Recent studies (see references below) examined the impact of the Atlantic Ocean variability and climate change on the U.S. East Coast and the major bays of the Mid-Atlantic Bight: the Chesapeake Bay, the Delaware Bay and the New York Bay. Variations in the North Atlantic Oscillation (NAO), the Atlantic Meridional Overturning Circulation (AMOC) and the Gulf Stream (GS) can affect the weather and the climate over coastal regions – a remote impact that is difficult to predict. Analysis of various observations, including coastal sea level, water temperature in bays and estuaries, river discharges and ocean currents show that significant portion of the coastal variability is linked to remote forcing influenced by NAO, AMOC and the GS. For example, surface currents from high-frequency radar measurements near the mouth of the three Mid-Atlantic bays mention above show variations that are driven by a combination of local estuarine dynamics, coastal wind-driven dynamics and remote forcing from the Atlantic Ocean. AMOC and the GS can affect water exchange between bays and the open ocean, and variations in NAO shift the wind pattern and storm track over the coast. Climate change over the northeastern U.S. caused increased precipitation and river discharges into bays and resulted in increased outflows from bays toward the Atlantic Ocean. The impact of extreme events such as hurricanes and winter storms can also be seen in the outflows from bays. A better understanding of remote forcing on the coast will help in predicting impacts of climate change and coastal sea level rise on the highly populated U.S. coasts.
References: http://dx.doi.org/10.1007/s10236-022-01536-6, https://doi.org/10.1007/s10236-024-01605-y, https://doi.org/10.1007/s10236-024-01656-1.
How to cite: Ezer, T.: Impact of open ocean variability on the U.S. Mid-Atlantic coasts and bays, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2168, https://doi.org/10.5194/egusphere-egu25-2168, 2025.
The sensitivity of Baltic Sea salinities to changed fresh water forcing and other forcing factors have been debated during the last decades, since changed salinities would have large impacts on the marine ecosystems, and since this parameter still shows a high degree of uncertainty in regional climate projections. In this study we perform a sensitivity study where fresh water forcing and salinities at the outer boundaries of the North Sea are perturbed in a systematic way in order to obtain a second-order Taylor polynomial of the statistical steady state mean salinity. The polynomial is constructed based on perturbations of 57-year long hindcast runs for the period 1961-2017 with a regional ocean model covering the North Sea and the Baltic Sea. The results show that the Baltic sea is highly sensitive to fresh water forcing and that only about one third of the boundary salinity change propagates into the Baltic Sea. The results are also analyzed in terms of a total exchange flow analysis in the entrance region, and it is found that the results to a large degree can be explained by (1) recirculation in the entrance region where the inflow water consists of two parts outflowing Baltic water and one part North Sea water, and (2) partitioning of increased (decreased) net outflow on increased (decreased) outflow and decreased (increased) inflow according to the fraction of time these occur.
How to cite: Arneborg, L., Hieronymus, M., Pemberton, P., Liu, Y., and Fredriksson, S.: Response of a semi-enclosed sea to perturbed freshwater and open ocean salinity forcing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10773, https://doi.org/10.5194/egusphere-egu25-10773, 2025.
In-situ observations around Madeira Island (32.6°N, 16.8°W) reveal that coastal processes are forced by the interaction between the insular shelf, local winds, and tides, often acting independently of far-field circulation. The Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) system was employed to investigate island shelf circulation; four different scenarios were modeled: three single-forcing cases (Case A: tidal forcing; Case B: local wind forcing; Case C: global model (far-field) forcing) and one combined-forcing case (Case D: all forcings). These simulations provide insight into the key coastal patterns and dominant frequencies associated with each scenario.
Case D was validated against in-situ data. Ocean currents were analyzed using Morlet wavelet techniques and rotary spectra. The findings indicate that wind forcing predominantly controls coastal circulation patterns on the western side of the island and on the northeastern coasts. On the eastern side, tides play a critical role in establishing and sustaining coastal currents. Along the northwest coast, basin-scale Atlantic circulation, including the Azores Current and mesoscale eddies, significantly influences coastal dynamics.
The main finding of this study is that coastal dynamics around oceanic islands are highly variable over a few kilometers, driven by both local and far-field factors, contrasting with traditional wake studies, which often overlook these essential dynamics of the insular shelf.
How to cite: Reis, J., Vieira, R., Silva, G., Bruno, M., and Caldeira, R.: Coastal shelf circulation around a deep-sea island in the Canary Basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10038, https://doi.org/10.5194/egusphere-egu25-10038, 2025.
Landers are structures designed to be deployed directly at the bottom of the sea, hosting scientific equipment to operate autonomously for long periods of time. The recent development of a remote-operated towed vehicle designed to cost-effectively deploy and recover oceanographic landers (the LanderPick vehicle) allows the design of experiments based on the massive deployment of low-cost landers.
In July 2023, 21 landers equipped with tilt current meters (Lowell TCM) and high-frequency thermistors (RBR SoloT) were deployed across the north and northwest Spanish shelves and upper slopes. The array was designed as five cross-shelf sections with four units each, at nominal depths of 50, 100, 200 and 500 meters, spanning across more than 350 nautical miles. Landers were recovered (most units) in September 2024, thus providing nearly 14 months of near-bed high-frequency environmental data. Records evidence seasonal circulation patterns and strong oscillations at tidal and inertial frequencies that vary according to location.
With a recording frequency of 5 seconds, the thermistors provide insights on turbulence intensity. In this study, we follow the methodology proposed by Cimatoribus et al. (2014) to estimate the turbulent dissipation rate from Eulerian high-frequency time-series. The procedure requires estimates of local background Brunt-Väisälä frequency, which are derived from climatologies of density profiles provided by a regional long-term observational program of essential ocean variables in the region (Radiales project). Near-bed turbulence shows a substantial increase after the arrival at seabed of the mixed layer development in autumn.
Additionally, the spatial and temporal variability of near-bed turbulence across the continental shelf observed by the fleet of landers is analysed in combination with results from additional landers located at intricate topography sites, such as canyons and seamounts. Low-cost lander structures are being further developed, pursuing to consolidate lander swarms or arrays as a tool for surveying near-bottom conditions and allowing the monitorization of a wider set of essential ocean variables.
How to cite: Márquez García, A., González-Pola Muñiz, C. M., and Fernández Graña, R.: Bottom dynamics and turbulence estimates from a fleet of landers in north/northwest Spanish shelf and slope, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17062, https://doi.org/10.5194/egusphere-egu25-17062, 2025.
We present shipboard observations of high-frequency internal waves (IW) propagating through the Winyah Bay plume on the South Atlantic Bight shelf (the US East Coast). Two surveys are analyzed: 6-7 June, 2023, and 23-24 May, 2024. On both occasions, the plume was affected by a moderate upwelling-favorable wind resulting in a significant offshore spreading of the Winyah Bay plume, well beyond its natural (unforced) offshore limit. While stratification conditions were roughly comparable in both years, IWs exhibited very different behavior, which is attributed to the properties of mean (averaged over multiple IW periods) currents. Specifically, IWs in May 2024 propagated as a dispersive train with a near-zero depth-averaged velocity component and highly polarized velocity fluctuations. The TKE dissipation values in the pycnocline were unaffected by the IW train passage. The mean current did not reverse with depth and its maximum magnitude in the direction of wave propagation (inferred from the wave velocity vector orientation) was less than 0.3 m/s. In contrast, in the 2023 observations there was a significant depth-averaged velocity component corresponding to the IW frequency band at a close to normal angle with depth-dependent velocity fluctuations. There were elevated values of TKE dissipation in the pycnocline exceeding corresponding values in the surface boundary layer. In addition to high TKE dissipation, salinity profiles exhibited clearly visible overturning events. The mean current velocity profile in the direction of the IW propagation had a distinctive two-layer structure reaching 0.4 m/s at the surface (seaward) and -0.2 m/s below the plume layer (shoreward). In both years, IW velocity structure closely resembled theoretical velocity profiles obtained from a numerical solution of the Taylor–Goldstein equation for the observed buoyancy and mean current profiles. We conclude that IW breaking with enhanced TKE dissipation occurs when IWs approach critical layers, where the wave phase speed matches the mean current. Critical layers can be readily encountered when the mean current reverses with depth such that its Doppler effect on the wave dispersion curve is minimal. We hypothesize that strong IW dissipation at critical layers along with nonlinear effects can generate the observed depth-averaged velocity component.
How to cite: Yankovsky, A., Voulgaris, G., Papageorgiou, C., and Fribance, D.: Interaction of high-frequency internal waves with the wind-driven river plume, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14148, https://doi.org/10.5194/egusphere-egu25-14148, 2025.
The rapid expansion of offshore wind farms (OWFs) in the North Sea necessitates a better understanding of its impacts on ocean dynamics, regional-scale sediment transport, and erosion and deposition patterns which may consequently influence future states of coastal morphology. Using 3-dimensional hydro-morphodynamic coupled numerical modelling which integrates parameterizations of OWF-effects in both atmosphere and ocean, we analysed how regional-scale sediment transport pathways as well as sediment exchange between the open North Sea and the Wadden Sea are affected by OWFs. We compared the simulation results from different OWF configurations representing present-day (operating), potential future (operating, in-construction and planned) scenarios. In particular, we investigated the OWF impact on the frontal systems, residual transport, accumulation of fine-grained sediment in the mud depocenters and sediment flux between the open North Sea and tidal basins in the Wadden Sea. Our results highlight the potential of OWFs in reshaping regional-scale sediment transport patterns, with implications for ecosystem functioning, marine spatial planning and coastal protection strategy. The outcomes may be used to align sustainable offshore wind energy development and coastal protection in the North Sea and at its coasts.
How to cite: Chen, J., Porz, L., Christiansen, N., Zhang, W., and Schrum, C.: Impact of offshore wind farms on regional-scale sediment transport pathways in the North Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8847, https://doi.org/10.5194/egusphere-egu25-8847, 2025.
Salt intrusion is known to be influenced by harbours and side channels. While the contribution of these features to tidal dispersion is well established in well-mixed estuaries, the governing processes in partially stratified system have remained understudied. We investigate the channel-harbour exchange in the New Meuse, a partially stratified branch of the Rhine-Meuse estuary.
The harbour basins subject to study are located just upstream of the junction with the Old Meuse and the New Waterway, in a region characterized by large gradients in the salinity range over short distances. During a field campaign, four shipboard surveys were conducted to study the channel-harbour exchange at two harbour basins under spring and neap tide conditions.
Decomposition of the instantaneous salt flux, aimed to unravel the exchange between the channel and the harbours, revealed large differences in the contribution of a continuous density-driven exchange. These differences were confirmed by numerical modelling of the systems. The reduced vertical exchange is attributed to a weaker salinity gradient in the main channel in front of the harbour entrance, which limits the pressure gradient between the harbour and the channel. Stark differences in the salinity range were found to be predominantly the result of interactions between the branches.
The numerical model was subsequently used to set up a balance to quantify the up-estuary salt flux resulting from the channel-harbour exchange (tidal trapping) for the different harbours in the New Meuse. This analysis showed that harbours, where the salinity range in front of the harbour was weak, contribute significantly less to the up-estuary salt flux, primarily due to the reduced vertical exchange. Additionally, the contribution of tidal filling and emptying of the harbour basins, which typically drive the dispersive effect of traps in well-mixed systems, was found to contribute negatively to the up-estuary salt flux. The negative contribution of tidal filling and emptying is enhanced by atypical tidal salinity variations in the main channel, due to interaction between the branches.
This leads to the surprising conclusion that some of the largest harbours, where the density-driven exchange between the channel and harbour was observed to be weak, contribute the least to the up-estuary salt flux.
How to cite: van Keulen, D., Kranenburg, W., and Hoitink, T.: Channel-harbour exchange and its influence on salinity dispersion in a partially stratified branch of the Rhine-Meuse estuary, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11295, https://doi.org/10.5194/egusphere-egu25-11295, 2025.
Marine heatwaves (MHWs), prolonged periods of unusually high ocean temperatures, have been observed worldwide and are expected to increase in both intensity and frequency due to anthropogenic climate change. This rise in MHW frequency and intensity has led to significant biological and ecological shifts, including changes in species distributions, large-scale mortality, and the decline or extinction of local species. The tidal Elbe discharges into the German Bight. It plays a crucial role in the region's ecology, serving as a dynamic estuarine ecosystem where freshwater from the river meets saline water from the North Sea. Within the framework of the ElbeXtreme project, we aim to better understand extreme events like MHWs to enhance the resilience of coastal ecosystems and human communities.
To this end, we MHW events in the tidal Elbe region from the upper estuary at Bunthaus to the lower estuary at Cuxhaven to better understand their characteristics, trends, and impacts over the period from 1988 to 2023. The characteristics of MHWs, such as intensity, duration, and frequency, are compared across different measuring stations sustained by local authorities and institutions. Surface water temperature data show high confidence (p-value < 0.01) in the observed increasing trend (0.2°C/decade) in temperature anomalies across all stations. Moderate MHWs are frequently observed, with an annual mean of 2.3 events, at various stations from Bunthaus to Cuxhaven. Only a few strong MHW events (2-3× the local difference between the climatological mean and the climatological 90th percentile) were identified in 2000, 2007, and 2018. The characteristics of MHWs show spatial variability along the estuary. The annual mean duration of events is approximately 33 days, decreasing from Cuxhaven to Bunthaus. In contrast, the annual mean intensity of events increases moving upstream. Meanwhile, the annual mean number of events along the estuary shows no significant change. Although the number and duration of MHWs do not show seasonal variation, summer and autumn exhibit stronger MHW intensity compared to spring and winter.
How to cite: Purkiani, K., Kieke, D., and Senet, C.: Identification of Marine Heatwaves and Their Characteristics in the Tidal Elbe River, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13719, https://doi.org/10.5194/egusphere-egu25-13719, 2025.
Gorgonians are coastal megabenthic organisms facing the threats of destructive fishing activities and mass mortality due to thermal anomalies in Mediterranean Sea. They are engineering species playing a significant role in the maintenance of biodiversity by providing habitat to several marine species (Rossi et al., 2017). Gorgonians often have an arborescent geometry, and when their populations are dense enough, they form three-dimensional forest canopies similar to terrestrial ones. Water flow is modified by the presence of the gorgonian canopy, with formation of a turbulent shear flow at the top of it. At this level, Reynolds stress is expected to present a maximum value suggesting an active momentum exchange and a significant mass transport (food and nutrients). Here, the gorgonian canopy flow is experimentally investigated in a flume using surrogates as in studies of aquatic flexible vegetated canopies (e.g., Sukhodolov et al., 2022). Laboratory experiments are conducted with artificial gorgonian canopies of different planar densities in a unidirectional open-channel flow. White gorgonians (Eunicella singularis) are mimicked by using 3D-printed surrogates with bending stiffness similar to the one of the real gorgonians allowing us to represent the drag force and the reconfiguration of the living organisms in water. Dynamic similarity between laboratory and in-situ conditions is ensured by using the same range of Reynolds number and the same Cauchy number. Simplified scaled symmetrical geometries are built respecting the geometrical aspect ratio and the main branching orders of the tree-shaped white gorgonians. 2D-2C PIV (Particle Image Velocimetry) flow measurements in vertical planes are performed to characterize the local flow conditions in and over gorgonian canopies. The high-spatial resolution of PIV measurements allows us to characterize most of the relevant flow scales; from the stem-scale wakes behind the tip branches of one colony to the canopy-scale turbulence forced by the vertical mixing layer near the top of the canopy, and finally to the much larger turbulent boundary-layer structures. Canopy-scale turbulence appears in high density canopies (H. M. Nepf, 2012), and thus characterizing the transitional regime between sparse and dense canopies is essential to define the minimum canopy density required for significant flow modification. This threshold is necessary to define the minimal conservation unit related to the canopy’s ecological functions.
Nepf, H. M.: Flow and Transport in Regions with Aquatic Vegetation, Annu. Rev. Fluid Mech., 44, 123–142, https://doi.org/10.1146/annurev-fluid-120710-101048, 2012.
Rossi, S., Bramanti, L., Gori, A., and Orejas, C. (Eds.): Marine Animal Forests: The Ecology of Benthic Biodiversity Hotspots, Springer International Publishing, Cham, https://doi.org/10.1007/978-3-319-21012-4, 2017.
Sukhodolov, A., Sukhodolova, T., and Aberle, J.: Modelling of flexible aquatic plants from silicone syntactic foams, Journal of Hydraulic Research, 60, 173–181, https://doi.org/10.1080/00221686.2021.1903590, 2022.
How to cite: Vonta, L., Moulin, F., Malaquin, L., Barron, J.-D., and Bramanti, L.: From surrogate modeling to flow characterization: Investigating the mean flow and turbulence structure inside and above canopies of Eunicella singularis , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10292, https://doi.org/10.5194/egusphere-egu25-10292, 2025.
We have advanced the high-resolution (1/24˚) regional ocean model for Northwest Pacific (KOOS-OPEM), developed by the Korea Institute of Ocean Science and Technology (KIOST) by updating its base model from MOM5 to MOM6. Using this updated model, we conducted sensitivity experiments to compare the performance of simulations under two different vertical coordinate systems: the hybrid z*-isopycnal and the z* coordinate. The results indicated that both coordinate systems successfully reproduced the Kuroshio separation point in close agreement with observation data. In addition, the hybrid coordinate configuration demonstrated a more realistic representation of the Northwest Pacific intermediate water compared to the z* coordinate configuration. However, the hybrid coordinate configuration exhibited a warm bias approximately 1°C greater than that of the z* system in the Kuroshio Current and the East/Japan Sea. To address this issue, we adjusted the maximum thickness of the isopycnal layers, which effectively mitigated the warm biases in these regions. Additionally, this study introduces the regional implementation of MOM6 for the Northwest Pacific coupled with the biogeochemistry model (OPEM-MOM6-COBALT). To address the limitations of the coarse initial conditions for the biogeochemical tracers, a 10-year spinup simulation was conducted to generate improved initial conditions for the biogeochemical tracers. This study evaluated the initial conditions, intended for use in hindcast simulations, against satellite and observational data. Furthermore, we constructed the coastal implementation of MOM6 for the Yeosu-Gwangyang Bay, which will be coupled with the biogeochemistry model using the initial and boundary condition generated from OPEM-MOM6-COBALT simulation. We plan to perform hindcast simulations with these physical-biogeochemical models and compare their performance against observation data.
How to cite: Chang, I., Kim, Y. H., Park, Y.-G., Tae, S., Park, N., Ross, A. C., Hallberg, R., and Stock, C. A.: Application of MOM6 for Regional and Coastal scale Coupled with the Biogeochemistry Model (COBALTv3), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15338, https://doi.org/10.5194/egusphere-egu25-15338, 2025.
In the Norwegian Trench, a deep region in the North Sea in front of the Norwegian coast, there are indications that resuspension events take place, but knowledge about the forcing of the deep currents is limited. Deep flows in this area are driven by diverse processes, showing influences of surface forcing, interactions with the North Atlantic across the continental shelf slope, and canyon dynamics. Here we present unique insights from a one-year time series of high-resolution, near-bed current velocities collected with two moored ADCPs in the Norwegian Trench. At a depth of 300 metres, the tidal contribution is highly variable because of the Spring-Neap tidal cycle and primarily visible in alongshore-directed velocities and pressure data. However, the largest velocities are not induced by periodic forcing, but are presumably generated by inflow of warmer Atlantic water (AW) into the trench and the canyons response to storm events. Both, AW inflow and storm events are detected during winter time. During storm events, current speeds can exceed 0.5 m/s. These velocities are high enough to lift the sediment up to at least 20 metres above the bed. Once resuspended, the sediment can stay over several days or even weeks in the water column and be transported by deep currents. These preliminary results indicate that the influence of storms on the near-bed flows in the Norwegian Trench is much larger than previously expected.
How to cite: Enge, A., van Prooijen, B. C., and Pietrzak, J. D.: Generation of high-energy flow events in a deep depositional area – The Norwegian Trench, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7888, https://doi.org/10.5194/egusphere-egu25-7888, 2025.
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.
Based on long-term coastal hydrometeorological observations and oceanographic surveys, as well as satellite images, the average conditions, seasonal and interannual variability of integral water exchange and buoyant plume generation were studied for the Dnipro-Buh estuary (DBE).
Analysis of publications and available information showed that a simple Knudsen's box model can be adapted for the conditions of shallow non-tidal estuaries. Hydrodynamic dimensional and non-dimensional criteria that determine the nature and further behavior of plumes after their exit from the estuary into the open sea were considered. The application of the criteria for determining the nature of the plume for outflows from the DBE showed that on the exit of estuary plume of transitional waters is produced. It has a surface-advective nature, without the effect of friction in the bottom boundary layer, being driven by buoyancy and Coriolis forces, and is influenced by wind-wave mixing.
The main factor in the plume dynamics on the shallow waters are the wind currents, which contribute or hinder the spread of transitional waters along the coast to the right of the estuary mouth, or pushing them into the open sea and even turning them to the opposite. During the low-wind weather, the initial impulse of the river runoff plays the main role. This was especially evident in the situation of an abnormally large runoff volume after the explosion of the Kakhovka HPP on 06.06.2023. The consequences of its impact on the marine environment are shown according to a number of satellite images.
Using the mixture analysis method, the statistical structure was investigated and one-dimensional clustering of empirical salinity histograms at 3 shore stations in the vicinity of the DBE was performed. It has been found that salinity probability distributions can be approximated by a set of 2-3 Gaussian functions. These functions, as a rule, correspond to waters of river origin, marine origin, and intermediate waters as a result of the interaction of the first two. Seasonal changes of these water masses' mean values and standard deviations were obtained for each shore station.
How to cite: Ilyin, Y. and Yankovsky, A.: Seasonal and inter-annual changes of structure and dynamics in the buoyant plume generated by the Dnipro-Buh estuary, Black Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4089, https://doi.org/10.5194/egusphere-egu25-4089, 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 1/12o 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.
Liaodong Bay, occupying over one-third of the Bohai Sea, hosts many international harbors, oil platforms, and millions of people. Each winter, the bay faces significant threats from sea ice, with rapid expansions often triggered by cold air outbreaks featuring strong southward winds and sharp drops in air temperature, posing risks to maritime activities and infrastructure. The influence of cold air outbreaks on sea ice dynamics in Liaodong Bay was investigated based on a high-resolution sea ice hindcast (1979–2023) produced by coupling the general ocean circulation model NEMO with the sea ice model LIM2. The results show that cold air outbreaks lead to an average increase of 12 nautical miles in floating sea ice distance from the coast, and account for more than half of the most rapid daily sea ice expansion. Sensitive experiments suggest that excluding cold air outbreaks from atmospheric forcing delays the onset of the sea ice season by an average of 7 days, reduces maximum sea ice extent by up to 42%, and shortens the sea ice season by approximately 12 days. While previous studies have emphasized the dominant role of air temperature in the development of sea ice in Liaodong Bay, this study highlights the role of wind during cold air outbreaks: the most pronounced sea ice expansion during the outbreaks always coincides with the strongest southward winds. Sensitive experiments confirm that strong winds drive the rapid expansion of sea ice extent within the first 24 hours during the onset of a cold air outbreak and remain the primary driver until the winds subside, while air temperature drops play a secondary role.
How to cite: Chi, L. and Guo, D.: Rapid Sea Ice Expansion Triggered by Cold Air Outbreaks: a case study in Liaodong Bay, Bohai Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20311, https://doi.org/10.5194/egusphere-egu25-20311, 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 Qin) while brackish water is ejected seawards at lower salinity classes (at a rate of Qout), 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 Qin=0. Thus, when formulated in salinity coordinates, estuarine mixing and exchange flow are directly related to each other. With this, Qin is a suitable measure for the exchange flow. This relation is approximately represented by the Knudsen mixing relation M=sinsoutQr=(sin-sout)sinQin, where M is the mixing (salinity variance decay), sin and sout are the characteristic salinities of the inflow and the outflow, respectively, and Qr is the river runoff. A recently published relation between exchange flow and mixing relies on the distribution of diahaline mixing: Qin=-1/2 dmest(sdiv)/dS, where mest(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 sdiv is the dividing salinity between inflow and outflow across the transect with sin>sdiv>sout. In this presentation, a method is presented how to directly calculate mest(sdiv) from sin, sdiv, sout and Qr. 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 Chesapeake Bay is the largest and most productive estuary in the United States, located in the Mid-Atlantic region, it encompasses six states (New York, Pennsylvania, Delaware, Maryland, Virginia, West Virginia) and the District of Columbia, with nearly 18 million people living within its watershed. The Bay plays a vital ecological and economic role in the region, supporting tourism, fishing and aquaculture, and serving as nursery habitat for many commercial fisheries species. Climate change is a serious concern threatening the health of Bay, and a number of long-term observational programs and modeling efforts have been developed to better understand physical and biogeochemical properties and processes in this complex system. Nevertheless, observations in the coastal ocean adjacent to the Bay are still scarce, and therefore less is known about changes in the oceanic source waters for the Bay. To fill in this gap, the Virginia Institute of Marine Science (VIMS) has developed a pilot coastal ocean observatory at the inner-shelf region adjacent to the Bay mouth. Preliminary results from a two month-long time series of physical (currents, sea level, salinity, temperature) and biogeochemical (dissolved oxygen, pH, chlorophyll) properties, collected using a moored bottom tripod during Spring-2024 will be presented and discussed.
How to cite: Mazzini, P., Gong, D., Rivest, E., Utzig Nardi, R., Slater, J., and Thomas, B.: Temporal variability of physical and biogeochemical properties in the vicinity of the Chesapeake Bay mouth, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14399, https://doi.org/10.5194/egusphere-egu25-14399, 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.
SPM concentration and composition is an indicator for the balance between physical (turbulence) and biogeochemical processes (production, remineralization). High SPM concentration coincides with a dominance of mineral particles and the occurrence of biomineral flocs. These high turbidity zones, generally located nearshore or in estuaries, are characterized by strong tidal currents, intensive resuspension and settling, flocculation in phase with the tides and high primary productions. With decreasing SPM concentration, organic matter becomes more dominant and biological flocs, for example phytoplankton cells or aggregates, are getting more prominent. Physical processes are less important, and flocculation occurs on seasonal time scales. Measuring SPM concentration and particle size distribution (PSD) using laser diffraction techniques (e.g. LISST-100x) has been a standard component of Belgium’s monitoring for the past 20 years, resulting in a good knowledge of its spatial and temporal variability. However, despite its relevance to better understand and monitor the coastal pelagic environment, the PSD derived from laser diffraction do not provide insights into the origin (flocs, biological particles) and composition (mineral, organic matter) of the SPM. Yet, this information is crucial to better understand the SPM dynamics and to better predict the floc density and the fate and flux of minerals, carbon and pollutants.
High-resolution underwater particle cameras are gaining popularity as they capture larger particles and provide data on their morphology and origin. By doing so and enabling researchers to visually see SPM, they offer a promising complement to laser diffraction-based instruments. This however doesn’t come without challenges, the main ones being related to image pre-processing (e.g. noise removal, histogram stretching, image reconstruction) and threshold definition as algorithms for particle detection and shape extraction may significantly impact PSD and derived parameters, requiring rigorous calibration and validation.
In this study, we address these gaps by developing a processing system using underwater high-resolution particle imagery and applying it on a test case: the intra-annual morphological variability of marine flocs. Images were taken in-situ four kilometers off the Belgian coast during six oceanographic campaigns on board the RV Belgica between April 2023 and March 2024. An open-source user-friendly Python algorithm was developed to extract particles from images after validation in the lab against known-size particles. Floc morphologies were characterized using six shape indicators and were compared to in-situ SPM concentration, turbidity, LISST-100x and LISST-200x measurements as well as different parameters from water sample analyses taken at the same time.
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.
Posters virtual: Wed, 30 Apr, 14:00–15:45 | vPoster spot 4
EGU25-20989 | Posters virtual | VPS18
Unveiling the Impact of Upwelling on Phytoplankton Productivity in the Arabian/Persian Gulf and Sea of OmanWed, 30 Apr, 14:00–15:45 (CEST) | vP4.13
This study explores the seasonal and lagged correlations between Chlorophyll-a (Chl-a) concentrations and vertical velocity (wT) to elucidate upwelling's role in driving phytoplankton productivity. In Oman (Region III), an immediate response to upwelling was observed, with the strongest correlation (r = 0.7) at lag 0 during peak upwelling months (June–July). In contrast, Iranian regions (I & II) exhibited delayed responses, with maximum correlations (r = 0.7) at lag 1 (occurring about a month later). This delay may result from processes like nutrient mixing and remineralization. Seasonal trends revealed sustained Chl-a concentrations in Oman, peaking at 2.39 mg m-3 in September, while Iran showed a steady decline after a July peak of 1.37 mg m-3. Stratification and horizontal currents modulated Chl-a distributions, with weaker stratification in Oman enabling efficient nutrient delivery. These findings reveal the intricate dynamics of upwelling-driven productivity across both semi -enclosed and open marine ecosystems. By examining regional variations in the context of broader oceanographic processes, this study offers valuable insights for the sustainable management of upwelling systems and for anticipating their responses to climate change.
How to cite: A. Ismail, K. and Salim, M.: Unveiling the Impact of Upwelling on Phytoplankton Productivity in the Arabian/Persian Gulf and Sea of Oman, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20989, https://doi.org/10.5194/egusphere-egu25-20989, 2025.
