In recent years, much work has been devoted to the characterization of the long-term variability of the circulation in the North Ionian Sea, which in the last three decades has been dominated by the so-called Bimodal Oscillation (BIOS). Here we further investigate this topic, both in the context of present climate and in a future scenario, analyzing the results of simulations made with the MED16 model. MED16 is a new, tide-including implementation of the MITgcm oceanic model, which covers the Mediterranean-Black Sea system with a horizontal resolution of 1/16° that is further increased at the Gibraltar and Turkish Straits. Three simulations have been performed: a hindcast run (1980-2010), used to validate the model; a historical run (1980-2005), which provides initial conditions for the scenario simulation; and a future climate (2006-2100) simulation, using atmospheric forcing under the Rcp8.5 emission scenario.

The hindcast run shows a variability of the surface circulation that is in good agreement with the observations, and indicates that during the period 1980–2010 the surface variability in the north Ionian is poorly correlated to that of the wind stress curl. The inversions of the circulation (switch from cyclonic to anticyclonic) that have been observed, and are well reproduced by the model, are apparently controlled by the Eastern Mediterranean Transient phenomenon: the huge volume of dense water produced by the Aegean Sea is the only forcing that may explain the strong anticyclonic surface circulation during the period 1993-1998. After that a prolonged cyclonic phase sets in, which weakens only during the 2004-2006 period.

On the other hand, the climatic projection over the next century shows a prevalence of the cyclonic circulation, well correlated to the prevalent positive wind stress curl, and  three clear inversions in which both the wind stress curl and the anomalies of dense water of Adriatic and Aegean origin appear to play a role. The simulation shows that the variability in the region is also affected by the strengthening and weakening of the cyclonic cell itself, which can modulate the ingression of the Atlantic Ionian Stream from the Sicily Strait and its path. This indicates that the multidecadal variability of the north Ionian circulation can play an important role in the control of the transport of the surface salinity in the Eastern Mediterranean Sea, even in extreme climatic conditions.

How to cite: Napolitano, E., Iacono, R., Carillo, A., Struglia, M. V., Palma, M., and Sannino, G.: Present and future long-term variability of the north Ionian surface circulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6352, https://doi.org/10.5194/egusphere-egu23-6352, 2023.

An Oceanic Regional Circulation Model (ORCM) is generally constructed by downscaling the large-scale information of an Oceanic Global Circulation Model (OGCM) through a nesting technique. Since the OGCM has relatively low resolution and so only has large-scale information, ORCM can only be built with large-scale information. Even if the ORCM is run with only large-scale information, small-scale fluctuations can be developed by “stimulating sources” such as the self-interaction of large-scale motions. However, it is not sufficient to generate small-scale fluctuations by itself in a short time, and if other stimulating sources, such as islands, coastlines, and strong advection, are absent, errors can occur (Van Tuyl and Errico, 1989; Pham and Hwang, 2020). Pham and Hwang (2020) suggested a method to introduce artificial small-scale fluctuations for boundary conditions that can reduce errors and generate small-scale features in a short period. This method was applied to the ocean of 330 km  220 km with a resolution of 1 km  1 km, and the accuracy of the applied model was higher than that of the original model. In this study, this small-scale addition method is developed to be applied to the coast smaller than the ocean, and the generated small-scale fluctuations are added in the vertical direction as well.

To construct the artificial small-scale fluctuations, we first need to analyze the regional energy spectrum. A high-resolution ORCM model is built using the OGCM data and used as reference data. The regional energy spectrum is defined in the high-resolution ORCM results, and small signals below a certain wavelength are removed with a low-pass filter using the Discrete Cosine Transform to mimic the low-resolution OGCM data. We then assume that energies cascade monotonically from the large scale. After the energy spectrum is extended from the larger scales to the smaller scales, this spectrum is transformed to realistic values using the Inverse Discrete Cosine Transform. The realistic values with small-scale features are added to the original values with large-scale features, which apply to all vertical layers. When this small-scale addition method is applied to the coast where the strong advection is present, the method does not significantly improve the accuracy, unlike when applied to the ocean. Therefore, in coastal areas where strong advection exists, another method is needed to increase accuracy in a short time.

References

Pham, V. S., & Hwang, J. H. (2020). Effects and recovery of small-scale fluctuations in one-way nesting for regional ocean modeling. Ocean Modelling, 145, 101524.

Van Tuyl, A. H., & Errico, R. M. (1989). Scale interaction and predictability in a mesoscale model. Monthly weather review, 117(3), 495-517.

Acknowledgement

This work was supported by the project entitled “Development of living shoreline technology based on blue carbon science toward climate change adaptation [grant number 20220526]” funded by the Ministry of Oceans and Fisheries (MOF), South Korea.

How to cite: Kim, B.-K. and Hwang, J. H.: A Study on One-way Nesting Technique for Oceanic Regional Circulation Modeling through Small-scale Information Restoration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6004, https://doi.org/10.5194/egusphere-egu23-6004, 2023.

An experiment has been carried out in the Adriatic Sea, in the framework of the Middle Adriatic Upwelling and Downwelling (MAUD) project. The CTD and ADCP data were collected by the yo-yo and shipborne measurements performed during the cruises whereas the temperature, pressure and dissolved oxygen time series were recorded by the probes deployed at the sea bottom. Additionally, the SST satellite data and the meteorological time series originating from permanent coastal stations were considered. Moreover, the high-resolution, 2-km meteorological (ALADIN) and 2.5-km oceanographic (ROMS) models were used to reproduce and interpret the experimental findings. Analysis of the data has concentrated on the end of May 2017, when a dense water dome was documented by the CTD measurements in the area between the island of Blitvenica (close to the east coast) and the island of Jabuka (in the open sea). Its center was observed at a distance of about 20 km from the coast. The dome left its mark on the sea surface, with the temperature above its center being slightly lower than in the surrounding areas as documented by both in situ and remotely-sensed data. The vmADCP measurements suggested that the surface circulation around the dome was cyclonic. At the time, a decrease of temperature close to the east coast was documented by the bottom probes and satellite images. The meteorological data and modeling results showed that the northern winds prevailed during the May 2017 experiment, suggesting that the open-sea and coastal upwelling occurred at the same time. In order to verify the interpretation, several schematized numerical experiments were conducted. The modelled wind fields were first decomposed into the curl and curl-free components, using the Helmholtz-Hodge decomposition. The components were then used to impose the forcing on the Adriatic model, assuming flat bottom and realistic bathymetry. Schematized simulations revealed that the wind curl was responsible for the offshore rising of pycnocline through Ekman pumping and therefore for the open-sea upwelling. On the other hand, in simulations with the curl-free wind component the pycnocline rose only close to the east coast and thus the coastal upwelling was reproduced.

How to cite: Orlic, M., Beg Paklar, G., Dzoic, T., Lucic Jelic, P., Medugorac, I., Mihanovic, H., Muslim, S., Pasaric, M., Pasaric, Z., Stanesic, A., and Tudor, M.: Open-sea and coastal upwelling in the Adriatic Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6387, https://doi.org/10.5194/egusphere-egu23-6387, 2023.

Submesoscale eddies form an important component of the circulation of the Southern California Bight (SCB), greatly impacting ecological processes. Despite their acknowledged significance in influencing ocean physics and biology, submesoscale eddies have been exceptionally hard to observe because of the technical challenges posed by both field and remote platforms. Here using a decade of high-frequency radar (HFR) surface current data we address this challenge for the SCB. Over the ten years of data, our research has mapped out the spatial distribution of submesoscale eddies and provided their seasonal and inter-annual variations. Between 2012 and 2021, a total of 235229 eddies were detected, averaging 452 eddies per week. Of these, 56% were cyclonic and 44% were anticyclonic. The contribution is roughly equal if eddies through their life spans are counted as one occurrence. This is because cyclonic eddies lived longer. The spatial distribution of eddies exhibited strong topographically related heterogeneity. Spatially coherent eddies, which reoccurred in certain locations over time, formed hotspots of eddy activity, largely in association with headlands. However, there were hotspots that did not seem to be associated with any typographic feature. Eddy temporal variations were examined at seasonal and interannual scales. On seasonal scales, eddies were found to be more numerous in the summer and early fall than in the spring. In August, the number of eddies was the highest, with 55% more observed eddies than in April, the least active month. The strong equatorward flow in the springtime seems to be linked with the reduced eddy activity at this time, likely due to the flow's suppressing effect on vortices and instabilities. At interannual scales, the eddy activity substantially increased in association with the 2014-2015 Blob event and the 2015-2016 El Niño. Observed eddies rose by 38% in 2014 compared to 2013 and remained high in 2015 and 2016. The results of this study are useful for the validation of numerical modeling studies in the SCB and could be of interest to the biological community to evaluate links between ecosystems and submesoscale activity along the highly productive coasts of the SCB.

How to cite: Payandeh, A. R., Libe Washburn, L., Emery, B., and Ohlmann, C.: Submesoscale Eddies in the Southern California Bight Derived from a Decade of High Frequency Radar Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3950, https://doi.org/10.5194/egusphere-egu23-3950, 2023.

The North Aegean Sea is a sub-basin of the Mediterranean which exhibits a range of oceanic processes at various scales. Due to the inflow of very light, mesotrophic Black-Sea waters it is the most productive region of the seas around the Hellenic Peninsula, although the regular seasonal coastal upwelling along its eastern shores does not contribute to its productivity. Despite the continuous buoyancy import by the Black Sea, the North Aegean hosts the densest waters of the Eastern Mediterranean. Finally, three semi-enclosed bays located in two islands of the North Aegean exhibit an alternating behavior as sources or sinks of buoyancy for the basin, while their productivity and natural beauty support a range of coastal activities. For the above reasons, the University of the Aegean has invested over several years in the development of a coastal oceanographic observatory (AEGIS), covering both the open North Aegean Sea and the three main bays of the islands of Lesvos and Lemnos. The Observatory consists of a numerical modeling component and an observational component.

The modeling component of the observatory consists of four coastal circulation models (for the three bays and the island of Lesvos) nested within a larger domain circulation model covering the whole Aegean Sea north of 37º N. Data assimilation, employing both satellite (sea-surface temperature and sea-level) and field data (employing mostly ARGO float observations) is used in the model of the extended domain (an implementation/configuration of the ROMS system), while the observations obtained in the coastal regions are currently used for coastal models’ (DELFT-3D FLOW and ROMS) validation. In addition to the above circulation models, SWAN is used to simulate the surface waves and DELFT-3D WAQ is being implemented to simulate the biochemical functioning at the various model domains.

The observational component at small geographical scales (in the Bays) comprise of continuous meteorological and oceanographic observations through an oceanographic mooring in the middle of the Bay of Kalloni, sea-level observations at the Bays of Kalloni and Gera, and High-Frequency radar observations of sea-surface currents and waves in a region east of Lemnos island, aiming to monitor the Black Sea outflow into the Aegean. The above continuous measurements are supplemented by periodic hydrographic and biogeochemical measurements in the three Bays, to validate the models and calibrate the in-situ continuous data. A recent addition to the AEGIS’s observational arsenal is an ocean glider aimed to capture the variability of the open North Aegean sea.

The AEGIS Observatory provides the necessary background to support strategic planning of human interventions at regional and local scales, such as Marine Spatial Planning or the construction of river dams affecting sensitive coastal basins. The implementation of the Coastal Laboratory has been supported by several projects, the most recent being the project “Coastal Environment Observatory and Risk Management in Island Regions AEGIS+” (MIS 5047038), implemented within the Operational Programme “Competitiveness, Enterpreneurship and Innovation” (NSRF 2014-2020), cofinanced by the Hellenic Government (Ministry of Development and Investments) and the European Union (European Regional Development Fund).

How to cite: Zervakis, V., Krasakopoulou, E., Tragou, E., Kolovoyiannis, V., Mamoutos, I., Potiris, M., Androulidakis, I., Mosiou, K., Kalatzi, M. I., Mazioti, A. A., Chatzilaou, C., Kougioumtzoglou, R. F., and Petalas, S.: Development of a Coastal Oceanographic Observatory for the North Aegean Sea: The AEGIS projects, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13065, https://doi.org/10.5194/egusphere-egu23-13065, 2023.

A data set detected by a high-resolution Lagrangian surface drifter is presented for the North Sea from 2017-2021. The North Sea is a marginal sea and is considered a shallow water shelf for most of its area, making its oceanographic dynamics quite different from those in the deep ocean. In contrast, it is less dominated by baroclinic dynamics but is strongly driven by tides, which results in a significant difference in the circulation patterns of particle motions. Numerous Lagrangian drifter observations have been deployed to gain a better understanding of the current behavior at the sea surface. Compared to Eulerian approaches and remote sensing methods, such as high-frequency radars and satellite altimeters, the Lagrangian measurement method can resolve fine current structures at spatial and temporal scales while covering a large region. In addition, Lagrangian methods are variable in space and time, allowing analysis of fine submesoscale fluid dynamics, such as divergence and eddy dynamics, by using clusters of drifters.

The methods suitable for calculating surface and tidal currents using drifter position data are presented. Thus, using the large amount of data collected from 2017 to 2021, this study provides a high-resolution mean surface current map and gridded representation of tidal dynamcis in the North Sea. Significant differences between the shallow water shelf and the deep area of the North Sea become apparent. While tidal currents dominate the shallow coastal areas, deep areas such as the Skagerrak register a high mean residual circulation driven by high density gradients. Comparison with other measured data proves that the chosen methods to calculate the currents are reliable. This presents the potential for Lagrangian measurements by surface drifters and the capability of the already detected data set, as it can be used for further analysis and to advance and calibrate numerical models.

How to cite: Deyle, L., Meyerjürgens, Dr. J., and Badewien, Dr. T.: Gridded Lagrangian surface drifter observations in the North Sea: An overview on high resolution tidal dynamics and surface currents, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15804, https://doi.org/10.5194/egusphere-egu23-15804, 2023.

The Orust-Tjörn fjord system is located on the west coast of Sweden and consists of several fjords with many small islands. The fjord system has more than one connection to the open water, enabling a generally counterclockwise circulation through the fjords. It is home to nature reservoirs, different industries on land and aquaculture farms. It is threatened for example by hypoxic areas, invasive species, water pollution and algae blooms with the water quality strongly been influenced by the water exchange in the fjord system. Therefore it is important to understand the circulation, the state and the exchange of w­ater between the fjords system and the open water outside the fjord.

Not much knowledge of the circulation inside the fjords and the drivers of the water exchange between the fjords and the open water exists. The reasons are that observations are spatially sparse and the resolution of regional ocean circulation models are generally too coarse to resolve this complex fjord system with its shallow and narrow straits between the different fjords. Therefore, we developed a setup of a coastal ocean circulation model with a horizontal resolution of 50 m to study the drivers of water exchange of the Orust-Tjörn fjord system. Within a sensitivity study a set of simulations are performed using (a) temporally constant wind forcing, (b) temporally and spatially constant sea level at the open boundaries (c) no tides, and (d) constant offshore density, i.e. temporally and spatially constant temperature and salinity profiles at the open boundaries. The simulation period is September 2016 – February 2017, which includes a high saline water inflow in October 2016.

Model results compare well with observations from moored high-frequency velocity, temperature and salinity instruments as well as regular monitoring data. Results show for example that the density difference between the southern and northern entrance of the Orust-Tjörn fjord system highly influences the water exchange between the fjords and open water. This is because with constant offshore density applied, near surface velocities of the Baltic current as well as the circulation above sill level within the fjord system weakens. The timing and strength of the high-saline inflow event is most sensitive to the cases of constant winds and constant offshore densities. In general, we will present a detailed analysis of the main drivers of water exchange above sill level.

How to cite: Brunnabend, S.-E., Axell, L., Garcia-Jove, M., and Arneborg, L.: What drives the water exchange above sill level in the Orust-Tjörn fjord system?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1363, https://doi.org/10.5194/egusphere-egu23-1363, 2023.

Celia storm was an intense event that hit the NW Mediterranean Spanish coast during March 2022. During those dates a study was conducted where 2 instrumented platforms were installed, together with the gathering of high-resolution topobathymetric information at the Sant Sebastià and Sant Miquel beaches (Barcelona). The information taken from this campaign helped to calibrate and validate separately the hydrodynamics of the models XBeach and COAWST. A nesting strategy was done between these models in order to improve the validation of XBeach hydrodynamics. The approach is designed for a pass from a pre-operational to an operational framework in the future.

The aim of the study is to integrate both models within a reasonable computational time and good accuracy which will help to forecast possible flooding and erosion hazards and consequently create an Early Warning System in the area. The full strategy comprises atmospheric and hydrodynamic forcings from CMEMS into COAWST that feed the hydrodynamic conditions of XBeach. The simulations were done using the MPI modules of the models to reduce the computational expense and the post-processing using Python/Matlab.

Results from the validation of the models will be presented as well as the inundation and the erosion derived from the storm impact at the area. Also, some methodologies that could be applied for validate both outputs will be discussed.

Funding: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101037097 (REST-COAST project).

Acknowledgments: The first author has the support of the Secretariat for Universities and Research of the Ministry of Business and Knowledge of the Government of Catalonia and the European Social Fund.

How to cite: Sánchez-Artús, X., Gracia, V., Espino, M., Liste, M., Mestres, M., and Sánchez-Arcilla, A.: COAWST-XBeach nesting strategy validation for the Celia storm at the Barceloneta beach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7107, https://doi.org/10.5194/egusphere-egu23-7107, 2023.

High-resolution wave forecasts are of critical importance for coastal safety, hazard prevention, and energy transition. Examples that benefit from detailed information of coastal sea states range from the adaptation of coastal protection to beach goer and marine safety and even include the growing market of marine renewable energy. While regional and global wave forecasts exist, local high-resolution details are often not accessible due to the associated computational cost.

In our work we use a neural network to apply a so-called super-resolution approach that can turn wave forecasts computed over coarse grids into substantially higher resolution at very low computation cost and with only little loss of overall quality. The idea is to train the neural network with pairs of coarse and fine-grid computations, so that later on wave computations over coarse grids can be converted into a higher resolution. While the amount of saved computation time varies with the level of resolution between coarse and fine grid, the super-resolution approach can be more than 50-times faster than a direct high-resolution computation and still provide good accuracy.

Here we will present a case study on a 44-year hindcast of the French Basque coast, with which we trained and tested multiple networks. We will comment on the dependency of model performance on the amount of training data and the difficulties of an unstructured grid, compared to a structured one. More specifically, structured grids can be handled as regular images, which makes the adaptation of classical and powerful convolutional neural networks to the problem relatively easy. The application to irregular grids, however, is not trivial and requires different approaches like graph neural networks or multi-layer perceptrons.  Lastly, we will compare the performance of a surrogate model, that is, a neural network that simply replaces completely a spectral wave model like SWAN, with our super-resolution approach, that uses coarse wave model computations as an input. We argue that both approaches are complementary and have their advantages and disadvantages in specific settings. 

How to cite: Kuehn, J., Abadie, S., and Roeber, V.: Neural-network-based super-resolution on unstructured meshes of coastal spectral wave computations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9173, https://doi.org/10.5194/egusphere-egu23-9173, 2023.

        Coastal areas host 53% of the world's population increasingly subject to risks related to climate change. In order to understand and prevent these risks, the prediction of coastal hydrodynamic and morphological evolution is essential. Bathymetry is a key geophysical variable in  A key parameter to improve numerical coastal hydrodynamics models is the bathymetry. High resolution satellites now allow to observe coastal areas at a regional to global scale in a most cost-efficient way rather than local traditional echo sounding bathymetry measurements. We present S2Shores (Satellite to Shores), a new state-of-the-art python library developed to estimate wave field characteristics such as wavelength, period, direction, celerity to derive bathymetry from satellites. The core code is optimized to process optical satellite imagery, moreover the library is built in an object-oriented structure allowing efficient and agile manipulation of the modules developed from input and output handling to post-precessing.  S2Shores is optimized, using parallel computing with Dask python library, to compute large spatial scale, or time series evolution bathymetry as well on HPC cluster as on local computer. For example a bathymetry of 4400 km² of ocean, around the French Gironde estuary, can be computed in 90 sec (using 30 cores and 9.5 Go memory usage) with a 500 meters output grid resolution. We present a work in progress new python library for bathymetry estimation that will be open to the public to use and propose collaborative improvements.

How to cite: Thoumyre, G., Bergsma, E., Almar, R., Giros, A., Lemai-Chenevier, S., Artigues, S., and Garlan, T.: A new python tool for coastal bathymetry estimation : S2Shores, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6088, https://doi.org/10.5194/egusphere-egu23-6088, 2023.

The rheological properties of natural mud are closely related to nautical depth estimation, wave propagation, and morphology evolution of muddy coast. In this study, the rheological properties of the natural mud collected from Luxi Island and Zhoushan Island in China were investigated. Shear stresses in steady state or oscillatory state were imposed on mud samples directly to obtain the yielding process under tidal currents or waves. The results showed that both apparent viscosity and complex viscosity experienced two sharp declines with increasing shear stress, indicating a two-step yielding nature of natural mud. Two yield stresses, namely, static yield stress and fluidic yield stress correspond to the yielding processes of elasticity and viscosity breakdown, respectively. The static yield stress in the oscillatory shear stress tests was lower than that in the steady shear stress tests, and the fluidic yield stress of natural mud in oscillatory shear stress tests was higher than that in the steady shear stress tests. The above phenomenon was explained by the viscoelastic-oscillation theory. Furthermore, the experimental results indicated that the initial storage modulus had a closer connection to both yield stresses in comparison with mud density. This study not only provided a guideline for having a better understanding of the two-step yielding process of natural mud, but will also provide scientific support for the assessment of fluid-mud formation, sediment transport and morphology evolution, the interaction between waves or tidal currents and muddy seabed, and protection of seafloor infrastructures.

How to cite: Xia, Y., Wang, S., He, Z., and Gu, H.: The yielding process of the natural mud under current and wave shear stress, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10962, https://doi.org/10.5194/egusphere-egu23-10962, 2023.

Changes in wave heights during the propagation toward the coastline are influenced by many environmental factors. Under the complex effect of environmental processes, wave heights change due to energy dissipation, and the waves break under certain conditions. Due to the importance of predicting the wave heights in coastal areas, improving the prediction performance of spectral wave models by incorporating better physical descriptions of wave growth and dissipation attracts the interest of researchers. In this study, we aimed to quantify the sensitivity of wave height predictions to changing growth and dissipation parameterizations in a spectral wave model SWAN Cycle III Version 41.31A. Spectral wave model SWAN is used to hindcast the significant wave heights measured between the dates October 17 and November 10, 2018, at Shkorpilovtsi in the western Black Sea. Model runs are executed on an unstructured mesh-based spectral model of the Black Sea. The model is forced by ERA5 wind fields provided by European Centre for Medium-Range Weather Forecast. ST6 physics package is considered in this study for sensitivity analysis. The performance improvement in the prediction of Black Sea wave heights provided by the default parameterization of ST6 physics in comparison to default model parameterizations of Komen, Janssen, Westhuysen is shown previously. Further investigation on the sensitivity of modeled wave heights to ST6 parametrization is conducted in this study. Chosen ST6 growth and decay parametrizations needs to be coupled with swell dissipation terms. SWAN model presents Ardhuin and Zieger swell dissipation models. Coupling with the swell models provided ten model runs in total which are to be compared with the in-situ measurements by using error metrics including correlation coefficient, root mean square error (rmse), and bias. Sensitivity analysis based on given model runs are performed to identify the contribution of each parameter to resultant wave heights. Sensitivity analysis indicated an 8-30% of underestimation in the highest waves for the study area.

Acknowledgments: This research is supported by The Scientific and Technological Research Council of Turkey (TÜBİTAK) under grant number 119N400 and RFBR 20-55-46005.

 Keywords: Spectral wave modeling, wave hindcasting, sensitivity analysis

How to cite: Ayat, B., Aydogan, B., Saprykina, Y., and Shtremel, M.: Sensitivity of wave predictions to growth and dissipation parameterizations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-830, https://doi.org/10.5194/egusphere-egu23-830, 2023.

Wave parameters set the base for the design of coastal structures. For this purpose, commonly modelled wave properties are employed. This approach is usually adequate in the open ocean conditions where variations in the wave properties are normally quite limited. The situation is different in the nearshore areas of basins of complicated shape where wave properties can be highly variable. Unfortunately, in many cases, long and sufficiently detailed wave measurements for model validation are not available. The use of default settings of wave models means that possible errors remain unknown. This approach could lead to overdimensioned structures or to structural failures. We address the magnitude of possible errors in such conditions by comparing the output of simple wave models (such as a fetch-based SMB model, the SWAN model forced with one-point homogenous wind, etc.) and a sophisticated multi-nested SWAN wave model forced with ERA-5 winds with recent wave measurements in various nearshore locations in the eastern Baltic Sea. We use records of different length over more than 10 years. While in some locations simple models or models forced with homogenous wind lead to acceptable results, in most areas more sophisticated models are needed to adequately replicate wave properties. The outcome of our analysis provides several site-specific hints for practical coastal engineering.

How to cite: Männikus, R., Soomere, T., and Suursaar, Ü.: How do simple wave models perform compared with sophisticated models and measurements in the eastern Baltic Sea?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1657, https://doi.org/10.5194/egusphere-egu23-1657, 2023.

The hydrodynamics and sediment characteristics of muddy estuaries and coasts during typhoons are closely related to geomorphic evolution, ecological environment, and economic development of coastal zones. Taking the macro-tidal turbid Hangzhou Bay (HZB) as an example, the sediment characteristics and the effects of wave-current interactions on sediment dynamics during Typhoon Mitag were studied using a well-calibrated numerical model. The model considers tides-wave-sediment interactions and the reconstructed typhoon wind field. The net sediment fluxes were controlled by residual currents and SSC. The waves and winds dominated the sediment resuspension. The combined interactions of currents and waves led to high SSC during the typhoon. In calm conditions, the impact of wave-current interactions was small except for the combined bottom stresses. The combined bottom stress was the primary wave-current interaction changing the sediment resuspension and increasing SSC, especially in shallow waters or during storms. The advection term, which played an essential role in reducing the SSC in HZB, mainly affected the SSC by enlarging the velocity. The wave dissipation term enhanced the vertical mixing, which involved the vertical exchange of suspended sediment and the currents. In the shallow waters of the southern bay, the wave dissipation term mostly led to the decrease of bottom stresses, the increase of currents, and the decrease of SSC, while the rise of SSC in the deep waters. The effects of the form drag, wave radiation stress, and refraction terms on suspended sediment dynamics were relatively small. The findings provide the theoretical foundations for the study of dynamics geomorphology in macro-tidal estuaries.

How to cite: Li, L., Ren, Y., Wang, X. H., and Xia, Y.: Sediment dynamics in Hangzhou Bay during Typhoon Mitag, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10898, https://doi.org/10.5194/egusphere-egu23-10898, 2023.

In a framework of changing climate, it is important to find alternative solutions for coastal protection. Indeed, the pressure of anthropogenic origin, combined with natural forcings, has contributed both to a worsening of the environmental quality of coastal areas, and to the triggering of erosion dynamics, with retreat of the sandy coast.

Tethered floating breakwaters, built as a regular lattice of reversed pendula, can provide an alternative solution for beach management. With respect to rubble mound breakwaters, this type of structures has small impact on water circulation, and, in the presence of rising sea levels, it is much more adaptable than an artificial reef. Depending on their efficiency, the cost-effectiveness of beach protection using tethered floats is favorable compared to the current hard-engineering strategies.

For this purpose, inspired by the concept of metamaterial wave control, a floating device has been tested in a wave flume with a two-dimensional periodic configuration. Metamaterials are engineered structures designed to interact with waves and manipulate their propagation properties. The device is built as an array of tethered submerged cylinders, with their axes parallel to the wave crests. The idea is to investigate the conditions which lead to the formation of bandgaps, which is the key factor for mitigating the incoming energy of the surface gravity waves.

Experimental results demonstrated the feasibility of the concept, and that wave attenuation can be significant, even using a limited number of cylinders. The analysis of the results, have allowed us to assess that two leading mechanisms, dissipation and reflection, contribute to wave attenuation. If the cylinders are fully immersed, dissipation induces a broad bandgap around a resonance frequency that depends on the characteristics of the single pendulum. Instead, wave scattering (reflection) is relevant around frequencies that can be predicted using the generalized Bragg condition and the second harmonic generation, where the most significant bandgaps in attenuation can be observed. The second harmonic generation effect is a typical non-linear phenomenon, linked to the geometrical configuration of the device. In our tests, this behavior can be observed even for very small amplitude incident waves.

In conclusion, these results show the possibility to tune the position of the attenuation bands in the wave spectrum by modifying system parameters, to make possible the implementation of an efficient wave absorber for coastal protection.

How to cite: Lorenzo, M., Pezzutto, P., De Lillo, F., Ventrella, F. M., De Vita, F., Ruol, P., Bosia, F., and Onorato, M.: An experimental study on a tethered floating metamaterial breakwater to attenuate surface gravity waves in a shallow water environment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13657, https://doi.org/10.5194/egusphere-egu23-13657, 2023.

Coastal vegetation can reduce extreme water levels during storm events, but the controlling factors and processes in complex estuary or delta systems are still unclear. This limits an effective implementation of nature-based coastal defences in delta mega-cities in low-lying coastal areas.

To explore the effects of vegetation on storm surge dynamics and currents, we used a Finite Volume Community Ocean Model implementation for the South China Sea and the Pearl River Delta. We numerically modelled how mangroves can offer coastal protection to the large coastal cities located in the delta, such as Guangzhou and Shenzhen, during strong typhoons, like Hato (2017).

Additionally, we analyzed how the effectiveness of mangroves changes under different sea level rise scenarios.

Water level attenuation by mangroves is effective during extreme water level conditions and differences in mangrove forests' properties drive their coastal protection function. The local (within-wetland) attenuation of extreme water levels is more effective with wide vegetation patches and higher vegetation drag. Narrower vegetation patches can still provide non-local (upstream) water level attenuation if located in the upper estuary channels, but their design needs to avoid amplification of water levels in other delta areas.

How to cite: De Dominicis, M., Wolf, J., van Hespen, R., Zheng, P., and Hu, Z.: Effectiveness of mangroves as nature-based coastal defences in the Pearl River Delta, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6519, https://doi.org/10.5194/egusphere-egu23-6519, 2023.

How to cite: Marino, M., Musumeci, R. E., Cavallaro, L., and Foti, E.: Coastal restoration measures to mitigate coastal flooding in a context of climate change: the case of the South-East of Sicily, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16529, https://doi.org/10.5194/egusphere-egu23-16529, 2023.

Morphological change of coastal and shelf seas is controlled jointly by physical, biological and anthropogenic processes and their interactions. While physical and anthropogenic drivers are normally regarded to exert a primary control on morphodynamics, the role of biota, especially benthos, in guiding long-term and large-scale evolution of coastal landscape/seascape is often overlooked and has received less attention. It was not until recent decades that research has revealed the importance of benthos in coastal protection. Further, as an indispensable part of the ecosystem, benthos not only consists of a significant part of organic carbon, but also plays a vital role in mediating carbon and nutrient fluxes across the sediment-water interface. The interaction between benthos and its ambient environment is twofold and dynamic. On one hand, coastal morphology, oceanographic forcing (e.g. tides, waves) and carbon/nutrient availability exert a first-order control on the type of habitats, as well as abundance and trait expression of benthos. On the other hand, benthos actively modifies its habitats and beyond to attain an optimized fitness for living conditions. Understanding such dynamic interactions is essential in management of coasts and shelf seas against present and future climatic threats and for sustainable use of coastal resources.

In this talk, we demonstrate the quantitative importance of fluid-sediment-benthos interactions in (1) guiding morphological development of a tidal embayment in the Wadden Sea and (2) carbon cycling in the great North Sea as exemplary case studies. We applied a novel 3-Dimensional physics-ecosystem coupled numerical model to resolve dynamic interactions among fluid forcing, organic carbon, sediment and benthos. Specifically, we aim to address two different but interrelated questions:

• How important are fluid-sediment-benthos interactions in coastal morphological development? and
• To what extent can such interactions affect carbon sequestration at a regional scale?

How to cite: Zhang, W., Arlinghaus, P., Porz, L., and Schrum, C.: Hydro-eco-morphodynamics and carbon cycling at coastal scales and beyond, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3309, https://doi.org/10.5194/egusphere-egu23-3309, 2023.

Plastics have become ubiquitous in the modern consumer economy. Unchecked production, failure to implement efficient recycling practices, and poorly defined global policy regarding production and disposal has led to a prevalent plastic problem. Over the past decade, microplastic pollution has emerged as a forefront concern of plastic in the global environment. As marine microplastic pollution becomes a predominant area of interest, it is important to understand microplastic sources, delivery pathways, and ultimate fate. Estuaries are key zones to monitor for microplastic pollution, due to their close proximity to source areas, and their natural ability to filter pollutants. The Galveston Bay watershed is located near the densely populated Houston, TX metro area and manufactures potentially half of the United States’ pre-production plastics. Using a Lagrangian particle-tracking method coupled with a validated 3D hydrodynamic model, we examined the transport behavior of microplastics, as well as export ability of the Galveston Bay estuary. Accounting for the variability of type and density of microplastics, multiple settling velocities were simulated to examine their effect on behavior. Four release sites were chosen near highly populated river connections. We found that settling velocity has significant impact on both local exposure time and retention time. Neutrally buoyant particles were flushed quickly out of the bay, while heavier particles migrated westward and spent far more time in the bay overall. Release location influenced percent of particles retained in bay, with a higher percent of particles still present from northern release locations than southern release locations after two years of simulation. The use of modelling studies to provide successful estimation of microplastic transport pathways and export efficiency of Galveston Bay will help contribute to a more robust understanding of microplastic behavior within estuarine environments.

How to cite: Summers, E., Du, J., Park, K., Kaiser, K., and Ryder, J.: Modelling transport pathways of varying microplastics in an estuarine environment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9577, https://doi.org/10.5194/egusphere-egu23-9577, 2023.

This work presents the steps towards the design and implementation of a marine observatory providing current and forecasted oceanic conditions relevant to the aquaculture sector, with particular focus on “Extreme Marine Events” such as marine heat waves, deoxygenation and storm surges. Examples of successful implementation of these guidelines in the framework of the EuroSea project are presented for two aquaculture sites: Deenish Island in Ireland and El Campello in Spain. In-situ measurements, remote-sensing observations and model forecasts are jointly provided to the end users. The process starts with the interaction with the stakeholders to understand their main needs and concerns, and is followed by the design of the software architecture that carries out the data acquisition, post-processing and visualization in an open-access web platform. User feedback is of paramount importance during the whole process to ensure that the services being offered in the end actually match the needs of the aquaculture sector.

How to cite: Pereiro, D., Belyaev Korolev, O., Bonnet Dunbar, M., Navarro, G., Cusack, C., Dabrowski, T., Nolan, G., and Graves, I.: An Observational and Warning System for the Aquaculture Sector in European Waters, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13650, https://doi.org/10.5194/egusphere-egu23-13650, 2023.

Complex processes involved in the river delta areas are not fully solved with a traditional structured-mesh model. A seamless unstructured-grid approach could serve as support to advance in the reproduction and understanding of the dynamics processes across different scales. In this work, a river-coastal-ocean continuum modeling representation has been developed for the Tiber River delta, including the surrounding coastaland open-ocean zones of the Lazio coast (Tyrrhenian Sea, Italy). This area has been selected because it includes important naturalistic sites but also a new commercial, fishery and leisure harbor whose the realization is scheduled for 2023. By using temperature and salinity profiles from near-river CTD data, we demonstrate that this representation simulates the coastal dynamic processes in the Tiber delta zone better than the classic coastal-ocean representation, minimizing calibration and sensitivity experiments. In this work, a large effort has been dedicated to the acquisition of new observations (CTD, drifters, currents radar, bathymetric survey) carried out over different spatial (open-ocean, coastal and near- and along-river) and temporal scales. Validation demonstrated that the model has good accuracy, also in reproducing the salt wedge intrusion along river. Furthermore, currents investigation suggested the existence of an anticyclonic gyre in proximity of the river mouth of the northern branch, mainly induced by river discharge and coastal morphology. These promising results in simulating cross-scale processes in a seamless fashion, will be included in the near future in an operational system for coastal forecasting.

How to cite: Causio, S., Bonamano, S., Federico, I., Piermattei, V., Piazzolla, D., Scanu, S., Madonia, A., De Cillis, G., Jansen, E., Coppini, G., and Marcelli, M.: River-coastal-ocean continuum modelling and assessment of nearshore dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14414, https://doi.org/10.5194/egusphere-egu23-14414, 2023.

It is well established that rivers are amongst the most important carriers of the plastic pollution found in the oceans. However, the main processes contributing to plastic and debris fate through riparian systems is still poorly known and understood. The Marine Litter Drifter project from the Arno River aims at using modern consumer software and hardware technologies to track the trajectories and evolution at sea of real Anthropogenic Marine Debris (AMD) from rivers, with a specific focus on the Arno River, in Italy. Innovative and low cost “Marine Litter Trackers” (MLT) were designed, assembled and used in this framework as they are reliable, robust, self-powered and they present almost no maintenance costs. Furthermore, they can be built not only by those trained in the field but also by those with no specific expertise, including high school students, simply by following the instructions.

Several dispersion experiments were successfully conducted using different types of trackers in different seasons and weather conditions. The maximum distance tracked was 2845 km for a period of 94 days. The activity at sea was integrated by lagrangian numerical models supporting the planning of the deployments and the recovery of the drifters. The models, in turn could benefit from the observed tracking data for calibration and validation and serve as tools to study and interpret the processes driving macro plastic displacement at sea. In this presentation we describe this activity and we discuss the dynamics of marine litter (ML) dispersion in the Tyrrhenian Sea on the basis of these integrated monitoring tools, as well as the potential of open-source approaches including the “citizen-science” perspective for both improving Big Data collection and educating/awareness-raising on AMD issues.

How to cite: Guarnieri, A., Merlino, S., Locritani, M., Delrosso, D., Biancucci, M., and Paterni, M.: Marine litter tracking system: a case study with open-source technology and a citizen science-based approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15601, https://doi.org/10.5194/egusphere-egu23-15601, 2023.