Circulation and deep water renewal in Douglas Channel, British Columbia, Canada
Date
2023-09-20
Authors
Wan, Di
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Abstract
Douglas Channel is the main waterway in the fjord system on the west coast of British Columbia (BC), Canada, connecting 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 thesis examines the sub-tidal circulation and deep water renewals in Douglas Channel using mooring data collected between 2013 and 2015. It was found that the overall circulation in Douglas Channel has a three-layer structure in winter and a four-layer structure in summer when deep water renewal occurs. The circulation is a mixture of estuarine flow, wind-driven flow, and the barotropic and baroclinic responses to changes to the surface pressure gradients. The surface current velocity fluctuation is dominated by the along-channel wind-driven currents, whereas a counter-wind velocity response is detected at 100--120 m depth. Further investigation of the wind-driven circulation shows that the physically narrow Douglas Channel is dynamically wide and the cross-channel geostrophic balance determines the along-channel velocity layer thicknesses and directions as found in wide channels. This result can be generalized to other flows, such as the surface outflow in the estuarine circulation, and provides a possible explanation to the disagreement between the thicknesses of the surface velocity layer and the stratification layer. At depth, the renewal events are connected to the availability of dense water on the shelf. The examination of the dense water variation leads to evidence that a long-range connection exists between the BC shelf water density and remote influences, expanding the studies of the processes and frequencies that influence upwelling on the BC coast to the quasi-biweekly and intraseasonal bands and the equatorial Pacific and northern California and Oregon regions. These findings will be able to direct future studies in this region, as well as the entire BC shelf upwelling dynamics.
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Keywords
Physical Oceanography, fjord, upwelling, BC coast, inlet, Kitimat fjord system, deep water renewal