Eulerian and Lagrangian Studies of Circulation on the Scotian Shelf and Adjacent Deep Waters of the North Atlantic with Biological Implications

Abstract

A thorough understanding of circulation and hydrography over the eastern Canadian Shelf remains a major challenge within the field of physical oceanography. Reliable predictions of physical oceanic conditions are of great importance to studies of marine animal distribution and migration in the region. This thesis examines the circulation, hydrography, and associated variabilities on the Scotian Shelf and adjacent deep waters. An Eulerian perspective is taken and extensive use is made of a newly developed state-of-the-art multi-nested ocean circulation modelling system. The model performance is assessed extensively against various observations. Model results are used to quantify the tide-topography interaction, wind-driven circulation, shelfbreak jet, cross-shelf transport, upstream/downstream areas, and residence time in the Sable Gully Marine Protected Area. A process study is conducted to investigate the contributions of tidal mixing and wind-driven coastal upwelling to the formation of cold surface water along the Nova Scotia's coast in summer. The important influence on coastal upwelling of small-scale irregularities in the coastline and nearshore bathymetry near the Halifax Harbour is identified and explained through model sensitivity studies.

This thesis also investigates how the distribution and migration of marine animals respond to changes in the physical marine environment. A Lagrangian perspective is taken and a new biophysical particle tracking model is developed by adding the migratory behaviors to the passive drift. An in-depth numerical study of the spawning migration of American and European eels is conducted to examine the influence of the North Atlantic circulation on their migration from the coastal ocean (e.g., Scotian Shelf) to the Sargasso Sea. The model results suggest that orientated swimming behavior is required for eels to reach their spawning areas within the expected time window. The presence of ocean currents increases the duration of migration and travelled distances, particularly for American eel migrating at low swimming speed. In addition, the implications of circulation for the northern bottlenose whale in the Gully and Atlantic salmon transiting the Scotian Shelf are briefly discussed. The expertise gathered in the present work can be used to develop similar models for other regions and species.