Search

Near-inertial oscillations (NIOs) on the inner Scotian shelf are studied using observations, a simple slab model, and two operational shelf circulation models. High-frequency radar and ADCP observations from December 2015 to February 2016 show that individual NIO events forced by time-varying wind stress typically lasted for three to four inertial periods. NIOs with speeds exceeding 0.25 m s−1 were observed in the offshore part of the study region, but their amplitudes decreased shoreward within ~40 km of the coast. The NIOs had spatial scales of ~80 and ~40 km in the alongshore and cross-shore directions, respectively. The NIO phases varied moving from west to east, consistent with the typical movement of winter storms across the study region. Evolving rotary spectral analysis reveals that the peak frequency fp of the NIOs varied with time by ~7% of the local inertial frequency. The variation in fp can be explained in part by local wind forcing as demonstrated by the slab model. The remaining variation in fp can be explained in part by variations in the background vorticity associated with changes in the strength and position of the Nova Scotia Current, an unstable baroclinic boundary current that runs along the coast to the southwest. Two operational shelf circulation models are used to examine the abovementioned features in the high-frequency-radar and ADCP observations. The models reproduce the spatial structure of the NIOs and, in a qualitative sense, the temporal variations of fp. [ABSTRACT FROM AUTHOR]

Abstract: The Sable Gully is the largest submarine canyon along the shelf break off the east coast of North America. The circulation and hydrography in the Gully have significant temporal and spatial variability. This paper presents a numerical study of the three-dimensional circulation and hydrography in the Gully using a multi-nested ocean circulation model. The model is forced by tides, wind stress and surface heat/freshwater fluxes. Model results are in fair agreement with the current and hydrographic observations made in the Gully in 2006 and 2007. A process study is conducted to examine the main physical processes affecting the circulation and hydrography, including tide–topography interaction, wind forcing, and the shelf-scale circulation over the eastern Canadian Shelf. The model results demonstrate that the circulation and hydrography above the canyon rim are influenced significantly by wind, particularly during storm events, while the subsurface flow over the shelf slope is affected by the shelf-scale circulation. There is also significant tide–topography interaction inside the Gully. [Copyright &y& Elsevier]

Halifax Harbour is located on the Atlantic coast of Nova Scotia, Canada. It is one of the world's largest, ice-free natural harbours and of great economic importance to the region. A good understanding of the physical processes controlling tides, flooding, transport and dispersion, and hydrographic variability is required for pollution control and sustainable development of the Harbour. For the first time, a multi-nested, finite difference coastal ocean circulation model is used to reconstruct the three-dimensional circulation and hydrography of the Harbour and its variability on timescales of hours to months for 2006. The model is driven by tides, wind and sea level pressure, air-sea fluxes of heat, and terrestrial buoyancy fluxes associated with river and sewage discharge. The predictive skill of the model is assessed by comparing the model simulations with independent observations of sea level from coastal tide gauges and currents from moored instruments. The simulated hydrography is also compared against a new monthly climatology created from all available temperature and salinity observations made in the Harbour over the last century. It is shown that the model can reproduce accurately the main features of the observed tides and storm surge, seasonal mean circulation and hydrography, and wind driven variations. The model is next used to examine the main physical processes controlling the circulation and hydrography of the Harbour. It is shown that non-linear interaction between tidal currents and complex topography occurs over the Narrows. The overall circulation can be characterized as a two-layer estuarine circulation with seaward flow in the thin upper layer and landward flow in the broad lower layer. An important component of this estuarine circulation is a relatively strong, vertically sheared jet situated over a narrow sill connecting the inner Harbour to the deep and relatively quiescent Bedford Basin. Local wind driven variability is strongest in winter as expected but it is also shown that a significant part of the temperature and salinity variability is driven by physical processes occurring on the adjacent inner continental shelf, especially during storm and coastal upwelling events. [ABSTRACT FROM AUTHOR]

Abstract: A coastal ocean observatory has been established in Lunenburg Bay, Nova Scotia since summer 2002 as part of a multi-agency research program of marine environmental observation and prediction over Atlantic Canada coastal waters. The observatory was operational when a category-2 hurricane (Juan) made land fall within 50-km of the bay in September 2003. The coastal response of the bay to Hurricane Juan is examined using a nested-grid coastal circulation modelling system. The nested-grid system is forced by the local wind, tides, and remotely generated coastal waves. A comparison of model results with observed surface elevations and currents demonstrates that the nested-grid system has reasonable skills in simulating the three-dimensional (3D) storm-induced circulation in the study region. The 3D model currents are used to examine the transport and dispersion of passive tracers, local flushing time, and retention and connectivity of passive particles in the bay during Hurricane Juan. Numerical results demonstrate that local wind forcing plays a dominant role in generating large dispersion and hydrodynamic connectivity in the bay during the storm. [Copyright &y& Elsevier]

Abstract: The baroclinic response of a stratified coastal embayment (Lunenburg Bay of Nova Scotia) to the observed wind forcing is examined using two numerical models. A linear baroclinic model based on the normal mode approach shows skill at reproducing the observed isotherm movements and sub-surface currents during a time of strong stratification in the bay. The linear model also shows that the isotherm movement in Lunenburg Bay is influenced by the wind forcing and propagation of baroclinic Kelvin waves from neighbouring Mahone Bay. The effects of nonlinearity and topography are investigated using a three-dimensional nonlinear coastal circulation model. The nonlinear model results demonstrate that the nonlinear advection terms generate a gyre circulation at the entrance of Lunenburg Bay, and the slope bottom topography at the mouth of the bay strengthens the sub-surface time-mean inflow on the southern side of the bay. A comparison of model-calculated currents in different numerical experiments clearly shows that baroclinicity plays a dominant role in the dynamics of wind-driven circulation in Lunenburg Bay. [Copyright &y& Elsevier]

The Bras d’Or Lakes (BdOL) are a large, complex and virtually land-locked estuary in central Cape Breton Island of Nova Scotia and one of Canada’s charismatic ecosystems, sustaining ecological and cultural communities unique in many aspects. The BdOL comprise two major basins, many deep and shallow bays, several narrow channels and straits and a large, geologically complex watershed. Predictive knowledge of the water movement within the estuary is a key requirement for effective management and sustainable development of the BdOL ecosystem. A three-dimensional (3D) primitive-equation ocean circulation model is used to examine the estuary’s response to tides, winds and buoyancy forcing associated with freshwater runoff in a series of numerical experiments validated with empirical data. The model results generate intense, jet-like tidal flows of about 1 m s−1 in the channels between the basins and connecting them to the ocean and relatively weak tidal currents in other regions, which agrees well with previous observations and numerical results. Wind forcing and buoyancy forcing associated with river runoff play important roles in generating the significant sub-tidal circulations in the estuary, including narrow channels, deep basins and shallow bays. The circulation model is also used to reconstruct the 3D circulation and temperature-salinity distributions in the summer months of 1974, when current and hydrographic measurements were made at several locations. The sub-tidal circulation in the estuary produced by the model is characterised by wind and barometric set-up and set-down in different sections of the system, and a classic two-layer estuarine circulation in which brackish, near-surface waters flow seaward from the estuary into the Atlantic Ocean, and deep salty waters flow landward through the major channel. The model results reproduce reasonably well the overall features of observed circulation and temperature-salinity fields made in the BdOL in 1974 but generally underestimate the observed currents and density stratification. The model discrepancies reflect the use of spatially mean wind forcing and spatially and monthly mean surface heat flux and the inability of the coarse model horizontal resolution (∼500 m) to resolve narrow channels and straits. [ABSTRACT FROM AUTHOR]

Dissolved oxygen (DO) in the global ocean is on the decline, resulting in the degradation of coastal habitats. As aquaculture production occurs in these regions, proper understanding of coastal DO dynamics is important for improved farm management (e.g. site selection). The main objective of this study was to quantify along-shore and cross-shore variability in DO dynamics, as well as onshore advection of offshore waters to the bays that could contain aquaculture farms. For that purpose, a Slocum underwater glider was deployed between September 25 and October 12, 2020 to collect high-resolution data of temperature, salinity and DO along a transect between Shelburne Bay and St. Margarets Bay, Nova Scotia, Canada, with an average distance of about 15 km from shore. The observations revealed the variable nature of cross-shore water properties. Shoreward bottom currents transport offshore waters to the coast, and combined with longer residence times, mixing of these waters with those present created a mosaic of differing water properties, with warmer, fresher, and less oxygenated shoreward waters. The glider intercepted an upwelling event due to strong and persistent southwesterly winds, which cooled the upper water layers by 6 °C and increased DO by 1.4 mg L−1. This strong upwelling event detected at 10 km from the coast was also captured 30 h later within St. Margarets Bay, depicting a potential offshore-inshore interaction. Therefore, bay-wide ecosystems and aquaculture production could be affected by intrusions of offshore waters. • Strong southwesterly winds persistent for 4 days created coastal upwelling, cooling the upper water layers by 6 °C. • An upwelling event detected at 10 km from the coast was also captured 30 h later within a coastal embayment. • Cross-shore transects revealed warmer, fresher, and less oxygenated shoreward waters compared to those more offshore. [ABSTRACT FROM AUTHOR]