A coupled hydrodynamic-wave-sediment model is used to simulate the broad-scale tidal circulation, surface waves, and suspended sediment concentrations (SSC) in Minas Basin, a 70-km long tidal estuary in the Bay of Fundy, during winter and summer periods. The model hydrodynamics are validated using acoustic-Doppler current profile observations, the surface SSC predictions are compared to satellite observations, and model results indicate that strong seasonal signals in SSC can be explained in part by seasonal changes in fetch-limited surface waves generated by local winds over the basin. The spatial and temporal variability of SSC is evaluated in this study by focussing on different forcing conditions from waves and tidal currents, the two primary physical process that influence the response of sediments in suspension. Model predictions in the intertidal areas indicate that surface waves can increase the bed shear stress from tidal currents alone by up to 1–5 Nm− 2, causing excess bed shear stresses to be higher and result in higher SSC by 100–200 gm− 3 particularly during wind events that are stronger and more frequent in winter months. Resuspension of sediments on tidal flats is driven by the combination of shear stresses from near-bed wave orbital velocities and tidal currents, and transport of the suspended materials over deeper areas of the basin is driven by advection from the strong tidal currents.

Acoustic Doppler Current Profilers and underwater gliders were simultaneously deployed as part of the Ocean Tracking Network to continuously monitor the Halifax Line (HL) and the Nova Scotia Current (NSC) between 2008 and 2014. The HL transects the Scotian Shelf, which connects dynamically important areas, such as the Grand Banks, the Gulf of Maine, and the Gulf of St. Lawrence (GSL). The oceanographic measurements made at the HL during this period provide a unique opportunity to study the temperature, salinity, and alongshore current conditions and variability at both seasonal and interannual time scales. The analysis of observations reveals that the water over the Scotian Shelf is mainly composed of water coming from the Gulf of St. Lawrence ( Cabot Strait subsurface water) in the upper layer (30 to 50 m, 81%) and Warm Slope Water below 100 m (77%), highlighting the connectivity between the GSL and the Scotian Shelf. The temperature-salinity characteristics of the Cold Intermediate Layer (CIL) observed along the HL and located mainly between 50 and 100 m, is indistinguishably influenced by both water coming from the Inshore Branch of the Labrador Current and CIL water formed in the GSL. These proportions stay similar over interannual time scales, suggesting that the 2012 warm anomaly observed over the Scotian Shelf is primarily driven by the advection of already anomalously warm water coming from offshore regions. The analysis of glider data also reveals that most of the alongshore transport over the Scotian Shelf occurs within the first 60 km from the coast, where the NSC is located. It was found that the freshwater discharge from the St. Lawrence River at Quebec and the alongshore transport across the NSC have a significant covariance (sigma(xy) = 0.37) at a 9-month lag. The Empirical Orthogonal Function (EOF) analysis demonstrates that most of the current variability (between 78 and 92%) can be explained by the first EOF, which represents the baroclinicity resulting from the freshwater outflow coming from the GSL. Part of the second EOF is associated with the local wind forcing and explains between 4 and 14% of the NSC variability.

Environmental impacts, including tidal regimes and sediment transport in the Minas Basin, caused by tidal power extraction in the Minas Passage have been investigated using a three-dimensional hydrodynamic model in which tidal power extraction is represented using an arbitrary method that adds a friction term to the standard momentum equations. Using the model results, changes in tidal processes and sediment transport in the Minas Basin are examined by comparing model results with and without power extraction. With the presence of power extraction, the tidal level decreases by 0.5-1.5% and the tidal phase increases by 1.2-1.8 degrees. Tidal currents decrease by 15-35% at the western head of the Minas Basin and increase by a comparable magnitude at the Southern Bight. The presence of power extraction could move the location of the tidal residual gyre in the western head of the Minas Basin south by about 2 km. Model results also show that less sediment would move into the central area of the Minas Basin but more sediment would be deposited into the Southern Bight at a rate of 8-12 mm y(-1). The effect of the deposition rate might be negligible in the northern part of the Bight where the water is deep but could be important in the intertidal areas.

Baleen and sperm whales, known collectively as the great whales, include the largest animals in the history of life on Earth. With high metabolic demands and large populations, whales probably had a strong influence on marine ecosystems before the advent of industrial whaling: as consumers of fish and invertebrates; as prey to other large-bodied predators; as reservoirs of and vertical and horizontal vectors for nutrients; and as detrital sources of energy and habitat in the deep sea. The decline in great whale numbers, estimated to be at least 66% and perhaps as high as 90%, has likely altered the structure and function of the oceans, but recovery is possible and in many cases is already underway. Future changes in the structure and function of the world's oceans can be expected with the restoration of great whale populations.

Total suspended matter (TSM) concentrations were derived from ocean colour imagery (MERIS satellite data) in Minas Basin. Analysis of time series of TSM in 1-km(2) pixel boxes revealed an annual cycle in TSM in most parts of the Basin. Higher TSM of up to 85 g/m(3) was observed in late-winter (February-March), and lower TSM of 5-10 g/m(3) characterized late-summer (July-August). The largest annual variation occurred in the centre of Basin, and the smallest variation occurred in shallow areas. Satellite-derived TSM, supported by in situ observations, were compared to predictions using the Delft3D model. Increasing model erosion rate in winter relative to summer improved agreement between model and satellite-derived TSM. In comparison with the satellite-derived estimates, the model underestimated TSM in. shallow areas in summer and overestimated it in winter. This discrepancy is likely due to inaccurate satellite-derived TSM in shallow, high-concentration areas of the Basin. (C) 2014 Elsevier Ltd. All rights reserved.

Decadal‐scale regime shifts in Northwest Atlantic shelf ecosystems can be remotely forced by climate‐associated atmosphere‐ocean interactions in the North Atlantic and Arctic Ocean Basins. This remote climate forcing is mediated primarily by basin‐ and hemispheric‐scale changes in ocean circulation. We review and synthesize results from process‐oriented field studies and retrospective analyses of time‐series data to document the linkages between climate, ocean circulation, and ecosystem dynamics. Bottom‐up forcing associated with climate plays a prominent role in the dynamics of these ecosystems, comparable in importance to that of top‐down forcing associated with commercial fishing. A broad perspective, one encompassing the effects of basin‐ and hemispheric‐scale climate processes on marine ecosystems, will be critical to the sustainable management of marine living resources in the Northwest Atlantic.

During recent decades, historically unprecedented changes have been observed in the Arctic as climate warming has increased precipitation, river discharge, and glacial as well as sea ice melting. Additionally, shifts in the Arctic's atmospheric pressure field have altered surface winds, ocean circulation, and freshwater storage in the Beaufort Gyre. These processes have resulted in variable patterns of freshwater export from the Arctic Ocean, including the emergence of great salinity anomalies propagating throughout the North Atlantic. Here, we link these variable patterns of freshwater export from the Arctic Ocean to the regime shifts observed in Northwest Atlantic shelf ecosystems. Specifically, we hypothesize that the corresponding salinity anomalies, both negative and positive, alter the timing and extent of water-column stratification, thereby impacting the production and seasonal cycles of phytoplankton, zooplankton, and higher-trophic-level consumers. Should this hypothesis hold up to critical evaluation, it has the potential to fundamentally alter our current understanding of the processes forcing the dynamics of Northwest Atlantic shelf ecosystems.

Conventional wisdom, based on observations spanning two and a half decades (1975-2000), asserts that inflow to the Gulf of Maine (GoM) occurs primarily in two areas: inshore on the Scotian Shelf off Cape Sable, Nova Scotia and on the eastern side of the Northeast Channel (NEC). In particular, the monthly mean currents in the eastern NEC have shown persistent inflow at all depths and in all seasons, except for the occasional, but brief; reversals near the bottom (similar to 200 m). Conversely, the flow on the western side of the NEC is normally directed out of the gulf in the surface layer and at mid-depth, consistent with the clockwise gyre over Georges Bank, but those currents do show relatively frequent reversals to inflow in the deeper layers (150-200 m), in sympathy with the flow on the eastern side. At some point between the year 2000, when the last Bedford Institute of Oceanography (BIO)/U.S. GLOBEC mooring was removed from the eastern NEC, and 2004, when a new mooring was placed there as part of the U.S. ocean observing array, a transformation occurred. The recent data, collected from a representative location in the eastern NEC, show a strongly seasonal current signal marked by persistent periods of outflow in the deep layers (>100 m), particularly in winter:This observation was first reported by Pettigrew et al. (2008), where the outflow currents occasionally extend to the surface layers as well, most notably in the winters of 2004-2005 and 2006-2007. Additional data and analyses reported here suggest that this new mode of behavior in the NEC currents could have important consequences for the GoM ecosystem. Possible causes for this "regime shift" in the NEC circulation and implications for the GoM deepwater nutrient fields and ecosystem are discussed.

The results from a numerical modelling system are presented for wave prediction inside Lunenburg Bay. The Bay, typical of the coast in Atlantic Canada, is an environment where ocean swell enters only from selected directions; wind-sea dominates the wave spectrum from other directions, and shallow water physics are important. The modelling system consisted of wave models for both the present time (nowcasts) and forecasts using the Simulating Waves Nearshore (SWAN) model inside the Bay. Nowcasts (stationary computations of the wave field that ran every 30 minutes) were driven by real-time observations of the directional wave boundary conditions, winds and water levels. Forecasts (48 hourly non-stationary computations) were driven by boundary conditions from the WAVEWATCH III ocean wave model (implemented on a larger domain) and winds from the Global Environmental Multiscale (GEM) atmospheric model. The results were compared with wave observations inside the Bay and provided in real-time. Model performance was assessed for a storm event with 2.8 m significant wave heights that occurred in October 2007, by comparing nowcast predictions, forecast predictions and observations. The nowcasts provided the best correlation, R2 = 0.75, with observations inside the Bay, since they were driven by observations made at the model boundary. The forecasts tended to underpredict the significant wave height and peak period, but overall the model results compared well with the data over a wide range of wind and wave conditions. Resume [Traduit par la redaction] Nous presentons les resultats d'un systeme de modelisation numerique pour la prevision des vagues dans la baie Lunenburg. La baie, typique de la cote dans le Canada atlantique, constitue un environnement ou la houle oceanique n'entre que par certaines directions, ou la mer du vent domine le spectre des vagues provenant d'autres directions et ou la physique des eaux peu profondes est importante. Le systeme de modelisation consistait en des modeles de vagues tant pour l'heure courante (previsions pour l'immediat) et que pour les previsions proprement dites, en utilisant le modele Simulation des vagues pres des cotes (SWAN) a l'interieur de la baie. Les previsions pour l'immediat (calculs stationnaires du champ de vagues executes toutes les 30 minutes) etaient basees sur des observations en temps reel des conditions de vagues directionnelles aux limites, du vent et des niveaux d'eau. Les previsions (calculs instationnaires de 48 heures) etaient basees sur les conditions aux limites fournies par le modele de vagues oceaniques WAVEWATCHIII (execute dans un domaine plus large) et sur les vents du modele atmospherique Global environnemental multiechelle (GEM). Nous avons compare les resultats aux observations de vagues faites dans la baie et fournies en temps reel. Nous avons evalue la performance du modele dans un cas de tempete ayant produit des vagues d'une hauteur significative de 2,8m en octobre 2007 en comparant les previsions pour l'immediat, les previsions et les observations. Les previsions pour l'immediat ont fourni la meilleure correlation, R2=0,75, avec les observations faites a l'interieur de la baie, etant donne qu'elles etaient basees sur des observations faites aux limites du modele. Les previsions avaient tendance a sous-prevoir la hauteur significative des vagues et la periode de pointe, mais dans l'ensemble les resultats du modele se comparaient bien aux donnees dans une vaste gamme de conditions de vent et de vagues.

The Minas Basin, the eastern end of the Bay of Fundy, is well known for its high tide ranges and strong tidal currents, which can be exploited to extract electricity power. The properties of the tidally-induced sediment transport in the Minas Basin, where significant changes in tidal processes may occur due to a recently proposed tidal power project, have been studied with a three-dimensional hydrodynamic model, an empirical bed load sediment transport model and surface sediment concentrations derived from the remotely-sensed images. The hydrodynamic model was evaluated against independent observational data, which include tidal elevation, tidal current (in the full water column and bottom layer), residual current profile and tidal asymmetry indicators. The evaluation shows that the model is in good agreement with the observations.The sediment transport includes two components, bed load and suspended particulate load. The bed load is calculated using the modelled bottom shear stress and the observed grain size data. The estimated features of bed load transport roughly agree with the observed patterns of the erosion and deposition in the Minas Basin and Cobequid Bay. The transport of the suspended load is estimated using the modelled velocity fields and the surface sediment concentration derived from remote-sensing images. The comparisons between the modelled results and the limited observations illustrate that the observed directions of suspended sediment transport are basically reproduced by the model. The modelled net suspended sediment input into the Minas Basin through Minas Passage is 2.4 x 10(6) m(3) yr(-1), which is comparable to the observed value of 1.6 x 10(6) m(3) yr(-1).The variations of the bed load and the suspended load in space and time are also presented. The total net transport, defined as the mean value of the sum of bed and suspended load transports during the tidal cycle, shows strong spatial variability. The magnitude of the transport flux ranges from 0.1 to 0.2 kg m(-1) s(-1) in Minas Channel and Minas Passage, 0.1 kg m(-1) s(-1) in Cobequid Bay, to 0.01 kg m(-1) s(-1) in the central Minas Basin and Southern Bight. In Minas Channel, the sediment transport follows the structure of the tidal residual circulation, which features a large anticlockwise gyre. The sediment in Minas Passage moves eastward and deposits into the central Minas Basin. However, the sediment from the eastern part of the Basin moves westward and deposits in the central Minas Basin as well. In the Cobequid Bay, sediment moves eastward and deposits in the upper bay. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.

Abstract An examination of current‐meter data gathered in 1967/68 on the continental shelf and slope off Nova Scotia has shown that meteorological forcing is an important source of energy. The response of currents to wind forcing is concentrated in a frequency band of 2.5 to 7 days. Daily mean currents of up to 25 cm/s appear to be associated with wind‐stress events. The highest correlations between wind and current are for the alongshore components of these variables. Wind‐induced currents may have been responsible for an intrusion of slope water onto the shelf which was observed in hydrographic sections from October and December 1968. Long data series (up to 167 days) formed by patching together shorter records demonstrate the existence of distinct low‐frequency variability at periods greater than 10 days. Some aspects of these motions suggest the presence of topographic Rossby waves on the shelf and slope. However, spatial and temporal coverage of data are not sufficient to define the sources of this v...

We present numerical simulations of the ocean surface waves generated by hurricane Juan in 2003 as it reached its mature stage (travelling from deep waters off Bermuda to Nova Scotia and making landfall near Halifax) using SWAN (v.40.31) nested within WAVEWATCH-III (v.2.22; denoted WW3) wave models, implemented on multiple-nested domains. As for all storm-wave simulations, spectral wave development is highly dependent on accurate simulations of storm winds during its life cycle. Due to Juan’s rapid translation speed (accelerating from 2.28ms−1 on 27 September, 1200UTC to 20ms−1 on 29 September, 1200UTC), an interpolation method is developed to blend observed hurricane winds with numerical weather prediction (NWP) model winds accurately. Wave model results are compared to in situ surface buoys and ADCP wave data along Juan’s track. At landfall, Juan’s maximum waves are mainly swell-dominated and peak waves lag the occurrence of the maximum winds. We explore the influence of surface waves on the wind and show that the accuracy of the wave simulation is enhanced by introducing swell and Stokes drift feedback mechanisms to modify the winds, and by limiting the peak drag coefficient under high wind conditions, in accordance with recent theoretical and experimental results.

Abstract In this study, three state-of-the-art operational forecast wave models are implemented on nested grids in order to achieve fine-resolution wave simulations (0.1°) in the Gulf of Maine and related northwest Atlantic waters. These models are the Simulating Waves Nearshore (SWAN) model, the Wave Action Model (WAM), and WAVEWATCH-III (hereafter WW3). Model performance is evaluated through comparisons with field measurements. Four composite model systems are compared: WAM and WW3 implemented on three nested domains, SWAN nested within WAM, and SWAN nested within WW3. Storm case studies include two intense midlatitude winter storms from January 2000 and January 2002. Although the models are comparable in terms of their overall performance and skill, it is found that WW3 provides a better statistical fit to the observed wave data compared with the other models, and that SWAN gives slightly better results if nested within WW3, rather than within WAM.

A semi-quantitative risk assessment model for dispersion of ballast water organisms in shelf seas is applied to the Scotian Shelf region of eastern Canada. The ballast water exchange process is simulated as the dispersion of tracer released into the surface layer of an ocean circulation model of the region. Circulation model variability is driven by wind stress from a cyclical year of forcing representing climatological storminess. Dispersion metrics related to invasion risk are developed and incorporated into a risk equation that computes the relative overall risk of invasion for ballast water exchange segments along vessel tracks crossing the shelf. Three hundred and sixty dispersion simulations are done for each segment of each of six tracks. Because the flow fields represent climatological variability in shelf circulation, the application of the risk assessment model captures the expected variability in invasion risk. Model results indicate that more than an order of magnitude variation in risk can exist along a given vessel track, and that tracks with offshelf segments provide a lower risk option compared to onshelf tracks. The model provides quantitative guidance to regulators regarding what is an acceptable trip diversion and can aid in numerous other management decisions.

We investigate the effects of surface waves on surface currents using surface drifter data from the Grand Banks and a coupled current‐wave‐drifter model. The theoretical basis of the study is Jenkins' theory of wave‐current interaction in which wind‐generated surface currents are modified by wind‐wave and wave‐current momentum transfers. The total surface current is the sum of the wave modified current, the Stokes drift and the tidal current. Jenkins' formulation was incorporated into the Princeton Ocean Model and applied to the Labrador Sea and the adjacent shelves. The wave energy spectrum from Wavewatch III was used to calculate the momentum transfer and the Stokes drift. A series of model experiments were conducted to simulate the drifter trajectories and examine the sensitivity of the simulations to model parameters. The results show that the Stokes drift is the dominant wave effect, which increases the surface drift speeds by 35% and veers the currents toward the wind directions. The net effect of wind‐to‐wave and wave‐to‐current momentum transfers reduces the surface speeds by a few percent. A statistical analysis of the model currents and drifter data shows that the inclusion of the wave effects improves the model simulations significantly. Model errors due to uncertainties in the model parameters including the eddy viscosity, wave spectrum, air drag of the drifters, and bottom friction are investigated. The model surface currents are shown to be most sensitive to the surface eddy viscosity and the wave energy spectra.

[i] A field program detected direct crossover of Scotian Shelf Water (SSC) from Browns to Georges Bank during winter/spring 1999 using (1) moored measurements, (2) drogued drifters, and (3) satellite imagery. Statistics of the 30-day trajectories indicate that (18, 55) ± 17% of the drifters crossed the (100, 200) m isobaths on Georges Bank. Transit times ranged from 2 to 26 days. Four of the drifters crossed onto the Northeast Peak (NEP) coinciding with the detection of Scotian Shelf Water at the central NEP mooring. These events are deemed significant because they serve to deliver particles from the Scotian Shelf directly to the gadoid spawning grounds on Georges Bank. Depths of the SSC layers lie between 15 and 50 m, and residence times for the Scotian Shelf Water on the NEP are estimated at 3 to 4 weeks. Canonical correlation analysis of the NEP temperature and salinity records suggest that 10% of the correlation structure among the variables is related to SSCs, while 70% is associated with the annual cycle. A search for SSC driving mechanisms reveals that (1) interannual variability of the annual freshwater discharge from the Gulf of St. Lawrence is not a factor, (2) Ekmanlike response of near-surface currents to southeast wind stress plays a role but is not the dominant factor, and (3) mesoscale baroclinic features penetrating Northeast Channel from offshore are the most likely cause. Furthermore, the incidence of SSCs may be related to offshore fronts whose proximity is positively correlated with the North Atlantic Oscillation index.

The predictive skill of a simple model of surface flow on the Scotian Shelf is assessed using oceanographic data collected in February 1996. The model is forced by wind stress, water density, and sea level along the open boundaries of the model domain. The skill of the model with respect to subtidal variations of alongshore current and bottom pressure is quantified by the ratio γ2 = Var(O − P)/Var(O), where Var(O − P) and Var(O) are the variance of the prediction errors and observations, respectively. Skill is highest for bottom pressure (γ2 = 0.2) followed, in order, by cross‐shelf gradients in bottom pressure (γ2 = 0.5), horizontally averaged currents (0.4 < γ2 < 0.7), and currents at individual current meters (0.6 < γ2 < 1.4). The skill of the model with respect to drifter position is quantified by the search radius, centered on the predicted drifter position, that ensures a 50% chance of locating the drifter. Skill varies significantly with time but is generally highest when the drifter motion is strongest. We conclude with a comparison of the performance of the model against predictions based on the release point of the drifters and the operational scheme presently used to guide marine search and rescue in this region.

Temperature and salinity variability over the crest and southern flank of Georges Bank are investigated using moored observations obtained from February to August 1995 and historical data. There was a large seasonal variation in water temperature, which decreased 1°C–2°C in February to a minimum of 5°C due to surface cooling and wind‐forced cross‐bank advection, and then increased steadily due to surface heating, reaching 10°C (southern flank) to 17°C (crest) in August. The crest warmed more than the southern flank because it is shallower. Temperature variability at shorter timescales (days to weeks) was primarily due to surface heating on the crest and horizontal advection on the southern flank. Salinity variability over the southern flank was primarily associated with two processes. Intrusions of warm, salty, shelf‐slope‐front water in May and August were associated with Gulf Stream warm‐core rings, but did not cause longer‐term changes on the southern flank or penetrate onto the crest. Alongbank advection brought low‐salinity, cool Scotian Shelf Water to the southern flank sites in March and early May, about three weeks after crossing the Northeast Channel onto the northeastern flank of Georges Bank (≈130 km away). This low‐salinity water on the southern flank in the spring did not penetrate immediately onto the crest. Instead, the crest salinity steadily decreased from April to August due to both precipitation (evaporation was small) and, based on historical data, a tidally forced, cross‐frontal exchange flow (0.01–0.02 m s−1) that both freshens and cools the crest.