Tidal Circulation Research Articles

PENGEMBANGAN ARDUINO DATA LOGGER MENGGUNAKAN TDR H3CR UNTUK SIMULATOR PASANG SURUT

Tides, crucial natural phenomena, significantly impact various aspects of life. Recognizing their importance, this study presents the development of a tidal simulator leveraging Arduino data logging and TDR H3CR technology. The simulator aims to mimic tidal processes, crucial for educational and research purposes. Traditional methods of acquiring tidal data are time-consuming and expensive. Thus, a simulator proves advantageous in reducing research time and costs. At Raja Ali Haji Maritime University, a tidal simulation model exists but with manual operation and limited data capture capabilities. To address these limitations, this study designed a new simulator utilizing H3CR, DC Water Pump, and DC Selenoid Valve for automated tidal circulation. The research method involved system design, component integration, and laboratory experiments. Calibration of components like the ultrasonic sensor HC-SR04 ensured accurate data collection. The overall system experiment validated the simulator's functionality, demonstrating its ability to replicate tidal processes effectively. Results indicated that the simulator produced tidal patterns resembling sinusoidal waves, with slight noise attributed to sensor limitations. The designed simulator serves as an efficient learning tool for understanding tidal phenomena, exhibiting comparable results to natural tidal data. This study contributes to the advancement of tidal simulation technology, offering a cost-effective and accessible solution for educational and research purposes.

Modeling of Barotropic Tide off the Southeastern Coast of the Kamchatka Peninsula in View of the Accuracy of Global Tidal Models in the Northwest Pacific Ocean

This study introduces the development and implementation of a regional numerical finite-volume model FESOM–C, specifically designed to accurately compute barotropic tidal dynamics in the Pacific waters adjacent to the southeastern region of the Kamchatka Peninsula. The dynamics of principal harmonics of the semidiurnal M2 and diurnal K1 tidal constituents are replicated, as well as the total tide, which encompasses 12 constituents. The computed results, obtained using a detailed unstructured grid, are interpreted through the Long-wave approach. The FESOM–C regional model revealed the variability of harmonic constants of tide and current characteristics within the shelf and canyon-cut continental slope, due to topographic scattering of tidal waves. The assessment includes the estimation of maximum currents and eddy structures associated with residual tidal circulation on the shelf and continental slope. To investigate the influence of varying open boundary conditions, sensitivity experiments have been conducted using data from two state-of-the-art global tidal models FES2014 and TPXO9. The findings reveal that the regional model’s solution exhibits only minimal dependency on this choice, and it aligns well with the limited available tidal data. Interestingly, the global models themselves demonstrate significant disparities in the tidal currents. Furthermore, we assess the accuracy of global tidal model solutions in a broader region encompassing the Sea of Okhotsk, as well as the Pacific waters along the Kuril Islands and the Kamchatka Peninsula. This assessment utilizes a verified database of tidal harmonic constants derived from the Soviet and British tide tables. While the average errors in tidal heights calculations remain minor and closely approximate officially declared values, certain areas within the region exhibit notable discrepancies in the outputs of the global models. These discrepancies are site-specific and vary depending on the particular model and tidal harmonic under consideration. This underscores the need for caution when applying results from global tidal models at the regional scale. Meanwhile, the importance of advancing regional tidal dynamics modeling remains evident.

ASSESSMENT OF THREE-DIMENSIONAL BAROCLINIC CIRCULATION MODEL FOR THE MUSI COASTAL AREA

The hydrodynamics of the Musi estuary ecosystem is influenced by the flow of water discharge from the river, tidal circulation within the estuary, and complex bathymetry. Numerical modeling is one of the best ways to explain the characteristics and processes occurring in the estuary. However, the obtained model requires validation to ensure its accuracy despite the complexity added by variability in tidal and bathymetric conditions, making the validation process more challenging. This difficulty can be overcome by using high-resolution data, which provides a refined understanding of the river-to-sea estuary flow and its variability. The validation process involves the use of conductivity-temperature-depth (CTD) instruments and mooring tidal stations. The validated model is considered capable of accurately simulating tidal propagation as it represents the temperature-salinity-density properties within the estuarine environment. The development of this model demonstrates the effective implementation of these parameters within the Musi estuary ecosystem domain. The 3D model simulation is used to consider the vertical discretization in the river-estuary-sea channel, which enhances the representation of temperature-salinity-density in the water column. The obtained results suggest that the 3D-MIKE modeling is well-suited for operational purposes, including the prediction of hydrodynamics and the management of estuarine areas, specifically in the Musi estuary ecosystem.

Sediment mobility over a dispersive inner shelf from combined wave and tide bed shear stress

The sediment transfers that take place between the beach and the depth of closure on the inner continental shelf play a major role in the evolution of sandy shores at different time scales. The depth of closure of the foreshore sedimentary prism, which is generally dependent on wave conditions, remains poorly constrained in the context of an internal macrotidal platform. This work aims to define and evaluate this theoretical depth, which delimits the extension of sedimentary exchanges, in particular by including the constraints applied on the sea bottom by the tidal circulation, which are very strong on the inner continental shelf of western Brittany. The use of wave (WAVEWATCH III®), tidal (MARS3D), and bottom sediment (EMODnet) databases allows us to follow an original cartographic approach to study closure depths, based on the formulations of Hallermeier (1978 and 1981) and Soulsby (1997). This cartographic approach is adapted to a spatial analysis of sediment mobility on a regional scale. First, the depth of closure shows a regional spatialisation of the seaward extension of the sediment mobility zone according to exposure to different wave climates and tidal ranges. Secondly, the method for calculating the depth of closure with the combined shear stresses (wave and tide), applied at the scale of the internal platform of western Brittany, allows the identification of three areas of movement of sedimentary particles according to critical mobility thresholds: 1) Area of no motion; 2) Area of transport and deposition; 3) Area of transport without deposition. The main contribution of this work is to propose at distinction between 2 offshore sediment motion limits, the transition to the upper plane bed (DoTupb), and the incipient motion of particle (DoTmotion). In addition, this study confirms the potential of transport and deposition of sand particles at depths >100 m in the most hydrodynamically intense areas, which implies the possibility of interconnections between hydro-sedimentary cells, through bypassing of headlands and crossing over rocky outcrops.

Morphological evolution of a complex drift‐aligned prograded barrier

AbstractPrograded barriers are coastal landforms with a worldwide distribution that provide a paleoenvironmental record within a sequence of successive ridges and intervening swales. Most barriers with variable terrestrial morphologies, also known as complex barriers, have been poorly studied. At the main entrance of Western Port, a bay in southeastern Australia, a morphologically complex barrier was formed as a function of its somewhat sheltered position and orientation in relation to sporadic swells and tidal circulation. LiDAR‐derived topography shows highly truncated and asymmetrical ridges both across and along the Somers–Sandy Point barrier plain. These uncommon morphologies are associated with an intricate hydrodynamic circulation subject to sporadic storms approaching at a sharp angle to the shoreline that eliminate a significant part of the sedimentary record but also redistribute vast quantities of sand to the downdrift shoreline, and a large and variable sandy bank that undergoes intense sediment movement. Optically stimulated luminescence (OSL) dating within a limited area on the western side revealed an age of ~2600 years for the innermost dated ridge, located about halfway across the plain. Significant erosion of the ridges' record occurred on the western side of the barrier between 2600 and 700 years ago and between 600 and 240 years ago, whereas undated ridges on the eastern side were preserved. This creates an opportunity for future research on past erosional events that would be of great value for coastal management and adaptation. Textural and elemental (XRF) sediment characteristics suggest that the type of material provided for barrier accretion remained the same throughout the late Holocene. Given the sustained growth of the barrier and other sandy parts of the bay, a net supply of marine sand from Bass Strait must have occurred. The proposed evolutionary model contributes to the understanding of the sediment budget for the bay as a whole.

The role of short‐term temperature variability and light in shaping the phenology and characteristics of seagrass beds

AbstractSeagrass beds inhabit highly heterogeneous temperature regimes that characterize the marine nearshore. Temperature directly influences seagrasses and also provides indirect information on other ecologically relevant environmental variables. Multiple temperature processes operate on seasonal and sub‐seasonal timescales (i.e., hours to months) and include variation from seasonal air–sea heat fluxes, advective heat transport from upwelling and tidal circulation, and daily heating and cooling of shallow waters. Despite this, seagrass–temperature studies typically only examine a single isolated temperature process, often seasonal heating/cooling or marine heatwaves. Furthermore, elucidation of relationships between different short‐term temperature processes and seagrass metrics could provide insights into biologically relevant temperature metrics for seagrasses. Here, we examine the effects of multiple short‐term temperature processes on Zostera marina beds in Atlantic Canada, by describing the seasonal phenology of bed characteristics, plant morphology, and physiology across different temperature regimes and by identifying relationships between different temperature and seagrass metrics. We also include water depth as a proxy for light availability. Four distinct short‐term temperature processes (median temperature, growing degree day [heat accumulation], daily temperature range, and time in the optimal temperature range [5–23°C]) were used to categorize temperature regimes across our study sites as warm and highly variable, or cool and less variable. We found that both temperature regime and light availability were important for leaf area index (LAI) and shoot density, which both decreased with increasing depth yet had the strongest seasonal differences and maximum rates of increase (shoot density) or lowest values and maximum rates of decrease (LAI) in warm and highly variable temperature regimes. These temperature regimes were also associated with seasonal patterns in number of leaves, reduced leaf lengths and number of leaves per shoot, and thinner rhizomes with less carbohydrate storage. Generalized additive models (GAMs) for each seagrass metric using the four temperature processes indicated that while median temperature displayed expected relationships with almost every seagrass metric, inclusion of other temperature processes revealed additional insights not evident from median temperature alone. Our study shows that different sources of short‐term temperature variation influence seagrass properties and that accounting for these will improve our understanding of the temperature–seagrass interaction.

Development and validation of a global 1∕32° surface-wave–tide–circulation coupled ocean model: FIO-COM32

Abstract. Model resolution and the included physical processes are two of the most important factors that determine the realism or performance of ocean model simulations. In this study, a new global surface-wave–tide–circulation coupled ocean model FIO-COM32 with a resolution of 1/32∘ × 1/32∘ is developed and validated. Promotion of the horizontal resolution from 1/10 to 1/32∘ leads to significant improvements in the simulations of surface eddy kinetic energy (EKE), the main paths of the Kuroshio and Gulf Stream, and the global tides. We propose the integrated circulation route error (ICRE) as a quantitative criteria to evaluate the simulated main paths of the Kuroshio and Gulf Stream. The non-breaking surface-wave-induced mixing (BV) is proven to still be an important contributor that improves the agreement of the simulated summer mixed-layer depth (MLD) against the Argo observations even with a very high horizontal resolution of 1/32∘. The mean error in the simulated mid-latitude summer MLD is reduced from −4.8 m in the numerical experiment without BV to −0.6 m in the experiment with BV. By including the global tide, the global distributions of internal tide can be explicitly simulated in this new model and are comparable to the satellite observations. Based on Jason-3 along-track sea surface height (SSH), wavenumber spectral slopes of mesoscale ranges and wavenumber frequency analysis show that the unbalanced motions, mainly internal tides and inertia-gravity waves, induced SSH undulation and are a key factor for the substantially improved agreement between model and satellite observations in the low latitudes and low-EKE regions. For the ocean model community, surface waves, tidal currents and ocean general circulations have been separated into different streams for more than half a century. This paper demonstrates that it is time to merge these three streams for a new generation of ocean model development.

Interactions between Surface Waves, Tides, and Storm-Induced Currents over Shelf Waters of the Northwest Atlantic

A coupled wave–tide–circulation model is used to investigate wave–current interactions (WCIs) over the shelf waters of the Northwest Atlantic (NWA) during Hurricane Earl (2010). WCIs have substantial impacts on hydrodynamics in the upper ocean. The significant wave heights are modulated by WCIs, particularly over regions with strong current gradients, with a reduction up to ~2.1 m (20%) during the storm. Noticeable decreases in surface elevations and tidal currents occur in regions with strong tides such as the Gulf of Maine, mainly due to the wave-enhanced bottom stress. Over regions with weak tidal currents, wave effects on currents are dominated by two competitive processes between wave-induced forces and wave-enhanced mixing. The former strengthens surface currents (up to ~0.55 m/s) and increases the peak storm surge (up to ~0.48 m). The latter is responsible for the reduction in storm-induced surface currents (up to ~0.94 m/s) and anticyclonic modulation of current directions. Vertically, WCIs extend the strong vertical current shear and shift it downward during the storm, which enhances the local mixing and changes the structures of near-inertial oscillations (NIOs). Moreover, tidal currents also change the magnitudes of the NIOs and subtidal currents and affect the intensity of WCIs.

Modelling the Effects of Oyster Tables on Estuarine Tidal Flow

Oyster farming may impact the estuarine tidal circulation with a series of effects on environmental conditions and cultures’ growth. Hydrodynamic numerical models set up in estuaries integrated the presence of oyster structures by simply increasing the bottom friction coefficient over farming areas. However, for elevated oyster tables in tidal environments, such default calibration ignored the temporal variations of the friction coefficient between the conditions of submerged or unsubmerged structures. Thus, an original formulation of the Chézy coefficient was here proposed to integrate these modulations. Assessed against measured and predicted vertical velocity profiles on a 1/2 scaled model, this formulation was implemented in a simulation of the tidal circulation within the Aber Wrac’h estuary (Brittany, France). Particular attention was dedicated to the changes induced on the current magnitudes and sediment transport. Oyster tables were found to impact current magnitudes in the vicinity of elevated structures, with major differences at times of local peak flood and ebb. These modifications were characterised by (i) a reduction of current magnitudes over oyster farming areas and (ii) a tidal-flow acceleration on both sides of these structures. Increased sediment transport was, therefore, expected in the vicinity of these cultures, with potential implications on seabed morphology and water quality.

The 18.6-year lunar nodal cycle may affect ecosystems on the Northwest Atlantic continental shelves

As one of the foremost global forcings, tidal circulation exerts a pervasive influence on biological and physical processes occurring in the world's oceans on hourly to decadal time scales. This research identified the 18.6-year periodic variation in the lunar orbital plane within an annually resolved 140-year (1875 to 2015) shell growth master chronology measured from 21 live collected Arctica islandica, a bivalve known to be one of the longest lived non-colonial animals. The potential ecological implications of this result warranted detailed inventory of underlying physical processes. The absence of long-term in situ hydrological data for the bivalve's habitat was circumvented by the use of satellite data and numerical modeling which show that coastal regions of the Northwest Atlantic shelf clearly record diurnal tidal currents influenced by the 18.6-year nodal lunar cycle. The approach described here demonstrates that combining physical and biological data can help to identify subtle ecological processes over long time-scales for accurately disentangling the latter from variation introduced by anthropogenic climate change.

Acoustic backscatter from bubbles as a (quasi)passive tracer of turbulent mixing in high-flow tidal channels

In high-flow tidal channels, the water column tends to be well-mixed vertically due to the high levels of turbulence. Under favorable circumstances, such as those in which wind waves incident at the channel entrance from the adjoining open ocean or large embayment are opposed by the tidal flow, the waves steepen and break as they propagate upstream, resulting in bubble injection at the sea surface. These bubbles are then mixed downward by the tidally generated turbulence, resulting in pronounced, surface-connected, downward-propagating plumes of high backscatter in records from bottom-mounted upward-looking acoustic Doppler current profilers, typically operating at 100s of kHz. Letting the backscatter amplitude represent a pseudo-concentration, C, we demonstrate that the vertical turbulent diffusivity, K, can be estimated from the vertical turbulent flux i < c′w′> along the axis of the vertical beam, and the mean vertical gradient, dC/dz. Intriguingly, and despite the fact that bubbles are positively buoyant, the resulting estimates of K are very close to the values of momentum diffusivity required to obtain good agreement between the observed tidal velocities and a data-validated numerical tidal circulation model for the particular channel in question

Hydrodynamic Variability of an Intermittently Closed Estuary over Interannual, Seasonal, Fortnightly, and Tidal Timescales

AbstractSmall low-inflow intermittently closed estuaries are common in Mediterranean climates worldwide; however, despite their important contributions to ecosystem services and coastal resilience, their dynamics have been less well studied relative to classical (i.e., deeper, persistent freshwater inflow) estuaries. It is known that infragravity wave propagation into these estuaries can induce strong currents and that closures lead to stagnating flows and declining water quality; however, how the estuarine circulation (tidal and subtidal) dynamically drives and responds to these conditions remains largely unknown. Here we analyze over 4 years of hydrodynamic observations in Los Peñasquitos Lagoon, a low-inflow, intermittently closed estuary in Southern California, to examine wave propagation into the estuary, sill accretion, and the estuarine circulation response over tidal, fortnightly, seasonal, and interannual time scales, providing an unprecedented view as to how these systems respond to changing forcing. Wave observations near the estuary inlet show that wave energy inside the inlet, which contributes to sill accretion, is dependent on water level relative to the sill height and has a tidal variation due to wave-current interactions. Tidal phase averages of conditions during open, pre-closure, spring, neap, and closed conditions highlight the large dynamic range that these estuaries experience. During open, low sill conditions, circulation and stratification are consistent with stratification-induced periodic straining and subtidal exchange varies with the fortnightly cycle as observed in many classical estuaries. However, as the sill grows, tidal circulation weakens and becomes strongly sheared and the subtidal exchange no longer scales with a classical theoretical pressure-friction balance.

Arsenic contamination at the Bagnoli Bay seabed (South Italy) via particle tracking numerical modeling: Pollution patterns from stationary climatic forcings.

Almost 140 years of industrial exploitation have severely degraded the environment of Bagnoli Coroglio (BC), the westernmost neighborhood of the city of Naples (Italy). In this peculiar area, however, geogenic processes overlap with the impact of human activities, making it difficult to distinguish between anthropogenic and geogenic pollution sources. This is particularly true for Arsenic, the concentration of which in the marine sediments largely exceeds the tolerable level for human health and the background value for local pyroclastics. After several studies have used traditional tools based on multivariate statistics, this article attempts at tackling the problem via numerical modeling, which provides a deeper insight into the physics that governs the pollution process. Therefore, we use a particle tracking model to assess whether arsenic levels in the seabed can be affected by the influx of thermal water from an artificial channel outfalling at the westernmost part of the coast The climatic forcings that drive the marine circulation are simplified to basic "scenarios", in which wind and waves are stationary in strength and direction. Since the simulation time is much less than the contamination timescale, the comparison between numerical results and measurements is essentially qualitative and concerns the shape of contamination contours. It was found the primary forcing that enables seabed pollution is the tidal circulation, which, moreover, acts continuously in time. Quantitative arguments based on regression analysis suggest the discharge of thermal water explains almost a quarter of the observed pollution, which is consistent with previous research based on multivariate statistics.

Towards an Integrated Observational System to Investigate Sediment Transport in the Tidal Inlets of the Lagoon of Venice

An observation system integrating satellite images, in situ water parameters and hydrodynamic measurements was implemented in a tidal inlet of the Venice Lagoon (Northern Adriatic Sea, Italy). The experimental infrastructure was developed to autonomously investigate suspended sediment dynamics in the two channels of the Lido inlet in relation to the longshore currents in the littoral zone and the tidal circulation along the lagoon channel network. It provided time series of turbidity at the surface, water flow and acoustic backscatter, which was converted into turbidity along the vertical column during different tidal phases and meteo-marine conditions. Accurate turbidity maps were derived from Sentinel-2 (Copernicus) and Landsat 8 (NASA) satellites. Long-term in situ data from field surveys enabled the calibration and intercalibration of the instrumental setup and validation of satellite-derived products. Time series from the instrumental network were analyzed in order to evaluate the temporal variability of suspended sediment in relation to tidal phases and the different meteo-marine conditions. The integration of available datasets with satellite images also permitted the testing of the methodology for a 3-D reconstruction of the suspended sediment pattern in calm sea conditions, under the effect of the sole hydrodynamical forcing. Remotely sensed data provide a synoptic distribution of turbidity in the inlet area allowing the analysis of the surficial patterns of suspended sediment and the inferring of information on the transport processes at different spatial scales. In calm sea conditions, the results show that the transport is driven by tidal currents with a net seaward transport related to a larger export of materials from the northern basin of the Lagoon of Venice. During typical northeasterly storms, materials mobilized on the beaches and in the shoreface are transported into the inlet and distributed into the lagoon channel network, following the flood tidal currents and determining net import of materials. The multitude of information provided by this system can support research on aquatic science (i.e., numerical simulations) and address end-user community practices. The ecosystem management will also benefit operational purposes, such as the monitoring of morphological transformations, erosion processes and planning of coastal defense in the future scenarios of sea level rise. The developed approach will also help to understand how the regulation of the inlet flow introduced by the operation of the flood barriers will affect the fluxes of particles and, in the long term, the lagoon morphodynamics.

Quantifying the environmental impact of a major coal mine project on the adjacent Great Barrier Reef ecosystems

A major coal mine project in Queensland, Australia, is currently under review. It is planned to be located about 10 km away from the Great Barrier Reef World Heritage Area (GBRWHA). Sediment dispersal patterns and their impact on marine ecosystems have not been properly assessed yet. Here, we simulate the dispersal of different sediment types with a high-resolution ocean model, and derive their environmental footprint. We show that sediments finer than 32 μm could reach dense seagrass meadows and a dugong sanctuary within a few weeks. The intense tidal circulation leads to non-isotropic and long-distance sediment dispersal patterns along the coast. Our results suggest that the sediments released by this project will not be quickly mixed but rather be concentrated where the most valuable ecosystems are located. If accepted, this coal mine could therefore have a far-reaching impact on the GBRWHA and its iconic marine species.

Numerical simulation of tidal circulation in the Obhur Lagoon, on the eastern coast of the Red Sea, Saudi Arabia

Numerical simulation of tidal circulation in the Obhur Lagoon, on the eastern coast of the Red Sea, Saudi Arabia

Influence of horizontal eddy viscosity and bottom friction coefficients on morphodynamic evaluations

The horizontal eddy viscosity (ε) and bottom friction coefficient (Kbr) are important hydrodynamic parameters in the computation of flow fields that dictate the morphodynamics. The effect of the variations in ε and Kbr as well as their combination on the prediction of hydrodynamics and morphodynamics in the Cochin harbor and adjoining nearshore area (9.9312° N, 76.2673° E) has been investigated in detail. A tidal circulation model to solve the shallow water equation is applied with the different parameterizations of ε and Kbr. In order to understand its effect, ε is expressed as a function of depth averaged velocity and length scale of computation mesh, whereas Kbr is expressed as a function of depth. The validation of the model is carried out with the measured currents. The improvement in the hydrodynamic and morphodynamic predictions is demonstrated by implementing the spatially and temporally varying ε The predictions are further improved by implementing a spatially varying Kbr. It is seen that the simulations with varying ε and Kbr predict the morphodynamic behavior close to the field values. The performance of the model predictions is discussed in terms of R2, RMSE and BSS (Brier Skill Score).

Can sea level rise help us restore coastal wetlands? The hydrologic restoration of the Slop Bowl, Brazoria National Wildlife Refuge, Texas

The Slop Bowl marsh in the Brazoria National Wildlife Refuge provides extraordinarily high quality, heavily used bird habitat. Much of this habitat has experienced hypersaline conditions due to both hydrologic alteration by humans and a rapidly and changing physical environment over the past several decades. Oil and natural gas extraction activities have resulted in excavation and channelization along pipelines and hydrologic obstruction by an access road. In addition, subsidence along growth faults has altered hydrologic pathways and lowered surface elevations in the center of the marsh. Our objective was to understand the underlying processes that contribute to hypersaline conditions and to evaluate possible restoration alternatives to reduce the severity of those conditions. Accordingly, we conducted extensive field and hydrologic modeling efforts, and identified the past, present, and future of this marsh habitat under a baseline scenario. We then compared various restoration action scenarios against this baseline. We found that, beginning in about 15 years, relative sea level rise will improve the hydrologic conditions by enhancing tidal flushing. However, if fill material is continually added to elevate the obstructing road as the sea rises, this hydrologic relief may never be realized. Moreover, we found that if a drought occurs during this critical period, a difference of only a few centimeters in the relative water level and road elevation, or changes in marsh surface elevations driven by fault motion and subsidence, may have catastrophic consequences. The modeling also suggests that several potential interventions can bridge this gap over the next 15 years and beyond. Actions that improve tidal circulation, reduce salinity, and enhance marsh accretion are being developed by the project team to enhance and restore habitat in the near term. The most optimal approaches evaluated thus far include the installation of culverts at critical locations, the excavation of a small channel, the modification of flow pathways, and the beneficial use of sediments and vegetative plantings. We conclude that, under specific circumstances or at unique locations such as the Slop Bowl marsh, sea level rise can be leveraged to improve coastal wetland health.

Numerical Simulation on the Diffusion of Alien Phytoplankton in Bohai Bay

In order to investigate the motion feature of alien phytoplankton in the Bohai Bay area, this manuscript builds a two-dimensional tide hydrodynamic model coupled with a particle tracking model to simulate the alien phytoplankton movement trajectory and the diffusion processes with different specific growth rates in three major ports of Bohai Bay (Caofeidian port, Tianjin port, and Huanghua port). The results show that the movement of alien phytoplankton is mainly affected by the tidal circulation near the port, and the diffusion trend is basically consistent with the residual flow in Bohai Bay. The distribution density of alien phytoplankton is directly affected by the specific growth rate of the population and is positively related to specific growth rate. The released alien phytoplankton in the three major ports are all concentrated around the ports area. The largest distribution density is in Tianjin port, and the possibility of red tide disasters is also greatest here compared with the other two major ports. It is necessary to strengthen the monitoring of alien organisms in the port area and actively prevent alien phytoplankton from entering Bohai Bay through ship ballast water.

Investigations Exploring the Use of an Unstructured-Grid, Finite-Volume Modelling Approach to Simulate Coastal Circulation in Remote Island Settings—Case Study Region, Vanuatu/New Caledonia

Understanding coastal circulation and how it may alter in the future is important in island settings, especially in the South West Pacific, where communities rely heavily upon marine resources, and where sea level rise (SLR) is higher than the global average. In this study we explore the use of an unstructured-mesh finite-volume modelling approach to assist in filling the knowledge gaps with respect to coastal circulation in remote island locations—selecting the Vanuatu and New Caledonia archipelagos as our example study site. Past limited observations and modelling studies are leveraged to construct and verify a regional/coastal ocean model based on the Finite-Volume Community Ocean Model (FVCOM). Following verification with respect to tidal behaviour, we investigate how changes in wind speed and direction, and SLR, alter coastal water levels and coastal currents. Results showed tidal residual circulation was typically associated with flow separation at headlands and islands. Trade winds had negligible effect on water levels at the coast, however, wind-residual circulation was sensitive to both wind speed and direction. Wind-residual currents were typically strongest close to coastlines. Wind residual circulation patterns were strongly influenced by Ekman flow, while island blocking, topographic steering and geostrophic currents also appear to influence current patterns. Tidal amplitudes and phases were unchanged due to SLR of up to 2 m, while maximum current speeds altered by as much as 20 cm/s within some coastal embayments. Non-linear relationships between SLR and maximum current speeds were seen at some coastal reef platform sites. Under higher sea levels, tidal residual currents altered by less than ±2 cm/s which is relatively significant given maximum tidal residual current speeds are typically below 10 cm/s. Our findings indicate that under higher sea levels, coastal processes governing sediment transport, pollutant dispersal and larval transport are likely to alter, which may have implications for coastal environments and ecosystems. Given winds influence coastal circulation and subsequent coastal processes, changes in trade winds due to climate change may act to further alter coastal processes. It is felt that the current modelling approach can be applied to other regions to help fill critical knowledge gaps.