Boundary layer velocity structure in a coldwater coral area of Haddock Channel, southwest Grand Banks.

• Main Author: Fowler, William A.
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2014
• Subjects: Newfoundland
• Online Access: https://research.library.mun.ca/8148/; https://research.library.mun.ca/8148/1/Fowler_WilliamArthur_masters.pdf

Gorgonian corals occur extensively at continental slope depths > 200 m off the southwest Grand Banks of Newfoundland. Among these corals, Keratoisis grayi forms gorgonian coral thickets on cobbles and boulders in otherwise muddy sand habitats. These thickets are believed to form a critical benthic habitat, in particular for juvenile fish, and as such are an integral part of the ecosystem. These coral thickets are impacted by bottom trawling activity which therefore could have far reaching consequences for the larger ecosystem. This thesis reports on a study of how the ocean bottom boundary layer is affected by the presence of coral thickets. This information is important both to establish the characteristics of coral habitat but also to demonstrate how the removal of corals modifies the boundary layer which would in turn modify the benthic environment. Bottom boundary layer currents in coral habitat in Haddock Channel were characterized using two 2-MHz acoustic Doppler current profilers.The profilers were deployed on the seafloor at a depth of 700 m, looking upward, for 85 hours, beginning July 17th, 2007. The effective vertical profiling range was 4 meters, with 1 meter depth resolution, sampling every 2.7 minutes. One instrument was placed in an area where bamboo corals (Keratoisis grayi ) extend approximately to 1 meter in height and occur with a density on the order of 1 colony per square meter (Coral Site). The second instrument was deployed 100 meters away in an area with visually similar sea floor characteristics, but from which the corals had been removed by a research bottom trawl (Mud Site). Mean flow speeds at both the Mud and Coral Site are on the order of 10 cm s⁻¹, which is consistent with previous current data from the general area. Observed currents showed some evidence of tidal forcing but other nonlinear processes clearly influence the current regime. Speed profiles were fitted to the logarithmic law of the wall to obtain bottom roughness zₒ, and friction velocity u∗ estimates. Both the Mud ...