Both, the overturning circulation in the ocean and the exchange flow in an estuary are directly linked to the transformation of water masses caused by small-scale mixing. The integral Water Mass Transformation (WMT) framework formulates how diffusive fluxes between water masses of different tracer concentrations are associated with mass fluxes across iso-tracer surfaces. Relations between local dia-surface fluxes and small-scale mixing in terms of local tracer variance dissipation have been derived by Klingbeil and Henell (2023). In my talk I will explain and demonstrate these relations between local diahaline fluxes, small-scale salinity variance dissipation and the large-scale circulation in estuaries. Klingbeil, K. and E. Henell (2023) A Rigorous Derivation of the Water Mass Transformation Framework, the Relation between Mixing and Diasurface Exchange Flow, and Links to Recent Theories in Estuarine Research. JPO. https://doi.org/10.1175/JPO-D-23-0130.1

How to cite: Klingbeil, K.: Linking small-scale salinity mixing and large-scale estuarine circulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22359, https://doi.org/10.5194/egusphere-egu24-22359, 2024.

The Rhine-Meuse Delta is a low-lying delta in the Netherlands that is subject to both significant salt intrusion events and storm surges. Typically, these events do not co-occur. Salt intrusion occurs in the summer months (June, July, August) during droughts, while the storm season runs from October till April. The increased sea water level during a storm surge can temporarily cause increased salt intrusion. Because of the short time scales and higher discharges, storm surges generally do not cause problems with freshwater availability, in contrast to summer droughts.  However, on December 5th 2013, a storm surge event caused a significant amount of salt water to intrude into the Rhine-Meuse Delta. This was followed by weeks of increased salinity in parts of the delta. We simulated the event using a 3D numerical model of the Rhine-Meuse Delta, to capture the dynamics of the system and to improve our understanding of salt intrusion during storm surges. The Rhine-Meuse Delta is a mixed wave tide dominated delta with two main branches. One of the branches, the New Waterway, has an open connection with the North Sea and is the main outlet of the River Rhine. The other branch, the Haringvliet, is closed off at low water by the Haringvliet Gates. The Haringvliet Gates were built as a storm surge barrier to protect against storm surges after the 1953 flood. In addition, they are routinely used to maintain stable water levels in the river branches for shipping and fresh water supply. During the 2013 storm surge event, the Haringvliet Gates were closed. However, sea water entered the Rhine-Meuse Delta via the Rotterdam Waterway, which effectively acted as a backdoor for salt intrusion into the Haringvliet. Consequently the Haringvliet basin stored the saltwater and delivered it to connected parts of the system in the weeks following. We will refer to this phenomenon as “basin salt reflux”. Uniquely our model captured the salinity dynamics of the system during the 2013 event. Both the modelled salinity peaks during the storm, as well as the higher salinities after the storm agreed with available observations.  We present new insights on the dynamics of a salt intrusion event triggered by a storm surge in a semi-enclosed coastal system. With climate change and sea level rise, these events will most likely occur more frequently in the future. This highlights the importance of fundamental understanding and advanced 3D modelling of salt intrusion in complex deltas during storm surges.

How to cite: Gerritsma, A., Verlaan, M., and Pietrzak, J.: The effects of a storm surge event on salt intrusion: Insights from the Rhine-Meuse Delta, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12125, https://doi.org/10.5194/egusphere-egu24-12125, 2024.

 Salt intrusion in estuaries threatens freshwater availability and agriculture in coastal regions. The geometries of most estuaries are heavily anthropogenically modified, for instance for shipping, land reclamation and flood protection. The response of the salt intrusion to modifications of the geometry is thoroughly studied for single channel estuaries. However, a significant fraction of earths estuaries consists of a network of channels, in which the dynamics are more complex, because it includes the distribution of water and salt at branching points. We aim to identify, quantify, and understand the differences in response to changes in the geometry occurring in estuarine networks compared to salt intrusion in single channel estuaries. To achieve this, we have developed an idealized width-averaged model, which solves for hydrodynamics and salt intrusion in an estuarine network. The advantages of this model are that it is flexible in its geometry and has a short runtime. The Rhine-Meuse Delta (the Netherlands) is taken as a reference case. A set of simulations using different geometries is performed with the calibrated model. An example of a result which we obtained is that channel deepening increases salt intrusion locally, but decreases salt intrusion elsewhere in the channel network. These results give insights in the vulnerability of salt intrusion in estuarine channel networks.

How to cite: Biemond, B., de Swart, H. E., and Dijkstra, H. A.: Sensitivity of salt intrusion in estuarine networks to geometry using an idealised model , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5127, https://doi.org/10.5194/egusphere-egu24-5127, 2024.

We present results on the Lagrangian transport of water parcels in a multiple-inlet coastal system: the Dutch Wadden Sea. We performed realistic hydrodynamic numerical simulations spanning 36 years, which are coupled to a Lagrangian module. The aim is to relate the characteristics of Lagrangian transport to the forcing. For this, the displacement of clouds of passive Lagrangian particles representing water columns is split into its advective and dispersive components, with the latter mainly due to chaotic tidal stirring. Advection is defined as the displacement vector of the center of mass of patches of passive particles, and the dispersion is quantified by the covariance matrix of their positions. Both quantities are determined for each tidal cycle spanning the duration of the simulations. Maps of advection reveal mostly large-scale features (basin-scale), whereas the spatial distribution of dispersion shows the predominance of localized structures covering mostly the regions around the inlets and strong bathymetric gradients. A strong correlation is found between the wind and the system-wide advection, showing a marked annual periodicity attributed to the seasonality of the wind forcing, which is stronger during winter and autumn. On the other hand, the magnitude of the tides (especially, due to the spring-neap cycle) governs the magnitude of the dispersion, i.e. mixing in the system. However, an enhancement in dispersion is observed during a few storms.  

How to cite: Fajardo-Urbina, J. M., Duran-Matute, M., Giesbergen, M., Vankan, G., Gräwe, U., Clercx, J. H. H., and Gerkema, T.: Variability of advection and dispersion due to tides and wind forcing in a multiple-inlet coastal system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14102, https://doi.org/10.5194/egusphere-egu24-14102, 2024.

Despite much academic progress and groundbreaking changes in thinking, research results on how sandy terrain forms its current profile shape and how it evolves in the short term based on the equilibrium profile state are minimal. In this study, based on the concept of wave phase potential, which was devised based on the equation of equilibrium beach profile in the surf zone, it is shown which type of beach profile is in equilibrium in the inflow of flat waves. In order to interpret the erosion problem caused by sea level rise on the basis of this concept, we will show how the beach profile responds to sea level rise. As a representative result, the beach retreat width due to sea level rise is given as a function of the dominant wave period and the beach scale factor (a factor obtainable from the sand grain size) as well as the sea level rise. This equation is compared to Bruun's proposal and also discusses the constraints in applying Bruun formula. The results of this study can provide a scientific basis for predicting how a seabed topography composed of sand can be formed or to reverse estimate the wave incident condition from the current landform and seabed conditions, as long as the inflow wave data and the sampled sand grain size data are available. Moreover, it shows how devastating the inundation erosion caused by sea level rise can be. It is time to judge how urgent it is to secure a coastal buffer zone behind this, and to hasten technical and policy responses to mitigate the damage caused by it. As an example of application, the sea level rise trend for the coast of the Korean Peninsula and the inundation erosion predicted for 2050, 2070 and 2100 for 350 beaches of the Korean Peninsula will be presented.

How to cite: Lee, J. L.: On the Equilibrium State of the Beach Profile Based on the Concept of Wave Phase Potential and Its Changes due to Sea Level Rise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9040, https://doi.org/10.5194/egusphere-egu24-9040, 2024.

High-flow tidal channels (Re~O(10⁸)) are characterized by strong bidirectional currents (3 m/s) and high turbulence intensities. As in most coastal environments, these strong flows are affected by wind and waves, especially during severe weather events. The combined occurrence of strong currents and wind-generated surface gravity waves is a nonlinear coupled process in which both the currents and the incident wave field are modified. In this work, the evolution of mean wave parameters in a high-flow tidal channel is evaluated for various wave and tidal flow conditions. Synchronous current, turbulence, and surface altimeter data measured by a bottom-mounted acoustic Doppler current profiler (ADCP) deployed in Grand Passage, a tidal channel within the Bay of Fundy in eastern Canada, are analyzed. Results indicate that wave growth and wave propagation are coupled with the magnitude and relative direction of the current. During each measured high-wind event, the significant wave height consistently increased, and the wavelength decreased, as the current magnitude increased when locally generated waves opposed the currents. To the contrary, the significant wave height was drastically reduced when the waves follow the currents even for a small current magnitude. In addition, elevated turbulence kinetic energy and vertical plumes of elevated acoustic backscatter amplitude were observed in the upper water column during high-wind events, likely bubbles injected into the free surface by breaking waves (whitecaps) and transported through the water column by the turbulence generated by tidal currents. Obtained results allow to identify when and where wave-current interactions are significant, what their implications are for the complex dynamics of tidal channels, and suggest that currents must be incorporated into forecast wave models to improve local sea state predictions and consequently navigation safety.

How to cite: Guerra, M., Hay, A. E., Sagredo, N., and Acuña, A.: Wave-current interactions in a high-flow tidal channel, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10528, https://doi.org/10.5194/egusphere-egu24-10528, 2024.

The Baltic Sea is one of the coastal seas worldwide that suffer most strongly from hypoxia. With its pronounced haline stratification, the Baltic Sea is naturally prone to oxygen deficiency, but the strong growth of hypoxic and anoxic regions since the middle of the 20th century was mainly driven by eutrophication due to large nutrient inputs from anthropogenic sources. Since the oxygen solubility is lower in warmer water and oxygen consumption rates are higher, increasing water temperatures due to climate change are expected to worsen oxygen conditions in the future. Today, the effects of warming are still considered minor compared to those of the high nutrient loads. However, we show, by analyzing 159-years long hindcast simulations of the Baltic Sea with three different models, that exceptionally high temperatures in certain parts of the western Baltic Sea additionally deteriorated the oxygen conditions during the course of the 20th century on an interannual scale. These high temperatures were not mainly caused by global warming but by a shift in the seasonality of saltwater inflows from the North Sea, namely an increase in warm summer and early autumn inflows and a decrease in colder winter inflows. This we can conclude from comparing the reference simulations with a sensitivity experiment that excludes global warming. Hence, we identify a new driver of hypoxia in the western Baltic Sea.

How to cite: Barghorn, L., Meier, H. E. M., Radtke, H., and Neumann, T.: Warm saltwater inflows strengthen oxygen depletion in the western Baltic Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-38, https://doi.org/10.5194/egusphere-egu24-38, 2024.

Anoxia in the central Baltic Sea is caused by the disproportion of the oxygen demand below the Baltic Sea halocline and the capability to transport sufficient amounts of oxygen from the well oxygenated upper water column through the halocline into the deeper Baltic Sea. Despite the fact of anoxia below the halocline, there is a growing evidence for a considerable oxygen transport through the halocline by turbulent mixing at the basin boundaries, i.e. the location where the halocline gets in the vicinity of the seafloor.

We used velocity data from moorings and ship based velocity shear microstructure measurements using a MSS profiler. The data was acquired during three different cruises/seasons in the Eastern Gotland Basin to identify key processes responsible for oxygen mixing events across the strong halocline. The MSS was equipped with a fast oxygen sensor allowing to quantify the vertical oxygen flux.

We focused on specific events with inertial waves, mean currents, and topographic waves as major dominating processes. During these events properties such as vertical shear, stratification and oxygen fluxes were analysed. With this information we were able to estimate the potential of the processes for the diapycnal oxygen transport. We found that inertial waves do not contribute much to the overall oxygen flux across the halocline, whereas topographic waves increase the oxygen flux considerably. Also the mean current lead to significant oxygen fluxes under certain shear and stratification conditions, suggesting that further attention should be turned to those.

How to cite: Thiele, O., Holtermann, P., and Umlauf, L.: Turbulent oxygen transport across the halocline of the central Baltic Sea: Identification of key physical processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16889, https://doi.org/10.5194/egusphere-egu24-16889, 2024.

For the European Commission, the EDITO consortium is creating the European Digital Twin Ocean, a platform that integrates coastal and oceanic modelling tools with ocean observation databases and computing infrastructure. Building on EMODnet and CMEMS, EDITO Model Lab will contribute by making the next generation of ocean models more accessible.

This work demonstrates one of the capabilities of the Digital Twin Ocean, focussing on human exploitation impacts on carbon fluxes. More specifically this what-if scenario is about the impact of upscaling the cultivation of shellfish in the North Sea on the carbon cycle. Upscaling the cultivation of shellfish is part of the envisioned “blue economy” and a promising option for multi-use of offshore wind parks. As shellfish are respiring organisms, they are a carbon source. At the same time shells are a carbon storage as they are built through biocalcification, a process that turns dissolved carbon and calcium into calcium carbonate.

The research aims to quantify the effects of upscaling shellfish cultivation in the North Sea on the carbon cycle. This is done by implementing a biocalcification module (Stechele & Lavaud, manuscript submitted for publication in 2024), in the Dynamic Energy Budget (DEB) module integrated in Delft3D-FM’s water quality process library (Troost et al., 2010; Deltares, 2023). Our work includes assumptions about how harvesting accounts for calcium carbonate leaving the sea and is therefore sequestrated.

How to cite: dols, F., lavaud, R., Stechele, B., Troost, T., Cornacchia, L., van Duren, L., Vilmin, L., Meszaros, L., El Serafy, G., Staneva, J., and Drillet, Y.: The impact of increased shellfish cultivation in the North Sea on the carbon cycle: a what-if scenario for the European Digital Twin Ocean. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17541, https://doi.org/10.5194/egusphere-egu24-17541, 2024.

The Cape Verde Archipelago (CVA) stands out with exceptional biological productivity sustaining a highly diverse ecosystem. Higher primary productivity in the proximity of islands, known as the Island Mass Effect (IME), has been systematically observed on global scale but the details of the interplay between physical and biogeochemical processes remain not fully understood. Within this study, a comprehensive analysis of the IME within the CVA based on 20 years of physical, chemical, and biological observational data sets is presented for the first time. Three main physical processes are identified to be responsible for the IME of the CVA and are investigated in detail: I. The interactions of tidal flows/internal waves with topography: Internal wave breaking at critical slopes leads to elevated mixing rates of a factor 100 larger than at reference points. II. The generation of island wakes in lee of Santo Antãoand Fogo: wind interactions with the island’s topography cause local wind shear in lee, which can generate productive vortex patterns extending for several island diameters downstream. III. The interaction of remotely-generated mesoscale eddies with the CVA itself: After central collision of open ocean eddies with islands or seamounts or when the eddy passes by very closely, we observe submesoscale frontal dynamics driven by mesoscale flow brought out of geostrophic balance, thereby enabling vertical mixing hotspots. Our observations particularly show the interactions between eddies and the internal wave field (modified by vertical shear of the mesoscale eddy, tides, bathymetry, or a combination of all these factors).
All these mechanisms (I., II., and III.), albeit diverse, uniformly augment vertical exchange by turbulent motions with strongly enhanced diapycnal mixing rates and/or vertical velocities and thereby promote elevated nutrient flux into the euphotic layer. This flux ultimately results in significantly higher phytoplankton concentrations in areas where these physical processes occur, thus providing the basis of the local pelagic food web consisting of mesozooplankton and micronecton up to larger predators.

How to cite: Schuette, F., Hans, A. C., Schulz, M., Brandt, P., Hummels, R., Körtzinger, A., Fiedler, B., Fischer, T., Hoving, H. J., and Hauss, H.: Interdisciplinary Insights into the Island Mass Effect of the Cape Verde Archipelago, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16835, https://doi.org/10.5194/egusphere-egu24-16835, 2024.

The exchange flow in estuaries is typically characterized by an inflow of salty water near the bottom and a surface outflow of brackish water, resulting from the mixing of river and ocean water. The exchange flow has been found to be a major driver of residence times and water quality conditions in estuarine systems and has also been found to influence biogeochemical processes such as hypoxia, nutrient fluxes, and the transport of contaminants. 
This study focuses on the spatial and temporal variability of exchange flow in a highly turbid and tidally-driven estuary located on the southwest coast of France, The Gironde. Stratification in the Gironde varies from well-mixed to partially stratified during low to high river flow conditions, respectively. Using validated numerical simulations, the exchange flow was calculated using the Total Exchange Flow (TEF) methodology under various river regimes. A mixing ratio was also quantified to assess the relative contribution of shear production to the salinity variance dissipation. Results show that the exchange flow in the Gironde is characterized by up to four salinity layers at the mouth reducing to two layers upstream. In addition, TEF outflow transport (Qout) increases slightly with river discharge, while the most substantial variability in Qout is due to along-channel variability in bathymetry and estuary width. The mixing ratio indicates that salinity variance dissipation was more influenced by the shear production than buoyancy near both the mouth and head of the estuary during spring tide. Towards the middle of the estuary, the ratio shows a weak contribution from the shear production whereas the mixing of salinity was high. During neap tide, the contribution of shear production to the salinity variance was elevated only downstream and mixing of salinity dominated. The next steps of this work will be to assess the impact of sediments on TEF and to compare the magnitude of the exchange flow in the Gironde to other systems globally.

How to cite: Rojas, C., Ross, L., and Sottolichio, A.: Total Exchange Flow and Mixing in a Tidally Driven Estuary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12222, https://doi.org/10.5194/egusphere-egu24-12222, 2024.

High spatial and temporal resolution hydrographic data collected by Southern Elephant Seals (Mirounga leonina, SESs) and satellite remote sensing data allow a detailed oceanographic description of the Argentine Continental Shelf (ACS). In-situ data were obtained from the CTD (Conductivity, Temperature, and Depth), accelerometer, and hydrophone sensors attached to five SESs that crossed the ACS between the 17th and 31st of October 2019. The analysis of the temperature (T) and salinity (S) along the trajectories allowed us to identify two different regions: north and south of 42°S. Satellite Sea Surface Temperature (SST) data suggests that north of 42°S, warm waters are coming from the San Matias Gulf (SMG). The high spatio-temporal resolution of the in-situ data shows regions with intense gradients along the T and S sections that were associated with a seasonal front that develops north of Península Valdés in winter due to the entrance of cold and fresh water to the SMG. The speed of the SESs is correlated with tidal currents in the coastal portion of the northern region, which is in good agreement with the macrotidal regime observed. A large number of Prey Catch Attempts (PCA), a measure obtained from the accelerometer sensor, indicates that SESs also feed in this region, contradicting suggestions from previous works. The analysis of wind intensity estimated from acoustic sensors allowed us to rule out the local wind as the cause of fast thermocline breakups observed along the SESs trajectories. Finally, we show that the maximum depth reached by the elephant seals can be used to detect errors in the bathymetry charts. Results presented have been accepted for publication in Remote Sensing

How to cite: Martinez, M. M., Ruiz-Etcheverry, L. A., Saraceno, M., Gros-Martial, A., Campagna, J., Picard, B., and Guinet, C.: Satellite and High-Spatio-Temporal Resolution Data Collected by Southern Elephant Seals Allow an Unprecedented 3D View of the Argentine Continental Shelf, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-688, https://doi.org/10.5194/egusphere-egu24-688, 2024.

The coastal waters of Central Norway showcase a great biodiversity. The Froan archipelago and the coral reefs of the Sula rise are highly productive, with several species of fish, clams and crab. Results from the ocean model system SINMOD show a high primary production in the area as a result of internal waves at the shelf break in combination with strong tidal mixing at the bank area of the Froan archipelago. Oceanographic conditions strongly impact on the phytoplankton community structure and succession in this region (Fragoso et al., 2019, Fragoso et al. 2021). Spring bloom dynamics is further sensitive to rapid changes in weather in the region (Fragoso et al, in revision).

In this study, we use the coupled biophysical SINMOD model to explore spatiotemporal variations in primary production. We aim to correlate these variations with internal waves, tidal mixing, and eddies across different regions of the complex shelf area. The observations from previous studies will be used to assess the model prediction skill. We will further investigate the fate of carbon in the system and use the model results to locate potential hot spots of biodiversity by investigating vertical transport of carbon as well as recycling of carbon in the water column. This work is part of an ongoing interdisciplinary project AMBIOS that aims to develop a fully autonomous system for the discovery of, and navigation to, marine microbial biodiversity hotspots.

How to cite: Ellingsen, I. H., Broch, O. J., and Moreira Fragoso, G.:  Identification of primary productivity hotspots and their association with oceanographic phenomena in the coastal region off Central Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18136, https://doi.org/10.5194/egusphere-egu24-18136, 2024.

This study investigates the characteristics of salinity-controlled submesoscale fronts in the Bay of Bengal (BoB), based on a high resolution model output (MITgcm LLC4320). Large horizontal gradients of temperature, salinity, and density are found in the northern bay, with salinity and density gradients being notably more pronounced than those of temperature. Density fronts in this region are controlled by salinity rather than temperature due to the amount of freshwater input. Salinity fronts are most often compensated by temperature in the upper ocean of the BoB, especially at small scales. Fronts are classified into 4 types based on the value of the Turner angle. Among them, the salinity-controlled fronts compensated by temperature play a leading role in the northern BoB from October to March, while salinity-controlled fronts reinforced by temperature become equally numerous during the rest of the year. Heat fluxes significantly affect the temporal variations of temperature compensated versus reinforced fronts, while freshwater fluxes only play a minor role. When compensated fronts get arrested, warm water sinks beneath the cool water, favoring the formation of a temperature inversion layer and a barrier layer.

How to cite: Duan, W., Cheng, X., Zhou, Y., and Gula, J.: Characteristics of salinity-controlled submesoscale fronts in the Bay of Bengal and their impact on the upper ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3946, https://doi.org/10.5194/egusphere-egu24-3946, 2024.

Ocean fine-scale dynamics such as submesoscale processes constitute one of the key points in understanding current velocities with a tridimensional approach. Their in situ observation remains challenging due to their short space and time extent and duration. The Northern Current in the Western Mediterranean Sea, corresponding to the Northern branch of the basin cyclonic circulation, can be influenced by wind events, inducing intrusions on the continental shelf and associated fine-scale dynamics. In order to detect these phenomena, the JULIO mooring (JUdicious Location for Intrusion Observation) located on the Eastern side of the Gulf of Lion’s shelf on the 100m isobath, measures tridimensional current velocities since 2012 using an acoustic Doppler current profiler (ADCP) at 300kHz. In addition, vertical velocities have been episodically measured with other methods such as the FreeFall-ADCP (FF-ADCP), and an autonomous Vertical Velocity Profiler (VVP) both developed at MIO. First, the JULIO time-series has shown a significant contribution of biology to vertical motions, with systematic negative vertical velocities measured at night time. This effect was particularly strong in the subsurface layer at 15 to 25 meters depth and enhanced during spring. Second, strong observed 3D-currents, coinciding with wind events, induce current shears and intrusions as well as vertical velocities in this dynamical coastal region with complex bathymetric constraints. Furthermore, the SWOT satellite mission launched in 2022 constitutes a powerful ally by providing a new tool to detect fine-scale features from the surface dynamics near JULIO, and especially during the daily fast sampling phase from April to July 2023. Given the impact of wind forcing on current dynamics in this region, the question arises to what extent the Northern Current and its intrusions on the continental shelf might be affected by climate change.

How to cite: Arnaud, M., Petrenko, A., Fuda, J.-L., Comby, C., Bosse, A., Ourmières, Y., and Barrillon, S.: Biological processes and wind contributions to 3-D fine-scale dynamics in a coastal area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17374, https://doi.org/10.5194/egusphere-egu24-17374, 2024.

Typhoon is a synoptic phenomenon that has significant impact on ocean. Mooring observations of nearly the full water column on the continental slope in the South China Sea revealed the ocean's response to Typhoon Mangkhut (2018). Mangkhut induced sea surface cooling ∼4°C that was biased to the right side of its track, which recovered with an e-folding time after approximately 1 week.  Mangkhut was a relatively fast-moving typhoon and caused a fast near-inertial response throughout the entire depth in its lee. The typhoon-induced upper ocean (deep-water) near-inertial current velocities were >1.5 m/s (∼0.08 m/s), with an e-folding time of approximately a week (2 weeks) and frequency of 1.04f (1.08f, where f is the local inertial frequency). The near-inertial currents were near-circular polarized in the upper ocean and near-rectilinear polarized with the main axis in the across-slope direction in deep water. The deep-water near-inertial waves amplified the vertical excursions of isotherms from ∼120 to ∼200 m, reduced the stratification, elevated vertical current shears, and enhanced turbulent dissipation rate, especially during 14–17 September when the effects of near-inertial waves and diurnal spring tides overlapped. A net cooling ∼0.15°C and salinity increase ∼0.05 psu were observed in the deep ocean after Mangkhut. Typhoon-induced near-inertial waves correspond to the intensification of southwestward along-slope mean near-bottom currents. This study indicates the immediate influence of typhoon in deep-water and contribute to the bottom mixing on the continental slope.

How to cite: Zhang, H.: Ocean Response to Typhoon Mangkhut (2018) on a Continental Slope in the South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6909, https://doi.org/10.5194/egusphere-egu24-6909, 2024.

The data collected from an array of five subsurface moorings, which are deployed along the direction of internal solitary wave (ISW) crests in the northern South China Sea (SCS) from October 2013 to June 2014, are used to investigate the three-dimensional structures of ISWs and their temporal variabilities. The measurements reveal that the ISWs are asymmetric along their crests, with the average amplitude in the southern portion being 70% larger than that in the northern portion. The observed three-dimensionally integrated energy and flux of ISWs are accurately calculated for the first time, reaching 53 TJ and 0.82 GW, respectively, on average. Over the whole observation period, the pattern of ISW crests was dominantly convex, accounting for 76.2% of all observed episodes. However, due to the changes in propagation speeds along the direction of ISW crests caused by either single or combined effects of mesoscale eddies and intruded Kuroshio, the ISW crests could deform into S-shaped and concave patterns, which accounted for 19.6% and 4.2%, respectively. Moreover, during November and December, the positions of the largest amplitude along ISW crests mostly shifted from the southern portion to the northern portion due to the energy refraction caused by mesoscale eddies, leading to the increase/decrease in wave intensity in the northern/southern portion. In early February, the intruded Kuroshio remarkably shifted ISW energy southward, which increased the wave amplitude in the southern portion by as much as 96%. These results clearly demonstrate that the intensities of three-dimensional ISWs could temporally vary out of phase between the northern and southern portions of crests due to the remarkable modulations by intense background processes.

How to cite: Yang, Y., Huang, X., Zhou, C., Zhang, Z., Zhao, W., and Tian, J.: Three-dimensional Structures of Internal Solitary Waves in the Northern South China Sea Revealed by Mooring Array Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2424, https://doi.org/10.5194/egusphere-egu24-2424, 2024.

Due to the regional differences between the North and South Yellow Sea, and under the influence of winter winds, the relative changes of the coastal current and the Yellow Sea warm current will lead to the instability of the front, which will lead to the cross-front transport of sediment. Therefore, the study of sediment exchange between the North and South Yellow Sea has become an indispensable part of the study of the Yellow Sea environment. In this paper, the current field and sediment concentration in the sorthern part of Chengshantou, a representative area of the Yellow Sea, were observed in winter in order to analyze the sediment exchange process between the North Yellow Sea and the South Yellow Sea in winter. The results show that in the north of Chengshantou sea area in winter, the current velocity does not change with the water depth when the water depth is more than 20 m, and the variation range is less than 5 cm/s, and the tides are regular semi-diurnal tides. The resuspension of sediments in the sea area is not controlled by the current velocity, but the sediment transport per unit width is mainly affected by the current velocity. Under the Shandong peninsula coastal current effect, suspended sediment is mainly transported from the north Yellow Sea to the South Yellow Sea, and the total difference between the southward and northward sediment is 442500 NTU×m² during the observation period of about one month. The largest two-day transport volume accounted for 41.2% of the total transport flux.

How to cite: Li, B., Jun, X., Duan, B., Wang, D., and Yu, L.: Resuspended sediment exchange between the north and south Yellow Sea in the north of Chengshantou, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1931, https://doi.org/10.5194/egusphere-egu24-1931, 2024.