In this work, we aim to provide climatology and future scenarios of the sea level and wave parameters over the Mediterranean Sea, focusing on the Adriatic Sea. The period for climatology covers all the years from 1994 to 2020, while two scenarios (IPCC RCP4.5, RCP8.5) are projected in the future (2021-2050) for the waves in the Adriatic Sea and compared to a historical control period (1981-2010). Past runs are forced by CERRA reanalysis wind and pressure fields, which have been validated against observed data, while future scenarios and control run for the Adriatic Sea wave climate are forced by the COSMO-CLM climatological model winds. The sea level is obtained through simulations with a hydrodynamic finite element model, named SHYFEM, and with an Ensemble Kalman Filter data assimilation system. We used all the available observations of sea level from local stations along the Mediterranean coasts, after processing them. Assimilation works well in reanalysis, providing an excellent reproduction of the sea level, obtained by the ensemble mean. The wave data is provided as a hindcast product, obtained by coupled runs of SHYFEM with the WAVEWATCH III (WW3) over the Mediterranean Sea. Moreover, in the Adriatic Sea, we provide WW3 results with high resolution, both for the historical period and for future scenarios. This work has been performed as part of the CoastClim project, a PNRR-Return project led by the University of Bologna.

How to cite: Bajo, M., Barbariol, F., Benetazzo, A., Ferrarin, C., Fernandez, L., and Davison, S.: Climate and scenarios of sea level and waves in the Mediterranean Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3704, https://doi.org/10.5194/egusphere-egu25-3704, 2025.

This study aims to comprehensively evaluate the Coastal-KOOS Level 2 model’s ability to predict near-surface currents throughout the Northwest Pacific, using an extensive dataset of 153 surface drifters deployed since 2020. These drifters were released in diverse oceanographic settings, including the Yellow Sea, East China Sea, and East/Japan Sea, which feature strong tidal forcing, boundary currents (e.g., the Kuroshio).

We utilized drifter trajectories to derive Eulerian velocities, which were then compared with model outputs. To further validate the drifter-derived velocities, we contrasted them with in situ measurements from multiple fixed observation sites in offshore Korean waters. We also examined the influence of Stokes drift and direct wind forcing by attempting to remove these components from the drifter velocities; however, the corrections had negligible impact on most trajectories, likely because the majority of each drifter’s body remained submerged, thereby limiting its wind exposure.

Forecast accuracy was quantified using several statistical metrics, including root-mean-square error (RMSE), correlation coefficient, and complex correlation (separating magnitude and directional agreement). The results indicate that Coastal-KOOS exhibits robust performance in regions dominated by tidal currents, such as parts of the Yellow Sea, where the model’s operational focus aligns well with actual conditions. In contrast, performance degrades in areas strongly influenced by the Kuroshio and in the East/Japan Sea, likely due to strong eddies and persistent warm currents that are not fully resolved by the current model configuration. In the Korea Strait and along the Chinese coast, the model generally captures flow directions more reliably than current magnitudes, underscoring the importance of regional calibration and higher-resolution modeling.

Future improvements will focus on integrating additional observational data, including temperature and sea surface height, to better capture the complex dynamics of offshore regions. These findings underscore the importance of regional calibration and high-resolution modeling in refining operational ocean predictions. Ultimately, a strengthened Coastal-KOOS framework will enhance the accuracy of search-and-rescue operations, environmental monitoring, and disaster response in waters around the Korean peninsula. 

How to cite: Jeong, S.-H., Choi, J.-Y., Choi, J.-W., Kim, D.-S., and Kwon, J.: Performance Evaluation of Coastal-KOOS Surface Current Forecasts Using an Extensive Drifter Dataset in the Northwest Pacific, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14152, https://doi.org/10.5194/egusphere-egu25-14152, 2025.

Internal tides, generated by the interaction of barotropic tides with topography, are key drivers of shelf dynamics, influencing cross-shelf transport, stratification, and mixing processes critical to coastal ecosystems and regional circulation. Using data from moorings and underwater gliders, we observed frequent large-amplitude internal tides over the Al-Batinah shelf and slope. These tides predominantly occur within the diurnal band, although semidiurnal patterns can become prominent, particularly when spring tides coincide with a low-energy phase of the diurnal amplitude modulation. In contrast, local barotropic tides are dominated by M2, with a less energetic diurnal component evident in both currents and sea level. This raises questions about the origin and predictability of the observed internal tides.
To assess predictability, we applied a skill score that compares harmonic predictions to observed signals over varying window lengths. For on-shelf baroclinic currents in summer, the skill score begins at 96% for short windows of a few days, declining to about 75% for a three-week period, after which further decreases are more gradual. This places internal tides on the Al-Batinah shelf at the high end of predictability compared to other regions.
Potential energy conversion was estimated using barotropic body forcing based on TPXO and WOA datasets, while reflection and transmission coefficients (α) were derived as the ratio of topographic to internal wave slopes. The body force map reveals enhanced energy conversion in the K1 band approximately 170 km across the Sea of Oman, where α > 1 indicates internal tide reflection toward the southeast. This aligns with the incoming direction of the internal tide energy flux observed on the Al-Batinah shelf, potentially explaining their dominance in the diurnal band. A comparison of a two-year temperature record from the local shelf edge with barotropic transport at the remote generation site shows high wavelet coherence in the K1 band. Fortnightly patterns are delayed by approximately two days, consistent with phase speeds associated with second- and third-order vertical modes.
In summary, internal tides on the Al-Batinah shelf are remarkably predictable. The dominance of the diurnal band could be explained by remote generation, while semidiurnal components likely reflect contributions from local generation processes. Understanding and predicting internal tides on the Al-Batinah shelf has implications for understanding how tidal energetic processes act to enhance diapycnal fluxes, which ventilate the regional oxygen minimum zone and drive coastal productivity.

How to cite: Bruss, G., Font, E., Queste, B., and Hall, R.: Internal Tides on the Al-Batinah Shelf: Predictability and Generation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15550, https://doi.org/10.5194/egusphere-egu25-15550, 2025.

This study aims to improve the understanding of seasonal circulation on the NW Portuguese continental shelf, located at the northern boundary of the Canary Current Upwelling System. The analysis is based on numerical simulations from the Regional Ocean Modelling System (ROMS), applied to the Western Iberia region, using a 15-year realistic dataset spanning 2004–2018. The investigation identifies key oceanic circulation features of the NW Portuguese shelf and the upper slope/outer shelf transition zone, providing new insights into the temporal evolution of flow patterns throughout the year. Circulation in the region is influenced by shoreline orientation, shelf geometry, and bathymetric features, such as the Porto and Aveiro canyons. Emphasis is placed on alongshore and cross-shelf transport patterns, including recurrent outer-shelf bottom eddies near the canyon’s southern sides and the persistence of a coastal poleward current on the inner shelf, even during the typical summer upwelling season. Special focus is given to the transitional months between the well-documented summer upwelling and winter downwelling regimes. Wind stress strength and direction, and the drop-off characteristics are highlighted as critical drivers of the monthly evolution of shelf flow patterns. This is particularly evident on the inner shelf, where circulation appears to be largely determined by the competition between these two effects, the first related with coastal upwelling/downwelling occurrence and the later with Sverdrup integrated poleward/equatorward transport.

How to cite: Leal Rosa, T., Peliz, Á., and Piecho-Santos, A. M.: Seasonal flow patterns on the NW Portuguese shelf, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17052, https://doi.org/10.5194/egusphere-egu25-17052, 2025.

While surface submesoscale processes have been extensively studied, their counterparts in the bottom boundary layer remain largely unexplored. However, a few recent studies have indicated that these subsurface structures, emerging mainly through flow-topography interactions, are instrumental not only for the turbulent boundary mixing but also for the forward cascade of mesoscale energy towards dissipation and the lateral exchange of boundary waters with the oceanic interior. These studies have investigated the genesis of submesoscales primarily in the open ocean, focusing in particular on the vicinity of strong permanent current systems, coastal jets, or dense water outflows. Here, we use the Baltic Sea as a natural laboratory to demonstrate that interior submesoscales can arise even in semi-enclosed, strongly stratified basins away from the major current systems, in regions where tides and coastal jets are virtually absent, and ephemeral wind-driven currents typically dominate over short timescales. Using realistic high-resolution numerical simulations, we demonstrate that submesoscale vortices and filamentary structures are ubiquitous in the interior, below the mixed layer, especially during storm events. High cyclonic/anticyclonic vorticities are generated at the lateral boundaries close to the bottom, as the interior flow interacts with the sloping topography, with the strong vorticity anomalies being subsequently transported from the boundary into the stratified interior in the form of eddies, fronts, and filaments. Negative potential vorticity patches, indicative of submesoscale overturning instabilities, also develop from these flow-topography interactions. Our results show that surface and subsurface submesoscales coexist but remain largely isolated in this strongly stratified environment. By analyzing a series of sequential storm events, we show that winds indirectly energize the interior submesoscale motions by accelerating the boundary currents, with the strongest structures forming during severe storm episodes. Reversal of surface winds reverses the currents, significantly affecting the submesoscale generation sites and the mixing hotspots that exhibit, consequently, transient behavior. The intense winds also induce coastal upwelling and downwelling with the up-and downwelling sites evolving into pronounced mixing hotspots, presenting enhanced dissipation rates, resulting predominantly from the susceptibility of the flow to submesoscale overturning instabilities. These findings highlight the broader significance of storm-forced submesoscale dynamics in wind-driven marine and limnic systems, extending their relevance beyond the Baltic Sea context.

How to cite: Chrysagi, E., Umlauf, L., Grawe, U., Burchard, H., and Naveira Garabato, A. C.: Storm-driven submesoscale motions over sloping topography: Insights from the Baltic Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9906, https://doi.org/10.5194/egusphere-egu25-9906, 2025.

River plumes transport large quantities of freshwater along our coastlines, affecting coastal dynamics and the movement of sediment and fish larvae. This study focuses on describing the local intra-tidal evolution of currents, stratification, and turbulence in the Rhine River plume in The Netherlands. While the mid to far-field Rhine River plume has been subject to a number of field campaigns and detailed modelling studies, e.g. on tidal straining, very little data exist in the near-mid field region. However, this region is particularly interesting due to the occurrence of plume fronts and internal waves and their influence on coastal dynamics. Moreover, river plume regions are often highly engineered. In the Dutch coastal region, several topographic depressions, sand pits, are present. Their number is expected to further grow as beach nourishments are increasingly used as a coastal protection measure against sea level rise. Yet we lack information about the impacts of such topography changes on the hydrodynamics within this system.

In this study, we present unique observations of the turbulent kinetic energy (TKE) dissipation rate in the near-mid field Rhine River plume and a sand pit, along with salinity, temperature, and current measurements. The novel field data was acquired in April 2024 during a cruise of the RV Pelagia and covers a tidal cycle over two days during neap tide. The campaign happened to take place after a storm event. Two moorings with CTDs and an upward-looking ADCP were deployed outside and inside the sand pit and were complemented by ship-based CTD, microstructure profiler, and ADCP measurements at the mooring sites and close to the sand pit edges.

An analysis of the currents and TKE dissipation rate outside the pit reveals enhanced surface-layer shear and turbulence during higher wind speeds on the first day. At the same time, the density measurements show strong stratification that almost constantly withstands wind-induced mixing. However, a few disruption events in stratification are observed. These events indicate the advection of fresher and saltier surface water due to wind-generated currents. Furthermore, our observations show strong cross-shore shear emerging in the mid-to-bottom layers as a result of the stratification-induced modification of the tidal ellipse. We present how this shear reduces the stability and increases vertical mixing in the aforementioned layers. Additionally, we show events of increased turbulence, which we attribute to the passage of a tidal plume front. This front is indicated by higher surface stratification with simultaneously increased surface and bed shear stress.

Presently, we are comparing the measurements in- and outside the pit. While we expect an increase in mean stability due to the deeper water column and unchanged mixing input, local mixing may be significantly enhanced. Particularly around the steep edges of the sand pit as well as within the mid-to-surface layers, we hypothesize finding increased turbulence due to eddy formation and topographic internal wave generation. Furthermore, we are looking into internal waves generated ahead of the tidal plume fronts, which may increase mixing levels throughout the river plume.

How to cite: Warmuth, L., Kranenburg, W., and Pietrzak, J.: The intra-tidal evolution of currents, stratification, and turbulence in a near- to mid-field river plume and the local effects of topography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15549, https://doi.org/10.5194/egusphere-egu25-15549, 2025.

The Yellow Sea Bottom Cold Water (YSBCW), a cold water mass in the bottom layer of the Yellow Sea, contributes significantly to maintaining high nutrient concentrations, supporting phytoplankton growth, and enhancing primary productivity, which are essential for the productivity and structure of regional marine ecosystems. This study produced a 13-year reanalysis dataset (2010–2022) to analyze the seasonal and interannual variability of the YSBCW. Numerical modeling was conducted using the Regional Ocean Modeling System (ROMS) with a horizontal resolution of 1/20° and 41 vertical layers. The model domain covered 117–150°E and 21–54°N. Atmospheric forcing was provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5, initial and boundary conditions by the Hybrid Coordinate Ocean Model (HYCOM), and tidal forcing by TPXO9. Data assimilation was performed daily using the Ensemble Kalman Filter (EnKF), assimilating sea surface temperature from the Operational Sea Surface Temperature and Ice Analysis (OSTIA) and temperature-salinity profiles collected by the Korea Institute of Ocean Science & Technology (KIOST), the National Institute of Fisheries Science (NIFS), the Korea Hydrographic and Oceanographic Agency (KHOA), and Argo floats. The reanalysis dataset reproduced the seasonal and interannual variability of the YSBCW and demonstrated its reliability through validation against observational data. Surface temperature analysis showed seasonal biases from -0.45°C in winter to 0.13°C in summer. The root mean square error (RMSE) values were 0.79°C in winter, the highest among all seasons, and 0.49°C in autumn, the lowest. The model captured the vertical distribution of the YSBCW well, although tidal effects and mixing were overestimated, resulting in stronger vertical mixing than that observed in the coastal regions. The annual YSBCW volume was calculated by determining the volume of water deeper than 30 m with a temperature below 10°C to analyze interannual variability. In August, the volume was largest in 2013 at 4 km³ and smallest in 2020 at nearly 0 km³. The average volume is around 3.5 km³, decreasing from 2019 to 2020 and then increasing from 2021 onwards. Spatially, the northern and eastern Yellow Sea showed relatively small changes in cold water distribution while the southern and western regions exhibited greater variability, with cold water below 10°C widely distributed in 2013 but almost absent in 2020. This reanalysis dataset reproduces the formation, dissipation, and interannual variability of the YSBCW. Future research will analyze how climate variability and atmospheric forcing influence the formation mechanisms and variability of the YSBCW.

How to cite: Kwon, K., Jung, H., and Jang, C. J.: Analysis of Interannual Variability of the Yellow Sea Bottom Cold Water Using Reanalysis Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5001, https://doi.org/10.5194/egusphere-egu25-5001, 2025.

Ocean frontal regions are pivotal for physical and biogeochemical processes, particularly in estuarine and coastal regions, where their dynamic processes are often associated with high-frequency phytoplankton blooms. In strongly tidal estuarine regions, the horizontal divergence in frontal regions is significantly regulated by tidal forcing. In this study, a high-resolution hydrodynamic model based on the Regional Ocean Modeling System was utilized to investigate the seasonal, spring-neap tides, and high-low water slack characteristics of horizontal divergence in the Changjiang River plume water frontal region. A divergence tendency equation was employed to diagnose the dynamic mechanisms and driving factors.

Results indicated that the horizontal divergence in the frontal regions exhibited a periodic characteristic, with positive divergence at high water slack and negative divergence at low water slack. This indicated that horizontal divergence consistently occurred during high water slack, while horizontal convergence was prevalent during low water slack. This characteristic was robust, persisting regardless of seasonal changes or spring-neap tidal cycles. The divergence tendency term (DVT) also followed a periodic pattern: positive during flood tides and negative during ebb tides, indicating increased horizontal divergence during flood tides and reduced divergence during ebb tides. The horizontal deformation term (HDF) and horizontal viscosity term (HVISC) were negligible, while the pressure gradient term (PRG) was consistently important. During spring tides, the driving factors for horizontal divergence showed no seasonal differences. In the northern frontal region, the PRG and vertical viscosity term (VVISC) dominated the DVT, while in the southern region, the divergence change term (DVC), VDF (vertical deformation), PRG, and VVISC jointly dominated the DVT. In contrast, during neap tides, the driving factors were seasonally regulated by changes in frontal position and shape, primarily influencing the VVISC. In the northern region, PRG remained consistently significant. If the VVISC was also significant, other terms became negligible; if the VVISC was insignificant, the VDF, DVC, and occasionally the Coriolis term (COR) collectively played a regulatory role. In the southern region, the VDF, DVC, and PRG were consistently dominant, while the importance of VVISC exhibited seasonal variations. The driving factors differed significantly between spring and neap tides in the northern region but were similar in the southern region, with the only distinction being the seasonal variation in the VVISC.

How to cite: Li, S., Zhong, Y., Zhou, M., Qu, L., and Zhang, Z.: Effects and mechanisms of tidal forcing on the frontal divergence/convergence of the Changjiang River plume, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5561, https://doi.org/10.5194/egusphere-egu25-5561, 2025.

The Qingdao Cold Water Mass (QCWM), located in the offshore waters near the Shandong Peninsula, exhibits notable seasonal variability and plays a crucial role in shaping hydrological conditions due to its distinct temperature and salinity structures. This study investigates the evolution of the QCWM in 2014 using cruise observations and the hydrodynamic model FVCOM. The potential evolution mechanisms of QCWM are analyzed, and Lagrangian particle experiments are conducted to explore the source and destination of the QCWM.

The QCWM in 2014 prevails below 20 m near the coast of the Shandong Peninsula. It emerges in April, stabilizes in May, and dissipates by June. Momentum analysis reveals that the anticyclonic circulation near the QCWM area, along with the weakness of the pressure gradient force, including both barotropic and baroclinic components, facilitates the formation and maintenance of the QCWM in spring. The emergence of the Yellow Sea Cold Water Mass (YSCWM) and the frontal circulation at the edges of the YSCWM on the eastern side of the QCWM in late spring, combined with the enhanced westward baroclinic force, destabilizes the QCWM and promotes its dissipation.

A series of Lagrangian particle tracking experiments suggest that the bottom water of the QCWM primarily originates from the local cold waters off the southeastern coast of the Shandong Peninsula. The bottom cold water in the QCWM dissipates locally rather than merging into the YSCWM. Tidal effects may further accelerate this dissipation by enhancing vertical mixing and intensifying the frontal circulation at the edges of the YSCWM.

How to cite: Qiu, S., Lettmann, K. A., Huang, H., and Chen, X.: Evolution Study of the Qingdao Cold Water Mass, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6206, https://doi.org/10.5194/egusphere-egu25-6206, 2025.

The ocean basins of Southeast Asia (SEA) are significantly influenced by a dynamic water cycle characterized by intense precipitation, evaporation, and substantial river runoff. The freshening of shelf seas in this region - where precipitation and river discharge exceed evaporation - plays a critical role in shaping regional ocean circulation and the marine environment. However, a lack of sufficient observational data has limited our understanding of these processes, particularly their seasonal and spatial variability.

In regional ocean modeling, climatological river runoff is usually employed to account for freshwater input. This approach may underrepresent seasonal extremes and might not fully capture the daily variation of river discharge, leading to substantial biases in the simulated sea surface salinity (SSS). To address this limitation, we implemented daily river runoff from the JRA55-do global reanalysis into a high-resolution (~4.5 km) regional ocean model based on Nucleus for European Modelling of the Ocean (NEMO).

The JRA55-do runoff dataset, produced by Japan Meteorological Agency (JMA) Meteorological Research Institute (MRI), derived from the CaMa-Flood global river routing model and provided on a 0.25°×0.25° grid. The JRA55-do runoff data was remapped onto the NEMO model grid. The model simulations were forced with 10 m winds and surface heat flux data from the ERA5 reanalysis, available from the European Centre for Medium-Range Weather Forecasts (ECMWF). Lateral boundary conditions and initial states were obtained from the GLORYS12, which is an ocean reanalysis dataset based on a 1/12^o eddy-resolving global NEMO and was carried out in the framework the European Copernicus Marine Environment Monitoring Service (CMEMS). Simulations were conducted for the year 2022, and the model outputs were validated against satellite observations of SSS and sea surface temperature (SST).

The results indicate that the high-resolution regional NEMO model successfully captured the seasonal variability of SSS observed in satellite data. Notably, the incorporation of river runoff improved the spatial representation of SSS in some areas. In a comparison, simulations using daily runoff demonstrated higher modelling skill in some regions than those with climatological runoff. By enhancing the accuracy of SSS in our regional ocean model, this study provides critical insights into the role of freshwater input in shaping the oceanographic processes of the Southeast Asia.

How to cite: Xu, X., Sasmal, K., Thompson, B., Tkalich, P., Dandapat, S., Kumar, R., Furtado, K., Zhang, H., He, X., Liu, Z., Liu, Z., and Wang, Y.: Implementation of daily river discharge into Southeast Asia regional ocean model NEMO, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10926, https://doi.org/10.5194/egusphere-egu25-10926, 2025.

The dynamical and thermal properties of the upper ocean are significantly influenced by wind forcing at the sea surface. In this study, numerical simulations with wind forcing applied at different time intervals (1, 3, 6, 12, and 24 hours) were conducted to analyze the heat budget of the surface mixed layer (ML) in the stratified Yellow Sea. The goal was to identify the physical processes modifying ML characteristics and determine the optimal temporal resolution of wind forcing to accurately simulate these processes. During summer, strong energy densities in the near-inertial and internal tide frequency bands drive vertical heat diffusion and entrainment at the ML base. Higher temporal resolution in wind forcing amplifies the activity of near-inertial waves (NIWs) in the upper thermocline, enhancing vertical mixing. This increased mixing thickens the ML, raises its salinity, and lowers its temperature, resulting in greater net heat flux into the surface layer. Consequently, high-frequency wind forcing leads to a reduction in ML temperature in the central Yellow Sea. Wind forcing intervals of 6 hours or less are essential to simulate saturated energy densities of inertial oscillations and vertical mixing in the thermocline at depths of 10–30 m. The enhanced NIWs induced by high-frequency wind variability are expected to transport more nutrients and CO2 from the subsurface to the thermocline and upper ocean layers, underscoring the ecological and biogeochemical impacts of wind forcing resolution in shelf seas.

How to cite: Choi, J.-W., Choi, B.-J., and Kwon, J.-I.: Effects of Wind Forcing Interval on Near-Inertial Waves and Vertical Mixing in the shelf seas around Korea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14137, https://doi.org/10.5194/egusphere-egu25-14137, 2025.

The mixed layer depth (MLD) plays a vital role in regulating climate by controlling the exchange of momentum, heat, and moisture between the ocean and atmosphere. Improving the simulation of MLD is therefore crucial for reliable climate predictions and projections. However, studies on the interannual variability of MLD using global reanalysis data are insufficient. In this study, we examined the interannual variability of winter (February) MLD in Korean waters over a 25-year period (1994–2018) using two reanalysis data sets, the HYbrid Coordinate Ocean Model (HYCOM) and CMEMS Global Ocean Reanalysis and Simulation (GLORYS), which have been widely used in climate change studies in Korean waters. The reanalysis MLD data were compared with observational estimates from the Korea Oceanographic Data Center (KODC) and NIFS Serial Oceanographic observations (NSO) for February, the month with the deepest MLD. The spatial distribution is relatively well simulated, but the long-term trend is poorly reproduced. Notably, the models underestimate the long-term mean MLD by approximately 25% in regions influenced by the Ulleung Eddy and the Yellow Sea Warm Current. The underestimated bias in the Ulleung Eddy can be attributed to the insufficient resolution of the reanalysis data sets in capturing the fine-scale structure of the Ulleung Eddy, while the bias in the Yellow Sea Warm Current region is possibly due to lack of tidal mixing in the reanalysis. Furthermore, while the observed MLD shows a deepening trend over most Korean waters during the study period, the models show negligible changes or even a shallowing trend, except in the East/Japan Sea showing a underestimated deepening trend. The models also tend to underestimate the magnitude of interannual variability of the MLD. Empirical Orthogonal Function (EOF) analysis reveals that MLD interannual variability is influenced primarily by variabilities of 10 m wind and 2 m air temperature (~18%), and secondarily by Tsushima Warm Current transport (TWC; ~11%). The TWC transport is closely related to the path of the East Korea Warm Current, suggesting that changes in the current's interannual variability could influence the MLD. Additionally, in other regions, TWC transport is influenced by the Kuroshio current transport, which determines the volume of transport entering Korean waters, thus explaining its association with MLD variability. This finding highlights the importance of oceanic processes in interannual variability in the winter MLD in Korean waters.

How to cite: Jung, H. and Jang, C. J.: Evaluation of mixed layer depth in Korean waters obtained by reanalysis data sets: spatial distribution and interannual variability, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15254, https://doi.org/10.5194/egusphere-egu25-15254, 2025.

This study investigates sea level interconnection across the Mediterranean and Black Seas using tide gauge measurements from 2010 to 2023. Intraseasonal sea level variations are analyzed alongside satellite altimetry, wind stress, and atmospheric pressure data to identify the primary drivers of sea level differences between these basins, linked through the Marmara Sea and the Straits. Spectral analysis offers valuable insights into how these drivers influence the time lag in sea level responses across the regions.

A combination of satellite altimetry and a linear analytical model is employed to examine the nonseasonal sea level lag between the interconnected basins. Field observations conducted during December 2021 and March 2022 provide additional context, shedding light to the exchange dynamics through the Istanbul Strait.

These findings offer a deeper understanding of the mechanisms governing sea level variability and exchange in this critical region, with implications for regional hydrodynamics and climate resilience.

How to cite: Yaman, F. and Çokacar, T.: Interconnection of Sea Levels Through the Strait System Between the Black Sea and the Mediterranean Interconnected Sea Level Dynamics Across the Mediterranean, Marmara, and Black Seas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20145, https://doi.org/10.5194/egusphere-egu25-20145, 2025.

As areas between open seas and landward located ports and cities, estuaries have a high ecological and social importance. In such areas, changes in salinity can have severe consequences. Hence, salt intrusion is an important parameter to understand and monitor. The unique ecosystem as well as the freshwater abstraction for e.g. agricultural irrigation or drinking water can suffer under increasing salt intrusion. 

A decomposition of the along-channel salt transport is a useful tool to understand the driving salt transport mechanisms as 
well as the impact of environmental changes. Cross-sectionally integrated as well as spatially resolved analyses have been performed and revealed insightful results.

However, to date these mechanisms are mainly analyzed at fixed geographic locations in the estuaries. Especially in tidal estuaries, however, the salt intrusion has a very high natural variability with tides and discharge shifting the salinity front on a kilometer scale. Therefore, fixed locations can experience a high salinity range, resulting in different salinity regimes. 
This makes it impossible to extract processes going on in the low salinity regimes that are critical for freshwater abstraction.

In this study, we address this issue by analyzing salt transport mechanisms following the salt intrusion front. 
We use a numerical model setup of the Weser River Estuary as an application for the decomposition method. This mesotidal estuary, located in
North-West Germany, connects the North Sea with major ports via a navigational channel. The channel is strongly influenced by anthropogenic measures like dredging.  Dredging can lead to a further landward salt intrusion. 
Here, we analyze the mechanisms driving the salt transport dynamics in critical low salinity areas and how a possible dredging scenario impacts those dynamics.

How to cite: Rummel, K., Klingbeil, K., and Burchard, H.: Decomposing estuarine salt transport mechanisms following the salt front, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1476, https://doi.org/10.5194/egusphere-egu25-1476, 2025.

In classical estuaries, salty ocean water is mixed with riverine freshwater such that brackish water is produced. To provide salt water for mixing in a long-term averaged estuarine state, ocean water needs to enter the estuary across a fixed estuarine transect at higher salinity classes (at a rate of Q_in) while brackish water is ejected seawards at lower salinity classes (at a rate of Q_out), establishing the estuarine exchange flow. This transect may be located anywhere in the estuary - river plume continuum. If no mixing takes place inside the estuary, riverine freshwater will leave the estuary across the transect (at zero salinity) and no salt water can enter, such that Q_in=0. Thus, when formulated in salinity coordinates, estuarine mixing and exchange flow are directly related to each other. With this, Q_in is a suitable measure for the exchange flow. This relation is approximately represented by the Knudsen mixing relation M=s_ins_outQ_r=(s_in-s_out)s_inQ_in, where M is the mixing (salinity variance decay), s_in and s_out are the characteristic salinities of the inflow and the outflow, respectively, and Q_r is the river runoff. A recently published relation between exchange flow and mixing relies on the distribution of diahaline mixing: Q_in=-1/2 dm_est(s_div)/dS, where m_est(s) is the diahaline mixing per salinity class across the part of the isohaline with salinity s which is situated inside the estuarine transect and s_div is the dividing salinity between inflow and outflow across the transect with s_in>s_div>s_out. In this presentation, a method is presented how to directly calculate  m_est(s_div) from s_in, s_div, s_out and Q_r. A respective relation for the part of the isohaline outside the transect is derived as well. The relation between the three estuarine mixing quantifications is presented and their usefulness for the estuary - river plume continuum is discussed.

How to cite: Burchard, H., Klingbeil, K., Li, X., Muche, Y., Reese, L., and Rummel, K.: Diahaline mixing at the estuary - river plume continuum, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2887, https://doi.org/10.5194/egusphere-egu25-2887, 2025.

Salt intrusion is a growing problem in deltas worldwide, and under climate change it is predicted to become an even greater problem. During extreme events like droughts salt intrusion can intrude far inland. To understand salt intrusion in urbanising deltas and come with solutions the research program SALTISolutions was carried out. One of the key elements of SALTISolutions was to understand what happens during a drought. To achieve this a dedicated field campaign was designed and conducted around the mouth of the Port of Rotterdam. Here we present some results from these unique measurements recorded during the major drought of 2022. We investigate the changes in ROFI dynamics during the drought using velocity, salinity and temperature data from various field campaigns near the mouth of the Rotterdam Waterway and within the delta. We describe the changes in the near field plume dynamics during the drought using the data from the moorings deployed around the mouth of the estuary. We show the importance of wind conditions for the connection between the near-field plume dynamics and salt intrusion, and how this changes for an extremely low discharge and shrinking river plume.

How to cite: Pietrzak, J. D., Wegman, T., Horner Devine, A., and Ralston, D.: Understanding salt intrusion in a salt wedge estuary under extreme drought conditions using data from a unique field campaign, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17886, https://doi.org/10.5194/egusphere-egu25-17886, 2025.

This research is motivated by an incident in the Saguenay Fjord (QC, Canada) that occured in 2019, where a cargo ship collided with a wharf while docking, resulting in minor material damage to both the vessel and the wharf under circumstances that remain unknown. Our hypothesis is that internal solitary waves may have contributed to the ship's unexpected drift. To test this hypothesis, CTDs, ADCPs and an echosounder were deployed during the summer of 2024. The measurements collected revealed the presence of internal waves over a two-week period. These observations show that trains of internal waves impacted the wharf daily and that they appear to be phase-locked with the tidal cycle. Internal waves of a wavelength of 60 m and a period of 40 s were recorded with amplitudes reaching 10 m and wave-induced horizontal currents of 1m.s^-1. These currents are potentially strong enough to affect the maneuverability of a cargo ship during docking. The results of this research could contribute to the improvement of navigation simulators, adding the ability to account for the effects of internal waves on docking maneuvers.

How to cite: Hupé, L., Grégorio, S., Bourgault, D., Chavanne, C., and Galbraith, P. S.: Observations of solitary internal waves near a dock and their impact on navigation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-377, https://doi.org/10.5194/egusphere-egu25-377, 2025.

A good understanding of dispersion mechanisms in estuaries is essential to understand the transport of physical and biogeochemical constituents in these systems. In well-mixed estuaries, up-estuary transport of salt is often dominated by tidal dispersion mechanisms. One such a mechanism is tidal trapping, where volumes of water are temporarily stored in dead zones, side channels or harbor basins adjacent to the main channel and released later on in the tidal cycle.

In this study, we analyze the dynamics and quantify the dispersive contribution of tidal trapping using an idealized numerical model. We take into account that this trapping can be the result of a diffusive exchange between the channel and trap, but also from the filling and emptying of the trap by a tidal flow, which is leading in phase compared to the tidal flow in the main channel. We systematically compare the dispersion effect for both types of channel-trap exchange, for combinations thereof and for the case where the water in the trap is mixed before returning to the main channel.

The results show that the largest trapping induced salt flux is obtained with advective out-of-phase exchange for the largest realistic tidal flow velocity phase difference of 90 degrees. This result is different from literature and we explain why. For small velocity phase differences, mixing of the trapped salinity field before release enhances the dispersive effect. A continuous diffusive channel-trap exchange on top of the advective exchange enhances the dispersive effect of the trap when the velocity phase difference is small, but can dampen it when the phase difference is large. We demonstrate that the effect of a trap is twofold: firstly, channel-trap exchange alters the salinity field and introduces an additional salt flux in the main channel over a distance equal to the excursion length; secondly, the altered salinity gradients are advected in both up- and down-estuary direction, influencing the tidal salt flux over a distance twice that of the tidal excursion length.

These insights in salt dispersion contribute to the understanding of transport in estuaries. 

How to cite: Kranenburg, W., van Keulen, D., and Hoitink, T.: Tidal trapping and its effect on salinity dispersion in well-mixed estuaries, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20272, https://doi.org/10.5194/egusphere-egu25-20272, 2025.

Coastal and Offshore fishery was catches at 1.5 million tons per year in the 1990s, but since 2010, catches have dropped sharply to 1.05 million tons. It is time to secure technology for assessing changes in fisheries environment due to changes in marine environment such as climate change, and forecasting technologies for distribution of major fish species and resources in order to establish long-term and short-term response and adaptation strategies for offshore fishery fluctuations. Therefore, we will implement a comprehensive offshore ecosystem change prediction system based on food chain for sustainable fishery ecosystem maintenance and scientific management of fishery resources.

Various models have been developed and are being used worldwide to reproduce and predict marine environments and ecosystems. As a way to build a Korean marine ecosystem model, there are a plan to introduce an excellent overseas model to improve its function and performance in consideration of domestic conditions and to develop its own. As a result of the comprehensive review, the model adopted a method to improve the model so as to introduce the excellent overseas model first, and secure the function appropriate to the domestic reality and characteristics rather than the self-development.

ATLANTIS and EwE were selected as a marine food-web based ecosystem model by comparing and analyzing functions of prediction model of changes in ecosystem currently in use globally. NEMURO, BSS, and primary productivity estimation models were added to link input and output data by model for effective operation and higher degree of production.

The prediction system has already been deployed with biochemical and oceanic circulation modules, and initial input conditions of the prediction model are currently being established, including calculation of biomass by age, identification of the structure of the food-web, and selection of physiological and ecological parameters by functional group. In this study, we are going to introduce and discuss the process of expanding from biochemical circulation to ecosystem and using it to predict fishery resources.

How to cite: Kim, C., Joo, H., Youn, S., Kang, S., Song, Y.-S., and Cho, C.: Development of marine ecosystem model around the Korean Peninsula, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7882, https://doi.org/10.5194/egusphere-egu25-7882, 2025.

The ichthyoplankton assemblage and its spatial distribution were studied in the eastern Adriatic Sea during two consecutive summers (2019–2020) using morphological identification, DNA barcoding and analysis of larval spatial dispersal. Ichthyoplankton samples were collected in five different areas: the western coast of Istria, Kvarner, the area along the outer coast of the island of Dugi otok, the Pomo Pit and southern Dalmatia. These locations were selected as starting points for the dispersion modelling.

The spatial distribution of ichthyoplankton was analyzed using a coupled modelling system that combined the hydrodynamic ROMS model with the individual-based Ichthyop model. The ROMS model was driven by surface momentum, heat and water fluxes calculated using output fields from the operational weather prediction ALADIN model as well as by Adriatic river inflows and tides. The open boundary conditions were obtained from the operational Mediterranean hydrodynamic model. The ROMS temperature, salinity and current fields were input for the Ichthyop model.  

Connectivity matrices were calculated between the individual areas, focusing on local retention, i.e. the proportion of released ichthyoplankton that remained in its place of origin. Dispersal distances were determined by measuring the distance between the initial location where the ichthyoplankton was released and its final location after drift, taking into account environmental factors such as currents. In addition to the influence of ocean currents, environmental factors such as temperature, salinity and chlorophyll-a (Chl-a) concentration played an important role in shaping the composition of ichthyoplankton, as shown by the RDA analysis, which revealed that early life stages of the fish families Sparidae and Serranidae were associated with higher sea temperatures, while those of Scombridae, Engraulidae, and Bothidae were linked to elevated Chl-a levels.

The obtained results provide important basic data for the sustainable management and conservation of the Adriatic ichthyoplankton and its habitats.

How to cite: Džoić, T., Beg Paklar, G., Zorica, B., and Stanešić, A.: Ichthyoplankton dispersion modelling in the Eastern Adriatic During Two Consecutive Summers (2019–2020), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17343, https://doi.org/10.5194/egusphere-egu25-17343, 2025.

How to cite: Delhaye, L., Taymans, C., and Fettweis, M.: Intra-annual variability of marine floc morphology in southern North Sea coastal waters using in-situ high-resolution underwater imaging , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10712, https://doi.org/10.5194/egusphere-egu25-10712, 2025.