjord: Douglas Channel, British Columbia

Douglas Channel, a deep fjord on the west coast of British Columbia, Canada, is the main waterway in the fjord system that connects the town of Kitimat to Queen Charlotte Sound and Hecate Strait. A 200 m depth sill divides Douglas Channel into an outer and an inner basin. This study examines the low‐frequency (from seasonal to meteorological bands) circulation in Douglas Channel from data collected at three moorings deployed during 2013–2015. The deep flows are dominated by a yearly renewal that takes place from May/June to early September. A dense bottom layer with a thickness of 100 m that cascades through the system at the speed of 0.1–0.2 m s−1, which is consistent with gravity currents. Estuarine flow dominates the circulation above the sill depth, and the observed landward net volume flux suggests that it is necessary to include the entire complex channel network to fully understand the estuarine circulation in the system. The influence of the wind forcing on the subtidal circulation is not only at the surface, but also at middepth. The along‐channel wind dominates the surface current velocity fluctuations and the sea level response to the wind produces a velocity signal at 100–120 m in the counter‐wind direction. Overall, the circulation in the seasonal and the meteorological bands is a mix of estuarine flow, direct wind‐driven flow, and the barotropic and baroclinic responses to changes to the surface pressure gradient caused by the wind stress. Key Points: An annual 3 month long deep water renewal replenishes the deep basin water in Douglas Channel The observed landward net volume flux suggests the importance of the complex channel network to the system Counter‐wind current velocity response is observed at 100–120 m depth