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The deepwater formation in the northern part of the South Adriatic Pit (Mediterranean Sea) is investigated using a unique oceanographic dataset. In situ data collected by a glider along the Bari–Dubrovnik transect captured the mixing and the spreading/restratification phase of the water column in winter 2018. After a period of about 2 weeks from the beginning of the mixing phase, a homogeneous convective area of ∼300-m depth breaks up due to the baroclinic instability process in cyclonic cones made of geostrophically adjusted fluid. The base of these cones is located at the bottom of the mixed layer, and they extend up to the theoretical critical depth Zc. These cones, with a diameter on the order of internal Rossby radius of deformation (∼6 km), populate the ∼110-km-wide convective site, develop beneath it, and have a short lifetime of weeks. Later on, the cones extend deeper and intrusion from deep layers makes their inner core denser and colder. These observed features differ from the long-lived cyclonic eddies sampled in other ocean sites and formed at the periphery of the convective area in a postconvection period. So far, to the best of our knowledge, only theoretical studies, laboratory experiments, and model simulations have been able to predict and describe our observations, and no other in situ information has yet been provided.

A submesoscale cyclonic eddy, less than 10 km in diameter, was observed in the Balearic Sea from inception to dissipation for more than a month in winter 2022 The feature was heavily sampled by freely-drifting (Lagrangian) instruments to study its kinematics, spatial structure and temporal evolution. The Lagrangian sensors included drifters, wirewalkers and profiling floats. Additional shipboard data (underway CTD, ADCP) and remote sensing images revealed that the eddy was formed by doming isopycnals, extending more than 200 m in depth, with dense salty water at the center. The near-surface chlorophyll concentration was maximum in the eddy center, as clearly seen in ocean color satellite images.The eddy formed in late February by pinching off from a larger cyclonic feature via the collapse of a sharp submesoscale ridge that connected it to a larger cyclone. Wavelet analysis of the drifter trajectories revealed that the submesoscale eddy had a maximum orbital speed of ~ 30 cm/s, at a radius of ~3 km. In its inner core, vorticity was as large as twice the local inertial frequency (Rossby number ~ 2). The surface drifters made looping tracks that were slightly elliptical. Tracked by the swarm of drifters until mid-March, the eddy remained surprisingly coherent as it moved to the South and then East with a drift speed between 2 and 5 cm/s. After a strong wind event, just a few drifters remained in the eddy until it weakened and dissipated in early April.These observations were a part of the CALYPSO program, an ONR Departmental Research Initiative that addresses the challenge of observing, understanding and predicting the three-dimensional pathways by which water from the surface ocean makes its way into the deeper ocean. Vertical transports by submesoscale fronts and eddies can play an important role in ocean and climate dynamics.

In October 2021, the Sicily Channel and the central-western Ionian Sea were affected by the passage of the tropical-like cyclone, or MEDICANE, Apollo. The system reached its maximum intensity between 29 and 30 October 2021 producing several damages, intense precipitations and huge coastal floodings in Sicily and Calabria regions. The surface circulation in the MEDICANE impacted area was characterized by permanent cyclonic vortices, offering the chance to describe the impact of a tropical-like cyclone on a pre-existing cold circulation structure. Atmospheric and ocean reanalyses (ERA5 and Marine Copernicus Service), as well as in-situ data from Argo floats, were used to describe the temporal evolution of Apollo, the resulting air-sea interaction, the thermohaline and biological response to its passage in the upper layer (0-150 m) of the western Ionian Sea. During the event, the core of the marine cyclone was characterized by a dramatic drop in temperature, corresponding to a local maximum in the wind-stress curl, Ekman pumping and current field relative vorticity. The strengthening of the cyclonic circulation led by the wind stress curl produced a strong vertical mixing in the surface layer (from 0 m to the Mixed Layer Depth - MLD) and an upwelling in the subsurface layer below the thermocline (MLD-150 m). The combined effect of vertical mixing and upwelling resulted in a shoaling of MLD, deep chlorophyll-a maximum, nutricline, and halocline. Oxygen and chlorophyll-a concentrations increased at surface, due to the enhanced oxygen solubility in the cooler water and higher productivity due to the increase of nutrients upwelled to the surface layer. These results show that the pre-existing cyclonic vortex along Apollo's trajectory leads to a different physical response compared to the one observed during previous MEDICANEs, confirming the influence of the conditions in place in driving the ocean’s reply to the extreme weather systems.

An array of Lagrangian instruments (more than 100 drifters and a profiling float) was deployed for several days in the coastal waters of the southeastern Ligurian Sea to characterize the near-surface circulation at the submesoscale (< 10 km). The drifters were trapped in an offshore-flowing filament and a cyclonic eddy that developed at the southwestern extremity of the filament. Drifter velocities are used to estimate differential kinematic properties (DKPs) and the relative dispersion of the near-surface currents on scales as small as 100 m. The maximum drifter speed is ~50 cm/s. The DKPs within the cluster exhibit considerable spatial and temporal variability, with absolute values reaching the order of magnitude of the local inertial frequency. Vorticity prevails in the core of the cyclonic eddy, while strain is dominant at the outer edge of the eddy. Significant convergence was also found in the southwestern flow of the filament. The initial relative dispersion on small scales (100–200 m) is directly related to some of the DKPs (e.g., divergence, strain and instantaneous rate of separation): The mean squared separation distance (MSSD) grows exponentially with time and the finite-size Lyapunov exponent (FSLE) is independent of scale. After 5–10 h of drift or for initial separations greater than 500 m, the MSSD and FSLE show smaller relative dispersion that decreases slightly with scale.

Intensive hydrographic and horizontal velocity measurements collected in the Alboran Sea enabled us to diagnose the three-dimensional dynamics of a frontal system. The sampled domain was characterized by a 40 km diameter anticyclonic eddy, with an intense front on its eastern side, separating the Atlantic and Mediterranean waters. Here, we implemented a multi-variate variational analysis (VA) to reconstruct the hydrographic fields, combining the 1-km horizontal resolution of the Underway Conductivity-Temperature-Depth (CTD) system with information on the flow shape from the Acoustic Doppler Current Profiler velocities. One advantage of the VA is given by the physical constraint, which preserves fine-scale gradients better than the classical optimal interpolation (OI). A comparison between real drifter trajectories and virtual particles advected in the mapping quantified the improvements in the VA over the OI, with a 15% larger skill score. Quasi-geostrophic (QG) and semi-geostrophic (SG) omega equations enabled us to estimate the vertical velocity (w) which reached 40 m/day on the dense side of the front. How nutrients and other passive tracers leave the mixed-layer and subduct is estimated with 3D advection from the VA, which agreed with biological sampling from traditional CTD casts at two eddy locations. Downwelling warm filaments are further evidence of subduction, in line with the w from SG, but not with QG. SG better accounted for the along-isopycnal component of w in agreement with another analysis made on isopycnal coordinates. The multi-platform approach of this work and the use of variational methods improved the characterization and understanding of (sub)-mesoscale frontal dynamics., This research was supported by the Office of Naval Research Departmental Research Initiative CALYPSO under program officers Terri Paluszkiewicz and Scott Harper. The authors' ONR Grant are as follows: N000141613130 (AP, SR and AM), N000141812418 (PMP), S. Johnston N000141812416 (TMSJ), N000141812138 (TO), N000141712517 and N00014191269 (LRC), N000141812139 and N000141812420 (AS) and N000141812139and (EDA). This article is also a contribution to the PRE-SWOT project funded by the Spanish Research Agency and the European Regional Development Fund (AEI/FEDER, UE) under grant agreement (CTM2016-78607-P).

The Northern Ocean Rapid Surface Evolution (NORSE) focuses on characterizing the key physical processes that govern the predictability of upper-ocean rapid evolution events. The principal experimental site is Jan Mayen Channel, which connects the Greenland and Norwegian Seas. During the fall 2022 process cruise, signals from a moored source transmitting a 135-second-long LFM upsweep in the 500–1500 Hz band every four hours were recorded by three SVP Drifters equipped with hydrophone arrays. Over a three-day period, the drifters moved north across Jan Mayen Channel toward the moored source. The individual recordings are subject to variable levels of ambient sound caused by changing wind conditions and platform noise. In recordings with positive SNR, an in-plane arrival is observed. In a subset of these recordings, a second arrival is observed having travel time consistent with a propagation path from the moored source, reflecting off the ridge on the south side of the channel, and arriving at the drifters. A third arrival is also observed having travel time consistent with reflection from face of the bathymetric rise on the east end of the channel which forms Jan Mayen Island. This talk will present the measurements and explain the data though forward modeling. [Work supported by ONR.]

The Mediterranean Sea is very sensitive to climatic changes due to its semi-enclosed nature and is defined as one of the hotspots in future climate change projections. In this study we use Argo float data to describe spatial variabilities and trends in Ocean Heat Content (OHC) within the entire Mediterranean Sea and for specified sub-basins (e.g. Western and Eastern Mediterranean, Gulf of Lion, South Adriatic). The amount of the OHC, spatially averaged in bins of 1 °x1 ° over the period 2001-2020, increases from west to east in the Mediterranean Sea.Time series of temperature and OHC from 2005 to 2020, estimated in the upper and intermediate layers (5-700 m) and deeper layer (700-2000 m), reveal significant warming trends and an increase of OHC: the upper 700 m of the Mediterranean Sea show a warming trend of 0.041±0.012 °Cyr-1, corresponding to a yearly increase in OHC of 3.59±1.02 Wm-2. The upper 700 m of the Western Mediterranean Sea are warming fastest with an increase in temperature at a rate of 0.070±0.015 °Cyr-1, corresponding to a yearly increase in OHC of 5.72±1.28 Wm-2.Mixing and convection events transport and disperse the temperature and OHC changes: significant warming trends are evident in the deeper layers (700-2000 m) of the two deep convection sites in the Mediterranean Sea (Gulf of Lion, South Adriatic), with an exceptionally strong warming trend in the South Adriatic from 2013 to 2020 of 0.058±0.005 °Cyr-1, corresponding to a yearly increase in OHC of 9.43±0.85 Wm-2. The warming of different water masses will show its feedback on ocean dynamics and the atmosphere (air-sea fluxes) in the next years, decades or even centuries when these warming waters spread or re-emerge. This will stress ecosystems and accelerate the extinction of several marine species. This study contributes to a better understanding of climate change in the Mediterranean region and should be another wake-up call for policy makers and society.

16 pages, 4 figures, 2 tables, Increasing interest in the acquisition of biotic and abiotic resources from within the deep sea (e.g., fisheries, oil–gas extraction, and mining) urgently imposes the development of novel monitoring technologies, beyond the traditional vessel-assisted, time-consuming, high-cost sampling surveys. The implementation of permanent networks of seabed and water-column-cabled (fixed) and docked mobile platforms is presently enforced, to cooperatively measure biological features and environmental (physicochemical) parameters. Video and acoustic (i.e., optoacoustic) imaging are becoming central approaches for studying benthic fauna (e.g., quantifying species presence, behavior, and trophic interactions) in a remote, continuous, and prolonged fashion. Imaging is also being complemented by in situ environmental-DNA sequencing technologies, allowing the traceability of a wide range of organisms (including prokaryotes) beyond the reach of optoacoustic tools. Here, we describe the different fixed and mobile platforms of those benthic and pelagic monitoring networks, proposing at the same time an innovative roadmap for the automated computing of hierarchical ecological information on deep-sea ecosystems (i.e., from single species’ abundance and life traits to community composition, and overall biodiversity), This work was developed within the framework of the Tecnoterra (ICM-CSIC/UPC) and the following project activities: ARIM (Autonomous Robotic sea-floor Infrastructure for benthopelagic Monitoring; MartTERA ERA-Net Cofound), ARCHES (Autonomous Robotic Networks to Help Modern Societies; German Helmholtz Association), RESBIO (Grant TEC2017-87861-R; Ministerio de Ciencia, Innovación y Universidades), RESNEP (Grant CTM2017-82991-C2-1-R; Ministerio de Ciencia, Innovacion y Universidades), MERCES (Marine Ecosystem Restoration in Changing European Seas - GA No. 689518), and IDEM (Implementing the MSFD to the Deep Mediterranean Sea, GA No. 11.0661/2017/750680/SUB/ENV.C2)

Issue sup1: Copernicus Marine Service Ocean State Report, Issue 5 Supplement.-- Karina von Schuckmann (Editor), Pierre-Yves Le Traon (Editor), Neville Smith (Chair) (Review Editor), Ananda Pascual (Review Editor), Samuel Djavidnia (Review Editor), Jean-Pierre Gattuso (Review Editor), Marilaure Grégoire (Review Editor), The work was supported by the Copernicus Marine Environment Monitoring Service (CMEMS) LATEMAR project. CMEMS is implemented by Mercator Ocean in the framework of a delegation agreement with the European Union. This work has also been conducted as part of the bilateral project EOLO-1 (“Extreme Oceanic waves during tropical, tropical-like, and bomb cyclones”) between CNR-ISMAR and the University of Tokyo (Japan; Prof. Takuji Waseda). Antonio Ricchi funding have been provided via the PON “AIM” - Attraction and international mobility program AIM1858058. Joanna Staneva acknowledges H2020 IMMERSE Project, Arno Behrens was supported by CMEMS Waveflow project and G. Gayer by ESA Black Sea and Danube Regional Initiative (EO4BS).

The Atlantic Water (AW) and Levantine Intermediate Water (LIW) are important water masses that play a crucial role in the internal variability of the Mediterranean thermohaline circulation. In particular, their variability and interaction, along with other water masses that characterize the Mediterranean basin, such as the Western Mediterranean Deep Water (WMDW), contribute to modify the Mediterranean Outflow through the Gibraltar Strait and hence may influence the stability of the global thermohaline circulation. This work aims to characterize the AW and LIW in the Mediterranean Sea, taking advantage of the large observational dataset provided by Argo floats from 2001 to 2019. Using different diagnostics, the AW and LIW were identified, highlighting the inter-basin variability and the strong zonal gradient that characterize the two water masses in this marginal sea. Their temporal variability was also investigated focusing on trends and spectral features which constitute an important starting point to understand the mechanisms that are behind their variability. A clear salinification and warming trend have characterized the AW and LIW in the last two decades (~0.007 and 0.008 yr−1; 0.018 and 0.007 °C yr−1, respectively). The salinity and temperature trends found at subbasin scale are in good agreement with previous results. The strongest trends are found in the Adriatic basin in both the AW and LIW properties. A subbasin dependent spectral variability emerges in the AW and LIW salinity timeseries with peaks between 2 and 10 years.

The Lagrangian dispersion statistics of the Black Sea are estimated using satellite-tracked drifters, satellite altimeter data and a high-resolution ocean model. Comparison between the in-situ measurements and the model reveals good agreement in terms of the surface dispersion. The mean sub-basin coherent structures and currents of the Black Sea are well reproduced by the model. Seasonal variability of the dispersion in the upper (15 m), intermediate (150 m) and deep (750 m) layers are discussed with a special focus of the role of sub-basin scale structures and currents on the turbulent dispersion regimes. In terms of the surface relative dispersion, the results show the presence of the three known turbulent exponential, Richardson and diffusive-like regimes. The non-local exponential regime is only detected by the model for scales

The circulation of the Eastern Mediterranean Sea is characterized by numerous recurrent or permanent anticyclonic structures, which modulate the pathway of the main currents and the exchange of the water masses in the basin. This work aims to describe the main circulation structures and thermohaline properties of the Eastern Mediterranean with particular focus on two anticyclones, the Pelops and the Cyprus gyres, using in-situ (drifters and Argo floats) and satellite (altimetry) data. The Pelops gyre is involved in the circulation and exchange of Levantine origin surface and intermediate waters and in their flow toward the Ionian and the Adriatic Sea. The Cyprus Gyre presents a marked interannual variability related to the presence/absence of waters of Atlantic origin in its interior. These anticyclones are characterized by double diffusive instability and winter mixing phenomena driven by salty surface waters of Levantine origin. Conditions for the salt finger regime occur steadily and dominantly within the Eastern Mediterranean anticyclones. The winter mixing is usually observed in December–January, characterized by instability conditions in the water column, a gradual deepening of the mixed layer depth and the consequent downward doming of the isohalines. The mixing generally involves the first 200 m of the water column (but occasionally can affect also the intermediate layer) forming a water mass with well-defined thermohaline characteristics. Conditions for salt fingers also occur during mixing events in the layer below the mixed layer.

The most prominent oceanographic features in the Central Mediterranean are decadal reversals of the Northern Ionian Gyre (NIG), interpreted in terms of internal processes. Altimetry data, drifter data and model surface salinity products are used in this paper to define some specific features of the circulation related to the anticyclonic or cyclonic NIG modes. Results not only highlight different shapes and intensities of the Mid-Ionian Jet and northern Ionian meander among the two circulation mode, but emphasize distinct behaviour within the same mode, imputable to the variability of the mesoscale quasi-permanent features. The wind-driven Messina Rise Vortex, on the western side of the northern Ionian, and the Pelops Gyre, on the eastern side of the northern Ionian, show different behaviour during the first (1993–1996) and the second (2006–2010) anticyclonic periods, related to the cyclonic activity along the dense water pathway. When the dense water was of Aegean origin (1993–1996; “Aegean” anticyclone), the cyclonic mesoscale activity on the eastern flank of the Ionian overwhelmed the anticyclonic wind forcing, and led to the disappearance of the Pelops Gyre. When the dense water was of Adriatic origin (2006–2010; “Adriatic” anticyclone), the strengthening of cyclonic mesoscale activity on the western flank of the Ionian caused the shape change of the Messina Rise Vortex, favouring its longitudinal extension. The zonally-elongated Messina Rise Vortex reduced the inflow of Atlantic Water in the northern Ionian, and induced a strengthening of the eastward flowing Mid-Ionian Jet in the southern Ionian and Cretan Passage. From these results, it emerges that the interannual variability of the wind-driven quasi-permanent mesoscale gyres in the Ionian is influenced by internal forcing (location of the deep water formation site – Aegean or Adriatic Sea), in turn related to the major local climatic shift occurred in the last decades (the Eastern Mediterranean Transient). We show that the interplay between decadal and interannual variability, or rather between basin-wide and mesoscale circulation, affected the intrinsic characteristics of the NIG reversals.

A network of High-Frequency radar (HFR) stations runs operationally in the Malta-Sicily Channel (MSC), Central Mediterranean Sea, providing sea surface current maps with high temporal (1 h) and spatial (3 × 3 km) resolutions since August 2012. Comparisons with surface drifter data and near-surface Acoustic Doppler Current Profiler (ADCP) observations, as well as radar site-to-site baseline analyses, provide quantitative assessments of HFR velocities accuracy. Twenty-two drifters were deployed within the HFR domain of coverage between December 2012 and October 2013. Additionally, six ADCP vertical current profiles were collected at selected positions during a dedicated field survey. External radio-frequency interferences lead to significant gaps in the HFR coverage, which were minimized by an interpolation technique applied to the surface current fields. The validation of HFR velocities was first performed for each individual station in the network, using data generated with both the ideal and the measured antenna patterns. The validation was then repeated with pairs of HFR stations using the site-to-site baseline error analysis. The analysis confirms that the baseline error estimations and the full validation metrics for this HFR frequency band are consistent, and in some aspects superior, when compared to results from similar studies in other regions. The validation with drifter tracks suggests that the adopted interpolation procedure does not in general impact on the comparison metrics, but may introduce biases when used to extrapolate currents in regions where radar geometrical constraints are suboptimal. The analysis of the percentage of contribution of individual HFR stations shown that the quality of HFR data is influenced by the network geometry.

The article of record as published may be found at https://doi.org/10.1175/JTECH-D-18-0097.1 Direct measurements of the relative water flow near the top and bottom of Coastal Ocean Dynamics Experiment (CODE) drifters were made in the northeast Pacific Ocean and the Mediterranean Sea in wind speeds as large as 15 m s21. These measurements confirmed that the CODE drifter is a good Lagrangian drifter with a mean downwind slip of about 0.1% of the wind speed. Substantial mean vertical shears across the drifter (top 1 m below the surface) were observed, reaching an amplitude of 12 cm s21 and corresponding to strong stratification (due to the proximity of river runoff) and strong winds.

This work focuses on the Tyrrhenian Intermediate Water, a water mass present in the Tyrrhenian Sea (Western Mediterranean Sea), which approximately lies between 100 m and 200 m of depth, and is characterized by a local minimum of temperature. Here, for the first time, a thorough investigation of the Tyrrhenian Intermediate Water has been performed, based on the analysis of long time series of observations (XBT, Argo float, dissolved oxygen data) and on modeling results. It was found that this water is present in a large part of the Tyrrhenian basin, and is a persistent feature of the basin hydrology. It is formed by winter convection, with some differences between the southern part of the basin and the northern part, where strong winter cooling produces deeper convection and mixing. The process of formation of the Tyrrhenian Intermediate Water has been investigated in detail, through the analysis of the experimental datasets, of dedicated numerical experiments with a one-dimensional mixed layer model, and of the outputs of a three-dimensional ocean circulation model. Such analysis has excluded remote contributions from intermediate waters produced in the western portion of the Western Mediterranean basin. On the other hand, the presence of the Tyrrhenian Intermediate Water has been found to impact not only the Tyrrhenian Sea hydrology, but also that of the adjacent Liguro-Provençal basin, because this water mass outflows from the Corsica Strait, and is transported as far as the Gulf of Lion, in the core of the region where deep waters are formed. Recent changes in the properties of this intermediate water mass have also been highlighted, which result from the warming of the neighboring water layers. © 2018 Elsevier Ltd

In the eastern Mediterranean Sea, satellites have observed events of spring surface‐chlorophyll increase in the Rhodes Gyre region recurring intermittently. Few in situ biogeochemical data, however, exist to confirm their consistency, elucidate their seasonal characteristics, or discriminate among the possible drivers. During the year 2018, an array of BGC‐Argo floats was deployed in the region, collecting the first‐ever annual time series of in situ profiles of biogeochemical parameters in this area. Their observations demonstrated that nitrates, driven by mixed‐layer dynamics, were available at surface from December 2018 onwards and could have sustained phytoplankton growth. Phytoplankton accumulation at the surface was observed by satellite only in March 2019 when the mixed‐layer depth shoaled. These findings confirm that blooms occurring before the start of seasonal stratification are not easily recorded by satellite observations and reaffirm the need to consolidate the BGC‐Argo network to establish time series of the evolution of biogeochemical processes. Plain Language Summary The Levantine Sea, the easternmost area of Mediterranean Sea, is considered one of the poorest oceans on the Earth in terms of abundance of phytoplankton, the microscopic organisms that fuel the marine food web. However, historical data and satellite maps of chlorophyll (the pigment that reveals phytoplankton presence in the water) show episodic increases in the concentration of this pigment in the area near the island of Rhodes. To elucidate the characteristics of these events, a set of six robotic instruments (i.e. the BGC‐Argo floats) was deployed in the Levantine Sea in 2018. A BGC‐Argo float is an autonomous, free‐floating instrument that makes oceanic observations over the first 2,000 meters of the water column on a regular basis. This article presents an analysis of the data collected by these six robots. They provided the very first annual time series of biogeochemical observations in area, including during winter, when ship and satellite data are hard to collect. Our results reveal the increase in phytoplankton occurring before the start of seasonal stratification, increase that is not easily recorded by satellite observations and reaffirm the need to consolidate the BGC‐Argo network to establish time series of the evolution of biogeochemical processes.

Horizontal and vertical motions associated with mesoscale (10–100 km) and submesoscale (1–10 km) features, such as fronts, meanders, eddies, and filaments, play a critical role in redistributing physical and biogeochemical properties in the ocean. This study makes use of a multiplatform data set of 82 drifters, a Lagrangian float, and profile timeseries of temperature and salinity, obtained in a ∼1-m/s semipermanent frontal jet in the Alboran Sea as part of CALYPSO (Coherent Lagrangian Pathways from the Surface Ocean to Interior). Drifters drogued at ∼1-m and 15-m depth capture the mesoscale and submesoscale circulation aligning along the perimeter of fronts due to horizontal shear. Clusters of drifters are used to estimate the kinematic properties, such as vorticity and divergence, of the flow by fitting a bivariate plane to the horizontal drifter velocities. Clusters with submesoscale length scales indicate normalized vorticity ζ/f > 1 with Coriolis frequency f and normalized divergence of urn:x-wiley:21699275:media:jgrc24446:jgrc24446-math-0001(1) occurring in patches along the front, with error variance around 10%. By computing divergence from drifter clusters at two different depths, we estimate minimum vertical velocity of urn:x-wiley:21699275:media:jgrc24446:jgrc24446-math-0002(−100 m day−1) in the upper 10 m of the water column. These results are at least twice as large as previous estimates of vertical velocity in the region. Location, magnitude, and timing of the convergence are consistent with behavior of a Lagrangian float subducting in the center of a drifter cluster. These results improve our understanding of frontal subduction and quantify convergence and vertical velocity using Lagrangian tools., This research was supported by the Office of Naval Research (ONR) Departmental Research Initiative CALYPSO under program officers Terri Paluszkiewicz and Scott Harper.

In this paper, the authors describe a measurement campaign carried out in October 2019 in the Barents Sea by the CMRE (Center for Maritime Research and Experimentation), DGA Naval Systems (French Defense Procurement Agency), FFI (Norwegian Defence Research Establishment) and SHOM on the N/O Pourquoi Pas? Two acoustic pingers were moored north (Tx1) and south (Tx2) of the Polar Front, and transmitted sequences composed of Linear Frequency Modulation (LFM) and CW (Continuous Wave) waveforms between 1 and 14 kHz. The front was located precisely using the sea surface temperature sensors. Several acoustic receivers were deployed south of the front in a strongly range-dependent environment. A 32-hydrophone acoustic array was also towed across the Polar Front. In addition, oceanographic moorings were deployed: a 24-element thermistor chain (on the Tx2 mooring) and a WireWalker (north of the Tx2 mooring). They provide vertical temperature (and also salinity and density) measurements. Temperature fluctuations are various time scales were highlighted by the oceanographic recordings. In parallel, the influence of these environmental fluctuations on the received signals (on the various passive moorings) and ambient noise is shown by analyzing the measured channel impulse responses, phasors and transmission loss.

This article belongs to the Special Issue Observing the Flow of Ocean Currents and Circulation Using Remote Sensing., An Algerian Eddy, anticyclonic vortex generated by the instability of the Algerian Current in the southwestern Mediterranean Sea, is studied using data provided by drifters (surface currents), Argo floats (temperature and salinity profiles), environmental satellites (absolute dynamic topography maps and ocean color images) and operational oceanography products. The eddy was generated in May 2018 and lasted as an isolated vortex until November 2018. Its morphology and kinematics are described in June–July 2018 when drifters were trapped in its core. During that period, the eddy was slowly moving to the NE (~2 km/day), with an overall diameter of about 200 km (slowly growing with time) and maximal surface swirl velocity of ~50 cm/s at a radius of ~50 km. Geostrophic currents derived from satellite altimetry data compare well with low-pass filtered drifter velocities, with only a slight overestimation, which is expected as its maximum vorticity corresponds to a small Rossby number of ~0.6. Satellite ocean color images and some drifters show that the eddy has an elliptical spiral structure. The looping tracks of the drifters trapped in the eddy were analyzed using two statistical methods: least-squares ellipse fitting and wavelet ridge analysis, revealing a typical eccentricity of about 0.5, a wide range of inclination and a rotation period between 3 and 10 days. Clusters of drifters on the northeastern limb of the eddy were also considered to estimate divergence and vorticity. The results indicate convergence (divergence) and downwelling (upwelling) at scales of 20–50 km near the northeastern (northwestern) edge of the eddy, in agreement with the quasi-geostrophic theory. Vertically, the eddy extends mostly down to 250 m depth, with a warm, low-salinity and low-density signature and with geostrophic currents near 50 cm/s in the top layer (down to ~80 m) reducing to less than 10 cm/s near 250 m. Near the surface, colder water is advected into it., This research was mainly funded by the US Office of Naval Research (ONR) as part of the CALYPSO Departmental Research Initiative through grants N00014-18-1-2418 and N00014-18-1-2138. LC and the SVP drifters were funded by ONR grants N00014-17-1-2517 and N00014-19-1-269. D.T., A.P. and S.R. were funded by ONR grant N00014-16-1-3130.

Surface dispersion properties give an immediate characterization of the spreading of passive and active tracers in the ocean, like pollutant and marine species. The Mediterranean sub-basins (Tyrrhenian, Adriatic, Ionian, Levantine and Aegean) are known as complex dynamic regions due to the presence of coherent structures on different motion scales. This paper focus on dispersion of the surface Mediterranean flow using the surface current data derived from two different drifter designs: the Coastal Ocean Dynamics Experiment (CODE) and the Surface Velocity Program (SVP) drifters. The absolute dispersion for small time scales (15 days) and spatial scale larger than DI, our results emphasize a similarity in all the sub-basins with the presence of a quasi Random-walk regime and a quasi diffusive regime for the absolute and relative dispersion, respectively.

The South Adriatic is one of the dense water formation site in the Mediterranean Sea. The variations of its thermohaline properties are relevant not only from an oceanographic and climatic point of view but also for the local impact on the vertical distribution of the biogeochemical parameters.The South Adriatic Pit has been extensively sampled during the last forty years by traditional shipboard techniques. Float and glider measurements became part of the investigation only in the last ten years, providing a more detailed and more uniform spatio-temporal dataset. From the analysis, evidences of important changes of the South Adriatic Pit salinity vertical distribution emerge in the last 5 years. In the past, the Levantine Intermediate Water (LIW) entered the South Adriatic at a depth between 100 and 300 m, highlighted by a maximum in the salinity. The recent findings suggest that the LIW is no longer characterized by the highest salinity along the vertical profiles, which is present instead in shallower subsurface layers. In addition, in most of the seasons a thick low salinity layer is evident in the top 50-100 m. Among those changes, some peculiar haline characteristics occur in 2012 and 2017; they will be analyzed in concert with auxiliary data and model outputs.

Mesoscale variability and associated eddy fluxes play crucial roles in the ocean dynamics, transport of water mass properties and ecology of the upper ocean. In the Southern Hemisphere, where the nearly zonal flow of the Antarctic Circumpolar Current (ACC) acts as a barrier to the direct poleward transport toward the Antarctica, the eddy flux across the ACC is the main mechanism that guarantees the heat budget and distributes physical and biogeochemical properties between subtropical and polar regions. We focused on a high dynamical region located between the South-West Indian Ridge and the South Pacific Ridge. In this area, the interaction between the ACC and the major bathymetric features produces relatively large values of eddy kinetic energy and eddy heat fluxes as well as a relevant forcing for the ACC path.The aim of this study is to evaluate the actual efficiency of mesoscale eddies to exchange heat and other properties across the different ACC fronts and to describe the vertical properties of the eddies, their tracks and evolution. To this end, we used in-situ and satellite data in conjunction with a hindcast simulation from 1958 to 2018 performed with a 1/10° ocean biogeochemistry model.Eddies are identified and tracked in both the model output and altimetry data while their thermohaline properties and vertical extension are described using model outputs and in situ data, which include available repeated XBT sections (i.e. New Zealand – Antarctica and Hobart – Antarctica) and Argo float profiles located inside these structures.Thanks to the joint analysis of model and observational data, we are able to 1) assess the ability of the 1/10° ocean model of simulating the eddy field properties, and to 2) better interpret the spatial and temporal variability of the observed eddy characteristics in the larger and longer framework of the ocean simulation.

The high-frequency dynamics (including tidal and inertial currents, internal and coastal-trapped waves) on the shelf break/slope southwest of Svalbard were explored in September-October 2019 using a variety of mobile and fixed sensors operated as part of the NARVAL19 Sea Trial. Ocean currents, temperature and salinity were measured in the water column with 6 moorings, 3 gliders and a wirewalker profiler. In addition near-surface (15 m) currents were measured with 24 satellite-tracked drifters.The collected data show some variability, mostly near the surface, associated with the lateral displacements or meandering of the Polar Front separating cool and low salinity waters on the shelf and warmer/saltier waters of Atlantic origin. The most striking signal, however, is at depth (in and below the thermocline) in the form of internal waves at semidiurnal tidal frequency.Preliminary results of spectral and harmonic analyses of the data collected by all the platforms are presented and discussed.