Monitoring Subsurface Dissolved Oxygen in Burrard Inlet
Presentation Abstract
The subsurface dissolved oxygen in Burrard Inlet is studied through instrument moorings and seasonal basin-wide CTD surveys. Located on the southern coast of British Columbia, Burrard Inlet is divided into the outer and inner basins, separated by a combination of contraction and underwater sill, known as First Narrows. Similarly, further to the east, Second Narrows separates the Vancouver Harbour from the eastern portion of the inlet, leading to Indian Arm, a deep and narrow fjord.
Time series from the Vancover Harbour basin mooring revealed intriguing features of tidal flushing and varied influence of vertical mixing at the First narrows through the spring-neap tidal cycle. Small floods under the neap tide bring the source Strait of Georgia water from the outer basin through the narrows with less mixing which sinks to depth. In contrast, strong mixing with highly oxygenated surface water during large floods lead to frequent replenishing of highly mixed water up to 1 mg L-1 higher in oxygen concentration and 1 kg m-3 lower in density. The dissolved oxygen at depth is shown to follow a distinct seasonal pattern with level ranging from 4.4 to 7.5 mg L-1 (47-79% saturation), comparable to that observed in the intermediate water of the Strait of Georgia.
Unlike the frequently flushed harbour basin, the deep water renewal in Indian Arm happens at most once a year. After a renewal in the winter of 2013/14, the deep Indian Arm oxygen shows a steady decline through remineralization of organic matter, dropping well below the hypoxic level by late 2015. The observed oxygen decline rate is about 3.7 mg L-1 yr-1, compared with an average decline of 3.3 mg L-1 yr-1 during the 1970s and 80s. The deep water density shows a steady decrease through diffusion, setting the condition for the next exchange event.
Session Title
General oceanography
Conference Track
Habitat
Conference Name
Salish Sea Ecosystem Conference (2016 : Vancouver, B.C.)
Document Type
Event
Start Date
2016 12:00 AM
End Date
2016 12:00 AM
Location
2016SSEC
Type of Presentation
Oral
Genre/Form
conference proceedings; presentations (communicative events)
Contributing Repository
Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.
Subjects – Topical (LCSH)
Water--Dissolved oxygen--British Columbia--Burrard Inlet
Geographic Coverage
Salish Sea (B.C. and Wash.); Burrard Inlet (B.C.)
Rights
This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.
Type
Text
Language
English
Format
application/pdf
Monitoring Subsurface Dissolved Oxygen in Burrard Inlet
2016SSEC
The subsurface dissolved oxygen in Burrard Inlet is studied through instrument moorings and seasonal basin-wide CTD surveys. Located on the southern coast of British Columbia, Burrard Inlet is divided into the outer and inner basins, separated by a combination of contraction and underwater sill, known as First Narrows. Similarly, further to the east, Second Narrows separates the Vancouver Harbour from the eastern portion of the inlet, leading to Indian Arm, a deep and narrow fjord.
Time series from the Vancover Harbour basin mooring revealed intriguing features of tidal flushing and varied influence of vertical mixing at the First narrows through the spring-neap tidal cycle. Small floods under the neap tide bring the source Strait of Georgia water from the outer basin through the narrows with less mixing which sinks to depth. In contrast, strong mixing with highly oxygenated surface water during large floods lead to frequent replenishing of highly mixed water up to 1 mg L-1 higher in oxygen concentration and 1 kg m-3 lower in density. The dissolved oxygen at depth is shown to follow a distinct seasonal pattern with level ranging from 4.4 to 7.5 mg L-1 (47-79% saturation), comparable to that observed in the intermediate water of the Strait of Georgia.
Unlike the frequently flushed harbour basin, the deep water renewal in Indian Arm happens at most once a year. After a renewal in the winter of 2013/14, the deep Indian Arm oxygen shows a steady decline through remineralization of organic matter, dropping well below the hypoxic level by late 2015. The observed oxygen decline rate is about 3.7 mg L-1 yr-1, compared with an average decline of 3.3 mg L-1 yr-1 during the 1970s and 80s. The deep water density shows a steady decrease through diffusion, setting the condition for the next exchange event.
