Salinity Profiles Research Articles

Reconstructing ocean carbon storage with CMIP6 Earth system models and synthetic Argo observations

Abstract. The ocean carbon store plays a vital role in setting the carbon response to emissions and variability in the carbon cycle. However, due to the ocean's strong regional and temporal variability, sparse carbon observations limit our understanding of historical carbon changes. Ocean temperature and salinity profiles are more widespread and rapidly expanding due to autonomous programmes, and so we explore how temperature and salinity profiles can provide information to reconstruct ocean carbon inventories with ensemble optimal interpolation. Here, ensemble optimal interpolation is used to reconstruct ocean carbon using synthetic Argo temperature and salinity observations, with examples for both the top 100 m and top 2000 m carbon inventories. When considering reconstructions of the top 100 m carbon inventory, coherent relationships between upper-ocean carbon, temperature, salinity, and atmospheric CO2 result in optimal solutions that reflect the controls of undersaturation, solubility, and alkalinity. Out-of-sample reconstructions of the top 100 m show that, in most regions, the trend in ocean carbon and over 60 % of detrended variability can be reconstructed using local temperature and salinity measurements, with only small changes when considering synthetic profiles consistent with irregular Argo sampling. Extending the method to reconstruct the upper 2000 m reveals that model uncertainties at depth limit the reconstruction skill. The impact of these uncertainties on reconstructing the carbon inventory over the upper 2000 m is small, and full reconstructions with historical Argo locations show that the method can reconstruct regional inter-annual and decadal variability. Hence, optimal interpolation based on model relationships combined with hydrographic measurements can provide valuable information about global ocean carbon inventory changes.

Assessment of predictability of the Loop Current in the Gulf of Mexico from observing system experiments and observing system simulation experiments

This study presents results from numerical model experiments with a high-resolution regional forecast system to evaluate model predictability of the Loop Current (LC) system and assess the added value of different types of observations. The experiments evaluate the impact of surface versus subsurface observations as well as different combinations and spatial coverage of observations on the forecasts of the LC variability. The experiments use real observations (observing system experiments) and synthetic observations derived from a high-resolution independent simulation (observing system simulation experiments). Model predictability is assessed based on a saturated error growth model. The forecast error is computed for the sea surface height fields and the LC frontal positions derived from the forecasts and control fields using two metrics. Estimated model predictability of the LC ranges from 2 to 3 months. Predictability limit depends on activity state of the LC, with shorter predictability limit during active LC configurations. Assimilation of subsurface temperature and salinity profiles in the LC area have notable impact on the medium-range forecasts (2–3 months), whereas the impact is less prominent on shorter scales. The forecast error depends on the uncertainty of the initial state; therefore, on the accuracy of the analysis providing the initial fields. Forecasts with the smallest initial error have the best predictive skills with reliable predictability beyond 2 months suggesting that the impact of the model error is less prominent than the initial error. Hence, substantial improvements in forecasts up to 3 months can be achieved with increased accuracy of initialization.

Sea-level trend variability in the Mediterranean during the 1993–2019 period

Sea-level change is one of the most concerning climate change and global warming consequences, especially impacting coastal societies and environments. The spatial and temporal variability of sea level is neither linear nor globally uniform, especially in semi-enclosed basins such as the Mediterranean Sea, which is considered a hot spot regarding expected impacts related to climate change. This study investigates sea-level trends and their variability over the Mediterranean Sea from 1993 to 2019. We use gridded sea-level anomaly products from satellite altimetry for the total observed sea level, whereas ocean temperature and salinity profiles from reanalysis were used to compute the thermosteric and halosteric effects, respectively, and the steric component of the sea level. We perform a statistical change point detection to assess the spatial and temporal significance of each trend change. The linear trend provides a clear indication of the non-steric effects as the dominant drivers over the entire period at the Mediterranean Sea scale, except for the Levantine and Aegean sub-basins, where the steric component explains the majority of the sea-level trend. The main changes in sea-level trends are detected around 1997, 2006, 2010, and 2016, associated with Northern Ionian Gyre reversal episodes, which changed the thermohaline properties and water mass redistribution over the sub-basins.

Spatial-temporal characteristics of the oceanic bottom mixed layer in the South China Sea

The oceanic bottom mixed layer (BML) plays an important role in transporting mass, heat, and momentum between the ocean interior and the bottom boundary. However, the spatial-temporal characteristics of the BML in the South China Sea (SCS) is not well understood. Using 514 full-depth temperature and salinity profiles collected during the time period from 2004 to 2018 and two particularly deployed hydrographic moorings, the temporal and spatial variations of the BML have been analyzed. The results show that the BML in the SCS exhibits significant inhomogeneity, with thickness and stability varying across different regions. Specifically, the BML is relatively thin and stable over the continental shelf and deep-sea regions, while it is thicker and less stable over the northern continental slope. The mean, median, and one standard deviation values of BML thickness over the entire SCS were found to be 73 m, 56 m, and 55 m, respectively. Further analysis reveals that energetic high-frequency dynamic processes, coupled with steep bottom topography, contribute to strong tidal dissipation and vertical mixing near the bottom over the continental slope, resulting in thicker BMLs. Conversely, dynamic processes in the deep ocean are less energetic and low-frequency, the topography is relatively smooth, and tidal dissipation and bottom vertical mixing are weaker, leading to a thinner BML. These findings enhance our understanding of the BML dynamics in the SCS and other marginal seas and provide insights to improve parameterizations of physical processes in ocean models.

Modeling of Hydrodynamic Dispersion in the Sidi Kirayr Locality’s Coastal Unconfined Aquifer West of Alexandria, Egypt

The finite difference method was used in this study to solve the two-dimensional hydrodynamic dispersion equation for a typical coastal unconfined aquifer. A mathematical model is prepared to solve this dispersion problem, which is then modeled and analyzed over time. The salinity profiles for the aquifer transition zone in the Sidi Kirayr locality are determined using the finite difference method. The computed salinity profiles are compared to those obtained from an actual well drilled in the area and used to determine electric conductivity. Profile correlation reveals a roughly parallel trend along the tested depth interval. Additionally, these results correlate well with the chemical analysis of water from the same well. The current work promotes the application of the solution methodology in comparable coastal regions in the absence of dispersion measures for the analyzed aquifer. This innovative approach can be used to forecast groundwater quality in comparable coastal regions. It can also help in selecting the ideal sites for man-made wells that pump groundwater.

Assimilation of sea surface salinities from SMOS in an Arctic coupled ocean and sea ice reanalysis

Abstract. In the Arctic, the sea surface salinity (SSS) plays a key role in processes related to water mixing and sea ice. However, the lack of salinity observations causes large uncertainties in Arctic Ocean forecasts and reanalysis. Recently the Soil Moisture and Ocean Salinity (SMOS) satellite mission was used by the Barcelona Expert Centre to develop an Arctic SSS product. In this study, we evaluate the impact of assimilating this data in a coupled ocean–ice data assimilation system. Using the deterministic ensemble Kalman filter from July to December 2016, two assimilation runs respectively assimilated two successive versions of the SMOS SSS product on top of a pre-existing reanalysis run. The runs were validated against independent in situ salinity profiles in the Arctic. The results show that the biases and the root-mean-squared differences (RMSD) of SSS are reduced by 10 % to 50 % depending on the area and highlight the importance of assimilating satellite salinity data. The time series of freshwater content (FWC) further shows that its seasonal cycle can be adjusted by assimilation of the SSS products, which is encouraging of the assimilation of SSS in a long-time reanalysis to better reproduce the Arctic water cycle.

Vegetation History and Estuarine Ecology of the Texas Gulf Coastal Plain in Relation to Climate and Sea-Level Changes According to Three Pollen Cores

The vegetation history of the Texas Gulf Coastal Plain in the Holocene is considered according to pollen evidence from three coring sites where both terrestrial and marine ecology are reconstructed. These pollen sites record oscillations in the limit of the Southeastern US Forest zone in relation to climate changes, with a major, southward migration of the forest limit and expansion of the range limit of Betula nigra being recorded in the 6th millennium BP and a northward migration in the 4th millennium BP. The appearance of Rhizophora pollen also indicates increased tropical influence in the Middle Holocene. Moreover, changes in the salinity profiles of estuaries are reconstructed in relation to broader coastal environmental changes, such as sea-level oscillations and the formation of barrier islands, with a major sea-level transgression phase being recorded in the 4th millennium BP and still-stand conditions after the 3rd millennium BP. These vegetation changes are finally compared to occupational evidence of prehistoric humans in the Central Texas Gulf Coastal Plain region in relation to ecological factors. Here, human occupation of the coastal zone is correlated with afforestation, the proliferation of pecan and the emergence of low-salinity estuaries.

Water Mass Variations in the Maluku Channel of the Indonesian Seas During the Winter of 2018–2019

AbstractAn autonomous underwater glider was deployed in the Maluku Channel during 1 December 2018 through 21 February 2019 to measure temperature and salinity profiles of the upper ∼1,000 m continuously. The measurements suggest intraseasonal variations of the Pacific water mass intrusions into the Maluku Channel, which has not been reported before. The North Pacific Tropical and Intermediate Waters are found to intrude episodically into the eastern Maluku Channel at the depths of 130–180 m and 250–300 m, respectively, during January through February of 2019, each lasting for a few days to a week. The Antarctic Intermediate Water was present in the middle and western Maluku Channel between 600 and 800 m with intraseasonal variability. The South Pacific Subsurface Water was only found to intrude into the eastern Maluku Channel between 250 and 300 m during the first two transections in early December of 2018. Concurrent meter data from three moorings in the Maluku and Talaud‐Halmahera Channels are used to verify the water mass movement. The subsurface and intermediate water mass variations here are found to be closely related to the swing of the Mindanao Current near the Maluku Channel. These intraseasonal water mass intrusions are important aspects of water exchange between the western Pacific Ocean and the Indonesian seas.

Wave Effects on the Initial Dilution of Untreated Wastewater Discharge for Santa Marta’s Submarine Outfall (Colombia)

The initial dilution generated by the final disposal of untreated wastewater through a submarine outfall in Santa Marta was examined with a near-field dilution model. Northward and eastward seawater velocity, salinity, and temperature profiles from a 3D hydrodynamic model were used to provide the oceanic conditions to calculate the dilution. The upwelling phenomenon occurs two times a year at the wastewater discharge site, the major from December to March and the minor in July, eliminating the stratification condition of seawater. The results of the dilution model showed that in these periods the plume reaches the water surface, achieving dilutions greater than 100. In addition, the external wave effect on the initial dilution of submarine outfall discharge in Santa Marta was determined. Surface waves increase dilution during the dry period of the year, when trade winds increase the surge and start the upwelling phenomenon. The dilution with/without waves factor is up to 1.90 for the center of the plume on the water column.

Estimation of nitrate concentration and its distribution in the northwestern Pacific Ocean by a deep neural network model

As a fundamental nutrient for marine biogeochemical processes, the magnitude and spatial distribution of nitrate concentrations are insufficiently measured in the interior ocean. In the present study, a deep neural network (DNN) model was developed to estimate nitrate concentrations in the upper northwestern Pacific Ocean (NPO). This model takes the temperature and salinity profiles as the primary input variables. Since the subtropical and tropical regions are featured by different spatial patterns of nitrate concentrations, we separately trained the model to improve the prediction skill. The predictive results indicate that the DNN model performs well in depicting both spatial and seasonal variability of nitrate concentrations. The sensitivity experiments show that temperature is the dominant factor for the nitrate estimation, while salinity has a relatively small effect, but it cannot be ignored in improving the prediction accuracy. Furthermore, using the temperature and salinity data from World Ocean atlas (2018), we found our DNN model has a good generalization ability on nitrate estimation in NPO. This model can be applied to further studies on nitrate's spatiotemporal variability and mechanism around the global ocean.

High-Resolution Model of Clew Bay—Model Set-Up and Validation Results

Clew Bay is an important aquaculture production area in Ireland. In this study, we focused on a high-resolution simulation of the Clew Bay region based on a regional ocean modeling system (ROMS). Freshwater discharges from eight rivers are included in the model and a wetting–drying scheme has been implemented. The Clew Bay model simulation was validated and calibrated with available observations (e.g., acoustic Doppler current profiler (ADCP), vertical salinity and temperature profiles, and a tide gauge) in the geographic area of the model domain. High correlations were found between the model data and observed temperature, salinity and water levels, along with small root mean square errors. This indicates that the model is able to reproduce the oceanographic phenomena in the study area. The Taylor diagram analysis showed a high correlation coefficient (R = 0.99) between the observed bottom temperature in the Inner Bay and Clew Bay model, along with a small centered root mean square error (RMSD = 0.5 °C). High correlation coefficients (R > 0.80) were found between the model and the two ADCPs for the zonal current component. There was a resemblance in structure between the model and the observed salinity profiles, indicating that freshwater was correctly implemented in the model. Moreover, the correlation coefficient between the model and the tidal sea surface height (SSH) was 0.99, with an RMSD of 0.09 m. We discovered that wind direction and speed had a significant impact on the bay’s water inflow rate. The model outputs can be used to provide scientists, fishermen, and decision-makers with hydrodynamic information on ocean conditions in the bay.

On the control of spatial and temporal oceanic scales by existing and future observing systems: An observing system simulation experiment approach

Ocean monitoring and forecasting systems combine information from ocean observations and numerical models through advanced data assimilation techniques. They are essential to monitor and report on past, present and future oceanic conditions. However, given the continuous development of oceanic models and data assimilation techniques in addition to the increased diversity of assimilated platforms, it becomes more and more difficult to establish how information from observations is used, and to determine the utility and relevance of a change of the global ocean observing system on ocean analyses. Here, a series of observing system simulation experiments (OSSE), which consist in simulating synthetic observations from a realistic simulation to be subsequently assimilated in an experimental analysis system, was performed. An original multiscale approach is then used to investigate (i) the impact of various observing system components by distinguishing between satellites and in situ (Argo floats and tropical moorings), and (ii) the impact of recommended changes in observing systems, in particular the impact of Argo floats doubling and enhancements of tropical moorings, on the fidelity of ocean analyses. This multiscale approach is key to better understand how observing system components, with their distinct sampling characteristics, help to constrain physical processes. The study demonstrates the ability of the analysis system to represent 40-80% of the temperature variance at mesoscale (20-30% for salinity), and more than 80% for larger scales. Satellite information, mostly through altimetric data, strongly constrains mesoscale variability, while the impact of in situ temperature and salinity profiles are essential to constrain large scale variability. It is also shown that future enhancements of Argo and tropical mooring arrays observations will likely be beneficial to ocean analyses at both intermediate and large scales, with a higher impact for salinity-related quantities. This work provides a better understanding on the respective role of major satellite and in situ observing system components in the integrated ocean observing system.

Ocean responses to Shaheen, the first cyclone to hit the north coast of Oman in 2021

On October 3rd, 2021, cyclone Shaheen made landfall on the northeast coast of Oman as a first-category cyclone after crossing the Sea of Oman. It is the first time in more than 130 years that a storm has made such extraordinary landfall on the northeast coast of Oman. This study intends to examine the effects of cyclone Shaheen on ocean cooling and biological response in the Sea of Oman (SO) and the the Arabian Sea (AS) using satellite remote sensing data, an Argo float, and the HYCOM model. The validation analysis of the HYCOM model and the Argo float showed strong correlations between vertical temperature profiles (R = 0.99) and vertical salinity profiles (R = 0.89). Furthermore, winds during the cyclone caused mixing and upwelling leading to Sea Surface Temperatures (SST) dropping 2.5 °C along southern Iranian coastlines, decreasing 5 °C along northern Oman's coastlines, and rising 1 °C across the Arabian Sea. As a result of the exitance of the cyclonic eddies in the Sea of Oman, a significant drop of 5 °C in SST was observed along the coastline of Oman caused by cold upwelled water from southern Iranian coastlines. Cyclone Shaheen's heavy rainfall caused the Sea Surface Salinity (SSS) in the Sea of Oman to drop from 36.7 to 36.8 psu. According to the results, Ekman pumping and upwelling processes predominated along the southern Iranian coast resulting in nutrient uplift and phytoplankton blooms (3 mg/m3). In contrast, strong stratification near the coast of Oman prevented nutrient uplift and led to low Chl-a concentrations. Due to the unique nature of cyclone Shaheen, it is essential to examine the complex dynamic and interaction between the ocean and atmosphere in the Sea of Oman and the Arabian Sea.

Circulation, stratification and salt dispersion in a former estuary after reintroducing seawater inflow

Around the world, estuaries have been partially or completely closed-off from the sea and their number may increase with rising sea levels. Concurrently, there is a trend to reintroduce seawater inflow into enclosed former estuaries for ecosystem improvement. This is also the case in the Haringvliet, a former estuary in the Rhine-Meuse Delta, closed-off in 1970 with floodgates blocking seawater inflow and regulating outflow. As the reintroduced salt water inflow can threaten fresh water intake, inflow, flushing and dispersion need to be well understood and carefully managed.Here we investigate stratification, flow circulation and salt transport in the Haringvliet by analyzing ADCP data collected in two former tidal channels, together with salinity time series and profiles. The profiles show that the incoming water reaches the deeper parts and that the system tends to be strongly stratified. Over time, the interface levels deepen in steps, mainly coinciding with floodgate discharge events, which are strongly correlated with the primary current velocities in the channels. However, even floodgate discharges for above average Rhine discharge conditions were insufficient to quickly flush or mix the salt out of the channels. This is consistent with calculated gradient Richardson numbers, which barely get in the range of critical values.For closed floodgates with no outward discharge, we found considerable depth-averaged upwind currents in the channels for axial winds. This reveals a dominant horizontal circulation, with downwind currents over the shallow parts and upwind currents over the deep parts of the system, explained by a local imbalance between the wind stress and pressure gradient force at both shoals and channels. This horizontal circulation is an important driver for inland salt transport, as increased salinity values were found at landward locations for seaward wind. This implies this is a condition with increased risks for fresh water availability. Analytical calculations confirmed the upwind currents in the channels can become sufficiently strong to transport salt mixed up at one side of the system to the other within the duration of a wind event. However, the current-related shear is likely not strong enough to induce interfacial mixing directly above the deep parts, and we hypothesize mixing mostly occurs when salt water reaches less deep areas after tilting of the pycnocline.The insights from this study are relevant for other formerly enclosed estuaries for which reintroduction of seawater inflow is considered, as well as presently open systems for which (partial) closure is discussed.

Moana Ocean Hindcast – a > 25-year simulation for New Zealand waters using the Regional Ocean Modeling System (ROMS) v3.9 model

Abstract. Here we present the first open-access long-term 3D hydrodynamic ocean hindcast for the New Zealand ocean estate. The 28-year 5 km×5 km resolution free-running ocean model configuration was developed under the umbrella of the Moana Project, using the Regional Ocean Modeling System (ROMS) version 3.9. It includes an improved bathymetry, spectral tidal forcing at the boundaries and inverse-barometer effect usually absent from global simulations. The continuous integration provides a framework to improve our understanding of the ocean dynamics and connectivity, as well as identify long-term trends and drivers for particular processes. The simulation was compared to a series of satellite and in situ observations, including sea surface temperature (SST), sea surface height (SSH), coastal water level and temperature stations, moored temperature time series, and temperature and salinity profiles from the CORA5.2 (Coriolis Ocean database for ReAnalysis) dataset – including Argo floats, XBTs (expendable bathythermographs) and CTD (conductivity–temperature–depth) stations. These comparisons show the model simulation is consistent and represents important ocean processes at different temporal and spatial scales, from local to regional and from a few hours to years including extreme events. The root mean square errors are 0.11 m for SSH, 0.23 ∘C for SST, and <1 ∘C and 0.15 g kg−1 for temperature and salinity profiles. Coastal tides are simulated well, and both high skill and correlation are found between modelled and observed sub-tidal sea level and water temperature stations. Moreover, cross-sections of the main currents around New Zealand show the simulation is consistent with transport, velocity structure and variability reported in the available literature. This first multi-decadal, high-resolution, open-access hydrodynamic model represents a significant step forward for ocean sciences in the New Zealand region.

Triple diffusive magneto convection in a fluid-porous composite system

A study on triple diffusive magneto convection is made for a fluid – porous composite system with rigid-rigid boundaries insulated to temperature and concentration. The porous layer of the composite system is modeled using Darcy–Brinkman model. The method of regular perturbation approach is employed to find the eigen-value for the problem considered. The critical Rayleigh number as criterion for the onset of convection is derived for step function, salting below and desalting above salinity profiles. The effect of various physical parameter on the onset of convection is graphically depicted and the stability of the system is analyzed.

A Computational Study of Magneto-Convective Heat Transfer Over Inclined Surfaces With Thermodiffusion

In this article, the ocean energy generator system is analysed. The need for sustainable renewable energy systems is continually growing, given the situation of the world’s energy supplies. Numerous similar systems, including photovoltaic solar collectors, biomass, and wind turbines are used for energy generation. The ocean energy generator system uses the magnetohydrodynamics transformation concept to convert kinetic energy to electrical energy. Similar to conventional generators, an ocean generator requires an applied magnetic field to generate current, making it a critical component of the system. To optimize the performance and efficiency of ocean generators, various devices utilizing superconducting magnets have been developed, including Hall current generators, rotating channels, rotating disc magnetohydrodynamics generators, and helicoid generators. However, these systems also involve complex heat, momentum, and mass transfer, which can be better understood through mathematical modeling. The similarity transformation are introduced to transform the mathematical model from partial differential equation system to ordinary differential equation system. By adopting this approach, the numerical solution is significantly simplified while still preserving numerous crucial physical aspects of the studied heat and material transport phenomena. The physical characteristics of sea waves are governed by the three variables of seawater: temperature, salinity, and pressure. Small dispersed particles also affect the generation of hydroelectric power from surface water. The behaviour of velocity, temperature, and salinity profile is observed for the variations of different parameters such as magnetic, Grashof number and heat source. The system is converted into an optimization problem and solved by a neural network procedure. The solutions are compared with reference solutions for validation. The errors, performance, testing and training data are also presented graphically. The data is typically visualized using histograms, line graphs, and other visual aids. This allows for easier comprehension and analysis of the data.

Reconstruction of 3-D Ocean Chlorophyll a Structure in the Northern Indian Ocean Using Satellite and BGC-Argo Data

We present a novel method using satellite and biogeochemical Argo (BGC-Argo) data to retrieve the 3-D structure of chlorophyll <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$a$ </tex-math></inline-formula> (Chla) in the northern Indian Ocean (NIO). The random forest (RF)-based method infers the vertical distribution of Chla using the near-surface and vertical features. The input variables can be divided into three categories: 1) near-surface features acquired by satellite products; 2) vertical physical properties obtained from temperature and salinity profiles collected by BGC-Argo floats; and 3) the temporal and spatial features, i.e., day of the year, longitude, and latitude. The RF-model is trained and evaluated using a large database including 9738 profiles of Chla and temperature-salinity properties measured by BGC-Argo floats from 2011 to 2021, with synchronous satellite-derived products. The retrieved Chla values and the validation dataset (including 1948 Chla profiles) agree fairly well, with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2} = 0.962$ </tex-math></inline-formula> , root-mean-square error (RMSE) = 0.012, and mean absolute percent difference (MAPD) = 11.31%. The vertical Chla profile in the NIO retrieved from the RF-model is more accurate and robust compared to the operational Chla profile datasets derived from the neural network and numerical modeling. A major application of the RF-retrieved Chla profiles is to obtain the 3-D Chla structure with high vertical resolution. This will help to quantify phytoplankton productivity and carbon fluxes in the NIO more accurately. We expect that RF-model can be used to develop long-time series products to understand the variability of 3-D Chla in future climate change scenarios.

Remote Sensing of Seawater Temperature and Salinity Profiles by the Brillouin Lidar Based on a Fizeau Interferometer and Multichannel Photomultiplier Tube

Brillouin spectroscopy is a powerful tool to measure the water temperature and salinity profiles of seawater. Considering the insufficiency of the current spectral measurement methods in real-time, spectral integrity, continuity, and stability, we developed a new lidar system for spectrum measurement on an airborne platform that is based on a Fizeau interferometer and multichannel photomultiplier tube. In this approach, the lidar system uses time-of-flight information to measure the depth and relies on Brillouin spectroscopy as the temperature and salinity indicator. In this study, the system parameters were first optimized and analyzed. Based on the analysis results, the performance of the system in terms of detection depth and accuracy was evaluated. The results showed that this method has strong anti-interference ability, and under a temperature measurement accuracy of 0.5 °C and a salinity measurement accuracy of 1‱, the effective detection depth exceeds 40.51 m. Therefore, the proposed method performs well and will be a good choice for achieving Brillouin lidar application in seawater remote sensing.

Tidal dynamics on the upper continental slope of the eastern Gulf of Cádiz: The interplay between water masses and its effects on seafloor morphology

Although the effects of tidal dynamics have been studied in shallow marine environments and morphologically restricted straits, the impact of these processes on deep-water marine environments remains to be studied in depth. This study highlights the influence of tides on the seafloor morphology of the eastern Gulf of Cádiz, near the exit of the Strait of Gibraltar. Two moorings, one with an Acoustic Doppler current profiler (ACDP) and another one with a thermistor chain, and local and regional profiles of salinity, temperature, and ADCP reveal the water mass distribution in the study area and associated oceanographic processes. The intermediate water masses flowing along the continental slope are the Eastern North Atlantic Central Water (ENACW) and the Mediterranean Outflow Water (MOW), bound by an interface located regionally at depths greater than 300 m, but identified locally at much shallower depths (up to 150 m) in the studied upper slope. The hydrodynamics of the area are governed by barotropic tidal currents, the MOW upper core, and the internal tides, which act at different time and spatial scales shaping the local terraced sea-floor morphology and determining the dominant sedimentary processes. The obtained results allow a better understanding of how secondary oceanographic processes are modulating the water mass circulation in this particular hot spot and their importance in explaining the formation and evolution of morphological depositional and erosional features.