Circulation In Bay Research Articles

Modelling of the residual circulation in Broken Bay and the lower Hawkesbury River, NSW

To elucidate the importance of lateral circulation in estuaries, a tidal circulation model was applied to Broken Bay and the lower Hawkesbury River estuarine system in New South Wales, Australia. The numerical simulation model solves the vertically averaged governing equations explicitly on a 61 × 51 finite difference grid, utilizing a 6.5-s computational step. The model is forced with an M2 tidal wave with a 1.1-m range, steady homogeneous wind stress, and river discharge. The time-averaged circulation is computed as residual transport velocities and consists of a series of residual circulation gyres. These gyres are due to tidal ebb-flood flow asymmetries and suggest the importance of lateral estuarine circulation. Very limited field data are consistent with this interpretation. Gyres in open areas change their sense of rotation in response to changing wind stress, whereas the gyres in the main channel appear to be independent of wind stress. With river discharge increased from 38 to 1250 m3 s-1, the gyres are replaced by strong ocean-directed residual velocities. The residual Stokes' drift is everywhere landward-directed and is weak except in shallow, constricted areas.

Observations of circulation and exchange processes in Jervis Bay, New South Wales

This paper discusses oceanographic observations obtained in and near Jervis Bay, a small coastal embayment of approximately 124 km2 situated on the New South Wales coast, during a series of measurement programmes spanning three years. Various mechanisms that drive water circulation within the bay and water exchange between the bay and the adjacent continental shelf are discussed. Current meter data from within the bay show surprisingly little correlation with the wind. Currents are characterized by persistent flows in one direction for periods of months, and it is suggested that influences from the shelf are responsible for driving the bay circulation. Flow through the bay entrance is weakly correlated with the wind at a period of around eight days, with near-surface inflow on the southern side of the entrance being in phase with deeper outflow on the northern side and vice versa. The shelf waters are well known for their coastally trapped waves. These have the potential to oscillate vertically the density surfaces on the shelf on a time scale of around eight days, and observations indicate that these waves are an additional mechanism driving circulation in the bay. The shelf waters are influenced by the warm East Australia Current and its eddies, and this appears to maintain a density contrast between the bay and the shelf for most of the year, with the shelf waters being less dense, which may be an additional mechanism driving bay circulation. Current-meter data from the bay entrance show a persistent northward current component in contrast to the strong southward flow of the East Australia Current on the shelf. Conductivity-temperature- depth data reveal cold, dense water flowing out of the bay during periods of strong winter cooling and the effects of warm eddies pushing warm water into the bay and displacing cold deeper water away from the bay. The heating/cooling cycle of the bay appears to be influenced by advection processes on the shelf as well as by aidsea heat and radiation exchanges.

The fortnightly mean circulation of chesapeake bay

Data from several current measurement programmes were used to examine the temporal and spatial variability of Chesapeake Bay circulation at time scales of 15 days and longer. First, year-long current records from two stations were analysed for response to runoff, wind stress and gravitational forcing. A strong spring freshet in April resulted in an annual maximum in the longitudinal density gradient, yet the surface current at mid-bay actually declined at the time of this maximum. The reason for this response lies in a prolonged period of northward wind which effectively reduced the strength of the two-layer gravitational flow. This shows that seasonal changes in the wind field can modulate the gravitational flow and that these annual wind shifts are a significant factor in the circulation of this estuary. Statistical analysis also indicates correlation between surface current and longitudinal wind at time scales of 15 days and longer, implying that meteorological effects cannot be completely filtered out at these frequencies. These data demonstrate that Chesapeake Bay circulation, unlike runoff, does not change by orders of magnitude between seasons, indicating that an examination of spatial patterns of circulation can be made using data collected during different deployment periods. A total of 168 current records from 1977 to 1983, averaged over periods of at least 15 days, were used to examine the spatial structure of the mean bay-wide circulation. Surface velocity, while predominantly down-bay, shows considerable longitudinal structure. This is to be expected considering the different meteorological conditions under which the data was collected. However, bottom observations show remarkably coherent up-bay flow regardless of the measurement period, illustrating the dominant role of topography and the importance of the gravitational mode in bay circulation.

Circulation and pollutant dispersion in Masan-Jinhae Bay of Korea

Circulation and dispersion of pollutants in the Masan-Jinhae Bay, Korea were studied through numerical experiments as well as hydrographic field survey. The field survey includes the measurements of water-level, currents, temperature, salinity and chemical oxygen demands(COD). To simulate the circulation and dispersion of pollutants discharged into the Bay, a two-dimensional finite element scheme was employed. The calculated tidal currents were consistent with the current-meter measurements. Using the circulation model, dispersion of pollutants was estimated resulting in very slow mixing with the open waters due to near-stagnancy of the inner bay waters.

Seasonal and spatial variations in the zooplankton community of an Eastern Antarctic coastal location

The zooplankton community of a shallow coastal area in Eastern Antarctica was found to be one of low species diversity dominated by Copepoda. It was comprised of the more common Antarctic oceanic copepod species, medusae, molluscs, euphausiids, several copepod species associated with the ice-water interface and, in summer, benthic fauna larvae. Most species of copepods displayed a marked seasonality in abundance with peak numbers between March and May. It is proposed that several factors, including phytoplankton seasonality contribute to the zooplankton species composition, zooplankton seasonality, and to the temporal differences in the period of maximum abundance between copepod species. Annual vertical migratory behaviour in conjunction with the circulation of Prydz Bay are important determining factors for those species which can be considered as oceanic; Calanoides acutus, Calanus propinquus, Ctenocalanus citer, Metridia gerlachei, Oithona similis and Oncaea curvata. However, for copepod species which can be classified as inshore residents, such as Stephos longipes, Paralabidocera antarctica and Drepanopus bispinosus, it is their association with the ice water interface that determines their seasonal appearance and abundance. Some differences were established between the zooplankton community of the Vestfold Hills and that of other Antarctic coastal regions. This may be attributed, in part, to the extensive shallow areas of the Vestfold Hills coastal region. Spatial distribution of the zooplankton with depth and between sites was investigated and found to be essentially homogenous. When differences were established, in the majority of cases all species present, all age classes and both sexes contributed to the differences.

Dynamical evaluation of the surface circulation using remote sensing of drifting ice floes

An analysis of ice drift from consecutive Landsat multispectral scanner images of the same area taken at 24‐h interval allowed the calculation of the surface circulation using a dynamical approach. Comparison between calculated and measured values shows that this method leads to a good approximation of the surface circulation in a region where ice floes are free drifting. On the other hand, the sole use of the floe drift over time to evaluate the currents leads to results that are far from the measured values. Tests made using various air and ice drag coefficients, and wind speeds and directions for different drift distances show that the error associated with these parameters is small. Although the values obtained using the numerical data involved considerably more effort and expense, the results were not significantly better than those found using photographic products. A good approximation of the surface circulation can thus be made using a simple digitization of the floe positions on photographic products. Application of the methodology to a set of four image pairs led to the recognition of two modes of circulation in southeastern Hudson Bay in spring 1985. This method can thus become a useful tool for rapid evaluations of surface currents in ice‐covered areas that can hardly be sampled otherwise.

Monitoring River Plume Transport and Mesoscale Circulation in Green Bay, Lake Michigan, Through Satellite Remote Sensing

This study investigates the transport and fate of the Fox River plume and the general circulation patterns within Lake Michigan's Green Bay utilizing satellite remote sensing imagery (Landsat TM and NOAA AVHRR). The calibrated satellite water color and thermal imagery shows the extreme lower portion of the bay as a distinct water mass (due to the influx of the Fox River) with a steep gradient in water transparency and surface temperature within the first 10 km from the river mouth. Fox River water and its heavy load of suspended and adsorbed material is advectively transported up along the bay's eastern shore in the form of a plume. Thus significant mixing of Fox River water is not restricted to the extreme lower portion of the bay but also is occurring in the middle portions of the bay. Similar water transparency but a distinct difference in thermal structure at the frontal zone between the Green Bay and Lake Michigan water masses indicates materials entering from the Fox River are largely retained within the bay rather than transported to the open waters of Lake Michigan.

The effects of a deep channel on the wind‐induced flushing of a shallow bay or harbor

Wind‐driven circulation in a shallow bay or harbor is greatly influenced by bottom bathymetry. As a result, the wind‐induced flushing time of the system can be significantly reduced by a deep channel dredged along the prevailing wind direction. In Koombana Bay, on the coast of southwest Australia, there exists a navigation channel of this type. Its effective flushing of the bay is studied here by current meter and drogue deployments, the use of HF radar to measure surface transport, and simulations with idealized long‐basin models and two‐dimensional and three‐dimensional numerical models.

A method for the determination of absolute geostrophic velocities in the sea

A method utilizing hydrographic data and vertically-averaged currents for the determination of absolute geostrophic velocities in the sea is described. Relative dynamic depths are interpolated on a selected grid of points by (i) using the linear least-squares estimation for a given function with “unknown data” and (ii) solving the Poisson equation with Dirichlet boundary conditions and a finite number of linear constraints within the domain investigated. Once the fields of relative velocities are computed and the measured vertically-averaged currents are interpolated on the grid using the same procedure as for the relative dynamic depths, the absolute currents may be calculated by simply subtracting the vertically-averaged relative velocities from the vertical averages of the currents. This method is illustrated by an example from the Rijeka Bay, a small basin in the northeast Adriatic Sea. The results for the Rijeka Bay are interesting from a qualitative point of view, whereas for the exact quantitative reproduction of the Bay circulation, higher-order dynamics should be invoked. It is concluded that the method in its original form is more suitable for the open sea, and the experiment needed for its application in such an environment is briefly described. DOI: 10.1111/j.1600-0870.1987.tb00291.x

The spectrum of subtidal variability in Chesapeake Bay circulation

The advent of long, continuous time series records of circulation in Chesapeake Bay has revealed the existence of large amplitude fluctuations within the subtidal range 0·03–0·6 cycles day −1. These fluctuations represent direct and indirect response of the estuary to variations in wind stress, fresh water inflow, and coastal sea level. The fluctuations in circulation are accompanied by synchronous fluctuations in transportable properties such as salinity and temperature. A quantitative model is presented to explain this variability within the main stem of Chesapeake Bay in terms of a linear reponse to irregular, time-varying meteorological forcing. The model calculates transfer functions and energy spectra of laterally averaged transport, surface elevation, and salinity in two layers separated by a halocline, over the frequency band 0·03–0·6 cycles day −1. Transfer functions between volume transport and wind stress obtained from one-month-long field experiments at three different cross sections in Chesapeake Bay are used to constrain model friction parameters. Using existing estimates for wind stress and coastal sea level energy spectra, energy spectra for volume transport and surface elevation are calculated as a function of longitudinal position. It is found that the observed volume transport spectrum at the mouth of the Bay can be explained quantitatively as the combined response to statistically indepentdent wind stress and sea level fluctuations. Variations in sea level account for 90% of the volume transport variance at the Bay mouth and dominate the volume transport spectrum below 0·375 cycles day −1. In the upper Bay, longitudinal wind stress accounts for most of the variance. A maximum in the volume transport spectrum at 0·4 cycles day −1, caused by a local maximum in the wind spectrum, is found at all upper Bay cross sections.

The meteorologically driven circulation in mid-Chesapeake Bay

The meteorologically driven circulation in mid-Chesapeake Bay

Numerical three-dimensional free surface circulation model for the South Biscayne Bay, Florida

A three– dimensional, time dependent free surface model has been developed for predicting circulation and surface height variations in a tidal bay. An explicit finite difference numerical solution is obtained by transforming the vertical coordinate in the governing model equations. The transformed geometry consists of a fixed, flat free surface and a constant depth basin for easy computation. The ocean–bay interface open boundary condition is incorporated into this hydrodynamic model without approximation, and yields rather accurate results for the bay circulation and tide level variations. The numerical method employs a staggered grid Richardson lattice, which has the inherent property of not requiring calculation of the tangential velocity components on solid surfaces. The momentum equations ignore horizontal diffusion which is small for the South Biscayne Bay, for which vertical diffusion and advection dominate.

Carbon production and export from Biscayne Bay, Florida. II. Episodic export of organic carbon

Seasonal meteorological events of high wind energy are important in the export of organic carbon from Biscayne Bay, Florida, by altering circulation and tidal flushing patterns coincident with increased resuspension. The accumulation of detrital organic carbon in the bay during productive summer months with light south-east breezes is reversed by the onset of the winter season and associated weekly cold fronts with sustained 15 knot northerly winds. The reversal of Biscayne Bay circulation patterns and increased discharge at Caesar's Creek result in an outwelling of dissolved organic carbon and particulate organic carbon. Southward advection at the seaward extremes of exchange channels prevents reintroduction of exported organic carbon by tidal currents.

Sediment distribution, circulation and provenance in a macrotidal bay: Garolim Bay, Korea

A study of the sedimentary regime in Garolim Bay has been carried out in connection with a feasibility study for tidal power development. At the mouth of the bay, sand is shown to be circulating round a central bank between an ebb and a flood channel. In the middle bay, clay and heavy-mineral distributions indicate a zone where finer sediments derived from offshore mix with those originating from the local streams. Quantities of land-derived sediments are presumed to be deposited near the shores during the rainy summer season and these are redistributed during the windy winter season, but the concentrations of suspended sediment are generally low. The influx of sediment appears to largely balance the increase in sea level. Siltation over the general area may not be seriously increased after construction of a barrage, but local siltation and scour near the barrage could be serious problems.

Modelling the Mean Barotropic Circulation in the Bay of Fundy and Gulf of Maine

Abstract Two dimensional, nonlinear numerical models are used to study the residual barotropic circulation generated by tides and steady winds in the Bay of Fundy and Gulf of Maine. The first a multi-grid model, is used to examine the Bay of Fundy with a coarse look at the Gulf of Maine. The circulation in the upper Bay of Fundy is predominantly tidally driven. The model clearly reproduces the major gyres observed at the head of the Bay. Steady wind stresses have some effect on the strength of these currents but little cited on the pattern. The counterclockwise gyre, observed in the body of the Bay of Fundy, is not reproduced in the model. The second model covers the lower Bay of Fundy and the Gulf of Maine with a single fine grid and is used to look at details in the Gulf of Maine. A clockwise circulation around Georges Bank and Nantucket Shoals is clearly indicated from tidal forcing alone. as is a gyre over the shallow part of Browns Bnak. Different steady wind-stress fields give rise to variations in ...

Occurrence, distribution, and feeding habits of juvenile lumpfish, Cyclopterus lumpus L. in the Bay of Fundy

Juvenile lumpfish (< 55 mm length) occur in near-surface waters of the Bay of Fundy from July to September. Samples collected simultaneously with neuston and subsurface nets indicate that the juveniles occur primarily in the top few centimetres of the water column. Seasonal changes in distribution may be related to wind drift of surface waters and the residual circulation of the inner Bay. The length–weight relationship (W = 8.7 L3.36 × 10−6) indicates allometric growth up to 50 mm, at which time lumpfish probably leave surface waters and adopt a pelagic or benthic existence. Juvenile lumpfish feed on a wide range of near-surface plankton, shifting with growth from harpacticoid copepods (particularly Harpacticus chelifer) to the amphipods Calliopius laeviusculus and Parathemisto gaudichaudi.

Sediment distribution, circulation and provenance in a macrotidal bay: Garolim Bay, Korea

Sediment distribution, circulation and provenance in a macrotidal bay: Garolim Bay, Korea

Seabed drifter movement in San Diego Bay and adjacent waters

The seabed drifter has been used successfully to provide valuable information in many estuarine and open sea environments. It was therefore selected for use in the San Diego area. Five hundred drifters were released in San Diego Bay and adjacent ocean waters to delineate bottom flow patterns. Four significant bottom drift regimes are differentiated: off-coastal, main bay channel, open and semi-enclosed docking basins. Mean residual bottom drift ranged between 0·17km day −1 off the coast to essentially zero in the docking basins. Off-coast drifter results (31% recovery) showed a persistent northmoving bottom current with shallow near-coast drift distances between 4 and 25 km. This nearshore north moving bottom current appears to cause a net bottom water inflow into the main San Diego Bay channel (44% recovery). In the open bay a reverse trend was observed from the 16% of the drifters recovered. At the head of the estuary, evaporative densification is believed to occur, with the heavier water sinking and moving outward, towards the estuary mouth, resulting in an area of opposing bottom water currents. In this area San Diego Gas and Electric power plant takes in an average 150 million gallons of cooling water daily which, discharged as warm surface water, is suggested as the surface divergence mode required to reconcile the observed flow. With the three San Diego Bay electric power plants utilizing more than 5% of the maximum tidal prism for cooling purposes, this flow may play a major role in the overall bay circulation and requires quantitative investigation.

A study of the circulation in bay of Ilha Grande and Bay of Sepetiba: part I, a survey of the circulation based on experimental field data

A study of the circulation in bay of Ilha Grande and Bay of Sepetiba: part I, a survey of the circulation based on experimental field data

A study of the circulation in Bay of Ilha Grande and Bay of Sepetiba: part II: an assessment to the tidally and wind-driven circulation using a finite element numerical model

A study of the circulation in Bay of Ilha Grande and Bay of Sepetiba: part II: an assessment to the tidally and wind-driven circulation using a finite element numerical model