Tidal Phase Research Articles

The behaviour of sea snakes (Emydocephalus annulatus) shifts with the tides

Tidal cycles are known to affect the ecology of many marine animals, but logistical obstacles have discouraged behavioural studies on sea snakes in the wild. Here, we analyse a large dataset (1,445 observations of 126 individuals) to explore tidally-driven shifts in the behaviour of free-ranging turtle-headed sea snakes (Emydocephalus annulatus, Hydrophiinae) in the Baie des Citrons, New Caledonia. Snakes tended to move into newly-inundated areas with the rising tide, and became more active (e.g. switched from inactivity to mate-searching and courting) as water levels rose. However, the relative use of alternative habitat types was largely unaffected by tidal phase.

Tidal and Subtidal Variations in Water Level Produced by Ocean‐River Interactions in a Subtropical Estuary

AbstractNear yearlong time series measurements of water level elevation from seven stations along the Suwannee River, Florida, were used to characterize, observationally and analytically, the propagation of tidal and subtidal signals along the estuary resulting from tide‐river interactions. Tidal amplitudes and phases were obtained from least squares fits to observed values and used to compare to an analytical model. Subtidal amplitude and phases were characterized by Hilbert empirical orthogonal functions (HEOFs), obtained through complex principal component analysis, and compared to an analytical solution. The landward attenuation of the tidal signal was replicated analytically. The subtidal signal (periods > tides) was also described analytically with an oceanic wave moving landward and a seaward river pulse. The subtidal analytical solution reproduced the competition between the landward and seaward waves and the zone where each wave dominated over the other. Depending on the phase of these landward and seaward subtidal waves, the resulting subtidal signal amplitude could either (a) attenuate landward to a certain location and then increase or (b) amplify landward up to a certain zone and then decrease.

Climatology of the main (24-h and 12-h) tides observed by meteor radars at Svalbard and Tromsø: Comparison with the models CMAM-DAS and WACCM-X

The paper presents climatology of the mean winds and diurnal and semidiurnal tides observed by meteor radars at high latitudinal stations Svalbard (78°N, 16°E) and Tromsø (70°N, 19°E) based on 18 years (2001–2018) and 16 years (2003–2018) of measurements, respectively. The main focus of the study is to clarify the features of the diurnal tide (DT) because it is poorly known particularly at high latitudes. The detailed analysis of both tidal amplitudes and phases indicated that the seasonal and altitude structure of the DT at these two not very distant stations are significantly different. Moreover, a very unusual vertical structure of the DT at Tromsø has been found where above altitudes of ~88–90 km the zonal and meridional components have opposite directions of vertical propagation. This unusual vertical tidal feature has been supported by the climatology of the DT obtained by the MF radar situated at Tromsø for the period of time 1997–2019. The paper presents also the comparison of the radar observations with two models: the assimilated CMAM-DAS and the specified dynamics (SD) WACCM-X. The WACCM-X simulated DT supports to large extent the climatology of the DT at Tromsø while the assimilated CMAM-DAS reproduced the evanescent character of the tide in summer up to altitude of ~88 km with almost the same amplitudes and phases as the observed ones. These results could be used as benchmarks for model simulations for understanding the forcing mechanisms of the DT at high latitudes of the considered region.

Applicability of analytical solutions to tidal propagation in circular islands

The propagation of tides into coastal aquifers is an important phenomenon in the migration of coastal contaminants, for the representation of shoreline boundary conditions in regional-scale groundwater models, and for the estimation of aquifer properties based on tidal amplitude attenuation and/or phase increase. In this study, an analytical solution to the propagation of tidal fluctuations in a radial flow field, applicable to circular islands, is compared to the existing straight-coastline (“Ferris”) solution. The analytical solution is compared to numerical simulation (using SEAWAT) of a simple-harmonic ocean tide and its propagation within a circular island. This represents the first attempt to combine a previous correction that allows SEAWAT to simulate axisymmetric flow and a modification to SEAWAT to create tidal boundary conditions. Bench testing the analytical solution against the numerical model confirms the numerical approach. The circular-island solution is compared to the Ferris solution in terms of tidal amplitude decay and phase shift. Whereas amplitude decay from the Ferris solution is valid only for near-shore locations within circular islands, the Ferris solution produces reasonable phase lag estimates for typical aquifer diffusivities and for most locations within circular islands. By comparing the Ferris and circular island solutions, we propose a correction factor to the Ferris solution that allows it to be applied in circular boundary settings. This extends the application of the widely applied Ferris solution to a broader range of situations.

Storm Surges in the Bohai Sea: The Role of Waves and Tides

A storm surge is a complex phenomenon in which waves, tide and current interact. Even though wind is the predominant force driving the surge, waves and tidal phase are also important factors that influence the mass and momentum transport during the surge. Devastating storm surges often occur in the Bohai Sea, a semi-enclosed shallow sea in North China, due to extreme storms. However, the effects of waves on storm surges in the Bohai Sea have not been quantified and the mechanisms responsible for the higher surges that affect part of the Bohai Sea have not been thoroughly studied. In this study, we set up a storm surge model, considering coupled effects of tides and waves on the surges. Validation against measured data shows that the coupled model is capable of simulating storm surges in the Bohai Sea. The simulation results indicate that the longshore currents, which are induced by the large gradient of radiation stress due to wave deformation, are one of the main contributors to the higher surges occurring in some coastal regions. The gently varying bathymetry is another factor contributing to these surges. With such bathymetry, the wave force direction is nearly uniform, and pushes a large amount of water in that direction. Under these conditions, the water accumulates in some parts of the coast, leading to higher surges in nearby coastal regions such as the south coast of the Bohai Bay and the west and south coasts of the Laizhou Bay. Results analysis also shows that the tidal phase at which the surge occurs influences the wave–current interactions, and these interactions are more evident in shallow waters. Neglecting these interactions can lead to inaccurate predictions of the storm surges due to overestimation or underestimation of wave-induced set-up.

CO2 effluxes from an urban tidal river flowing through two of the most populated and polluted cities of India.

Urbanized rivers flowing through polluted megacities receive substantial amount of carbon from domestic sewage and industrial effluents which can significantly alter the air-water CO2 flux rates. In this regard, we quantified the partial pressure of CO2 in the surface water (pCO2(water)), air-water CO2 fluxes, and associated biogeochemical parameters in the Hooghly River, India, flowing through two of the most polluted cities of the country, Kolkata and Howrah, over a complete annual cycle during spring tidal phase (SP) and neap tidal phase (NP). This urbanized part of Hooghly River was always supersaturated with CO2 having an annual mean pCO2(water) and air-water CO2 flux of ~ 3800 μatm and ~ 49 mol C m-2 year-1, respectively. Significant seasonal variability was observed for both pCO2(water) and air-water CO2 flux (pre-monsoon, 3038 ± 539 μatm and 5049 ± 964 μmol m-2 h-1; monsoon, 4609 ± 711 μatm and 7918 ± 1400 μmol m-2 h-1; post-monsoon, 2558 ± 258 μatm and 4048 ± 759 μmol m-2 h-1, respectively). Monthly mean pH and total alkalinity varied from 7.482 to 8.099 and from 2437 to 4136 μmol kg-1, respectively, over the annual cycle. pCO2(water) showed significant positive correlation with turbidity and negative correlation with electrical conductivity and gross primary productivity (GPP). High water discharge could have facilitated high turbidity, especially during the monsoon season, which led to depletion in GPP and enhancement in pCO2(water) which in turn led to very high CO2 effluxes. The CO2 efflux rate in this urbanized riverine stretch was substantially higher than that observed in previous studies carried out in the less urbanized estuarine stretch of Hooghly. This indicates that the presence of highly urbanized and polluted metropolis potentially enhanced the pCO2(water) and CO2 effluxes of this river. Similar observations were made recently in some Asian and Australian urban rivers.

PETROLOGY AND PETROGENESIS OF SIAH KOOH VOLCANIC ROCKS IN THE EASTERN ALBORZ

Siah Kooh area is northeast of Shahroud city and is located in eastern Alborz. The lithologic composition of the volcanic rocks in the area consists of andesite, basalt, trachyandesite and quartztrachite. Plagioclase, olivine, and augite phenocrysts as the main minerals and apatite and magnetite, sericite, chlorite and apacite minerals are sub-minerals of volcanic rocks that are located in the glass slabs. Quartz is also found in fine-grained rock pulp and sometimes in phenocrysts. The dominant texture in these rocks are porphyritic, amygdaloidal and microlithic. According to geochemical studies of basaltic magmatic volcanic rocks, calc-alkaline potassium is high and negative Nb anomaly, Ce / Pb ratio and enrichment of rocks of light rare earth elements (LRRE) and high LREE / HREE ratio indicate contamination. The crust is an indicator of the presence of the garnet phase in the mantle source. On the other hand, the similarity of their trace elements to Oceanic Basalts (OIB) is a clear evidence of their relevance to this environment. Early basaltic magma originated from a mantle with a garnet-lherzolite composition with a partial melting rate of 15–12%. FeOtotal values in basalts and other structural evidence indicate the formation of these rocks in the early stages of intra-continental rifting which can be attributed to the pressure drop caused by intra-continental tidal phases associated with deep faults during the orogenic phases. Alpine attributed to Eocene time.

Effect of topography on the cold water region in the east entrance area of Qiongzhou Strait

A cold water region will occur in the east entrance area of Qiongzhou Strait when upwelling develops off the northeast coast of Hainan Island. The effect of topography on this cold water region was investigated by combining satellite observations and numerical simulations. Multi-source high-resolution remote-sensed sea surface temperature images revealed that the western periphery of the cold water region frequently occurred at a quasi-fixed location with similar jagged structure. Compared with observations, the numerical model employed in this study could satisfactorily simulate the intense tidal currents in the strait, and reasonably reproduce the jagged western periphery of the cold water region. Under strong westward tidal flow, the cold upwelling water intruded deeply into the interior strait, whereas under sustained eastward tidal currents, much stronger tidal currents occurred where there were deeper waters connecting the inner strait, therefore the cold upwelling water faded towards east faster and formed the concave parts (looking in east-to-west direction) of the western periphery of the cold water region; conversely, convex parts would develop over the adjacent shallower shoals. The eastward movement of the cold water was dominated by topography-modified tidal currents, and only after sustained eastward tidal currents (usually in the second half or near the end of the eastward tidal current phase), the western periphery of the cold water region would occur at a quasi-fixed location with similar jagged shape. Moreover, the development of the upwelling off the northeast coast of Hainan Island, which was the precondition of the cold water region, was found to be mainly driven by sustained SE ~ S winds.

Role of nutrients in the development of floating green tides in the Southern Yellow Sea, China, in 2017

The largest-scale green tides in the world caused by Ulva prolifera have been recurring annually in the Southern Yellow Sea since 2007. In this study, spatio-temporal variations of green tides and nutrients were investigated in the spring and summer of 2017, and the roles of different nutrients in the development of green tides are discussed. The results showed that the development of green tides could be divided into two parts according to the distinct growth phases of green tides: (1) the development area (DA), which was located south of 35°N and characterised by the quick expansion of green tide and high-content nutrient; (2) the accumulation area (AA), which was located north of 35°N and characterised by high U. prolifera coverage area and low-content inorganic nutrients. Through calculation of nutrient reductions, we found that DA provided 96% of nitrogen and 87% of phosphorus for the development of green tides in 2017, and the dominant nutrient species were dissolved inorganic nitrogen and dissolved organic phosphorus. Regarding AA, the dominant nitrogen component was dissolved organic nitrogen. Thus, we conclude that reducing the level of nutrient input in order to alleviate the eutrophication of seawater in the Jiangsu coastal area may be an important measure for reducing the scale of green tides.

Variations of Mesospheric Neutral Winds and Tides Observed by a Meteor Radar Chain Over China During the 2013 Sudden Stratospheric Warming

AbstractThe neutral winds in the mesospheric and lower thermospheric region obtained from a meteor radar chain within the latitudinal range of 18–53°N were decomposed to examine the latitudinal structures of the tides and mean winds during the sudden stratospheric warming (SSW) event in 2013. The zonal wind reversed from eastward to westward and the westward wind was larger at middle latitudes than that at low latitudes during the SSW. Meanwhile, a sharp increase in the northward wind was noticeable at all stations. The amplitudes of the diurnal and semidiurnal tides decreased from 5 to 13 January and increased subsequently. At the same time, the terdiurnal tides increased in amplitude, especially at Beijing, Wuhan, and Kunming, in response to the SSW. Moreover, the tidal phases showed a large shift that corresponded to a great increase in tidal wavelengths in the semidiurnal and terdiurnal components. The wavelet analysis further revealed that the quasi 6‐day wave oscillations dominated in the winds at Kunming and Sanya stations, as well as the quasi 16‐day wave dominated in the zonal wind, and the quasi 11‐day and 16‐day waves were prevailing in the meridional winds at Beijing and Wuhan. In the same vein, the quasi 16‐day and quasi 11‐day waves were prominent in the zonal and meridional winds during 1–18 January at Mohe. Therefore, the tide‐planetary wave interactions played a significant role in modulating the behaviors of the mesospheric and lower thermospheric dynamics during the SSW event.

Studying the Wake of an Island in a Macro-Tidal Estuary

Tidal flow can generate unsteady wakes, large eddies, and recirculation zones in the lee or around complex natural and artificial obstructions, such as islands, headlands, or harbours. It is essential to understand the flow patterns around such structures given the potential impacts they can have on sedimentation, the marine environment, ecology, and anthropogenic activities. In this paper, the wake around an island in a macro-tidal environment has been studied using a widely used hydro-environmental model, Telemac-2D. Current data collected using moored acoustic Doppler current profilers (ADCPs) were used to validate and refine the Telemac-2D model. Four different turbulence models and several different solver options for the k- ε model were tested in this study to assess which representation could best replicate the hydrodynamics. The classic k- ε model with the solver of conjugate residual was the most suitable method to simulate the wake in the lee of the island. The model results showed good correlation with measured data. The island wake parameter used to predict the wake behaviour and its predictions matched the model results for different tidal conditions, suggesting that the island wake parameter could be used to predict the wake behind obstacles in macro-tidal environments. The model predictions showed the development of a wake is similar between ebb and flood tides in the neap tide while showing more difference in spring tide. With the increase of velocity in the neap tide, two side-by-side vortices will appear and then changing to stable Karman Vortex Street. During the ebb phase of spring tide, the wake will develop from a stable vortex to an unstable Karman Vortex Street, while the wake remained stable with two vortices during an flood tide.

Tidal regime shift in Lingdingyang Bay, the Pearl River Delta: An identification and assessment of driving factors

AbstractBoth natural changes (e.g., tidal forcing from the ocean and global sea level rise) and human‐induced changes (e.g., dredging for navigation, sand excavation, and land reclamation) exert considerable influences on the long‐term evolution of tidal regimes in estuaries. Evaluating the impacts of these factors on tidal‐regime shifts is particularly important for the protection and management of estuarine environments. In this study, an analytical approach is developed to investigate the impacts of estuarine morphological alterations (mean water depth and width convergence length) on tidal hydrodynamics in Lingdingyang Bay, Southeast China. Based on the observed tidal levels from two tidal gauging stations along the channel, tidal wave celerity and tidal damping/amplification rate of different tidal constituents are computed using tidal amplitude and phase of tidal constituents extracted from a standard harmonic analysis. We show that the minimum mean water depth for the whole estuary occurred in 2006, whereas a shift in tidal wave celerity for the M2 tide component occurred in 2009. As such, the study period (1990–2016) could be separated into pre‐human (1990–2009) and post‐human (2010–2016) phases. Our results show that the damping/amplification rate and celerity of the M2 tide have increased by 31% (from 7 to 9.2 m−1) and 28% (from 7 to 9 m·s−1) respectively, as a consequence of the substantial impacts of human interventions. The proposed analytical method is subsequently applied to analyse the historical development of tidal hydrodynamics and regime shifts induced by human interventions, thus linking the evolution of estuarine morphology to the dominant tidal hydrodynamics along the channel. The observed tidal regime shift is primarily caused by channel deepening, which substantially enlarged the estuary and reduced effective bottom friction resulting in faster celerity and stronger wave amplification. Our proposed method for quantifying the impacts of human interventions on tidal regime shifts can inform evidence‐based guidelines for evaluating hydraulic responses to future engineering activities.

The amplitudes and phases of tidal constituents from Harmonic Analysis at two stations in the Gulf of Aden

Amplitudes and phases of the tidal constituents are computed from harmonic analysis for the ports of Aden and Djibouti from the hourly Sea Level data for the year 2008 at these locations. The analysis shows that the tides are of mixed nature in the area. The ratio F = K1 + O1/M2 +S2 gives a value of 0.87 and 0.85 for Aden and Djibouti stations. The high astronomical tide and low astronomical tides are respectively 1.138 m and − 1.681 m for Aden port and 1.144 m and − 1.671 m for Djibouti port. Tidal amplitudes and phases at both stations are found closely similar. The major constituents of semi-diurnal waves are M2, S2 and N2 tides with amplitudes of 0.476, 0.215 and 0.129 m. The dominant diurnal waves are K1, O1 and P1 tides with amplitudes of 0.401, 0.201 and 0.121 m respectively. Other tidal constituents represented by third, fourth and sixth diurnal constituents, they have small amplitudes. In these groups, the M3, M4 are the major components with amplitudes of 0.005 m, 0.003 m respectively.

Channel curvature effects on estuarine circulation in a highly stratified tropical estuary: The São Francisco river estuary (Brazil)

The effects of the channel curvature on estuarine circulation were assessed in the São Francisco river estuary. This estuary is a deltaic front system, with a highly stratified salinity distribution. The assessment was based on field experiments where currents and salinity and temperature were monitored during a semi-diurnal tidal cycle in two cross-sections with distinct curvatures (radii of 2 and 8 km). The least-squares method was used to determine the mean velocity (residual velocity), and the tidal velocity amplitude and phase for the M2 harmonic. The results for the M2 harmonic were compared to an analytical solution that considers a simplified momentum balance between barotropic pressure gradient and bottom friction. The model skill for these two results was 0.44 and 0.63 for sections #A and #B, respectively. The differences between these results indicate that there are other dynamically influential forces for the longitudinal momentum balance besides those included in the analytical solution. The baroclinic pressure gradient presented values two orders of magnitude greater than the bottom friction, demonstrating the dynamic importance of this force. Although centrifugal acceleration is a component of the lateral momentum balance, it also plays a role in the distribution of longitudinal currents in the cross-section, displacing the maximum currents towards the exit of the curve. In addition to the channel curvature effect, the influence of the bathymetry was also observed on the tidal amplitude in the cross-sections and on the depth-averaged residual longitudinal velocities along the sections, with the highest average speed in the shallowest areas of each section.

Numerical modeling of Maranhão Gulf tidal circulation and power density distribution

Marine resources are outstanding among renewable energy for their wide occurrence and diverse possibilities of exploitation. The tidal resource can be harnessed by the use of both potential (sea level) and kinetic energy (tidal currents). Maranhao coast presents one of the largest tidal ranges and strongest currents on Brazilian coastline, providing a good source of renewable energy. A 3D hydrodynamic model is implemented to numerically simulate the tidal circulation in the Maranhao Gulf so as to examine the tidal behavior and associated energy distribution. Amplitudes and current speeds are substantially increased by the estuary’s geomorphology and the shallow bathymetry. M2 tidal component presents the highest amplitudes among the tidal constituents, being the most energetic. Spring-neap cycle constitute an important factor in energy assessment due to their significant difference in power density and exchanged water volume between estuary and continental shelf. Maximum current velocities of 3 m s−1 are found around Medo Island, where tidal range can reach nearly 5.5 m. Three potential regions are located within the Sao Marcos Estuarine Complex, presenting surface velocities ranging from 1 to 2.15 m s−1 and power density as high as 5 kW m−2. The estuary is long and presents significant variations of tidal phase that allows a geographical disposition of turbines in order to lower the downtime.

Secondary Gravity Waves Generated by Breaking Mountain Waves Over Europe

AbstractA strong mountain wave, observed over Central Europe on 12 January 2016, is simulated in 2D under two fixed background wind conditions representing opposite tidal phases. The aim of the simulation is to investigate the breaking of the mountain wave and subsequent generation of nonprimary waves in the upper atmosphere. The model results show that the mountain wave first breaks as it approaches a mesospheric critical level creating turbulence on horizontal scales of 8–30 km. These turbulence scales couple directly to horizontal secondary waves scales, but those scales are prevented from reaching the thermosphere by the tidal winds, which act like a filter. Initial secondary waves that can reach the thermosphere range from 60 to 120 km in horizontal scale and are influenced by the scales of the horizontal and vertical forcing associated with wave breaking at mountain wave zonal phase width, and horizontal wavelength scales. Large‐scale nonprimary waves dominate over the whole duration of the simulation with horizontal scales of 107–300 km and periods of 11–22 minutes. The thermosphere winds heavily influence the time‐averaged spatial distribution of wave forcing in the thermosphere, which peaks at 150 km altitude and occurs both westward and eastward of the source in the 2 UT background simulation and primarily eastward of the source in the 7 UT background simulation. The forcing amplitude is 2 that of the primary mountain wave breaking and dissipation. This suggests that nonprimary waves play a significant role in gravity waves dynamics and improved understanding of the thermospheric winds is crucial to understanding their forcing distribution.

First measurements of tides in the stratosphere and lower mesosphere by ground-based Doppler microwave wind radiometry

Abstract. Atmospheric tides are important for vertical coupling in the atmosphere, from the stratosphere down to the troposphere and up to the thermosphere. They are planetary-scale gravity waves with well-known periods that are integer fractions of a day and can be observed in the temperature or wind fields in the atmosphere. Most lidar techniques and satellites measure atmospheric tides only in the temperature field and continuous measurements of the tides in the wind field of the stratosphere and lower mesosphere are rare, even though, with modern lidars, they would be feasible. In this study, we present measurements of the diurnal tide in the wind field in the stratosphere and lower mesosphere by ground-based microwave wind radiometry for two different campaigns in tropical and polar regions. Further, we compare our measurements to MERRA-2 reanalysis data. In the tri-monthly mean, we find a good correspondence in the amplitude and phase of the diurnal tide between measurements and reanalysis with the most important features of the diurnal tides represented in both data sets. When looking at shorter timescales, we find significant differences in the data sets. We make an attempt to examine these differences and discriminate between atmospheric variability and noise, and we present some hints for intermittent diurnal tides. We conclude that continuous ground-based observations of tides in the middle atmospheric wind field are feasible, and they deliver consistent results for the mean amplitude and phase of the diurnal tide in the tri-monthly mean. We further discuss the limitations in regards to short timescale observations of tides and the possibility to provide additional insight into middle atmospheric dynamics that is complementary to temperature observations and reanalysis data.

Effects of prolonged mouth closure in a temporarily open/closed estuary: a summary of the responses of invertebrate communities in the uMdloti Estuary, South Africa

Prolonged mouth closure in estuaries is often associated with hypersalinity, mainly as a result of reduced freshwater inflow. However, on the KwaZulu-Natal coast, South Africa, temporarily open/closed estuaries have a tendency towards hyposalinity during closed mouth conditions, primarily because of their perched nature reducing saltwater intrusion, but also due to persistent freshwater inputs, together with seepage of saline water through the sand berm into the sea. We investigated a system, the uMdloti Estuary, experiencing extended periods of mouth closure over two years with the aim of documenting the response of invertebrates to such conditions. Specifically, estuarine invertebrate biodiversity was severely diminished, which was attributed to persistently low salinity, rather than poor water quality due to the absence of flushing. Secondly, a distinct brackish/freshwater community established itself within the mesozooplankton and benthic invertebrate assemblages, including invasive species. Marine overwash of the berm and a short mouth breaching aided the return of estuarine species for only very brief periods (weeks). We conclude that although estuarine species are quick to re-colonise the estuary after a breach, prolonged mouth closure along extended stretches of coast might severely reduce estuarine invertebrate biodiversity. Management options are preferably the provision of an adequate freshwater inflow to allow natural breaching, or else artificial breaching, to facilitate several openings per year as well as for a long enough tidal phase to permit the establishment of an estuarine salinity gradient.

Fast-changing upwelling off the west coast of Hainan Island

In this study, we investigated the short-term dynamics of upwelling off the west coast of Hainan Island (UWH) by combining Moderate Resolution Imaging Spectroradiometer (MODIS) infrared sea surface temperature (SST) images and Regional Ocean Modeling System (ROMS) simulations. MODIS observations showed that the UWH could exhibit rapid temporal variations, where the SST could increase or decrease by more than 1 °C within 3 h. Further investigations based on ROMS simulations suggested that flood tides could rapidly intensify the UWH, whereas ebb tides could rapidly weaken the UWH. Strong horizontal advection by intense tidal currents and high vertical velocity due to divergence/convergence triggered by progressive tidal waves were identified as the intrinsic physical mechanisms responsible for the rapid SST variations in the UWH. These findings were verified based on a MODIS-observed fast-cooling UWH event and a MODIS-observed fast-warming UWH event. Analyses of the timing of occurrence, tidal phase, and spatial patterns of the significant variations in the SST for these events all agreed with the hypothesis stated above. Model–data fusion analysis indicated that when a neap tide or transition period for tidal currents occurs, the influence of the tidal flow on the UWH is weak because of the associated weak horizontal advection and divergence/convergence.

Seasonality of hydrographic conditions and foraminiferal species in Guanabara Bay (Rio de Janeiro, Brazil)

Guanabara Bay was characterized through benthic foraminiferal assemblages and its correlations with changes resulted from physical processes in semidiurnal and seasonal time scales. Biological and physical sampling were made in 26 oceanographic stations distributed in the bay and four anchored stations sampled during the semidiurnal tidal cycle and in the neap and spring tidal phases; the experiments were performed in July (2000) and February (2001). The top 1–2cm of undisturbed sediments were taken, stained and preserved in alcohol solution for biological analysis. Physical properties were sampled with a CTD/Current temperature depth (Falmouth model 2AD) and vertical profiles of salinity, temperature, intensity and current velocity were measured in the water column in the anchored stations. The distribution of foraminifera presented a similar biodiversity pattern, both in winter and summer seasons. The low diversity and high dominance of a few opportunistic-tolerant species demonstrate that GB is highly impacted. During winter and summer, the bay entrance presented high bottom salinities (35,0 to 35,5UPS), higher currents in spring tide (0,85 to –0,81 ms−1, during ebbing and flooding, respectively), being classified as a partially mixed (type 2a) system, with S=0,99 and S=0,86, an indication that the tidal diffusion was the main process responsible for the inward salt transport. Foraminiferal species that can be correlated to this more dynamic and saltier environment are Cassidulina subglobosa, Discorbis williamsoni, Pseudononion atlanticum. The water mass close to the Governador Island is a chocked part of the system where velocities are lower (0,2 to -0,2 ms−1, maximum speeds of flooding and ebbing, respectively) indicating weak tidal influence. The residual circulation, driven by the river discharge and density stratification, indicates lower velocities (-0,04 to 0,03 m s−1). East of the Governador Island, the environmental conditions during the spring tide of the summer favors the transport of anthropogenic substances towards the coast. Stations located in the inner parts of the bay presented similar characteristics, related to low water renovation state, revealing high anthropic impact in the region. Foraminiferal species linked to these low renewable water environments and dynamics are Ammonia tepida, Buliminella elegantissima, Bolivina striatula, Bulimmina elongata, Fursenkoina pontoni.