This report describes pilot experiment for the ONR DRI titled CALYPSO, which aims to study three-dimensional pathways from the surface ocean to interior. The study used two ships, the NRV Alliance (100m), and the RV SOCIB (23m) to map the circulation generated by the front between Atlantic and Mediterranean water in the Alboran Sea and to conduct high-resolution frontal surveys. The study employed a large number of drifters and conducted underway profiling from the ship.

Long-term, high-frequency monitoring is increasingly required to detect ecological change in human-impacted coastal zones, yet fixed underwater imaging commonly produces relative counts that are difficult to standardize across time and sites. We analyzed a nine-year (2016-2024) time series from a cabled fixed camera deployed at the entrance of a Mediterranean harbor (Mallorca, western Mediterranean), imaging a small wreck at 8 m depth. An automated workflow combining image-quality filtering, Retinex correction, and deep-learning-based detection and classification generated continuous fish observations across 17 taxonomic categories. To improve comparability and ecological interpretability of camera-derived abundance signals, we developed two complementary indicator streams: (i) daily occurrence (presence-absence) from full-frame imagery to characterize seasonal and interannual structure, and (ii) daylight hourly fish density standardized by an estimated sampled water volume within a defined area of interest (individuals m-3 h-1). This volume-standardized density is intended as an index contingent on camera geometry and visibility conditions. Taxon-specific generalized mixed models and volume-based hurdle models related these indicators to environmental covariates (temperature, chlorophyll-a, irradiance, photoperiod, precipitation, and a sea-level-based flux proxy) and to a discrete post-2021 structural shift. Across taxa, results revealed pronounced season-dependent diel structure in volume-standardized density and a marked post-2021 shift in fish occurrence and/or density for several common coastal groups, with environmental effects varying by taxon and season. Overall, volume standardization provides a practical route to transform automated detections from fixed cameras into more comparable, indicator-oriented metrics for tracking abrupt change and environmentally driven variability in coastal fish assemblages.

Ocean currents are crucial in regulating Earth's climate, with a significant impact in the distribution of ocean properties. During the Calibration/Validation phase of the Surface Water and Ocean Topography (SWOT) satellite mission, we performed a high-resolution, multi-platform experiment to evaluate SWOT's ability to resolve small-scale features, focusing on a similar to 25 km-radius anticyclonic eddy in the Western Mediterranean Sea. Acoustic Doppler Current Profiler (ADCP) recorded maximum velocities of 30 cm/s at 155 m depth and underwater glider data identified biconvex isopycnals, classifying the eddy as intrathermocline. SWOT successfully captured the sea level signal and surface geostrophic currents of the eddy, showing notable error reduction over conventional altimetry: 24% in sea level representation compared to glider observations, and 35% and 31% in horizontal velocity magnitude compared to Acoustic Doppler Current Profiler and drifter measurements, respectively. This study highlights SWOT's potential in resolving small-scale ocean dynamics.

The Black Sea is a semi-enclosed basin with substantial river discharges. These inflows are crucial for the Black Sea's hydrography, nutrient supply, and ecological dynamics. The interplay of atmospheric forcing, river inflows, and mesoscale dynamics contribute to the formation of distinct water masses in the Black Sea. In the northern part, the extended shelf is prone to seasonal hypoxia and eutrophication, while the southern part is deep and stratified, marked by anoxic waters below 100m, rendering the Black Sea an immense meromictic sea. In the framework of the DOORS project (Developing Optimal and Open Research Support), during the DOORS field campaign, a first glider mission was performed in the Romanian Exclusive Economic Zone from May 6 to June 17, 2023, covering 288 nautical miles and conducting 863 physical and biogeochemical profiles at 1000m. The glider performed ten repeated transects perpendicular to the shelf parallel to the Danube Cone. Each transect has been completed approximately within four days, revealing the spatial and temporal characteristics of the region. At the shelf break, the isopycnals notably steepen and relax. In addition, intense surface heat gain of up to 3 oC induced strong stratification in two weeks, decreasing the density and MLD. The glider observations also captured small-scale eddies that contribute to the re-stratification process. These re-stratification events are essential to be monitored as they provide insights into the dynamic processes that affect the thermohaline characteristics of the water column and impact the nutrient availability in the euphotic layer. Understanding these events is essential for predicting and managing changes in the stratification, which plays a fundamental role in the upper layer circulation. By integrating glider-based observations with the broader regional Earth system dynamics context, our research supports a comprehensive understanding of the Black Sea's role in the global ocean climate system.

The FaSt-SWOT sea trial experiments, conducted in the Balearic Sea (Western Mediterranean Sea) between 25-28 April and 7-10 May 2023, aimed at collecting multi-platform in-situ observations of meso- and submesoscale ocean structures in the area covered by the SWOT satellite during its initial fast-sampling phase. The general objectives of the FaSt-SWOT project are twofold: 1) participate with these data to the satellite cal/val activities, and 2) improve the characterization and understanding of the fine-scale dynamics by combining in-situ multi-platform and satellite data with high-resolution numerical models and machine-learning-based computational techniques. The experiments consisted in 2 phases both using multi-scale ship-based instruments (CTD, Moving Vessel Profiler, thermosalinograph, ADCP and GoPros), autonomous platforms (surface drifters and gliders), and satellite observations (SST, ocean color and altimetry). In addition, 2km-resolution data-assimilative modelling simulations were produced to provide a complementary view of the fine-scale ocean variability. Finally, machine-learning-based optimization algorithms were also tested to define adaptive sampling strategies during the experiment. The sampling first focused on a 20km-diameter anticyclonic eddy detected under the swath of the satellite thanks to satellite imagery and drifter trajectories. Several cross-sections of the Moving Vessel Profiler and underwater gliders provided insights into the vertical structure of temperature and salinity fields and the associated signals in chlorophyll and dissolved oxygen. Two gliders were programmed to perform back-and-forth sections during a 3-week time with a 1-day delay between them, allowing to evaluate the temporal variability of the ocean fields at the period of repetitivity of the satellite. The second phase started 9 days after the end of the first one. A 48-hour dense radiator-like pattern was performed by R/V SOCIB, allowing to characterize the evolution of the small eddy observed during the first leg. A total of 45 surface drifters were deployed during the two phases to evaluate in-situ surface currents and their associated convergence and divergence in the vicinity of the eddy. While conventional altimetry was not able to properly represent the sea level signature of the observed eddy, initial SWOT measurements indicate an improved detection capability by the new satellite. In addition, high-resolution numerical simulations reproduce a small anticyclonic eddy with similar characteristics as that of the observed eddy. These simulations are used to provide a more general understanding of the situation, indicate the origin of the eddy in the frontal area between recent and modified Atlantic waters, and provide insights into the vertical extension of the small mesoscale structure. We provide here an overview of the whole FaSt-SWOT dataset, including both observing and modelling components. A more detailed analysis of the measurements is provided in a companion presentation.

Abstract. Spanning over a century, a traditional way to monitor sea level variability by tide gauges is – in combination with modern observational techniques like satellite altimetry – an inevitable ingredient in sea level studies over the climate scales and in coastal seas. The development of the instrumentation, remote data acquisition, processing and archiving in last decades allowed for extending the applications towards a variety of users and coastal hazard managers. The Mediterranean and Black seas are an example for such a transition – while having a long tradition for sea level observations with several records spanning over a century, the number of modern tide gauge stations are growing rapidly, with data available both in real-time and as a research product at different time resolutions. As no comprehensive survey of the tide gauge networks has been carried out recently in these basins, the aim of this paper is to map the existing coastal sea level monitoring infrastructures and the respective data availability. The survey encompasses description of major monitoring networks in the Mediterranean and Black seas and their characteristics, including the type of sea level sensors, measuring resolutions, data availability and existence of ancillary measurements, altogether collecting information about 236 presently operational tide gauge stations. The availability of the Mediterranean and Black seas sea level data in the global and European sea level repositories has been also screened and classified following their sampling interval and level of quality-check, pointing to the necessity of harmonization of the data available with different metadata and series at different repositories. Finally, an assessment of the networks’ capabilities for their usage in different sea level applications has been done, with recommendations that might mitigate the bottlenecks and assure further development of the networks in a coordinated way, being that more necessary in the era of the human-induced climate changes and the sea level rise.

After the launch of the Surface Water and Ocean Topography (SWOT) satellite planned for 2022, the region around the Balearic Islands (western Mediterranean Sea) will be the target of several in situ sampling campaigns aimed at validating the first available tranche of SWOT data. In preparation for this validation, the PRE-SWOT cruise in 2018 was conceived to explore the three-dimensional (3D) circulation at scales of 20 km that SWOT aims to resolve, included in the fine-scale range (1–100 km) as defined by the altimetric community. These scales and associated variability are not captured by contemporary nadir altimeters. Temperature and salinity observations reveal a front that separates local Atlantic Water in the northeast from recent Atlantic Water in the southeast, and extends from the surface to ~150 m depth with maximum geostrophic velocities of the order of 0.20 m s−1 and a geostrophic Rossby number that ranges between −0.24 and 0.32. This front is associated with a 3D vertical velocity field characterized by an upwelling cell surrounded by two downwelling cells, one to the east and the other to the west. The upwelling cell is located near an area with high nitrate concentrations, possibly indicating a recent inflow of nutrients. Meanwhile, subduction of chlorophyll-a in the western downwelling cell is detected in glider observations. The comparison of the altimetric geostrophic velocity with the CTD-derived geostrophic velocity, the ADCP horizontal velocity, and drifter trajectories, shows that the present-day resolution of altimetric products precludes the representation of the currents that drive the drifter displacement. The Lagrangian analysis based on these velocities demonstrates that the study region has frontogenetic dynamics not detected by altimetry. Our results suggest that the horizontal component of the flow is mainly geostrophic down to scales of 20 km in the study region and during the period analyzed, and should therefore be resolvable by SWOT and other future satellite-borne altimeters with higher resolutions. In addition, fine-scale features have an impact on the physical and biochemical spatial variability, and multi-platform in situ sampling with a resolution similar to that expected from SWOT can capture this variability.

The cruise was organized into 2 legs, the first without the equipment in the container and the second, with the equipment after the container was picked up in Almería.

The Mediterranean community represented in this paper is the result of more than 30 years of EU and nationally funded coordination, which has led to key contributions in science concepts and operational initiatives. Together with the establishment of operational services, the community has coordinated with universities, research centers, research infrastructures and private companies to implement advanced multi-platform and integrated observing and forecasting systems that facilitate the advancement of operational services, scientific achievements and mission-oriented innovation. Thus, the community can respond to societal challenges and stakeholders needs, developing a variety of fit-for-purpose services such as the Copernicus Marine Service. The combination of state-of-the-art observations and forecasting provides new opportunities for downstream services in response to the needs of the heavily populated Mediterranean coastal areas and to climate change. The challenge over the next decade is to sustain ocean observations within the research community, to monitor the variability at small scales, e.g., the mesoscale/submesoscale, to resolve the sub-basin/seasonal and inter-annual variability in the circulation, and thus establish the decadal variability, understand and correct the model-associated biases and to enhance model-data integration and ensemble forecasting for uncertainty estimation. Better knowledge and understanding of the level of Mediterranean variability will enable a subsequent evaluation of the impacts and mitigation of the effect of human activities and climate change on the biodiversity and the ecosystem, which will support environmental assessments and decisions. Further challenges include extending the science-based added-value products into societal relevant downstream services and engaging with communities to build initiatives that will contribute to the 2030 Agenda and more specifically to SDG14 and the UN's Decade of Ocean Science for sustainable development, by this contributing to bridge the science-policy gap. The Mediterranean observing and forecasting capacity was built on the basis of community best practices in monitoring and modeling, and can serve as a basis for the development of an integrated global ocean observing system.

In the last 10 years, new monitoring and modelling technologies have emerged allowing real-time observation and forecasting of the coastal ocean at regional and local scales. These technologies are at the core of multi-platform integrated observing and forecasting systems, such as the Balearic Islands Coastal Ocean Observing and Forecasting System (SOCIB). New capabilities to characterise the state of the ocean and its variability at finer spatial and temporal scales are emerging, supporting science and products for society. SOCIB has a well-defined mission to deliver ocean observing for the benefit of science and society. From initiation in 2010, SOCIB has provided high-quality, free and open data. In order to increase our utility, we developed a Products and Services Strategy rooted in business best practice. Ten sectors - groups of users with common data needs - were identified, for which SOCIB has information and knowledge of high value. Dedicated products were developed in cooperation with the end-users: beach lifeguards/managers and sustainable marine resources managers. We illustrate an integrative approach, combining business concepts with collaborative software development methodologies and ocean observing science, to turn ocean observations and forecasts into products and services, with benefits for society in the sustainable blue economy era.

The AlborEX (Alboran Sea Experiment) consisted of a multi-platform, multi-disciplinary experiment carried out in the Alboran Sea (western Mediterranean Sea) between 25 and 31 May 2014. The observational component of AlborEx aimed to sample the physical and biogeochemical properties of oceanographic features present along an intense frontal zone, with a particular interest in the vertical motions in its vicinity. To this end, the mission included 1 research vessel (66 profiles), 2 underwater gliders (adding up 552 profiles), 3 profiling floats, and 25 surface drifters.Near real-time ADCP velocities were collected nightly and during the CTD sections. All of the profiling floats acquired temperature and conductivity profiles, while the Provor-bio float also measured oxygen and chlorophyll a concentrations, coloured dissolved organic matter, backscattering at 700 nm, downwelling irradiance at 380, 410, and 490 nm, as well as photo-synthetically active radiation (PAR).In the context of mesoscale and sub-mesoscale interactions, the AlborEX dataset constitutes a particularly valuable source of information to infer mechanisms, evaluate vertical transport, and establish relationships between the thermal and haline structures and the biogeochemical variable evolution, in a region characterised by strong horizontal gradients provoked by the confluence of Atlantic and Mediterranean waters, thanks to its multi-platform, multi-disciplinary nature.The dataset presented in this paper can be used for the validation of high-resolution numerical models or for data assimilation experiment, thanks to the various scales of processes sampled during the cruise. All the data files that make up the dataset are available in the SOCIB data catalog at https://doi.org/10.25704/z5y2-qpye (Pascual et al., 2018). The nutrient concentrations are available at https://repository.socib.es:8643/repository/entry/show?entryid=07ebf505-bd27-4ae5-aa43-c4d1c85dd500 (last access: 24 December 2018).

The challenges associated with meso- and submesoscale variability (between 1-100 km) require high-resolution observations and integrated approaches. Here we describe a major oceanographic experiment designed to capture the intense but transient vertical motions associated with mesoscale and submesoscale features in an area characterized by strong fronts. Finescale processes were studied in the eastern Alboran Sea (Western Mediterranean) about 400 km east of the Strait of Gibraltar, a relatively sparsely sampled area. In-situ systems were coordinated with satellite data to provide a full description of the physical and biogeochemical variability. Hydrographic data confirmed the presence of an intense salinity front formed by the confluence of Atlantic Waters, entering from Gibraltar, with the local Mediterranean waters. The drifters coherently followed the northeastern limb of an anticyclonic gyre. Near real time data from acoustic current meter data profiler showed consistent patterns with currents of up to 1m/s in the southern part of the sampled domain. High-resolution glider data revealed submesoscale structures with tongues of chlorophyll-a and oxygen associated with the frontal zone. Numerical results show large vertical excursions of tracers that could explain the subducted tongues and filaments captured by ocean gliders. A unique aspect of AlborEx is the combination of high-resolution synoptic measurements of vessel-based measurements, autonomous sampling, remote sensing and modeling, enabling the evaluation of the underlying mechanisms responsible for the observed distributions and biogeochemical patchiness. The main findings point to the importance of fine-scale processes enhancing the vertical exchanges between the upper ocean and the ocean interior.

Trabajo presentado en el Ocean Surface Topography Science Team Meeting, celebrado en Boulder, Colorado, Estados Unidos, del 8 al 11 de 2013

We present the evolution, from its conception until today, of an established and internationally recognized Glider Facility. During 8 years of glider activity, new infrastructures and methodologies have been developed increasing glider missions, data, quality and availability. From 2005 to 2010, IMEDEA operated 4 Slocum G1 gliders following a research project approach. Since 2011, SOCIB, with in kind contribution from IMEDEA, is in charge of gliders’ operation and maintenance, increasing the glider fleet with 4 new vehicles (2 Slocum G2 gliders and 2 iRobot Seagliders). SOCIB has established one permanent endurance line in the Balearic Islands and provides open access glider time to third parties. We describe the progress of the Glider Facility, the results obtained and the objectives and actions foreseen in the near future.