M2 Tide Research Articles

Multidecadal Evolution of the Turbidity Maximum Zone in a Macrotidal River Under Climate and Anthropogenic Pressures

AbstractClimate and human pressures can influence the evolution of estuarine sediment dynamics concurrently, but the understanding and quantification of their cause–effect relationships are still challenging due to the occurrence of complex hydro‐morpho‐sedimentary feedbacks. The Garonne Tidal River (GTR, upper Gironde Estuary, France) is a clear example of a system stressed by both anthropogenic and climate change, as it has been subject to decreasing river discharges, natural morphological changes, and gravel extraction. To understand the relative effect of each hydrological and geomorphological pressure on the turbidity maximum zone (TMZ), the sediment dynamics in the GTR over the last six decades was evaluated using the width‐averaged idealized iFlow model. Model results show a gradual increase in tidal amplitude and currents over the decades that has led to the upstream shift of the landward sediment‐transport capacity components (external M4 tide, spatial settling lag, and tidal return flow). The upstream displacement of the TMZ between the 1950s and the 2010s was estimated to be at least 19 km, of which about three fourth was induced by geomorphological changes and one fourth by hydrological changes. Concerning the geomorphological changes, the natural evolution of the lower Gironde morphology was the main pressure inducing the displacement of the TMZ in the GTR. Anthropogenic and natural changes in morphology and bed roughness in the GTR itself also contributed to this evolution. The natural geomorphological changes were, in turn, probably promoted by the evolution of sediment dynamics, so this study reveals the closed circle that governs the intensification of the TMZ.

The Effect of Sea Ice on Tidal Propagation in the Kitikmeot Sea, Canadian Arctic Archipelago

AbstractThe tides in the Kitikmeot Sea, in the southern Canadian Arctic Archipelago, are found to be heavily influenced by seasonal sea‐ice formation and blocking in a strait. Data from a moored current profiler in Dease Strait exhibit strong tidal damping during wintertime seasonal sea‐ice cover, with 50%–60% reduction in tidal elevation and 65% reduction in tidal velocities. We used a 3D unstratified barotropic numerical tidal model of the region to show that the observed wintertime tidal damping likely requires both high sea‐ice friction and a partial sea‐ice blockage in Victoria Strait (VS), the eastern gateway of the Kitikmeot Sea, where tidal‐induced ridging causes thick, rough ice to accumulate over its shallow sill. Our analysis of the model shows different dynamics for the M2 and K1 tides. Both tidal constituents are dominated by the Atlantic tides entering through VS. Overall, ∼90% of the M2 tidal energy entering VS does not reach Dease Strait because, in addition to dissipation in VS (∼25%), it is significantly diverted into adjoining bays and around an amphidrome in eastern Queen Maud Gulf (∼65%). In contrast, the smaller K1 tide is less diverted into the subsidiary channels, after ∼20% dissipation in VS and only ∼25% in adjoining bays, it propagates far into the region and is amplified due to resonance in Dease Strait and Coronation Gulf, resulting in larger tidal height than the M2 tide in Coronation Gulf.

Is there a quasi 60-year oscillation in global tides?

We analyze long-term tide gauge records to examine whether there is a quasi 60-year oscillation in global tides. We find that there is a significant 55-year cycle at more than half of the tide gauges analyzed. For M2 tide, the amplitudes of the 55-year cycle range from 1.82 ± 0.80 mm (Los Angles) to 26.34 ± 6.75 mm (Cuxhaven), while for S2 tide, the amplitudes of the 55-year cycle range from 1.02 ± 0.48 mm (San Francisco) to 8.61 ± 2.25 mm (Cuxhaven). At Cuxhaven, shallow water constituents M4, MS4 and M6 tides which obtain energy from M2 and S2 tides also show significant 55-year cycles. It is found that the 55-year cycle significantly influences the estimation of the long-term trend of tidal amplitudes at Newlyn, Cuxhaven, Eastport and Victoria. The influence of the 55-year cycle on long-term trends of tidal amplitudes at Cuxhaven is the strongest among these stations. At Cuxhaven, the long-term trend of M2 (S2) amplitudes sharply increases from 0.68 ± 0.10 (0.22 ± 0.03) mm/yr to 0.93 ± 0.06 (0.31 ± 0.03) mm/yr when the 55-year cycle is removed. It is also found that the 55-year cycle in tides can partly explain the rapid change in M2 and S2 tides since 1980s in the North Atlantic. Quasi-60 year variations in sea levels and sea water temperature may be responsible for the 55-year cycle in tides while the detailed mechanisms still need further research.

Adjoint estimation and interpretation of spatially varying bottom friction coefficients of the [formula omitted] tide for a tidal model in the Bohai, Yellow and East China Seas with multi-mission satellite observations

In order to estimate the spatially varying bottom friction coefficients (BFCs) in the Bohai, Yellow and East China Seas (BYECS), multi-mission satellite observations from TOPEX/Poseidon, Jason-1 and Jason-2 are assimilated into a two-dimensional tidal model with an adjoint method. This work aims to: (1) study the characteristics of spatially varying BFCs in BYECS; and (2) find out the possible sources and mechanisms of spatially varying BFCs. In the numerical experiment, the M2 tide is simulated and the spatially varying BFCs in BYECS are estimated by assimilating observations from tidal gauge stations and multi-mission altimeters. The simulated M2 tide matches well with the tide gauge data, indicating the reasonability of present methodology of spatially varying BFCs. The characteristics and possible mechanisms of the spatially varying BFCs in BYECS are concluded and discussed, and the main conclusions include: (1) the values of BFCs in shallow water are usually larger than those in deep water, which can reach the order of 10−2 in shallow areas; (2) the values of BFCs generally decrease with the strengthened depth-averaged tidal current velocity in BYECS; (3) the high-value BFC areas near the coasts always appear in the downstream sides of headlands or peninsulas, which are possibly caused by the propagation of tidal waves; (4) the high-value BFC area along Jiangsu coast is affected by the bottom morphology of radially distributed tidal sand ridges, which might enhance the form drag; (5) the high-value BFC areas in the middle of the South Yellow Sea and Fujian coast correspond to the muddy areas, where the mixture of different sediment types changes the bottom roughness.

Assessing the Influence of Shoreline Adaptation on Tidal Hydrodynamics: The Role of Shoreline Typologies

AbstractIn coastal embayments, tidal dynamics are influenced by mean sea level and shoreline configuration. As sea levels rise and coastal communities modify their shorelines to mitigate future flooding, spatial patterns of inundation, tidal amplitude, and tidal phase will change in response. Here we apply a hydrodynamic model to systematically investigate the effect of local‐scale, spatially refined shoreline protection on regional tidal dynamics and peak water levels in San Francisco Bay, California. We find that individual shoreline protection scenarios produce relatively small changes in tidal amplitudes at 50 and 100 cm of sea‐level rise but can result in amplification of the M2 tide by up to 40% at 200 cm of sea‐level rise. Protection of shorelines with gradually sloping topography and space for floodwater accommodation generally has the largest influence on tidal response, both locally and regionally. In the northern part of San Francisco Bay, tides down‐estuary of protected shorelines move closer to a standing wave, while up‐estuary tides become more progressive. In the southern part of the bay, which is already close to a standing wave, effects are more localized and variable. Overall, the tidal response to shoreline protection is a function of both the geographic location within the embayment as well as the geomorphic characteristics of the local landscape that is protected. Understanding the relative influence of local shoreline modifications on tidal dynamics under a range of sea‐level rise scenarios is critical to developing effective shoreline adaptation alternatives that maximize flood mitigation.

Estimation of the electric current density in the Gulf of California induced by the M2 tidal current

The electric current density generated in the Gulf of California by the interaction between the ocean currents produced by the M2 tide and the geomagnetic field was calculated in this study. The value of the geomagnetic field in the Gulf of California was determined from World Magnetic Model 2010 data; the tidal velocities of the seawater were calculated using a three–dimensional hydrodynamic–numerical model forced by the M2 tide with a horizontal cell resolution of 3’ × 3’ and 12 vertical layers. The results showed that the electric current density is maximum during the fastest flood and ebb currents; it exhibits sinusoidal behavior, and the largest amplitudes always appear in the upper layer. The electric field and the electric potential difference exhibit similar behaviors. Important areas for the generation of electric fields are in the upper Gulf of California, Colorado River Delta, archipelago region, and Ballenas and Salsipuedes channels.

A feature point scheme for improving estimation of the temporally varying bottom friction coefficient in tidal models using adjoint method

Refined estimation of bottom friction coefficient (BFC) is significantly important for coastal engineers to determine precisely the hydrodynamic conditions and sediment transport rates, which can be realized by assimilating observations of sea surface elevation using the adjoint method. In this study, a new method, named as feature point scheme (FPS), is developed to further improve the estimation of temporally varying BFC. In FPS, BFCs at some feature points are assumed to be independent and BFCs at other temporal points are obtained by interpolating BFCs at feature points.By assimilating artificial observations in twin experiments, it is demonstrated that FPS can improve the estimated temporally varying BFC, especially with the nonuniformly distributed feature points and nonuniform spline interpolation (nonuniform FPS). The M2 tide and four principal tidal constituents in the Bohai Sea are then simulated by assimilating real satellite-retrieved observations with FPS. In all the experiments, the performance of the tidal model with nonuniform FPS outperforms those using other schemes. The experimental results indicate that the temporally varying BFC is related to the tidal constituents. Moreover, the temporal variation of estimated BFC has a significantly negative correlation with the current speed, which is possibly related with the sediment transport.

An Assessment of Global Ocean Barotropic Tide Models Using Geodetic Mission Altimetry and Surface Drifters

AbstractThe accuracy of three data-constrained barotropic ocean tide models is assessed by comparison with data from geodetic mission altimetry and ocean surface drifters, data sources chosen for their independence from the observational data used to develop the tide models. Because these data sources do not provide conventional time series at single locations suitable for harmonic analysis, model performance is evaluated using variance reduction statistics. The results distinguish between shallow and deep-water evaluations of the GOT410, TPXO9A, and FES2014 models; however, a hallmark of the comparisons is strong geographic variability that is not well summarized by global performance statistics. The models exhibit significant regionally coherent differences in performance that should be considered when choosing a model for a particular application. Quantitatively, the differences in explained SSH variance between the models in shallow water are only 1%–2% of the root-mean-square (RMS) tidal signal of about 50 cm, but the differences are larger at high latitudes, more than 10% of 30-cm RMS. Differences with respect to tidal currents variance are strongly influenced by small scales in shallow water and are not well represented by global averages; therefore, maps of model differences are provided. In deep water, the performance of the models is practically indistinguishable from one another using the present data. The foregoing statements apply to the eight dominant astronomical tides M2, S2, N2, K2, K1, O1, P1, and Q1. Variance reduction statistics for smaller tides are generally not accurate enough to differentiate the models’ performance.

Rapid reduction of tidal amplitude due to form drag in a narrow channel

Reversing Falls is a large sill in a narrow section of the Saint John River on the northern coast of the Bay of Fundy, Canada. Reversing Falls limits tides from propagating farther up the river and impedes river water flowing seaward. This work aims to describe the physical processes that control flow over Reversing Falls by using output from a regional numerical model. We find form drag is more important than frictional drag for limiting the M2 tide propagation over Reversing Falls. Despite large tides and strong stratification suggestive of estuarine processes, the dynamics at Reversing Falls are dominated by a steady balance between drag and the surface pressure gradient, with the distinction that all terms in this river-like dynamical balance change sign on a semi-diurnal tidal cycle.

Southward Internal Tides in the Northeastern South China Sea

AbstractThe M2 internal tides in the northeastern South China Sea are studied using satellite altimeter data from 1992–2018. By an improved mapping technique that combines plane wave analysis and two‐dimensional spatial filtering, multiple internal tides are separately extracted with weak internal tides becoming detectable. The satellite results reveal for the first time a 300‐km‐long southward M2 internal tidal beam in the northeastern South China Sea. The generation source is on the steep continental slope at the southern entrance to the Taiwan Strait. It ranges from 118–120°E along 22°N. Combining satellite‐observed internal solitary waves and internal tides, it is found that the onshore radiation evolves into nonlinear solitary waves and the offshore radiation in the form of linear internal tides. Based on the 26‐year‐coherent satellite results, the integrated southward energy flux is 0.18 GW, about 10% of the westward energy flux from the Luzon Strait. In the northeastern South China Sea, the westward and southward internal tides form a multiwave interference field, which features significant spatial variations in the magnitude and direction of energy flux. Further analyses reveal that the steep continental slope radiates southward semidiurnal M2 and S2 internal tides, but not diurnal K1 and O1 internal tides.

A reciprocal acoustic transmission experiment for precise observations of tidal currents in a shallow sea

Observations of ocean currents are important information in the fields of ocean science and engineering. Reciprocal acoustic transmissions have the potential to operationally measure tidal currents in coastal seas. This study investigates the capability of the reciprocal transmissions to measure tidal currents, particularly in relation to high-frequency variations. We conducted a reciprocal acoustic transmission experiment in an area of complex coastlines in the Seto Inland Sea, Japan, in October 2019. During this experiment, a burst transmission was used, and the system performed six transmissions with 1-min intervals between them every 10 min. The estimated path-averaged currents agreed with the currents obtained from a shipboard acoustic Doppler current profiler (ADCP) on an hourly basis and had captured high-frequency variations that were not captured by the hourly ADCP observations. The measurement noise of the estimated currents, which was determined as the variation within the six transmissions, was 2.5 cm s−1 and was small enough to trace the variations in the currents over the time series even for the variations with periods considerably shorter than M2 tide. The reciprocal transmission’s capability to capture high-frequency variations will improve the capability to reproduce current velocity fields when inversion or data assimilation methods are applied.

Energetics and spatio-temporal variability of semidiurnal internal tides in the Bay of Bengal and Andaman Sea

Energetics of semidiurnal barotropic and internal tides in the Bay of Bengal (BoB) and Andaman Sea (AS) are studied using the simulations from a high-resolution ocean general circulation model. Barotropic M2 tide, which is the largest tidal constituent in this region, loses about 65.5 GW of energy in the BoB and AS. Most of this barotropic energy (46.5 GW) is dissipated by means of bottom friction in the shallow regions, such as the head of the bay and the Gulf of Martaban. Due to the interaction of barotropic tides with bottom topography, about one-third of the barotropic M2 energy (19.1 GW) gets converted into internal tides and most of this conversion (84%) occurs over the Andaman–Nicobar (AN) Ridge. On the contrary to the estimates in earlier studies, our results show that a large part (59%) of this internal tide energy in the BoB and AS gets dissipated far away from the generation sites. Compared to the BoB, energy dissipation rates are found to be large over the entire AS and it could result in enhanced vertical mixing in this region. Further, analysis of the temporal variability of conversion within the model domain shows that energy conversion in the semidiurnal band varies between 11 to 27 GW over a spring–neap cycle. Seasonal variability in the stratification due to river runoff significantly changes the conversion of tidal energy at the generation sites in the northern BoB and AS. Our study revealed that westward radiating internal tides from AN Ridge undergo path alteration (refraction) due to the time-varying mesoscale circulation and such path alterations cause large intraseasonal variability in internal tide activity and redistribution of internal tide energy available for mixing in the remote areas such as the continental margins of the western BoB.

Identifying lateral boundary conditions for the M2 tide in a coastal model using a stochastic gradient descent algorithm

While lateral boundary conditions are crucial for the physical modeling of ocean dynamics, their estimation may lack accuracy in coastal regions. Data-assimilation has long been used to improve accuracy, but most of the widely-used methods are difficult to implement. We tried a new and an easy-to-implement method to estimate boundary conditions. This method uses data assimilation with a stochastic gradient descent and successive approximations of the boundary conditions. We tested it with twin experiments and a more realistic setting on a tidal model in the lagoon of Ouano, in New-Caledonia. The method proved successful and provided good estimation of the boundary conditions with various settings of subsampling and noise for the pseudo-data in the twin experiments, but there were important oscillations in the experiments with more realistic settings. Here we present those results and discuss the use of our new and easy-to-implement method.

Instabilities and vertical mixing in river plumes: application to the Bay of Biscay

In the Bay of Biscay (north-east Atlantic), long-living eddies and the frontal activity that they induce substantially contribute to mesoscale and submesoscale dynamics. Tides and river plumes also contribute to frontal activity. Biological productivity is sensitive to river plume fronts and to external forcings (tides and wind). Considering the importance of river plumes, we study here the structure, stability and vertical mixing processes in such river plumes (similar to those generated by the Gironde river). Restratification budget is considered here for evaluating stirring (frontogenetic/frontolytic) or vertical mixing (parametrised here from Ertel potential vorticity mixing) processes. Using high-resolution idealised numerical simulations, we analyse the evolution of the bulge and of the coastal part of this plume and we conduct sensitivity experiments to the river discharge, to southwesterly winds and to M2 tides. The bulge and the coastal current are stable (unstable) in case of moderate (high) river discharge, due to mixed barotropic/baroclinic instabilities. In the unstable case, near surface symmetric and vertical shear instabilities develop in the coastal current and in the core of the bulge where the Rossby number is large. When southwesterly winds blow, the river plume is squeezed near the coast by Ekman transport. The river plume is then subject to frontal symmetric, baroclinic, barotropic and vertical shear instabilities in the coastal part, north of the estuary (its far field). Conversely, in the presence of M2 tides, the river plume is barotropically, baroclinically and symmetrically unstable in its near field. Interior vertical mixing is induced by advective (stirring) and frontogenetic processes. Frontogenesis is dominant in the far-field (in the presence of southwesterlies) or in the near-field (when M2 tide is active). Frontogenesis is important in the far-field region in unforced river plumes (both with moderate and high river discharges). Potential vorticity is eroded in the far-field when southwesterlies blow. This is primarily due to the frictional processes which are dominant at the surface. This study has identified the instabilities which affect a river plume in different cases, and the local turbulent processes which alter the stratification.

Numerical study of tides in the Malacca Strait with a 3-D model

Malacca Strait (MS) has an important role and potential for many countries. It is a major transportation route for oil and commodities across continents. In addition, various activities such as shipping, fishing, aquaculture, oil drilling, and energy are also carried out in MS. Tides strongly affect the MS environment so that it becomes a major parameter in MS management. This paper is the first study, which presents MS tidal hydrodynamics based on a baroclinic and nonhydrostatic approach. Tidal hydrodynamics in MS and the surrounding waters were assessed using tidal forces, temperature, salinity, and density. This study analyzes the amplitude, phase, current ellipses, and semi-major axis of the tides. These variables are obtained from the simulation results of the three-dimensional numerical models of M2 tides and combined tides (M2, S2, N2, K1, and O1) with nonhydrostatic models. Then the results obtained are verified by observation data. Amplitude and phase of the tidal wave in MS originate from two directions, namely the northern part of MS (Andaman Sea) and the South China Sea (SCS). Tides from the north of MS propagate into the MS, while tides from the SCS travel to Singapore Waters (SW) and the south of MS. This causes a complex residual flow in SW and shoaling in the middle of MS. Shoaling in the middle of MS is characterized by a large amplitude and semi-major, as in B. Siapiapi. The results of this analysis show that tidal waves are dominated by semidiurnal types rather than diurnal types. The M2 current ellipse has dominantly anticlockwise rotation along the west of the MS, while along the east of MS, it has generally a clockwise rotation.

A comparison of predicted and observed ocean tidal loading in Alaska

SUMMARY We investigate the elastic and anelastic response of the crust and upper mantle across Alaska to mass loading by ocean tides. GPS-inferred surface displacements recorded by the Plate Boundary Observatory network are compared with predictions of deformation associated with the redistribution of ocean water due to the tides. We process more than 5 yr of GPS data from 131 stations using a kinematic precise point positioning algorithm and estimate tidal contributions using harmonic analysis. We also forward calculate load-induced surface displacements by convolving ocean-tide models with load Green’s functions derived from spherically symmetric Earth models. We make the comparisons for dominant tidal harmonics in three frequency bands: semidiurnal (M2), diurnal (O1) and fortnightly (Mf). Vector differences between predicted and observed ocean tidal loading (OTL) displacements are predominantly sub-mm in magnitude in all three frequency bands and spatial components across the network, with larger residuals of up to several mm in some coastal areas. Accounting for the effects of anelastic dispersion in the upper mantle using estimates of Q from standard Earth models reduces the residuals for the M2 harmonic by an average of 0.1–0.2 mm across the network and by more than 1 mm at some individual stations. For the relatively small Mf tide, the effects of anelastic dispersion (<0.03 mm) are undetectable within current measurement error. Incorporating a local ocean-tide model for the northeastern Pacific Ocean reduces the M2 vertical residuals by an average of 0.2 mm, with improvements of up to 5 mm at some coastal stations. Estimated RMS observational uncertainties in the vertical component for the M2 and O1 tides are approximately ±0.08 mm at the two-sigma level (±0.03 mm in the horizontal components), and ±0.21 mm for the Mf harmonic (±0.07 mm in the horizontal components). For the M2 harmonic, discrepancies between predicted and observed OTL displacements exceed observational uncertainties by about one order of magnitude. None of the ocean tide and Earth model combinations is found to reduce the M2 residuals below the observational uncertainty, and no single forward model provides a best fit to the observed displacements across all tidal harmonics and spatial components. For the O1 harmonic, discrepancies between predicted and observed displacements are generally several-fold larger than the observational uncertainties. For the Mf harmonic, the discrepancies are roughly within a factor of two of the observational uncertainties. We find that discrepancies between predicted and observed OTL displacements can be significantly reduced by removing a network-uniform tidal-harmonic displacement, and that the remaining discrepancies exhibit some regional-scale spatial coherency, particularly for the M2 harmonic. We suggest that the remaining discrepancies for the M2, O1 and Mf tides cannot be fully explained by measurement error and instead convey information about deficiencies in ocean-tide models and deviations from spherically symmetric Earth structure.

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.

Tides in the southern area of the Kara Sea in the vicinity of the Belyi island

A number of promising hydrocarbon deposits are known in the south-western part of the Kara Sea. A safe development of these deposits requires hydrometeorological support, including sea-level observations. The paper deals with sea-level data of autonomous anchored buoy station. The period of observation is about 2 years, and the observation dataset is divided into 2 periods due to the displacement of the buoy station. The coordinates of the first position of the buoy station are known but they had been changed after the displacement (possibly due to the action of the ice ridge keels).Data from two time series of observations are studied by harmonic analysis, using the method of least squares by AARI version. According to the average monthly and mean annual values of the main tides it is found that the data includes two independent series. It is determined that the second series may be considered uniform. In order to locate of the anchored buoy station we calculated new coordinates using the empirical tidal charts of the M2 wave.As a result, the harmonic constants of the eight main tidal waves for the Belyi Island area are presented for the first time. The new data confirms the amphidromic system in tides O1 and Q1 , between the Zhelaniya Cape and the Belyi Island. According to the new data the maximum seasonal variation in the range of M2 tide was observed in June, and the minimum of the phase angle was observed in July. This unusual seasonal variation of the M2 tide corresponds to previous observations data from the Uedinenia Island.The authors have no competing interests.

Modelling Internal Tides in the Strait of Canso

ABSTRACT A three-dimensional regional circulation model is used to investigate the internal M2 tide structure in the Strait of Canso located in eastern Nova Scotia, Canada. The embayment, an active shipping port, was found to have M2 baroclinic velocities occasionally reaching 0.15 m s−1 and typically faster than the barotropic tide. An internal tide spatial structure develops, characterized by the first vertical mode, and highly sensitive to the details of stratification. A region near the mouth of the Strait, with a strong cross-bathymetry barotropic flow was identified as the main generating site. The regular “canyon-like” features of the Strait concentrate the energy towards the bottom and head and, under favourable conditions, reflect energy from the head, forming a standing wave. The modelling study found that, although some internal tide is generated year-round, only summer stratification conditions were favourable for standing wave development because of both increased internal energy levels and longer wavelengths capable of transporting the energy farther up the Strait. A balanced internal energy budget for the area highlights a tendency towards local dissipation and enhanced mixing rates. Persistent convection cells and upwelling zones suggest possible impacts on biological activity, sediment, and oil spill dynamics in the region. The findings are validated with current meter and water level observations.