Search

A long‐standing hypothesis is that the steady along‐shelf circulation in the Northwest Atlantic (NWA) coastal ocean is driven by buoyancy input from continental freshwater runoff. However, the forcing from the freshwater runoff has not been adequately evaluated and compared with other potential driving mechanisms. This study investigates the roles of both wind stress and freshwater runoff in driving the mean along‐shelf flow in the NWA coastal ocean and examines other potential drivers using a newly developed high‐resolution regional model with realistic forcing conditions. The results reveal that wind stress has a larger impact than freshwater runoff on the overall mean circulation and along‐shelf sea‐level gradient on the NWA shelf. While the continental freshwater input consistently contributes to the equatorward along‐shelf flow and higher sea level along the coast, wind stress is more effective for the setup of the broad‐scale circulation pattern by driving the along‐shelf flow on the Labrador Shelf and opposing the flow in the Mid‐Atlantic Bight and on the Scotian Shelf. In addition to the local wind and continental runoff, the sub‐Arctic inflow from higher latitude is an essential part of the NWA shelf circulation system. This remote driver directly contributes to the along‐shelf flow and insulates the shelf flow from the Gulf Stream on the southern shelves. Plain Language Summary: This study addresses a long‐standing question of what drives the mean equatorward flow along the Northwest Atlantic continental shelf. The results show that the mean along‐shelf flow is influenced more by wind stress than local buoyancy forcing resulting from the freshwater discharges from rivers and glaciers, which has long been considered the dominant driver of the along‐shelf circulation. Remote forcing through inflow from higher latitude is also important in maintaining the broad‐scale mean along‐shelf flow and sea level. This work also provides updated views of the circulation dynamics and momentum balance of the mean along‐shelf circulation, contributing to the understanding of both the current and future states of our ocean and climate systems. Key Points: Wind forcing plays an important role in setting up the mean along‐shelf flow in the Northwest Atlantic (NWA) coastal oceanLocal buoyancy from continental runoff is not as significant as previously hypothesizedRemote subpolar inflow is an essential part of the NWA shelf circulation system [ABSTRACT FROM AUTHOR]

Astronomical tides in the South Atlantic Bight are simulated with a fine-resolution (down to ∼10 m), shallow-water equations, finite element model that fully represents the contiguous geometry of the system, including the: width- and depth-variable continental shelf; inlet-punctuated coastline; and riverine and intertidal character of the estuaries. Tidal levels are analyzed for the entirety of the South Atlantic Bight which produces highly detailed maps (resolution of 10–100 m) of tidal datums (MLW—mean low water, MHW—mean high water) throughout the estuarine rivers and intertidal zones. Model skill (performance) when evaluated over 142 gaging stations is R 2  = 92% for tidal datums (MLW and MHW) and less than 10% error for the full astronomical tide signal inside the estuaries, and within 0.01 m s –1 error for M 2 shelf velocities. Tidal analysis reveals a sensitivity of the M 2 -resonant shelf circulation in the South Atlantic Bight with respect to the tidal inlets, estuarine rivers and intertidal zones, primarily from the Florida/Georgia border to Winyah Bay (South Carolina). The inlets generate an ‘openness’ the South Atlantic Bight coastline, but more important are the geometric-dynamic influences of the estuarine rivers (the cause-effect being enhanced resonance due to extended effective shelf width) and intertidal zones (the cause-effect being tidal decay due to energy dissipation). The riverine and intertidal features of the coastline subtly change the mode of tidal propagation over the continental shelf. Dynamically, the standing wave behavior (resonance) of astronomical tides in the South Atlantic Bight is a function of the shelf and coastline geometries. Modeling and assessment of coastal and shelf circulation should consider the domain as a continuum, including high-resolution definition of the coast's estuaries and intertidal zones. [ABSTRACT FROM AUTHOR]

The marine waters across Tasmanian's eastern continental shelf are biologically productive and home to economically important fisheries and aquaculture industries. However, the marine climate there is poorly understood. We use a high-resolution (∼2 km in the horizontal), three-dimensional ocean model for eastern Tasmania (ETAS) to examine the simulated mean state and seasonal cycle of temperature, salinity and three-dimensional flow field, and the evaluation of daily model outputs against in situ and remote observations for the 1993–2014 period. We also use the model to examine the roles of river input and tidal forcing. The model is evaluated against remotely-sensed sea surface temperature and in-situ observations of sea level and subsurface temperature, salinity, and currents. The mean state demonstrates the influence of two well-known boundary currents (the East Australian Current, EAC, and the Zeehan Current, ZC) as well as the effects of local freshwater input from river runoff. The EAC is dominant in summer and the ZC in winter; the influence of the EAC also increases northwards and in the offshore direction. In addition, the model indicates the presence of a semi-permanent subsurface (50–100 m depth) northward flow trapped near the coast. Cool freshwater runoff from the Derwent and Huon Rivers directly impacts the temperature and salinity in their estuaries but has little influence further across the shelf. Tidal forcing impacts the mean state through tide-river interactions which flush Frederick Henry Bay and Norfolk Bay with freshwater. Tidal forcing also impacts the variability of temperature all along the coastline, most likely due to changes in the turbulent mixing near to the coast. The ETAS model output data are available as a high-resolution representation of the mean state, seasonal variations, and interannual variability of Tasmania's eastern continental shelf marine climate. [ABSTRACT FROM AUTHOR]

A terrain-following ocean model is implemented for simulating three-dimensional tidal and residual circulations in the Gulf of Khambhat and its adjacent oceans on the west coast of India. The model is forced with time varying tidal levels and momentum fluxes at the western and southern boundaries. Simulated tidal levels and currents compare well with the observation at tide gauge and current-meter stations. Estimated residual circulation in the region has several notable features that include strong southward along channel flow inside the gulf, northwestward propagating coastal boundary jet currents parallel the 60 m isobaths, southward slope currents, alongshore coastal currents on the southeastern flank of the shelf and a number of meso-scale eddies. All these features of residual circulation are captured well by the satellite imagery of Chlorophyll concentration mapped in the month of March, the period when tide plays dominant role on the control of net circulation in the region. [ABSTRACT FROM AUTHOR]