scholarly journals Effects of Tidal Range Variability and Local Morphology on Hydrodynamic Behavior and Salinity Structure in the Caeté River Estuary, North Brazil

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Geórgenes H. Cavalcante ◽  
David A. Feary ◽  
Björn Kjerfve
Keyword(s):  
Vertical Mixing ◽  
River Estuary ◽  
Salt Transport ◽  
Stokes Drift ◽  
Salt Flux ◽  
Tidal Range ◽  
North Coast ◽  
Vertical Diffusion ◽  
The North ◽  
North Brazil

Tidal influence and local morphology on circulation and salt transport are investigated in the Caeté river estuary, a well-mixed estuary along the north coast of Brazil. Velocity, temperature, and salinity data were collected in three different locations along the estuary’s main channel, over three single, 13 h tidal cycles. The aim of this study was to investigate the relationship between tidal distortion and salinity by using classical methods of comparison of three cross-channel circulation characteristics, as well as computation of salt flux and vertical mixing. Findings indicate a flood-ebb asymmetry in currents, due to the distinct funneling morphology of the estuary, with shallow marginal areas being dominant towards the estuary head, while both stratification and shear dominate near the estuary mouth. The tidal currents enhanced vertical diffusion in the mid- and lower reaches, explaining the prevailing weakly stratified conditions, while the dominant well-mixed conditions in the upper estuary are a result of a combination of stronger flood currents and negligible vertical saline gradient. The predominant downstream salt transport supports the conclusion that there is little accumulation of salt in the Caeté river estuary. In addition, findings indicate that tidal correlation and Stokes drift are important components in the upper estuary, while tidal correlation played an important role in the middle estuary, with fluvial discharge most important in the lower estuary.

Correlated Millennial-Scale Changes in Surface Hydrography and Terrigenous Sediment Yield Inferred from Last-Glacial Marine Deposits off Northeastern Brazil

1998 ◽  
Vol 50 (2) ◽  
pp. 157-166 ◽  
Author(s):  
Helge W. Arz ◽  
Jürgen Pätzold ◽  
Gerold Wefer
Keyword(s):  
North Atlantic ◽  
Isotope Composition ◽  
Sediment Cores ◽  
Ice Cores ◽  
Northeastern Brazil ◽  
Salt Flux ◽  
Terrigenous Sediment ◽  
The North ◽  
North Brazil ◽  
The North Atlantic

The stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern Brazil. Stable oxygen isotope records of the planktonic foraminiferal species Globigerinoides sacculiferand Globigerinoides ruber(pink) reveal sub-Milankovitch changes in sea-surface hydrography during the last 85,000 yr. Warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high XRF intensities of Ti and Fe, and which suggest humid conditions in northeast Brazil. These tropical signals correlate with climatic oscillations recorded in Greenland ice cores (Dansgaard-Oeschger cycles) and in sediment cores from the North Atlantic (Heinrich events). Trade winds may have caused changes in the North Brazil Current that altered heat and salt flux into the North Atlantic, thus affecting the growth and decay of the large glacial ice sheets.

scholarly journals Determination of spatially varying Van der Burgh's coefficient from estuarine parameter to describe salt transport in an estuary

2010 ◽  
Vol 7 (6) ◽  
pp. 8781-8808
Author(s):  
D. C. Shaha ◽  
Y.-K. Cho
Keyword(s):  
Spatial Variation ◽  
Salinity Gradient ◽  
Spring Tide ◽  
Vertical Mixing ◽  
River Estuary ◽  
Relative Strength ◽  
Salt Transport ◽  
K Value ◽  
Relative Contribution ◽  
Spatially Varying

Abstract. The estuarine parameter ν is widely accepted as describing the relative contribution of the tide-driven and density-driven mixing mechanism of salt transport in estuaries. Van der Burgh's coefficient K is another parameter that also determines the relative strength of two mechanisms. However, a single value of K, which has been considered in previous studies, can not represent the spatial variation of these mechanisms in an estuary. In this study, the spatially varying K has been determined from the ν value calculated using intensively observed longitudinal salinity transects of the Sumjin River Estuary with exponential shape. The spatially varying K describes the spatial variation of these mechanisms reasonably well and is independent of the river discharge downstream of the estuary during spring tide where the strong tides cause well mixed conditions. However, K values increase upstream and are found to depend on the freshwater discharge, with suppressing vertical mixing. The K value has been scaled on the basis of the ν value and ranges between 0 and 1. If K is <0.4, the up-estuary salt transport is entirely dominated by tide-driven mixing during spring tide near the mouth. If 0.4 < K < 0.8, both tide-driven and density-driven mixing contribute to transporting salt in the central regimes. If K > 0.8, the salt transport is almost entirely by density-driven circulation in the upper most regimes during both spring and neap tides. In addition, another K-based dispersion equation has been solved by using this spatially varying K. The spatially varying K demonstrates density-driven circulation more prominently at the strong salinity gradient location compared with a single K value.

scholarly journals The Production and Dissipation of Compensated Thermohaline Variance by Mesoscale Stirring

2009 ◽  
Vol 39 (10) ◽  
pp. 2477-2501 ◽  
Author(s):  
K. Shafer Smith ◽  
Raffaele Ferrari
Keyword(s):  
Large Scale ◽  
Vertical Mixing ◽  
Small Scale ◽  
Vertical Diffusion ◽  
The North ◽  
Salinity Gradients ◽  
Scale Temperature ◽  
The Mean ◽  
Geostrophic Turbulence ◽  
Quasigeostrophic Model

Abstract Temperature–salinity profiles from the region studied in the North Atlantic Tracer Release Experiment (NATRE) show large isopycnal excursions at depths just below the thermocline. It is proposed here that these thermohaline filaments result from the mesoscale stirring of large-scale temperature and salinity gradients by geostrophic turbulence, resulting in a direct cascade of thermohaline variance to small scales. This hypothesis is investigated as follows: Measurements from NATRE are used to generate mean temperature, salinity, and shear profiles. The mean stratification and shear are used as the background state in a high-resolution horizontally homogeneous quasigeostrophic model. The mean state is baroclinically unstable, and the model produces a vigorous eddy field. Temperature and salinity are stirred laterally in each density layer by the geostrophic velocity and vertical advection is by the ageostrophic velocity. The simulated temperature–salinity diagram exhibits fluctuations at depths just below the thermocline of similar magnitude to those found in the NATRE data. It is shown that vertical diffusion is sufficient to absorb the laterally driven cascade of tracer variance through an amplification of filamentary slopes by small-scale shear. These results suggest that there is a strong coupling between vertical mixing and horizontal stirring in the ocean at scales below the deformation radius.

scholarly journals Mangrove vegetation in Amazonia: a review of studies from the coast of Pará and Maranhão States, north Brazil

2008 ◽  
Vol 38 (3) ◽  
pp. 403-420 ◽  
Author(s):  
Moirah Paula Machado de Menezes ◽  
Uta Berger ◽  
Ulf Mehlig
Keyword(s):  
Mangrove Forest ◽  
Local Population ◽  
Tree Height ◽  
North Coast ◽  
Litter Fall ◽  
Mangrove Tree ◽  
The North ◽  
North Brazil ◽  
Associated Species ◽  
Rural Construction

The present study is a compilation of the literature about vegetation of mangrove forest of the north coast of Brazil. It synthesizes the knowledge about this important ecosystem and lists the currently available literature. The study focuses on the coast of Pará and Maranhão states, which are covered by a continuous belt of mangroves. The mangrove flora comprises six mangrove tree species and several associated species. Mangrove tree height and stem diameter vary as a function of abiotic local stand parameters. Seasonal variation in rainfall and salinity affect the species' phenology and litter fall. Local population use products derived from mangrove plants for different purposes (e.g. fuel; medicinal; rural construction). The increase in the coastal population has given rise to conflicts, which impact on mangrove forest.

scholarly journals Modeling Influence of Stratification on Lateral Circulation in a Stratified Estuary

2009 ◽  
Vol 39 (9) ◽  
pp. 2324-2337 ◽  
Author(s):  
Peng Cheng ◽  
Robert E. Wilson ◽  
Robert J. Chant ◽  
David C. Fugate ◽  
Roger D. Flood
Keyword(s):  
Lower Layer ◽  
Cell Structure ◽  
Vertical Mixing ◽  
River Estuary ◽  
Vertical Diffusion ◽  
Lateral Asymmetry ◽  
Differential Diffusion ◽  
Deep Channel ◽  
Lateral Circulation ◽  
Stratified Estuary

Abstract The dynamics of lateral circulation in the Passaic River estuary is examined in this modeling study. The pattern of lateral circulation varies significantly over a tidal cycle as a result of the temporal variation of stratification induced by tidal straining. During highly stratified ebb tides, the lateral circulation exhibits a vertical two-cell structure. Strong stratification suppresses vertical mixing in the deep channel, whereas the shoal above the halocline remains relatively well mixed. As a result, in the upper layer, the lateral asymmetry of vertical mixing produces denser water on the shoal and fresher water over the thalweg. This density gradient drives a circulation with surface currents directed toward the shoal, and the currents at the base of the pycnocline are directed toward the thalweg. In the lower layer, the lateral circulation tends to reduce the tilting of isopycnals and gradually diminishes at the end of the ebb tide. A lateral baroclinic pressure gradient is a dominant driving force for lateral circulation during stratified ebb tides and is generated by differential diffusion that indicates a lateral asymmetry in vertical mixing. Over the thalweg, vertical mixing is strong during the flood and weak during the ebb. Over the shoal, the tidally periodical stratification shows an opposite cycle of that at the thalweg. Lateral straining tends to enhance stratification during flood tides and vertical diffusion maintains the relatively well-mixed water column over the shoal during the stratified ebb tides.

scholarly journals Exchange Flows in Tributary Creeks Enhance Dispersion by Tidal Trapping

2021 ◽  
Author(s):  
Adrian Mikhail P. Garcia ◽  
W. Rockwell Geyer ◽  
Noa Randall
Keyword(s):  
Tidal Marsh ◽  
Salinity Gradient ◽  
River Estuary ◽  
Main Channel ◽  
Salt Flux ◽  
Time Varying ◽  
Exchange Flow ◽  
Salt Balance ◽  
The North ◽  
Salinity Anomaly

Abstract The North River estuary (Massachusetts, USA) is a tidal marsh creek network where tidal dispersion processes dominate the salt balance. A field study using moorings, shipboard measurements, and drone surveys was conducted to characterize and quantify tidal trapping due to tributary creeks. During flood tide, saltwater propagates up the main channel and gets “trapped” in the creeks. The creeks inherit an axial salinity gradient from the time-varying salinity at their boundary with the main channel, but it is stronger than the salinity gradient of the main channel because of relatively weaker currents. The stronger salinity gradient drives a baroclinic circulation that stratifies the creeks, while the main channel remains well-mixed. Because of the creeks’ shorter geometries, tidal currents in the creeks lead those in the main channel; therefore, the creeks never fill with the saltiest water which passes the main channel junction. This velocity phase difference is enhanced by the exchange flow in the creeks, which fast-tracks the fresher surface layer in the creeks back to the main channel. Through ebb tide, the relatively fresh creek outflows introduce a negative salinity anomaly into the main channel, where it is advected downstream by the tide. Using high-resolution measurements, we empirically determine the salinity anomaly in the main channel resulting from its exchange with the creeks to calculate a dispersion rate due to trapping. Our dispersion rate is larger than theoretical estimates that neglect the exchange flow in the creeks. Trapping contributes more than half the landward salt flux in this region.

scholarly journals Determination of spatially varying Van der Burgh's coefficient from estuarine parameter to describe salt transport in an estuary

2011 ◽  
Vol 15 (5) ◽  
pp. 1369-1377 ◽  
Author(s):  
D. C. Shaha ◽  
Y.-K. Cho
Keyword(s):  
Spatial Variation ◽  
Salinity Gradient ◽  
Vertical Mixing ◽  
River Estuary ◽  
Relative Strength ◽  
Salt Transport ◽  
K Value ◽  
Relative Contribution ◽  
Spatially Varying

Abstract. The estuarine parameter v is widely accepted as describing the relative contribution of the tide-driven and density-driven mixing mechanism of salt transport in estuaries. Van der Burgh's coefficient K is another parameter that also determines the relative strength of two mechanisms. However, a single value of K, which has been considered in previous studies, can not represent the spatial variation of these mechanisms in an estuary. In this study, the spatially varying K has been determined from the v value calculated using intensively observed longitudinal salinity transects of the Sumjin River Estuary with exponential shape. The spatially varying K describes the spatial variation of these mechanisms reasonably well and is independent of the river discharge downstream of the estuary where the strong tides cause well mixed conditions. However, K values increase upstream and are found to depend on the freshwater discharge, with suppressing vertical mixing. The K value has been scaled on the basis of the v value and ranges between 0 and 1. If K < 0.3, the up-estuary salt transport is entirely dominated by tide-driven mixing near the mouth. If 0.3 < K < 0.8, both tide-driven and density-driven mixing contribute to transporting salt in the central regimes. If K > 0.8, the salt transport is almost entirely by density-driven circulation in the upper most regimes. In addition, another K-based dispersion equation has been solved by using this spatially varying K. The spatially varying K demonstrates density-driven circulation more prominently at the location of strong salinity gradient compared with a single K value.

scholarly journals Hydrodynamics of a tropical estuary: Buranhém River, Porto Seguro, Brazil

RBRH ◽  
2018 ◽  
Vol 23 (0) ◽  
Author(s):  
Ana Carolina Rodrigues de Sá Silva ◽  
Marcos Eduardo Cordeiro Bernardes ◽  
Arcilan Trevenzoli Assireu ◽  
Eduardo Siegle ◽  
Paulo Henrique Gomes de Oliveira Sousa ◽  
...  
Keyword(s):  
Urban Areas ◽  
Vertical Mixing ◽  
Salt Transport ◽  
Tidal Range ◽  
Hydrodynamic Characteristics ◽  
Tropical Estuary ◽  
Residual Currents ◽  
Velocity Gradients ◽  
Vertical Density ◽  
First Time

ABSTRACT Estuaries are dynamic environments that are highly vulnerable to anthropogenic influences, especially when adjacent to urban areas. In this study it is assessed for the first time the hydrodynamic characteristics of the Buranhém estuary (Northeast Brazil). The aim is to define the salt transport mechanisms and the hydrodynamics and stratification patterns of this tropical estuary, under both spring and neap tidal conditions. Fieldwork was carried out during 8 days covering varying tidal range conditions (July 30th to August 7th, 2015). Salinity and temperature were continuously monitored at moored stations at both the surface and bottom, whereas velocity profile was sampled by a bottom-mounted instrument. Average velocity in the water column was 0.46 m.s-1 during flood tides and 1.0 m.s-1 during ebb tides. Residual currents were seaward, with ebb dominance. The dominant salt transport mechanism is turbulent diffusion. Most of the layer Richardson values did not exceed 2, indicating well mixed conditions mainly during spring tides. Stratification varies with tide condition, with spring tides being able to further mix the vertical structure. Vertical velocity gradients that generate vertical mixing overcome the stabilizing effects generated by vertical density gradients.

scholarly journals Circulation and salt balance in the São Francisco river Estuary (NE/Brazil)

RBRH ◽  
2017 ◽  
Vol 22 (0) ◽  
Author(s):  
Geórgenes Cavalcante ◽  
Luiz Bruner de Miranda ◽  
Paulo Ricardo Petter Medeiros
Keyword(s):  
River Discharge ◽  
Neap Tide ◽  
Spring Tide ◽  
River Estuary ◽  
Salt Transport ◽  
Salt Flux ◽  
Sao Francisco River ◽  
Tidal Cycles ◽  
São Francisco River ◽  
And Diffusion

ABSTRACT In order to evaluate how river discharge and tidal currents forcing influence the circulation and salt transport within the São Francisco River-Estuary, a two 25 hour surveys campaigns and along-channel profiles were performed in the estuary main channel (18/19 and 25/26 February 2014). The current intensity showed higher asymmetry between flood (v<0) and ebb (v>0) currents in spring tide (-0.6 and 1.1 m/s), as compared to neap tide (-0.4 and 1.0 m/s), which was attributed to the intense buoyancy energy enhanced by the stronger discharge in spring. Overall, salinity presented high stratified conditions and varied between 0.0<S<36.6, and 0.5<S<36.1 from surface to bottom, during spring and neap, respectively. Although river discharge reduced from spring to neap tide partially mixed-highly stratified conditions (type 2b) remained in both periods, with advection and diffusion contributing with 34% and 66% to the net upstream salt flux in spring, respectively, and 56% and 44% in neap tide, respectively, which was attributed to the balance of tidal and baroclinic forcing and river discharge. The dominant downstream advective salt transport in both spring (12.5 kg.m-1s-1) and neap (15.2 kg.m-1s-1) tidal cycles suggests that there is little salt accumulation inside the São Francisco estuary.

Wastewater dispersion measurements in the Fraser River estuary, Canada, for the Annacis Island Wastewater treatment plant outfall

1998 ◽  
Vol 38 (10) ◽  
pp. 293-300 ◽  
Author(s):  
D. O. Hodgins ◽  
R. E. Corbett ◽  
D. S. Parker ◽  
W. K. Faisst ◽  
J. R. Ellis
Keyword(s):  
Vertical Mixing ◽  
Monitoring Program ◽  
Treatment Plant ◽  
River Estuary ◽  
Fraser River ◽  
The North ◽  
Low Concentrations ◽  
Strong Current ◽  
North Bank ◽  
Lateral Mixing

Detailed measurements of effluent dilution and dispersion were completed in 1995 in the Fraser River estuary, Canada, as part of a larger study to design an environmental effects monitoring program. Wastewater is discharged at rates of 4-9 m3/s through an 18-port, 3-barrel diffuser in about 10 m of water in a tidal estuary 24 km upstream of the mouth. Rhodamine WT dye was used as a tracer and coordinated in situ measurements were carried out using a towed fluorometer system and a profiling system, each operated from separate vessels. Dispersion measurements were obtained for high and low river discharge conditions and for the complete tidal cycle. The surveying methods proved to be effective for both weak and strong current conditions. It was found that vertical mixing was rapid in the unstratified portion of the estuary and usually complete within 200-500 m of the diffuser. Lateral mixing was relatively slow and cross-channel mixing was not observed even at distances exceeding 12 km. Maximum intertidal zone exposure to effluent occurred on ebb tides but at low concentrations (dilution &gt; 300:1) and confined to the north bank of the river. Minimum dilutions, of the order of 5:1 to 10:1, were found over the outfall at slack tide as the current reversed.

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