In this study an individual-based numerical model with three-dimensional (3D) and time-dependent fields of circulation and hydrography is used to examine the effects of the physical environment and various biological behaviours on the distribution and movement of particles in the Gulf of St. Lawrence and adjacent waters. The 3D circulation and hydrographic fields are simulated by a numerical ocean circulation model. The model domain covers the St. Lawrence Estuary (SLE), the Gulf of St. Lawrence (GSL), the Scotian Shelf, the Gulf of Maine, and their adjacent waters. The basis of the individual-based model is a numerical scheme that tracks the movement of particles carried by ocean currents. Several swimming behaviours of marine animals are considered with efficient seaward migration in the GSL as the goal. Electronic tagging data for the American eel (Anguilla rostrata) are used as guidance in specifying the behaviours. It is demonstrated that particles that undergo an observed behaviour, known as selective tidal stream transport, are able to exit the SLE more efficiently than particles that are carried passively by the 3D ocean currents. Outside the SLE, particles that search for and swim towards higher salinity move further downstream than those that have a preference for deeper water or swim in random directions.

Interactions between surface waves and ocean currents over the northwest Atlantic during Hurricanes Earl and Igor (2010) are investigated using a coupled wave‐circulation model and observational data. Our results show that the coupled model improves the model performance in simulating the surface waves, sea level, water temperature, and salinity. By including the wave‐current interactions (WCIs), the maximum significant wave heights (SWHs) are reduced by more than 10% along the storm tracks and more than 20% over eddies. In the Gulf of Maine (GoM), the simulated SWHs and peak wave periods are also modulated by strong tidal currents. Surface waves, in turn, reduce the semidiurnal tidal amplitudes (up to ∼9%) and currents (up to ∼40%) in the GoM due mainly to the wave‐enhanced bottom stress. Surface waves also increase the peak storm surge (up to ∼19%) during these hurricanes, which is mostly attributed to the wave‐induced forces through Stokes drift and wave dissipation but slightly compensated by the wave‐enhanced bottom stress. The hurricane‐driven surface currents are modulated by waves toward the clockwise direction with a decrease in current speeds of more than ∼60%. This is attributed to the reduced current shear and density gradient resulting from mixing enhanced by wave breaking, but compensated by wave‐induced forces. Salinity and temperature are also modulated by surface waves, mostly through the wave‐induced forces and enhanced mixing by wave breaking. Overall, the coupled model produces higher surface salinity and stronger surface cooling due to the inclusion of the WCIs.

This study presents DalROMS-NWA12 v1.0, a coupled ocean circulation–sea ice–biogeochemistry modelling system for the northwest Atlantic Ocean (NWA) in which the circulation and biogeochemistry modules are based on ROMS (Regional Ocean Modeling System). The circulation module is coupled to a sea ice module based on the Community Ice CodE (CICE), and the physical ocean state simulated by the circulation module drives the biogeochemical module. Study of the biological carbon pump in the NWA is one of the main intended applications of this model. Global atmospheric and ocean reanalyses are used to force DalROMS-NWA12 at the sea surface and as part of its lateral boundary input, respectively. The modelling system is also forced by tides, riverine freshwater input, and continental runoff. The physical ocean state and sea ice from two simulations of the period 2015–2018, with and without nudging of the simulated temperature and salinity towards a blend of observations and reanalysis, are examined in this study. Statistical comparisons between model results and observations or reanalyses show that the control (nudged) simulation outperforms the prognostic (un-nudged) simulation in reproducing the paths of the Gulf Stream and the West Greenland Current, as well as propagation of the estuarine plume in the Gulf of St. Lawrence. The prognostic simulation performs better in simulating the sea ice concentration. The biogeochemical module, which is run only in the control simulation, performs reasonably well in reproducing the observed spatiotemporal variations in oxygen, nitrate, alkalinity, and total inorganic carbon. To examine the effects of tides and sea ice on the physical fields in the study area, results of simulations from which either component is absent are compared to results of the prognostic simulation. In the absence of tides, Ungava Bay in summer experiences a simulated surface salinity that is higher by up to ∼7 psu than in the simulation with tides, as well as experiencing changes in horizontal distributions of surface temperature and sea ice. Without coupling to the sea ice module, the circulation module produces summertime sea surface temperatures that are higher by up to ∼5 °C in Baffin Bay.

A nested-grid modelling system is used to quantify effects of winds and tides on the three-dimensional (3D) circulation and hydrography over the southwestern Scotian Shelf (swScS) and surrounding areas in 2018. The performance of the nested-grid modelling system is assessed by comparing model results with observations and reanalysis data. Analysis of model results demonstrates that both winds and tides enhance the vertical mixing and modify the 3D circulation over the swScS. In winter (summer), the wind-induced vertical mixing warms (significantly cools) the sea surface temperature (SST) over the Scotian Shelf (ScS). In addition to intense vertical mixing associated with winter convection, the wind-induced mixing raises the sea surface salinity (SSS) by entraining the relatively salty sub-surface waters with the surface waters. The effect of wind-induced vertical mixing is evident in the upper water columns of ~40 m (~15 m) in February (August) 2018 over the swScS, reflecting the typically stronger wind forcing in winter than in summer. The wind forcing also enhances the seaward spreading of river runoff. Strong tidal mixing and advection also play an important role in affecting the hydrography and density-driven currents over the Bay of Fundy (BoF), Georges Bank (GeB), and swScS. In summer, tides significantly reduce the SST, increase the SSS, and affect large density-driven currents over the BoF, GeB, and swScS. Winds and tides also modify the large-scale ocean circulation, eddies, meanders, and frontal structures in the deep waters off the swScS through the modulation of baroclinic hydrodynamics.

Moored observations and numerical model results are used to describe the circulation during 1998 in Santa Maria Basin (SMB) and Santa Barbara Channel (SBC), located to the northwest and southeast, respectively, of a bend in the southern California coastline. Singular value decomposition (SVD) analysis of observed wind stress and currents yields a first mode that represents large‐scale alongshore flow variability that appears to be wind driven, and a second mode which mostly represents flow variability in SBC and appears coherent with wind stress shear there. A three‐dimensional numerical ocean circulation model is used to simulate the flow. The model‐derived surface heat flux is most similar to observation‐derived values in summer and least similar in winter, and more similar in SMB than in SBC. Empirical orthogonal function (EOF) analysis of the Coriolis and pressure gradient terms for modeled near‐surface currents supports the hypothesis that the large‐scale flow variability of the first mode is wind‐driven. It further suggests that an alongshore pressure gradient drives the poleward flow along SBC's northern shelf. Wind stress curl (of which the shear along SBC is a part) or its gradient may govern such a pressure gradient, although this could not be ascertained. Modeled and observed currents are similar in their directions, but both the annual mean and variance tend to be smaller for modeled flow. SVD analysis shows that modeled and observed flows have similar modes of variability. Remotely driven flow may play a role in SMB, especially in summer.

A three-dimensional shelf circulation model is used to simulate the seasonal variability of circulation and hydrography on the Scotian Shelf over the eastern Canadian seaboard. The model is a modified form of an operational forecast system known as DalCoast3. The model is forced by forecast winds and atmospheric pressure produced by GEM, a Canadian numerical weather prediction model. Climatological temperature and salinity are used to initialize the model, and as lateral open boundary inputs. The monthly mean currents from a baroclinic circulation model of the northwest Atlantic Ocean are used as inputs to represent remotely forced flows. A new data assimilation method developed by Thompson et al. (2006b) is used to constrain model temperature and salinity to their respective climatologies, while allowing short-term (O(days)) variations to evolve prognostically. The model produces southwestward flows along the Nova Scotian coast and along the shelf break, which have been observed in the past. The pattern of simulated volume transport over the Scotian Shelf is qualitatively similar to those from past model studies, and the transport across a section on the inner shelf is also comparable to values calculated from observations.