STUDY OF CIRCULATION, HYDROGRAPHY AND DISSOLVED OXYGEN CONCENTRATION OVER COASTAL WATERS OF THE SCOTIAN SHELF

Abstract

The main objective of this thesis is to examine the temporal and spatial variability of circulation, hydrography, and dissolved oxygen concentration (DO) over coastal waters of the Scotian Shelf. A simple oxygen model is coupled to level 3 sub-model of a nested-grid circulation-ice modelling system for the southeastern Canadian shelf (seCS). Performances of both the nested-grid modelling system and oxygen model are assessed by comparing model results with available observations and reanalysis data. Model results produced by the nested-grid modelling system during the summer in 2018 are used to examine the effects of atmospheric and tidal forcing on general circulation, temperature, and salinity over the seCS. A process study is conducted using the coupled circulation-oxygen model for investigating main physical processes affecting the temporal and spatial variability of DO over coastal waters off southwest Nova Scotia during the summer in 2018. Analysis of model results demonstrates that both winds and tides affect coastal circulation and enhance the vertical mixing over the coastal waters. Winds significantly affect the hydrography and DO in the upper water column through wind effects on the air-sea fluxes and vertical mixing. Tides affect the local DO maxima at the subsurface of about 20 m through mainly tide-induced mixing. A sensitivity study is conducted using the coupled model to examine the effects of the net water respiration (NWR) and sediment oxygen consumption (SOC) on the DO produced by the oxygen model over the coastal waters. The NWR consumes a relatively large amount of dissolved oxygen (up to 8 mmol m-3 in August 2018) in the subsurface water in summertime, due to the distributions of chlorophyll and biomass. The SOC has relatively large effects (up to 15 mmol m-3 in August 2018) on the DO near the sea bottom.